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[Display omitted] • CrO 4 2− was almost completely removed from alkaline Cr(VI) contaminated wastewater. • CrO 4 2− was transformed into chromium ferrite (Cr 0.5-x Fe 2.5+x O 4) by one-step process. • Chromium ferrite was formed by reaction of amorphous Cr 0.25 Fe 0.75 (OH) 3 with Fe2+. • Increasing temperature and pH could promote the formation of chromium ferrite. Current technologies for removal of Cr(VI) are generally fit for acidic wastewater. In this study, a new ferrite process for removal and recycling of Cr(VI) from alkaline wastewater to produce the valuable chromium ferrite has been developed. The results show that this new ferrite method is a one-step process which can be divided into two successive reactions including Cr(VI) reduction to form coprecipitation (Cr 0.25 Fe 0.75 (OH) 3) and subsequently magnetic conversion of Cr 0.25 Fe 0.75 (OH) 3 induced by Fe2+ under the same alkaline condition. The total Fe/Cr mole ratio of 5:1 is at least required for the chromium ferrite transformation. Increasing temperature and pH can enhance the interaction of Fe2+ with Cr 0.25 Fe 0.75 (OH) 3 and further promote the formation of chromium ferrite, while suppressing the generation of nonmagnetic by-product goethite. Almost pure chromium ferrite is formed under proposed optimum conditions (Fe/Cr = 7:1, 65 °C and pH of 9) with Cr(VI) removal ratio around 100%. The Cr(VI) remained in the filtrate can be reduced to 0.01 mg/L which is much lower than the limits concentration for surface water (≤0.05 mg/L). The chromium ferrite product whose molecular formula can be expressed as Cr 0.5-x Fe 2.5+x O 4 (where 0 ≤ x < 0.5) presents good magnetic properties and has the potential to be recycled as a useful material. [ABSTRACT FROM AUTHOR]

Development of nanofilters with the ability to remove toxic metal ions from effluent wastewater will be of immense help to the leather industry. In this study, fibrous nanofilter (FNF) was prepared using microfibrillated cellulose and tea leaf microparticles blended in poly (vinyl) alcohol. FNF was analysed for its efficacy to remove hazardous metals from tannery effluent wastewater. The FNF had promising traits of tensile strength (19.24 + 0.05 Mpa), elongation at break (22.31 + 0.12%), flexibility (10.88 + 0.05%), water absorption (37.86 + 0.14%) and desorption (32.54 + 0.33%). The metal adsorption studies clearly reflected the removal of toxic Cr (VI) ions from the effluent water by FNF. The study establishes an economically feasible and highly efficient way to remove hazardous metal ions from effluent wastewater. [ABSTRACT FROM AUTHOR]

This study aims to remove Copper (Cu(II)) and Chromium (Cr(VI)) from aqueous solution using activated carbon (AC) from fennel seeds and potassium permanganate (KMnO4) treated fennel seeds. The activated carbon adsorbents were prepared from fennel seeds at different temperatures (500, 600 and 700°C). These adsorbents were designated as FS-500, FS-600 and FS-700. Each adsorbent was then chemically treated with KMnO4 solution to develop activated adsorbents, KMFS-500, KMFS-600 and KMFS-700. These six adsorbents were used for the binary adsorption of Cu(II) and (Cr(VI)) from an aqueous solution. The adsorbents were characterized by FTIR, SEM, UV-Vis and XRD. FTIR confirmed the presence of oxygen functional groups such as hydroxyl (-OH), carboxyl (-COOH) and carbonyl (-C = O) on the surface of the adsorbents. XRD confirmed a decrease in crystallinity as the temperature increased. SEM images showed that the morphology of the adsorbents was porous. KMFS-700 and FS-700 adsorbed more Cu(II) and Cr(VI) ions than KMFS-600, KMFS-500, FS-600 and FS-500. The maximum adsorption capacities for Cu(II) and Cr(VI) by FS-700 were 19.886 and 8.510 mg/g; for FS-600, it was 15.423 and 1.202 mg/g, and for FS-500, it was 16.921 and 1.722 mg/g, respectively. The maximum adsorption capacities for Cu(II) and Cr(VI) by KMFS-700 were 19.786 and 10.572 mg/g; for KMFS-600 it was 15.735, 8.109 mg/g, and for KMFS-500, it was 17.648 and 3.479 mg/g, respectively. All the adsorbents showed a stronger affinity for Cu(II) than Cr(VI). Kinetic studies showed that Cu(II) and Cr(VI) adsorption followed a pseudo-second-order reaction confirming that a chemical process controlled adsorption. [ABSTRACT FROM AUTHOR]

The textile industries release a substantial amount of effluents into water resources every year. The vast majority of these effluents are composed of heavy metals that bind the textile fibres with dyes. This work proposes to use an adsorption system composed of clay-minerals (kaolinite and montmorillonite) and molecular sieve (zeolite) for separating the Cu2+ and Cr6+ ions, considering the pH changes of aqueous solutions. The adsorbent materials were characterized using the following state of the art techniques such as X-ray fluorescence, X-ray diffraction, Raman spectroscopy and Cation exchange capacity. During the adsorption tests, the contact time of the adsorbates (Cu2+ and Cr6+ ions in concentrations of 100, 50, 10 and 5 mg/L) with the adsorbents vary from 1 to 4 h in acidic and alkaline conditions (pH 3.5 and 7.5). The results indicate maximum adsorption of Cu2+ (at pH 3.5) and Cr6+ (at pH 7.5) ions on application of the zeolitic material. The clay minerals conclusively proved to be less efficient when compared to zeolite. It can be concluded that the adsorption system has achieved the desired efficiency, with substantial removal of Cu2+ and Cr6+ ions for zeolites in synthetic wastewater solutions of the textile industry. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are the efficient and sustainable approach for the removal of toxic metals and generate energy concurrently. This article highlighted the effective use of rotten rice as an organic source for bacterial species to generate electricity and decrease the metal concentrations from wastewater. The obtained results were corresponding to the unique MFCs operation where the 510 mV voltage was produced within 14-day operation with 1000 Ω external resistance. The maximum power density and current density were found to be 2.9 mW/m2 and 168.42 mA/m2 with 363.6 Ω internal resistance. Similarly, the maximum metal removal efficiency was found to be 82.2% (Cd), 95.71% (Pb), 96.13% (Cr), 89.50% (Ni), 89.82 (Co), 99.50% (Ag), and 99.88% (Cu). In the biological test, it was found that Lysinibacillus strains, Chryseobacterium strains, Escherichia strains, Bacillus strains are responsible for energy generation and metal removal. Furthermore, a multiparameter optimization revealed that MFCs are the best approach for a natural environment with no special requirements. Lastly, the working mechanism of MFCs and future recommendations are enclosed. [ABSTRACT FROM AUTHOR]

The objective of this study was to prepare bio adsorbents from agro-industrial wastes from yam starch (YSR) and plantain (PSR) production for its use in the removal of Cr (VI) and Ni (II) in aqueous solution in batch and continuous packed-bed column systems. Bromatological analysis showed that the biomaterials are rich in cellulose, lignin, hemicellulose, and SEM micrographs that evidence a mesoporous structure characteristic of materials of lignocellulosic origin. FTIR evidenced functional groups such as hydroxyl, carbonyl, and methyl, possibly involved in the uptake of metal ions. EDS and FTIR analysis after adsorption confirmed that the retention of the metals on the surface of the adsorbent materials was successful. Cr (VI) and Ni (II) removal efficiencies above 80% were achieved using YSR and PSR in batch systems at the different conditions evaluated. The optimum conditions for removing Ni (II) on PSR were a bed height of 11.4 cm and a temperature of 33 °C, while for YSR, they were: 43 °C and 9 cm for temperature and bed height respectively. The variable with the most significant influence on the removal of Cr (VI) in a batch system on the two bio adsorbents was temperature. In contrast, the adsorbent dose and temperature are relevant factors for PSR Ni (II) removal. Therefore, the residues from the preparation of yam and plantain starch have high potential for removing heavy metals from wastewater and are presented as an alternative for their final disposal. [ABSTRACT FROM AUTHOR]

Herein, 3D flower-like δ-MnO 2 , MXene and δ-MnO 2 /MXene in-situ hybrid (IH) composites were prepared (via hydrothermal and solution treatment methods) for the effective removal of Cr (VI) from the contaminated water. The effect of various experimental parameters including contact time, pH levels and initial Cr (VI) ions concentration was determined and compared under static conditions. The kinetics of Cr (VI) adsorption onto δ-MnO 2 , MXene, and IH confirmed the existence of a pseudo-second-order model. The obtained results reveal that the removal of Cr (VI) largely depends on the pH of the solution. The adsorption isotherm data fits best for Freundlich model, illustrating a multi-site adsorption mechanism of Cr (VI) ion on these adsorbents. The maximum Cr (VI) adsorption capacities onto δ-MnO 2 , MXene and IH are 235.65 mg g−1, 273.1 mg g−1 and 353.87 mg g−1, respectively. The study reveals that hetero-engineered approach of synthesizing transition metal oxides with MXenes provides abundant opportunities to remove contaminants from water with better efficiency due to reduction and electrostatic interaction. [ABSTRACT FROM AUTHOR]

Various attempts have been made to assess the wastewater characteristics (pH, biochemical oxygen demand, and chemical oxygen demand) and heavy metals (nickel (Ni), cadmium (Cd), chromium (Cr), and copper (Cu)) in electroplating wastewater being discharged from large scale industrial units. The results showed that the concentration of heavy metals was found to be in the following order: Ni was 27.57 mg/L, Cr was 60.10 mg/L, Cu was 0.80 mg/L, and Cd was below the detectable limit (BDL). Furthermore, the treatment efficiency for Ni containing electroplating wastewater was comparatively evaluated through ozone oxidation and physicochemical process (coagulation and flocculation). The wastewater treated with ozone showed effective results for up to 30–40 min and achieved 42% Ni and 26% Cr removal efficiencies. In coagulation and flocculation, six beaker jar tests were conducted to remove Ni and Cr by using three different coagulants and non-ionic polyacrylamide. Among all these coagulants, aluminum sulfate was found more effective in combination with polymer. The optimum removal efficiency was achieved at 90 mg/L doses of aluminum sulfate and 100 mg/L of polymer for 98% and 99% removal of Ni and Cr, respectively. Therefore, it can be concluded that the physiochemical processes (coagulation and flocculation) were the most efficient method as compared to ozone treatment. [ABSTRACT FROM AUTHOR]

Background: High-strength wastewater defined by elevated levels of hazardous pollutants measured in BOD, heavy metals, nutrients and other toxic substances. This kind of wastewater discharged to water body without treatment from different industrial sectors that adversely affects aquatic environment and downstream water consumers. The general objective of this study is to investigate efficient substrate with selected plant type for constructed wetland to remove hazardous pollutants from tannery wastewater. This study was conducted at Modjo town, Modjo tannery PLC. Plug flow experimental study design was carried out. The substrate (Pumice) was collected around the study area and chemical characteristics were determined. Chrysopogon zizanioides was planted and grown for 5 months before running tannery wastewater for the treatment. The composite wastewater was introduced to the constructed wetland from Modjo leather industry, Ethiopia. The physicochemical analysis of the sample wastewater was done before and after treatment at four different hydraulic retention time. Results: Characterization of the untreated tannery wastewater revealed that the mean concentration of BOD5, COD, TSS, PO4-P, TP, NO3-N, TN and total chromium were 1641 ± 373.6, 6953.33 ± 339.4, 1868 ± 863.1, 88.06 ± 40.8, 144.53 ± 20.8, 116.66 ± 26.6, 650.33 ± 93.6 and 18.33 ± 6.7 mg/l respectively beyond the permissible limits. The maximum removal efficiency of the constructed wetland in pumice bed revealed that BOD5 at HRT 7and 9 days (96.42%, 96.30%), COD at HRT 5 and 7 days (96.76%, 96.91%), NO3-N at HRT 5 and 7 days (99.99%, 99.68%), TN (98.67%, 99.00%), PO4-P HRT 7and 9 days (96.97%,100%), TP at HRT 5 and 7 days (94.79%, 96.17%) and total Chromium at HRT 5 and 7 days (98.36%, 98.91%) respectively. Whereas, the removal efficiency of constructed wetland bed with gravel substrate used as a control subject with similar condition to pumice showed lower performance. The result between pumice and gravel bed was tested for their significance difference using two sample t-test statistics. Based on the test statistics, the pumice substrate perform better than the gravel significantly at 95% confidence interval, p-value = 0.01. Conclusion: Pumice substrate and Chrysopogon zizanioides have a potential ability to remove hazardous pollutants from tannery wastewater in horizontal subsurface constructed wetlands. [ABSTRACT FROM AUTHOR]

Chromium exists in many forms according to their valence from 0 to VI. Most dominant and stable valences of Chromium are III and IV. Chromium is non degradable, harmful and toxic pollutants which negatively affect the environment. It transfers to one trophic level to another via the food chain and continues their cycle in the nature. Bacteria, fungi, algae and plants are the best constituents of biomass which reduces the toxicity of heavy metals in the ecosystem. Bioremediation is a natural process for waste treatment in an industrial area. This comprehensive review article describes the sources of chromium contamination in wastewater and soils, various treatment technologies for the removal of chromium from water/ wastewater and different bacteria dependent possible bioremediation of this metalin aneco-friendly and cost effective manner. [ABSTRACT FROM AUTHOR]

In this study mixture of coconut shell and coir was used for Cr (VI) removal from synthetic wastewater and statistical tool Response Surface Modeling (RSM) was applied to optimize process parameters. The solution pH (2–6), reaction time (20–100 minutes) and adsorbent quantity (0.03–0.2 g) was optimized to find the maximum response of Cr (VI) removal using statistical Box-Behnken design (BBD) software. The equilibrium data obtained by the batch experiment were analyzed by ANOVA and found fitted in a second-order polynomial equation through multiple regression analysis. The optimum value of pH, adsorbent quantity and reaction time for 99% of Cr(VI) was found as 2, 0.1 g and 100 minutes, respectively. By using non-linear regression method it was found that Freundlich isotherm and Pseudo-second-order kinetic with high correlation coefficient (R2), low Chi-square (χ2) and root mean squares errors (RMSE), best describe the adsorption of Cr (VI) on mixture of coconut shell and coir (MCSC) surface. Positive enthalpy (ΔH°) and negative Gibbs free energy (ΔGo) values confirm the endothermic and spontaneous nature of adsorption process. Pre and post adsorption phenomenon was confirmed by characterization of adsorbent using AFM, FTIR, SEM, and EDX analysis. The adsorbent MCSC has regenerative property and can be reused 3–4 times after treating with alkaline medium (0.2 N NaOH) and offered more than 60% removal of Cr (VI) at the fourth cycle. It can be inferred based on this study that MCSC is an effective adsorbent for Cr (VI) removal and can be used on an industrial scale for social and environmental benefit. Novelty statement An agriculture waste mixture of coconut shell and coir (MCSC) without the addition of any chemical reagent, was used for Cr(VI) removal. As per literature survey and best of our knowledge, the adsorbent MCSC has not been reported for Cr (VI) removal. In the previous study, authors reported either coconut coir pith or coconut shell or coconut charcoal as adsorbent for Cr (VI) removal. The adsorbent MCSC is efficient even at very low doses (0.1 g) as compared to the reported adsorbent. In this study, several statistical tools have been used for the optimization of adsorption parameters. Besides, the material has been characterized before and after adsorption by different sophisticated methods like AFM, SEM-EDX, and FTIR. A desorption study has also been conducted using 0.2 N NaOH medium showing its regenerating capacity up to four-cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microfluidics for photocatalytic reduction of hexavalent chromium. • Rector design for effective photocatalytic conversion of Cr(VI) to Cr(III). • Efficiency of 95 % at a flow rate of 50 µl/min using serpentine microreactor. • Superior reduction efficiency of TiO 2 in the anatase phase than in the rutile phase. • Quantification of reduction efficiency using paper-based devices. The presence of hexavalent chromium (Cr(VI)) in water exceeding 0.05 mg/L constitutes a threat to both human health and the environment. Hence, the development of efficient methods for the removal and quantification of Cr(VI) in wastewater is of utmost importance. The photocatalytic reduction represents a valuable approach for transforming the toxic Cr(VI) into a non-toxic trivalent form of chromium (Cr(III)). However, this method encounters several challenges, including a slow reaction rate, the need for an acidic environment, high catalyst loading, and limited recovery efficiency. This study introduces an efficient microfluidic platform for the conversion of Cr(VI) in wastewater by integrating various reactor designs. We explored the use of nanosized TiO 2 as a photocatalyst in both pure anatase and rutile phases and a combination of anatase/rutile phases to assess their reduction performance. A remarkable conversion efficiency of 95 % was attained by utilizing a serpentine microreactor coated with a photocatalyst in the anatase phase. In contrast to the traditional batch photoreduction method, which reported a conversion efficiency of only 72 %, microreactor technology demonstrates a superior photoreduction performance. The pseudo-first-order kinetics was observed and the rate of reaction was calculated to be 0.199 sec −1. In addition to confirming the photoreduction of Cr(VI), we have also presented a robust yet user-friendly approach for quantifying Cr(VI) by combining paper-based devices with a smartphone-enabled colorimetric technique. Finally, we employed machine learning (ML) algorithms to predict photoreduction efficiencies using a multiple linear regression model to gain an understanding of the impact of various parameters and the root mean square error (RMSE) for the model prediction was calculated to be equal to 0.92 indicating the overall performance of the ML model was excellent. [ABSTRACT FROM AUTHOR]

In this study, a waste disposable facial cleansing tissue-based MIL-100(Fe)/MoS 2 nanosystem was constructed to remove Reactive Brilliant Blue and Cr(VI) simultaneously. [Display omitted] • A waste disposable facial cleansing tissue-based nanosystem was got by loading MIL-100(Fe)/MoS 2. • This system could remove Reactive Brilliant Blue (KN-R) and Cr(VI) simultaneously. • This nanosystem could be easily separated from water after KN-R/Cr(VI) treatment. • This work has a high application prospect for printing/dyeing wastewater treatment. • This work offers a promising method for the resource of disposable facial cleansing tissue. Reactive Brilliant Blue (KN-R) and hexavalent chromium (Cr(VI)) are two types of environmental pollutants that can be simultaneously released into the environment through industrial wastewater and domestic sewage, leading to severe combined pollution. Therefore, the simultaneous and effective removal of both KN-R and Cr(VI) is a critical challenge to reduce their environmental impacts. In this work, a waste disposable facial cleansing tissue (DFCT)-based nanosystem was fabricated to simultaneously remove KN-R and Cr(VI) from water. This nanosystem, called DFCT/MIL-100(Fe)/MoS 2 , incorporated polyhedral MIL-100(Fe) and flower-shaped MoS 2 onto the DFCT surface. MoS 2 exhibited high reduction and adsorption capabilities for Cr(VI), while MIL-100(Fe) possessed high adsorption abilities for KN-R through chelation. Moreover, DFCT had excellent immobilization capacity for both MIL-100(Fe) and MoS 2 , making it convenient for DFCT/MIL-100(Fe)/MoS 2 to be removed from water after treating KN-R and Cr(VI). The maximum removal efficiencies of DFCT/MIL-100(Fe)/MoS 2 for KN-R and Cr(VI) could reach 96.4 % and 97.9 % in 13 h and 5 h, respectively. The removal process fit the Langmuir (R2 = 0.9956 of KN-R and R2 = 0.9976 of Cr(VI)) and pseudo-second-order kinetic models (R2 = 0.9876 of KN-R and R2 = 0.9922 of Cr(VI)). Thermodynamic data indicated that the removal process of KN-R and Cr(VI) was spontaneous and endothermic. Furthermore, pot experiments result demonstrated that DFCT/MIL-100(Fe)/MoS 2 could reduce the harm of KN-R and Cr(VI) for water spinach and enhance the food safety. This work presents a valuable method for remediating KN-R/Cr(VI)-contaminated water with significant application potential. [ABSTRACT FROM AUTHOR]

Chromium-containing wastewater causes serious environmental pollution due to the harmfulness of Cr(VI). The ferrite process is typically used to treat chromium-containing wastewater and recycle the valuable chromium metal. However, the current ferrite process is unable to fully transform Cr(VI) into chromium ferrite under mild reaction conditions. This paper proposes a novel ferrite process to treat chromium-containing wastewater and recover valuable chromium metal. The process combines FeSO 4 reduction and hydrothermal treatment to remove Cr(VI) and form chromium ferrite composites. The Cr(VI) concentration in the wastewater was reduced from 1040 mg L−1 to 0.035 mg L−1, and the Cr(VI) leaching toxicity of the precipitate was 0.21 mg L−1 under optimal hydrothermal conditions. The precipitate consisted of micron-sized ferrochromium spinel multiphase with polyhedral structure. The mechanism of Cr(VI) removal involved three steps: 1) partial oxidation of FeSO 4 to Fe(III) hydroxide and oxy-hydroxide; 2) reduction of Cr(VI) by FeSO 4 to Cr(III) and Fe(III) precipitates; 3) transformation and growth of the precipitates into chromium ferrite composites. This process meets the release standards of industrial wastewater and hazardous waste and can improve the efficiency of the ferrite process for toxic heavy metal removal. [Display omitted] • FeSO 4 hydrothermal treatment removes most Cr(VI) from alkaline wastewater. • Cr(VI) turns into magnetic chromium ferrite composites. • Hydrothermal treatment boosts ferrochromium spinel multiphase formation and growth. [ABSTRACT FROM AUTHOR]

Heavy metal pollution in water caused by industrial activities has become a global environmental issue. Among them, manganese mining and smelting activities have caused the combined pollution of Cr(VI) and Mn(II) in water, posing a serious ecotoxicological risk to ecological environments and human health. To efficiently remove Cr(VI) and Mn(II) from wastewater, a novel biochar supported nanoscale zerovalent iron-calcium alginate composite (CA/nZVI/RSBC) was synthesized by liquid-phase reduction and calcium alginate embedding methods. The adsorption performance and mechanisms of Cr(VI) and Mn(II) by CA/nZVI/RSBC were investigated. The maximum adsorption capacities of Cr(VI) and Mn(II) onto CA/nZVI/RSBC fitted by the Langmuir model were 5.38 and 39.78 mg/g, respectively, which were much higher than the pristine biochar. The iron release from CA/nZVI/RSBC was comparatively lower than that of nZVI/RSBC. Mn(II) presence enhanced the reduction of Cr(VI) by CA/nZVI/RSBC. The results of XRD, XPS, and site energy distribution analysis indicated that redox was the predominant mechanism of Cr(VI) adsorption, while electrostatic attraction dominated Mn(II) adsorption. This study provides a novel alternative way for the simultaneous removal of Cr(VI) and Mn(II) in wastewater. [Display omitted] • CA/nZVI/RSBC shows a good performance for Cr(VI) and Mn(II) removal. • The iron release of CA/nZVI/RSBC is lower than that of nZVI/RSBC. • The presence of Mn(II) promotes the reduction of Cr(VI) by CA/nZVI/RSBC. • The main process of Cr(VI) adsorption is redox and for Mn(II) is electrostatic attraction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Shows selective adsorption of Cr(VI) with Q m of 143 mg/g. • Complete removal of Cr(VI) and conversion into Cr 2 O 3 , ZnCrO 4 demonstrated. • Other ions of filtered water are precipitated as chlorapatite and removed. • Demonstrates the extraction of water from tannery effluent for reuse. To counter the toxic effects of Cr(VI) ions in industrial wastewater, adsorption onto a suitable adsorbent is prudent, but the resulting secondary waste accumulation and cleaning are challenging. Herein, biocompatible alginic acid has demonstrated selective adsorption of Cr(VI) ions with the subsequent conversion of the secondary waste into valuable materials. The maximum sorption was found to be 143 mg/g, and the adsorption follows the Langmuir model and pseudo-second-order kinetics. The process was tested with a simulated tannery effluent where selective Cr(VI) adsorption was achieved, and the secondary waste was converted to Cr 2 O 3 and ZnCrO 4. The remaining ions present Na+, Cl+, SO 4 2- have been consolidated into an apatite mineral with the molecular formula of Ca 4.1 Na 0.9 (P 0.7 S 0.3 O 4) 3 Cl. Overall, our integrated process of removing and converting Cr(VI) ions into beneficial by-products opens up a window of opportunities for large-scale water purification and industrial applications. [ABSTRACT FROM AUTHOR]

Cr (VI) accumulates in an aqueous environment and exhibits huge harm to human health and the ecological system. Developed lignin biomass materials are complicated to prepare and have limited properties, and advances in lignin phenolic modification are lacking. Herein, an aminated poplar lignin-pyrogallol (PLP-PEI) with a simple design and adjustable phenolic hydroxyl content was developed using the acid hydrolysis-phase separation (AH-PS) method, and modified by the atom transfer radical polymerization (ATRP) strategy. Through diverse characterization analysis, the structural changes of PLP-PEI in the step-by-step synthesis process were monitored. An effective biomass capture system (Bio-Cap) was shown via systematically investigating the adsorption behaviors of Cr (VI) on PLP-PEI under various environmental conditions. Benefiting from introducing phenolic hydroxyl and amino groups, PLP-PEI demonstrated efficient adsorption capacity (598.80 mg/g for Cr (VI)). Additionally, the material also exhibited advantages, including monomeric chemisorption properties, strong reduction capability, and stable regeneration properties. Multiple driving forces were involved in the capture and removal process of Cr (VI), including complexation and electrostatic interaction. The low-cost natural biomass resources supported the industrial-scale synthesis and practical application of advanced aminated lignin polyphenol material, which showed outstanding advantages and enormous potential in the field of water environmental restoration. • Lignin polyphenol was prepared by simple one-stepping from raw biomass material. • Adjustable phenolic hydroxyl group of lignin polyphenol was achieved. • High content of phenolic hydroxyl group can significantly convert Cr (VI) to Cr (III). • Multiple driving forces contributed to efficiently removing Cr (VI). [ABSTRACT FROM AUTHOR]

We have utilised our TeO 2 –ZnO nanocomposites for Yamuna wastewater treatment in natural sunlight wherein the sampling site was Nigam Bodh Ghat, Kashmere Gate, Delhi. In BET isotherm, TZ NCs exhibited type IV isotherm forming a H3 like hysteric loop sustaining mesoporous characteristic with an increase in surface area, pore volume and pore diameter of 56.76 m2/g, 0.257 cc/g and 17.18 nm respectively, when compared to pristine ZnO NPs. Yamuna wastewater treatment was carried out using various concentrations of TZ NCs (range 0.1–0.3 g/500 mL) under natural sunlight. Post-treatment, all the physicochemical parameters such as DO, BOD, COD, Nitrates, Ammonia and Phenolic contents were found to be reduced to 10 times bringing Yamuna water parameters within safe limits. Our TZ NCs have shown to have high selectivity for the removal of Chromium from water. Out of all the three concentrations 0.2 g/500 mL or 0.4 mg/mL is the most optimum concentration of TZ NCs for complete Yamuna wastewater treatment. Also, the bacterial culture present in Yamuna water was killed by 90% using TZ having MIC of 0.1 mg/mL. The antibiofilm activity of TZ against K.pneumoniae MTCC 109 was also checked using Congo Red Agar Assay. The presence of heavy metals, their corresponding degradation and leaching studies were analysed using ICP-OES. TZ NCs showed a very minimal leaching rate of Zinc into the water, proving no toxicity associated with these nanocomposites. Further, to observe the safe disposal of TZ NCs into the soil, TZ NCs were utilised for ecotoxicity studies. Scheme 1. Schematic illustration showing the synthesis of TZ nanocomposites and removal of pollutants from waste water. [Display omitted] • Photocatalytic Yamuna waste water treatment using TZ NCs • Removal of Nitrates, ammonia, phenolic pollutants from Yamuna wastewater • Removing 90% bacterial pathogenicity from Yamuna wastewater • Improvement in the BOD, COD and DO values after treatment • 91% Chromium removal from Yamuna wastewater [ABSTRACT FROM AUTHOR]

In this study, dielectric barrier discharge (DBD) plasma combined with titanium dioxide/reduced graphene oxide/copper oxide (TiO 2 /rGO/Cu 2 O) composites for simultaneous removal of hexavalent chromium (Cr(Ⅵ)) and tetracycline (TC) from wastewater were explored systematically. The TiO 2 /rGO/Cu 2 O composites were successfully prepared to improve the specific surface area and charge carrier separation rate. When Cr(Ⅵ) and TC coexist, the two pollutants have better removal efficiency without changing the initial pH. Moreover, the removal efficiency of Cr(Ⅵ) and TC could be further improved in the DBD-TiO 2 /rGO/Cu 2 O system, indicating that the TiO 2 /rGO/Cu 2 O composites also exhibited good synergistic effects with the DBD plasma. The mechanism exploration showed that the TiO 2 /rGO/Cu 2 O composite catalyst could be activated in DBD system to produce various active species by photocatalytic reaction, among which photo-generated electrons and •O 2 − could significantly enhance Cr(Ⅵ) reduction, while photo-generated holes and •OH could improve TC degradation. More importantly, the intermediate products obtained from TC degradation can be oxidized to •CO 2 − by photo-generated holes, which can also facilitate the reduction of Cr(Ⅵ). This study shows that DBD combined with TiO 2 /rGO/Cu 2 O composites are capable of simultaneous Cr(Ⅵ) reduction and TC degradation, which would provide novel ideas for practical wastewater remediation. [Display omitted] • Synergistic effect of Cr(Ⅵ) and TC in DBD-TiO 2 /rGO/Cu 2 O system was confirmed. • The removal rate of Cr(Ⅵ) and TC were simultaneously enhanced by adding TiO 2 /rGO/Cu 2 O. • e−,.•O 2 − and •CO 2 − production play important roles in enhancing Cr(Ⅵ) reduction. • h+ and.•OH generated DBD- TiO 2 /rGO/Cu 2 O system can induce TC degradation. [ABSTRACT FROM AUTHOR]

In this paper, metallic copper (Cu) was supported on nanoscale zero-valent iron (nZVI) to form a nanoscale bimetallic composite (nZVI-Cu), which was used to activate persulfate (PS) to simultaneously remove the compound contaminants Cr(VI) and tetracycline hydrochloride (TCH) in simulated wastewater. nZVI, nZVI-Cu, and nZVI-Cu-activated PS (nZVI-Cu/PS) were characterized by SEM, TEM, XRD, and XPS. The effects of the bimetallic composite on Cr(VI) and TCH removal were compared in the nZVI, nZVI-activated PS (nZVI/PS), nZVI-Cu, and nZVI-Cu/PS systems. The results showed that nZVI and Cu can form a nanobimetallic system, which can create galvanic cells; thus, the galvanic corrosion of nZVI and the transfer of electrons are accelerated. For a single contaminant, the removal efficiency of Cr(VI) and TCH is the highest when nZVI is loaded with 3 wt% and 1 wt% Cu, respectively. The ratio of nZVI-Cu with 3 wt% Cu to PS is 7:1, and the removal efficiency of Cr(VI) and TCH compound contaminants is ~ 100% after 60 min under acidic conditions, which indicates that the Cr(VI) reduction and TCH oxidation were complete in the nZVI-Cu/PS system. The mechanisms of simultaneous removal of Cr(VI) and TCH in the nZVI-Cu/PS system are proposed. The removal of Cr is because of the adsorption-reduction effects of the nZVI-Cu bimetallic material. The degradation of TCH is mainly due to the action of oxidative free radicals generated by Fe2+-activated PS. The free radical capture experiments showed that SO- 4· plays a major role in the process of TCH degradation. [ABSTRACT FROM AUTHOR]

The process of phytoremediation by using aquatic plants is a new, low cost and ecofriendly method for improving water quality and waste water. In the present study the ability of Azolla pinnata R.Br. and Salvinia molesta Mitchell to uptake Cr (VI) from aqueous environment as well as their potential application for phytoremediation were assessed. During 15 days of the experiment the ferns were grown on the nutrient solution containing hexavalent chromium ions, each in a concentration of control, 0.07, 0.09, 0.11 and 0.13 mg/l. The biomass productivity and relative growth of Azolla pinnata R.Br. was increased and in case of Salvinia molesta Mitchell it was decreased with increase in the metal concentration of the treatment medium. The protein content in different concentration of chromium was more as compared to the control but showed a decreasing trend with increasing concentration. After 15 days of treatment, the concentration of Cr (VI) in the medium decreased between 72.86 - 97.69 % and 75.71 - 90 % by Azolla pinnata R.Br. and Salvinia molesta Mitchell respectively. Both the fern took a lesser quantity of metal from 0.07 mg/l treatments compared to 0.09 mg/l, 0.11 mg/l and 0.13 mg/l treatments. In the Azolla pinnata R.Br. tissue the concentration of heavy metal under investigation ranged from 0.106 - 0.216 mg/gm dry weight and for Salvinia molesta Mitchell ranged from 0.094 - 0.321 mg/gm dry weight. Increasing concentration of Cr (VI) in the growth medium increased the bioconcentration factor of Azolla pinnata R.Br. and Salvinia molesta Mitchell up to an optimum value of 1630.76 and 2469.23 respectively. In the present study the higher BCF of Salvinia molesta Mitchell shows that it is a better candidate for phytoremediation of Cr (VI) from the treatment solution than Azolla pinnata R.Br. Overall results indicate that Azolla pinnata R.Br. and Salvinia molesta Mitchell can be used for phytoremediation of Cr (VI) from polluted water as it is a low cost method satisfying the discharge standards. [ABSTRACT FROM AUTHOR]

• Green and efficient adsorbent, CeO 2 NPs were synthesized by azadirachta indica leaf extracts. • CeO 2 NPs exhibits good characterization attributes and efficient for Cr and d removal from wastewater. • Kinetic modeling, isotherm models were suitable for chemisorption of NPs for the removal of these metals. • The green CeO 2 NPs have a potential adsorbent for Cr and Cd removal from wastewater. Chromium and cadmium are two hazardous heavy metals that are known carcinogens and can cause a range of health problems as well as changes in the regular functioning of the environment. Green nanotechnology has sparked a lot of attention in recent years as a potential solution to heavy metal concerns. Because of their unique chemical, physical, and biological properties that make them favorable for a wide range of uses, application of cerium oxide nanoparticles (CeO 2 NPs) has gained in popularity. CeO 2 NPs have a larger surface area than larger particles, leading in improved biochemical reactivity, catalytic activity, and environmental effectiveness. In this study, CeO 2 NPs were made from green procedure by the use of plant extract from Azadirachta indica. The stat of the art techniques were utilized to study the physical characteristics of the synthesized CeO 2 NPs. These nanoparticles were utilized as bio-sorbents to extract chromium (Cr) and cadmium (Cd) ions from wastewater. In standard testing conditions, the CeO 2 nanoparticles exhibited high removal efficiency, removing 93% of Cr within approximately 15 min of contact time, and achieving 89% removal of Cd. To acquire the best results for industrial-scale applications and to simplicity the reuse of these heavy metals, exact experimental conditions that improve the absorbance efficiency must be identified. Despite the fact that nanoparticles have demonstrated great efficiency and selectivity in extracting and recovering chromium from wastewater, further study is needed to optimize their production and performance for industrial-scale applications. [ABSTRACT FROM AUTHOR]

The present study demonstrates an innovative circular economic process to repurpose agricultural waste, nutmeg fruit rind into an effective adsorbent followed by its value addition/safe disposal, thereby seamlessly aligning with the principles of green chemistry and sustainable waste management. Low-cost bio-sorbents are one of the most promising substances for pollutant removal in water treatment research. Fruit shells and peels are annoying to the environment because they contribute to solid trash after consumption and add to the daunting challenge of municipal solid waste management. This study investigated the potential of nutmeg fruit rind waste, a readily available agricultural byproduct, for the removal of hexavalent chromium (Cr(VI)) from contaminated streams. The findings highlight the significant removal efficiency of Cr(VI) ions through adsorption onto the nutmeg fruit rind waste, underscoring its potential as an affordable and eco-friendly solution for wastewater treatment. The study showed that pH, adsorbent dosage, adsorbate concentration, contact time, and temperature significantly influence adsorption. The insights into the adsorption mechanism revealed that the electrostatic interaction, hydrogen bonding, ion exchange, and surface complexation primarily contributed to the removal of Cr(VI) ions. The kinetics studies matched well with the pseudo-second-order kinetic model, and the sorption fits the Sips isotherm, while thermodynamic studies confirmed the spontaneity and exothermic nature of the process. The quantitative removal of Cr(VI) and other co-existing heavy metals from real textile wastewater samples was demonstrated. Finally, the spent adsorbent was subjected to anaerobic digestion to recover biogas and Cr(VI), which offers a sustainable solution to mitigate the contamination risk associated with discarding the spent adsorbent while contributing to resource recovery. [Display omitted] [ABSTRACT FROM AUTHOR]

The discharge of hexavalent chromium [Cr(VI)] in industrial wastewater into the natural environment can seriously cause harm to the environment and human health. We modified chitosan (CS) with Co and polydopamine (PDA) to synthesize a spherical adsorbent (CS–Co/PDA HCl) for Cr(VI) removal from wastewater. Co doping can help CS–Co/PDA HCl maintain a high adsorption capacity (666.7 mg g-1) for Cr (VI) while retaining a complete bead shape after multiple recycling. In addition, CS–Co/PDA HCl can maintain 96% of its initial adsorption capacity after five adsorption cycles, demonstrating a strong regeneration ability. Under competitive conditions, the adsorption capacity of CS–Co/PDA HCl for Cr(VI) greatly exceed its adsorption capacity for Ni (II) and Mn (II). Because of the high selectivity of CS–Co/PDA HCl for Cr(VI), 1 kg of CS–Co/PDA HCl (cost approximately $31) could reduce the concentration of Cr(VI) in 87 m3 of secondary electroplating wastewater containing various complex components to the drinking water standard. Owing to the high selective adsorption capacity of CS–Co/PDA HCl for Cr(VI) and its good regeneration ability and expected economic feasibility, CS–Co/PDA HCl can find potential applications in removing Cr(VI) from real wastewater. [Display omitted] • CS-Co/PDA HCl beads can be easily separated from the water and regenerated (99–96%). • The adsorption capacity of CS-Co/PDA HCl for or Cr(VI) were 666.7 mg g–1 at 25 °C. • The Cr (VI) of 87 m3 secondary wastewater was removed by 1 Kg of the CS-Co/PDA HCl. • CS-Co/PDA HCl exhibited excellent affinity for Cr(VI) and anti-interference ability. • CS-Co/PDA HCl has good biocompatibility with negligible cytotoxicity. [ABSTRACT FROM AUTHOR]

Environmental pollution is the greatest challenge of the modern age due to unprecedented industrialization and urbanization that has led to the contamination of water resources with a wide range of pollutants. The release of untreated industrial and municipal wastewater to water bodies further intensifies the problem. The presence of heavy metals and organic contaminants in water poses significant threats to humans, aquatic life, and the environment. Adsorption is one of the famous water treatment technologies due to its simplicity, low cost, efficiency, and minimal secondary pollution. The selection or synthesis of an effective adsorbent is key to the success of the adsorptive removal of pollutants. In this work, we synthesized an adsorbent consisting of a mesoporous hyper-cross-linked polyamide/polyamine 3D network through a single-step Michael addition reaction. The adsorbent was characterized by FTIR, PXRD, TGA, SEM, and TEM to investigate its functional moieties, material nature, thermal, morphological, and internal structural features, respectively. Due to its mesoporous structure, presence of functional groups, and 3D hyper-cross-linked network, it efficiently removed heavy metals (Cd, Cr, and Pb) from aqueous media. The effect of various parameters such as sample pH, adsorbent dosage, contact time, and adsorbate concentrations was thoroughly investigated. The experimental data were analyzed by a variety of isotherm models wherein Langmuir was found to be the best fit for explaining the adsorption of all the metals. The adsorption kinetics was best explained by the pseudo-second-order model. The maximum adsorption capacities for Cd, Cr, and Pb were 60.98 mg g−1, 119 mg g−1, and 9.302 mg g−1, respectively. The synthesized adsorbent was also tested for removal of organic dyes, and it showed selective and fast removal of Eriochrome Black T. Polymeric resins can be promising materials for adsorptive remediation of pollutants in aqueous media. [Display omitted] • Synthesis of novel hyper-cross-linked polymeric resin (TABAMA) through one step Michael addition reaction. • The polymeric resin showed excellent performance in adsorptive removal of Cd, Cr, and Pb from water. • Pre and post adsorption characterization of the adsorbent was performed. • TABAMA showed potential for practical application in ultrafast removal of inorganic and organic pollutants. [ABSTRACT FROM AUTHOR]

The use of green, non-toxic raw materials is of great significance to the sustainable development of the environment, among which epigallocatechin gallate (EGCG) is a renewable carbon source from plants. At present, there is a lack of research on the metal-polyphenol nanomaterials their use in water decontamination. In this study, a novel SA/EGCG@Ti/SA/PVDF (SESP) sandwich membrane was prepared to effectively solve the problems of difficult recovery of nanomaterials and the leaching of metal ions. The membrane was made by scraping SA on the surface of the PVDF substrate as the bottom protective layer, depositing EGCG@Ti NPs as the functional layer, then coating SA as the surface isolation layer, and finally cross-linking with anhydrous calcium chloride. Results showed that EGCG@Ti NPs dispersed well on the surface of the SA/PVDF basement membrane. SESP sandwich membrane had good hydrothermal and acid-base stability, and it can be applied to wastewater with multiple co-existing heavy metals (e.g. , Cu, Pb, Cd, and Ni). The contact angle and pure water flux of the SESP sandwich membrane with a negatively charged surface were 14.0–15.6° and 171.40 L/m2 h, respectively. The pure water flux of the regenerated membrane after BSA pollution recovered to 98.68 L/m2 h, and the interception efficiency and the interception flux of Cr(VI) were 100 % and 72.92 L/m2 h at 40 min of interception, respectively. Additionally, the removal efficiency of Cr(VI) by SESP sandwich membrane was maintained above 83 % for simulated wastewater and 100 % for actual wastewater after five adsorption-desorption cycles. Cr(VI) and Cr(III) can be removed simultaneously with the negatively charged SESP sandwich membrane. EDS and XPS analysis showed that the removal of Cr(VI) was controlled by the Donnan effect, anion exchange, chelation/complexation, and reduction mechanism. In contrast, Cr(III) was mainly influenced by electrostatic attraction and chelation/complexation mechanisms. In conclusion, the newly prepared sandwich membrane has good application potential in treating Cr(VI) wastewater. [Display omitted] • SESP membrane was first synthesized based on EGCG and titanium salts. • Cr(VI)(10 mg/L) removal by the SESP membrane was not susceptible to pH changes. • Cr(VI) removal rate in the actual wastewater maintained 100 % after 5 adsorption-desorption cycles. • SESP membrane had high thermal stability and salt resistancy. • Cr(VI) and Cr(III) can be simultaneously removed by SESP sandwich membrane. [ABSTRACT FROM AUTHOR]

Industrialization and population growth have adversely affected our environment. Heavy metal-contaminated industrial wastewater and the extensive use of fossils fuel are the prime reason for the degradation of the environment. In this research work, removal of heavy metals (Ni, Fe, and Cr) was achieved from synthetically prepared wastewater in a two-step process, i.e., metal-impregnation and hydrothermal liquefaction (HTL). In the first stage, metal removal was investigated via batch impregnation process using wheat straw by varying parameters such as pH (2 − 12), biomass dosages (0.5 – 1.5 g), and contact time (up to 48 h). The maximum metal removal achieved at this stage was 55 – 65 % (Ni – 58.78 ± 1.5 %, Fe – 62.55 ± 1.8 %, and Cr – 63.51 ± 1.7 %). In the second stage, almost complete removal of heavy metals (99.9 %) was accomplished during the hydrothermal liquefaction of metal-loaded wheat straw and filtered wastewater (used as solvent) collected after the biosorption process. The HTL experiment of metal-impregnated wheat straw was performed by varying temperatures, biomass–to–wastewater ratio, and residence time. Nano-metals (oxides/hydroxides) were formed in the 10–50 nm range during the impregnation process, enhancing the HTL product's yield and selectivity. MP-AES analyzed the heavy metals concentration, and XRD confirmed the formation/reduction of nano-metals. TEM and FE-SEM analysis illustrated the particle size and morphology. CHNS, FTIR, and GC-MS analysis identified the heavy and light bio-oil compositions. In the present study, we have addressed the issues of heavy metal removal and fulfilling the energy demand gap via a greener and eco-friendly approach with the concept of waste–treat–waste and waste–to–energy. The present method provides an efficient outcome and can be a sustainable solution for the two prominent issues. [Display omitted] • Metals removal (61.61 %) from wastewater by metal-impregnation into biomass matrix. • Formation of nanometals (M+n) during metal-impregnation process of size 22.0 nm. • Achieved almost complete heavy metal removal (99.9 %) after hydrothermal treatment. • Maximum bio-oil yield (36.25 wt%) was produced for metal-impregnated wheat straw. • Crystalline nanoparticle formation at 350 °C significantly enhances bio-oil yield. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Carbon-coated montmorillonite nanocomposite (CMt) was used to remove Cr(VI). • XANES and STXM provided insight into the mechanisms of Cr(VI) removal by CMt. • Phenolic groups contributed to the reduction of Cr(VI) to Cr(III). • Reduced Cr(III) occurred as precipitated Cr(OH) 3 and Cr(III)-acetate complex. Abstract A carbon-coated montmorillonite nanocomposite (CMt), obtained by hydrothermal carbonization of montmorillonite suspension in glucose, was used to remove Cr(VI) from aqueous solutions. The distribution and speciation of Cr immobilized by CMt were assessed by transmission electron microscopy with energy-dispersive X-ray analysis, X-ray absorption near edge structure (XANES), and scanning transmission soft X-ray microscopy (STXM). The variation in the functional groups and molecular structures of CMt was also investigated. The capacity of CMt for adsorbing Cr(VI) was markedly superior to that of the parent montmorillonite, showing maximum uptake of 100 and 12.4 mg g−1 at pH 2 and 8, respectively. The Cr K-edge XANES and STXM analyses indicated that Cr(VI) was reduced to Cr(III) under both acidic and alkaline conditions, while a Cr(OH) 3 precipitate and Cr(III)-acetate complex were the predominant species present on the CMt surface. The Fourier transform infrared spectroscopy and C K-edge XANES further suggested that the phenolic groups in CMt could serve as electron donors, facilitating Cr(VI) reduction. The combined results indicate that electrostatic attraction, Cr(VI) reduction, complexation, and precipitation are involved in the removal of Cr(VI) by CMt. [ABSTRACT FROM AUTHOR]

Highlights • Cr(VI) concentrations had distinct effects on the microbial communities and system performance. • Cr(VI) inhibited metabolic pathway and functional genes of the microbial communities in sludge. • Cr(VI) especially inhibited gene abundance those involving in denitrification pathway. • Microbe comprising functional genes had very high diversity and were adversely affected by Cr(VI). Abstract This is the first study exploring the effects of persistent Cr(VI) treatment on microbial communities and function as well as the process efficiency of an A 2 O system. The inhibitory effect was clearly higher at a high Cr(VI) concentration than a low Cr(VI) concentration, and different Cr(VI) concentrations had distinct effects on the microbial communities as well as on the performance efficiency of the system. Functional annotation analysis indicated that Cr(VI) stress inhibited most of the metabolic pathway and functional genes of the microbial communities, especially those involved in the denitrification pathway. Network analysis was used to investigate the co-occurrence patterns between denitrification genes and microbial taxa; the results indicated that microorganisms with functional genes had high diversity and were adversely affected by Cr(VI) exposure. This study is the first to establish a relationship between Cr(VI) stress and microbial communities and function as well as to determine the underlying mechanisms and roles of Cr(VI) in A 2 O sludge. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Biosorbent, porous carbon, and Fe/Cs directly prepared from Lake Erie HAB biomass. • Algal powder biosorbent has oxygen functional groups that improve phenol removal. • HAB-based carbon is microporous, improving phenol removal via π-π stacking. • Fe/Cs have high Cr(VI) removal due to synergistic reduction and adsorption. • Fe/C-FAC maintains up to 95% Cr(VI) removal performance in wastewater. Abstract Lake Erie experiences annual harmful algal blooms (HAB), but generated HAB biomass may provide a waste-based precursor for environmental remediation materials. Three classes of materials (i.e., algal powder biosorbent, porous carbon, and iron/carbon (Fe/C) composite) are prepared from HAB biomass. Algal powder is nonporous with diverse functional groups. Porous carbon, prepared via one-pot carbonization and activation, has surface area up to 430 m2/g. Fe/Cs are prepared by cultivating HAB biomass in iron-rich media, followed by one-pot pyrolysis. Fe/Cs have over 6 wt% iron (Fe0 and Fe 3 O 4) and nitrogen doping (up to 4 wt%). Materials were applied in phenol and Cr(VI) removal tests to identify preferred products for use in water treatment applications. In deionized water, porous carbon removes the most phenol (52 mg/g), followed by algal powder (38 mg/g) and Fe/C (33 mg/g). Micropore volume and functional groups improve phenol removal. Cr(VI) removal follows: Fe/C (43 mg/g) > porous carbon (28 mg/g) > algal powder (17 mg/g), with synergistic adsorption and reduction elevating Fe/C's performance. Cr(VI) and phenol removal studies were completed with variable pH, ionic strength, and water composition to highlight application potential. This work proposes HAB biomass reuse for pollution control, investigating interaction mechanisms between materials and contaminants. [ABSTRACT FROM AUTHOR]

Attapulgite clay also known as palygorskite is a mineral clay which possess good adsorption properties based on its adsorption capacity, porous structure and moderate cation exchange properties. The study investigated the effectiveness of naturally occurring and hydrochloric acid modified attapulgite as adsorbents for Cr (VI) remediation in wastewater. The physical properties of the clay were characterized using a range of techniques. X-ray diffraction confirmed the purity of the clay while BET analysis indicated an increase in surface area from 131.4 to 183.2 m2/g after acid modification. The modified attapulgite was predicted to have an adsorption capacity of 75 mg/g compared to 2.1 mg/g for the naturally occurring attapulgite. The increase in adsorption capacity was attributed to a change in surface area as well as changes in the surface chemistry of the clay. The adsorption isotherms were best described by the Langmuir mono-layer adsorption model while the kinetics fit the Langren first order kinetics model. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Higher Cr(VI) removal and longer longevity were achieved in synergistic system. • The synergism contained HFB-ZVI/Fe 3 O 4 composite and Na 2 EDTA complexation. • The composite strongly captured Cr(VI) by electrostatic attraction and exchange. • Na 2 EDTA complexation retarded passivation and produced more reactive sites. • Na 2 EDTA recovery and column regeneration were successfully demonstrated. Abstract The application of zero-valent iron (ZVI) for Cr(VI) removal often presents limitations due to its easy passivation. In this study, a column packed with hydroxyl-functionalized ball-milled ZVI/Fe 3 O 4 (HFB-ZVI/Fe 3 O 4) composite, assisted with Na 2 EDTA complexation, was developed to achieve sustainable treatment of Cr(VI)-containing wastewater. The results showed that at influent Cr(VI) concentration of as high as 50 mg/L, effluent Cr(VI) concentration below 0.5 mg/L was sustained for bed volume of as high as 1271 BV along with 2 g/L Na 2 EDTA concentration. Through the hydroxyl-functionalized treatment, FeOOH coating containing surface-adhering Fe(II) on the composite surface can be formed. Hydrolysis and auto-reduction of Fe(II)/Fe(III) species caused proton accumulation, resulting in remarkable attraction of anionic Cr(VI) via electrostatic interaction and exchange. Therefore, the reduction of Cr(VI) to Cr(III) was considerably enhanced. On the other hand, Na 2 EDTA complexation suppressed the growth of passivation layer and generated fresh corrosion products, thereby providing additional reactive sites for Cr(VI) removal. Additionally, Na 2 EDTA recovery and spent column regeneration were successfully proven. The remarkable effectiveness of Cr(VI) removal from actual electroplating wastewater confirmed the potential of the HFB-ZVI/Fe 3 O 4 composite-packed column and Na 2 EDTA assistance-coordinated system in full-scale application. [ABSTRACT FROM AUTHOR]

Abstract A bioremedial approach was investigated on the removal of Cr(VI) from aqueous solution using a novel chromium reducing bacteria isolated from coalmine wastewater. Cr(VI) removal efficacy of the bacterium was determined in a series of batch studies under the influence of various parameters viz., pH (1–7), temperature (20–40 °C), initial metal concentration (1–150 mg/L), agitation speed (80–150 rpm) and substrate concentration (1–5 mg/L). Oxygen involvement in the removal process was determined by different incubation conditions. Substrate consumption and its resultant biomass generation were considered for determining the viability of the microbe under varied metal concentration. The microbial isolate survived in Cr(VI) tainted solution with initial concentration of 1–140 mg/L, among which maximum remediation was found in 60 mg/L Cr(VI) loaded solution. The bacterial species also survived in other metal solution viz., Fe(II), As(V), Cu(II), Pb(II), Zn(II), Mg(II), Mn(II) apart from Cr(VI). Multiple approaches were tested to facilitate understanding of the bacterial Cr(VI) removal mechanism. The bacteria accumulated metal ions in the exponential growth phase both on and within the cell. Underlying latent factors which governed the bacterial growth and its removal activity was determined with the classical Monod equation. The isolated bacterium also survived in the bimetallic solutions with significant removal of Cr(VI). The microbial species isolated from mining area was identified as Pseudomonas brenneri by 16s rRNA molecular characterization. Hence, the isolated novel bacterium illustrated promising involvement towards bio-treatment of Cr(VI) laden wastewater. Graphical abstract Image 1 Highlights • Cr(VI) reducing bacterium was isolated from coalmine area. • The isolate was identified as Pseudomonas brenneri by 16s rRNA characterization. • The incubation condition parameters were optimized. • Cr(VI) bioremediation efficiency was tested for both single and bimetallic solutions. • Cr(VI) bioremedial process was substantiated with Monod's equation. [ABSTRACT FROM AUTHOR]

Abstract A novel amino-functionalized vermiculite (AVT)-supported nanoscale zero-valent iron (AVT-nZVI) was successfully synthesized for Cr(VI) removal from simulated electroplating rinse wastewater. Since the agglomeration and oxidation of nZVI could be weakened and the reaction rate between Cr(VI) and nZVI could be enhanced for the novel AVT-nZVI, an efficient Cr(VI) removal could be achieved. The experimental results showed that 100% of Cr(VI) removal was obtained with AVT-nZVI, whereas only 87.5% was achieved by nZVI after reacting for 60 min with 20.0 mg L−1 Cr(VI) (pH = 5.0). After four cycles, the removal efficiency of Cr(VI) by AVT-nZVI still maintained at above 70%, suggesting that AVT-nZVI exhibited a good performance of reusability. The stability of AVT-nZVI particles was better than nZVI, which was confirmed by the steady-state polarization measurements. Furthermore, the removal of Cr(VI) by AVT-nZVI was proved to be in accordance with the pseudo-second-order adsorption kinetics and Langmuir model. Based on the experiments and characterization, the reaction mechanism of Cr(VI) removal by AVT-nZVI was clarified. The protonated amino groups (-NH 3 +) on the AVT promoted negative Cr(VI) species to be adsorbed on AVT-nZVI surface. Besides, Cr(VI) was reduced by Fe (0) to Cr(III), which was eventually adsorbed on the surface of AVT-nZVI particles as the Cr(III)-Fe(III) co-precipitates. Graphical abstract Image 1 Highlights • AVT-nZVI was synthesized for treatment of Cr(VI)-containing water. • AVT inhibited the aggregation of nZVI particles and increased their reactivity. • AVT-nZVI exhibited better performance of stability than nZVI. • Reaction mechanisms of Cr(VI) removal by AVT-nZVI were proposed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Very efficient treatment of high strength real tannery wastewater. • Complete synergistic removal of total chromium in chemical-less UVC/VUV process. • Comprehensive study of the mechanisms involved in removal of Cr, S2− and COD. • Total and hexavalent chromium mass balance in electrocoagulation+UVC/VUV system. Abstract Accelerated treatment of tannery wastewater was conducted using the electrocoagulation process combined with UVC/VUV photoreactor. In order to better determine the mechanisms, synthetic solutions were studied before the tannery wastewater. For synthetic solutions (50 mg/L Cr(VI) and sulfide), almost complete removals of Cr(VI) and sulfide were obtained in pH levels ≤7 in 30 min. For real tannery wastewater, the highlighted parameters were chemical oxygen demand (COD) = 20600 mg/L, total chromium (Cr(T)) 30.11 mg/L, Cr(VI) = 6.95 mg/L and sulfide = 66.13 mg/L. The combined system exhibited excellent performance by which the final COD of the effluent reached 96.88 mg/L (99.52% removal efficiency). Cr(T) and sulfide removal efficiencies were 100% and 98.27%, respectively. An interesting phenomenon was observed in UVC/VUV process which was reflected as appearance of white flocs along with complete removal of Cr(T). Energy dispersive X-ray (EDX) analysis and Cr(T) tracing of the flocs as well as mass balance analysis indicated that a specific condition (typically in case of solution pH) had led to the generation of Al(OH) 3 -based flocs from the aluminate ion. Actually, using the proposed combined system brought about advanced oxidation of oxidisable inorganic (S2−) and organic (COD) contents in simultaneous with the reduction of Cr(VI) through a multi-lateral mechanism including advanced reduction (H 2 O photoionization-generated electrons) which was boosted by sulfide and organic content of tannery wastewater. Co-precipitation of Cr(OH) 3 and Al(OH) 3 was determined as the main mechanism for complete removals of Cr(T) and sulfide. It can be concluded that the selected combination is an efficient and promising method for the treatment of real industrial tannery wastewaters. [ABSTRACT FROM AUTHOR]

Abstract A series of expanded graphite/layered double hydroxides (EG/LDHs) nanocomposites were prepared by a green method combining mechanical chemistry and hydrothermal synthesis, which had the advantages of simplicity, easy for industrial-scale production, no use of organic solvents and no waste water generation. The obtained product showed a regular crystal structure and uniform particle size. It was found that a variety of oxygen-containing functional groups were generated at the edge of the graphite nanosheets and inside the sheets. Batch adsorption experiments of Cr(VI) were carried out and the products after adsorption were analyzed by X-ray photoelectron spectroscopy (XPS) in order to explore the adsorption behavior of the graphite nanosheets and EG/LDHs nanocomposites. The results showed that EG/LDHs nanocomposites can be effectively applied to remove Cr(VI) from aqueous solution by physico-chemical adsorption. The adsorption isotherm of adsorbents obtained under different milling conditions can be well described by the Langmuir model. EG/LDHs nanocomposite, produced by ball milling for 5 h at rotational speed of 900 rpm, displayed the optimal Cr(VI) adsorption performance. The presence of oxygen-containing functional groups was beneficial to Cr(VI) adsorption, and the adsorbents induced reduction of Cr(VI) to Cr(III). The green synthesis of EG/LDHs nanocomposites is low-cost and environmental friendly, which is advantageous for advanced treatment of Cr(VI)-containing wastewater. Graphical abstract Image 1 Highlights • The nanocomposite was prepared by a green method without producing wastewater. • The obtained product has a regular crystal structure and uniform particle size. • Composite contains abundant oxygen-containing functional groups and defect sites. • The total cost of raw materials and energy consumption is economical. [ABSTRACT FROM AUTHOR]

Abstract Biosorption was carried out in this study using the biomass of microalgae Scenedesmus sp. as adsorbent for the removal of hexavalent chromium or Cr(VI) from solution. Different relevant parameters like initial pH, contact time, initial Cr(VI) concentration, biosorbent dosage, particle size, and temperature were examined to evaluate their effect. They were found to be effective with the maximum of 92.89% Cr loading onto the biomass. The FTIR analysis revealed the presence of easily hydrolyzed functional groups like aldehydes, amides, carboxylic acids, phosphates, and halides, which charged positively below the point of zero charge at pH 2.65. The biosorption proceeded through the anionic adsorption mechanism and followed the pseudo-first order kinetic model. Its feasibility was confirmed as the experimental data closely fitted to both Langmuir and Freundlich isotherms. The biosorption was spontaneous. Its spontaneity increased with the increase of temperature. The positive entropy change suggested the randomness at the solid-liquid interface. This study recommended that the toxic Cr(VI) could be removed from different contaminated water samples in the nearby chromite mines using the microalgae biomass. However, it requires attention in some other sides like activation of biomass, interference of other ions, elevation of the experimental pH, the large biomass generation and harvesting, desorption of the Cr-loaded biomass, and recovery of the energy value of the waste biomass. [ABSTRACT FROM AUTHOR]

Flower-like AuPtPd-Fe3O4 new nanohybrid prepared through a scalable synthetic approach was tested for the effective and simultaneous removal of Humic Acids and Cr (VI). Field emission scanning electron microscopy (FESEM) equipped with an energy dispersive X-ray (EDX) probe, X-ray diffractometer (XRD) and thermogravimetric analysis (TG-DTG) were used for characterization. The nanocatalyst, at the end of the preparation process, results dispersible in water. Calibration equations were plotted for the removal evaluation of Cr(VI) and Humic Acids in water samples. Electrochemical tests were carried out at pH 3.0 and 30 mA. Humic Acids were highly mineralized with TOC removal efficiency of 95%. In 3 h, 99 % of total Cr was removed. [ABSTRACT FROM AUTHOR]

Hexavalent Chromium species are classified as hazardous compounds due to their high toxic potential, considering also their remarkable solubility and redox potential. Various processes have been developed to remove/recover Cr(VI) species from polluted groundwater, such as membrane processes, ion-exchange and adsorption and chemical or biochemical reduction. Indeed, the reduction/removal process of Cr(VI) through iron-based materials usually leads to a pH increase of the reaction medium, allowing to facilitate the subsequent precipitation of the Cr(III) species. In this context, the use of iron based nano-particles (IBNs) supported on bio-polymer matrix allowed to maximize the Cr(VI) removal capacities of iron-based materials, leading to the production of high active and eco-compatible nano-materials. The use of chitosan as surfacemodified agent, allows the reduction of aggregation forces among the produced IBNs, leading to higher surface active areas and chemical reactivity. At the same time, the use of a bio-polymer increases the ecocompatibility of the IBNs, reducing the possible interaction with bacteria and microorganisms during the treatment process. In this work chitosan-nanomagnetite particles were synthetized and employed as packing material inside fixed-bed lab-scale column (height 25 cm and diameter of 1.5 cm) to remove, in continuous, Cr(VI) species from synthetic wastewaters. The tests were performed at different inlet flow-rate values (2, 5 and 7 mL/min) at fixed Cr(VI) initial concentration (20 mg/L) and varying the solution pH (pH=4 and 7). The obtained breakthrough curves were then modeled according to the classical dynamic Thomas model. [ABSTRACT FROM AUTHOR]

The present study reports about the development of heterogeneous Fenton process by means of nano zerovalent iron particles (nZVI) as heterogeneous catalyst for the treatment of a synthetic tannery wastewater (STW). The experimental tests were conducted using a pilot Fenton plant for the investigation of the scale-up possibility of the treatment process, studying the influence of initial pH (varied in the range 3-7) and catalyst/oxidant ratio (Cat/Ox wt%) on the overall efficiency of the process. The target wastewater prepared in laboratory, was characterized by a high initial COD0=1200 mg/L and the monitored parameters during the process were COD and hexavalent chromium (Cr(VI)) concentrations. Two different Cat/Ox ratios were tested (20 and 35%) whereas the H2O2 amount was fixed equal to 0.75*COD0. The treatment process was performed for the first 2 h in batch, whereas the remaining 8 h were conducted in continuous. The optimal operating parameters (Cat/OX=35%, pH=3) allowed to reach a COD removal efficiency of 70% and a total Cr(VI) removal. [ABSTRACT FROM AUTHOR]

The production of functionalized nano-composites represents an important research activity in the environmental remediation field. The use of iron-based nano-particles (IBNs) supported on bio-polymer matrix might lead to the development of active nano-materials characterized by a notable eco-compatibility. Chitosan is a biodegradable biopolymer that can be effectively used to produce active nano-composites with IBNs. In this study, a chitosan-magnetite nano-composite was produced in the laboratory and used in batch experimental tests for the removal of Hexavalent Chromium, Cr(VI), in aqueous solutions. Cr(VI) is considered one of the most toxic compounds present in the Mediterranean Area due to its carcinogenic and mutagenic characteristics, besides its notable solubility and mobility in the environment. The most effective way for the remediation of Cr(VI)-polluted groundwater is represented by the combination of chemical reduction and coprecipitation processes, generating Cr(III) species, characterized by very low toxicity and solubility in comparison to Cr(VI) ones. The synthesized nano-composite was used in batch lab-scale reactors and the kinetics of the process was studied varying the initial nano-composite concentration (0.25, 0.5, 0.75, 1 g/L) at fixed Cr(VI) initial concentration (20 mg/L). In addition, the initial pH influence on the Cr(VI) removal efficiency was analyzed in the range 3-7. [ABSTRACT FROM AUTHOR]

The mixing operation and design of agitated vessels for various chemical engineering applications may still represent a challenge due to the complexity of hydrodynamic fields established inside the reaction system. Computational Fluid Dynamics (CFD) is considered a valuable tool for the investigation of the complex turbulent flow field proper of mechanically agitated vessel (MAV). The use of CFD may effectively support the process engineer for the selection of the most proper impeller/vessel geometry and operative conditions to achieve homogeneous and fully turbulent conditions. In this work, experimental tests and CFD simulations were performed to study the Cr(VI) removal efficiency through nano-hematite particles (nHP) in MAV. More in detail, some solutions of Cr(VI) were treated using lab-made nHP, produced by a spinning disk reactor, in labscale agitated vessel and the kinetic of the removal process was experimentally studied varying the reactor/impeller configuration (impeller geometry) and the impeller rotational velocity. The obtained results were interpreted according to a CFD model of the system hydrodynamic field based on the k- turbulent model whereas the kinetic data were fitted to a suitable mass transfer kinetic model. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Synthesis of Fe 3 O 4 @SiO 2 -Tet-Pd(II) using a simple method. • Characterization of catalyst by FT-IR, XRD, FESEM, EDS, TEM and TG-DTA. • Catalytic reduction of Cr(VI), 2,4-DNPH and 4-NP by Fe 3 O 4 @SiO 2 -Tet-Pd(II). Abstract In the present work, a new catalytic system based on palladium(II)-tetrazole complex immobilized on silica-coated Fe 3 O 4 (Fe 3 O 4 @SiO 2) nanoparticles ([Fe 3 O 4 @SiO 2 -Tet-Pd(II)]) is introduced. In the first stage, the geometry optimization and calculations of structural and electronic properties of molecular system 5-phenyl-1 H -tetrazole-Pd (II) complex have been carried out at UB3LYP/6-31G∗/LANL2DZ level of theory. Then, the [Fe 3 O 4 @SiO 2 -Tet-Pd(II)] was prepared via immobilizing 5-phenyl-1 H -tetrazole as a suitable ligand on the surface of Fe 3 O 4 @SiO 2 as a support. The [Fe 3 O 4 @SiO 2 -Tet-Pd(II)] as a novel magnetically catalyst was characterized by XRD, FT-IR, FE-SEM, EDS, TG-DTA and VSM. This heterogeneous catalytic system demonstrated high activity in the reduction of 2,4-dinitrophenylhydrazine (2,4-DNPH), 4-nitrophenol (4-NP) and Cr(VI) in the present of NaBH 4 as the reduction agent at room temperature and was reusable five times with no obvious decrease of catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract Sulfated carboxymethyl cellulose nanofilter membrane by crosslinking of glutaradehyde (GA) supported on polysulfone membrane (SCMC-GA-NF) was prepared and characterized by FTIR, XRD, SEM and EDS. The modeling of Cr (VI) removal from tannery industries wastewater by utilizing synthesized SCMC-GA-NF was studied by response surface methodology. The initial pH (4,8,12), pressure (2, 4, 6 bar) and SO 3 /Pyridine:CMC ratio (1:1, 2:1, 3:1) in filter were selected as independent variables in box behnken design while Cr(VI) removal % was considered as the response function. The maximum Cr(VI) removal efficiency of 79.85% was obtained at pH = 4, pressure = 3 bar and SO 3 /Pyridine:CMC ratio (1:1) in filter. The reusability of SCMC-GA-NF was found to be suitable. The current study indicated that the prepared SCMC-GA-NF is an efficient filter for removal of Cr(VI) from aqueous solutions. [ABSTRACT FROM AUTHOR]

Abstract Silicon-rich biochar-supported nanoscale zero-valent iron (nZVI) was studied to evaluate enhanced removal of hexavalent chromium (Cr(VI)) in solution. The compositional structures of the nZVI and biochar-supported nZVI were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectra before and after Cr(VI) reaction. The removal amount of Cr(VI) by nZVI-RS700 (rice straw pyrolyzed at 700 °C) was considerably greater than that by nZVI and other biochar-supported nZVI samples. Upon the silicon was removed from RS700 (nZVI-RS700(-Si)), a significant decreased removal of Cr(VI) was observed. It was revealed that nZVI supported by silicate particles of biochar and the promotion of iron oxidation by SiO 2 both contribute to the enhanced Cr(VI) removal. We found that the reduction and adsorption both contributed to the removal of Cr(VI), ferrous chromite (FeCr 2 O 4) was observed on the surface of the nZVI-RS700 composite. The formation of FeCr 2 O 4 is attributed to the reduction of Cr(VI) by nZVI and the adsorption of chromium oxide with iron on the surface of RS700. Therefore, RS700-supported nZVI can be used as a potential remediation reagent to treat Cr(VI)-contaminated groundwater. Graphical abstract The mechanism of Cr(Ⅵ) removal by biochar support nanoscale zero-valent iron. Image Highlights • Silicon particles in biochar served as a support site for nZVI. • SiO 2 in biochar promotes the oxidation of iron. • Cr(VI) removal was enhanced by silicon-rich biochar. • NZVI-RS700 showed the highest Cr(VI) removal due to reduction and coprecipitation. • It was proved that Cr(VI) removal by nZVI-RS700(-Si) was significantly decreased. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Iron-based nanoparticles were successfully prepared by using Nephrolepis auriculata extracts. • Polyphenols, ketones and organic acids in extracts were responsible for reducing Fe3+. • 90.93% of Cr(VI) from aqueous solution was removed using iron-based nanoparticles. Abstract The use of plant extracts as reducing agents may be preferable to use of chemical reduction reagent (i.e. sodium borohydride) to synthesis of iron-based nanoparticles for using in wastewater treatment. This report describes the successful synthesis of iron-based nanoparticles (NA-Fe-NPs) using extracts of Nephrolepis auriculata. TEM and XRD indicated that the core of NA-Fe-NPs were amorphous and spherical with size ranging from 40 to 70 nm. Meanwhile, FT-IR revealed that the flavonoids, polyphenols, organic acids in extracts were responsible for reducing Fe3+ and coating/stabilizing the iron-nanoparticles. The removal of Cr(VI) wastewater using NA-Fe-NPs suggested that 90.93% of Cr(VI) were removed, demonstrated the feasibility of the materials for environmental remediation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Novel hydrogels were synthesized by anionic and cationic modification. • −COOH and NR 3 + groups on hydrogels increases Cr(VI) adsorption capacity. • The modified hydrogels had superior maximum adsorption capacity of Cr(VI). • Adsorbents can be easily regenerated for succeeding adsorption cycles. Abstract Two modified hydrogels, CL- g - p AA and CL- g - p DMC, are prepared from hydrogels graft copolymerization with acrylic acid and methacryloxyethyl trimethyl ammonium chloride, respectively. The as prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Scanning electron microscopy (SEM) and Thermogravimetric (TG). Batch experiments were performed to determine the ability of CL- g - p AA and CL- g - p DMC to remove Cr(VI) from solution. The effect of pH, dosage and co-existing anions on Cr(VI) removal were investigated along with regeneration activity. The adsorption of Cr(VI) decreases with the increase of pH and temperature. The introduction of −COOH and-[N+(CH 3) 3 ] (NR 3 +) groups on hydrogels increases Cr(VI) adsorption capacity. Based on cost and actual water considerations the optimum adsorption occurs at pH 5, at a temperature of 298 k, with an adsorbent dose of 0.1 g L−1 and with the contact time 500 min for the Cr (VI) removal. The usual metal ions of natural water would not inhibit the complexion reaction between hydrogels and Cr(VI). The modified hydrogels exhibited adsorption capacities of 85.47 mg g−1 for CL- g - p AA and 105.26 mg g−1 for CL- g - p DMC. The adsorption kinetic studies display adsorption to be the pseudo-second-order rate model. The adsorption isotherms of Cr(VI) on the CL- g - p AA and CL- g - p DMC were well fitted by the Langmuir isotherm equation. The Cr(VI) adsorption is endothermic and the CL- g - p DMC exhibits high regeneration efficiency. From the results, it was concluded that CL- g - p AA and CL- g - p DMC were underlying materials for the separation and preconcentration of Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]

The use of industrial waste to synthesize materials of technological interest is a rational way to minimize or solve environmental pollution problems. This work reports the removal of chromium ions from tannery effluent using magnetic hybrid adsorbents synthesized from waste biomass: coconut mesocarp (HCN), sugar cane bagasse (HBS), sawdust (HS), and termite nest (HT). The presence of organic matter and the cobalt ferrite phase in the structures of the materials were confirmed by XRD and FTIR analyses. Removal assays performed at different pH values showed the effectiveness of the adsorbents for removal at the natural pH of the effluent (pH 4.75), with adsorption capacity exceeding 6.6 mg g−1 for all the hybrids studied. The adsorption processes showed fast kinetics, with the HS hybrid removing 5.1 mg g−1 of the chromium species present in the effluent in the first 5 min. The HS hybrid presented the highest removal capacity, 6.7 mg g−1, while HBS showed the lowest, 6.6 mg g−1. The removal at equilibrium showed the following increasing order of efficiency of the hybrids: HBS < HCN < HT ≈ HS. The HCN and HT adsorbent matrices saturated with chromium ions (HCNCr and HTCr) showed excellent catalytic performance in the reduction of 4-nitrophenol, with 99.9% conversion within 180-240 s. The other hybrids did not present catalytic activity. The materials showed high capacities for reuse in two successive reduction cycles. The findings highlight the effectiveness of an industrial symbiosis approach to the development of new technologically important materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • P-n heterostructured TiO 2 /NiO double-shelled hollow spheres were prepared. • A cubic-structured NiO layer is grown on surface of anatase TiO 2 hollow sphere. • TiO 2 /NiO show high photocatalytic activity for papermaking wastewater degradation. • The COD Cr removal rate of wastewater reaches 98.1% after 6 h of photodegradation. Abstract P-n heterostructured TiO 2 /NiO double-shelled hollow spheres were prepared through sol–gel and hydrothermal processes. TiO 2 /NiO nanomaterials were comprehensively characterized, and the results reveal that a cubic-structured NiO layer is successfully grown on the surface of the anatase TiO 2 hollow sphere to achieve a p-n heterostructure. The thickness of TiO 2 shell is ∼20 nm, and that of NiO shell is 10–25 nm. Compared with the pure TiO 2 hollow spheres, the prepared p-n heterostructures display a considerably higher photocatalytic activity for papermaking wastewater degradation under UV light irradiation. The chemical oxygen demand removal rate of papermaking wastewater reaches 98.1% after 6 h of photodegradation with DSTN2 as the photocatalyst. The enhanced photocatalytic activity is due to the synergetic effects of p-n heterostructures and the large specific surface area of the catalyst; these effects may promote the separation of photogenerated electron–hole pairs. [ABSTRACT FROM AUTHOR]