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Nanostructured ZnNiBi-NO3-Layered Double Hydroxides (LDHs) was synthesised, followed by the simple co-precipitation method using Zn(NO3)2.6 H2O, Ni(NO3)2.6 H2O and Bi(NO3)3 as the precursors. Synthesised LDHs was characterised by various techniques such as infrared (IR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and thermal gravimetric analysis (TGA). ZnNiBi-NO3 LDHs were applied as efficient adsorbents for speciation analysis and preconcentration/separation of Cr(VI)/Cr(III) ions in aqueous samples prior to their trace determinations by microsample injection system-coupled flame atomic absorption spectrometry (MIS-FAAS). ZnNiBi-NO3 LDHs worked well for speciation and preconcentration/separation of Cr(VI)/Cr(III) ions at an optimum of pH 3.0 and adsorbent dosage of 400 mg. LOD and LOQ of Cr(VI) ions were calculated to be 0.03 and 0.10 μg L−1, respectively with a preconcentration factor of 400. The total saturation capacity of ZnNiBi-NO3 LDHs for Cr(VI) ions was investigated and found to be 46.0 mg g−1. The mthod was reproduced with RSD ≤1.4% of five replicates. The accuracy of method was evaluated by analysing 10–100 μg L−1 Cr(VI) ions standard solutions, and Cr(VI) ions were recovered ≥96.9% with RSD ≤2.4%. The developed method worked well on wastewater samples. [ABSTRACT FROM AUTHOR]

Industrialization activities have increased the discharge of wastewater that is polluted with hexavalent chromium (Cr(VI)), posing risks to ecosystems and humans. The photocatalytic reduction of Cr(VI) is viewed as a promising method for the removal of Cr(VI) species. However, developing photocatalysts with the desired catalytic activity, recyclability, and reusability remains a challenge. Herein, a composite aerogel was designed and fabricated with a Ti-based metal–organic framework (MIL-125-NH2) and carboxylated nanocellulose. MIL-125-NH2 presents a strong visible-light response, and the interactions between the amino groups of MIL-125-NH2 and the carboxyl groups of cellulose produce a strong interface affinity in the composites. The as-prepared aerogels exhibited a micro/macroporous structure. At an optimal MIL-125-NH2 loading of 55 wt%, the MC-5 sample showed a specific surface area of 582 m2·g−1. MC-5 achieved a photocatalytic Cr(VI) removal efficiency of 99.8%. Meanwhile, the aerogel-type photocatalysts demonstrated good stability and recycling ability, as MC-5 maintained a removal rate of 82% after 10 cycles. This work sheds light on the preparation of novel photocatalysts with three-dimensional structures for environmental remediation. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr(VI)) has attracted much attention because it is a harmful pollutant. In this study, acid hydrolyzed hydrothermal double modified starch (AHS) and hydroperoxide oxidized starch (HOS) are prepared from natural starch and used for the reduction of chromium (VI) in aqueous systems. The effects of hydrothermal acidolysis and oxidative modification of starch on the reduction rate of Cr(VI) are discussed, including the changes of solubility, swelling power, particle size, content of straight‐chain starch, and carbonyl/carboxylic group content. The results of response surface methodology (RSM) optimization show that the influence of reaction conditions on the reduction rate of Cr(VI) by NS is as follows: reaction time > initial pH of solution > reaction temperature > starch to Cr(VI) mass ratio; and on the reduction rate of Cr(VI) by AHS and HOS is as follows: initial pH of solution > reaction time > starch to Cr(VI) mass ratio > reaction temperature. [ABSTRACT FROM AUTHOR]

A hybrid composite, denoted as arginine-functionalized polyaniline@jujube shells (Arg-PANI@JS), was designed by oxidative polymerization of monomer-aniline on the surface of jujube shells matrix in the occurrence of arginine. This adsorbent was subsequently characterized and used in hexavalent chromium Cr(VI) adsorption assays. An experimental batch adsorption setup was utilized to assess the effectiveness of the newly developed adsorbent in detoxifying Cr(VI) ions from the solution. The experimental results were successfully anticipated by a pseudo-second-order model (PSO) and the Freundlich isotherm with a maximum uptake capacity of 1142.86 mg.g−1. The thermodynamic investigation showed that the process was both spontaneous and endothermic. The pivotal driving force behind elucidating the binding mechanism of Cr(VI) species was determined to be electrostatic interactions. Furthermore, our assessment demonstrated that the Arg-PANI@JS composite can be readily regenerated using a NaOH solution and effectively reutilized for removing Cr(VI) from aqueous solutions. Consequently, these findings underscore the promising practical utilization of the Arg-PANI@JS composite in wastewater treatment. [ABSTRACT FROM AUTHOR]

Metal–organic framework UiO-66-NH2 powder used for effective removal of Cr(VI) from water is difficult to recover after usage. In this study, UiO-66-NH2 was in-situ grown on polyacrylonitrile (PAN) nanofiber membrane using water as solvent and trifluoroacetic acid as structure regulator, via hydrothermal method for adsorption of Cr(VI) ions. The optimal proportion of trifluoroacetic acid, hydrothermal synthesis time and pH level were 30%, 4 h and pH = 2, respectively. Scanning electron microscopy showed that UiO-66-NH2 was uniformly and densely coated on the PAN nanofibers. N2 adsorption–desorption experiments and thermogravimetric analysis showed large surface area (680.99 m2/g) and good thermal stability of PAN@UiO-66-NH2, compared to PAN nanofiber membrane. The adsorption capacity of PAN@UiO-66-NH2 nanofiber membrane for Cr(VI) at 298 K was 312.25 mg/g. Kinetic studies revealed that the adsorption process was consistent with Langmuir isotherm and pseudo-second-order model. The composite showed good reusability in Cr(VI) removal in 5 cycles. Based on Zeta potential, the influence of pH and XPS analysis, PAN@UiO-66-NH2 nanofiber membrane effectively adsorbs Cr(VI) through electrostatic interaction. PAN@UiO-66-NH2 nanofiber membrane is therefore considered as an efficient and reusable adsorbent with high potential for Cr(VI) removal in industrial wastewater. [ABSTRACT FROM AUTHOR]

In this study, we present the results of the first comparison of the elimination of toxic Cr(VI) ions, which are hazardous contamination of the environment, from aqueous solutions using ion exchangers (IEs) and polymer materials (PMs) impregnated with D2EHPA or ionic liquids (Cyphos IL 101 and Cyphos IL 104). Sorption of Cr(VI) ions and desorption from the formulated sorption materials were carried out. In comparison, classical solvent extraction was accomplished. Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and atomic force microscopy (AFM) have been used for characterization of the structure of developed IEs and PMs. The highest efficiency of adsorption of Cr(VI) ions was obtained using PMs with ionic liquids (>82%). Desorption from these materials were also very efficient (>75%). On the contrary, the application of IEs allowed for obtaining the best results of both, sorption and desorption processes when using D2EHPA (75% and 72%, respectively). The application of PMs and IEs is part of the green chemistry, and the conducted elimination of chromium(VI) ions using developed materials allows for the conclusion that they can potentially be used on a larger scale, e.g., for the treatment of industrial wastewater rich in Cr(VI) ions. [ABSTRACT FROM AUTHOR]

In this work, porous sludge biochar (PSBC) was prepared by molten salt-assisted pyrolysis of municipal sludge, and PSBC loaded with Fe3O4 (Fe3O4@PSBC) was synthesized by chemical precipitation. The effects of pH (2.0–10.0), sorbent dosage (0.1–2 g/L), coexisting ions (Ca2+, Mg2+, Cu2+, Pb2+, Cl–, SiO32-, NO3-, CO32-, SO42-, and PO43-), adsorption temperature (288, 298, and 308 K), initial Cr(VI) ion concentrations (50–150 mg/L), and adsorption time (5–300 min) on the removal of Cr(VI) ions by the sorbent were investigated. The mechanism of the removal of Cr(VI) ions was characterized by scanning electron microscope (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The result showed that the removal of Cr(VI) ions on PSBC and Fe3O4@PSBC had a strong dependence on the pH of solution. The maximum adsorption capacity of Cr(VI) ions by PSBC and Fe3O4@PSBC was 162 and 209 mg/g, respectively, at a dosage of 0.4 g/L, pH of 3, and temperature of 298 K. The removal process of Cr(VI) ions could be fitted by the Langmuir isotherm model and pseudo-second-order kinetic model. The breakthrough curves were in good agreement with the theoretical values of the Thomas model. The mechanism of the removal of Cr(VI) ions by Fe3O4@PSBC mainly contain complexation, reduction, and electrostatic interaction. This work proposes a new removal material for Cr(VI)-containing wastewater. HIGHLIGHTS A porous Fe3O4@PSBC sorbent was prepared to remove Cr(VI) from aqueous solutions.; The maximum Cr(VI) adsorption capacity of Fe3O4@PSBC was 209 mg/g.; The Cr(VI) removal mechanism mainly included complexation, reduction, and electrostatic interaction.;

• Tuning luminescence and sensing abilities based on novel Eu/Tb@Zr-MOF composites. • Optimized fluorescence emission peaks and fluorescence sensing resolution. • Excellent water stability and long-lasting luminous intensity. • Fairly high fluorescence quenching constants and rather low detection limits. Identification and detection of low concentration heavy metal Cr(VI) ions is one of the focus in water environment monitoring field. But, development of fluorescent sensing probes with high sensitivity, selectivity and anti-interference capabilities is still challenging. Given that the antenna effect of organic units can induce rare earth ions to emit high purity fluorescence, two novel luminous materials Eu@Zr-MOF and Tb@Zr-MOF were deliberately assembled by anchoring of Eu3+ and Tb3+ on a 2D Zr-MOF. Compared with the weak fluorescence of Zr-MOF, they emit the strong bright red and bright green luminescence signals of immobilized rare earth Eu(III) and Tb(III), respectively. And their luminescent intensity can be well maintained in water for >7 days. Prominently, Eu@Zr-MOF and Tb@Zr-MOF are fully capable of high-efficiency fluorescence quenching recognition and quantitative detection of Cr 2 O 7 2− ions (from 0 to 280 μM), by virtue of their respective maximum emission signal at 618 and 546 nm, exhibiting fairly K SV values of 7.7 × 104 and 6.4 × 104 M−1, rather low detection limit (DL) values of 6.63 and 4.82 ppb, which are quite impressive performances even compared to other reported MOFs-based photochemical sensors. This study affords a feasible avenue for designing qualified fluorescence sensors to address some intractable environmental problems, i. e. recognition and detection of heavy metal ions from water. A photoluminescence and fluorescence sensing properties tuning strategy was designed and carried out by respectively anchoring Eu3+/Tb3+ on a water-stable 2D Zr-MOF, enabling highly efficient identification and detection of Cr 2 O 7 2− ions with high sensitivity, selectivity and anti-interference capabilities. [Display omitted] [ABSTRACT FROM AUTHOR]

Water pollution caused by hexavalent chromium [Cr-(VI)] ions has attracted increasing attention because Cr-(VI) ions are highly toxic and carcinogenic, which may cause serious harm to aquatic organisms and human health. More and more research has focused on the sensing or adsorption of Cr-(VI) ions. However, so far, it is still a challenge to prepare advanced materials that can simultaneously detect and adsorb Cr-(VI) ions. Herein, we present a facile and effective strategy to prepare a chitosan–sulfur quantum dots (CS-SQDs) composite hydrogel with both excellent sensing and uptake capability toward Cr-(VI) ions. The CS-SQDs show excellent fluorescence stability against pH variation, high ionic strength, UV–light irradiation, and long-term storage. Moreover, the CS-SQDs exhibit sensitive and selective fluorescence responsiveness to Cr-(VI) ions. The detection limit can reach 176.2 nM. Additionally, the CS-SQDs also show high uptake capability and favorable reusability for the adsorptive removal of Cr-(VI) ions with a maximum adsorption capacity of 186.22 mg g–1. The adsorption behavior is spontaneous, and the adsorption process conforms to Langmuir isotherm and pseudo-second-order kinetic models. This work provides an effective strategy for the preparation of multifunctional hydrogels with the potential to simultaneously monitor and remove water contaminants. [ABSTRACT FROM AUTHOR]

Magnetic mesoporous carbon (MMC) and magnetic activated carbon (MAC) are good functionalized carbon materials to use when applying environmental techniques. In this work, a series of efficient magnetic composite adsorbents containing Fe3O4 and carbon were prepared successfully and used for the adsorption of Cr(VI) ions in petrochemical wastewater. The morphology and structure of these magnetic adsorbents were characterized with FTIR, TG, XRD, VSM, BET, and SEM technologies. The effect of different factors, such as pH, adsorption time, initial Cr(VI) ions' concentration, Fe3O4 loading, and adsorption time, on the adsorption behavior were discussed. The results showed that the 8%Fe3O4@MMC adsorbent exhibited a high removal rate, reutilization, and large adsorption capacity. The corresponding adsorption capacity and removal rate could reach 132.80 mg·g−1 and 99.60% when the pH value, adsorption time, and initial Cr(VI) ions' concentration were 2, 180 min, and 80 mg·L−1 at 298 K. Four kinds of adsorption isotherm models were used for fitting the experimental data by the 8%Fe3O4@MMC adsorbent at different temperatures in detail, and a kinetic model and thermodynamic analysis also were performed carefully. The reutilization performance was investigated, and the Fe3O4@MMC adsorbent exhibited greater advantage in the adsorption of Cr(VI) ions. These good performances can be attributed to a unique uniform pore structure, different crystalline phases of Fe3O4 particles, and adsorption potential rule. Hence, the 8%Fe3O4@MMC adsorbent can be used in industrial petrochemical wastewater treatment. [ABSTRACT FROM AUTHOR]

Rice husk (RH) is one of the widespread agricultural waste materials in the world. At present, most of the husks are either burned out or thrown away as waste, causing serious environmental pollution. This study prepared the hydroxyapatite-modified carbonized rice husk (HAP@ CRH) nanocomposites from rice husk (RH) with modifications, aiming to explore the feasibility of preparing heavy metal ion sorbents. The preparation process affecting its adsorption properties on Cr(VI) ions was systematically investigated, which was optimized by carbonizing RH at 600°C for 2.0 h to produce CRH and then depositing hydroxyapatite particles on the surface of CRH with a Ca2+/CRH ratio of 0.2 g/g. The physiochemical properties of samples were characterized. After modifications to be HAP@CRH, the surface presented a honeycomb-like structure as its porosity increased. The Brunauer--Emmett--Teller specific surface area increased from 1.06 m2/g (RH) to 193.64 m2+/g (CRH) and 183.91 m2+/g (HAP@CRH) respectively, the total pore volume increased from almost zero to 0.089 and 0.202 cm³/g, respectively. The results demonstrated the effective adsorption property of HAP@CRH for Cr(VI) ions as the removal rate of 98.57% and the adsorption amount of 5.91 mg/g were achieved within 24.0 h with adsorbent dosages of 5.0 g/L for initial Cr(VI) concentration of 30 mg/L at 30°C and pH 2.0. This study is expected to promote the utilization of wasted rice husk biomass and provide a new economic and feasible adsorption material for wastewater treatment so as to achieve the purpose of treating waste with waste. [ABSTRACT FROM AUTHOR]

Preparation of the substituted thiourea ligand, synthesis of ZnS, preparation of polymer nanocomposites, and their application in water treatment.

In present study, nitrate anion containing CdCr layered double hydroxides (LDH) was synthesized, and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) and energy-dispersive X-ray-scanning electron microscopy techniques (EDX-SEM). The characteristic diffraction peaks in the XRD pattern of CdCr-NO3 LDH at 2θ values of 15.10 and 26.02° correspond to (003) and (006) planes (hkl), respectively of crystal system of the LDH, revealing layered structure of material with basal (d) spacing of d003: 0.59 nm and d006: 0.34 nm, containing intercalated water and nitrate anions. Stretching vibrations in FT-IR spectrum of the LDH at 3,378.01 and 1,355.51 cm-1 confirmed the intercalation of water and nitrate ions, respectively, in between hydrotalcite-like layers. EDX study confirmed that CdCr-NO3 LDH contained 20.07%, 72.75% and 7.18% of O, Cd(II) and Cr(III), respectively. SEM image revealed that nanostructured material is porous and layered in nature. TGA-DSC confirmed the thermal stability of material at below 509.44°C. CdCr-NO3 LDH was investigated as an efficient adsorbent for capturing of Cr(VI) ions form industrial effluents. The adsorption was optimized by factorial design approach. Maximum response of CdCr-NO3 LDH for capturing/adsorption of Cr(VI) ions was achieved at optimum concentration of Cr(VI) ions: 10 mg L-1, pH: 4.0, adsorbent amount: 40 mg and shaking time: 30 min at 25°C. Method worked well on real wastewater samples. [ABSTRACT FROM AUTHOR]

The main objective of the present study is to develop artificial neural networks (ANN) to predict the adsorption efficiency of multi-walled carbon nanotubes (MWCNTs) on Cr(VI) removal. Polydisperse MWCNTs were synthesized at 750 °C on alumina supported Fe-Co-Mo catalyst using CVD (chemical vapor deposition)-assisted spray pyrolysis of Azadirachta indica (Neem) oil under inert Argon (Ar) atmosphere. Growth of MCWNTs with inner diameters between 9 and 14 nm was corroborated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction analysis (XRD), and Raman spectral evidence assessments. The metal-ion adsorbent capacity (Cr-VI) of the as such prepared MWCNTs was examined for industrial purposes. Different parameters such as adsorption isotherms, kinetics, and thermodynamic parameters were analyzed for the removal of metal ions with MWCNTs. The results of isotherm, kinetic, and thermodynamic study indicated that the process suited well with Langmuir isotherm, pseudo second-order kinetics, and followed endothermic reaction, respectively. The effects of parameters such as adsorbent dosage, concentration of chromium ion (Cr-VI), pH, and contact time were studied to optimize the maximum removal of Cr(VI). In order to optimize the process conditions using Artificial Neural Networks, Box-Behnken design (BBD) was used to design the batch adsorption experiments, and the resulting datasets were used as the input for ANN. To predict the adsorption efficiency, various ANN architectures were examined using different training algorithms, number of neurons in the hidden layer, and the transfer function for the hidden and output layers. A neural network structure with Levenberg–Marquardt (LM) training algorithm, 14 hidden neurons, and tangent sigmoid transfer function at the hidden layer and logarithmic sigmoid transfer function at the output layer furnished the best level of prediction results. Comparing with experimental data, the optimal model capitulated mean square error (MSE),and correlation coefficient (R2) of 0.0324 and 0.99512, respectively. The results showed that ANN is well-organized in predicting the adsorption efficiency of MWCNTs for Cr(VI) metal ion removal process. [ABSTRACT FROM AUTHOR]

Activated carbon/bentonite/magnetite nanobiocomposite was used to remove Cr(VI) ions from water. The physical properties of the nanocomposite were characterized by various spectroscopic analyses. The specific surface area of the nanocomposite was 337.96 m2g−1, which is a significant value. The maximum uptake efficiency and maximum uptake capacity of the adsorbent were 98 % and 29.32 mg g−1, respectively, which are also considerable values. The maximum uptake efficiency was obtained at pH 9, after 80 min, at a nanocomposite dosage of 2 g L−1, an ion concentration of 5 mg L−1, and a temperature of 25 °C. The thermodynamic study indicated that the sorption process was spontaneous and exothermic. The nanocomposite reusability study after six cycles of reuse demonstrated that the bionanocomposite can be used for up to three cycles without significant change in its uptake efficiency. [ABSTRACT FROM AUTHOR]

This work describes the synthesis of a novel magnetic graphene oxide composite for removal of Cr(VI) ions. The synthesized nanosorbent were characterized with various techniques such as FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis and vibrating sample magnetometry (VSM). This material is illustrated to represent a viable sorbent for the removal of Cr(VI) ions. A Box-Behnken design was applied to optimize the parameters affecting the removal of Cr(VI). Three variables including sorption time, amount of the magnetic sorbent and sample pH were optimized in the removal process. Besides, the recovery of the sorbent was studied. Equilibrium isotherms were studied, and three models were applied to analyze the equilibrium adsorption data. The results revealed that the adsorption process obeyed the Langmuir model. Kinetic studies indicated the adsorption process followed a pseudo-second-order model. Maximum sorption capacity of the sorbent for Cr(VI) ions was 250 mg g-1.

In the present study, nanostructured β-Cd(OH)2 adsorbent was synthesized, characterized by Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy analysis, and applied for Cr(VI) ions capturing (adsorption) from environmental aqueous samples. The central composite design of 18 adsorption experiments was employed for multivariate sorption optimization. Maximum adsorption (%) of Cr(VI) ions was calculated and found to be 98.5% with relative standard deviation (RSD) ≤ 3.5 at optimum concentration 15 mg L–1, pH 4.0, adsorbent dosage 50 mg, shaking time 20 min and shaking speed 120 rpm at 25°C. Langmuir, Freundlich and Dubinin–Radushkevich isotherms fitted well to adsorption data with correlation coefficient (R²) of 0.993, 0.982 and 0.994, respectively. Mono-layered (Qm) and multi-layered (Kf) capacities of β-Cd(OH)2 adsorbent for Cr(VI) ions retention were calculated and found to be 202.02 ± 2.0 and 4.95 ± 2.5 mg g–1, respectively. Sorption energy was calculated and found to be 8.45 ± 2.0 kJ mol–1, indicated chemisorption or ion exchange mechanism for Cr(VI) ions adsorption onto β-Cd(OH)2 adsorbent. [ABSTRACT FROM AUTHOR]

A rare photoluminescent nitroxide pyridine bisphosphonate-based metal–organic framework, [Eu4(L)3(H2O)6]n (1) [H4L = 2,6-bis(phosphonomethyl)pyridine 1-oxide], was prepared under hydrothermal conditions and has a 3D supramolecular structure built from phosphonate linkers bridging Eu3+. It was characterized by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), thermogravimetric analyses (TGAs), etc. The luminescence spectra of 1 show the strong characteristic luminescence of Eu3+ ions, and 1 shows high water stability, thermal stability, and chemical stability. Furthermore, luminescence studies have shown that 1 can be used as a fluorescent probe for detecting trace amounts of Cr(VI) ions and acetone in water samples with excellent sensitivity, great selectivity, and reproducibility. The detection limits are as low as 0.61 μM, 0.63 μM, and 0.0066 vol% for Cr2O72-, CrO42-, and acetone, respectively. The fluorescence quenching of 1 by Cr(VI) ions and acetone may be due to spectral overlap and absorption competition. This is the first example of a Eu-based pyridine phosphonate fluorescence sensor for simultaneous detection of Cr(VI) ions and acetone. [ABSTRACT FROM AUTHOR]

Rapid industrialization has compelled the use of water quality monitors for maintaining drinking water standards. The present article demonstrates RGO/Ni2O3 hierarchical nanostructures as a sensing layer for flexible sensors to detect Cr(VI) ions in water. The device showed a maximum response of 6.61 times for 50 ppm of Cr(VI) ions (response time ~3.24 s with a calculated limit of detection (LOD) of ~0.494 ppb). The sensors were highly repeatable (four identical devices were tested) and reusable. The sensor was observed to degrade under repeated compression due to possible rearrangement of grain boundaries. An anomaly in the sensor response characteristics with increasing Cr(VI) ion concentration was observed and explained mathematically on the basis of kinetics studies based on batch adsorption experiments. The studies revealed that the adsorption was governed by only surface defects at lower concentrations (< 1 ppm), while at higher concentrations (>1 ppm) a synergistic activity of both the surface heterogeneity and the effect of adsorbed ions was observed providing a nonlinear response characteristics. To explain the effect of compression on the sensing response, a “stress-assisted sensing model” was proposed which explained the unexpected behavior of the device. The device demonstrated high specificity toward Cr(VI) ions over other heavy metal cations commonly found in drinking water. Thus, the RGO/Ni2O3 nanostructured sensing layer demonstrated promising sensing performance as flexible micro sensors for futuristic electronics. [ABSTRACT FROM AUTHOR]

Accurate, simple and quick detection methods for Cr(VI) detection are urgently needed for water quality monitoring. Herein, a novel and facile method of detecting Cr(VI) (Cr 2 O 7 2−/CrO 4 2−) ions is developed via the fluorescent detection technology based on metal-organic frameworks (MOFs) doped with sulfur quantum dots (SQDs) (SQDs@UiO-66-NH 2). The blue-light-emitting SQDs@UiO-66-NH 2 composites exhibit excellent fluorescent properties in water environment with high quantum yield (68%) and ideal fluorescent stability, thus demonstrating excellent potential for serving as a chemical sensor. After characterizing the performance and stability of SQDs@UiO-66-NH 2 , qualitative and quantitative detection of Cr 2 O 7 2− and CrO 4 2− ions was successfully conducted. The fluorescence of SQDs@UiO-66-NH 2 composites in aqueous solution was quenched effectively with more than 90% quenching efficiency by Cr(VI) via the inner filter effect. The detection system provides considerable advantages such as rapid response (10 s), high sensitivity with a low detection limit of 0.16 μM in a broad linear range of 0–200 μM (R2 = 0.99) for Cr 2 O 7 2− and 0.17 μM for CrO 4 2− in a broad linear range of 0–220 μM (R2 = 0.99), high selectivity and reproducibility for at least five cycles with simple washing with alcohol. In practical applications, the sensor showed rapid response, high sensitivity and excellent recoveries (96.7%–105.4%) for detecting Cr 2 O 7 2− in real water samples. Furthermore, a SQDs@UiO-66-NH 2 -based fluorescent test paper was successfully developed, providing a simple, reliable and portable method for Cr(VI) (Cr 2 O 7 2−/CrO 4 2−) detection in water environment. Image 1 • A luminescent sensor (SQDs@UiO-66-NH 2) with high quantum yield via PSM method was fabricated. • Qualitative and quantitative detection of Cr(VI) with rapid, sensitive and selective response achieved via IFE effect. • Portable SQDs@UiO-66-NH 2 -based fluorescent test paper was facilely developed for Cr(VI) detection. • Satisfied recoveries obtained with the sensor applied in Cr(VI) detection in real water samples. [ABSTRACT FROM AUTHOR]

Metal-free and Cu(II)-lipophilic porphyrins [H2Pp and Cu(II)Pp] loaded on titanium dioxide in the anatase phase (TiO2) were prepared and used as a heterogeneous catalyst for the photoreduction of Cr(VI) to Cr(III) in aqueous suspensions under UV–Vis light irradiation. TiO2 impregnated with copper(II) porphyrin [TiO2@Cu(II)Pp] was the most effective in photocatalyst reduction of toxic chromate Cr(VI) to non-toxic chromium Cr(III). We further evaluated an experimental design with the scope of fast optimization of the process conditions related to the use of TiO2 or TiO2-porphyrin based photocatalysts. A full factorial design as a chemometric tool was successfully employed for screening the affecting factors involved in photoconversion catalysis, with the modification of TiO2 both with porphyrin H2Pp and Cu(II)Pp. The studied experimental factors were the catalyst amount, the concentration of Cr(VI) ions, and the pH of the medium. The performed multivariate approach was successfully used for fast fitting and better evaluation of significant factors affecting the experimental responses, with the advantage of reducing the number of available experiments. Thus, the stability of the optimized TiO2 embedded Cu(II)Pp was investigated, confirming the high reproducibility and suitability for environmental purposes. [ABSTRACT FROM AUTHOR]

In this work, eggshell powder was used as a low-cost adsorbent for the removal Cr(VI) and Co(II) ions from aqueous solutions as a function of contact time, adsorbent concentration, adsorbate concentration, pH and temperature. Eggshell powder was characterized by X-ray diffraction, scanning electron microscopy and N2 physisorption measurements. The kinetic studies showed that the experimental data of both solid–liquid systems studied were well adjusted to pseudo-second order kinetics and Langmuir isotherm models. The results showed that the metal ion adsorption equilibrium was attained after 300 min of contact time for the Cr(VI) ion and 180 min for the Co(II) ion. The Co(II) ion adsorption capacity of eggshell powder was found to be approximately four times greater than the Cr(VI) ion. From the Langmuir isotherms, the maximum adsorption capacities of 0.6815 and 2.2888 mg/g were found for Cr(VI) and Co(II) ion, respectively. The thermodynamic parameters were evaluated and showed that Cr(VI) and Co(II) ion adsorption onto eggshell powder were endothermic and spontaneous processes under the studied conditions. These findings demonstrate the important role of eggshell powder as a readily available and low-cost adsorbent for the efficient removal of Cr(VI) and Co(II) ions present in aqueous media. [ABSTRACT FROM AUTHOR]

A novel polyaniline@Almond shell (PANI@AS) biocomposite was synthesized via facile in situ chemical polymerization method. The as-synthesized adsorbent was characterized using various analytical techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and potentiometric titration. A batch adsorption system was applied with the aim of investigating as-synthesized adsorbent ability to remove Cr(VI) ions and Orange G (OG) textile dye from aqueous solutions. Obtained results revealed that adsorption process was strongly depended upon the physicochemical parameters. The adsorption of Cr(VI) and OG dye onto PANI@AS was better described by the pseudo second-order-kinetic model and followed the Freundlich isotherm model. The maximum uptakes were 335.25 for Cr(VI) and 190.98 mg g−1 for OG dye. We further evaluated that PANI@AS biocomposite could be regenerated easily with NaOH solution and efficiently reused for Cr(VI) and OG dye removal from aqueous media. Thus, these results indicated the potential practical application of PANI@AS biocomposite for wastewater treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • L-cysteine functionalized gold nanoparticles embedded melamine-based covalent organic framework (Cys-AuNPs@COF) as a highly effective and efficient adsorbent. • Removal of Cr(VI) ions from aqueous environments using synthesized Cys-AuNPs@COF. • A portable, low-cost, and highly sensitive device with a smartphone colorimeter platform for the measuring of Cr(VI) ions. • Response surface methodology (RSM) for investigating effective parameters. • Investigation of adsorption isotherms, kinetics, and reusability of Cys-AuNPs@COF. Due to the growing concern about the environmental effects of heavy metals, researchers are developing materials that possess high absorption capacity in addition to selectivity and high absorption speed. Recently, covalent organic frameworks (COFs) have been considered as emerging and promising adsorbents for the removal of many types of pollutants. In this work, a novel and selective adsorbent (Cys-AuNPs@COF) was prepared by embedding gold nanoparticles functionalized with L-cysteine in melamine-based COF for the removal of Cr(VI) ions from wastewater. The synthesized Cys-AuNPs@COF were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction analysis (XRD), Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX), Thermo-gravimetric analysis (TGA), and elemental mapping (EMA) analysis. The removal of Cr(VI) ions was performed using a batch mode process by taking advantage of response surface methodology (RSM) based on a central composite design (CCD) model. The maximum adsorption capacity of Cys-AuNPs@COF was 151.5 mg g−1. The experimental results followed the Langmuir model and showed pseudo-second-order kinetics. A portable, low-cost, and highly sensitive device with a smartphone colorimeter platform was developed for in situ measurement of trace amounts of chromium (VI) ions. Due to its simplicity and versatility, this method has the potential to serve as an alternative to conventional field analysis methods. [ABSTRACT FROM AUTHOR]

This work describes the synthesis of a novel magnetic graphene oxide composite for removal of Cr(VI) ions. The synthesized nanosorbent were characterized with various techniques such as FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis and vibrating sample magnetometry (VSM). This material is illustrated to represent a viable sorbent for the removal of Cr(VI) ions. A Box-Behnken design was applied to optimize the parameters affecting the removal of Cr(VI). Three variables including sorption time, amount of the magnetic sorbent and sample pH were optimized in the removal process. Besides, the recovery of the sorbent was studied. Equilibrium isotherms were studied, and three models were applied to analyze the equilibrium adsorption data. The results revealed that the adsorption process obeyed the Langmuir model. Kinetic studies indicated the adsorption process followed a pseudo-second-order model. Maximum sorption capacity of the sorbent for Cr(VI) ions was 250 mg g-1. [ABSTRACT FROM AUTHOR]

A CuS-BSA nanocomposite is synthesized and exhibited a peroxidase-enzyme mimic towards the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) through the generation of hydroxyl radicals for the rapid, sensitive and selective detection of Cr(VI). • A water dispersible CuS-BSA nanocomposite is synthesized under mild conditions. • CuS-BSA displays an enzyme-like activity towards TMB oxidation in presence of H 2 O 2. • The enzyme-like activity is enhanced in the presence of Cr(VI) ions. • A selective and sensitive Cr(VI) detection is achieved. This work describes a selective and sensitive colorimetric approach for the detection of heavy metal Cr(VI) ions in water using the peroxidase-like property of CuS-BSA nanocomposite. CuS-BSA nanocomposite is synthesized via a simple chemical route and characterized by various sophisticated instrumental techniques like transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV/Vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis. The hydrodynamic size and surface charge of CuS-BSA nanocomposite were determined by using dynamic light-scattering (DLS) and zeta potential measurements. The peroxidase-like activity of CuS-BSA nanocomposite towards the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to produce a blue colored charge transfer product (oxTMB), which is observable by the naked eye, is quantitatively assessed by UV/vis spectrophotometry at 654 nm. The CuS-BSA nanocomposite is subsequently applied for sensing of Cr(VI) metal ions. The sensor displays two linear ranges, 0–100 nM and 1–20 μM; the lower linear range was used to determine a detection limit of 50 nM towards Cr(VI), which is below the permissible limit determined by the United States Environmental Protection Agency (U.S. EPA). The practical performance of this sensor is successfully demonstrated using various environmental water samples spiked with different concentrations of Cr(VI). This method offers the advantages of being rapid, highly selective and sensitive platform, which holds great potential in environmental applications. [ABSTRACT FROM AUTHOR]

Water stable Zn(II) coordination polymer used as highly selective and sensitive luminescent sensor for Cr(VI) and MnO 4 − ions in the aqueous phase. Three isostructural coordination polymers have been synthesized and structurally characterized by IR, TGA, PXRD and X-ray single crystal diffraction. The 1D butterfly chains assembled to a novel 3-D supramolecular framework via hydrogen bonding and π–π stack. The complex 1 exhibited high fluorescence stability in water solution and can simultaneously detect Cr 2 O 7 2−, CrO 4 2− and MnO 4 − ions in aqueous media with high quenching constant and low detection limits of 6.82 × 104 M−1 and 4.06 μM for Cr 2 O 7 2−, 1.38 × 103 M−1 and 26.1 μM for CrO 4 2− ions, 3.1 × 104 M−1 and 6.73 μM for MnO 4 −. The result of interference study displayed that the compound can selectively detect Cr(VI) and MnO 4 − anions, indicating compound 1 may be a potential material for sensing Cr(VI) and MnO 4 − anions. [ABSTRACT FROM AUTHOR]

Abstract High-performance adsorption toward Congo red and Cr(VI) depends on the design of hierarchical nanostructures. Herein, hierarchical porous Ni/Co-layered double hydroxide (NiCo-LDH) hollow dodecahedra were synthesised by etching zeolitic imidazolate framework-67 (ZIF-67) as a self-sacrificing template with Ni(NO 3) 2. The synthesised NiCo-LDH showed better adsorption property for adsorbing Congo red and Cr(VI) ions (Cr 2 O 7 2−) than NiCo 2 O 4 -NiO, which was obtained by calcining NiCo-LDH at 350 °C. The adsorption processes of Congo red and Cr(VI) ions very well fitted the pseudo-second-order model. The Langmuir model was more suitable than the Freundlich model in describing the adsorption isotherm, and the theoretical maximum adsorption capacities of Congo red and Cr(VI) ions were 909.2 and 99.9 mg g−1 at 30 °C, respectively. Furthermore, the synthesised NiCo-LDH was recyclable and could selectively adsorb anionic dyes. This work can serve as a basis for designing and manufacturing excellent adsorbents for water treatment. Graphical abstract Unlabelled Image Highlights • Monodispersed Ni/Co-LDHs are synthesised. • NiCo-LDH has a hollow pore structure and high specific surface area. • NiCo-LDH has excellent adsorption property for Congo red and Cr(VI). [ABSTRACT FROM AUTHOR]

Abstract An ultrasensitive Visible light-triggered photoelectrochemical (PEC) sensor was designed based on ideal photoactive lead sulfoiodide (Pb 5 S 2 I 6) as low band gap crystal, which hydrothermally synthesized rapidly at low temperature (160 °C) in hydrochloride acid media followed by its incorporation into polydopamine as reactive photo-biointerface, through a facile in situ electropolymerization method, coated on nanoporous TiO 2 grown by anodization on Ti foil. The structure of as-prepared samples and their photoelectrochemical properties were fully characterized. This unique photo-sensitive Pb 5 S 2 I 6 catalyst-based PEC bioassay was constructed for the detection of low-abundant Cr(VI) ion in real samples. Applying central composite design, individual and mutual interaction effects were evaluated to obtain optimized solution pH, applied potential and radiant light wavelength as operational factors influencing the PEC efficiency for Cr(VI) detection. At optimal condition, the proposed sensor due to effective suppress in electron–hole recombinations showed a very low detection limit of 3.0 nM, over a broad linear concentration range of 0.01–80 μM in addition to high sensitivity versus 1.9 μA/μM Cr(VI). Proposed PEC sensor displayed high selectivity, reproducibility and stability as well as improved excitation conversion efficiency, which make it highly applicable using solar energy. The potential applicability of the designed sensor was evaluated in water, tomato juice and hair color. Highlights • Ideal photoactive Pb 5 S 2 I 6 chalco-halides crystal was prepared. • Pb 5 S 2 I 6 catalyst-based PEC bioassay detect of low-abundant Cr(VI) ion in real samples. • Long lifetime of 9.30 × 10−2 s was obtained for photogenerated electrons. • Signal-on Photoelectrochemical behavior was observed in the presence of Cr(VI). [ABSTRACT FROM AUTHOR]

Composites of magnetic biochar derived from spent coffee grounds were prepared using MoS 2 decorated by plasmonic silver nanoparticles (MoS 2 –Ag), which were used for the bioremediation Cr6+ ions. The composites were characterized by electron microscopy, X-ray diffraction, Raman, and UV-VIS spectroscopy. The bioremediation of Cr6+ ions was enhanced almost two times compared to microalgae, Spirulina maxima. Such an increased activity is attributed to heterojunction formation of Biochar@MoS 2 –Ag composite due to the synergetic effects of surface plasmon resonance of AgNPs inducing amplified local electric field, thus simultaneously increasing the absorption of MoS 2 under visible or near-infrared light. The combination of Biochar@MoS 2 –Ag and Spirulina maxima powder was effective for the separation (microalga-based absorption and accumulation of Cr6+ ions) of photo-induced carriers (composite-assisted to breakdown Cr6+ ions). This study offers efficient eco-friendly treatment of Cr6+ ions by reporting the first enhanced bioremediation of Cr(VI) ions by microalgae using MoS 2 –Ag-modified biochar obtained from consumed coffee grounds. • Magnetic biochar made a composite of MoS 2 –Ag for bioremediation. • X-ray, Raman, FT-IR, and BET used for physiochemical characterization. • Spirulina maxim a microalgae was combined for the reduction of Cr6+ ions. • Magnetic biochar MoS 2 –Ag composite showed enhanced bioremediation. [ABSTRACT FROM AUTHOR]

Biodegradable polymers, biochars and metal organic frameworks (MOFs) have manifested as top prospects for elimination of harmful pollutants. In the current study, Ti-MOF was synthesized and decorated with TiO 2 nanoparticles, then embedded into watermelon peel biochar and functionalized with chitosan hydrogel to produce Ti-MOF@TiO 2 @WMPB@CTH. Various instruments were employed to assure the effective production of the bionanocomposite. The HR-TEM and SEM studies referred to excellent surface porosity and homogeneity of Ti-MOF@TiO 2 @WMPB@CTH bionanocomposite, with 51.02-74.23 nm. Based on the BET analysis, the mesoporous structure has a significant surface area of 366.04 m 2  g -1 and a considerable total pore volume of 11.38 × 10 -2  cm 3  g -1 , with a mean pore size of 12.434 nm. Removal of doxorubicin (DOX) and hexavalent chromium (Cr(VI)) was examined under various experimentations. Pseudo-second order kinetic models in addition to Langmuir isotherm offered the best fitting. Thermodynamic experiments of the two contaminants demonstrated spontaneous and endothermic interactions. After five subsequent adsorption and desorption cycles, Ti-MOF@TiO 2 @WMPB@CTH bionanocomposite demonstrated an exceptional recyclability for the elimination of DOX and Cr(VI) ions, reaching 97.96 % and 95.28 %, respectively. Finally, the newly designed Ti-MOF@TiO 2 @WMPB@CTH bionanocomposite demonstrated a high removing efficiency of Cr(VI) ions and DOX from samples of real water., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A novel zinc(II) metal-organic framework (MOF) {[(CH 3 ) 2 NH 2 ] 2 [Zn 5 (TDA) 4 (TZ) 4 ] . 4DMF} n ( 1 ) (H 2 TDA = thiophene-2,5-dicarboxylic acid and HTZ = 1 H -1,2,4-Triazole) based on Zn 5 (COO) 2 (TZ) 4 pentametallic clusters and thiophene-2,5-dicarboxylic acid was synthesized and structurally characterized via the mixed-ligand strategy. This MOF exhibits a uninodal 6-connected anionic framework with pcu topology and shows solvent stability. Post-functionalization via cation exchange of 1 with Eu 3+ and Tb 3+ afforded two lanthanide (III) functionalized MOFs: Eu 3+ @1 and Tb 3+ @1 . 1 as well as Eu 3+ @1 and Tb 3+ @1 were utilized as a highly selective and sensitive turn-off luminescent sensors for detecting aniline, benzaldehyde in DMF and Cr 2 O 7 2− , CrO 4 2− in water with low detection limits. More importantly, it is rather rare in MOF-based luminescent probes that 1 and its lanthanide (III) post-functionalized materials ( Eu 3+ @1 and Tb 3+ @1 ) can detect aniline, benzaldehyde, Cr 2 O 7 2− and CrO 4 2− . Furthermore, the sensitivity of 1 as luminescent probes for detecting aniline and benzaldehyde could be improved via post-functionalization with Eu 3+ ions. [ABSTRACT FROM AUTHOR]

Abstract The anionic polyacrylamide AN PAM (with various contents of carboxyl groups) adsorption mechanism on the montmorillonite surface was examined. The effect of hazardous chromium(VI) ions addition was studied. The anionic polyacrylamide is a popular soil flocculant, commonly used to prevent erosion of arable soils. On the other hand, polymeric macromolecules can increase the accumulation of various toxic substances, such as heavy metal ions (among others Cr(VI) ions) in soil minerals. For this purpose the adsorption properties of soil mineral – montmorillonite in relation to mixed system containing AN PAM and Cr(VI) ions was investigated. The impact of solution pH, order of individual adsorbates addition, chromium(VI) ions concentration and anionic groups content in the polymeric macromolecules were determined. The montmorillonite was characterized using the low-temperature nitrogen adsorption/desorption method, XRF, FTIR and SEM techniques. In turn, the adsorption and electrokinetic properties of examined montmorillonite – AN PAM - Cr(VI) systems were examined by means of spectrophotometry, potentiometric titration and microelectrophoresis methods. Highlights • Adsorption of anionic polyacrylamide (PAM) flocculant on the montmorillonite surface was examined. • Effects of PAM carboxyl groups content, Cr(VI) ions presence, order of adsorbates addition and solution pH were studied. • Hydrogen bonds between the PAM functional groups (mainly amide ones) and CrO 4 2− and HCrO 4 − ions can be formed. • Order of individual adsorbates addition has no effect on the adsorbed amounts of both polymer and chromium(VI) ions. • Under specific conditions soil mineral particles connected with the polyacrylamide flocculant can cumulate heavy metal ions. [ABSTRACT FROM AUTHOR]

Metal oxide-Carbon composites have aroused great interesting towards specific anionic contaminants removal from the polluted environment. In this study, aiming at removing toxic chromate ion [Cr(VI)] from aqueous solutions, a novel approach was developed to produce surface-enhanced MgO-coated biochar adsorbent from sugarcane harvest residue (SHR). It was found that sulfuric acid hydrolysis and MgO-coating both facilitated the removal of Cr(VI) by biochars, and the maximum sorption capacities for the pristine biochar (SHR 550 ), MgO-coated biochar (MgSHR 550 ), and acid-assisted MgO-coated biochar (MgASHR 550 ) that derived from the Langmuir isotherm model were 20.79, 54.64, and 62.89 mg g −1 , respectively. Additionally, the Cr(VI) removal was a pseudo-second-order kinetic model controlled process with equilibrium reached within 24 h. The mechanism investigation revealed that Cr(VI) ions was directly sorbed by the MgO-coated biochars via the chemical interaction between MgO and Cr(VI), whereas the sorption-coupled reduction of Cr(VI) to Cr(III) governed the sorption of Cr(VI) on the SHR 550 . Although the increases of solution pH (>2.0) and KNO 3 concentration (>0.05 mol L −1 ) reduced the Cr(VI) removal by biochars, while there were lower secondary pollution risks in MgO-coated biochar treatments due to the suppressed release of Cr(III) in solutions. This work could provide guidance for the production of efficient biochar for the removal of Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Ca x H 4-x Si 4 W 12 O 40 /Ca 2 Ta 2 O 7 was prepared via an in-situ deposition reaction. • The composite exhibited a good photocatalytic efficiency in reducing Cr(VI) ions. • The composite presented a better stability due to the formation of Ca x H 4-x Si 4 W 12 O 40. • The agglomeration of H 4 Si 4 W 12 O 40 were prevented by Ca-O linkage with Ca 2 Ta 2 O 7. • A probable mechanism of reducing Cr(VI) is proposed by DFT simulation. A novel heterogeneous photocatalyst Ca x H 4-x Si 4 W 12 O 40 /Ca 2 Ta 2 O 7 was prepared by planting silicotungstic acid on the surface of calcium tantalate. The materials are characterized by X-ray diffraction (XRD), scanning electron microspectroscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transformation infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectroscopy (UV–vis), Energy-dispersive X-ray spectroscopy (EDS), BET surface area, and Malvern ZEN3690 Particle Analyzer (ZP). The results recovered Ca 2 Ta 2 O 7 presented regular octahedron morphology with the cubic phase structure, and H 4 Si 4 W 12 O 40 uniformly grew on the surface of Ca 2 Ta 2 O 7 with the form of Ca x H 4-x Si 4 W 12 O 40. The primary Keggin structures of H 4 Si 4 W 12 O 40 was found to remain intact as noticed by XRD and FTIR. The modification of H 4 Si 4 W 12 O 40 on Ca 2 Ta 2 O 7 surface contributed the increase in negative zeta potential and red shifts. The as-prepared catalyst exhibited greatly enhanced UV photocatalytic efficiency in the reduction of Cr(VI) ions as high as 94.6% under the optimum conditions (Ca 2 Ta 2 O 7 to H 4 Si 4 W 12 O 40 was 1:2). Moreover, the composite presented an excellent reusability, which was mainly ascribed to the locally formation of water-insoluble Ca x H 4-x Si 4 W 12 O 40. A probable mechanism involved in the enhanced reducible activity and well recycled performance via Ca O binding linkage of H 4 Si 4 W 12 O 40 and Ca 2 Ta 2 O 7 is proposed by DFT simulation. This work will be significant in the design of heteropoly acid as stable heterogeneous photocatalyst applied to heavy metal ions reduction. [ABSTRACT FROM AUTHOR]

Wastewater (WW) remediation technologies were the most crucial issues all over the world at present time. Thus, the remediation of Cr (VI) ions from real WW was conducted using green biocompatible and biodegradable pristine (CNM) and succinic anhydride functionalized cellulose nanomaterial (S-CNM) adsorbents. Both CNM and S-CNM adsorbents were prepared by using sulfuric acid hydrolysis method and characterized for particle sizes, functional groups, and surface morphologies by using XRD, FT-IR, and SEM instruments, respectively. The physicochemical properties of the collected WW were investigated. Next, both the prepared adsorbents were applied for the remediation of Cr (VI) ions from WW. The remediation processes is spontaneous and have higher remediation efficiencies of Cr (VI) ions from WW. The Cr (VI) ions remediation mechanism was evaluated from both the Cr (VI) ions adsorption isotherms and kinetic concepts. Both Langmuir and Freundlich Cr (VI) ions adsorption isotherm models were certainly fixed to a maximum Cr (VI) ions uptake capability (q _max ) of 60.24 and 156.25 mg g ^−1 by CNM and S-CNM sorbents, respectively, and it follows pseudo-second-order (PSO) kinetics model through chemisorption processes. The Cr (VI) ions uptake capabilities were hindered by the presence of organic matter and any other competing pollutants in the WW. The S-CNM sorbent was selected for the regeneration study due to its higher efficiencies of remediation relative to CNM sorbent and the study was conducted through desorption of Cr (VI) ions by using HCl. Findings have shown that the sorbent was easily recyclable and applicable for the remediation of pollutants from real WW after consecutive 13th cycles.

Chitosan as adsorbent has been used widely, however it was not effective yet for metal ions adsorption in industrial scale. In acidic condition, chitosan’s active site tends to decrease. This drawback can was solved by coating of chitosan active site on alumina. This paper discloses to overcome that limitation. The charateristic of the active side was analysed by FTIR spectrometry toward vibration N-H group at 1679.15 cm-1, C=O group of oxalate at 1703.30 cm-1, and Al-O group of alumina at 924.07 cm-1. The adsorption capacity of the developed adsorbent was tester to adsorb Cr(VI) ions under various of pH value such as 1, 2, 3, 4, 5, 6, and 7. The contact time affect toward the adsorption was also reported in 20, 30, 40 50, 60, 70, and 80 minute. In addition, the concentration effects (100, 200, 300, 400, 500, and 600 ppm) was also studied. Chromium (VI) was measured using spectronic-20. Adsorption capacity was obtained at 66.90 mg/g under optimum conditions pH 2, and contact time 60 minute, respectively.

In the current work, novel environmentally friendly water-soluble fluorescent carbon dots coated with chitosan (CDs/CTS) were successively synthesized via a facile and green preparation procedure. The fluorescent carbon dots were prepared through a simple, convenient and one-step hydrothermal method in the presence of cellulose as a raw material. The CDs/CTS were connected together via intermolecular hydrogen bonds interaction and chemical bonds between hydroxyl and amino groups in the chitosan polymeric chains and hydroxyl groups of fluorescent carbon dots. This approach can be applied for milligram-scale preparation of these water-soluble particles. The CDs/CTS material showed blue fluorescence under UV exposure. The structure and morphology of as-prepared CDs/CTS were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The as-prepared CDs/CTS exhibited excellent fluorescent property and good stability. The fluorescence of as-prepared CDs/CTS could be quenched by the Cr(VI) ions. The effects of environmental factors on the fluorescence intensity were investigated in detail, and the obtained results showed that the optimum conditions for the Cr(VI) ions determination were as follows: 1:3 of mass ratio of CDs/CTS, 9.5 of pH and 20 min of reaction time. Under optimized experimental conditions, a novel fluorescent probe was developed for the detection of Cr(VI) ions, which exhibited wide linear ranges (0-600 μmol/L) and excellent selectivity. The proposed method was directly applied for the determination of Cr(VI) ions in water and soil samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A water-soluble fluorescent carbon dots (FCDs) from cellulose was prepared using one-pot simple hydrothermal method. In this work, a novel fluorescent probe material, fluorescent carbon dots-linked isophorone diisocyanate and β-cyclodextrin (FCDs-IPDI-CD), was prepared with FCDs, isophorone diisocyanate (IPDI) and β-cyclodextrin (β-CD) as raw materials. The structure and morphology of FCDs-IPDI-CD were characterized using the Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The as-prepared FCDs-IPDI-CD exhibits excellent emission property and high stability. The fluorescence of the FCDs-IPDI-CD could be quenched by Cr(VI) ions, and the results indicate that FCDs-IPDI-CD can be used as an effective fluorescent probe for the detection of Cr(VI) ions with good selectivity and sensitivity in an aqueous solution. The influences of environment factors (such as pH, reaction time) on relative fluorescence intensity were studied. According to the optimum conditions, a new sensitive method detecting Cr(VI) ions was established. The method has been successfully applied to detect Cr(VI) ions in water and soil samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Lagerstroemia speciosa bark (LB) embedded magnetic nanoparticles were prepared by co-precipitation of Fe 2+ and Fe 3+ salt solution with ammonia and LB for Cr(VI) removal from aqueous solution. The native LB, magnetic nanoparticle (MNP), L. speciosa embedded magnetic nanoparticle (MNPLB) and Cr(VI) adsorbed MNPLB particles were characterized by SEM–EDX, TEM, BET-surface area, FT-IR, XRD and TGA methods. TEM analysis confirmed nearly spherical shape of MNP with an average diameter of 8.76 nm and the surface modification did not result in the phase change of MNP as established by XRD analysis, while led to the formation of secondary particles of MNPLB with diameter of 18.54 nm. Characterization results revealed covalent binding between the hydroxyl group of MNP and carboxyl group of LB particles and further confirmed its physico-chemical nature favorable for Cr(VI) adsorption. The Cr(VI) adsorption on to MNPLB particle as an adsorbent was tested under different contact time, initial Cr(VI) concentration, adsorbent dose, initial pH, temperature and agitation speed. The results of the equilibrium and kinetics of adsorption were well described by Langmuir isotherm and pseudo-second-order model, respectively. The thermodynamic parameters suggest spontaneous and endothermic nature of Cr(VI) adsorption onto MNPLB. The maximum adsorption capacity for MNPLB was calculated to be 434.78 mg/g and these particles even after Cr(VI) adsorption were collected effortlessly from the aqueous solution by a magnet. The desorption of Cr(VI)-adsorbed MNPLB was found to be more than 93.72% with spent MNPLB depicting eleven successive adsorption–desorption cycles. [ABSTRACT FROM AUTHOR]

The article focuses on sequestration of toxic Cr(VI) ions from industrial wastewater using waste biomass, and talks of alternative biotechnological innovation, biosorption, biosorbents such as fungi, bacteria, algae, and thermodynamics.