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Conversion of hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) is an effective way to reduce its environmental risk, especially via photoreduction process. However, over a wide range of pH values, it is still a great challenge to achieve a high removal rate, and the disposal of produced Cr(III) should be concerned. In this work, we implemented a high removal rate at 98% for Cr(VI) and total chromium (Cr(T)) over a wide pH range (4–10) through the synergistic effect of adsorption, photoreduction and immobilization on the surface of BiOBr0.25I0.75. The substitution of bromine by iodine reduced the adsorption energy of Cr(VI) on BiOBr0.25I0.75, promoting the adsorption of Cr(VI). Meanwhile, the introduced iodine upshifted the conduction band (CB), enhancing the reduction ability for Cr(VI) to Cr(III). The negative surface of BiOBr0.25I0.75 can capture Cr(III), achieving a high removal rate for Cr(T). The pH-independent feature for Cr(VI) and Cr(III) removal make BiOBr0.25I0.75 a potential material for chromium-containing wastewater treatment. This work provides an effective strategy for removing chromium over a wide pH range.

Electrocatalytic reduction of Cr(VI) to less toxic Cr(III) is deemed as a promising technique. Conventional electrocatalytic reduction is always driven by a constant cathodic potential, which exhibits a repelling action to Cr(VI) oxyanions in wastewater and consequently suppresses reduction kinetics. In order to remarkably accelerate Cr(VI) electrocatalytic reduction, we applied a pulsed potential on an Fe2+-NiFe LDH/NF electrode synthesized by in situ growth of Fe2+-doped NiFe LDH nanosheets on Ni foam using a spontaneous redox reaction. Under anodic potential section, HCrO4– anions are adsorbed on the electrode surface and reduced to Cr(III) by Fe2+. Then, Cr(III) ions are desorbed from the electrode surface under coulombic force. The regeneration of Fe2+ and direct reduction of Cr(VI) are achieved under cathodic potential section. The pulsed potential can achieve complete elimination of Cr(VI) within 60 min at an initial concentration of 10 mg L−1, and the removal efficiency shows a 60% increase with respect to that under constant cathodic potential.

All-solid-state Z-scheme photocatalysts, containing Cu2O, TiO2 (rutile), and Au as the electron mediator, were prepared and applied to the reduction of Cr(VI) in aqueous solutions. The Cu2O–Au–TiO2 composites were prepared by loading Au core–Cu2O shell hemisphere particles on TiO2 (rutile) nanorods using a two-step photocatalytic deposition process. Under ultraviolet–visible (UV–vis) light illumination, the Cu2O–Au–TiO2 composites exhibited higher photocatalytic Cr(VI) reduction activities than those exhibited by single TiO2 (rutile) and Cu2O. In this reaction, a precipitate containing Cr, which was considered to be Cr(OH)3, was deposited site-selectively on the Au core–Cu2O shell particles of the composites, indicating that the reduction site of the composite was Cu2O, and the reaction proceeded according to the Z-scheme. The Cu2O–Au–TiO2 composites also exhibited photocatalytic activity under visible light illumination. The oxidation state of Cu in the Cu2O–Au–TiO2 composite gradually changed from Cu(I) to Cu(II) during the photocatalytic Cr(VI) reduction. However the composite maintained its high photocatalytic performance even after oxidation. The role of Au in the Cu2O–Au–TiO2 composite was examined by comparing the properties of the Cu2O–Au–TiO2 composite with those of the Cu2O–TiO2 composite prepared via direct Cu2O deposition on TiO2.

Piezocatalysis, driven by mechanical energy and piezoelectric effect, is of great potential in addressing the environmental issues. In this work, a piezoelectric catalyst was fabricated by growing few-layer MoS2 nanosheets onto CuS, for the piezocatalytic degradation of Rhodamine B (RhB), methylene blue (MB) and hexavalent chromium (Cr (VI)). The excellent removal efficiency of Cr (VI) and RhB can be reached 100% within 180 s, through the piezocatalysis of CuS/MoS2-0.6 driven by mechanical stirring in the dark. Impressively, the piezoelectric current of CuS/MoS2-0.6 is 48 and 35.7 times higher than that of pure CuS and MoS2, respectively. The significantly enhanced piezocatalytic performance can be ascribed to the formation of CuS/MoS2 heterojunction and the piezoelectric field generated by MoS2 nanosheets, which promotes the efficient separation of electrons and holes. This study provides insights into strategies to improve catalytic performance through utilizing mechanical energy and opens a new horizon for environmental remediation.

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 (Cr0.25Fe0.75(OH)3) and subsequently magnetic conversion of Cr0.25Fe0.75(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 Cr0.25Fe0.75(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 Cr0.5-xFe2.5+xO4 (where 0 ≤ x

To efficiently remove high concentrations of hexavalent chromium (Cr(VI)), calcium–aluminum-layered double hydroxide (CaAl-LDH, denoted as CAL), and polypyrrole-modified CAL (CAL-PPy) were prepared by hydrothermal and in situ polymerization methods, respectively. The chemical structure, morphology, and elemental results indicated that the chain-like polypyrrole was decorated with hexagonal CAL. The specific surface area of CAL-PPy increased from 8.746 m2/g to 24.24 m2/g. The adsorption performances of CAL and CAL-PPy for aqueous Cr(VI) were investigated using batch equilibrium experiments. The decontamination process of aqueous Cr(VI) (100 mg/L) reached the equilibrium state within 50 min, and the kinetic data met the pseudo-second-order kinetic equation. The Langmuir model described the isothermal data properly, and the obtained theoretical adsorption capacity of CAL for Cr(VI) at 318 K was 34.06 mg/g, while that of CAL-PPy was 66.14 mg/g. The removal mechanisms involved electrostatic attraction, surface complexation, anion exchange, and reduction to low-toxicity Cr(III). Therefore, CAL and CAL-PPy have underlying applications in treating real wastewater containing Cr(VI).

Heterojunction engineering has been regarded as a promising strategy to sufficiently utilizing photogenerated charge carriers, thus benefiting the improvement of photocatalytic performance. Herein, Ag3PO4/WO3 S-scheme heterojunction was synthesized via a simple deposition-precipitation process, and its photocatalytic activity was evaluated by monitoring water splitting and pollutant degradation under visible light. As a result, Ag3PO4/WO3 with optimized ratio photocatalyst showed enhanced photocatalytic activity in oxygen production (306.6 μmol·L-1·h-1) relative to pure Ag3PO4 (204.4 μmol·L-1·h-1). Additionally, it also exhibits rapid toxicity elimination efficiency over hexavalent chromium ions (Cr6+) and ciprofloxacin (CIP) with degrading rate of 72% and 83% within 30 min, respectively. According to a series characterization, a possible S-scheme photocatalytic mechanism of Ag3PO4/WO3 was demonstrated in detail, which endowed the heterojunction with strong redox abilities to provide powerful diving force towards the photocatalytic reaction. This work presents an innovative perspective to construct Ag3PO4-based S-scheme heterojunctions for boosting photocatalytic performance for various applications.

A low-temperature hydrothermal process was developed to synthesize erdite adsorbent from a solid waste sludge contained 10.2% Fe, 6.2% Al and 1.4% Si, alongside 59.5% water content. At 90℃, adding Na2S and NaOH could convert it into erdite nanorods with a diameter of 80 nm and a length of 100 nm. In the sludge, only Fe oxyhydroxide was involved in the formation of erdite, and the other Al/Si-bearing compounds were dissolved in an alkaline medium. The dissolved Al/Si-bearing compounds were further removed, forming faujasite so that the used medium was purified and then entirely recycled into the next conversion stage. No secondary waste was generated in the pilot-scale conversion, and the adsorption efficiency of the prepared products to wastewater with a high initial Cr(VI) concentration of 1000 mg/L was more than 99.5%. The adsorption data complied with the pseudo-second-order kinetics. During the wastewater treatment, hexavalent chromium anion diffused to erdite surface and replaced -OH/-SH groups of adjacent structural Fe to form a stable complex ligand. In addition, the redox reaction between hexavalent chromium and the -SH group occurred to generate a trivalent chromium complex on the Fe/S-bearing flocs surface.

The present study investigates ameliorative effect of silicon nanoparticles (SiNPs) and indole acetic acid (IAA) alone and in combination against hexavalent chromium (CrVI) toxicity in rice seedlings. The results of the study revealed protective effects of SiNPs and IAA against CrVI toxicity. The 100μM of CrVI imposed toxic effects in rice seedlings at morphological, physiological and biochemical levels which coincided with increased level of intracellular CrVI and declined level of endogenous nitric oxide (NO). The CrVI enhanced levels of superoxide radicals (SOR) (59.51% and 50.1% in shoot and root, respectively) and H2O2 (19.5% and 23.69% in shoot and root, respectively). However, when SiNPs and IAA were applied to plants under CrVI stress, they enhanced tolerance and defence mechanisms as manifested in terms of increased biomass, endogenous NO, photosynthetic pigments, and antioxidants level (ascorbate-glutathione cycle). It was also noticed that CrVI arrested cell cycle at G2/M phase whereas growth was restored as compared to control when SiNPs and IAA were supplemented. Thus, the hypothesis that combined application of SiNPs and IAA will be effective in alleviating CrVI toxicity is validated from the results of this study. Moreover, in SiNPs and IAA-mediated mitigation of CrVI toxicity, endogenous NO has a positive role. The importance of the study will be that the combination of SiNPs and IAA can be utilized against heavy metal stress and even when supplied alone, they will enhance the crop productivity parameters with and without stress conditions.

This paper aims to synthesis a recyclable adsorbent from solid waste using a clean and environmentally friendly method to deal with Cr(VI) water pollution. Magnetic zeolite/chitosan composites (ZFA/MCS) were prepared by the neutralization method. The adsorption properties of ZFA/MCS, prepared by the neutralization method for Cr(VI) ions under different conditions especially cross-linking, were investigated in detail. The results showed that cross-linked ZFA/MCS generally showed higher adsorption capacity than uncross-linked ones. The uncross-linked ZFA/MCS and cross-linked ZFA/MCS showed a saturated adsorption capacity of 25.67 mg·g−1 and 28.47 mg·g−1 at pH = 3 and 30 °C, respectively. The experimental values were followed Langmuir adsorption equations and pseudo-second-order kinetic model, indicating that the adsorption was probably monolayer coverage and chemical adsorption, respectively. The effect of temperature proved that the adsorption was spontaneous and endothermic. Therefore, the adsorbent with excellent recyclability and adsorbability was successfully fabricated via a green synthetic strategy.

Hexavalent chromium [Cr(VI)] is a heavy metal pollutant in the environment released through leather tanning. In this context, the present study was envisaged to isolate and identify chromium reducing bacteria in order to employ them towards detoxification of chromium. In general, bacteria are ecofriendly and cost-effective which can be efficiently used in bioremediation processes. The collected tannery effluents yielded considerable Bacillus species. These isolates demonstrated well for their resistance which showed exceptional Cr(VI) reduction within 48 h under aerobic conditions. Mostly, chromium resistance confers through Chromate transporters which involves metabolic reduction of toxic Cr(VI) to non-toxic Cr(III). Distribution of chr genes in Bacillus species were identified from their genome through UniProt. Treatment of raw tannery effluent employing these isolates individually or as a consortia reduced Cr(VI) significantly. Thus, these bacterial strains, could evolve as a potential organisms to reduce toxic Cr(VI) to its non-toxic Cr(III) form in chromium contaminated sites.

The ecosystems and human health were seriously threatened by hexavalent chromium (Cr(VI)) in wastewater. In this article, using the idea of the highly matched energy band structure between indium sulfide (In2S3) and MIL-53(Fe), a Type-II heterojunction has been constructed by loading In2S3 on MIL-53(Fe) microrod to overcome the fault like high recombination rates of photogenerated electron-holes of In2S3. The composite with 20:1 mass ratio of In2S3 to MIL-53(Fe) (IM-2) was adopted as an optimal sample for efficient photocatalytic Cr(VI) reduction under visible light. Various characterization techniques were used to verify the characteristics of composites and delved into the structure-effect relationship between this heterojunction and its activity. Results showed that the reaction rate constants of the photoreduction process over IM-2 was ~ 4 and 26 times higher than those of pure In2S3 and MIL-53(Fe), respectively, and the catalyst could maintain superior removal efficiency (88.6%) and steady crystal structure after four cycles. First-principles calculations further illustrated that the heterostructure formed between In2S3 and MIL-53(Fe) could effectively accelerate the separation of photogenerated electrons and holes, thus improving the photocatalytic reduction performance. Moreover, the active species analyses revealed that the superoxide radicals and electrons were mainly involved in the reduction of Cr(VI).

Graphical abstract, Highlights • Cr(VI) can induce inflammatory, oxidative stress, and apoptosis in rat liver. • Cr(VI) induces inflammatory response in the liver by inhibiting deacetylation. • Oxidative stress caused by Cr(VI) is related to the inhibition of deacetylation. • Cr(VI) aggravates hepatocyte apoptosis by inhibiting deacetylation in rats. • Cr(VI) induces liver injury via inhibition of the deacetylation of Sirt1., Introduction Hexavalent chromium (Cr(VI)), one of the toxic heavy metals, poses a serious threat to human and animal health. Protein acetylation regulates the structure and function of most proteins in a variety of ways. However, the hepatotoxicity of Cr(VI) and whether it is related to deacetylation remains largely unknown. Objectives We aimed to explore the link between the deacetylation of silent information regulator two ortholog 1 (Sirt1) and hepatotoxicity induced by Cr(VI) exposure, and to better clarify the biological mechanism of liver injury induced by Cr(VI). Methods We established a model of liver injury of K2Cr2O7 by injecting rats intraperitoneally for 35 days continuously and adding resveratrol (Res) to further explore the link between deacetylation and hepatotoxicity. Results The results revealed that Cr(VI) induced inflammatory response and apoptosis in hepatocytes. Furthermore, Cr(VI) reduced Sirt1 expression and inhibited the deacetylation of Sirt1 to downstream key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2), Forkhead box O3 (FOXO3), and nuclear factor-kappa B (NF-κB). Conversely, when Res was administered as an activator of Sirt1, the deacetylation of Sirt1 was enhanced, and inflammatory response and apoptosis were significantly alleviated. Conclusion In summary, this work firstly demonstrates that Cr(VI) induces liver injury in rat by inhibiting the deacetylation of Sirt1, which is of positive significance for protecting the natural environment and animal health from chronic Cr poisoning.

In order to enhance the slag resistance of Al2O3-spinel castables, (Al,Cr)2O3 is added into Al2O3-spinel system as a pre-synthesized micro-powder. Firstly, (Al,Cr)2O3 micro-powder is synthesized by sintering under reduction conditions to prevent the formation of hexavalent chromium. The Al2O3-spinel castables are prepared using tabular alumina, fused spinel, α-Al2O3 micro-powder, calcium aluminate cement and (Al,Cr)2O3 micro-powder as the raw materials. The bulk density, porosity, mechanical properties, and slag resistance of the samples are tested. Afterward, the effects of (Al,Cr)2O3 micro-powder (0–3 wt%) on the slag resistance and microstructures of the Al2O3-spinel castables are assessed by X-ray diffraction (XRD) and energy-dispersive (SEM-EDS) analysis. The results show that the addition of (Al,Cr)2O3 micro-powder can could inhibit the deteriorating effects of Cr3+ on the mechanical properties of the samples. The microstructure results also shows that with the addition of the (Al,Cr)2O3 micro-powder, a secondary solid solution of Ca(Al,Cr)12O19 formed, causing the unit cell to become larger. In the slag erosion area, CA6 crystals formed with network-like interwoven structures, high density, and greater thickness. These characteristics significantly reduce the erosion and permeability indices of the castables, and improve the slag erosion resistance of the material.

Cr-refractories usually contain Cr(III) compounds that can convert into carcinogenic Cr(VI) compounds such as CaCrO4 and Ca4Al6CrO16 under alkaline and oxygen-rich conditions. Literature provides insight into the characteristics, thermal stability, and aqueous solubility of CaCrO4, while there is hardly any data available on Ca4Al6CrO16. The present paper comprehensively studied high-temperature stability and leaching kinetics and other characteristics of Ca4Al6CrO16 by using high-temperature XRD, TG-DSC, XPS, Raman, and TRGS 613. XPS confirmed that chromium in Ca4Al6CrO16 is present in the +6 oxidation state. Ca4Al6CrO16 is thermally stable up to 1500 °C in the air but decomposes in nitrogen above 1258 °C to form the Cr3+-containing phases CaCr2O4 and Ca6Al4Cr2O15. The Ksp of Ca4Al6CrO16 in deionized water is 1.0381 × 10−22, 4.5723 × 10−21 and 2.3489 × 10−20 at 12, 25, and 40 °C, respectively. The leaching process of Ca4Al6CrO16 is chemical reaction controlled, with an apparent activation energy of 58.78 kJ/mol.

Cadmium (Cd), lead (Pb), and hexavalent chromium (Cr(VI)) are often found in soils and water affected by metal smelting, chemical manufacturing, and electroplating. In this study, synthetic iron sulfide nanoparticles (FeS NPs) were stabilized with carboxymethyl cellulose (CMC) and utilized to remove Cr(VI), Cd, and Pb from an aqueous solution. Batch experiments, a Visual MINTEQ model, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectrometer (XPS) analysis were used to determine the removal efficiencies, influencing factors, and mechanisms. The FeS NP suspension simultaneously removed Cr(VI), Cd, and Pb from an aqueous solution. The concentrations of Cr(VI), Cd, and Pb decreased from 50, 10, and 50 mg·L-1 to 2.5, 0.1, and 0.1 mg·L-1, respectively. The removal capacities were up to 418, 96, and 585 mg per gram of stabilized FeS NPs, respectively. The acidic conditions significantly favored the removal of aqueous Cr(VI) while the alkaline conditions favored the removal of Cd and Pb. Oxygen slightly inhibited the removal of Cr(VI), but it had no significant influence on the removal of Cd and Pb. A potential mechanism was proposed for the simultaneous removal of Cr(VI), Cd, and Pb using FeS NPs. The interactions of the three heavy metals involved a cationic bridging effect on Cr(VI) by Cd, an enhanced adsorption effect on Cd by [Cr,Fe](OH)3, precipitation of PbCrO4, and transformation of PbCrO4 to PbS. Therefore, FeS NPs have a high potential for use in the simultaneous removal of Cr(VI), Cd, and Pb from contaminated aqueous solutions.

Hexavalent chromium (VI) is a potent carcinogen for humans, while trivalent chromium (III) is an important element in glucose metabolism. In atmospheric water droplets, oxidation of Cr(III) to Cr(V...

Identification of the factors controlling the migration of hexavalent chromium (Cr (VI)) in soil can provide valuable information for pollution control and risk assessment. In this study, we assessed the processes of transportation and migration of Cr (VI) in soil by batch and column experiments. Breakthrough curves were used to examine the mobility of Cr (VI) in soil columns. Most of them could be described by a typical S-shaped curve. The Yoon–Nelson model and Thomas model were applied to predict the behavior of Cr (VI) in soil and obtained parameters to characterize the rate and capacity of adsorption. It was observed that all obtained parameters changed along with soil properties. Moreover, stepwise multiple regression and grey correlation analysis were used to determine the main control factors by evaluating the relationship between soil properties and dynamic or static parameters. The results showed Fe oxide content was the key factor no matter in static or dynamic adsorption while soil texture had a great influence on the transportation of Cr (VI) in soil columns. Also, in the actual situation, the external input condition should not be ignored. Our research provides meaningful information for authorities to develop better soil management and remediation strategies.

In this study, the removal of hexavalent chromium from the aqueous solution using birds' feathers amended by polyaniline is investigated. Firstly, various bird feathers and polyaniline composites are synthesized and used in batch experiments to separate hexavalent chromium. Results show optimal performance of polyaniline and bird feathers composite in chromium removal. Among the bird's feather and polyaniline composites, the polyaniline/ostrich feathers/polyethylene glycol composite has the most optimal performance with a removal percentage of about four times more than that of activated carbon (87.36 %), at pH = 6 and the contact time of about 30 min. Analysis of cavities size as well as analysis of BET specific surface shows that specific surface area of polyaniline/ostrich feathers/polyethylene glycol composite with 36.22 m2/g is higher than other composites. Scanning electron microscope (SEM) images taken from the surface of the composites show better and more uniform coverage of polyaniline on the ostrich feather in the polyaniline/ostrich feather/polyethylene glycol composite. The XRD analysis and FTIR analysis confirm the synthesis of aniline on the resulted composite and it is declared that the structure of the achieved composite is amorphous.

In the present study, an innovative carbon self-doped g-C3N4 (CCN) loaded with ultra-low CeO2 (0.067–0.74 wt%) composite photocatalyst is successfully synthesized via a facile one-pot hydrothermal and calcination method. The CeO2/CCN exhibits superior photocatalytic performance for tetracycline degradation (78.9% within 60 min), H2O2 production (151.92 μmol L-1 within 60 min), and Cr(VI) reduction (99.5% within 40 min), which much higher than that of g-C3N4, CCN, CeO2, and CeO2/g-C3N4. The enhanced photocatalytic performance is originated from the fact that the doping of C can efficaciously broaden the utilization range of solar light and improve the reduction ability of photogenerated electrons. Meanwhile, the ultra-low loading of CeO2 can effectually promote the migration of photogenerated electrons and enhance the specific surface area. Besides, the experiments of pH effect and cycle ability indicate that CeO2/CCN has excellent durability and stability. Finally, the photocatalytic mechanism of CeO2/CCN is systematically discussed. This work proves that combining element doping and semiconductor coupling is a promising strategy to design high-efficiency g-C3N4-based photocatalysts.

In this study, ZnO, SnO2 and their composite (ZnO-SnO2) were synthesized by green route using aqueous extract of Solanum macrocarpon fruit and were used for the photo-reduction of hexavalent chromium. The synthetic route involved a two-step procedure, induced by temperature via calcination at 350 and 600 °C. The composite was prepared by the treatment of a mixture of the precursor compounds to a temperature up to 800 °C, and the extension of the temperature to 1000 °C, resulted in the emergence of ZnO-SnO2-Zn2SnO4 (ZTO). The nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV–vis spectroscopy. The XRD studies of the binary oxides confirmed a hexagonal wurtzite structure for the ZnO and a tetragonal phase SnO2, without any change in the diffraction patterns or supplementary diffraction peaks. The morphology of the nanoparticles indicated fairly spherical shapes for the ZnO, that tend to agglomerate with increase in temperature. The SnO2 showed rectangular shapes at both temperatures of reaction, while the ZnO-SnO2 composite showed the presence of both morphologies of the component binary oxides. In the photo-enhanced degradation study, under ultra-violet light, the effect of pH (2–8), concentration of chromium(VI) (2 – 8 ppm), and photocatalyst dosage (25 - 150 mg/L) on the reduction of Cr(VI) to Cr(III) were investigated. The reduction showed higher efficiency in acidic environment than in the alkaline environment, and also with increase in photocatalyst dosage. The composite exhibited the highest photoreduction efficiency, above 90%, at the optimum condition of pH 2, 150 mg/L photocatalyst, 2 ppm chromium solution after 90 min. These low-cost and nontoxic metal oxide and their green synthesized composite have great potentials for Cr(VI) pollution clean-up from waste water.

Hexavalent chromium (Cr(VI)) compound is considered as a common environmental and occupational pollutant due to widespread application in industry and agriculture. Cr(VI) as a carcinogen poses a serious threat to human health and the underlying mechanisms need further investigation. Previous studies had demonstrated the characteristic expression profiling after Cr(VI) treatment in vitro and in vivo at the levels of gene and protein. The comprehensive metabolic signatures were also conducive to discover potential biomarkers for effects assessment of Cr(VI) toxicity. In the current study, Ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) non-targeted metabolomics was applied to analyze serum metabolic changes in 77 chromate exposure workers and 62 controls. Thirteen metabolites were found significantly decreased and 41 metabolites were increased, which were involved in arginine and proline metabolism, and glycerophospholipid metabolism by bioinformatic analysis. Furthermore, there were significant negative correlations between blood Cr level and Arginine, PC(18:2/24:4) and PC(14:0/16:0), subgroup analyses indicated that these correlations were observed in male-only subgroups, and were not found among chromate workers and controls separately. Diet could be a potential confounder which was not controlled rigorously in this study. These findings provided preliminary clues to investigate the underlying mechanisms of Cr(VI)-induced toxicity and were required to be further verified in future researches.

Chromium is a potentially poisonous and carcinogenic species, which originates from human activities and various industries such as leather, steel, iron, and electroplating industries. Chromium is present in various oxidation states, among which hexavalent chromium (Cr(VI)) is highly toxic as a natural contaminant. Therefore, chromium, particularly Cr(VI), must be eliminated from the environment, soil, and water to overcome significant problems due to its accumulation in the environment. There are different approaches such as adsorption, ion exchange, photocatalytic reduction, etc. for removing Cr(VI) from the environment. By converting Cr(VI) to Cr(III), its toxicity is reduced. Cr(III) is essential for the human diet, even in small amounts. Today, biopolymers such as alginate, cellulose, gum, pectin, starch, chitin, and chitosan have received much attention for the removal of environmental pollutants. Biopolymers, particularly polysaccharides, are very useful compounds due to their OH and NH2 functional groups and some advantages such as biodegradability, biocompatibility, and accessibility. Therefore, they can be widely applied in catalytic applications and as efficient adsorbents for the removal of toxic compounds from the environment. This review briefly investigates the application of polysaccharide-based (nano)materials for efficient Cr(VI) removal from the environment using adsorption/reduction, photocatalytic, and chemical reduction mechanisms.

Ferrous sulfide (FeS) nanoparticles constitute an effective hexavalent chromium (Cr(VI)) treatment reagent. However, FeS nanoparticles aggregate easily, significantly limiting their engineering applicability. To overcome this shortcoming and further improve Cr(VI) removal efficiency, this study used tannic acid (TA) to modify FeS nanoparticles. The results demonstrated that TA-modified FeS nanoparticles, TA-nano-FeS, had a significantly reduced tendency to agglomerate, and maintained particle diameters of 10–100 nm, which were much shorter than diameters of FeS nanoparticles. In addition, TA-nano-FeS could combine the surface-active functional groups of TA. The maximum removal capacity of TA-nano-FeS was 381.04 mg/g, which was 2.92 and 1.83 times higher than those of TA and nano-FeS, respectively. Furthermore, the acidic condition was more beneficial for Cr(VI) removal, and the coexisting cations (Ca2+ and Mg2+) slightly decreased the removal efficiency of Cr(VI). Adsorption, reduction, and co-precipitation were the removal mechanisms, and the reaction products included FeCr2O4, Cr2O3, Fe2O3, Cr(OH)3, and S8. The results provided valuable information for the practical application of TA-nano-FeS in Cr(VI) removal.

BackgroundExposure to hexavalent chromium [Cr(VI)] occurs widely in occupational settings across the EU and is associated with lung cancer. In 2025, the occupational exposure limit is set to change to 5 μg/m3. Current exposure limits are higher, with 10 μg/m3 as a general limit and 25 μg/m3 for the welding industry. We aimed to assess the current burden of lung cancer caused by occupational exposure to Cr(VI) and to evaluate the impact of the recently established EU regulation by analysing different occupational exposure limits.MethodsData were extracted from the literature, the Global Burden of Disease 2019) study, and Eurostat. We estimated the cases of cancer attributable to workplace exposure to Cr(VI) by combining exposure-effect relationships with exposure data, and calculated related DALYs and health costs in scenarios with different occupational exposure limits.ResultsWith current EU regulations, 253 cases (95%UI 250.96–255.71) of lung cancer were estimated to be caused by Cr(VI) in 2019, resulting in 4684 DALYs (95%UI 4683.57–4704.08). In case the welding industry adopted 10 μg/m3, a decrease of 43 cases and 797 DALYs from current values is expected. The predicted application of a 5 μg/m3 limit would cause a decrease of 148 cases and 2746 DALYs. Current costs are estimated to amount to 12.47 million euros/year (95%UI 10.19–453.82), corresponding to 39.97 million euros (95%UI 22.75–70.10) when considering costs per DALY. The limits implemented in 2025 would lead to a decrease of 23.35 million euros when considering DALYs, with benefits of introducing a limit value occurring after many decades. Adopting a 1 μg/m3 limit would lower costs to 1.04 million euros (95%UI 0.85–37.67) and to 3.33 million euros for DALYs (95%UI 1.89–5.84).DiscussionAssessing different scenarios with different Cr(VI) occupational exposure limits allowed to understand the impact of EU regulatory actions. These findings make a strong case for adapting even stricter exposure limits to protect workers’ health and avoid associated costs.

In this paper, a dry particle-particle coating technique was implemented to develop magnetic adsorbent from natural mineral constituents. Iron ore, specifically banded iron formation (BIF), was used as guest magnetic particles while serpentine (Serp) was used as host adsorptive material. Surface characterizations for the synthesized composite were investigated. The results confirmed the formation of a composite that combines both magnetic and adsorptive properties. The capability of the composite for hexavalent chromium Cr(VI) removal was investigated under different conditions. A maximum adsorption capacity of 138 mg/g was achieved. The adsorption of Cr(VI) onto the magnetic composite (BIF@Serp) was further thermodynamically and kinetically investigated. The results indicated that the adsorption follows 1.2-order kinetics and occurs spontaneously with an exothermic nature. Application of BIF@Serp for the treatment of real tannery effluent was conducted, the composite showed an excellent removal performance not only with Cr(VI) but also with other heavy metals and organic contaminants.

Background Biosorption method for Cr(VI) removal from domestic and industrial wastewater is widely desirable technicality due to its high efficiency, natural affinity, selectivity, easily operation, low costs and eco-friendly procedures. The presented work demonstrates the sequestration of hexavalent chromium ion, Cr(VI) from contaminated water by the biosorbent Artemisia monosperma (AM) powder modified by trimethyloctadecylammonium bromide (TOAB). Methods Analytical tools of XRD, FTIR, SEM, EDS, TGA and XPS were used from one side to characterize the developed modified biosorbent TOAB@AM and from the other side to investigate the Cr(VI) adsorption. Operational parameters of pH, adsorbent dose, contact time, coexisting ions and temperature that affect adsorption process were optimized. Significant Findings Adsorption kinetics emerges the best linearity when applying the pseudo-second-order model referring to the chemisorption assumption in controlling sorption process of TOAB@AM biosorbent and Cr(VI) ions. Adsorption isothermal results are distinctly well fitted with Langmuir correlation. Furthermore, adsorption thermodynamics reveals the spontaneity and exothermic modality in adsorbing Cr(VI) onto TOAB@AM biosorbent with less randomness behavior. The optimal operational conditions for Cr (VI) removal are pH = 3; 0.1g dose of TOAB@AM; and 40 min contact time that result in adsorption capacity of Cr (VI) about 36.9 mg/g. Merits of low cost, high selectivity, and adsorptive potency of the novel TOAB@AM biosorbent towards Cr(VI) ions makes it a worthy alternative for remediating water sources from Cr(VI) contaminates within a facile and fast avenue.

The present investigation aims to remove Cr(VI) by flower like Cerium Phosphate Polypyrrole nanocomposite material (CePO4-PPY). The material was synthesized by in situ oxidative polymerization method and characterized by FTIR, Raman, XRD, XPS, Zeta potential, N2 adsorption–desorption isotherms, and TGA-DTA analysis. Field emission scanning electron microscopy and transmission electron microscopy images revealed the flower-like morphology of the synthesized nanocomposite. Meanwhile, the fabrication of polypyrrole on cerium phosphate nanoparticles provided a plentiful of active adsorption sites to interact with hexavalent chromium ions. The Cr(VI) adsorption followed the pseudo-second-order kinetic and Langmuir isotherm model showing a high adsorption capacity of 117.78 mg g−1 at room temperature at lower pH. The high tolerance capacity of CePO4-PPY in the presence of other co-anions makes it a highly efficient adsorbent. The adsorption dynamic study demonstrated that the rate-determining step was controlled by surface diffusion, pore diffusion, and film diffusion. XPS spectra confirmed the simultaneous adsorption of Cr(VI) and in situ chemical reduction to Cr(III). Regeneration studies illustrated the efficiency of more than 80%, even after five cycles. Therefore, CePO4-PPY nanocomposite could be a unique alternative to act as a promising adsorbent for the effective treatment of Cr(VI) containing wastewater.

Paddy soil and irrigation water are commonly contaminated with hexavalent chromium [Cr(VI)] near urban industrial areas, thereby threatening the safety of agricultural products and human health. In this study, we develop a porous and high specific area bone char (BC) to support nanoscale zero-valent iron (nZVI) and apply it to remediate Cr(VI) pollution in water and paddy soil under anaerobic conditions. The batch experiments reveal that BC/nZVI exhibits a higher removal capacity of 516.7 mg/(g•nZVI) for Cr(VI) than nZVI when normalized to the actual nZVI content, which is 2.8 times that of nZVI; moreover, the highest nZVI utilization is the nZVI loading of 15% (BC/nZVI15). The Cr(VI) removal efficiency of BC/nZVI15 decreases with increasing pH (4 – 10). Coexisting ions (phosphate and carbonate) and humic acid can inhibit the removal of Cr(VI) with BC/nZVI15. Additionally, BC exhibits a strong advantage in promoting Cr(VI) removal by nZVI compared to the widely used biochar and activated carbon. Our results demonstrate that reduction and coprecipitation are the dominant Cr(VI) removal mechanisms. Furthermore, BC/nZVI15 shows a significantly higher reduction and removal efficiency as well as a strong anti-interference ability for Cr(VI) in paddy soil, as compared to nZVI. These findings provide a new effective material for remediating Cr(VI) pollution from water and soil.

In this work, Bi2XO6 (X = W, Mo) are synthesized at different temperatures. The results of tests find the optimal temperatures of Bi2WO6 and Bi2MoO6 are 180 and 160°C (BW-180, BM-160). Then, BW-180 and BM-160 are further compounded with different contents of CuS. The results of photoelectrochemical (PEC) tests show that CuS can improve the PEC performance of semiconductor materials, and it has better performance when CuS mass fraction is 5%. These maybe the photoelectron potentials generated by CuS/Bi2XO6 (X = Mo, W) heterojunction reduce the combination of photogenerated electrons and holes. When the PEC sensor based on 5%-CuS/BW-180 detects Cr(VI), it has a linear range of 1–80 μmol/L with detection limit of 0.95 μmol/L, while the PEC sensor based on 5%-CuS/BM-160 detects Cr(VI) has a linear range of 0.5–230 μmol/L and a detection limit of 0.12 μmol/L. Thus, 5%-CuS/Bi2XO6 has potential application in hexavalent chromium detection.

Chromium is a common harmful pollutant with high toxicity and low bearing capacity of soil and water. Excellent salinity resistance, a wide pH range, and high regeneration capacity were essential for qualified adsorbents used in removing hexavalent chromium (Cr(VI)) from polluted water. Herein, iron oxalate modified weak basic resin (IO@D301) for the removal of Cr(VI) was prepared by the impregnation method. The IO@D301 was characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Owing to abundant amine, carboxyl groups and iron ions existing on the surface, IO@D301 possesses high adsorption and salinity resistance capacity for Cr(VI). The maximum adsorption capacity of IO301 towards Cr(VI) reached 201.30 mg·g-1 at 293 K and a pH of 5. The adsorption equilibrium was well fitted by the Freundlich model, and the adsorption process was described by the pseudo-first-order kinetics model as spontaneous and exothermic. The mechanism may be identified as electrostatic attraction, coordination, and reduction, which was confirmed by FT-IR and X-ray photoelectron spectroscopy.

Iron sulfide (FeS) nanoparticles have emerged as promising materials for a wide range of applications. Despite the growing interest, only conventional wet chemical synthesis approaches for FeS are prevalent, while alternate nontoxic green synthesis methods have not yet been explored. In this study, we demonstrate a novel green approach for the reduction of iron sulfate salt to iron sulfide nanoparticles using aqueous extracts from date tree (Phoenix dactylifera) seeds (ds-FeS nanoparticles). Detailed characterization techniques revealed the formation of spherical FeS nanoparticles with a mean nominal size of 68 nm, while spectroscopy studies confirmed the role of date seed phytochemicals in the synthesis and capping of ds-FeS. We also demonstrate the potential of using ds-FeS for water treatment by efficiently removing two different types of pollutants- ciprofloxacin (pharmaceutical) and hexavalent chromium (heavy metal). Results from this study maybe useful towards further exploration and optimization of eco-friendly synthesis routes for nanoscale iron sulfides.

Pyrite is the most abundant sulfide semiconductor mineral with excellent optical properties. However, few reports have investigated its photocatalytic activity because of the low photogenerated carrier separation efficiency. In this work, a Z-scheme FeS2/Fe2O3 composite photocatalyst was fabricated in situ via structural transformation of pyrite through heat treatment. A remarkably enhanced photocatalytic performance was observed over the FeS2/Fe2O3 composite photocatalyst. Compared with the pristine pyrite, the degradation efficiency of carbamazepine (CBZ) reached 65% at the added hexavalent chromium (Cr(Ⅵ)) concentration of 20 mg/L and the Cr(Ⅵ) was nearly completely reduced in the mixed system using FeS2/Fe2O3 within 30 min under simulated solar light irradiation. The enhanced photocatalytic activity can be attributed to the efficient separation and transfer of photogenerated carriers in the FeS2/Fe2O3 composite photocatalyst. This facilitated the generation of •OH, hole (h+) and •O2− species, which participated in the photocatalytic reaction with CBZ. Based on the measurement of the active species and electric properties, a Z-scheme electron transfer pathway was proposed for the FeS2/Fe2O3 composite photocatalyst. This work broadens the application potential of pyrite in environmental remediation.

The study proposes the use of microbial fuel cell (MFC) technology to reduce toxic Cr(VI) present in industrial wastewater to less toxic trivalent chromium [Cr(III)], while generating electricity through a bioelectrochemical oxidation-reduction process. Factors influencing the treatment process and electricity generation include the concentration of Cr(VI) in wastewater, substrate types used for anodes, types of microorganisms involved, types of cathode and anode, surface area of the cathode and anode, and pH and temperature of cathodic and anodic solutions. While other heavy metals in wastewater may be removed by MFC technology, Cr(VI) removal is more efficient in terms of electricity generation. Previous research indicated that the maximum electrical power generated by Cr(VI) removal through the use of MFCs is 1600 mW/m2, which is expected to increase as the factors affecting this process are optimized. Based on current data, MFC-based electricity generation along with Cr(VI) removal is a potential future source of sustainable energy. However, research priorities need to focus on reducing the cost of MFC technology by using economical and effective materials and increasing electricity production.

The bimetallic zero-valent magnesium: zinc composition was used as a suitable reductant agent to remove hexavalent chromium from industrial wastewater. The efficiency of the proposed bimetallic composition in removal process was inspected in both batch and flow systems. Response surface methodology was employed in a batch system to investigate the effects on the removal efficiency of different operational conditions. Central composite design was used for process optimization and evaluation of process effects and interactions parameters including weight percentages and amount of bimetallic composition, pH, contact time, stirring rate, temperature of solution and the primary concentration of hexavalent chromium that the optimum conditions were 25:75% (WMg/WZn), 1 g, pH 3, 10 min, 750 rpm, 40 °C and 50 ppm, respectively. Efficiency of hexavalent chromium pollutant elimination for the batch and flow systems at optimum conditions that optimized for batch system and the used optimized parameters for flow system, was 97.10% and 94.50%, respectively. Moreover, wastewater of barium chromate production line was applied as a real sample containing of hexavalent chromium, while the removal efficiency in batch and flow systems was 91.70% and 91.20% for this real sample, respectively.

A new catecholamine polymer, tannin-polyethyleneimine (TA-PEI) was fabricated via mussel-inspired polymerization for highly efficient hexavalent chromium (Cr(VI)) adsorption. The TA-PEI adsorbent was prepared with a mass ratio of TA to PEI of 3:1. This adsorbent had an ultra-high Cr(VI) removal capacity because of its amines and phenolic hydroxyl groups, with values reaching 707.96 mg/g under 308 K, which is higher than that of most PEI-based and TA-bearing adsorbents. The developed adsorbent also achieved rapid Cr(VI) adsorption, with adsorption capacity values reaching 554.94 mg/g in 15 min. Further, it displayed excellent chemical reduction ability when converting Cr(VI) to low toxicity Cr(III), as well as its good adsorption selectivity of Cr(VI) in a solution bearing coexisting ions. In a continuous adsorption experiment, the adsorbent exhibited a Cr(VI) solution treatment capacity of up to 30 L/g with a Cr(VI) concentration of 10 ppm. With its high adsorption capacity and rapid adsorption rate, this low cost and easily prepared adsorbent may have widespread potential for Cr(VI) removal and enrichment.

Searching for an economically evoked photocatalyst to meet the need for sustainable energy, LDH proved itself successful. The inorganic pollutant hexavalent chromium sparked as a major concern to society. Different treatment methods are available to reduce the toxicity level of chromium (VI) from water. The divalent magnesium, cobalt, and nickel cations are incorporated in the brucite layer of LDH keeping fix the trivalent Al3+. The LDHs was synthesized following the low cost co-precipitation method in 2:1 M ratio. Here we compared the photocatalytic activity of as-synthesized Co Al LDH, Ni Al LDH and Mg Al LDHs towards chromium (VI) reduction taking 10 ppm chromium solution for 1 h under solar light irradiation. The synthesized sample was thoroughly characterized by XRD, FTIR, PL, UV–vis spectra and TEM analysis. The XRD result indicates the pure formation of LDH phase with the degree of crystallization, which depends on the incorporated metal, which confirmed the LDH formation. Co Al LDH revealed superior photocatalytic activity than Ni Al LDH and Mg Al LDH following pseudo first-order kinetics. The larger crystallinity Co Al LDH exhibited 99% Cr(IV) degradation than Ni Al LDH (87%) and Mg Al LDH (51%) at pH 5. This study provides a good insight in comparing the photocatalytic activity of Co Al LDH, Ni Al LDH and Mg Al LDH towards Cr (VI) degradation under visible light irradiation.

Biocathode application in microbial fuel cell has been developed as a sustainable technology for heavy metal reduction. However, most biocathodes require pretreatment with acclimatization inversion. Here, a biocathode MFC based on strain Corynebacterium vitaeruminis LZU47-1 without acclimatization inversion was constructed for hexavalent chromium reduction. The maximum power generation by the biocathode MFC with C. vitaeruminis LZU47-1 increased by 24.5% and 53.4% in inversion and abiotic cathode groups, respectively. Compared with the inversion (72.52%) and abiotic cathode groups (64.75%), the biocathode group achieved a Cr(VI) removal efficiency of 98.63%. Furthermore, electrochemical analysis such as SEM-EDS, XPS and CV test were conducted to elucidate the adsorption-reduction mechanism for Cr(VI) reduction. MiSeq sequencing revealed that Geobacter (51.28%) was enriched on the anode biofilm in the biocathode group than inversion (38.52%) and abiotic cathode groups (31.74%). Therefore, this study provides a convenient and highly effective method for enhancing power output and Cr(VI) reduction in biocathode MFCs.

Cr (VI) contamination in water is of immense concern and has far-reaching effects because of its bioaccumulation, non-biodegradable nature and carcinogenic effect. Chromium has been released carelessly to the natural water ecosystem as waste from various industrial processes like electroplating, metal finishing, dye synthesis, leather tanning, chromite extraction, and steel manufacturing. Among the many available technologies for Cr (VI) removal, adsorption is the most popular one due to its easiness, scalability and energy saving nature. Different techniques have been utilized to synthesize porous and non-porous ZnFe2O4. Among various methods, a sol–gel method has been implied to prepare porous ZnFe2O4 while the solution combustion method was implied to synthesize non-porous ferrite material. The structural phases, textural properties, morphological aspects, and functional groups were meticulously analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and surface area (SBET) of the synthesized adsorbents. The comparative studies for Cr (VI) removal by porous and non-porous spinel ferrite were carried out at an initial pH 3. Compared to non-porous ZnFe2O4, porous ZnFe2O4 shows an enhanced removal of hexavalent chromium which was about 99%. The high surface area of porous ZnFe2O4 (48 m2/g) as compared to non-porous ZnFe2O4 (15 m2/g) is the key reason for showing enhanced Cr (VI) adsorption. Another reason for enhanced adsorption in the case of porous ZnFe2O4 is the existence of the strong electrostatic force of interaction between the adsorbent and chromate ions.

Among numerous heavy metals, hexavalent Chromium [Cr (VI)] place a potential threat and mostly seen in several industrial effluents such as leather tanning, printing, ceramics. For removal of Cr from waste water, reduction of Cr (VI) to Cr (III) is preferred due to less toxicity of Cr (III) than Cr (VI). Among various reduction processes, Cr (VI) reduction by photocatalysis is favoured owing to its greener approach and behaviour. Graphene nanocomposite photocatalysts show higher photo reduction efficiency due to large surface area and extraordinary electron conductance of graphene. As there is almost no resistance on the surface of graphene, so electrons move freely and faster resulting excellent surface charge transfer; therefore enhanced photocatalytic Cr (VI) reduction. We have systematically investigated the origin and enhancement of photo-reduction Cr (VI) by graphene nanocomposites photocatalysts. Graphene based metal oxides nanocomposites, metal sulphides, 0D/2D heterojunction nanocomposites, non-metallic nanocmposites, plasmonic nanocomposites and Z-scheme nanocomposites photocatalysts have been highlighted and discussed.

Hexavalent chromium (Cr(VI)) has carcinogenic, nephrotoxic, hepatotoxic, and neurotoxic effects. Exposure to Cr(VI) can also lead to hematological alterations and blood biochemical changes. The literature on Cr(VI) toxicity concerns mostly adult forms of vertebrates. In this study, an attempt was made to determine the effect on the developing chicken embryo of Cr(VI) in ovo administration. It was observed that chromium affected the hatchability of chicks in a dose-dependent manner. At a dose from 25 to 250 μg per egg, Cr(VI) resulted in a statistically significant reduction of hatchability. Chromium administrated at lower doses (1.56 and 2.5 μg per egg) caused a statistically insignificant increase of hatchability. However, chromium at a level of LD50 (15.6 μg per egg) or 1/10 LD50 (1.56 per egg) did not cause major changes in hematological parameters or plasma biochemical indices in newly hatched chicks. The same doses did not lead to any histopathological changes in the liver.

In this study, different carbon quantum dots (CQDs)/NaBiO3 hybrid materials were synthesized as photocatalysts to effectively utilize visible light for the photocatalytic degradation of contaminants effectively. These hybrid materials exhibit an enhanced photocatalytic reduction of hexavalent chromium (Cr(VI)) in the aqueous medium. Zero-dimensional nanoparticles of CQDs were embedded within the two-dimensional NaBiO3 nanosheets by the hydrothermal process. Compared with that of the pure NaBiO3 nanosheets, the photocatalytic performance of the hybrid catalysts was significantly high and 6 wt.% CQDs/NaBiO3 catalyst exhibited better photocatalytic performance. We performed the first-principles density functional theory calculations to study the interfacial properties of pure NaBiO3 nanosheets and hybrid photocatalysts, and confirmed the CQDs played an important role in the CQDs/NaBiO3 composites. The experimental results indicated that the enhanced reduction of Cr(VI) was probably due to the high loading of CQDs (electron acceptor) on NaBiO3, which made NaBiO3 nanomaterials to respond in visible light and significantly improved their electron-hole separation efficiency.

The large scale amplification of industrial discharge in the modern era is resulting in widespread water pollution, especially from various industrial effluents and wastewater containing heavy metals, posing a severe threat to our environment. In order to combat such problems, this work aims on Multifunctional Fluorescent Nano-Sensor (MFNS) mediated simultaneous detection and removal of hexavalent chromium from real life wastewater which further converts it into an energy harvesting material, namely, “Waste capacitor”. This smart material can detect the presence of the targeted heavy metal (Cr(VI)) in the wastewater and can entrap it by using a facile adsorption process. Thereafter, it will change its microstructure which further enhances its dielectric properties. Morphology, microstructure and optical properties of the synthesized material have been studied thoroughly and a turn-off based fluorescence sensing has been reported herein. Photoinduced electron transfer (PET) based fluorescence quenching is mainly responsible for this sensing mechanism. The selectivity and sensitivity of the material during fluorescence sensing have also been studied by using standard Stern-Volmer method showing that the synthesized material is tremendously selective and sensitive towards the specific target ion. High surface area with slit-like porous structure enhances the adsorption based removal of the contaminant. Nearly 76% of contaminants have been removed by using this smart material. After adsorbing specified target, this MFNS changes its microstructure and results in superior dielectric constant with a minimal tangent loss. Tremendous sensitivity (in nM range), selectivity towards the specific contaminant and adsorption of toxic heavy metal and converting it into a green energy harvesting material (waste capacitor) makes this smart multifunctional material a real waste to wealth converter.

The solid waste material ferrochromium slag from the metallurgical industries encounters with disposal problem because of the presence of chromium. From the chemical composition study, the waste slag was observed to contain sizeable amount of environmentally harmful residual chromium. Chromium speciation in the slag was observed to exist as mostly immobile trivalent state. But there may be possibility of its conversion to leachable hexavalent chromium and its subsequent release from slag matrix causing chromium pollution problems. Elution of chromium from slag was studied under adverse environmental situations. The importance of factors influencing chromium elution from the slag samples were assessed using full factorial design analysis and accordingly regression equations were developed for elution of both hexavalent and total chromium. The significant physico-chemical factors affecting elution of chromium from slag matrix are obtained to be pH, size of particle, time of contact and their combinations.

Heavy metals present in industrial effluents enter the biological cycle through aquatic organisms. Heavy metals undergo bioconcentration and prove to be toxic even in trace quantities. Chromium is necessary for carbohydrate metabolism, but in higher concentrations, it tends to be harmful. Hexavalent chromium Cr (VI) ions are prevalent, and its toxicity causes environmental and public health concerns. Chromium (IV) based industrial effluents have become a worldwide menace. This collection of toxic metals ions from effluent streams affects both humans and the environment. The non-depleting heavy metal ions cause severe damage to the environment. Environmental pollution affects both human life and eco-system. Water pollution from municipal sources and industries are matter of concern. The solution to the fast-depleting natural water bodies and acquifiers is to reuse treated effluent. Several remediation technologies are available, for reclaiming effluent after treatment for heavy metals like Cd, Cr, Cu, Hg, Ni, Pb, and Zn. This paper attempts to assimilate concise information on removing hexavalent chromium through laboratory experiments to implement cost-effective, plausible industrial treatments practically. The importance of efficient industrial effluent treatment lies in the recovery of heavy metals and usage of the treated effluent. A list of techniques is thought of for the treatment of heavy metals removal that has minimal impact on the environment in liquid / solid phases, cost of treatment, and scaling up to industrial levels. Adsorption is one of the prominent techniques used for heavy metals treatment. The adsorption kinetics and isotherms help understand the reduction of Cr (VI) from effluent streams. The wastewater treatment techniques currently employed treat hexavalent chromium-containing effluent streams with low-cost industrial byproducts. Emphasis is on novel techniques of wastewater treatment electrochemical techniques for Cr (VI), contributing to various environmental problems based on their toxicity.

This paper reviews the acute and chronic health issues faced by the welders and their successful control strategies. The major health issues associated with welding are reported to be i) respiratory problems ii) skin cancer iii) metal fume fever. From the literature survey carried out, it was found that respiratory issues are caused by particulate emission from the welding source, skin cancer by UV emitted from the welding arc and fume fever by exposure to Al2O3, ZnO, and Fe2O3 emanating from the welding process. These adverse health effects can be effectively controlled by reducing the fume emission, evolved gas emission, and harmful radiations at the source itself. From the systematic literature survey, it was also found that reactive metal addition, nano-calcite addition, nano-alumina addition, titania addition, and composite coating can reduce these harmful effects to the welders. The addition and coating of reactive metals can bring tremendous changes in fume formation rate (FFR) and hexavalent chromium formation. Studies based on different elemental addition on the electrode flux and core wire are found to be scarce. Therefore, future studies in this specific area should address these problem directly.

The present study aims to analyse the potential crosstalk between nitric oxide (NO) and hydrogen sulfide (HS) in triggering resilience of maize (Zea mays L.) seedlings to hexavalent chromium (Cr VI). Exogenous application of 500 μM sodium nitroprusside (SNP, as a NO donor) or sodium hydrosulfide (NaHS, as a HS donor) to 9-day-old maize seedlings, countered a Cr (200 μM) -elicited reduction in embryonic axis biomass. Cr caused cellular membrane injury by enhancing the levels of superoxide and hydroxyl radicals as well as methylglyoxal, and 4-hydroxy-2-nonenal. The application of SNP or NaHS considerably improved the endogenous NO and HS pool, decreased oxidative stress and lipid peroxidation by suppressing lipoxygenase activity and improving some antioxidant enzymes activities in radicles and epicotyls. Radicles were more affected than epicotyls by Cr-stress with enhanced electrolyte leakage and decreased proton extrusion as indicated by lesser H-ATPase activity. HS appeared to mitigate Cr toxicity through up-regulated H-ATPase and glyoxalase pathways and by maintaining optimal GSH levels as downstream effects of ROS and MG suppression. Hence, HS-mediated the regeneration of GSH pool is associated with the attenuation of MG toxicity by enhancing S-lactoglutathione and D-lactate production. Taken together, our results indicate complementary roles for HS and GSH to strengthen membrane integrity against Cr stress in maize seedlings., The authors are thankful for the financial support from the Tunisian Ministry of Higher Education, Scientific Research and Technology (LR18ES38). Work at the Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, UK was supported by a visiting fellowship grant to Oussama Kharbech. Research in the laboratory of FJC is supported by ERDF co-financed grants financed by the Ministry of Economy and Competitiveness (AGL2015-65104-P) and Junta de Andalucía (group BIO192), Spain.

The present study investigates the efficiency of marine green macroalga Ulva fasciata to remove Cr(VI) from aqueous solutions. The alga was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-rays (EDAX) and BET analyses. The effects of various operating parameters such as pH (1–9), biosorbent dose (0.05–0.25 g), initial concentration (10–200 mg/l) and temperature (30–50 °C) were also examined. At concentrations of 10 and 20 mg/l, it was observed that Cr(VI) was completely removed from the solutions after only 5 min contact time. The adsorption experiment data fully showed the applicability of the Harkins-Jura isotherm model. Amongst the applied kinetic models, pseudo-second-order kinetic model was the best fitted one. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) revealed the feasibility of spontaneous random exothermic adsorption. The results indicated the high removal efficiency of Cr(VI) from its aqueous solutions by the raw alga Ulva fasciata because of its low-cost, ecofriendly and promising biosorbent quality.

Herein, for the first time, the adsorption mechanism of HCrO4− and CrO42− (as models of Cr(VI)) by bacterial cellulose (BC), polyaniline (PANI), and BC/PANI was performed using Density Functional Theory (DFT) in both acidic and neutral pH. For this purpose, three forms of neutral, partially (pp), and fully protonated (fp) were assumed for PANI in neutral and acidic media to elucidate the influence of pH. The results indicated that the formation of hydrogen bonds (H-bond) had the main contribution in the adsorption of CrO42− and HCrO4− onto both BC and PANI. Besides, the adsorption energy of PANI was nearly 3 times as much as BC in both acidic and neutral pH. The design of the BC/PANI complex improved the stability of PANI by increasing in HOMO-LUMO energy gap from 1.1 eV to 1.97 eV. The establishment of more H-bonds, and the appearance of two different types of H-bonds, O⋯H and N⋯H, and their smaller distances (average 1.5 A), were observed in HCrO4−/BC-fp-PANI complexes, while one type of hydroxyl H-bond (average 2 A) was detected in CrO42−/BC-pp-PANI. It proved the adsorption of Cr(VI) is more favorable in acidic pH. The small value of charge transferred (−0.001–0.01) showed that interfacial interaction was governed by physisorption.

In this research, compost was used as raw materials in the production of biomass adsorbent granules using drum granulation technique. Different concentrations of aqueous sodium silicate solution were used as the binding agents. Chromium and Methylene Blue solutions were selected as model adsorbates for heavy metals and dyes, respectively. The results obtained showed that the concentration of sodium silicate used had a positive influence on the mechanical strength of the granules, increasing the concentration would increase the compressive strength of the granules. The adsorbent granules had sufficient strength to survive wet conditions they were subjected during the adsorption study. However, increasing the concentration has a negative influence on the adsorption properties of the compost granules for both Chromium and Methylene Blue.