Reduction Of Chromium Research Articles

Three-Dimensional Multihierarchical Hexagonal/Cubic ZnIn2S4 S-Scheme Heterophase Junction for Superior Photocatalysis.

It is an important strategy to design composite materials with a special microstructure and a tunable electronic structure through structural compatibility. In this work, a novel hexagonal/cubic ZnIn2S4 polymorphic heterophase junction with a three-dimensional multihierarchical structure is successfully constructed by in situ growth of hexagonal ZnIn2S4 nanosheets on the surface of cubic ZnIn2S4 flower-like microspheres prepared by topological chemical synthesis. On the one hand, the multihierarchical architecture provides large specific surface area, abundant active sites, and excellent light trapping capability. On the other hand, the construction of a direct S-scheme heterophase junction enables the formation of a special charge-transfer channel under the force of a built-in electric field, which not only improves the separation efficiency of carriers but also ensures the stronger reaction activity of charges. The prepared ZnIn2S4 heterophase junction composite photocatalyst exhibits greatly boosted photocatalytic efficiency in rhodamine B degradation, hexavalent chromium reduction, and water splitting for hydrogen production, which are 12.3, 6.5, and 3.1 times higher than that of pure hexagonal ZnIn2S4 and 8.1, 5.1, and 2.3 times higher than that of pure cubic ZnIn2S4, respectively, demonstrating its significant potential for applications in energy and environmental fields.

Reduction of Cr(VI) by planktonic cells and biofilm of Acinetobacter sp. (ADHR1) isolated from electroplating wastewater

In this research it was possible to analyze the capacity of Acinetobacter sp. (ADHR1) bacteria to reduce chromium (VI). Bacteria isolated from residual effluents from automobile chrome plating processes auto parts were identified by phenotypiic and genotypic methods. ADHR1 was able to 100% reduce Cr(VI) to Cr(III), resulting in: 100–500 mg / L of Cr(VI) in a lapse of time between 18 to 24 h; likewise, it was possible to show the reduction process in concentrations of 2000 mg / L which was 73% as a result. In addition to this, it was also possible to show that planktonic cells had a greater capacity to reduce hexavalent chromium compared to biofilm cells. The ChrR gene was amplified by PCR confirming the presence of the chromate reductase enzyme. The reduction in chromium was attributed to the presence of the nicotinamide adenine dinucleotide hydrogen (NADH) dependent enzyme chromate reductase in the cytosolic fraction and in the membrane associated fraction. In conclusion, Acinetobacter sp. (ADHR1) used in the study showed great potential to reduce different concentrations of Cr(VI). This research represents a truly eco-friendly alternative in the removal of sites contaminated by metals, knowing the Acinetobacter sp. (ADHR1) has the ability to reduce Cr(VI).

Phenyl-modified carbon nitride based multifunctional gel for the detection, adsorption, photocatalytic reduction and recycling of chromium(VI) in wastewater

It is of vital significance to explore effective and economical multifunctional materials for the detection, remediation and recycling of heavy metal (Cr(VI)). Herein, two-dimensional (2D) phenyl-modified carbon nitride (PCN) polymer was prepared through thermal polymerization of phenylguanidine carbonate. The incorporation of phenyl groups endowed PCN polymer with both strong green fluorescence and high photocatalytic activity for the reduction of Cr(VI). An multifunctional gel for simultaneous detection, adsorption, photo-reduction and recycling of Cr(VI) was further prepared by assembling PCN with polyethyleneimine–N,N’-methylenebisacrylamide (PEI-MBA) gel. PCN-PEI-MBA gel showed a sensitive fluorescence / colorimetric dual-mode detection of Cr(VI). Meanwhile, PCN-PEI-MBA gel displayed preeminent adsorption capacity of 3055.9 mg g−1, surpassing previously reported adsorbents. Under visible-light irradiation, the absorbed Cr(VI) in PCN-PEI-MBA gel was photocatalytically reduced into Cr(III) with visual real-time monitoring the detoxification process and Cr(III) can be further recycled as Cr2O3 by calcination of PCN-PEI-MBA gel. Finally, PCN-PEI-MBA gel was utilize to adsorb and recycle Cr(VI) from the chromium-plating wastewater and detect the concentration of remaining Cr(VI) in the wastewater. This work provides an all-in-one treatment strategy for the detection, remediation and resource recycling of Cr(VI) in practical wastewater.

LED-enhanced photocatalytic reduction of hexavalent chromium by Cu-doped ZnO nanorods: kinetic modeling, cost analysis, and toxicity assessment

ABSTRACT This study unveils the synthesis and application of Cu-doped ZnO nanorods (NRS) as an efficient catalyst for the photocatalytic reduction of hazardous hexavalent chromium (Cr6+) in water. Synthesized via a simplified co-precipitation method, the NRS demonstrated enhanced performance, achieving an 89.35% Cr6+ reduction efficiency under optimal conditions. The catalyst’s performance was significantly augmented in the presence of hydrogen peroxide (H2O2) and revealed a first-order kinetic model. Radical trapping experiments highlighted the pivotal role of hydroxyl radicals in the photocatalytic process. A comparative analysis of the NRS with LED/ZnO and undoped ZnO underscores the superior efficiency of the Cu-doped variant. Moreover, the applicability of this system was validated in real water and wastewater matrices containing Cr6+, indicating its promising potential for industrial and environmental applications. An in vivo bioassay using Daphnia magna further confirmed the reduced toxicity post-treatment, underscoring the environmental friendliness of this innovative approach. The findings present Cu-doped ZnO nanorods as a promising, effective, and eco-friendly catalyst for the remediation of Cr6+ contaminated water, marking a significant stride towards sustainable and efficient water treatment solutions.

Mo–P sites boosting interfacial charge transfer of 2D/3D MoS2/TiO2 heterostructure for efficient photocatalytic hydrogen production and chromium(vi) reduction

Spatial separation of photogenerated carriers via the active Mo–P sites on 2D/3D phosphorous-doped MoS2/TiO2 heterostructure can realize the highly efficient photocatalytic hydrogen production and Cr(vi) reduction.

Hydrothermal preparation of Nb5+-doped α-Fe2O3 nanorods for efficient visible light-driven photocatalytic reduction of hexavalent chromium

Nb5+ doped α-Fe2O3 (Nb-Fe2O3) nanorods with different Nb5+ contents were prepared using a low-temperature, short-time, one-pot hydrothermal method. All the prepared Nb-Fe2O3 products showed better photocatalytic activities than α-Fe2O3 nanorods in the reduction of aqueous Cr(VI) under visible light (wavelength > 420 nm). 4% Nb-Fe2O3 had the maximum photocatalytic activity, which was 2.24 times that of α-Fe2O3 nanorods and surpassed those of many newly reported visible light photocatalysts. Moreover, the photocatalytic efficiency of 4% Nb-Fe2O3 can be further improved by proper increasing its dosage, decreasing the initial pH and Cr(VI) concentration of K2Cr2O7 solution. Furthermore, 4% Nb-Fe2O3 showed rather good photocatalytic stability and reusability. Besides, 4% Nb-Fe2O3 was efficient in visible light-driven photocatalytic reduction of Cr(VI) in diluted black chrome plating solution. Nb5+-doping can efficaciously enhance the abilities of α-Fe2O3 in absorbing visible light and transferring and separating photogenerated carriers, thereby contributing to the elevated photocatalytic activity of Nb-Fe2O3.

Synergistic effect of adsorption-photocatalytic reduction of Cr(VI) in wastewater with biochar/TiO2 composite under simulated sunlight illumination.

Photocatalysis, which is an alternative technology to conventional methods, utilizes solar energy as the driving force to address environmental concerns and has attracted widespread attention from chemists worldwide. In this study, a series of photocatalytic materials composed of agricultural waste and titanium dioxide (TiO2) nanomaterial was prepared for the synergistic adsorption-photocatalytic reduction of hexavalent chromium in wastewater under mild conditions. The results showed that the TiO2 nanomaterial exhibited a higher photogenerated carrier separation efficiency and performance for the adsorption-photocatalytic reduction of Cr(VI) after loading straw biochar (BC). When the loading amount of BC was 0.025 g (i.e., TBC-3), the removal efficiency of Cr(VI) was as high as 99.9% under sunlight irradiation for 25 min, which was 2.9 and 3.5 times higher than that of pure TiO2 and BC samples, respectively. Additionally, after four cycles of experiments, the removal efficiency of Cr(VI) by TBC-3 remained at about 93.0%, proving its good chemical ability in our reaction system. Its excellent adsorption-photocatalytic performance is mainly attributed to the synergistic effect of the strong adsorption of BC and the outstanding photocatalytic performance of TiO2. Finally, the possible mechanism for the synergistic adsorption-photocatalytic reduction on BC/TiO2 to remove the highly toxic Cr(VI) in wastewater was proposed.

Disposal of highly toxic waste chromium solutions

The aim of the study is to determine the effect of organic reductants (sawdust) on the degree of reduction of chromium (VI) ions in the complex processing of waste chromium-containing solution (electrolyte) of plating production, as at the same time to determine the optimum conditions of the process. Experimental results showed that organic reductants (sawdust, and lignin) in an acid environment work as a reagent-reductant of chromium (VI) ions. The process of reduction of chromium (VI) ions to chromium (III) proceeds intensively for the first 20-30 min and is completed within 50 minutes, while about 1.0-2.5% of chromium (VI) ions remain unreduced, and 97.0-99.0% of chromium (VI) ions of the total amount pass into trivalent form. Chromium (VI) ions are reduced at the first stage of the process, the bulk of them are converted into chromium (III) ions and emitted as chromium (III) hydroxide, and wastewater is further purified at the second stage. When using lignin, the reduction in the concentration of chromium (VI) ions is insignificant, since the number of active functional groups in its structure is limited. Model studies presented in this work and their approbation on production wastewater showed expediency and sufficiently high efficiency of using woodworking wastes (sawdust) to reduce chromium (VI) ions from the spent solutions. Sawdust consists mainly of cellulose; its structure contains functional groups that act as a reductant during oxidation. Further study of the process mechanism and characteristics is essential for the development of recommendations for their utilization.

Titania modifications with fluoride, sulfate, and platinum for photochemical reduction of chromium (VI)

In this work, Titania was modified by sulfation or fluorination and platinum on the surface to improve the Cr (VI) reduction efficiency compared to the bare TiO2 material synthesized by the sol-gel method. The synthesized materials were characterized by XRD, SBET, UV-Vis DRS, XRF, TEM, FTIR, and XPS. The modifications led to higher stability in the Anatase phase and surface area of this semiconductor. The addition of F and Pt in TiO2 led to absorption increases in the visible region of the electromagnetic spectrum. A correlation between the new physicochemical properties obtained after TiO2 modification and the photocatalytic performance of this material was observed. The best result in chromium reduction was obtained using Pt-S-TiO2 as the photocatalyst; this material showed a suitable combination of surface area, high UV-Vis absorption, high hydroxylation, and the existence of Pt nanoparticles on the surface, which favors an increased electron-hole pair half-life. Different reaction parameters were also evaluated, which demonstrated that the best photocatalytic performance was obtained under an N2 atmosphere, a light intensity of 120 W/m2, and 2 hours of total reaction time. Likewise, it was noted that an increase in reaction time from 2 to 5 hours, had a detrimental effect on reducing Cr (VI) efficiency.

Biorreducción in vitro de cromo hexavalente utilizando consorcios microbianos

Constant industrial development has increased the chromium use, resulting in chromium discharge into wastewater. The implementation of microbial bioremediation has been proposed as an ecological, efficient and economical alternative for the implementation of microorganisms to reduce chromium to a less toxic form. Our objective was to evaluate the Cr (VI) removal capacity of microbial consortia at different concentrations. Accordingly, an activation and identification of microorganisms from chromium-containing wastewater was carried out. Seven microbial consortia were established and their synergy, individual and consortium growth curves were evaluated. Subsequently, a scaled adaptation of the consortia was carried out with eight concentrations of Cr (VI). Reciprocal regression models and growth curves were used to identify the consortium with the highest removal. Synergy was found in the consortia evaluated; growth curves of consortia showed higher absorbance than individually, with higher absorption in the Candida famata-Serratia sp. Consortium. However, in the scaled adaptation, greater Cr (VI) reduction capacity was demonstrated in Candida tropicalis-Serratia sp. with 79.20% at a concentration of 100 ppm with a total chromium reduction of 31.12%. At the same time, a greater adaptation of the consortia to high concentrations of Cr (VI) was identified. This is the first research to report C. tropicalis-Serratia sp. microbial consortium with a positive interaction and higher metabolic reduction capacity, which will have a positive impact on bioremediation of chromium-containing wastewater.

Investigation of Hexavalent Chromium Reduction in Strong Saline and Acidic Nitro-Phosphate Solutions

Investigation of Hexavalent Chromium Reduction in Strong Saline and Acidic Nitro-Phosphate Solutions

Methods for Electrolyte Treatment and Hexavalent Chromium Reduction in Industrial Electrochemical Machining (ECM)

Electrochemical Machining (ECM) is a metal removal process that operates on the principle of anodic dissolution. ECM has the ability to produce complex shapes in difficult-to-machine alloys with precision and excellent surface finish. However, since most of these alloys contain chromium, one of the major challenges to ECM’s wider utilisation in industry is how to eliminate the resulting hexavalent chromium (Cr+6) from the spent electrolyte. This paper presents methods for controlling the Cr+6 level to within the permitted guidelines for an industry application of ECM, and reducing it to trivalent chromium (Cr+3), to then precipitating it from the electrolyte solution,The workpiece material – Triboloy (Co; Mo; Cr alloy) has hitherto not been machined by ECM and hence no literature exists on how to treat the by-products generated. This research involves experimental analysis of various Cr+6 to Cr+3 chemical reduction methods for ECM of Tribaloy in sodium nitrate electrolyte, using spent electrolyte samples. The reduction in Cr+6 is assessed over time. It was observed that the concentration of Cr+6 decreased within a span of two minutes. Subsequently, the solution pH level was increased by the addition of an alkali to precipitate the Cr+3 ions, which then can be filtered out from the solution. The optimum solution for hexavalent chromium is thus implemented in the industrial electrolyte system for successfully machining the Tribaloy component.

Kinetic studies and bioremediation potential of chromate reductase-characterized Aspergillus flavus from tannery effluent

Chromium is among the major environmental pollutants endangering the health of all living things, including humans. Conventional methods for chromium detoxification are expensive, so bioremediation using fungi as potential agents for the detoxification of chromium is justified. This study aims to investigate chromium-resistant fungi capable of reducing or transforming Cr (VI) to less toxic Cr (III) from tannery effluents. The fungi were isolated from tannery wastewater and identified using 16S rRNA gene sequencing. Chromate reductase was isolated from pure fungal isolate and purified using molecular weight estimation and gel filtration chromatography. Aspergillus flavus, in an interesting turn of events, demonstrated 97% chromate reduction. The chromate reductase from Aspergillus flavus has KM of 0.015 mM and a Vmax of 0.25 mol/min. Furthermore, the enzyme's activity was constant at its peak at pH 7.0 and 50 oC, with a single band displaying a molecular weight of 44 kDa for a pure protein. The data suggest that A. flavus can be a good candidate for the detoxification of Cr (VI) in industrial effluents. The efficiency of which can be attributed to the action of chromate reductase in the A. flavus.

Технологические решения и опыт промышленной переработки жидких хромсодержащих отходов

Analysis of the list of liquid wastes of hazard classes I and II in the Federal Classification Catalog of waste (FCCW) showed that one of the most common wastes is wastewater, waste technological solutions containing chromium ions(III, VI). This type of waste accounts for up to 15% of the total amount of liquid technogenic waste of hazard classes I and II, formed as a result of the activities of electroplating and chemical enterprises. Hexavalent chromium compounds belong to the class of toxic, extremely dangerous substances, the maximum permissible concentration (MPC) in the water of drinking water bodies for chromium (VI) is 0.05 mg/L. A feature of this type of waste is the increased salt background characteristic of electrolytes used in electroplating industries. The article presents experimental data, as well as basic technological solutions for the neutralization of chromium-containing wastewater and waste technological solutions. A technological scheme containing four main stages is proposed: reduction of hexavalent chromium, isolation of trivalent chromium from aqueous solutions, separation of accompanying compounds of heavy and non-ferrous metals, filtration post-treatment of the solution. Experimental studies have shown that, depending on the ionic composition of the medium, the efficiency of isolation of trivalent chromium compounds from aqueous solutions by electroflotation varies from 8 to 95%. The introduction of an anionic flocculant makes it possible to increase the degree of extraction to 99% or more.

Amine-functionalized Schiff base covalent organic frameworks supported PdAuIr nanoparticles as high-performance catalysts for formic acid dehydrogenation and hexavalent chromium reduction

Formic acid (FA) holds significant potential as a liquid hydrogen storage medium. However, it is important to improve the reaction rates and extend the practical applications of FA dehydrogenation and Cr(VI) reduction through the development of efficient heterogeneous catalysts. This study reports the synthesis of a uniformly dispersed PdAuIr nanoparticles (NPs) catalyst loaded with amine groups covalent organic frameworks (COFs). The alloyed NPs demonstrated exceptional effectiveness in FA dehydrogenation rate and Cr(VI) reduction. The initial turnover of frequency (TOF) value for FA dehydrogenation without additives was 9970 h−1 at 298 K, the apparent activation energy (Ea) was 30.3 kJ/mol and the rate constant (k) for Cr(VI) reduction was 0.742 min−1. Additionally, it showcased the ability to undergo recycling up to six times with minimal degradation in performance. The results indicate that its remarkable catalytic performance can be attributed primarily to the favorable mass transfer attributes of the aminated COFs supports, the strong metal-support interaction (SMSI), and the synergistic effects among the metals. This study offers a novel perspective on the advancement of efficient and durable heterogeneous catalysts with diverse capabilities, thereby making significant contributions to the fields of energy and environmental preservation.

Synthesis of cobalt doped nickel titanate nanomaterials for enhanced photocatalytic reduction of chromium

A series of cobalt doped nickel titanate nanomaterials where cobalt % is varied from 1 to 10% have been successfully synthesized by solvothermal method followed by calcination at 600 °C. Synthesized materials are characterized by XRD, FE-SEM, HR-TEM, BET surface area, DRS UV-Vis-NIR, XPS and PL spectroscopy. XRD and HR-TEM confirm the existence of NiTiO3 ilmenite structure with crystallite size in the range of 20–30 nm. HR-TEM of cobalt doped NiTiO3 shows the presence of tiny single atom cobalt metal sitting on NiTiO3, surface which induces the surface plasmon resonance effect. XPS of the doped NiTiO3 exhibits Ti3+ formation accompanied with oxygen vacancies resulting in the extended light absorption in the Vis-NIR region. The photocatalytic efficiency is studied monitoring the photoreduction of carcinogenic Cr (VI) under visible light. 3% cobalt doped NiTiO3 achieves 100% reduction of 30 ppm Cr (VI) solution within 60 min whereas pristine NiTiO3 shows only 50% efficiency under identical conditions. The trapping experiment shows the direct transfer of photogenerated electrons for the reduction of Cr (VI) following a first order kinetics. The two-fold enhanced activity of cobalt doped NiTiO3 is due to the collective effect of oxygen vacancies, efficient Vis-NIR absorption and surface plasmon resonance effect.

Facile green synthesis of Ni/NiO/MoO3 nanocomposite for Photocatalytic, chromium (VI) Reduction, electrochemical dopamine (DA) and humidity sensor applications

Many researchers concentrated their efforts on chemical method for the synthesis of metal oxide nanocomposite (NCs). This article focused on developing a rapid method to prepare Ni/NiO/MoO3 NCs using leaf powder of Butea monosperma as a novel green fuel. Synthesised NCs were characterised using XRD, FT-IR, UV–Visible, Photoluminescence spectroscopy, SEM- EDAX, and TEM analysis. XRD pattern prove the orthodromic structured MoO3 nanoparticles (NPs), rhombohedral structure of Ni/NiO NCs and observed the average crystallite size of 25 nm. The band gap of Ni/NiO/MoO3 NCs was found to be 2.9 eV and TEM analysis revealed irregularly shaped morphologies. Results of photocatalytic dye-degradation of methylene blue dye under various conditions proven the good photocatalytic activity. Additionally, Ni/NiO/MoO3 NCs shows 60 % toxic chromium (VI) reduction. Ni/NiO/MoO3 NCs were successfully employed for the electrochemical detection of dopamine, showcasing good sensing performance. It is also an ideal material for humidity sensor with sensitivity of 4.8 MΩ/%RH and limit of detection of 5 % RH. All the above results indicate the diverse application of the Ni/NiO/MoO3 NCs.

Reduction of Chromate via Biotic and Abiotic Pathways in the Presence of Three Co-contaminating Electron Acceptors.

Bioreduction of Cr(VI) to Cr(III) is a promising technology for removing Cr(VI), but Cr(VI) reduction alone cannot support microbial growth. This study investigated the reduction of Cr(VI) in the presence of three electron acceptors that typically coexist with Cr(VI): NO3-, SO42-, and Fe(III). All three systems could reduce Cr(VI) to Cr(III), but the fate of Cr, its impacts on reduction of the other acceptors, and its impact on the microbial community differed. Although Cr(VI) was continuously removed in the NO3--reduction systems, batch tests showed that denitrification was inhibited primarily through impeding nitrite reduction. The SO42- and Fe(III) reduction systems reduced Cr(VI) using a combination of biotic and abiotic processes. Across all three systems, the abundance of genera capable of reducing Cr(VI) increased following the introduction of Cr(VI). Conversely, the abundance of genera that cannot reduce or resist Cr(VI) decreased, leading to restructuring of the microbial community. Furthermore, the abundance of sulfide oxidizers and Fe(II) oxidizers substantially increased after the introduction of chromate. This study provides fundamental knowledge about how Cr(VI) bioreduction interacts with bioreductions of three other co-contaminating electron acceptors.

Engineering extracellular electron transfer to promote simultaneous brewing wastewater treatment and chromium reduction

Microbial fuel cell (MFC) technology has been developed for wastewater treatment in the anodic chamber, and heavy metal reduction in the cathodic chamber. However, the limited extracellular electron transfer (EET) rate of exoelectrogens remained a constraint for practical applications of MFCs. Here, a MFC system that used the electricity derived from anodic wastewater treatment to drive cathodic Cr6+ reduction was developed, which enabled an energy self-sustained approach to efficiently address Cr6+ contamination. This MFC system was achieved by screening exoelectrogens with a superior EET rate, promoting the exoelectrogenic EET rate, and constructing a conductive bio-anode. Firstly, Shewanella algae-L3 was screened from brewing wastewater acclimatized sludge, which generated power density of 566.83 mW m−2. Secondly, to facilitate EET rate, flavin synthesis gene operon ribADEHC was overexpressed in engineered S. algae-L3F to increase flavins biosynthesis, which promoted the power density to 1233.21 mW m−2. Thirdly, to facilitate interface electron transfer, carbon nanotube (CNT) was employed to construct a S. algae-L3F-CNT bio-anode, which further enhanced power density to 3112.98 mW m−2. Lastly, S. algae-L3F-CNT bio-anode was used to harvest electrical energy from brewing wastewater to drive cathodic Cr6+ reduction in MFC, realizing 71.43% anodic COD removal and 98.14% cathodic Cr6+ reduction. This study demonstrated that enhanced exoelectrogenic EET could facilitate cathodic Cr6+ reduction in MFC.

Forming a chromium-based interstrand DNA crosslink: Implications for carcinogenicity

The reduction of the carcinogen chromate has been proposed to lead to three Cr(III)-containing DNA lesions: binary adducts (Cr(III) and DNA), interstrand crosslinks, and ternary adducts (Cr(III) linking DNA to a small molecule or protein). Although the structures of binary adducts have recently been elucidated, the structures of interstrand crosslinks and ternary adducts are not known. Analysis of Cr(III) binding to an oligonucleotide duplex containing a 5’-CG site allows elucidation of the structure of an oxide- or hydroxide-bridged binuclear Cr(III) assembly bridging the two strands of DNA. One Cr(III) is directly coordinated by the N-7 atom of a guanine residue, and the complex straddles the helix to form a hydrogen bond between another guanine residue and a Cr(III)-bound aquo ligand. No involvement of the phosphate backbone was observed. The properties and stability of this Cr–O(H)–Cr-bridged complex differ significantly from those reported for Cr-induced interstrand crosslinks, suggesting that interstrand crosslinks resulting from chromate reduction may be organic in nature.