Reduction Of Chromium Research Articles

Stability Mechanism of Hexavalent Chromium Reduction by Nano-zerovalent Iron Under Different Environments

Stability Mechanism of Hexavalent Chromium Reduction by Nano-zerovalent Iron Under Different Environments

Ferrous disulfide and iron nitride sites on hydrochar to enhance synergistic adsorption and reduction of hexavalent chromium

In this study, a novel hydrochar containing ferrous disulfide (FeS2) and iron nitride (FeN) was prepared via a one-pot hydrothermal method to enhance the synergistic adsorption and reduction of hexavalent chromium (Cr(VI)). This material (Fe3-SNHC) exhibited a Cr(VI) removal capacity of 431.3 mg·g−1 and high tolerance to coexisting anions at pH 2. Adsorption occurred via monolayer chemisorption. Variation in material structure and density functional theory calculations proved that multiple active sites formed by interactions between heteroatoms improved the chemical inertness of hydrochar. FeN and FeS2 with two electron-donating groups had strong reducing ability to facilitate the conversion of Cr(VI) to trivalent chromium. It was concluded that next to electrostatic adsorption and complexation, synergistic reduction among multiple active sites were the dominant mechanisms involved in the removal Cr(VI). This study shows that Fe3-SNHC is a promising and environment-friendly material for Cr(VI) to remove it from wastewater.

Isolation and Molecular Characterization of Chromium Reducing Haloalkaliphilic Bacteria from Alkaline Lonar Lake

Heavy metals generated mainly through many anthropogenic processes, and some natural processes have been a great environmental challenge and continued to be the concern of many researchers and environmental scientists. This is mainly due to their highest toxicity even at a minimum concentration as they are nonbiodegradable and can persist in the aquatic and terrestrial environments for long periods. Chromium ions, especially hexavalent ions (Cr(VI)) generated through the different industrial process such as tanneries, metallurgical, petroleum, refractory, oil well drilling, electroplating, mining, textile, pulp and paper industries, are among toxic heavy metal ions, which pose toxic effects to human, plants, microorganisms, and aquatic lives.The present study deals with isolation and molecular characterization of bacteria from alkaline lonar crater, having ability to survive and remediate the chromium. In the present study, 26 bacterial isolates were obtained from twelve samples of water, matt and sediment collected from Lonar Lake. Among these isolates, a well characterized isolate ASJ 21 was subjected for molecular characterization on the basis of 16S rRNA gene sequencing. On the basis of 16S rRNA gene sequencing, isolate ASJ 21 was identified as Lysinibacillus mangiferihumi. The chromium remediation ability of Lysinibacillus mangiferihumi was studied spectrophotometrically by using Di-phenyl carbazide assay and the study revealed that the isolate Lysinibacillus mangiferihumi reduced 88% of chromium and rate reduction of chromium was found to be 0.916 µg/mL after 96h of incubation period, showing the ability of microorganisms to tolerate the chromium concentration at alkaline pH and potential to remediate and detoxify hexavalent Chromium (VI) to trivalent Chromium (III) as well.

Optimizing electronic states of Pd/WO3 nanofibers for enhanced catalytic reduction of hexavalent chromium with formic acid

Through theoretical calculations, we show that integrating Pd with WO3 nanomaterials can trigger the interfacial electron transfer from Pd to WO3, thus upshifting the d-band center (εd) of Pd to optimize toxic hexavalent chromium (Cr(VI)) reduction. The elevated εd can derive stronger chemisorption capability toward crucial formic acid molecules, notably lowering the thermodynamic energy barrier and speeding up the kinetics process. In order to realize this concept, we synthesized unique Pd/WO3 nanofibers by loading Pd nanoparticles onto electrospun WO3 nanofibers through an in situ photodeposition technique. Extensive structural, morphological, and X-ray photoelectron spectrometer (XPS) characterizations confirm the successful formation of the above nanofibers. As anticipated, the as-designed Pd/WO3 nanofibers exhibit enhanced catalytic performance in the Cr(VI) reduction with a high turnover frequency (TOF) value of 62.12 min−1, surpassing a series of reported Pd-based catalysts. Such nanofibrous WO3-induced electronic modification of Pd with a high specific area leads to catalytic enhancement, providing a novel model for catalyst design.

Influence of red yeast rice extract fermentation on fucoidan profiles, inorganic elements and flavor properties of the kelp Saccharina japonica

This study evaluated the efficacy of fermentation on Saccharina japonica (SJ). Changes of fucoidan, heavy metals, iodine and flavor profiles of fermented SJ (FSJ) were determined. Results showed that fermentation decreased the yield and molecular weight of fucoidan and increased the levels of phenolic compounds. The antioxidant activity of fucoidan also increased. It is notable that the fermentation process resulted in a significant reduction of iodine, lead, chromium and cadmium. The flavor properties of SJ during the fermentation process were evaluated. A total of 44 volatile compounds were identified which were correlated with the odor attributes of FSJ. FSJ fermented for five days (FSJ-5) showed the highest overall score for desirable aroma properties dominated by “fruity” and “sweet” odors. The results proved that fermentation is a promising methodology to improve the bioactivity, safety and flavor properties of SJ.

Efficient Photocatalytic Reduction of Hexavalent Chromium by BiVO4-Decorated MXene Photocatalysts and Their Charge Carrier Dynamics.

The synergistically MXene (Ti3C2Tx) co-catalyst-decorated BiVO4-based heterostructured photocatalysts have been synthesized by a hydrothermal approach with varied loading concentrations of MXene (Ti3C2Tx) to drive the hexavalent chromium reduction efficiently. The formation of the heterostructured photocatalyst was confirmed by the appearance of X-ray diffraction (XRD) peaks corresponding to the monoclinic BiVO4 phase and MXene (Ti3C2Tx) and also the antisymmetric (834 cm-1) and symmetric stretching (715 cm-1) of tetrahedral VO4 and D (1330 cm-1) and G (1570 cm-1) bands corresponding to MXene (Ti3C2Tx) in the Raman spectrum. The worm-like structures of BiVO4 nanocrystals grew onto the lamellar sheets of MXene (Ti3C2Tx), as shown by field emission scanning electron microscopy (FESEM), and has an increased surface area of 15.62 m2g-1 in the case of BVO-20-TC. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of V5+ and Ti3+states, and the uniform distribution of BiVO4 nanocrystals over lamellar sheets of MXene (Ti3C2Tx) is evident from energy-dispersive X-ray (EDX) analysis. The ultraviolet-diffuse reflectance spectroscopy (UV-DRS) spectra suggest a decrease in the band gap energy of BVO-20-TC to 2.335 eV, promoting a higher degree of visible light harvesting. Upon optimization, by varying the pH, the amount of the photocatalyst, and the concentration of Cr(IV), BVO-20-TC exhibits the highest photocatalytic efficiency (96.39%) while using a Cr(VI) concentration of 10 ppm at pH 2 and 15 mg of the photocatalyst, and the photoreduction of Cr(VI) to Cr(III) follows the pseudo-first-order reaction. The decrease in the PL intensity in BVO-20-TC reveals a faster transfer of electrons from MXene (Ti3C2Tx) to BiVO4. Further, the higher degree of band bending at the BiVO4/MXene (Ti3C2Tx) heterojunction, revealed from the Mott-Schottky analysis, facilitates efficient charge transfer and eventually faster and efficient photoreduction of Cr(VI) to Cr(III). The reusability and stability test undertaken for BVO-20-TC reveals that even after five cycles, the Cr (VI) photoreduction efficacy is retained. This work provides insights into photoreduction of Cr (VI) by using such heterostructures.

THE ROLE OF SULFUR-CONTAINING AMINO ACIDS IN THE PREVENTIVE NUTRITION OF WORKERS IN CONTACT WITH CHROMIUM

In the world, a large number of workers are exposed to fumes, mists and dusts containing Chromium and its compounds. One of the ways to prevent chromium intoxication is the enrichment of food rations with substances that have antioxidant and complexing ability. Attention is focused on the recommendations on the use of sulfur-containing amino acids and sulfur-rich proteins in the composition of food products for the prevention of intoxication in workers who come into contact with chromium in production. The mechanism of reduction of hexavalent chromium compounds by cysteine was considered. It has been shown that the process of reduction of chromates with cysteine is accompanied by the oxidation of cysteine to cystine and subsequent complexation with trivalent chromium. The structure of chromium III cystinate was confirmed by IR and electron spectroscopy and elemental analysis. It has been established that in the formed chelate complex [Cr(SNO2C3H6)6Cr], chromium (III) has a bond with cystine through the amino and carboxyl groups, LD50 is 2100 mg/kg and is less toxic than inorganic chromium (III) salts. The article analyzes protein raw materials rich in cysteine, which can be recommended to satisfy the daily requirement of cysteine, or to reduce chromium intoxication of workers working in a work area with a high content of chromium salts.

Influencing factors and mechanism of Cr(VI) reduction by facultative anaerobic Exiguobacterium sp. PY14.

Microbial reduction is an effective way to deal with hexavalent chromium [Cr(VI)] contamination in the environment, which can significantly mitigate the biotoxicity and migration of this pollutant. The present study investigated the influence of environmental factors on aqueous Cr(VI) removal by a newly isolated facultative anaerobic bacterium, Exiguobacterium sp. PY14, and revealed the reduction mechanism. This strain with a minimum inhibitory concentration of 400 mg/L showed the strongest Cr(VI) removal capacity at pH 8.0 because of its basophilic nature, which was obviously depressed by increasing the Cr(VI) initial concentration under both aerobic and anaerobic conditions. In contrast, the removal rate constant for 50 mg/L of Cr(VI) under anaerobic conditions (1.82 × 10-2 h-1) was 3.3 times that under aerobic conditions. The co-existence of Fe(III) and Cu(II) significantly promoted the removal of Cr(VI), while Ag(I), Pb(II), Zn(II), and Cd(II) inhibited it. Electron-shuttling organics such as riboflavin, humic acid, and anthraquinone-2,6-disulfonate promoted the Cr(VI) removal to varying degrees, and the enhancement was more significant under anaerobic conditions. The removal of aqueous Cr(VI) by strain PY14 was demonstrated to be due to cytoplasmic rather than extracellular reduction by analyzing the contributions of different cell components, and the end products existed in the aqueous solution in the form of organo-Cr(III) complexes. Several possible genes involved in Cr(VI) metabolism, including chrR and chrA that encode well-known Chr family proteins responsible for chromate reduction and transport, respectively, were identified in the genome of PY14, which further clarified the Cr(VI) reduction pathway of this strain. The research progress in the influence of crucial environmental factors and biological reduction mechanisms will help promote the potential application of Exiguobacterium sp. PY14 with high adaptability to environmental stress in Cr(VI) removal in the actual environment.

Chemical bonding and facet modulating of p-n heterojunction enable vectorial charge transfer for enhanced photocatalysis

Heterojunctions have been proved to be the promising photocatalysts for hazardous contaminants removal, but the inferior interfacial contact, low carrier mobility and random carrier diffusion seriously hamper the photoactivity improvement of the conventional heterojunctions. Herein, SO chemically bonded p-n oriented heterostructure is fabricated via selectively anchoring of p-type Ag2S nanoparticles on the lateral facet of n-type Bi4TaO8Cl nanosheet. Such a p-n heterojunction engineering on specific facet of Bi4TaO8Cl semiconductor derives ingenious double internal electric field (IEF), which not only effectively creates the spatially separated oxidation and reduction sites, but also delivers the powerful driving forces for impactful spatial directed photocarrier transfer along the cascade path. Additionally, our experimental and theoretical analyses jointly signify that the interfacial SO bond could serve as an efficient atomic-level interfacial channel, which is conducive to encouraging the vectorial charge separation and migration kinetic. As a result, the Ag2S/Bi4TaO8Cl oriented heterojunction exhibits significantly enhanced visible light driven photocatalytic redox ability for tetracycline oxidation and hexavalent chromium reduction than those of single component and the traditional random/mixed heterojunctions. This study could provide a deeper insight into the synergistic effects of multi-IEF modulation and interfacial chemical bond bridging on optimizing the photogenerated carrier behaviors.

Construction of novel bimetallic Ti/Ce-MOFs for ratiometric fluorescence sensing of trace copper and photocatalytic reduction of chromium (Ⅵ)

A new bimetallic-centered MOFs, NH2-MIL-125(Ti/Ce), was synthesized by partially replacing Ti with Ce. The doping of Ce endowed the MOFs oxidase-like activity and enabled the construction of a ratiometric fluorescence sensing system in combination with o-phenylenediamine (OPD) for detecting trace Cu2+ with a limit of detection of 16 nM and a linear range of 0.02–50 μM. Trace Cu2+ was successfully quantified in real water samples. The doping of Ce also increased the photocatalytic capability of the MOFs by about 2 times, achieving excellent reduction of Cr(Ⅵ) under natural light conditions.

Sulfur-doped Sb4Mo10O31 bimetallic sulfur-oxide catalyst for highly efficient reduction of toxic organic and hexavalent chromium under dark

Sulfur-doped Sb4Mo10O31 bimetallic sulfur-oxide catalyst (labeled as SbMoSO) was synthesized by thermal hydrolysis using different amounts of S precursor CH3CSNH2 (TAA). SbMoSO catalysts for reducing toxic organic pollutants (4-nitrophenol (4-NP)), organic dyes (Methyl orange (MO), Methylene blue (MB), Rhodamine B (RhB)), and heavy metal ions Cr(VI) in water were studied. SbMoSO-2 catalyst showed the best catalytic performance. 10 mg SbMoSO-2 ultimately reduced 100 mL of 10 ppm 4-NP within 10 min in the presence of 5 mg NaBH4, while 100 mL of 50 ppm MO, 20 ppm MB, and 50 ppm RhB solutions were reduced entirely within 10 min, 6 min, and 8 min, respectively. The activity of the used catalyst, which was recovered and dried, was tested again for the sixth time and was still up to 95.3%. SbMoSO also performed good stability and durability for reducing organic pollutants and heavy metal ions. The fact of heterovalent conversion of Mo4+ ↔ Mo6+ is conducive to electron transfer and lowers the electron-hole recombination efficiency. Likewise, the stack nanosheet-like morphology of the catalyst can also provide a larger specific surface area and more active sites to facilitate the reduction reaction. Therefore, this study illustrates that the S incorporation into metallic/bimetallic oxides is a promising approach for designing the tuned electronic structure of metallic/bimetallic sulfur-oxide catalysts with boosted catalytic performance.

Cr(VI) removal and mechanism from simulated polluted groundwater by Klebsiella variicola H12-CMC-FeS@biochar assisted permeable reactive barrier

Permeable reactive barrier(PRB) is an attractive technique for in situ polluted groundwater remediation. Klebsiella variicola H12-Carboxymethylcellulose -FeS@biochar (K.variicola H12-CMC-FeS@biochar) was used as filling medium in PRB to remove chromium contamination from simulated groundwater. The results showed that the chromium removal efficiency was 94 %, which was more effective than k. variicola H12 or biochar respectively and the optimal solid-liquid ratio was 30:1. Ionic strength and initial chromium concentration in groundwater have greater influence on the treatment effect. Scanning electron microscopy(SEM) and fluorescence microscopy showed that biofilm covered on the surface of the material. X-ray Photoelectron Spectroscopy(XPS) indicated that most of hexavalent chromium(Cr(VI)) and trivalent chromium(Cr(III)) were adsorbed by k. variicola H12-CMC-FeS@biochar. Cr(III) originated from the reduction of chromium by K. variicola. Furthermore, quantitative real-time polymerase chain reaction(qPCR) results showed that the expression level of ChrA, ChrB and ChrR genes increased, which contributed to relieve cytotoxicity. These changes improved the resistance of k. variicola H12 to Cr(VI), promoting Cr(VI) reduction. In summary, biofilm adsorption and microbe reduction were the two primary ways to enhance the chromium removal efficiency. It provided a new method for treating in-situ groundwater pollution by PRB technology using biochemical materials as mediums.

Energy-efficient reduction of hexavalent chromium on a rotating packed bed of woven steel screens

This study investigates the rate of hexavalent chromium (Cr6+) reduction by scrap iron using a rotating packed bed of horizontally stacked woven iron screens. The primary focus is on enhancing the diffusion-limited reduction of Cr6+ by taking advantage of the centrifugal force induced by bed rotation and the high turbulence-promoting ability of the screen wires. The results show that the rate of diffusion-controlled reduction of Cr6+ increases with the increase in bed rotational speed, initial concentration of Cr6+, and mesh number. A correlation has been developed to predict the mass transfer coefficient under the studied conditions and serve in designing and scaling up industrial reactors. Additionally, the energy utilization efficiency of the reactor has been assessed as a performance indicator to be used for comparing the performance of the present reactor with other reactors which use different methods of mass transfer enhancement such as pulsation. Under optimum conditions, 99 % of Cr6+ was reduced to Cr3+ within 20 min and the energy consumption was 0.04–0.72 W/kg. The rotating bed with woven steel screens provides a low-cost and effective means of enhancing the rate of Cr6+ reduction, contributing to the development of more sustainable wastewater treatment solutions.

Impacts of fulvic acid and Cr(VI) on metabolism and chromium removal pathways of green microalgae

Green microalgae are highly efficient and cost-effective in the removal of heavy metals from water. However, dissolved organic matter (DOM), such as fulvic acid (FA), can impact their growth and heavy metal accumulation. Nonetheless, the specific mechanisms underlying these effects remain poorly understood. This study investigated the effects of different FA concentrations on the development, metabolism, and chromium (Cr) enrichment of Chlorella vulgaris, a standard green microalga. The findings revealed that low FA concentrations alleviated Cr-induced stress, stimulated microalgal growth, and enhanced energy conservation by suppressing chlorophyll synthesis. The highest chromium enrichment and reduction rates of 38.73% and 57.95% were observed when FA concentration reached 20 mg/L of total organic carbon (TOC). Furthermore, FA facilitated chromium removal by C. vulgaris through extracellular adsorption. Examination of microalgal cell surface functional groups and ultrastructure indicated that FA increased adsorption site electrons by promoting extracellular polymeric substance (EPS) secretion and enhancing the oxygen content of acidic functional groups. As a result, FA contributed to elevated enrichment and reduction rates of Cr in microalgal cells. These findings provide a theoretical basis for the prevention and control of heavy metal pollution in water environments.

Synthesis of highly efficient novel two-step spatial 2D photocatalyst material WS2/ZnIn2S4 for degradation/reduction of various toxic pollutants

In this article, we report the synthesis, characterization of novel biofriendly 2D/2D heterostructure WS2/ZnIn2S4 material in which 2D WS2 nanosheets are uniformly distributed spatially onto the spherically arranged 2D leaves of ZnIn2S4. We then studied the in-depth photocatalytic degradation activity of this novel nanocomposite and its pristine component materials on cationic dye: malachite green, anionic dye: congo red and reduction of heavy metal: chromium(VI) and the degradation efficiency of composite material was also tested on rhodamine-B, methylene blue, methyl orange dyes and acetaminophen/paracetamol drug. Form factor, structure factor and shape factor analysis has been carried out using X-ray diffractometry (XRD). Bond vibrations, functional groups and phonon vibration mode analysis has been done based on Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. Morphological and compositional analysis has been done using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDAX) and X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM). Surface area and pore size/distribution was characterized using Brunauer–Emmett–Teller (BET) method and Barrett-Joyner-Halenda Model. Degradation pathways and intermediate products are proposed using the high-performance liquid chromatography (HPLC). Photocatalytic activity of the nanocomposite WS2/ZnIn2S4 is compared with pristine ZnIn2S4 and pristine WS2, which shows more than 50% enhancement in both efficiency and rate of degradation/reduction for all the pollutants. A scavenger study was carried out to get insight of primary and secondary reactive oxygen species (ROS) taking part in degradation. Exciton lifetime, surface charge and stability, and flat band positions were studied based on time-correlated single photon counting (TCSPC) also known as time-resolved photoluminescence (TRPL), zeta potential, and Mott-Schottky respectively. Rate kinetics study was performed to analyze the physical and chemical behaviour of the nanocomposite with pollutants in consideration. Results show ∼100%, ∼90%, and ∼95% degradation efficiency by the heterostructure for malachite green (MG), congo red (CR), and reduction of heavy metal chromium (Cr(VI)) respectively within 5 min, which is a huge improvement as compared to pristine WS2 and pristine ZnIn2S4, both of which show the efficiencies of only ∼25% to∼75% in all the cases.

Cr(VI) Reduction and Fe(II) Regeneration by Penicillium oxalicum SL2-Enhanced Nanoscale Zero-Valent Iron.

Nanoscale zero-valent iron (nZVI) faces significant challenges in Cr(VI) remediation through aggregation and passivation. This study identified a Cr(VI)-resistant filamentous fungus (Penicillium oxalicum SL2) for nZVI activation and elucidated the synergistic mechanism in chromium remediation. P. oxalicum SL2 and nZVI synergistically and effectively removed Cr(VI), mainly by extracellular nonenzymatic reduction (89.1%). P. oxalicum SL2 exhibited marked iron precipitate solubilization and Fe(II) regeneration capabilities. The existence of the Fe(II)-Cr(V)-oxalate complex (HCrFeC4O9) indicated that in addition to directly reducing Cr(VI), iron ions generated by nZVI stimulated Cr(VI) reduction by organic acids secreted by P. oxalicum SL2. RNA sequencing and bioinformatics analysis revealed that P. oxalicum SL2 inhibited phosphate transport channels to suppress Cr(VI) transport, facilitated iron and siderophore transport to store Fe, activated the glyoxylate cycle to survive harsh environments, and enhanced organic acid and riboflavin secretion to reduce Cr(VI). Cr(VI) exposure also stimulated the antioxidative system, promoting catalase activity and maintaining the intracellular thiol/disulfide balance. Cr(VI)/Fe(III) reductases played crucial roles in the intracellular reduction of chromium and iron, while nZVI decreased cellular oxidative stress and alleviated Cr(VI) toxicity to P. oxalicum SL2. Overall, the P. oxalicum SL2-nZVI synergistic system is a promising approach for regenerating Fe(II) while reducing Cr(VI).

Robust, magnetic, and effective Pd-based nanocatalyst for reduction of toxic hexavalent chromium and nitrophenols

A serial of magnetic and robust nanocatalysts of Pd nanoparticles with a mean size of 4 nm evenly supported on N-doped porous carbon with Co wrapped (Co-NC) were fabricated by a facile route at room temperature. Among these, 18 %Pd/Co-NC has regular morphology and exhibits the highest activity towards reduction of Cr (VI) with HCOOH and nitrophenols with NaBH4 in aqueous solution. What is more, 18 %Pd/Co-NC has a higher catalytic activity than that of 20 % commercial Pd/C towards the reduction of Cr(VI). The excellent performance may be due to the Pd nanoparticles of small size, uniform dispersion on Co-NC, large BET surface area, abundant active sites, nitrogen doping, and synergetic effect between Pd and the support of Co-NC. The introduction of Co nanoparticles to the support not only provides magnetism but also may prevent the oxidation of Pd, thus facilitating the separation of the catalyst from the solution and providing more active Pd species to catalyze the reduction reaction. The catalyst can be separated easily by an external magnet and remain the activity without obvious decline after the recycling experiment, indicating the catalyst has a good stability in acidic or basic solution. What is more, K2Cr2O7 can be catalytically reduced by Pd/Co-NC in an industrial environment, confirming the catalyst has a potential application in the remediation of industrial wastewater.

Feasibility of using Cr-containing vitrification product as cement admixture: Structural evolution and chromium immobilization

With China already committing to bring carbon dioxide emissions to a peak before 2030, reducing the amount of used cement is an economical and effective measure. In this study, chromium-containing vitrification products were used as a cement admixture to achieve chromium reduction and immobilization. This study presents the effect of MgO/B2O3/Cr2O3 on the relationship between the network structure and chemical resistance of a Cr-containing glass matrix. The acid/alkali resistance of the glass specimens improved with an increase in Cr2O3 content under the same matrix composition. With the replacement of CaO by MgO, the chemical resistance of boron-free glass specimens improved, while that of Mg/B-containing glass specimens significantly decreased. The behaviors of the glass matrix in chemical environments affected the hydration and chromium immobilization of cement clinkers. In paste specimens, the pozzolanic reaction of the glass powder enhanced the densification of specimens. The mechanical strength was attributed to the filling effect of pozzolanic gels and undissolved glass powder in the mortar samples. B-containing glass powder negatively affected the mechanical strength and chromium immobilization of cement samples, while an appropriate amount of MgO and Cr2O3 was beneficial to the physical and chemical properties of the material. Therefore, chromium-containing waste glass can be effectively used to produce eco-friendly building materials.

Efficient reduction of hexavalent chromium over functionalized-graphene-supported Pd nanoparticles

Efficient reduction of hexavalent chromium over functionalized-graphene-supported Pd nanoparticles

Insights into the proton-enhanced mechanism of hexavalent chromium removal by amine polymers in strong acid wastewater: Reduction of hexavalent chromium and sequestration of trivalent chromium

Adsorption is a green technology of treating heavy metal-contaminated strong acid wastewaters for the recycling of heavy metal and reuse of strong acid. Herein, three amine polymers (APs) with different alkalinities and electron donating abilities were prepared to investigate the adsorption-reduction processes of Cr(VI). It was found that the removal of Cr(VI) was controlled by the concentration of –NRH+ on the surface of APs at pH > 2, which relies on the alkalinity of APs. However, the high concentration of NRH+ significantly facilitated the adsorption of Cr(VI) on the surface of APs and accelerated the mass transfer between Cr(VI) and APs at strong acid environment (pH ≤ 2). More importantly, the reduction of Cr(VI) was enhanced at pH ≤ 2, due to the high reduction potential of Cr(VI) (E ≥ 0.437). The ratio of reduction to adsorption (α) of Cr(VI) was above 0.70, and the proportion of Cr(III) bonding on Ph-AP excessed 67.6 %. Finally, a proton-enhanced mechanism of Cr(VI) removal was verified by analyzing FTIR and XPS spectra as well as constructing DFT model. This study provides a theoretical basis for the removal of Cr(VI) in the strong acid wastewater.