Carcinogenic Hexavalent Chromium Research Articles

The Influence of Water Concentration on High-Temperature Reactive Evaporation and Condensation of Cr in 800°C Air

Deleterious reactive evaporation of chromium from stainless steels commonly used in solid oxide electrochemical systems is well-documented; however, interactions between Cr vapor species and surrounding interfaces during complex and dynamic system exposures is poorly understood. Understanding the interactions between Cr vapor species and downstream components during operation is critical for improving system performance and safeguarding environmental, health and safety, as many condensed Cr compounds contain toxic and carcinogenic hexavalent chromium Cr(VI). Furthermore, the interactions between volatilized Cr species and surrounding interfaces are dependent upon dynamic chemical environments. The objective of this study is to systematically investigate and report on condensation pathways of Cr vapors within representative system environments with variable water concentrations. To accomplish this objective, an experimental platform was designed to generate Cr vapor species from the reactive evaporation of chromia (Cr2O3) powder with high-temperature (>1100 K) air/H2O mixtures, and expose downstream ceramic insulation materials (e.g., aluminosilicate fibers) at reduced temperatures (<600 K). Insulation material chemical compositions investigated include pure silica (SiO2) and alumina (Al2O3) to combinations thereof with and without inclusions of alkaline earth metals (e.g., Ca, Mg, Sr). Materials are studied as a function of exposure conditions using complementary materials characterization tools such as SEM-EDX, XPS, and diphenyl carbazide reactions to assess Cr(VI) concentrations. Reactive evaporation of Cr from chromia occurs in the presence of oxygen and/or water vapor to form various Cr-containing vapor species. Thermodynamic data reveals an equilibrium partial pressure increase of several orders of magnitude at elevated (>500 K) temperatures for all Cr vapor species. In the presence of water vapor, the partial pressure of Cr oxyhydroxide (CrO2(OH)2(g)) is greater by many several orders of magnitude and becomes the dominant species up to ~1500 K. The research objective is to explore effects of water vapor in air on Cr condensation and speciation on different ceramic insulation materials. The experimental setup thus far has exposed aluminosilicate fibers to volatilized Cr species from Cr oxide powder at 1100 K for 150 hours under varying water vapor conditions: 0 vol%(dry), 3 vol%, and 10 vol% H2O. Preliminary results show an increase in Cr(VI) formation on fibers exposed to volatile Cr species as water vapor content increases. See Figure 1 for an overview of the experimental concept, Cr(VI) test kit, and preliminary results for dependency on water vapor. Analyses of these results will be presented and discussed in context of potential implications for SOFC/SOEC systems. Figure 1

Hexavalent chromium [Cr(VI)]-induced ribosomal DNA copy number variation and DNA damage responses and their associations with nucleolar protein HRAS in humans and cells

The carcinogenicity of hexavalent chromium [Cr(VI)] and its compounds has been widely recognized, yet the mechanism of genetic damage is still not fully understood. The ribosomal DNA (rDNA) copy number is recently considered a potential marker of cancer-associated stress. To investigate the roles of rDNA copy number variation (CNV) in DNA damage responses (DDRs) induced by Cr(VI) and the potential mechanism from nucleolar protein HRAS, a cross-sectional study in Cr(Ⅵ)-exposed workers and an in vitro experiment using HeLa cells were conducted. Our results showed increased levels of rDNA CNV, DDRs, and HRAS expression in Cr(VI)-exposed workers. Generalized linear regression analyses showed that Cr(VI) exposure was significantly positively associated with increased levels of rDNA CNV, DDRs, and HRAS expression in Cr(VI)-exposed workers. Moreover, there were pairwise associations between rDNA CNV, DDRs, and HRAS levels. Mediation analyses found that rDNA CNV significantly mediated the association between Cr(VI) exposure and DDRs. The in vitro experiments further confirmed that Cr(VI) treatment induced increased levels of rDNA CNV, DDRs, and HRAS expression in HeLa cells. Cr(VI)-induced rDNA CNV, ATM activation, and apoptosis damage were then strongly enhanced by HRAS depletion with siRNA in vitro, suggesting the important role of HRAS in CNV and DDRs caused by Cr(VI). The combined results of the human and cell line studies indicated that Cr(VI) exposure might enhance rDNA CNV by regulation of HRAS expression, which leads to Cr(VI)-induced genetic damage.

All-solid-state MoS2/WO3 photoelectrodes as high-efficiency catalysts for reductive/sorptive/recycling of hexavalent chromium

Photoelectrocatalysis (PEC) is an effective approach to eliminate carcinogen hexavalent chromium (Cr(VI)) in wastewater, in which high-performance catalysts are crucial. Herein, controlled growth of thin molybdenum disulphide (MoS2) nanosheets on self-supported tungsten trioxide (WO3) created an all-solid-state MoS2/WO3 heterojunction serving as electrode and catalyst simultaneously for removing Cr(VI). Countless small and thin MoS2 nanoflakes build in a huge and porous interface for harvesting lights and adsorbing chromium species. And the highly conductive WO3 substrate facilitates the transfer of those photoexcited-electron and therefore suppresses the recombination between electrons and holes. Furthermore, assisted by bias potential, electron streams from external circuit render an electron-rich interface at the MoS2/WO3 cathode, accelerating the Cr(VI) reduction by PEC. At −1.2 V, the PEC reduction efficiency of Cr(VI) reaches 100% within 30 min, surpassing the pristine WO3 by 2.7 times. The generated Cr(III) ions can be immobilized on the porous MoS2/WO3 cathode through electrostatic attraction, enabling removal of total chromium. More importantly, the Cr(III) anchored to the catalyst can be effortlessly recovered by eluting with clean water, which also refreshes the MoS2/WO3 cathode. This study provides a new approach to fabricating photoelectrodes for sustainable PEC reduction and treatment of Cr(VI) containing wastewater.

Selective picomolar detection of carcinogenic chromium ions using silver nanoparticles capped via biomolecules from flowers of Plumeria obtusa

Biocompatible silver nanoparticles (Ag-NPs) were synthesized by employing an eco-friendly approach of green chemistry with flower extract of Plumeria obtusa. Flavonoids are the main phytochemical constituents found in flowers of Plumeria obtusa, out of which rutin is the most abundant and acts as a controller. The synthesized Ag-NPs were studied using UV–vis spectroscopy, X-ray diffractometry (XRD), transmission electron microscopy (TEM), fourier transform infrared (FTIR) analysis, zeta potential and dynamic light scattering (DLS) analysis. The Ag-NPs showed their characteristic surface plasmon resonance (SPR) peak at around 430 nm. This peak depended on various physicochemical parameters such as extract concentration, reaction time, temperature and pH. The formation of the FCC lattice of Ag-NPs with an average particle size of 13 ± 1 nm was confirmed. The zeta potential of −22.7 mV of Ag-NPs indicated their stability in colloidal suspensions. The biosynthesized Ag-NPs were used for developing a sensing method for carcinogenic hexavalent chromium ions (Cr6+) in various aqueous mediums that can be utilized in the diagnosis of any contamination in drinking water or food by cancer-causing Cr6+ ions with a very efficient limit of detection (LoD) of 95 ± 2 pM (recorded at pH ∼ 7.2), which is the lowest reported value for green synthesized nanomaterials and also overcome limitations such as a lack of sensitivity, accuracy, low detection limit and proper explanation. In addition, the antibacterial action of Ag-NPs was investigated against a gram-positive bacterium, Staphylococcus aureus. Thus, based on the results, the Ag-NPs synthesized in this study can be resorted to applications like biosensing and biomedicine.

Inhibition of Hexavalent Chromium Release from Drinking Water Distribution Systems: Effects of Water Chemistry-Based Corrosion Control Strategies.

In drinking water distribution systems, the oxidation of zerovalent chromium, Cr(0), in iron corrosion scales by chlorine residual disinfectant is the dominant reaction to form carcinogenic hexavalent chromium, Cr(VI). This study investigates inhibitive corrosion control strategies through adjustments of chemical water parameters (i.e., pH, silicate, phosphate, calcium, and alkalinity) on Cr(VI) formation through oxidation of Cr(0)(s) by free chlorine under drinking water conditions. The results show that an increase in pH, silicate, alkalinity, and calcium suppressed Cr(VI) formation that was mainly attributed to in situ surface precipitation of new Cr(III) solids on the surface of Cr(0)(s), including Cr(OH)3(s), Cr2(SiO3)3(s), CrPO4(s), Cr2(CO3)3(s), and Cr10Ca(CO3)16(s). The Cr(III) surface precipitates were much less reactive with chlorine than Cr(0)(s) and suppressed the Cr redox reactivity. The concentration of surface Cr(III) solids was inversely correlated with the rate constant of Cr(VI) formation. Adding phosphate either promoted or inhibited the Cr(VI) formation, depending on the phosphate concentration. This study provides fundamental insight into the Cr(VI) formation mechanisms via Cr(0) oxidation by chlorine and the importance of surface precipitation of Cr(III) solids with different corrosion control strategies and suggests that increasing the pH/alkalinity and addition of phosphate or silicate can be effective control strategies to minimize Cr(VI) formation.

Covering extracellular polymeric substances to enhance the reactivity of sulfidated nanoscale zerovalent iron toward Cr(VI) removal

For effective removal and recovery of carcinogenic hexavalent chromium (Cr(VI)), we synthesized sulfidated nanoscale zerovalent iron@extracellular polymeric substances (SnZVI@EPS) with the aim of combining the respective advantages of EPS and SnZVI. EPS was introduced during the synthesis of SnZVI and successfully covered SnZVI, resulting in a larger specific surface area and better environmental friendliness of SnZVI@EPS over that of SnZVI (108.6362 vs. 10.9331 m2/g, 4.04-log vs. 6.42-log Escherichia coli reduction). SnZVI@EPS was more effective than SnZVI in removing Cr(VI) (64.90 mg/g vs. 43.76 mg/g), also under anaerobic, aerobic, wide pH, and high concentration of coexisting ions. The total Cr removal by SnZVI@EPS was higher than that of SnZVI (64.64 mg/g vs. 41.83 mg/g). The pseudo-second order model described well the adsorption process of SnZVI and SnZVI@EPS with equilibrium removal capacity of 44.21 and 66.18 mg/g for 20 mg/L Cr(VI) removal. Chemisorption and monolayer-based adsorption were dominated during Cr(VI) adsorption by SnZVI@EPS. The covered EPS provided better Cr(VI) removal and Cr(III) precipitation of SnZVI@EPS than SnZVI through the faster electron transfer, stronger solid–liquid reactions between SnZVI@EPS and Cr(VI), and additional binding sites for Cr(III)-Fe(III) coprecipitation. This work proved that environmental friendliness and efficient Cr(VI) removal and recovery of SnZVI can be improved by EPS modification.

Development of a novel green coating process with laser

Corrosion causes costs of about 3–4% of each country’s gross domestic product, and due to the climate change, the corrosion rates on infrastructure are likely to increase furtherly in the future1,2. For corrosion protection, hard chrome plating (HCP) is commercially used since the early 20th3. Yet the biggest drawback concerns environmental protection, since toxic and carcinogenic hexavalent chromium Cr6+ is used. As an alternative, thermal spray (TS) is increasingly used since the last 20 years. Nevertheless, the coatings are technologically constrained in regard to high porosity, low material efficiency and poor bonding to the base material. Therefore, the demand for an environmental friendly and economical process that produces high-quality coatings is increasingly coming into the research focus. With laser, dense, metallurgically bonded and therefore well-adhering coatings with high material efficiency of > 90% can be produced from a large number of metallic alloys without the need to use environmentally harmful chemicals or noise emissions. However, the typical area coating rate of < 0.4 m2/h is significantly lower than that of TS of about 10 m2/h4,5, and is too small for coating large-scale components. In this regard, a novel coating process with laser was developed in this work. By decoupling the melding of powder from the coating speed, the coating speed of < 2 m/min in conventional laser coating can be increased to > 500 m/min. Defect-free layers that metallurgically bond to the base material with a thickness of 50–250 µm and a material efficiency of > 90% can be achieved. According to the results, an area coating rate up to 20 m2/h is achievable. The pioneer work of applications in offshore and automobile sectors show, this process is already providing beneficial for the industry.

The design of praseodymium galena nanospheres: An effective photocatalyst for the remediation of carcinogenic phenothiazine and chromium contaminants

Herein, we report the synthesis of nanosphere-shaped praseodymium lead sulfide nanoparticles (PrPbS NPs) using a simple environmentally benign sonochemical technique, which have been well characterized using various spectroscopic and microscopic techniques. The nanosphere shaped PrPbS NPs were applied as a dual role photocatalyst for the degradation of hazardous methylene blue (MB) dye and the conversion of carcinogenic hexavalent chromium (Cr6+) to trivalent chromium (Cr3+) under visible light irradiation. The effective experimental parameters, such as the catalyst dosage (30 mg in 100 mL), initial concentration (30 mg/L and 20 mg/L), and pH influence (pH 7.0 and pH 3.0) of the environmental pollutant were studied. In addition, the effect of scavenging particles for the degradation of MB and Cr6+ were analyzed with help of various scavenging particles. The mechanisms for the photodegradation of MB and conversion of Cr6+ were predicted using radical scavenger measurements. Moreover, degradation efficiencies toward MB and hexavalent Cr6+ of 99.2 and 96.6%, respectively were achieved in the presence of the PrPbS NPs. These results reveal the PrPbS nanospheres are synthesized by an ecofriendly procedure and applied as photocatalyst for the effective degradation of MB and Cr6+.

Redox-Active Magnetic Composites for Anionic Contaminant Removal from Water.

Global water security is jeopardized by the presence of anthropogenic contaminants, which can persist resiliently in the environment and adversely affect human health. Surface adsorption of polluting species is an effective technique for water purification. In this work, redox-active magnetic compounds were designed for the targeted removal of inorganic and organic anions in water via polymeric redox-active vinylferrocene (VFc) and pyrrole (Py) moieties. An Fe3O4@SiO2@PPy@P(VFc-co-HEMA) composite was prepared in a four-step process, with the outermost layer possessing heightened hydrophilicity as a result of the optimized incorporation of 2-hydroxyethylmethacrylate (HEMA) monomers into the backbone of the ferrocene macromolecule. The synthesized materials are able to separate carcinogenic hexavalent chromium oxyanions and other charged micropollutants, and exhibit a 2-fold or greater enhancement in adsorption uptake once the redox-active ferrocene groups are oxidized to ferrocenium cations, with capacities of 23, 49, 66, and 95 mg/g VFc for maleic acid, 2-(6-methoxy-2-naphthyl)propionic acid (Naproxen), (2,4-dichlorophenoxy)acetic acid (2,4-D), and (2-dodecylbenzene)sulfonic acid (DBS), respectively, and a > 99% extractability of chromium in the 1 ppm range. The application of redox-active components to a magnetic particulate scaffold improves maneuverability and phase contact, giving rise to new potential aqueous separation process frameworks for water or product purification.

Polypyrrole-based adsorbents for Cr(VI) ions remediation from aqueous solution: a review.

Anthropogenic activities are principally responsible for the manifestation of toxic and carcinogenic hexavalent chromium (Cr(VI)) triggering water pollution that threatens the environment and human health. The World Health Organisation (WHO) restricts Cr(VI) ion concentration to 0.1 and 0.05 mg/L in inland surface water and drinking water, respectively. The available technologies for Cr(VI) ion removal from water were highlighted with an emphasis on the adsorption technology. Furthermore, the characteristics of several polypyrrole-based adsorbents were scrutinized including amino-containing compounds, biosorbents, graphene/graphene oxide, clay materials and many other additives with reported effective Cr(VI) ion uptake. This efficiency in Cr(VI) ions adsorption is attributed to enhanced redox properties, increased number of functional groups as well as the synergistic behaviour of the materials making up the composites. The Langmuir isotherm best described the adsorption processes with maximum adsorption capacities ranging from 3.40-961.50 mg/g. The regeneration of Cr(VI) ion-laden adsorbents was studied. Ion exchange, electrostatic attractions, complexation, chelation reactions with protonated sites and reduction were the mechanisms of adsorption. Nevertheless, there are limited details on comprehensive adsorbent regeneration studies to prolong robustness in adsorption-desorption cycles and utilization of the Cr(VI) ion-laden adsorbent in other areas of research to limit the threat of secondary pollution.

Effect of electrode modification on the production of electrical energy and degradation of Cr (Ⅵ) waste using tubular microbial fuel cell

&lt;abstract&gt; &lt;p&gt;Carcinogenic hexavalent chromium is increasing worldwide due to the increased electroplating, welding and textile industry. On the other hand, molasses, the sugar factory's byproduct with high organic compounds (sugars), may pollute the environment if it is not processed. However, microbial fuel cell (MFC) seems to be a promising technology due to its ability to produce electrical energy from pollutant degradation using microbes while reducing hexavalent chromium to trivalent chromium with less toxicity. Carbon felt was used at both electrodes. This research aimed to determine the effect of modifying the anode with rice bran and cathode with Cu catalyst towards electricity generation and pollutant removal in molasses and reducing Cr (Ⅵ) into Cr (Ⅲ) using tubular microbial fuel cells. Moreover, the effect of mixing Sidoarjo mud and &lt;italic&gt;Shewanella oneidensis&lt;/italic&gt; MR-1 as electricigen bacteria toward electrical energy production and pollutant removal was determined. Experiments revealed that the S/CM/AM variable, which only used &lt;italic&gt;Shewanella oneidensis&lt;/italic&gt; MR-1 as an electricigen bacteria with both modified electrodes, produced the highest total power density of 530.42 mW/m&lt;sup&gt;2&lt;/sup&gt; and the highest percentage of Cr (Ⅵ) reduction of 98.87%. In contrast, the highest microbial population of 66.5 × 10&lt;sup&gt;10&lt;/sup&gt; cells/mL, 61.28% of Biological Oxygen Demand (BOD&lt;sub&gt;5&lt;/sub&gt;) removal and 59.49% of Chemical Oxygen Demand (COD) were achieved by SSi/CM/AM variable, mixing &lt;italic&gt;Shewanella oneidensis&lt;/italic&gt; MR-1 and Sidoarjo mud as an electricigen bacteria with both modified electrodes. Therefore, this study indicates that double chamber tubular microbial fuel cells may be a sustainable solution for managing molasses and carcinogen hexavalent chromium.&lt;/p&gt; &lt;/abstract&gt;

Inferred inactivation of the Cftr gene in the duodena of mice exposed to hexavalent chromium (Cr(VI)) in drinking water supports its tumor-suppressor status and implies its potential role in Cr(VI)-induced carcinogenesis of the small intestines

Carcinogenicity of hexavalent chromium [Cr (VI)] has been supported by a number of epidemiological and animal studies; however, its carcinogenic mode of action is still incompletely understood. To identify mechanisms involved in cancer development, we analyzed gene expression data from duodena of mice exposed to Cr(VI) in drinking water. This analysis included (i) identification of upstream regulatory molecules that are likely responsible for the observed gene expression changes, (ii) identification of annotated gene expression data from public repositories that correlate with gene expression changes in duodena of Cr(VI)-exposed mice, and (iii) identification of hallmark and oncogenic signature gene sets relevant to these data. We identified the inactivated CFTR gene among the top scoring upstream regulators, and found positive correlations between the expression data from duodena of Cr(VI)-exposed mice and other datasets in public repositories associated with the inactivation of the CFTR gene. In addition, we found enrichment of signatures for oncogenic signaling, sustained cell proliferation, impaired apoptosis and tissue remodeling. Results of our computational study support the tumor-suppressor role of the CFTR gene. Furthermore, our results support human relevance of the Cr(VI)-mediated carcinogenesis observed in the small intestines of exposed mice and suggest possible groups that may be more vulnerable to the adverse outcomes associated with the inactivation of CFTR by hexavalent chromium or other agents. Lastly, our findings predict, for the first time, the role of CFTR inactivation in chemical carcinogenesis and expand the range of plausible mechanisms that may be operative in Cr(VI)-mediated carcinogenesis of intestinal and possibly other tissues.

Excellent Properties of Ni-15 wt.% W Alloy Electrodeposited from a Low-Temperature Pyrophosphate System

Electrodeposited Ni-W alloy coatings are considered to be one of the most suitable candidate coatings to replace carcinogenic hexavalent chromium coatings. In this work, Ni-W alloys are electrodeposited from pyrophosphate baths containing different concentrations of Na2WO4 2H2O (CW) at 40 °C. Both CW and the applied current density can affect the W content in the coatings. The effect of CW becomes weaker with the increased current density. The Ni-W alloys with 15 ± 5 wt.% W (Ni-15 wt.% W) are obtained from the bath containing 40 g L−1 CW at a high current of 8 A dm−2. The microhardness, corrosion resistance and hydrogen evolution reaction (HER) are measured with a microhardness tester and an electrochemical workstation. The modified properties are studied by heat treatment from 200 to 700 °C. The highest microhardness of 895.62 HV and the better HER property is presented after heat treatment at 400 °C, while the best corrosion resistance in 3.5 wt.% NaCl solution appears at 600 °C.

Pipes could release toxic chromium into tap water

A new study shows that the carcinogen hexavalent chromium can slip into drinking water when commonly used chlorine disinfectants corrode cast-iron water distribution pipes ( Environ. Sci. Technol. 2020, DOI: 10.1021/acs.est.0c03922 ). Until now, most scientists thought that chromium found in drinking water originated from natural sources or industrial pollution. Haizhou Liu and his team at the University of California, Riverside, found another possible source by scraping some of the crusty scale out of two sections of cast-iron pipes from US drinking water systems. Cast iron is widely used in these pipes and contains significant amounts of Cr(0) in the alloy to help prevent corrosion. The scientists incubated the scale samples in a solution of hypochlorous acid, the oxidizing sanitizer commonly used to treat drinking water. The disinfectant-treated scales rapidly cranked out Cr(VI), whereas scales in water with no disinfectant produced none of the toxic metal species. Also, when exposed

An amine functionalized ZnCr LDH/MCM-41 nanocomposite as efficient visible light induced photocatalyst for Cr(VI) reduction

Achieving photocatalytic carcinogenic hexavalent chromium (Cr(VI)) reduction by utilising a visible light promoted semiconductor based nanocomposite is challenging as a eco-friendly and sustainable approach. Mesoporous MCM-41 modified ZnCr Layered double hydroxide (LDH) nanocomposite was prepared by in-situ co precipitation method having great porosity, large surface area, high chemical stability and plentiful surface –OH grafting sites. These sites can be easily tailored with APTES group as amine source using a facile reflux process to design amine functionlisation ZnCr LDH/MCM-41 nanohybrid material. The structural identity, textural properties, optical response and functional groups of the as-prepared materials were systematically analysed by powder X-ray diffraction (PXRD), N2 adsorption–desorption technique, ultraviolet–visible diffuse reflectance (UV–vis DRS) and fourier-transform infrared (FTIR). It is revealed that the amine functionlisation ZnCr LDH/MCM-41 possesses enhanced visible-light absorption property in compared to ZnCr/MCM-41 nanocomposite, which was attributed to the chromophoric amino group of the organic linker. Under optimum conditions, amine functionlisation ZnCr LDH/MCM-41 exhibited 95% Cr(VI) reduction in 2 h from aqueous solution under visible-light irradiation, which was 1.2 times higher than that of unmodified ZnCr LDH/MCM-41 nanocomposite and 1.5 times superior than pure ZnCr LDH. The lowest PL intensity of amine functionlisation ZnCr LDH/MCM-41 supported the optimum photocatalytic activity. Under the explore of visible light, the presence of LMCT spectra (O2p → Cr-3dt2g and Zn 4 s) an d–d transition (Cr-3d-t2g → Cr-3 deg) in the ZnCr LDH are the key reason for excited of photoelectrons and transportation from amine functionlisation ZnCr LDH/MCM-41 to Cr(VI), accelerating the reduction process of Cr(VI). In summary, amine functionalized MCM-41 modified ZnCr LDH could be prospective photocatalyst candidate for the treatment of Cr(VI)-contained wastewater under visible light irradiation.

CeO2/g-C3N4/V2O5 ternary nano hetero-structures decorated with CQDs for enhanced photo-reduction capabilities under different light sources: Dual Z-scheme mechanism

Abstract In this work, a carbon quantum dots (CQDs) decorated dual Z-scheme CeO2/g-C3N4/V2O5 heterojunction (CCGV) was rationally synthesized by simple hydrothermal method. The crystal structure, morphology, and optical properties of the photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectroscopy. CCGV catalyst shows high visible absorption, including near infra-red region and solar light via two-channel charge transfer (dual Z-scheme), reduced recombination, and up-conversion effect of CQDs. The heterojunction was used for visible assisted photo-reduction of carcinogenic hexavalent chromium ions (Cr(VI)) with a 99% reduction in 100 min without any sacrificial agent or hole scavenger. The reaction becomes more rapid with tartaric acid as a scavenger with a complete reduction in just 30 min under visible light. Photogenerated electrons are the dominant active species, followed by ●O2−, as revealed by the scavenging experiments. The use of sacrificial agents and scavengers suggests that photogenerated electrons were the dominant active species followed by ●O2− radicals. The electrochemical impedance spectroscopy and photoluminescence results confirm highly reduced recombination, high charge separation, and charge transfer capacity in the dual Z-scheme heterojunction. The conduction band edges of CeO2 and V2O5 (which are protected by the dual charge transfer) have an appropriate potential for the rapid reduction of hexavalent chromium. The XPS scan of the catalyst after separation shows the presence of Cr in the +3 oxidation state, suggesting complete photo-reduction. This study is promising for developing wide spectrum active simple heterojunction photocatalysts for pollutant removal with high efficiency.

An ex-situ and in vitro approach towards the bioremediation of carcinogenic hexavalent chromium

Chromium, ranking the second most among toxic heavy metal pollutants in the world, causing respiratory, cardiovascular and renal problems in human beings is under study herein. We examined the biological remediation of the carcinogenic Cr (VI) polluted soils by indigenous yeast isolates. The total element analysis of the treated sample was determined by Energy Dispersion X-ray Micro Analysis (EDXMA). The sample under study was observed to have a high concentration of 458.29 mgKg−1 Cr (VI), determined by Atomic Absorption Spectroscopy (AAS) and DPC analysis. The most tolerant isolate designated as CSR was used for in vitro and ex-situ bioremediation studies of Cr (VI). The isolate achieved significant bioremediation of 86% in vitro and 75.12% in ex-situ method. The optimal conditions for in vitro bioremediation were found to be 28 °C and a pH of 6. The ITS1, 5.8S rRNA and D1, D2 domain of LSU rRNA gene characterization of the isolate CSR illustrated that it belongs to Ustilago genera. The isolate was deposited in NCBI GenBank as Ustilago sp. CSR (KY284846). Although, Ustilago is generally a pathogenic fungus, our study opens up the scope of using Ustilago spp. for bioremediation of the carcinogenic heavy metal Chromium.

Design of novel solar-light driven sponge-like Fe2V4O13 photocatalyst: A unique platform for the photoreduction of carcinogenic hexavalent chromium

In past days, the occurrence of toxic heavy metal ions into the water and soil environment causes a major health risk to the living organisms. In this work, we mainly focused on the photoreduction of hexavalent chromium (Cr6+) using novel sponge-like Fe2V4O13 photocatalyst under visible light irradiation. The sponge-like Fe2V4O13 was tailored through hydrothermal process using ferric chloride and sodium metavanadate precursors without the addition of any templates. The surface morphology, elemental analysis and various physical properties are characterized by numerous spectroscopic techniques. Interestingly, the sponge-like Fe2V4O13 demonstrated proficient photocatalytic performances towards the reduction of Cr6+ into Cr3+. The obtained UV–visible spectroscopy results portrayed that sponge-like Fe2V4O13 could reduce above of Cr6+ solution within 40 min. The effect of operational reaction parameters such as catalyst dosage, initial Cr6+ concentration and pH of the solution was optimized. Moreover, the sponge-like Fe2V4O13 holds very good stability even after five consecutive cycles. This study could open new insights for the design novel nanostructured binary metal oxides for environmental applications.

Effect of surface treatments on the localized corrosion resistance of the AA2198‐T8 aluminum lithium alloy welded by FSW process

In this work, the effect of eight types of surface treatments on the corrosion resistance of friction stir welded samples of an AA2198‐T8 Al‐Cu‐Li alloy were tested and compared in an attempt to find suitable alternatives to toxic and carcinogenic hexavalent chromium treatments. All the samples were anodized and subjected to different post‐anodizing treatments. The post‐anodizing treatments were (1) hydrothermal treatment in Ce (NO3)3 6H2O solution; (2) hydrothermal treatment in Ce (NO3)3 6H2O solution with H2O2; (3) hydrothermal treatment in boiling water; (4) hexavalent chromium conversion coating; and (5) immersion in BTSE (bis‐1,2‐(triethoxysilyl) ethane. The corrosion resistance of the treated samples was evaluated by immersion tests in sodium chloride solution (0.1 mol L−1 NaCl) and electrochemical impedance spectroscopy (EIS) of the friction stir weldment. The results showed that among the alternative treatments, the Ce‐containing solutions presented the best corrosion resistance, especially when used without peroxide.

Effects of Na: Al and water: solid ratios on the mechanical properties of fly ash based geopolymer

Every segment industry infrastructure like onshore/offshore setup, power generation and water management is part of a complex system which involves large investment. Unfortunately, these infrastructures easily susceptible to be attacked by corrosion, resulting in hundreds of millions of dollars in losses. Conventionally, steel is protected by anticorrosive chromate coatings. But these coatings contain carcinogenic hexavalent chromium compound which may cause to environment and health related issues. To reduce those impacts, conventional coatings are replaced by water-based alternatives and inorganic coatings. Geopolymer as a green inorganic material with superior properties is in great research to be explored as a new coating material. The present paper outlines briefly the potential of geopolymer as a coating material through the mechanical performance test of adhesion and flexural strength. Scanning electron microscopy (SEM) was used to examine the morphology of geopolymer and unreacted fly ash matrix. The test was conducted by varying two aspects of Na: Al and water: solid ratios. The findings show both the alkali and water content plays a asignificant role in geopolymerization. The increase in water content at low Na/Al ratio causes dilution of activator thus resulted in decreased of adhesion and flexural strength.