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In this study, a novel and effective modified microbial reducing agent was developed to detoxify Cr(VI) from aqueous solutions. This was achieved by carefully controlling specific salt components in the growth medium. Based on the single-salt modification, several effective modified salts were selected and added to the medium for synergistic modification. The results showed that the synergistic modification with NH 4 Cl and KH 2 PO 4 had the best detoxification effect on Cr(VI), reaching 98.5% at 100 mg/L Cr(VI), which was much higher than the 43.7% of the control (original Luria-Bertani medium). This enhancement was ascribed to the ability of NH 4 Cl and KH 2 PO 4 to stimulate the growth of Stenotrophomonas sp. D6 promoted chromate reductase secretion. The protein content of the modified medium supernatant was significantly increased by 10.76% compared to that before modification. Based on the micro-characterization, the main process for the elimination of Cr(VI) is microbial reduction rather than biosorption. Most of the reduced Cr was found in the extracellular suspension, thereby suggesting that the primary reduction occurred outside the cells, whereas only a small fraction was detected intracellularly. Overall, this study provides a simple and effective method for microbial treatment of heavy metals in aqueous solutions. [Display omitted] • The composition of salt in the medium was optimized to improve the removal of Cr(VI). • Enhancing reductase secretion of strains by adding NH 4 Cl and KH 2 PO 4 into medium. • Efficient reusability of the Co-modified strain lyophilized powder. [ABSTRACT FROM AUTHOR]

• The low valent Re complex in the reduction solution was in-situ analysis by EXAFS and UV–vis. • The hourglass crystal of Re was firstly prepared. • The speciation of Re in the hourglass cyrstal was low valent dimeric Re-DTPA by EXAFS and DET calculation. • The low valent Re in the hourglass crystal is stable in the air. This paper studied the fate of Re in the presence of polyaminocarboxy ligand (DTPA, EDTA and NTA) under reducing condition. When SnCl 2 as reducing agent, the results indicated the low valent Re was formed. And batch experiments studied the effect of pH and different ligands on the formation of low valent Re complex, the acid condition was favoured for the formation of low valent Re complex, and the order of complexing toward the low valent Re was the following: DTPA > EDTA > NTA. In the condition of pH = 1, DTPA as ligand, the hourglass crystal was obtained. Using ESI-MS, solid-state UV–Vis–NIR spectra, EXAFS, DFT calculation et al, the darkened patch of the hourglass crystal was demonstrated to be Re, and its speciation was dimeric Re 2 (μ-O) 2 DTPA. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Overhaul wastewater was treated with ozonation-microelectrolysis-ozonation process. • Microelectrolysis could destroy the structure of MDEA, but ozone had no effect. • The effects of operating parameters on MDEA removal were investigated. • The degradation mechanism of MDEA in microelectrolysis was discussed. Abstract In this study, the microelectrolysis system was applied to generate strong reductants, such as free hydrogen [H] and O ∙ , and thus removing N -Methyldiethanolamine (MDEA) in overhaul wastewater. Effects of initial influent pH, mass ratio of filings to wastewater, air aeration rate, and reaction temperature on the removal of MDEA were investigated intensively. Experimental results indicate that optimum removal rate of MDEA can be obtained at pH = 2, inlet air rate = 1 L min−1, mass ratio of filings to wastewater = 1:1 and temperature = 25 °C. About 96.0% Total Organic Carbon (TOC) in overhaul wastewater can be mineralized by ozonation–microelectrolysis–ozonation (OMIO) treatment process. By analyzing the effluent at various stages, it was established that microelectrolysis played a leading role in the destruction of MDEA. The degradation mechanism of MDEA has been clarified through detecting the degradation products with Gas Chromatography–Mass Spectrometer (GC–MS). Subsequently, ozone reacts with intermediate products generated by MDEA degration through OH· pathway under alkaline condition. In short, these results suggest that OMIO system should be proposed as a promising treatment process for the MDEA wastewater. [ABSTRACT FROM AUTHOR]

Attention has been long focused on enhancing permanganate (Mn(VII)) oxidation capacity for eliminating organic contaminants via generating active manganese intermediates (AMnIs). Nevertheless, limited consideration has been given to the unnecessary consumption of Mn(VII) due to the spontaneous disproportionation of AMnIs during their formation. In this work, we innovatively introduced green polyaspartic acid (PASP) as both reducing and chelating agents to activate Mn(VII) to enhance the oxidation capacity and utilization efficiency of Mn(VII). Multiple lines of evidence suggest that Mn(III), existing as Mn(III)-PASP complex, was generated and dominated the degradation of bisphenol A (BPA) in the Mn(VII)/PASP system. The stabilized Mn(III) species enabled Mn(VII) utilization efficiency in the Mn(VII)/PASP system to be higher than that in Mn(VII) alone. Moreover, the electrophilic Mn(III) species was verified to mainly attack the inclusive benzene ring and isopropyl group to realize BPA oxidation and its toxicity reduction in the Mn(VII)/PASP system. In addition, the Mn(VII)/PASP system showed the potential for selectively oxidizing organic contaminants bearing phenol and aniline moieties in real waters without interference from most of coexisting water matrices. This work brightens an overlooked route to both high oxidation capacity and efficient Mn(VII) utilization in the Mn(VII)-based oxidation processes. [Display omitted] ● PASP significantly promoted the oxidation of BPA by Mn(VII). ● Mn(III)-PASP complex was the dominant reactive species. ● PASP enhanced the utilization efficiency of Mn(VII). ● Mn(VII)/PASP system alleviated the toxicity of BPA. ● Mn(VII)/PASP system showed selective reactivity toward organics. [ABSTRACT FROM AUTHOR]

Microbial biotransformation of Cr(VI) is a sustainable approach to reduce Cr(VI) toxicity and remediate Cr(VI) contamination. In this study, Bacillus cereus SES with the capability of reducing both Cr(VI) and Se(IV) was isolated, and the effect of Se supplementation on Cr(VI) reduction by Bacillus cereus SES was investigated. Se(IV) addition enabled 2.6-fold faster Cr(VI) reduction, while B. cereus SES reduced 96.96% Se(IV) and produced more selenium nanoparticles (SeNPs) in the presence of Cr(VI). Co-reduction products of B. cereus SES on Cr(VI) and Se(IV) were SeNPs adsorbed with Cr(III). The relevant mechanisms were further revealed by proteomics. Se(IV) supplementation mediated the synthesis of Cr(VI) reductants and stress-resistant substances, thus enhancing Cr(VI) resistance and promoting Cr(VI) reduction. Meanwhile, high Se(IV) reduction rate was associated with Cr(VI)-induced electron transport processes, and Cr(VI) mediated the up-regulation of flagellar assembly, protein export and ABC transporters pathways to synthesis and export more SeNPs. Furthermore, Se combined with B. cereus SES had the potential to reduce the toxicity of Cr(VI) via reducing the bioavailability of Cr and improving the bioavailability of Se in soil. Results suggested that Se could be an efficient strategy to enhance the remediation of B. cereus SES on Cr contamination. [Display omitted] • Bacillus cereus SES co-reduced Cr(VI) and Se(IV) to SeNPs adsorbed with Cr(III). • Se(IV) supplementation enabled 2.6-fold faster Cr(VI) reduction. • Se(IV) induced the synthesis of Cr(VI) reductants and stress-resistant substances. • Cr(VI) facilitated the biosynthesis and export of selenium nanoparticles (SeNPs). • Se enhanced the remediation of Bacillus cereus SES on Cr(VI) contamination. [ABSTRACT FROM AUTHOR]

1,3-Dinitrobenzene (1,3-DNB) is listed by the USEPA as a priority pollutant. 1,3-DNB has two nitro functional groups (-NO 2) bound to the benzene ring, with a +III nitrogen oxidation states, and strong electronegativity, and therefore can be reductively degraded by gaining electrons. Weeds that contain a high proportion of polyphenols can supply electrons and act as natural reducing agents. This study investigated the potential of various weeds to reductively remove 1,3-DNB from aqueous phase. The Taguchi L9 Orthogonal experimental design method was used to explore the optimum operational parameters. According to the analyzed characteristics of weeds, including total phenol content, antioxidant capacity, metal chelating capacity, reducing capacity, and environmental adaptability, the weed Sphagneticola trilobata , containing 11.93 mg of gallic acid equivalent per gram of weed (mg-GAE/g-weed), was selected for 1,3-DNB degradation experiments. The results showed that the optimum reaction conditions for the degradation of 1,3-DNB in the aqueous phase using Sphagneticola trilobata were: pH 3, a weed dose of 10 g/L, reaction time of 14 day, and initial 1,3-DNB concentration of 0.5 mM. According to ANOVA analysis, the weed dose was the most significant factor in the experiment, and each 1 mg of 1,3-DNB degraded required 120 mg of dry weeds. [Display omitted] • Weeds are rich in polyphenols and act as natural reductants. • Sphagneticola trilobata weed exhibits the potential to reductively degrade 1,3-DNB. • Four factors are investigated including 1,3-DNB concentration, weed dose, pH, and reaction time. • The optimum reaction parameters are determined using Taguchi L9 Orthogonal Array. • The weed dose is the most influential factor for degrading 1,3-DNB. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are becoming a class of pollutants with high global concerns. Research on the aging of MPs has focused on oxidative environments, it is of great interest to study the aging of MPs under reduction conditions. In this study, a reduction environment was constructed by purging nitrogen and adding reducing agents (NaBH 4 , VC, Na 2 S, C 2 Na 2 O 4) to understand the aging behavior and mechanism of MPs. The results proved that PVC occurred aging under four reduction conditions, and the aging degree was the strongest under NaBH 4 reduction condition. The aged PVC became broken, particle size decreased, and dechlorination phenomenon was observed. These phenomena were more obvious under the reduction condition in light, which was the superposition of photo-aging and reduction aging. The functional group components of PVC changed (C-C/C C increased, and oxygen-containing functional groups decreased) under reduction conditions, but photo-aging was dominant in the light system. Electron transfer occurred during the reduction process, and the EDC of PVC aged increased and EAC decreased. This study may shed light on a highly efficient aging pathway of MPs that is often overlooked in nature, contributing to understanding the aging behavior of MPs in complex environments. [Display omitted] • Aging of MPs by reducing agents in dark and light system. • PVC was broken and dechlorinated under reduction conditions. • The functional groups of MPs changed significantly after reduction aging. • Electron transfer occurred and reducing agents provided electrons. • Provide help for the aging of MPs in complex environment. [ABSTRACT FROM AUTHOR]

The aging of microplastics (MPs) occurs extensively in the environment, and understanding the aging mechanisms of MPs is essential to study the properties, fate and environmental impact of MPs. We proposed a creative hypothesis that polyethylene terephthalate (PET) can be aged by reducing reactions with reducing agents. Simulation experiments based on the principle of reduction of carbonyl by NaBH 4 were conducted to test the correctness of this hypothesis. The results showed that after 7 days of experiments, physical damage and chemical transformation occurred in the PET-MPs. The particle size of MPs was reduced by 34.95–55.93 %, and the C/O ratio was increased by 2.97–24.14 %. The changing order of surface functional groups (C O > C-O > C-H > C-C) was obtained. The occurrence of reductive aging and electron transfer of MPs was further supported by electrochemical characterization experiments. These results together reveal the reductive aging mechanism of PET-MPs: C O is firstly reduced to C-O by BH 4 - attack, and then further reduced to · R. The resulting · R recombines to form new C-H and C-C. This study is beneficial to deepen the understanding of the chemical aging of MPs, and can provide a theoretical basis for further research on the reactivity of oxygenated MPs with reducing agents. [Display omitted] • First study on reactivity of MPs with reducing agents. • A reduction system was established using NaBH 4 , Na 2 MoO 4 and HCl. • Reduction reactions and electron transfer occurred in the system. • Significant aging of MPs was observed in a short period of time. • Provide new ideas for the degradation pathway of MPs. [ABSTRACT FROM AUTHOR]

Shooting ranges are a source of environmental concern around the world as they are a source of toxic antimony (Sb) and lead (Pb). In-situ chemical stabilization is a strategy to reduce metal(loid) leaching and bioavailability. However it is difficult to find the right treatment due to the fact that Pb is a cation and Sb an anion, under oxidised conditions and they often show the opposite mobility in soil, on the application of amendments. A batch experiment was set up with two soils (slightly acidic and alkaline), two red mud based amendments (ViroSoil™ 1 and 2) alone and in combination with two reducing agents (zero valent iron and iron sulphate), to assess the effect of the treatments on metal(loid) leaching and compare it to unamended soil and soil amended with goethite, a known Sb adsorbent. Iron sulphate was effective at reducing Sb leaching due to the reduction of Sb V to Sb III which bound more strongly to iron (hyr)oxides in soil. However it had an adverse effect on the leaching of Pb due to its acidifying effect and reductive dissolution of manganese (hyd)roxides. Combining ViroSoil™ amendments with FeSO 4 still reduced Sb leaching but also Pb leaching and proved a suitable treatment. [ABSTRACT FROM AUTHOR]

A stable silver nanoparticles/carbon quantum dots (Ag/CQDs) composite was prepared by using CQDs as reducing and stabilizing agent. The CQDs synthesized with polyethyleneimine (PEI) showed an extraordinary reducibility. When Hg 2+ was presented in the Ag/CQDs composite solution, a color change from yellow to colorless was observed, accompanied by a shift of surface plasmon resonance (SPR) band and decrease in absorbance of the Ag/CQDs composite. On the basis of the further studies on TEM, XPS and XRD analysis, the possible mechanism is attributed to the formation of a silver-mercury amalgam. Hence, a two dimensional sensing platform for Hg 2+ detection was constructed upon the Ag/CQDs composite. Based on the change of absorbance, a good linear relationship was obtained from 0.5 to 50 μM for Hg 2+ . And the limit of detection for Hg 2+ was as low as 85 nM, representing high sensitivity to Hg 2+ . More importantly, the proposed method also exhibits a good selectivity toward Hg 2+ over other metal ions. Besides, this strategy demonstrates practicability for the detection of Hg 2+ in real water samples with satisfactory results. [ABSTRACT FROM AUTHOR]

The fabrication of montmorillonite (Mt) decorated with lysozyme-modified silver nanoparticles (Ag/lyz-Mt) was reported. The lysozyme (lyz) was served as both reducing and capping reagent. Coupling the bactericidal activity of the lyz with AgNPs, along with the high porous structure and large specific surface area of the Mt, prevented aggregation of AgNPs and promoted nanomaterial-bacteria interactions, resulting in a greatly enhanced bactericidal capability against both Gram positive and Gram negative bacteria. This paper systematically elucidated the bactericidal mechanisms of Ag/lyz-Mt. Direct contact between the Ag/lyz-Mt surface and the bacterial cell was essential to the disinfection. Physical disruption of bacterial membrane was considered to be one of the bactericidal mechanisms of Ag/lyz-Mt. Results revealed that Ag + was involved in the bactericidal activity of Ag/lyz-Mt via tests conducted using Ag + scavengers. A positive ROS (reactive oxygen species) scavenging test indirectly confirmed the involvement of ROS (O 2 − , H 2 O 2 , and OH) in the bactericidal mechanism. Furthermore, the concentrations of individual ROS were quantified. Results showed that Ag/lyz-Mt nanomaterial could be a promising bactericide for water disinfection. [ABSTRACT FROM AUTHOR]

In this study, the effects of reducing agents on the degradation of tetrachloroethene (PCE) were investigated in the Fe(II)/Fe(III) catalyzed sodium percarbonate (SPC) system. The addition of reducing agents, including hydroxylamine hydrochloride, sodium sulfite, ascorbic acid and sodium ascorbate, accelerated the Fe(III)/Fe(II) redox cycle, leading to a relatively steady Fe(II) concentration and higher production of free radicals. This, in turn, resulted in enhanced PCE oxidation by SPC, with almost complete PCE removal obtained for appropriate Fe and SPC concentrations. The chemical probe tests, using nitrobenzene and carbon tetrachloride, demonstrated that HO was the predominant radical in the system and that O 2 − played a minor role, which was further confirmed by the results of electron spin resonance measurements. PCE degradation decreased significantly with the addition of isopropanol, a HO scavenger, supporting the hypothesis that HO was primarily responsible for PCE degradation. It is noteworthy that Cl − release was slightly delayed in the first 20 min, indicating that intermediate products were produced. However, these intermediates were further degraded, resulting in the complete conversion of PCE to CO 2 . In conclusion, the use of reducing agents to enhance Fe(II)/Fe(III) catalyzed SPC oxidation appears to be a promising approach for the rapid degradation of organic contaminants in groundwater. [ABSTRACT FROM AUTHOR]

In the field of nitrogen oxides (NO x) abatement, developing selective catalytic reduction (SCR) catalysts that can operate stably in the practical conditions remains a big challenge because of the complexity and uncertainty of actual flue gas emissions. As water vapor is unavoidable in the actual flue gas, it is indispensable to explore its effect on the performance of SCR catalysts. Many studies have proved that the effects of H 2 O on de-NO x activity of SCR catalysts were indeed observed during SCR reactions operated under wet conditions. Whether the effect is promotive or inhibitory depends on the reaction conditions, catalyst types and reducing agents used in SCR reaction. This review focuses on the effect of H 2 O on SCR catalysts and SCR reaction, including promoting effect, inhibiting effect, as well as the effecting mechanism. Besides, various strategies for developing a water-resistant SCR catalyst are also included. We hope that this work can give a more comprehensive insight into the effects of H 2 O on SCR catalysts and help with the rational design of water-resistant SCR catalysts for further practical application in NO x abatement field. [Display omitted] • The effect of H 2 O on the deNO x performance of SCR catalysts includes promotion and inhibition. • The effect mechanism of H 2 O on the deNO x performance of SCR catalysts was systematically reviewed. • H2O not only interacts with the catalyst surface, but also interferes with the SCR reaction. • Strategies to enhance the H 2 O resistance of SCR catalysts were reviewed. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg + ) is one of the common organic species of mercury, and has much higher toxicity than inorganic mercury. Based on the selective enhancement of the activity of nanozyme (NA-CDs/AuNPs) by MeHg + , a novel colorimetric nanoprobe for MeHg + assay is proposed. The noradrenaline-based carbon dots (NA-CDs) as the reducing agent was applied to prepare the NA-CDs/AuNPs. The formation of gold amalgamation (Au@HgNPs) between nanozyme and MeHg + allows to simultaneously accelerate the electron transfer from Au and Hg to NA-CDs and the generation of radicals (i.e. ∙OH, ∙O 2 - and ∙CH 3 ). The NA-CDs/AuNPs has an outstanding anti-interference performance even in the presence of different mercury. Further density functionality theory (DFT) calculations revealed that the formation of Au@HgNPs via MeHg + contributes to the significantly lowered activation energy, resulting in the peroxidase-like activity generation and acceleration. This leads to rapid (10 min) and specific colorimetric detection of MeHg + with the detection limit of 0.06 μg L -1 . This introduces a novel method for simple and sensitive detection of MeHg + , giving a new horizon for the assay of organometallic compounds., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Abiotic reductive extraction of arsenic from contaminated soils was studied with various reducing agents and combinations of reducing and chelating agents in order to remediate arsenic-contaminated soils. Oxalate and ascorbic acid were effective to extract arsenic from soil in which arsenic was associated with amorphous iron oxides, but they were not effective to extract arsenic from soils in which arsenic was bound to crystalline oxides or those in which arsenic was mainly present as a scorodite phase. An X-ray photoelectron spectroscopy study showed that iron oxides present in soils were transformed to Fe(II,III) or Fe(II) oxide forms such as magnetite (Fe 3 O 4 , Fe II Fe 2 III O 4 ) by reduction with dithionite. Thus, arsenic extraction by dithionite was not effective due to the re-adsorption of arsenic to the newly formed iron oxide phase. Combination of chelating agents with reducing agents greatly improved arsenic extraction from soil samples. About 90% of the total arsenic could be extracted from all soil samples by using a combination of dithionite and EDTA. Chelating agents form strong complexation with iron, which can prevent precipitation of a new iron oxide phase and also enhance iron oxide dissolution via a non-reductive dissolution pathway. [ABSTRACT FROM AUTHOR]

Iron sulphate (FeSO 4 ) and colloidal nano zero-valent iron (nZVI) as reducing agents were compared, with the aim of assessing their effectiveness in hexavalent chromium [Cr(VI)] removal from a contaminated industrial soil. Experiments were performed on soil samples collected from an industrial site where a nickel contamination, caused by a long-term productive activity, was also verified. The influence of reducing agents amount with respect to chromium content and the effectiveness of deoxygenation of the slurry were discussed. The soil was fully characterized before and after each test, and sequential extractions were performed to assess chemico-physical modifications and evaluate metals mobility induced by washing. Results show that both the reducing agents successfully lowered the amount of Cr(VI) in the soil below the threshold allowed by Italian Environmental Regulation for industrial reuse. Cr(VI) reduction by colloidal nZVI proved to be faster and more effective: the civil reuse of soil [Cr(VI) < 2 mg/kg] was only achieved using colloidal nZVI within 60 min adopting a nZVI/Cr(VI) molar ratio of 30. The reducing treatment resulted in an increase in the amount of chromium in the oxide–hydroxide fraction, thus confirming a mechanism of chromium-iron hydroxides precipitation. In addition, a decrease of nickel (Ni) and lead (Pb) content in soil was also observed when acidic conditions were established. [ABSTRACT FROM AUTHOR]

Microbial remediation of heavy metals in soil has been widely studied. However, bioremediation efficiency is limited in practical applications because of nutritional deficiency, low efficiency, and competition with indigenous microorganisms. Herein, we prepared a biochar-based microbial agent (BMA) by immobilizing the microbial agent (MA, containing Bacillus subtilis , Bacillus cereus , and Citrobacter sp.) on biochar for the remediation of U and Cd in soil. The results showed that BMA increased soil organic matter, cation exchange capacity, and fluorescein diacetate hydrolysis activity and dehydrogenase activity by 58.7%, 38.2%, 42.9%, and 51.1%. The availability of U and Cd were significantly decreased by 67.4% and 54.2% in BMA amended soil, thereby reducing their accumulation in vegetables. BMA greatly promoted vegetable growth. Additionally, BMA significantly altered the structure and function of rhizosphere soil microbial communities. Coincidently, more abundant ecologically beneficial bacteria like Nitrospira , Nitrosomonas , Lysobacter , and Bacillus were observed, whereas plant pathogenic fungi like Fusarium and Alternaria reduced in BMA amended soil. The network analysis revealed that BMA amendment increased the tightness and complexity of microbial communities. Importantly, the compatibility of niches and microbial species within co-occurrence network was enhanced after BMA addition. These findings provide a promising strategy for suppressing heavy metal accumulation in vegetables and promoting their growth. [Display omitted] • The synergistic effect of BC and MA enhanced U and Cd immobilization. • The growth of vegetables was promoted by BMA. • The stability of rhizosphere microecology was enhanced by BMA. • Ecologically beneficial bacteria increased in BMA amended soil. • Several plant pathogenic fungi reduced in BMA amended soil. [ABSTRACT FROM AUTHOR]

Cr(VI) from oxidation of geogenic Cr(III) minerals is gradually becoming the primary source of Cr(VI) in soils and groundwater instead of direct emissions. Thermodynamically, natural oxidants of Cr(III) are limited to O 2 and Mn oxides. The oxidation of Cr(III) occurs commonly in oxic soils but the difference in the oxidative dissolution of Cr(III) by Mn oxides in different redox soils (especially under anoxic conditions) is not fully understood and field evidence is lacking. Here, the relationship between Cr(VI) and Mn oxides in basalt-origin soil profiles under three different redox conditions (anoxic, suboxic and oxic) was studied. The oxidative dissolution of chromite was validated by synthesising δ-MnO 2 that was close to biogenic Mn oxides under anoxic and oxic conditions. In anoxic soils, high levels of Cr(VI) were detected in the same horizons as those where Cr(III)-minerals co-existed with Mn(III/IV) oxides, suggesting an exclusive pathway for Cr(VI) generation through oxidation by Mn oxides where there was a deficiency of other oxidants, such as O 2. In oxic soils, the highly abundant Fe oxides combined with Cr(III) to form Cr(III)-Fe(III) oxyhydroxides and Cr(VI) was generated mainly via slow oxidation by O 2. The chromite oxidation experiment results also indicated that a high abundance of Mn oxides could promote chromite oxidative dissolution to generate Cr(VI), even under anoxic conditions. Additionally, the form of Cr and the reactivity and abundance of Mn oxides and reducing agents controlled the net content of Cr(VI) in the soil. This study showed that, even under reducing conditions, Cr(III) is readily oxidised by Mn oxides to generate Cr(VI) in reductant-deficient and Mn-rich soils, which may lead to the continuous introduction of Cr(VI) into groundwater and agricultural soils. [Display omitted] • Fe oxides are the main minerals controlling the mobility of Cr in soils. • Cr(VI) is produced by Mn oxides oxidation in anoxic soils. • Cr(VI) is produced by the slow oxidation of O 2 in oxic soils. • Cr(III) oxidation by Mn oxides is inhibited by Fe oxides in oxic soils. [ABSTRACT FROM AUTHOR]

The environmental behavior of antimony (Sb) has recently received greater attention due to the increasing global use of Sb in a range of industrial applications. Although present at trace levels in most natural systems, elevated Sb concentrations in aquatic and terrestrial environments may result from anthropogenic activities. The mobility and toxicity of Sb largely depend on its speciation, which is dependent to a large extent on its oxidation state. To a certain extent, our understanding of the environmental behavior of Sb has been informed by studies of the environmental behavior of arsenic (As), as Sb and As have somewhat similar chemical properties. However, recently it has become evident that the speciation of Sb and As, especially in the context of redox reactions, may be fundamentally different. Therefore, it is crucial to study the biogeochemical processes impacting Sb redox transformations to understand the behavior of Sb in natural and engineered environments. Currently, there is a growing body of literature involving the speciation, mobility, toxicity, and remediation of Sb, and several reviews on these general topics are available; however, a comprehensive review focused on Sb environmental redox chemistry is lacking. This paper provides a review of research conducted within the past two decades examining the redox chemistry of Sb in aquatic and terrestrial environments and identifies knowledge gaps that need to be addressed to develop a better understanding of Sb biogeochemistry for improved management of Sb in natural and engineered systems. [Display omitted] • Research over the last 20 years examining Sb redox processes in environmental systems were comprehensively reviewed. • Abiotic oxidation of Sb(III), the relevant minerals and oxidants, and the conditions promoting oxidation are discussed. • Abiotic reduction of Sb(V), the associated reductants, and the key conditions are discussed. • Microbial oxidation/reduction of Sb and the associated metabolic processes are discussed. • Future aspects of Sb redox research are proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] U, Np, Pu, Am extraction using sc-CO2. [•] Use of reducing agents to prevent Np extraction. [•] Use of complexing agents to prevent Pu extraction. [ABSTRACT FROM AUTHOR]

Abstract: Silver/iron oxide composite nanoparticles have been synthesized successfully via a facile one-pot green route by the use of l-arginine, which created an aqueous solution of about pH 10 and acted as a reducing agent for the successive formation of iron oxide and Ag nanoparticles. The product was characterized to be silver-coated iron oxide and iron oxide hydroxide composite nanoparticles with a mean diameter of about 13.8±3.0nm and 8.53% of Ag in weight. It exhibited good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. The reduction reaction followed the pseudo-first-order kinetics. The corresponding rate constants increased with the increases of temperature and catalyst amount but decreased with the increase of initial 4-NP concentration, revealing an activation energy of 28.2kJ/mol and a diffusion controlled mechanism. In addition, this product had quite good stability. No significant activity loss was observed after reuse for 5 cycles. [Copyright &y& Elsevier]

The combination of ozone (O 3) and chemical reagents (such as H 2 O 2) shows synergies on the radical formation and micropollutant degradation. The promoting performance was associated with various parameters including chemical reagents, micropollutants, solution pH, and the water matrix. In this review, we summarized existing knowledge on radical formation pathways, radical yields, and radical oxidation for different synergistic ozonation processes in various water matrices (such as groundwater, surface water, and wastewater). The increase of radical yields by synergistic ozonation processes was positively related to the increase of O 3 -decay, with the increase being 1.1–4.4 folds than ozonation alone (0.2). Thus, synergistic ozonation can promote the degradation rate and efficiency of O 3 -resistant micropollutants (second order rate constant, k P,O3 < 200 M−1 s−1), but only slightly affects or even minorly inhibits the degradation of O 3 -reactive micropollutants (k P,O3 > 200 M−1 s−1). The water matrices, such as the dissolved organic matters, negatively suppressed the degradation of micropollutant by quenching O 3 -oxidation and radical oxidation (i.e. maximum promoting was decreased by 1.3 times), but may positively extend the promoting effects of synergistic ozonation to micropollutants that are more reactive to O 3 (i.e. k P,O3 was extended from <200 to <2000 M−1 s−1). The formation of bromate would be increased through increasing radical oxidation by synergistic ozonation, but can be depressed by relative higher H 2 O 2 as the reducing agent of HOBr/OBr− intermediate. The increase in bromate formation by O 3 /permononsulfate is a considerable concern due to permononsulfate cannot reduce the HOBr/OBr− intermediate. [Display omitted] • Synergism between O 3 and reagents is qualitatively and quantitatively summarized. • Synergistic ozonation increases radical oxidation while decreases O 3 oxidation. • Promoting effects depends on the water matrix and O 3 -reactivity of micropollutants. • Decrease of O 3 and radical consumption and oxidation byproduct are necessitated. [ABSTRACT FROM AUTHOR]

In this study, with the green tea extraction solution as a reducing agent and green tea residues as a raw material of biochar, green nano zero-valent iron biochar (G-nZVI-BC) was prepared with the green synthesis method and then combined with potassium persulfate to degrade p-nitrophenol in water. Compared with zero-valent iron-loaded biochar (C-nZVI-BC) prepared by the traditional chemical liquid phase synthesis method, G-nZVI-BC containing tea polyphenols further improved dispersibility of Fe0 on biochar, prevented nZVI agglomeration on BC, and promoted PNP degradation. The system constructed by G-nZVI-BC/PDS showed the high oxidation resistance than the C-nZVI-BC/PDS system, thus endowing the synthesis material with long-term reactivity. Both the radical pathway and non-radical pathways contributed to catalytic degradation and free radicals played a key role. The G-nZVI-BC/PDS system realized the good removal effect on PNP in the pH range of 3.06–9.23. The reusability of G-nZVI-BC and the PNP removal effect in water body conditions indicated that G-nZVI-BC had a good application prospect in the field of water treatment. [Display omitted] • PDS activated with G-nZVI-BC can effectively degrade PNP. • The green synthesis method further improved the dispersibility of Fe0 on biochar. • G-nZVI-BC prepared by the green synthesis method had long-term reactivity. • Radical and non-radical pathways promoted catalytic degradation of p-nitrophenol. • The waste of tea residues was fully utilized in the degradation. [ABSTRACT FROM AUTHOR]

Soil contamination due to chlorinated organics prompts an important environmental problem; however, the iron-based reduction materials and complicated ground environment are the main barriers to implementation and promotion of in situ soil remediation. Therefore, this study aims to evaluate the reductants zero-valent iron (ZVI) and its activated carbon composite (AC-ZVI) in terms of their self-oxidation and selectivity in soil experiments. The results indicated that saturated moisture conditions were beneficial for degradation due to the dispersal of the pollutants from soil particles. Particularly, increasing the water/soil ratio to the over-saturated state would decrease the selectivity of ZVI and AC-ZVI. Meanwhile, increasing the reductant loading decreased the selectivity of ZVI and AC-ZVI, whereas the high initial concentration increased the selectivity of AC-ZVI. In addition, the self-oxidation of ZVI (3.0 ×10 -3 h -1 ) is 4.2 times higher than that of AC-ZVI (0.7 ×10 -3 h -1 ), and the selectivity of AC-ZVI (48%) is 6.9 times higher than that of ZVI (7%), which confirmed that AC-ZVI is a superior iron-based amendment in saturated moisture conditions. Therefore, this study provides a reliable and feasible evaluation method for in situ remediation process, and deepens the understanding of the effects of moisture contents., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Microbial extracellular polymeric substances (EPS) significantly influence metal behavior in the environment, but the electron transfer reaction between EPS and copper that determine the speciation and fate of copper is lacking. Here, we investigated the role of EPS from Shewanella oneidensis MR-1, Bacillus subtilis , and Saccharomyces cerevisiae and its redox state in the Cu(II) reduction under anoxic conditions. Both pristine and reduced EPS mediated copper transformation from Cu(II) to Cu(I) within 10 min. The Cu(II) reduction efficiency by the reduced EPS was ten times higher than that by the pristine EPS, which could be ascribed to the varied electron transfer ability of EPS. Multiple spectroscopic results indicated that c -type cytochromes and O-/N-containing groups were effective redox moieties responsible for copper transformation. The c -type cytochromes contributed for about 80% to the overall electron flux in S. oneidensis MR-1 EPS, which was significantly higher than in B. subtilis (27%) and S. cerevisiae EPS (22%). In contrast, functional groups such as phenolic and amide, dominated Cu(II) reduction for the B. subtilis and S. cerevisiae EPS. This study emphasizes the significant contribution of microbial EPS that serve as reducing agents and electron transfer mediators for cupric reduction and cuprous formation in the natural environments. [Display omitted] • EPS served as electron donor and electron transfer media for Cu(II) reduction. • The reduction of Cu(II) to Cu(I) was controlled by the redox states of EPS. • Ratio of EPS/Cu concentration affected the Cu redox transformation kinetics. • The c -type cytochrome and O-/N-containing groups dominated Cu(II) reduction. • The electron flow for Cu(II) reduction was dependent on microbial species. [ABSTRACT FROM AUTHOR]

In this study, antibiotic bacteria residues (ABRs) is proposed as a novel green reducing agent and it is found that the reducing agent can realize the efficient recovery of the valuable metals in spent cathode powder (SCP), reduce the environmental pollution and realize the high-value utilization of the biomass waste. The leaching efficiency of Ni, Co, Mn and Li can reach 99.57%, 98.50%, 98.99% and 99.90% respectively under the optimal conditions of 3 mol L -1 H 2 SO 4 , mass ratio of ABRs to SCP of 0.8:1, liquid/solid ratio of 30:1 mL g -1 , the temperature of 363 K and time of 2.5 h. Leaching kinetics results shows that the reaction process is controlled by the chemical reaction with apparent activation energy exceeding than 40 kJ/mol. More importantly, the detailed ABRs leaching mechanism is proposed that the metabolite of CaC 2 O 4 and reducing sugar in ABRs provide a synergistic reduction effect on the recovery of valuable metals. Furthermore, acid leaching residue can be regenerated to obtain lithium-ion anode materials with excellent electrochemical properties. The entire process is a sustainable green recycling strategy by using waste ABRs waste to treat spent lithium-ion batteries (LIBs), recovering valuable metals efficiently and minimizing environmental pollution., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Researchers have been committed to reducing the hazardous pollutants by developing efficient catalysts while ignoring the pollution caused by the use of toxic surface capping agents, reductants and/or organic solvents in the catalyst preparation process. To alleviate such problems, we here report a novel one-step oxygenated functional group-driven electroless deposition strategy to synthesize clean and uniformly distributed Pd nanoparticles (NPs) using porous carbon nanosheets (PCN) as both substrates and reducing agents. It is observed that the oxygenated functional groups enriched PCN possesses a low work function and allows the spontaneous reduction of PdCl 4 2− ions to Pd NPs deposited on the PCN support (Pd/PCN). The particle size of Pd NPs can be flexibly modulated by simply controlling the immersing time and thereby their maximum catalytic performances can be achieved. Specifically, the optimal Pd/PCN-08 with a Pd loading of 3.0 wt% shows an excellent activity with a turnover frequency of 0.38 min−1 for electrocatalytic hydrodechlorination (ECH) of 4-chlorophenol (4-CP), superior to the previously reported materials. The stability of Pd/PCN-08 for 4-CP ECH is impressive in repetitive cycles. This work proposes a facile and efficient strategy to synthesize high-performance catalysts for detoxifying the hazardous organic pollutants. ga1 • The abundant oxygenated functional groups enable PCN with strong reducibility. • The spontaneous redox between PdCl 4 2− and PCN leads to the formation of Pd/PCN. • Pd/PCN-08 exhibited a high reaction constant of 3.9 × 10−2 min−1 toward 4-CP ECH. • The stability of Pd/PCN-08 for 4-CP ECH was impressive in repetitive cycles. [ABSTRACT FROM AUTHOR]

In this work, a Fenton-like system with MnO x -Fe 3 O 4 /biochar composite (FeMn/biochar) and reducing agents (RAs) was constructed for pollutant degradation, aiming to enhance Fenton-like performance from both degradation efficacy and operational cost aspects. Batch experiments revealed that five well-characterized RAs (sodium borohydride (SBH), sodium thiosulfate (STS), ascorbic acid (AA), hydroxylamine (HA) and oxalic acid (OA)) could impact performance of FeMn/biochar-H 2 O 2 system through multiple mechanisms, including variation of solution pH, competition for H 2 O 2 , electrostatic attraction and acceleration of metal redox cycle. Significantly, only OA and HA obviously enhanced the catalytic capacity of Fenton-like process and HA increased ciprofloxacin degradation efficiency from 38.2% to 92.8% with a low economic consumption as 4.16 US$/m3, well in agreement with the accelerated Fe(III/II) cycle and Mn(III/II) cycle in FeMn/biochar-H 2 O 2 -HA system. The accelerated metal redox cycle could enhance the decomposition of H 2 O 2 into •OH and •O 2 −, which were verified to be the main reactive oxygen species responsible for ciprofloxacin degradation by radical trapping experiments. Meanwhile, FeMn/biochar-H 2 O 2 -HA system could also work effectively in real wastewaters, and exhibited favorable catalytic performance towards oxytetracycline, tetracycline, methyl orange, methylene blue, Rhodamine B, and naphthalene, indicating the applicability of FeMn/biochar-H 2 O 2 -HA system in oxidizing refractory pollutants in wastewaters. ga1 • Influence mechanism of five reducing agents on FeMn/biochar-H 2 O 2 were studied. • HA enhanced CIP degradation to 92.8% via promoting Fe(II) and Mn(II) regeneration. • ROS played important role on organic pollutants degradation. • FeMn/biochar-H 2 O 2 -HA process was effective in degrading CIP in real wastewater. [ABSTRACT FROM AUTHOR]

• Both Na 2 S 2 O 4 and FeSO 4 are recommended for use in soil washing because of their ability to enhance the removal of heavy metals. • Na 2 S 2 O 4 removes more Cu and Zn than FeSO 4. • FeSO 4 removes more Ni than Na 2 S 2 O 4. • DOC solution encourages the removal of heavy metals while preserving most of the nutrients in the soil. • Chemical reductant washing coupled with DOC washing is a novel and effective technology for soil remediation. General acid washing is commonly used to treat heavy metal-contaminated soils, but it is sometimes difficult to achieve remediation aims in severely polluted soils. If we expose the surfaces of Fe oxide minerals to reductive dissolution during washing treatment, more of the metals initially adsorbed to these surfaces will be liberated, which may encourage the removal of heavy metals. Initially, the metal extraction capabilities of nine chemical reductants were compared in ten soil samples polluted by Cr, Cu, Zn, and Ni. Sodium dithionite (Na 2 S 2 O 4) and ferrous sulfate (FeSO 4) were screened for subsequent intensive research. In summary, the Na 2 S 2 O 4 solutions had higher Cr, Cu, and Zn removal rates than either the FeSO 4 or acid solution. Application of dissolved organic carbon (DOC) further increased the removal of heavy metals by complexation. About 15%, 86%, 32%, and 52% of the Cr, Cu, Zn, and Ni, respectively, were removed from the representative soil (M-2) by two-stage washing using 0.2 M Na 2 S 2 O 4 coupled with 1,500 mg L−1 DOC solution at pH 2.0. Meanwhile, most soil fertility was preserved: ammonium nitrogen was increased 3.9 times; the increase in exchangeable potassium was 33%; and the reduction in available P was only 10%. [ABSTRACT FROM AUTHOR]

• Dosing reducing agents resulted in enhanced pollutant degradation and expansion of pH range. • Dosing manner of RA was a key factor governing its roles in Fenton system. • Catalytic mechanisms of the three reducing agents in Fenton system were proposed. • Electrical energy per order was used to estimate the costs of three reducing agents. Fenton reaction is widely used for hazardous pollutant degradation. Reducing agents (RAs) have been proven to be efficient in promoting the generation of HO• in Fenton reaction by accelerating the redox cycle of Fe3+/Fe2+. However, the roles of different RAs in Fenton reaction remain unrevealed. In this work, the catalytic activity of three RAs, i.e., hydroxylamine (NH 2 OH), ascorbic acid (AA) and cysteine (Cys), on the degradation of benzoic acid (BA) and the hydroxyl radical formation in the Fenton-RAs system were investigated. Results show the catalytic performance of RAs in BA degradation by Fenton reaction followed an order of NH 2 OH > AA > Cys. Compared with the conventional Fenton system, the effective pH range in the Fenton-NH 2 OH system extended from 3.0 to 5.0, while the optimal pH in the Fenton-AA and Fenton-Cys systems ranged from 3.0 to 4.0. The Fenton-AA system exhibited a two-stage reaction toward BA degradation, which was different from the Fenton-NH 2 OH and Fenton-Cys systems. Furthermore, the dosing manner of AA was found to be a key factor governing its role in the Fenton-AA system. This observation suggests the different mechanisms behind the enhancement of the three RAs in Fenton system. Different from NH 2 OH and Cys, AA would inhibit the generation of HO•, especially at the fast stage of degradation process, where Fe3+ has not accumulated yet. In addition, the economic analysis using the electrical energy per order indicates Fenton-NH 2 OH system was economically feasible with the lowest energy input, compared to Fenton-AA and Fenton-Cys systems. These results are useful to better understand the roles of RAs in Fenton system, and also provide guidance about the selection and dosing manner of suitable RAs in the advanced oxidation processes. [ABSTRACT FROM AUTHOR]

• Residual ferrous causes underestimation of Cr(VI) leaching concentrations in TCLPs. • CLCRP is caused by the decline of this underestimation with time. • Natural flushing and oxygen-median oxidation reduce residual ferrous with time. • CLCRP disappears when this underestimation is corrected. • Residual ferrous and Cr(VI) are separated by precipitate layer in treated CBSM. Toxicity characteristic leaching procedure (TCLP) is a prevalent way to evaluate the treatment effectiveness for Cr(Ⅵ)-bearing solid matrices (CBSM). But when a certain amount of residual reductants are present in the treated CBSM, Cr(Ⅵ) leaching concentration rebound phenomenon (CLCRP) occurs, which invalidates the TCLP. This study explores the microstructure of ferrous-reduced CBSM and proves that the residual Cr(Ⅵ), Fe x Cr 1-x (OH) 3 precipitate and residual ferrous are separately distributed in a three-layer structure. In natural scenarios, the residual ferrous in the out-layer is firstly flushed away by rainfall and groundwater or oxidized by dissolved oxygen, resulting in the decrease of ferrous with time. Residual Cr(Ⅵ), due to being blocked by precipitate layer, is less flushed away. While in TCLP, all of released residual ferrous and Cr(Ⅵ) are in the leachate and react till one of them is almost exhausted, resulting in the underestimation of Cr(Ⅵ) leaching concentrations. The longer the samples experience the natural scenarios, the less of the residual ferrous, resulting in the decline of underestimation of Cr(Ⅵ) leaching concentrations with time. This study also provides a pretreatment which can effectively reduce the residual ferrous, achieving more accurate Cr(Ⅵ) leaching concentrations and eliminating CLCRP. [ABSTRACT FROM AUTHOR]

The aim of this study is to develop the process relies on the UV irradiation of ZnO and I - , i.e. UV/ZnO /I - (UZI), to create both oxidizer and reducer agents simultaneously for photo-degradation of the Ciprofloxacin (CIP). This paper shows that while applying UV irradiation, UV/ZnO and UV/I - for 20 min can lead to achieve 37.5%, 58.12%, and 61.4% photo-degradation of 100 mg L -1 CIP at pH 7, respectively. Moreover, the UZI treatment can provide 91.54% photo-degradation efficiency. The LC-MS analysis of the UZI effluent indicates that 10 min process was adequate to degrade CIP into simple ring-shaped metabolites while 15 min treatment, mostly of CIP intermediates were linear and biodegradable organic compounds. Furthermore, fourteen little fragments were identified in the CIP photo-degradation via UZI, during the photoreaction time of 2.5 to 20 min. Then, a pseudo first-order kinetics equation was utilized to model the observed photo-degradation process. Finally, the computational results show that the increased concentration of the CIP solution from 100 to 400 mg L -1 decreases the observed rate constant (k obs ) from 0.4125 to 0.2189 min -1 while increases the photoreaction rate (r obs ) from 41.25 to 87.56 mg L -1  min -1 ., (Copyright © 2019 Elsevier B.V. All rights reserved.)