Search

In this study, nZVI/LDH composites were prepared by loading nano zero-valent iron (nZVI) on layered double hydroxide (LDH) surface for adsorption coupled reduction of nitrate (NO 3 --N). The results showed that the removal of NO 3 --N and total nitrogen (TN) by the nZVI/LDH composites was 88.64% and 77.63%, respectively, with a selectivity of 55.21% for N 2 and only 1.86% for ammonia nitrogen (NH 4 +-N) within 180 min. The valence states of various N forms during the adsorption-reduction process were investigated. The mechanism of synergistic adsorption-reduction degradation of NO 3 --N was proposed by measuring the contents of NO 3 --N, nitrite (NO 2 --N), and NH 4 +-N in the aqueous and adsorbed phases in the reaction process, including rapid adsorption of initial NO 3 --N, chemical reduction of adsorbed NO 3 --N and resorption of the final product. The nZVI/LDH also maintained up to 82.56% NO 3 --N removal in natural water, with aging experiments proved that the composites maintained 60.48% NO 3 --N removal after 15 days. Therefore, the composites may have great application prospects for NO 3 --N removal in micro-polluted water. [Display omitted] • The nZVI/LDH composites was synthesized for removal of nitrate in micro-polluted water. • nZVI/LDH improved nitrogen selectivity and removed total nitrogen simultaneously. • The mechanism of synergistic adsorption-reduction removal of nitrate was proposed. • The nZVI/LDH composites showed stable and efficient performance in real water. [ABSTRACT FROM AUTHOR]

Mechanism of hexavalent chromium removal (Cr(VI) as CrO 4 2-) by the weak-base ion exchange (IX) resin ResinTech® SIR-700-HP (SIR-700) from simulated groundwater is assessed in the presence of radioactive contaminants iodine-129 (as IO 3 -), uranium (U as uranyl UO 2 2+), and technetium-99 (as TcO 4 -), and common environmental anions sulfate (SO 4 2-) and chloride (Cl-). Batch tests using the acid sulfate form of SIR-700 demonstrated Cr(VI) and U(VI) removal exceeded 97%, except in the presence of high SO 4 2- concentrations (536 mg/L) where Cr(VI) and U(VI) removal decreased to ≥ 80%. However, Cr(VI) removal notably improved with co-mingled U(VI) that complexes with SO 4 2- at the protonated amine sites. These U–SO 4 2- complexes are integral to U(VI) removal, as confirmed by the decrease in U(VI) removal (<40%) when the acid chloride form of SIR-700 was used instead. Solid phase characterization revealed that CrO 4 2- is removed by IX with SO 4 2- complexes and/or reduced to amorphous Cr(III)(OH) 3 at secondary alcohol sites. Tc(VII)O 4 - and I(V)O 3 - also undergo chemical reduction, following a similar removal mechanism. Oxyanion removal preference is determined by the anion reduction potential (CrO 4 2->TcO 4 ->IO 3 -), geometry, and charge density. For these reasons, 39% and 69% of TcO 4 - and 17% and 39% of IO 3 - are removed in the presence and absence of Cr(VI), respectively. [Display omitted] • SIR-700 weak-base IX resin with SO 4 2- parent anion removes ≥ 97% Cr(VI) and U(VI). • Cr(VI) is reduced to Cr(III)(OH) 3 phase at secondary alcohol sites. • Other anions also removed by IX and reduction, following the trend Cr(VI) > Tc(VII) > I(V). • U(VI) removed by complexation with SO 4 2- parent anion, Cl--form had low U(VI) uptake. [ABSTRACT FROM AUTHOR]

A shift beyond conventional environmental remediation to a sustainable pollutant upgrading conversion is extremely desirable due to the rising demand for resources and widespread chemical contamination. Electrochemical reduction processes (ERPs) have drawn considerable attention in recent years in the fields of oxyanion reduction, metal recovery, detoxification and high-value conversion of halogenated organics and benzenes. ERPs also have the potential to address the inherent limitations of conventional chemical reduction technologies in terms of hydrogen and noble metal requirements. Fundamentally, mechanisms of ERPs can be categorized into three main pathways: direct electron transfer, atomic hydrogen mediation, and electrode redox pairs. Furthermore, this review consolidates state-of-the-art non-noble metal cathodes and their performance comparable to noble metals (e.g., Pd, Pt) in electrochemical reduction of inorganic/organic pollutants. To overview the research trends of ERPs, we innovatively sort out the relationship between the electrochemical reduction rate, the charge of the pollutant, and the number of electron transfers based on the statistical analysis. And we propose potential countermeasures of pulsed electrocatalysis and flow mode enhancement for the bottlenecks in electron injection and mass transfer for electronegative pollutant reduction. We conclude by discussing the gaps in the scientific and engineering level of ERPs, and envisage that ERPs can be a low-carbon pathway for industrial wastewater detoxification and valorization. [Display omitted] • Electron transfer, atomic hydrogen, and dynamic redox pairs are three pathways of ERPs. • Rational design of non-noble catalysts is comparable to that of platinum group metal. • The charge-negativity and many transferred electrons lead to sluggish ERPs kinetics. • Pulsed current and flow-through overcome the limits of electron and mass transfer. • Research focused on the local pH environment near the cathode is suggested. [ABSTRACT FROM AUTHOR]

• By a redox process more than 97% Ni is recovered from waste of electroless industry. • The order of reagents in the process affects the amount of Ni removed. • By chemical precipitation spherical Ni magnetic particles are obtained. • The magnetic properties of the particles depend on their size and composition. • An oil based Ni particle´s suspension reveal interesting magnetoviscous effects. The discarded solutions by the chemical nickel industry have high amounts of nickel, this is why they are considered hazardous wastes for the health and the environment. On the other side, Ni particles can have potential applications in the developing of magnetorheological fluids currently being used to improve the performance of mechanical devices. The present study raises the treatment of a residual effluent from a chemical nickel industry by applying a chemical precipitation which uses sodium hypophosphite as a reducer, and varying the order of the reagents involved in the conditioning of the reaction with respect to the reducer. The recovered solids were studied using different material characterization techniques to recognize the chemical composition (X-Ray Fluorescence, Inductively Coupled Plasma Mass Spectrometry), crystallinity and morphology (X-Ray Diffraction, Scanning Electron Microscope), surface charge and size distribution (Dynamic Light Scattering). By the chemical reduction treatment it was possible to decrease the amount of nickel in the residual between 97.25% and 99.50%, obtaining Ni particles that were then tested to be used in magnetic fluids. To this purpose a suspension was prepared by mixing the Ni particles with silicone oil in a constant solid/liquid ratio, and the rheological behavior of this suspension was evaluated as a function of the magnetic field and the deformation applied, revealing an interesting magnetorheological behavior. [ABSTRACT FROM AUTHOR]

• Novel MMBC fabrication from RM and lignin wastes via one-step pyrolysis in N 2 atmosphere. • MMBC exhibited hierarchical porous structure, various functional groups, and metallic Fe. • Incorporated RM promoted syngas generation and hydrocarbons decomposition of lignin. • Demonstrated multifunctionality (adsorption, reduction, and catalysis) of MMBC. This study fabricated a new and multifunctional mixed metal-biochar composites (MMBC) using the mixture of two abundant industrial wastes, red mud (RM) and lignin, via pyrolysis under N 2 atmosphere, and its ability to treat wastewater containing various contaminants was comprehensively evaluated. A porous structure (BET surface area = 100.8 m2 g−1) was created and metallic Fe was formed in the MMBC owing to reduction of Fe oxides present in RM by lignin decomposition products during pyrolysis at 700 °C, which was closely associated with the transformation of liquid to gaseous pyrogenic products. The potential application of the MMBC was investigated for the removal of heavy metals (Pb(II) and Ni(II)), oxyanions (As(V) and Cr(VI)), dye (methylene blue), and pharmaceutical/personal care products (para-nitrophenol and p CBA). The aluminosilicate mineral, metallic Fe, and porous carbon matrix derived from the incorporation of RM and lignin contributed to the multifunctionality (i.e. , adsorption, chemical reduction, and catalytic reaction) of the MMBC. Thus, engineered biochar composites synthesized from selected industrial wastes can be a potential candidate for environmental applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel method was developed to improve the stability and reactivity of Fe0. • The oxidation of Fe0 was suppressed by Fe 3 C in the treatment of methyl orange. • Fe 3 C revealed an excellent removal efficiency for methyl orange in a wide pH range. Abstract The efficiency of zero-valent iron (Fe0) for the degradation of contaminants in water or soil can be highly reduced by side reactions with oxygen or water. This work was conducted to test whether this drawback can be effectively suppressed by the carbonation of Fe0 with pyrolyzed biomass, which forms a Fe 3 C composite. The composite Fe 3 C was characterized and its reactivity and stability were assessed in batch tests with methyl orange (MO) as a model pollutant. The results indicated that the removal rate of MO on Fe 3 C composite was higher than that of Fe0 (7.587 mg/(g·min) vs. 4.306 mg/(g·min)) at pH 4, where the degradation mechanism was confirmed by high-performance liquid chromatography-mass spectrometry. More importantly, the produced iron oxide in the Fe 3 C composite was highly suppressed. Regeneration studies showed that after three times of cycling, the removal efficiency of MO on Fe 3 C composite was kept to 99.42%, but Fe0 almost lost its reactivity. In situ chemical reduction of a colorimetric redox probe (indigo-5, 5′-disulfonate, I2S) quantitatively demonstrated that Fe 3 C composite has the reduction kinetics of I2S obviously slower than Fe0, indicating that Fe 3 C composite improved the stability of incorporated Fe0 to resist the side oxidation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ag/Bi°-BiVO 4 catalysts with multi-active sites were fabricated toward high-efficient reduction of aromatic nitrobenzene. • The catalysts presented excellent catalytic activity and good stability to 4-NP reduction. • The BiVO 4 , Bi° and Ag offered multi-active sites to synergistically act on the reduction of nitrophenol. Abstract In this work, we report on the preparation of silver nanoparticles modified bismuth/bismuth vanadate (Bi°-BiVO 4) catalyst with multi-active sites toward efficient reduction of aromatic nitrobenzene, aiming to tailor the synergistic effects of multi-active sites and specify the underlying catalytic mechanism. The as-prepared catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray and X-ray photoelectron spectroscopy. It is observed that Ag nanoparticles with diameter of ˜30 nm were anchored evenly on the surface of rod-shaped BiVO 4 , which offered multi-active sites to contact with the reactants effectively and transfer interfacial electron to 4-nitrophenol (4-NP) rapidly. The activity factor k of Ag/Bi°-BiVO 4 for 4-NP reduction is estimated to ˜3933.4 min−1 g−1, which is much higher than that obtained from pristine BiVO 4 catalyst, Bi° and noble metal Ag nanoparticles. According to the experimental results, the reaction mechanism and reaction path of 4-NP reduction for BiVO 4 , Bi and Ag were studied through the density functional theory (DFT) theoretical calculation, which suggested that they exhibit synergistic catalytic effect in the reaction process. This work may provide a feasible foundation for the mechanism research of semiconductor reduction to 4-nitrophenol. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The first derivative of XANES for As(III) adsorbed systems of all adsorbents are observed to have with mixed oxidation. • As(V) adsorbed samples of Ni, and Cu systems agree with that of As(V) standards. • Both reduction and oxidation behavior of arsenic is observed on to these metal oxide adsorbents. • EXAFS analysis was observed with As O bond distances in the range of 1.7–1.8 Å. • The As-M bond distances are around 2.7, 3.2 and 3.6 Å confirmed the formation of surface complexes. Abstract The present study is about surface complexation behavior of arsenic species adsorbed onto ternary metal oxide adsorbents (Ni-Al-Fe, Co-Al-Fe, Mn-Al-Fe, and Cu-Al-Fe). The analysis is carried out by X-ray absorption spectroscopy (XAS) tool. XANES (μ(E) vs. E) spectra close to the absorption edge (i.e., As K -edge) of all samples are observed along with the As(III) and As(V) standards. The first derivative of XANES for Ni-As(V), and Cu-As(V) samples agree with that of As(V) standards, respectively. Whereas, As(III) adsorbed adsorbent systems (i.e., Ni, Co, Mn, and Cu) are observed with mixed oxidation state of arsenic. A total of 65–85 % is observed with initial oxidation state (As(III) or As(V)), and remaining 15–35 % is observed with modified oxidation state (As(V) or As(III)) that explains the occurrence of possible charge transfer. EXAFS analysis shows the As-O bond distances in the range of 1.7–1.8 Å. The corresponding As-M bond distances are around 2.7, 3.2, and 3.6 Å which confirms the formation various edge sharing (2E), and corner sharing (2C, 1V) surface complexes. Surface coverage is understood as an important parameter as bidentate attachments (2E, 2C) are evident in As(III), and As(V), but monodentate attachments (1V) are only observed in As(V). [ABSTRACT FROM AUTHOR]

Chromium (Cr) is a highly toxic element, which is widely present in environment due to industrial activities. One of most applicable technique to clean up Cr pollution is chemical reduction. However, the Cr(VI) concentration in soil increases again after remediation, and meanwhile the yellow soil would appear, which is commonly called as "yellowing" phenomenon. To date, the reason behind the phenomenon has been disputed for decades. This study aimed to introduce the possible "yellowing" mechanism and the influencing factors based on the extensive literature review. In this work, the concept of "yellowing" phenomenon was explained, and the most potential reasons include the reoxidation of manganese (Mn) oxides and mass transfer were summarized. Based on the reported finding and results, the large area of "yellowing" is likely to be caused by the re-migration of Cr(VI), since it could not sufficiently contact with the reductant under the effects of the mass transfer. In addition, other driving factors also control the occurrence of "yellowing" phenomenon. This review provides valuable reference for the academic peers participating in the Cr-contaminated sites remediation. [Display omitted] • Mn-based oxides is the most important pathway in Cr(III) reoxidation. • Mass transfer is an important reason for "yellowing" phenomenon in sites. • Measurement error of Cr(VI) misleads monitoring and underestimates "yellowing". [ABSTRACT FROM AUTHOR]

With a similar structure to perfluorooctane sulfonate (PFOS), 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFAES) has been widely used as a mist suppressant in the chromium plating industry in China since the 1970s. After being disregarded for the past 30 years, 6:2 Cl-PFAES has now been detected in environmental matrices and human sera, suggesting potential health concerns. We carried out a subchronic exposure study to investigate the reproductive toxicity of 6:2 Cl-PFAES exposure (0, 0.04, 0.2, and 1.0 mg/kg/d body weight, 56 d) in adult male BALB/c mice. Results showed that relative epididymis and testis weights decreased in the 1.0 mg/kg/d group compared with the control. However, no changes were observed in the serum levels of testosterone, estradiol, follicle-stimulating hormone (FSH), or luteinizing hormone (LH), nor in the histopathological structure of the epididymis and testis and sperm count. In addition, 56 d of consecutive gavage of 1.0 mg/kg/d of 6:2 Cl-PFAES did not affect male mouse fertility. RNA sequencing showed that no genes were significantly altered in the testes after 6:2 Cl-PFAES exposure. Several testicular genes, which are sensitive to PFOS exposure, were also detected using Western blotting, and included steroidogenic proteins, STAR, CYP11A1, CYP17A1, and 3β-HSD and cell junction proteins, occludin, β-catenin, and connexin 43; however, none were changed after 6:2 Cl-PFAES exposure. Except for a decrease in the relative epididymis and testis weights in the 1.0 mg/kg/d group, 6:2 Cl-PFAES exposure for 56 d exerted no significant effect on the serum levels of reproductive hormones or the testicular mRNA profilesin adult male mice, implying a relative weak reproductive injury potential compared with that of PFOS. [ABSTRACT FROM AUTHOR]

This study aims at investigating the efficiency and kinetics of 2,4-DCP degradation via advanced reduction processes (ARP). Using UV light as activation method, the highest degradation efficiency of 2,4-DCP was obtained when using sulphite as a reducing agent. The highest degradation efficiency was observed under alkaline conditions (pH = 10.0), for high sulphite dosage and UV intensity, and low 2,4-DCP concentration. For all process conditions, first-order reaction rate kinetics were applicable. A quadratic polynomial equation fitted by a Box-Behnken Design was used as a statistical model and proved to be precise and reliable in describing the significance of the different process variables. The analysis of variance demonstrated that the experimental results were in good agreement with the predicted model (R 2  = 0.9343), and solution pH, sulphite dose and UV intensity were found to be key process variables in the sulphite/UV ARP. Consequently, the present study provides a promising approach for the efficient degradation of 2,4-DCP with fast degradation kinetics. [ABSTRACT FROM AUTHOR]

A cleaner process is tremendously required to deal with the vanadium tailings, which may cause serious environmental problem due to the high content of water soluble hazardous elements such as V and Cr. This problem can be possibly solved by proposed high temperature reduction–magnetic separation process, in which, V, Cr and Fe can be recycled as ferroalloy. The thermodynamic calculation results reveal that a higher temperature (>1127.8 °C) promotes the reduction of Fe, V and Cr, and improves the recovery rates of V and Cr in liquid iron. The reduction behavior of vanadium tailings was investigated using XRD, TG/DSC, SEM, EDS and ICP-OES techniques. The EDS results show that a small portion of V was remained in the slag phase when roasted at 1300 °C, while nearly all of V and Cr can concentrate in ferroalloy at 1400 °C. Approximatly 90% of V and 95% of Cr recovery in magnetic fraction can be obtained for the magnetic separation step. A small portion of V and Cr is remained in the non-magnetic final tailings, however, the hazardous potential assessments results indicate that such kind of tailings can safely use as secondary materials or stockpiled as an end-waste. [ABSTRACT FROM AUTHOR]

Nitrate and radioiodine ( 129 I) contamination is widespread in groundwater underneath the Central Plateau of the Hanford Site. 129 I, a byproduct of nuclear fission, is of concern due to a 15.7 million year half-life, and toxicity. The Hanford 200 West Area contains plumes covering 4.3 km 2 with average 129 I concentrations of 3.5 pCi/L. Iodate accounts for 70.6% of the iodine present and organo-iodine and iodide make up 25.8% and 3.6%, respectively. Nitrate plumes encompassing the 129 I plumes have a surface area of 16 km 2 averaging 130 mg/L. A nitrate and iodate reducing bacterium closely related to Agrobacterium , strain DVZ35, was isolated from sediment incubated in a 129 I plume. Iodate removal efficiency was 36.3% in transition cultures, and 47.8% in anaerobic cultures. Nitrate (10 mM) was also reduced in the microcosm. When nitrate was spiked into the microcosms, iodate removal efficiency was 84.0% and 69.2% in transition and anaerobic cultures, respectively. Iodate reduction was lacking when nitrate was absent from the growth medium. These data indicate there is simultaneous reduction of nitrate and iodate by DVZ35, and iodate is reduced to iodide. Results provide the scientific basis for combined nitrogen and iodine cycling throughout the Hanford Site. [ABSTRACT FROM AUTHOR]

Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosphogypsum stack was examined by pore-water and solid analysis, selective extractions, microscopy and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The negative impact of this stack on estuarine environments is a concerning problem. In the weathering profile, total concentrations of most pollutants increase with depth; instead, dissolved contents in pore-waters increase to middle of the saturated zone but then decrease drastically down to reach the marsh due to sulfide precipitation. Excess of acid-volatile sulfide plus pyritic sulfur over metals bound to the oxidizable fraction indicates that sulfide precipitation is the main mechanism responsible for metal removal in the marsh. Thus, abundant pyrite occurred as framboidal grains, in addition to other minor sulfides of As, Zn and Cu as isolated particles. Moreover, high contents of elemental sulfur were found, which suggest partial sulfide oxidation, but marsh may have capacity to buffer potential release of contaminants. The importance of sulfur species was quantitatively confirmed by XANES, which also supports the accuracy of selective extraction schemes. Accordingly, managing pore-water quality through organic carbon-rich amendments over phosphogypsum stacks could lead to a decrease in contaminant loading of leakages resulting from weathering. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO 2 ) nanoparticles have been applied in diverse commercial products, which could lead to toxic effects on aquatic microbes and would inhibit some important ecosystem processes. The study aimed to investigate the chronic impacts of TiO 2 nanoparticles with different concentrations (5, 50, and 500 mg L −1 ) on Populus nigra L. leaf decomposition in the freshwater ecosystem. After 50 d of decomposing, a significant decrease in decomposition rates was observed with higher concentrations of TiO 2 nanoparticles. During the period of litter decomposition, exposure of TiO 2 nanoparticles led to decreases in extracellular enzyme activities, which was caused by the reduction of microbial especially fungal biomass. In addition, the diversity and composition of the fungal community associated with litter decomposition were strongly affected by the concentrations of TiO 2 nanoparticles. The diversity and composition of the fungal community associated with litter decomposition was strongly affected. The abundance of Tricladium chaetocladium decreased with the increasing concentrations of TiO 2 nanoparticles, indicating the little contribution of the species to the litter decomposition. In conclusion, this study provided the evidence for the chronic exposure effects of TiO 2 nanoparticles on the litter decomposition and further the functions of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Finding the materials, which help to control the water pollution caused by organic and bacterial pollutants is one of the challenging tasks for the scientific community. 2D sheets of WO 3 and composite of WO 3 and reduced graphene oxide (rGO) have been synthesized in a well-controlled way using a hydrothermal method. The as synthesized 2D sheet of WO 3 and rGO-WO 3 composite were characterized by various techniques. The 2D sheets of WO 3 and rGO-WO 3 composite are efficiently utilized for the photocatalytic degradation of methylene blue (MB) and Rhodamine B (RhB) dyes under sunlight. The rGO-WO 3 composite reveals excellent photocatalytic degradation of RhB dye by degrading it upto 85% under sunlight. However, the MB dye was degraded by 32%. The greater degradation of RhB dye was explained in terms of the molecular electrostatic potential. We found that RhB has a more positive potential compared to MB dye where O 2 − and OH ̊ radicals interact more strongly, resulting in a greater degradation of the RhB dye. The antibacterial activity of the 2D sheets of WO 3 and rGO-WO 3 composite was also investigated on gram positive ( B. subtilis ) and gram negative ( P. aeroginosa ) microbes for the first time. [ABSTRACT FROM AUTHOR]

The large amount of synthetic dyes in effluents is a serious concern to be addressed. The chemical reduction is one of the potential way to resolve this problem. In this study, linear and crosslinked polyurethanes i.e. LPUR & CLPUR were synthesized from toluene diisocyanate (TDI), polyethylene glycol (PEG;1000 g/mole) and tetraethylenepentamine (TEPA). The structure and morphology of synthesized materials were examined by FTIR, SEM and BET. The CLPUR was found stable in aqueous system with 0.80 g/cm 3 density and 16.4998m 2 g −1 surface area. These materials were applied for the reduction of methylene blue in presence of NaBH 4 . Both, polymers catalyzed the process and showed 100% reduction in 16 and 28mins., respectively, while, the reduction rate was significantly low in absence of these materials, even after 120mins. Furthermore, negligible adsorption was observed with only 7% removal of dye. The best reduction rates were observed at low concentration of dye, increasing concentration of NaBH 4 and with more dosage of polymeric catalyst. The kinetic study of process followed zero order kinetics. It was hence concluded that both synthesized polymers played a catalytic role in reduction process. However, stability in aqueous system and better efficiency in reduction process endorsed CLPUR as an optimal choice for further studies. [ABSTRACT FROM AUTHOR]

The present works demonstrate the formation of reduced graphene oxide (r-GO) and aminopyridine (r-GO-(AmPy) n ) hybrid by submerged liquid plasma process. Raman spectra shows the ID/IG ratio of GO, r-GO and r-GO-(AmPy) n are 2.2, 1.91 and 2.0, respectively. The decrease in ID/IG ratio of r-GO clearly indicate the reduction of oxygen functional groups and restoration of sp 2 network in r-GO domain. The pyridinic and pyrrolic functional group present in rGO-(AmPy) n hybrids shows a distinct redox peaks in cyclic voltameter at the scan rates of 5, 10 and 25 mV/s. The r-GO-(AmPy) n hybrid displayed an excellent electrochemical performance with a high specific capacitance of 418, 400 and 381 F/g at the current densities of 0.1, 0.2 and 0.3 A/g, respectively. Electro chemical generation of H 2 O 2 at the rGO-(AmPy) n surface was evaluated and found to be 0.72 mmol for the fixed reaction time of 60 min. Similarly, conversion of H 2 O 2 to OH radical with a coated Fe 3 O 4 plate catalyst was found to be 0.15 mmol. A H 2 O 2 / OH radicals generated in the electrochemical cell was used for the degradation of methyl parathion. During the degradation (7.5 mg/L), two intermediates like methylparaoxon, and p-nitrophenol were identified by the Gas Chromatography and Mass Spectrometer analysis. [ABSTRACT FROM AUTHOR]

We developed a novel stabilized nanoscale zerovalent iron (NZVI) particles with Ni using an electron conducting polymer, polyvinylpyrrolidone (PVP), to selectively dechlorinate trichloroethylene (TCE) to non-toxic intermediates. The size of the PVP stabilized NZVI-Ni ((PVP-NZVI-Ni), average diameter: ∼20 nm) is smaller than that of bare NZVI (50–80 nm) due to the prevention of agglomeration of the resultant iron particles by PVP. PVP-NZVI-Ni showed a complete removal of TCE in 1 h with superior dechlorination kinetics ( k obs = 5.702 h −1 ) and ethane selectivity (98%), while NZVI-Ni showed 5 times slower dechlorination kinetics (1.218 h −1 ). Other PVP-NZVI-metals (i.e., Cu, Sn, Co, and Mn) also enhanced the TCE dechlorination, but they were much slower ( k obs = 0.024−0.411 h −1 ) than that of PVP-NZVI-Ni. In column test, PVP-NZVI-Ni exhibited better mobility (95% of PVP-NZVI-Ni recovery in the eluent) than NZVI-Ni (1%). In addition, PVP-NZVI-Ni reductively transform TCE to ethane even under 10 cycles of repeated TCE dechlorination treatment. [ABSTRACT FROM AUTHOR]

Perfluorooctanoic acid (PFOA) is widespread in the environment, which causes serious health and safety concerns. A mechanistic study on reductive defluorination of PFOA by titanium(III) citrate in the presence of catalysts was conducted. Vitamin B 12 was used to catalyze reduction reactions by shuttling electrons from a reducing agent (electron donor) to PFOA to produce a Co-carbon bond intermediates. In the presence of copper nanoparticles, a precursor complex, B 12 -C 7 F 14 COOH, adsorbed on the metal surface, followed by a hydrogenolytic reaction to form less-fluorinated products. The synergistic effect between vitamin B 12 and copper nanoparticles enhances the reductive activities by electron-transfer reactions and hydrogenolysis. The efficient reduction of PFOA to less-noxious compounds was demonstrated with a copper dose of 2 g L −1 , titanium(III) citrate (45 mM), and vitamin B 12 (0.2 mM) with an initial pH of 9.0 and 70 °C. In this anoxic aqueous solution, the biomimetic reductive system effectively removed 65% of PFOA. The mass balance on fluoride matched the observed degradation of PFOA, while no short-chain intermediates were detected. [ABSTRACT FROM AUTHOR]

In this study, a novel strategy was developed to fabricate highly flame retardant polymer foam composite materials coated by synthesized silicone resin (SiR) polymer via a facile dip-coating processing. Applying the SiR polymer coating, the mechanical property and thermal stability of SiR-coated polymer foam (PSiR) composites are greatly enhanced without significantly altering their structure and morphology. The minimum oxygen concentration to support the combustion of foam materials is greatly increased, i.e. from LOI 14.6% for pure foam to LOI 26–29% for the PSiR composites studied. Especially, adjusting pendant group to Si O Si group ratio (R/Si ratio) of SiRs produces highly flame retardant PSiR composites with low smoke toxicity. Cone calorimetry results demonstrate that 44–68% reduction in the peak heat release rate for the PSiR composites containing different R/Si ratios over pure foam is achieved by the presence of appropriate SiR coating. Digital and SEM images of post-burn chars indicate that the SiR polymer coating can be transformed into silica self-extinguishing porous layer as effective inorganic barrier effect, thus preserving the polymer foam structure from fire. Our results show that the SiR dip-coating technique is a promising strategy for producing flame retardant polymer foam composite materials with improved mechanical properties. [ABSTRACT FROM AUTHOR]

The present study, a novel haloalkaliphilic Cr(VI) tolerant bacterial strain, Cellulosimicrobium funkei AR8, was isolated and characterized for its high Cr(VI) reduction. In batch experiments, Cr(VI) reduction was evaluated under different parametric conditions which include different pH (5–9), temperature (25–45 °C), NaCl (0–3%) and Cr(VI) concentrations (100–250 μg/ml). Variations in the cell surface functional groups and morphology of the bacterial cells after Cr(VI) reduction were characterized by FT-IR and SEM–EDX. FT–IR analysis revealed that cell surface functional groups such as alkanes, amide and amines are involved in chromium biosorption and SEM–EDX results showed that biosorption and immobilization of chromium species on the cell surface. Bioconversion of Cr(VI) into Cr(III) by strain AR8 was confirmed by XRD and Raman spectroscopy analysis. Intracellular localization of reduced product (Cr(III)) was visualized by TEM analysis. Various instrumentation analysis verified that Cr(VI) removal mechanism of C. funkei AR8 strain was achieved by both extra and intracellular reducing machinery. Toxicity study revealed that the bacterially reduced product exerted less toxic effects on phenotypic, survival (91.31%), hatching (84.04%) and heart function (115 ± 1.03 beats/min) of zebrafish ( Danio rerio ) embryos. Higher Cr(VI) reducing ability of the strain under haloalkaliphilic condition suggests the C. funkei AR8 as a novel and efficient strain for remediating Cr(VI) contaminated industrial effluents with high salinity and alkalinity. [ABSTRACT FROM AUTHOR]

The widespread distribution of chromium(VI) in the environment leads to groundwater contamination. The use of iron sulfide (FeS) to remove Cr(VI) has therefore been proposed. However, aggregation is one of the main problems associated with the use of FeS nanoparticles prepared by traditional methods In this study, we used sodium alginate (SA) to stabilize FeS nanoparticles (FeS-SA). SA could prevent aggregation of FeS by the concurrent electrostatic repulsion and steric hindrance. Homogeneously dispersed FeS-SA nanoparticles 100 nm in diameter were observed. FeS-SA showed high efficiency in Cr(VI) removal, corresponding to an enhancement of efficiency from 65% (7.50 mmol Cr(VI) per g FeS) to 100% (11.54 mmol Cr per g FeS) relative to that achieved with naked FeS. Analysis of reaction products by X-ray diffraction and X-ray photoelectron spectroscopy revealed the co-existence of α-FeOOH, S 8 , and Cr(OH) 3 that apparently were introduced by Fe(II), S(−II), and Cr(VI), respectively. In-depth analysis of the removal mechanism revealed that reduction and adsorption respectively account for 82% and 18% of the Cr removal. In addition, higher pH and CaCl 2 concentration resulted in lower removal efficiency. This study provides a promising application of SA in enhancing FeS reactivity for the remediation of groundwater pollution. [ABSTRACT FROM AUTHOR]

As a major byproduct generated in the alumina industry, bauxite ore residue is an important reserve of scandium and titanium. In this study, the feasibility and mechanism of enriching Sc 2 O 3 and TiO 2 from a non-magnetic material, which was obtained from carbothermal reductive roasting and magnetic separation of bauxite ore residue, were investigated based on a two-step (acidic and alkali) leaching process. It was revealed that approximately 78% SiO 2 and 30–40% of CaO, FeO and Al 2 O 3 were removed from a non-magnetic material with 0.0134 wt.% Sc 2 O 3 and 7.64 wt.% TiO 2 by phosphoric acidic leaching, while about 95% Al 2 O 3 and P 2 O 5 were further leached by subsequent sodium hydroxide leaching of the upper-stream leach residue. A Sc 2 O 3 -, TiO 2 - rich material containing 0.044 wt.% Sc 2 O 3 and 25.5 wt.% TiO 2 was obtained, the recovery and the enrichment factor of Sc 2 O 3 and TiO 2 were about 85% and 5, respectively. The enrichment of Sc 2 O 3 was attributed to higher pH (>3.3) of phosphoric acid solution than its dissolution pH 0 , and the enrichment of TiO 2 was mainly associated with the insoluble perovskite (CaTiO 3 ) in the acidic solution at ambient temperature. As Sc 2 O 3 and TiO 2 cannot be dissolved in the alkali solution, they were further enriched in the leach residue. [ABSTRACT FROM AUTHOR]

In the present research, we aimed to fabricate a novel electrochemical sensor based on Cu metal nanoparticles on the multiwall carbon nanotubes-reduced graphene oxide nanosheets (Cu/MWCNT/RGO) for individual and simultaneous determination of nitrite and nitrate ions. The morphology of the prepared nanocomposite on the surface of glassy carbon electrode (GCE) was characterized using various methods including scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy. Under optimal experimental conditions, the modified GCE showed excellent catalytic activity toward the electro-reduction of nitrite and nitrate ions (pH = 3.0) with a significant increase in cathodic peak currents in comparison with the unmodified GCE. By square wave voltammetry (SWV) the fabricated sensor demonstrated wide dynamic concentration ranges from 0.1 to 75 μM with detection limits (3S b /m) of 30 nM and 20 nM method for nitrite and nitrate ions, respectively. Furthermore, the applicability of the proposed modified electrode was demonstrated by measuring the concentration of nitrite and nitrate ions in the tap and mineral waters, sausages, salami, and cheese samples. [ABSTRACT FROM AUTHOR]

Bromate (BrO 3 − ) is a possible human carcinogen regulated at a strict standard of 10 μg/L in drinking water. Various techniques to eliminate BrO 3 − usually fall into three main categories: reducing bromide (Br − ) prior to formation of BrO 3 − , minimizing BrO 3 − formation during the ozonation process, and removing BrO 3 − from post-ozonation waters. However, the first two approaches exhibit low degradation efficiency and high treatment cost. The third workaround has obvious advantages, such as high reduction efficiency, more stable performance and easier combination with UV disinfection, and has therefore been widely implemented in water treatment. Recently, advanced reduction processes (ARPs), the photocatalysis of BrO 3 − , have attracted much attention due to improved performance. To increase the feasibility of photocatalytic systems, the focus of this work concerns new technological developments, followed by a summary of reducing agents, activation methods, operational parameters, and applications. The reaction mechanisms of two typical processes involving UV/sulfite homogeneous photocatalysis and UV/titanium dioxide heterogeneous photocatalysis are further summarized. The future research needs for ARPs to reach full-scale potential in drinking water treatment are suggested accordingly. [ABSTRACT FROM AUTHOR]

Most of the previously reported studies have focused on the change in the size, morphology, and composition of metal nanocatalysts for improving their catalytic activity. Herein, we report poly(diallyldimethylammonium chloride) [PDDA]-stabilized nanoparticles (NPs) of platinum (Pt) and palladium (Pd) as highly active and efficient catalysts for hydrogenation of 4-nitrophenol (4-NP) in the presence of NaBH4. PDDA-stabilized Pt and Pd NPs possessed similar particle size and same facet with citrate-capped Pt and Pd NPs, making this study to investigate the inter-relationship between catalytic activity and surface ligand without the consideration of the effects of particle size and facet. Compared to citrate-capped Pt and Pd NPs, PDDA-stabilized Pt and Pd NPs exhibited excellent pH and salt stability. PDDA could serve as an electron acceptor for metal NPs to produce the net positive charges on the metal surface, which provide strong electrostatic attraction with negatively charged nitrophenolate and borohydride ions. The activity parameter and rate constant of PDDA-stabilized metal NPs were higher than those of citrate-capped metal NPs. Compared to the previously reported Pd nanomaterials for the catalysis of NaBH4-mediated reduction of 4-NP, PDDA-stabilized Pd NPs exhibited the extremely high activity parameter (195 s −1 g −1 ) and provided excellent scalability and reusability. [ABSTRACT FROM AUTHOR]

Nano particles Fe, Cu/Fe and Mn/Fe supported on NaY zeolite (F@Y, CF@Y, and MF@Y) were prepared by two-step processes consisting of ion exchange and liquid-phase reduction. The characterization by XRD, SEM-EDX and BET-N 2 adsorption demonstrated that Fe, Cu/Fe and Mn/Fe nano particles were successfully loaded onto NaY zeolite and exhibited larger BET surface area compared to nano-Fe 0 (nZVI). Laboratory experiments showed that nitrate removal by metals@Y in unbuffered conditions reached nearly 100% at a dosage of 4 g/L after 6 h of reaction. Moreover, the nitrate removal was not sensitive to the initial solution pH. Even at a high pH of 9.0, metals@Y exhibited nitrate reduction above 94%. CF@Y demonstrated high N 2 selectivity, due to the high content of Cu (20 wt%) and Fe (41 wt%) in CF@Y and the highly active metallic sites on its surface with positive charge. Kinetic data showed a good fit to a first-order kinetic model during early reaction times. A close fit to both a second-order and an nth-order kinetic model was shown for the whole of the reaction period. The data suggest that both liquid phase mass transfer and the intrinsic reaction rate control the process of nitrate reduction by metals@Y. [ABSTRACT FROM AUTHOR]

In this study, liquid culture systems containing rhamnolipid-solubilized, separate-phase, and multi-state hexadecane as the carbon source were employed for examining the effect of rhamnolipid solubilization on the bioavailability of hexadecane. Experimental results showed that the uptake of rhamnolipid-solubilized hexadecane by Pseudomonas aeruginosa ATCC 9027, a rhamnolipid producing strain, was enhanced compared to the uptake of mass hexadecane as a separate phase, indicating rhamnolipid solubilization increased the bioavailability of hexadecane for this bacterium. For Pseudomonas putida CICC 20575 which does not produce but degrade rhamnolipid, the uptake of either rhamnolipid-solubilized hexadecane or multi-state hexadecane was inhibited. The reduction of bioavailability was assumed to be the consequence of the blocking effect caused by the partition of rhamnolipid molecules at the hexadecane-water interface. The results show that how rhamnolipid solubilization changes the bioavailability of hexadecane depends on the bacterial compatibility to rhamnolipid. The study adds insight into the knowledge of biosurfactant-associated bioavailability of hydrophobic organic compounds (HOCs), and is of importance for application of biosurfactants in bioremediation of HOCs. [ABSTRACT FROM AUTHOR]

In this study, a novel process for the removal of toxic lead from the CRT funnel glass and synchronous preparation of high silica glass powder was developed by a carbon-thermal reduction enhanced glass phase separation process. CRT funnel glass was remelted with B 2 O 3 in reducing atmosphere. In the thermal process, a part of PbO contained in the funnel glass was reduced into metallic Pb and detached from the glass phase. The rest of PbO and other metal oxides (including Na 2 O, K 2 O, Al 2 O 3, BaO and CaO) were mainly concentrated in the boric oxide phase. The metallic Pb phase and boric oxide phase were completely leached out by 5 mol/L HNO 3 . The lead removal rate was 99.80% and high silica glass powder (SiO 2 purity >95 wt%) was obtained by setting the temperature, B 2 O 3 added amount and holding time at 1000 °C, 20% and 30 mins, respectively. The prepared high silicate glass powders can be used as catalyst carrier, semipermeable membranes, adsorbents or be remelted into high silicate glass as an ideal substitute for quartz glass. Thus this study proposed an eco-friendly and economical process for recycling Pb-rich electronic glass waste. [ABSTRACT FROM AUTHOR]

Herein, we report rGO/Fe 3 O 4 nanocomposites (NCs) free from noble metals, synthesized by facile one step chemical reduction method, for electrochemical detection of arsenite in water by square wave anodic stripping Voltammetry (SWASV). The synthesized NCs were characterized for its optical, morphological and structural properties. The NCs modified glassy carbon (GCE), NCs/GCE, electrodes showed a higher sensitivity (0.281 μA/ppb) and lower LOD (0.12 ppb) under optimized experimental conditions. The proposed NCs/GCE electrodes show no interference towards arsenite species in the presence of common cationic interferants, namely, Cu(II), Pb(II), Ni(II), Co(II), Cd(II), Cr(II), Zn(II), etc. In addition, the proposed electrode demonstrates a good stability, reproducibility and potential practical application in electrochemical detection of arsenite. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated that the rate at which Fe(II)-Fe(III) oxyhydroxide systems catalyze the reduction of reducible contaminants, such as 4-chloronitrobenzene, is well correlated to their thermodynamic reduction potential. Here we confirm this effect in the presence of Fe(III) oxyhydroxide phases not previously assessed, namely ferrihydrite and nano-goethite, as well as Fe(III) oxyhydroxide phases previously examined. In addition, silicate is found to decrease the extent of Fe(II) sorption to the Fe(III) oxyhydroxide surface, increasing the reduction potential of the Fe(II)-Fe(III) oxyhydroxide suspension and, accordingly, decreasing the rate of 4-chloronitrobenzene reduction. A linear relationship between the reduction potential of the Fe(II)-Fe(III) oxyhydroxide suspensions and the reduction rate of 4-chloronitrobenzene (normalized to surface area and concentration of sorbed Fe(II)) was obtained in the presence and absence of silicate. However, when ferrihydrite was doped with Si (through co-precipitation) the reduction of 4-chloronitrobenzene was much slower than predicted from its reduction potential. The results obtained have significant implications to the likely effectiveness of naturally occurring contaminant degradation processes involving Fe(II) and Fe(III) oxyhydroxides in groundwater environments containing high concentrations of silicate, or other species which compete with Fe(II) for sorption sites. [ABSTRACT FROM AUTHOR]

The chemical precipitation of Ni ions from industrial wastewater at alkaline pH values creates waste chemical sludge (e.g., Ni(OH) 2 ). We herein focused on Ni removal via chemical reduction using dithionite, by converting Ni(II) to its elemental or other valuable forms. Without the presence of a chelator (e.g., citrate), the nickel reduction efficiency increased with increasing dithionite:Ni molar ratio, reaching ∼99% at ratios above 3:1. The effect of pH on Ni reduction was in agreement with the standard redox potentials (pe 0 ) of dithionite, which became more negative with an increase in pH leading to greater Ni reduction efficiencies. With the formation of Ni-citrate chelates, however, the Ni reduction deteriorated. Elevated pH and temperature improved nickel reduction, due to the greater reducing power of dithionite. The optimal pH value for Ni(II) reduction was found to be ∼8. Injecting Cu seed particles enhanced the rate and amount of Ni reduced. NiS and Ni 3 S 2 were identified in the crystal of the resulting solids by X-ray crystallography, and the presence of elemental Ni was explained by X-ray photoelectron spectroscopy. The chemical reduction of actual printed circuit board wastewater with the dithionite:Ni(II) molar ratio dose of 12:1 retrieved ∼99% nickel after 30-min reaction at 40 °C. [ABSTRACT FROM AUTHOR]

Uranium containing radioactive wastewater is seriously hazardous to the natural environment if it is being discharged directly. Herein, nano-flake like Fe loaded sludge carbon (Fe-SC) is synthesized by carbothermal process from Fe-rich sludge waste and applied in the immobilization of uranium in aqueous. Batch isotherm and kinetic adsorption experiments are adopted to investigate the adsorption behavior of Fe-SC to uranium in aqueous. XPS analyses were conducted to evaluate the immobilized mechanism. It was found that the carbonized temperature played significant role in the characteristics and immobilization ability of the resulted Fe-SC. The Fe-SC-800 carbonized at 800 °C takes more advantageous ability in immobilization of uranium from aqueous than the commercial available AC and powder zero valent iron. The adsorption behavior could be fitted well with the Langmuir isotherm adsorption model and pseudo-second order model. The equilibrium adsorption amount and rate for Fe-SC-800 is high to 148.99 mg g −1 and 0.015 g mg −1 min −1 , respectively. Both reductive precipitation and physical adsorption are the main mechanisms of immobilization of uranium from aqueous by Fe-SC-800. [ABSTRACT FROM AUTHOR]

The effects of electrochemical oxidation (EO), Fered-Fenton and solar Fered-Fenton processes using a recirculation flow system containing an electrochemical cell and a solar photo-reactor on biochemically treated landfill leachate were investigated. The most successful method was solar Fered-Fenton which achieved 66.5% COD removal after 120 min treatment utilizing the optimum operating conditions of 47 mM H 2 O 2 , 0.29 mM Fe 2+ , pH 0 of 3.0 and a current density of 60 mA/cm 2 . The generation of hydroxyl radicals ( OH) are mainly from Fered-Fenton process, which is enhanced by the introduction of renewable solar energy. Moreover, Fe 2+ /chlorine and UV/chlorine processes taking place in this system also result in additional production of OH due to the relatively high concentration of chloride ions contained in the leachate. The energy consumption was 74.5 kWh/kg COD and the current efficiency was 36.4% for 2 h treatment. In addition, the molecular weight (MW) distribution analysis and PARAFAC analysis of excitation emission matrix (EEM) fluorescence spectroscopy for different leachate samples indicated that the organics in the leachate were significantly degraded into either small molecular weight species or inorganics. [ABSTRACT FROM AUTHOR]

In this work, a comparative study using anodic oxidation, Fenton and electro-Fenton treatments was performed in order to determine the synergic effect for the removal of thiamethoxan. The results determined that electro-Fenton process showed high efficiency in comparison with Fenton or anodic oxidation. After that, this hybrid process was optimized and the influence of iron catalyst concentration and applied current intensity on the degradation and mineralization were evaluated. Degradation profiles were monitored by high performance liquid chromatography (HPLC) being satisfactorily described by pseudo-first order kinetic model. At the optimal experimental conditions (300 mA and 0.2 mM Fe +2 ), the complete degradation of thiamethoxam was achieved after 10 min. On the other hand, mineralization of thiamethoxam was monitored by total organic carbon (TOC) decay reaching more than 92% of TOC removal after 8 h. Furthermore, a plausible mineralization pathway for the thiamethoxam degradation was proposed based on the identification of by-products such as aromatic intermediates, carboxylic acids and inorganic ions released throughout electro-Fenton process. [ABSTRACT FROM AUTHOR]

The relevant environmental hazard related to the presence of pharmaceuticals in water sources requires the development of high effective and suitable wastewater treatment technologies. In the present work, a hybrid process coupling electro-Fenton (EF) process and aerobic biological treatment (Bio-EF process) was implemented for the efficient and cost-effective mineralization of beta-blocker metoprolol (MPTL) aqueous solutions. Firstly, operating factors influencing EF process were assessed. MTPL solutions were completely mineralized after 4 h-electrolysis under optimal operating conditions and BDD anode demonstrated its oxidation superiority. The absolute rate constant of MTPL oxidation by OH ( k MTPL ) was determined by the competition kinetics method and found to be (1.72 ± 0.04) × 10 9 M −1 s −1 . A reaction pathway for the mineralization of the drug was proposed based on the identification of oxidation by-products. Secondly, EF process was used as pre-treatment. An increase of BOD 5 /COD ratio from 0.012 to 0.44 was obtained after 1 h EF treatment, along with 47% TOC removal and a significant decrease of toxicity, demonstrating the feasibility of a post-biological treatment. Finally, biological treatment successfully oxidized 43% of the total TOC content. An overall 90% mineralization of MPTL solutions was achieved by the Bio-EF process, demonstrating its potentiality for treating wastewater containing pharmaceutical residues. [ABSTRACT FROM AUTHOR]

In the reduction-melting process, lead can be recovered from cathode ray tube funnel glass (PbO = 25 wt%); however, resulting glass residues still contain approximately 1–2 wt% of unrecovered lead. For environmental protection in the residue disposal or recycling, it is important to evaluate the quantities of water-soluble species among the unrecovered lead. This study examined water-soluble lead species generated in the reduction-melting process of the funnel glass and factors determining their generation. In the reduction-melting, metallic lead was generated by reducing lead oxides in the glass, and a part of the metallic lead remained in the glass residue. Such unrecovered metallic lead can dissolve in water depending on its pH level and was regarded as water-soluble lead. When 10 g Na 2 CO 3 was added to 20 g funnel glass during reduction-melting, the resulting glass contained high concentrations of sodium. In a water leaching of the glass, the obtained leachate was alkalized by the sodium-rich glass (pH = 12.7–13.0). The unrecovered metallic lead in the glass was extracted in the alkalized leachate. The quantity of the unrecovered metallic lead (water-soluble lead) in the glass decreased when the melting time, melting temperature, and carbon dosage were controlled during reduction-melting. [ABSTRACT FROM AUTHOR]

Elevated concentration of arsenic (As) prevailed in deep aquifers of Chianan Plain, Taiwan. Arsenic release in relation to microbially induced transformations and shift in bacterial communities in deep aquifer sediments of Budai, southwestern Taiwan were investigated using microcosm experiments and substrate amendments over 90 days of anaerobic incubation. The results revealed that As reduction was independent of Fe reduction and a modest rate of sedimentary As release into aqueous phase occurred at the expense of the native organic carbon. Addition of lactate resulted in a parallel increase in As(III) (3.7-fold), Fe(II) (6.2-fold) and Mn (3.5 fold) in aqueous phase compared to un-amended slurries and the enrichment of sequences related to mostly Bacillus , Flavisolibacter , and Geobacter spp, suggesting the important role of these bacteria in As enrichment through reductive dissolution of As-bearing Fe and Mn minerals. The increase in phosphate-extractable As in solid phase with concomitant rise in As in aqueous phase over the course of incubation further attested to the importance of reductive dissolution in promoting As release. Furthermore, the increase in arrA gene abundance with addition of labile carbon suggests that dissimilatory As reduction also may contribute to As enrichment in the water of the deep aquifer of Budai. [ABSTRACT FROM AUTHOR]

Dinitroaniline herbicides such as trifluralin and pendimethalin are persistent bioaccumulative toxins to aquatic organisms. Thus, in-situ remediation of contaminated sediments is desired. This study investigated whether black carbons (BCs), including apple wood charcoal (BC1), rice straw biochar (BC2), and activated carbon (BC3), could facilitate abiotic reduction of trifluralin and pendimethalin by sulfides of environmentally-relevant concentrations in anoxic coastal sediments. The reduction rates of trifluralin and pendimethalin increased substantially with increasing BC dosages in the sediments. This enhancing effect was dependent on BC type with the greatest for BC3 followed by BC1 and BC2, which well correlated with their specific surface area. The pseudo-first order reduction rate constants ( k obs ) for BC3-amended sediment (2%) were 13- and 14 times the rate constants in the BC-free sediment. The reduction rates increased with increasing temperature from 8 to 25 °C in the BC-amended sediment, following the Arrhenius relationship. Finally, through molecular modeling by density functional theory and reaction species identification from mass spectra, molecular pathways of trifluralin and pendimethalin reduction were elucidated. In contrary to the separate sequential reduction of each nitro group to amine group, both nitro groups, first reduced to nitroso, then eventually to amine groups. [ABSTRACT FROM AUTHOR]

Hollow porous gold nanoparticles (HPGNPs) were synthesized via a one-step solution phase method at ambient temperature. The particle size, ranging from 80 nm to 350 nm, was easily controlled by changing the concentration of HAuCl 4 . The morphology and the structure of the as-prepared HPGNPs were investigated by SEM, TEM, HRTEM and XPS. Langmuir isotherm analysis yielded values of 8973 m 2 /g for the outer surface area and 58724 m 2 /g for the inner surface area for the 80 nm HPGNPs. Due to a special hollow porous nanostructure, the HPGNPs exhibited superior catalytic activity and stability for the reduction of 4-nitrophenol (4-NP). No significant inactivation of the 80 nm HPGNPs was observed, even after recycling for six cycles or storing for more than 1 month. Due to these excellent properties, it is expected that HPGNPs can be used in such applications as water pollutant removal and environmental remediation. [ABSTRACT FROM AUTHOR]

To remove the toxic and refractory pollutants in the phthalonitrile resin wastewater and improve its biodegradability, a combined process (i.e., CaCl 2 + AA + Fe/Cu/air) was developed to pretreat this wastewater obtained from a phthalonitrile resin manufacturing plant in southwestern China. First, CO 3 2− was precipitated and removed by adding CaCl 2 . Furthermore, its ultra-high concentrated NO 2 − (22.7 ± 0.1 g/L) was reduced into N 2 by adding amidosulphonic acid (AA). Meanwhile, two control experiments were setup to confirm the superiority of the combined process (i.e., CaCl 2 + AA). Subsequently, the wastewater was further treated by Fe/Cu/air process after the removal of CO 3 2− and NO 2 − . The results suggest that the developed method not only could effectively remove the ultra-high concentrated CO 3 2− (＞99%) and NO 2 − (＞99%), but also could obtain high COD (58.8%) and colority (95.2%) removal efficiencies. Meanwhile, B/C ratio of this wastewater increased from 0.19 to 0.45, which suggests the biodegradability also was improved significantly. Finally, the high treatment efficiency was mainly attributed to the synergistic effects of CaCl 2 , AA and Fe/Cu/air. Therefore, the combined process is a promising pretreatment process for the ultra-high concentrated wastewater from phthalonitrile resin manufacturing. [ABSTRACT FROM AUTHOR]

Considering the recent stringent regulations governing diesel NO x emission, an aftertreatment system for the reduction of NO x in the exhaust gas has been proposed and studied. The proposed system is a hybrid method combining nonthermal plasma and NO x adsorbent. The system does not require precious metal catalysts or harmful chemicals such as urea and ammonia. In the present system, NO x in diesel emission is treated by adsorption and desorption by adsorbent as well as nonthermal plasma reduction. In addition, the remaining NO x in the adsorbent is desorbed again in the supplied air by residual heat. The desorbed NO x in air recirculates into the intake of the engine, and this process, i.e., exhaust gas components’ recirculation (EGCR) achieves NO x reduction. Alternate utilization of two adsorption chambers in the system can achieve high-efficiency NO x removal continuously. An experiment with a stationary diesel engine for electric power generation demonstrates an energy efficiency of 154 g(NO 2 )/kWh for NO x removal and continuous NO x reduction of 70.3%. Considering the regulation against diesel emission in Japan, i.e., the new regulation to be imposed on vehicles of 3.5–7.5 ton since 2016, the present aftertreatment system fulfills the requirement with only 1.0% of engine power. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr(VI)), a heavy-metal contaminant, can be easily reduced to less toxic trivalent chromium (Cr(III)) by sulfite ions (S(IV)). However, S(IV) has not drawn as much attention as the ferrous ion has. We report herein a novel Cr(VI)–S(IV)–O 2 system containing sulfite ions that rapidly and simultaneously reduces Cr(VI) and oxidize organic pollutants in the presence of oxygen in aqueous solutions. This Cr(VI)–S(IV)-O 2 system contains the initiator Cr(VI), the reductant S(IV), and the oxidant O 2 , which produce oxysulfur radicals (mainly SO 4 − and SO 5 − ) and hydroxyl radicals (OH ). The Cr(VI)/S(IV) molar ratio, pH, and oxygen content play important roles in the entire reaction system. Acidic conditions (pH 3.0) facilitated degradation of organic compounds and reduction of Cr(VI) as well. In addition, experiments of rapid degradation of several kinds of organic pollutants such as azo dye (acid orange 7, AO7), aniline, phenol, bisphenol A etc were also conducted. Preliminary results show that the removal rates of the analogs of phenols or aromatic amines in this Cr(VI)–S(IV)–O 2 system have a relationship with the electronic parameters (Hammett constant, σ) of the substituted groups. Thus, the Cr(VI)–S(IV)–O 2 system, provides an excellent strategy of “waste control by waste” for removing multiple industrial contaminants. [ABSTRACT FROM AUTHOR]

In this study, a novel process for detoxification and reutilization of waste cathode ray tube (CRT) funnel glass was developed by carbon thermal reduction enhanced acid leaching process. The key to this process is removal of lead from the CRT funnel glass and synchronous preparation of glass microspheres. Carbon powder was used as an isolation agent and a reducing agent. Under the isolation of the carbon powder, the funnel glass powder was sintered into glass microspheres. In thermal reduction, PbO in the funnel glass was first reduced to elemental Pb by carbon monoxide and then located on the surface of glass microspheres which can be removed easily by acid leaching. Experimental results showed that temperature, carbon adding amount and holding time were the major parameters that controlled lead removal rate. The maximum lead removal rate was 94.80% and glass microspheres that measured 0.73–14.74 μm were obtained successfully by setting the temperature, carbon adding amount and holding time at 1200 °C, 10% and 30 min, respectively. The prepared glass microspheres may be used as fillers in polymer materials and abrasive materials, among others. Accordingly, this study proposed a practical and economical process for detoxification and recycling of waste lead-containing glass. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) emitted during the electronic waste dismantling process (EWDP) were treated at a pilot scale, using integrated electrostatic precipitation (EP)-advanced oxidation technologies (AOTs, subsequent photocatalysis (PC) and ozonation). Although no obvious alteration was seen in VOC concentration and composition, EP technology removed 47.2% of total suspended particles, greatly reducing the negative effect of particles on subsequent AOTs. After the AOT treatment, average removal efficiencies of 95.7%, 95.4%, 87.4%, and 97.5% were achieved for aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, as well as nitrogen- and oxygen-containing compounds, respectively, over 60-day treatment period. Furthermore, high elimination capacities were also seen using hybrid technique of PC with ozonation; this was due to the PC unit’s high loading rates and excellent pre-treatment abilities, and the ozonation unit’s high elimination capacity. In addition, the non-cancer and cancer risks, as well as the occupational exposure cancer risk, for workers exposed to emitted VOCs in workshop were reduced dramatically after the integrated technique treatment. Results demonstrated that the integrated technique led to highly efficient and stable VOC removal from EWDP emissions at a pilot scale. This study points to an efficient approach for atmospheric purification and improving human health in e-waste recycling regions. [ABSTRACT FROM AUTHOR]

Alkaline ascorbic acid (AA) exhibits the potential to reductively degrade nitrobenzene (NB), which is the simplest of the nitroaromatic compounds. The nitro group (NO 2 − ) of NB has a +III oxidation state of the N atom and tends to gain electrons. The effect of alkaline pH ranging from 9 to 13 was initially assessed and the results demonstrated that the solution pH, when approaching or above the p K a2 of AA (11.79), would increase reductive electron transfer to NB. The rate equation for the reactions between NB and AA at pH 12 can be described as r = ((0.89 ± 0.11) × 10 −4 mM 1−(a + b) h −1 ) × [NB] a = 1.35 ± 0.10 [AA] b = 0.89 ± 0.01 . The GC/MS analytical method identified nitrosobenzene, azoxybenzene, and azobenzene as NB reduction intermediates, and aniline (AN) as a final product. These experimental results indicate that the alkaline AA reduction of NB to AN mainly proceeds via the direct route, consisting of a series of two-electron or four-electron transfers, and the condensation reaction plays a minor route. Preliminary evaluation of the remediation of spiked NB contaminated soils revealed that maintenance of alkaline pH and a higher water to soil ratio are essential for a successful alkaline AA application. [ABSTRACT FROM AUTHOR]

Iron-alginate beads (Fe-ABs) were successfully prepared by the ion-gelation method, and applied as heterogeneous Fenton catalysts for the removal of a malodorous compound ‘indole’. Similarly, copper-enriched alginate beads (Cu-ABs) were synthesized and tested as like-Fenton catalyst, however, their application proved not to be effective for this purpose. Fe-ABs catalysts were characterized by FTIR, SEM, EDS and AAS spectroscopy. Results pointed out that the parameters affecting Fenton catalysis must be carefully chosen to avoid excessive iron release. Under optimal conditions, complete indole removal and considerably high reduction of TOC, without significant leaching was achieved. Indole decay followed a pseudo-first-order kinetics. The absolute rate constant for indole hydroxylation was 3.59 × 10 9 M −1 s −1 , as determined by the competition kinetics method . Four reaction intermediates (Isatin, Dioxindole, Oxindole and Anthralinic acid) were identified by ULC/MS/MS analysis. Short-chain aliphatic carboxylic acids like formic, acetic, oxalic, maleic, oxamic and pyruvic acids were identified by ion exclusion chromatography and as end-products. Based on the identified by-products, a plausible mineralization pathway was proposed. Moreover, the catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity. [ABSTRACT FROM AUTHOR]

Two-dimensional reduced graphene oxide (2D rGO) was employed as both a shape-directing medium and support to fabricate 2D γ-MnO 2 /2D rGO nano-hybrids (MnO 2 /rGO) via a facile hydrothermal route. For the first time, the 2D/2D hybrid materials were used for catalytic ozonation of 4-nitrophenol. The catalytic efficiency of MnO 2 /rGO was much higher than either MnO 2 or rGO only, and rGO was suggested to play the role for promoting electron transfers. Quenching tests using tert-butanol, p-benzoquinone, and sodium azide suggested that the major radicals responsible for 4-nitrophenol degradation and mineralization are O 2 ̄ and 1 O 2 , but not OH. Reusability tests demonstrated a high stability of the materials in catalytic ozonation with minor Mn leaching below 0.5 ppm. Degradation mechanism, reaction kinetics, reusability and a synergistic effect between catalytic ozonation and coupling peroxymonosulfate (PMS) activation were also discussed. [ABSTRACT FROM AUTHOR]

In this work, a simple, cost-effective, and environmental-friendly strategy was developed to synthesize gold nanoparticles (Au NPs) decorated graphene hydrogel with the use of tannic acid. This facile route involved the reduction of graphene oxide (GO) in the presence of tannic acid to form tannic acid functionalized graphene hydrogel, followed by loading and in situ reduction of AuCl 4 − ions in the graphene hydrogel network benefiting from the abundant phenol groups of tannic acid. Tannic acid (TA), a typical plant polyphenol widely present in woods, not only reduced GO and induced the self-assembly of reduced graphene oxide into graphene hydrogel, but also served as the reducing agent and stabilizer for the synthesis and immobilization of Au NPs, avoiding extra chemical reagent and any stabilizer. The obtained Au NPs decorated graphene hydrogel (Au@TA-GH) was fully characterized and exhibited much higher catalytic activities than the unsupported and other polymer-supported Au NPs toward the reduction of methylene blue (MB). In addition, the high catalytic activity of Au@TA-GH could withhold in different pH solution conditions. Another distinct advantage of Au@TA-GH as catalysts is that it can be easily recovered and reused for five cycles. [ABSTRACT FROM AUTHOR]