Stable Isotope Ratios Trace the Rice Uptake of Cadmium from Atmospheric Deposition via Leaves and Roots.

Cadmium (Cd) stable isotopes provide a novel technique to investigate the fate of Cd in the environment, but challenges exist for tracing the sources in the plants. We performed individual rice leaf and root exposures to dry and wet deposition using customized open-top chambers (OTCs) in the greenhouse and in the field next to a smelter, respectively. The field experiment also included a control without Cd deposition and a "full" treatment. The exposure experiments and isotope signatures showed that leaves can directly take up atmospheric Cd and then translocate within rice plants to other tissues, contributing 52-70% of Cd in grains, which exceeded the contribution (30-48%) by root exposure. The Cd isotopes in leaves, nodes, internodes, and grains demonstrate that roots preferentially take up Cd from wet deposition, but leaves favor uptake of Cd from dry deposition. The Cd uptake by leaves is redistributed via nodes, allowing for upward transport to the grains but preventing downward transport to the roots. Leaves favor uptake of heavy isotopes from atmospheric deposition (ΔCd114/110Leaf-Dust: 0.10 ± 0.02‰) but retain light isotopes and transport heavy isotopes to the nodes and further to grains. These findings highlight the contribution of atmospheric deposition to rice and Cd isotopes as a useful tracer for quantifying sources in plants when different isotopic compositions are in sources.

Degradation of benzene derivatives in the CuMgFe-LDO/persulfate system: The role of the interaction between the catalyst and target pollutants.

A novel insight on the role of interactions between target pollutants and the catalyst in the copper-containing layered double oxide (LDO)-catalyzed persulfate (PS) system was elucidated in the present study. 4-Chlorophenol (4-CP), as a representative benzene derivative with a hydroxyl group, was completely removed within 5 min, which was much faster than the reaction of monochlorobenzene (MCB) without a hydroxyl group, with the degradation efficiency of 31.7% in 240 min. Through the use of radical quenching and surface inhibition experiments, it could be concluded that the interaction between 4-CP and CuMgFe-LDO, rather than free radicals, played a key role in the decomposition of 4-CP, while only the free radicals participated in the MCB degradation process. According to electron paramagnetic resonance and X-ray photoelectron spectroscopy data, the formation of a Cu(II)-complex between phenolic hydroxyl groups and surface Cu(II) was primarily responsible for the degradation of phenolic compounds, in which PS accepted one electron from the complex and generated sulfate radicals and chelated radical cations. The chelated radical cations transferred one electron to Cu(II) followed by Cu(I) generation and pollutant degradation successively.

Multifunctional Pd/Fe-biochar composites for the complete removal of trichlorobenzene and its degradation products.

To elucidate the effect of structure and property of biochar on the structure-activity relationship among the composites of biochar supported Pd/Fe and 1,2,4-trichlorobenzene (1,2,4-TCB) and its dechlorination products, biochar supported Pd/Fe nanoparticles with different mass ratios were investigated for the enhanced removal of 1,2,4-TCB (52 µmol/L) and its dechlorination products. 1,2,4-TCB was removed through the electrochemical dechlorination by Pd/Fe and adsorption by biochar simultaneously. As the mass ratio of CS700 to Pd/Fe was 0.1:1, biochar within the Pd/Fe-CS7000.1 system played a significant role in the adsorption of 1,2,4-TCB. However, there is little adsorption to biochar for dechlorination products due to strong competition by 1,2,4-TCB. As the mass ratio of CS700 to Pd/Fe was increased to 5:1, 1,2,4-TCB was completely removed from the solution by the composites within 0.5 h. The dechlorination products (1,2-DCB, MCB, benzene and trace 1,3-DCB) were completely sequestered on solid phase but absent in aqueous solution. However, the excessive biochar increased the inaccessibility of 1,2,4-TCB or decreased the reactive sites of Pd/Fe leading to the less dechlorination of 1,2,4-TCB. The alkaline biochar did not influence the chemical reactivity of Pd/Fe in the composites and buffered the acid and alkaline solutions with pH being maintained at neutral conditions under initial pH ranging from 3.07 to 10.03. The highly hydrophobicity of biochar could maintain the affinity of the composite for the chlorinated compounds even if the concentration of 1,2,4-TCB was up to 80.9% of its aqueous solubility. This study provides efficient synergistic removal support for the treatment of TCB affected groundwater.

Syngas production and gas-N evolution over heterogeneously doped La-Fe-O perovskite-type oxygen carriers in chemical looping gasification of microalgae.

Chemical looping gasification (CLG) is a promising technology for syngas production with low pollutant emission. In this study, doped La-Fe-O perovskites including LaFeO3 (LF), LaFe0.5Ni0.5O3 (LN5F5) and La0.3Ba0.7FeO3 (L3B7F) were developed for microalgae CLG. The as-prepared perovskites exhibited an outstanding performance in syngas production with accumulative syngas yield > 33 mol/kg. For gas-N evolution, perovskites were beneficial to the formation of NH3 and HCN, while the iron ore may convert precursors to NO. Below 400 °C, NOx can be stored on the perovskite surface in the form of nitrite/nitrate species. When the temperature was above 700 °C, NOx can be selectively reduced by reducing components in tar or syngas under the catalysis of L3B7F, resulting in the final reduction of NOx emission. Thus, CLG over L3B7F may be a promising way for efficient utilization of microalgae to overcome the intractable nitrogen-related obstacles in the commercial application of biomass gasification technologies.

Efficient Remediation of p-chloroaniline Contaminated Soil by Activated Persulfate Using Ball Milling Nanosized Zero Valent Iron/Biochar Composite: Performance and Mechanisms.

In this study, efficient remediation of p-chloroaniline (PCA)-contaminated soil by activated persulfate (PS) using nanosized zero-valent iron/biochar (B-nZVI/BC) through the ball milling method was conducted. Under the conditions of 4.8 g kg-1 B-nZVI/BC and 42.0 mmol L-1 PS with pH 7.49, the concentration of PCA in soil was dramatically decreased from 3.64 mg kg-1 to 1.33 mg kg-1, which was much lower than the remediation target value of 1.96 mg kg-1. Further increasing B-nZVI/BC dosage and PS concentration to 14.4 g kg-1 and 126.0 mmol L-1, the concentration of PCA was as low as 0.15 mg kg-1, corresponding to a degradation efficiency of 95.9%. Electron paramagnetic resonance (EPR) signals indicated SO4•-, •OH, and O2•- radicals were generated and accounted for PCA degradation with the effect of low-valence iron and through the electron transfer process of the sp2 hybridized carbon structure of biochar. 1-chlorobutane and glycine were formed and subsequently decomposed into butanol, butyric acid, ethylene glycol, and glycolic acid, and the degradation pathway of PCA in the B-nZVI/BC-PS system was proposed accordingly. The findings provide a significant implication for cost-effective and environmentally friendly remediation of PCA-contaminated soil using a facile ball milling preparation of B-nZVI/BC and PS.

Significant roles of surface functional groups and Fe/Co redox reactions on peroxymonosulfate activation by hydrochar-supported cobalt ferrite for simultaneous degradation of monochlorobenzene and p-chloroaniline.

CoFe2O4/hydrochar composites (FeCo@HC) were synthesized via a facile one-step hydrothermal method and utilized to activate peroxymonosulfate (PMS) for simultaneous degradation of monochlorobenzene (MCB) and p-chloroaniline (PCA). Additionally, the effects of humic acid, Cl-, HCO3-, H2PO4-, HPO42- and water matrices were investigated and degradation pathways of MCB and PCA were proposed. The removal efficiencies of MCB and PCA were higher in FeCo@HC140-10/PMS system obtained under hydrothermal temperature of 140 °C than FeCo@HC180-10/PMS and FeCo@HC220-10/PMS systems obtained under higher temperatures. Radical species (i.e., SO4•-, •OH) and nonradical pathways (i.e., 1O2, Fe (IV)/Co (IV) and electron transfer through surface FeCo@HC140-10/PMS* complex) co-occurred in the FeCo@HC140-10/PMS system, while radical and nonradical pathways were dominant in degrading MCB and PCA respectively. The surface functional groups (i.e., C-OH and CO) and Fe/Co redox cycles played crucial roles in the PMS activation. MCB degradation was significantly inhibited in the mixed MCB/PCA solution over that in the single MCB solution, whereas PCA degradation was slightly promoted in the mixed MCB/PCA solution. These findings are significant for the provision of a low-cost and environmentally-benign synthesis of bimetal-hydrochar composites and more detailed understanding of the related mechanisms on PMS activation for simultaneous removal of the mixed contaminants in groundwater.

Electron induced efficient dechlorination of trichlorethylene with S doped Fe2B: The enhancement mechanism of S.

In this work, S doped Fe2B (Fe2B-S) was synthesized by sintering method and applied for the enhanced dechlorination of trichlorethylene (TCE). The degradation ratio (D) of TCE was 99.8% with reaction rate constant (kobs) of 0.956 h-1 by 10.0at% S doped Fe2B (corresponding to Fe2B-S10.0), compared to D and kobs values 37.3% and 0.067 h-1 by Fe2B, respectively. The major dechlorination products of acetylene, ethene, ethane and C3-C6 hydrocarbon compounds were observed from a reductive ß-elimination pathway. S doped and undoped Fe2B could form the first-level in-situ galvanic cell, and the returned S provided a second-level galvanic cell to further enhance electron transfer. The doped S worked as electron donor to increase the density of localized unpaired electrons, and the electron enriched Fe atoms leading to stronger reducibility were verified by the density functional theory (DFT) calculation. This work provides a complete insight into the enhancement mechanism of S doped Fe2B and guides the potential design of zero-valent iron (ZVI) with properties tailored for chlorinated hydrocarbons dechlorination.

Hydrothermally assisted synthesis of nano zero-valent iron encapsulated in biomass-derived carbon for peroxymonosulfate activation: The performance and mechanisms for efficient degradation of monochlorobenzene.

A facile, green and easily-scalable method of synthesizing stable and effective nano zero-valent iron (nZVI)­carbon composites for peroxymonosulfate (PMS) activation was highly desirable for in-situ groundwater remediation. This study developed a two-step hydrothermally assisted carbothermal reduction method to prepare nZVI-encapsulated carbon composite (Fe@C) using rice straw and ferric nitrate as precursors. The hydrothermal reactions were conducive to iron loading, and carbothermal temperature was crucial for the aromatization and graphitization of hydrothermal carbonaceous products, the reductive transformation of iron oxides into nZVI and the development of porous structure in composites. At carbothermal temperature of 800 °C following hydrothermal reactions, the stable Fe@C800 with nZVI encapsulated in the spherical carbon shell was obtained and exhibited the best catalytic performance for PMS activation and the degradation of monochlorobenzene (MCB) in a wide range of pH values (3-11) with removal efficiency after 120 min reaction and first-order kinetic rate constant (k1) of 98.7% and 0.087 min-1 respectively under the optimum conditions of 10 mM PMS and 0.2 g·L-1 Fe@C800. The inhibiting effects of common co-existed anions (i.e., Cl-, HCO3- and H2PO4-) and humic acid in groundwater on the removal of MCB in Fe@C800/PMS system was also investigated. Both OH-dominated radical processes and nonradical pathways involving 1O2 and surface electron transfers were accounted for PMS activation and MCB removal. The inner nZVI was protected by the carbon shell, endowing Fe@C800 with high reactivity and good reusability. Additionally, 81.2% and 73.5% of MCB removal rates were achieved in tap water and actual contaminated groundwater respectively. This study not only provided a novel strategy to synthesize highly effective and stable nZVI­carbon composites using the agricultural biomass waste for PMS induced oxidation of organic contaminants in groundwater, but also enhanced the understanding on the activation mechanism of iron­carbon based catalysts towards PMS.

Degradation of 1,4-dioxane by biochar activating peroxymonosulfate under continuous flow conditions.

1,4-Dioxane degradation under both batch-scale and column experiments has been investigated within the biochar activated peroxymonosulfate (PMS) system for in-situ remediation of 1,4-dioxane contaminated groundwater. In case of the batch experiments, the 1,4-dioxane degradation efficiencies were significantly increased with the increased biochar pyrolysis temperatures. The optimized 1,4-dioxane degradation efficiency at 89.2% was achieved with 1.0 g L-1 of biochar (E800) and 8.0 mM PMS. In the absence of PMS, the breakthrough rates of 1,4-dioxane in biochar packed column experiments under the dynamic flow conditions were relatively slow compared with those in sand packed columns. Simultaneously, based on the integrated areas (IA) from the 1,4-dioxane breakthrough curves, the degradation efficiency at 70.2% was estimated in biochar packed column (WE800:WSand = 1:9) under continuous injections of 16.0 mM PMS. Electron paramagnetic resonance (EPR) indicated that hydroxyl, sulfate and superoxide radicals were generated within the biochar/PMS systems and alcohol quenching experiments suggested that the dominated hydroxyl and sulfate radicals were responsible for 1,4-dioxane degradation. The findings of this study suggested that the biochar activated PMS system is a promising and cost-effective strategy for the remediation of 1,4-dioxane contaminated groundwater.

Spectrophotometric determination of persulfate by oxidative decolorization of azo dyes for wastewater treatment.

Persulfate can efficiently decolorize azo dyes through oxidizing these compounds, which enabled us to develop a method of rapid spectrophotometric determination of persulfate for monitoring the wastewater treatment on the basis of the oxidation decolorization of azo dyes. Four azo dyes with different molecular structures were investigated as probes, and the influences of operation parameters including reaction time, solution pH, initial dye concentration, and initial concentration of activator Fe(2+) were checked on the determination of persulfate. Under optimum conditions, the decolorization degree of the dyes responded linearly with persulfate concentration for all the four azo dyes, and the linear range and detection limit were found to be 2.0-150 µmol L(-1) and 0.62 µmol L(-1) for rhodamine B, 2.0-100 µmol L(-1) and 0.42 µmol L(-1) for methylene blue, 4.0-150 µmol L(-1) and 0.50 µmol L(-1) for methyl violet, and 20-150 µmol L(-1) and 8.1 µmol L(-1) for orange II. A persulfate treatment of a spiked wastewater sample was satisfactorily monitored with the new method.

Characteristic Evaluation and Process Simulation of CuFe2O4 as Oxygen Carriers in Coal Chemical Looping Gasification.

Chemical looping gasification (CLG) has been described as an innovative and low-cost gasification technology to convert carbonaceous fuels into synthesis gases. Oxygen carrier (OC) is the key to resolve the contradiction between rapid carbon conversion and appropriate partial oxidation of coal. At present, the solid fuel conversion in the CLG process is limited by an iron-based OC, and a copper-based carrier has difficulty in maintaining the reduction atmosphere. Hence, CuFe2O4 has been proposed as a high-performance OC because of its synergistic effect. The present study first conducted a characteristic evaluation on CuFe2O4, including the reducibility and oxygen release capacity. The results showed that the addition of copper made a great contribution to the reduction process, and the presence of ferrite better relieved the deep oxygen loss of CuFe2O4. The thermodynamic limitation and evolution behavior of CuFe2O4 in the reduction process were discussed for the simulation. An Aspen model of the CLG process with coal as the fuel and CuFe2O4 as the OC was then established and validated by the experimental data. By consideration of the high carbon conversion and high syngas productivity in the operation, an OC/fuel mass ratio of approximately 1.25-2.25 and a gasification temperature range of 800-900 °C were thought to be optimal in the coal CLG process.

Synergistic effects of lanthanum ferrite perovskite and hydrogen to promote ammonia production during microalgae catalytic pyrolysis process.

Ammonia (NH3) production from nitrogen-enriched renewable resources pyrolysis is a green, clean, and sustainable technology. In this paper, lanthanum ferrite perovskite (LaFeO3) and hydrogen (H2) atmosphere were combined to enhance NH3 production during microalgae pyrolysis. The catalytic pyrolysis of microalgae pyrolysis was carried out in a fixed bed reactor. The results show that the synergistic effects between H2 and LaFeO3 promote the fuel-nitrogen transfer into gas phase, while nitrogen in biochar and bio-oil significantly decreases. H2 and LaFeO3 not only favor the conversion of protein-N to pyridinic-N, pyrrolic-N, and quaternary-N in char, but also accelerate the deamination of amides, pyrroles, and pyridines, thus facilitating the formation of NH3. Pyrolysis temperature plays a considerable role in distribution and conversion of N-species. Increasing temperature increases NH3 and HCN yields, the maximum NH3 yield reaches 47.40 wt% at 800 °C. Moreover, LaFeO3 shows considerable stability during 10 cyclic operations.

Mechanistic insights into fast adsorption of perfluoroalkyl substances on carbonate-layered double hydroxides.

Layered double hydroxide (LDH) with the metal composition of Cu(II)Mg(II)Fe(III) was prepared as an adsorbent for fast adsorption of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA). 84% of PFOS and 48% of PFOA in relation to the equilibrium state were adsorbed in the first minutes of contact with 0.1 g/L of suspended µm-sized LDH particles. The adsorption mechanisms of PFOS and PFOA on the CuMgFe-LDH were interpreted. Hydrophobic interactions were primarily responsible for the adsorption of these compounds in accordance with the different adsorption affinities of long-chain (C8, Kd = 105 L/kg) and short-chain (C4, Kd = 102 L/kg) perfluorinated carboxylic acids. PFOA adsorption on CuMgFe-LDH was strongly suppressed under alkaline conditions while PFOS uptake was only slightly affected in the pH range from 4.3 to 10.7, indicating a significant role of electrostatic interactions for PFOA adsorption. The adsorption of PFOS and PFOA was rather insensitive to competition by monovalent anions. The previously reported 'memory effect' of calcined CuMgFe-LDH for sorption of organic anions was not confirmed in the present study. Spent CuMgFe-LDH could be easily regenerated by extraction with 50 vol% methanol in water within 1 h and maintained a high PFOS removal in subsequent usage cycles.

Trichloroethylene dechlorination rates, pathways, and efficiencies of ZVMg/C in aqueous solution.

The removal mechanism from the reductive dechlorination of trichloroethylene (TCE) by zero valent magnesium (ZVMg) in aqueous solution is systematically studied. Following the preparation and characterization of ball-milled micro ZVMg with graphite (ZVMg/C) particles, this paper evaluated the TCE reaction rates, pathways, utilization rates and aging effects of ZVMg/C particles in aqueous solution under uncontrolled pH conditions. Overall, 38 µM of TCE was transformed by 10 g/L of ZVMg/C to methane (62.51%) and n-hexane (11.86%) and ethane (7.40%) and other alkene and alkyne products through the catalytic hydrogenation pathway. The measured surface area normalized pseudo-first order rate constants (KSA) were up to 9.31 × 10-2 L/m2/h and the utilization rate of Mg0 accounted for around 60%. The KSA were decreased to 1.90 × 10-2 L/m2/h in case of ZVMg/C being exposed in the atmosphere for 6 days due to 7.3% reduction in the utilization rate of Mg0 from the initial 85.2%, and 5.11 × 10-2 L/m2 h in case of ZVMg/C aged in water for one day. The removal efficiencies of approximately 56%, 58% and 87% by 10 g/L of ZVMg/C were achieved in the contaminated groundwater comprising 38 µM of TCE, 43 µM of 1,2-dichlorobenzene and 8.12 µM of trichlormethane. Therefore, it is concluded that ZVMg/C is viewed as a potential and effective remediation reagent for the groundwater remediation.

Nonradicals induced degradation of organic pollutants by peroxydisulfate (PDS) and peroxymonosulfate (PMS): Recent advances and perspective.

Nonradical persulfate oxidation processes have emerged as a new wastewater treatment method due to production of mild nonradical oxidants, selective oxidation of organic pollutants, and higher tolerance to water matrixes compared with radical persulfate oxidation processes. Since the case of the nonradical activation of peroxydisulfate (PDS) was reported on CuO surface in 2014, nonradical persulfate oxidation processes have been extensively investigated, and much achievement has been made on realization of nonradical persulfate activation processes and understanding of intrinsic reaction mechanism. Therefore, in the review, nonradical pathways and reaction mechanisms for oxidation of various organic pollutants by PDS and peroxymonosulfate (PMS) are overviewed. Five nonradical persulfate oxidation pathways for degradation of organic pollutants are summarized, which include surface activated persulfate, catalysts-free or catalysts mediated electron transfer, 1O2, high-valent metals, and newly derived inorganic oxidants (e.g., HOCl and HCO4-). Among them, the direct oxidation processes by persulfate, nonradical based persulfate activation by inorganic/organic molecules and in electrochemical methods is first overviewed. Moreover, nonradical based persulfate activation mechanisms by metal oxides and carbon materials are further updated. Furthermore, investigation methods of interaction between persulfate and catalyst surface, and nature of reactive species are also discussed in detail. Finally, the future research needs are proposed based on limited understanding on reaction mechanism of nonradical based persulfate activation. The review can offer a comprehensive assessment on nonradical oxidation of organic pollutants by persulfate to fill the knowledge gap and provide better guidance for future research and engineering application of persulfate.

Nano-magnetite supported by biochar pyrolyzed at different temperatures as hydrogen peroxide activator: Synthesis mechanism and the effects on ethylbenzene removal.

Nano-magnetite supported by biochar (nFe3O4/BC) pyrolyzed at temperatures of 300 °C-600 °C was developed to activate hydrogen peroxide (H2O2) for the efficient degradation of ethylbenzene in aqueous solution. It was revealed that the degradation efficiency of ethylbenzene and TOC removal were 96.9% and 36.2% respectively after the reaction for 40 min in the presence of initial concentration of 0.1 mmol L-1 ethylbenzene, 2.76 g L-1 nFe3O4/BC500 with the mass ratio of nFe3O4 to BC500 of 4:1 and 2.0 mmol L-1 H2O2 at pH 7.0. Based on electron paramagnetic resonance (EPR), quenching experiment and X-ray photoelectron spectroscopy (XPS) data, both OH and O2- radicals were generated in the nFe3O4/BC500 activated H2O2 system, and the OH radicals were the predominant species for the degradation of ethylbenzene. Through electron transfer process, mechanisms of Fe(II), phenolic hydroxyl group and persistent free radicals (PFRs) on BC surfaces accounted for the generation of OH radicals, and Fe(III) in nFe3O4 and formed from Fe(II) oxidation responsible for the generation of O2- radicals in the nFe3O4/BC activated H2O2 system were proposed.

Field demonstration of enhanced removal of chlorinated solvents in groundwater using biochar-supported nanoscale zero-valent iron.

The application of biochar-supported nanoscale zero-valent iron (biochar-nZVI) was successfully implemented in a field demonstration for the first time. To overcome the significant shortcomings of nZVI agglomeration for in-situ groundwater remediation, biochar-nZVI was injected into groundwater using direct-push and water pressure driven packer techniques for a site impacted by chlorinated solvents in the North China Plain. The field demonstration comprising two-step injections was implemented to demonstrate the effectiveness of nZVI and biochar-nZVI respectively. The outcome of the demonstration revealed a sharp reduction of contaminant concentrations of chlorinated solvents in 24 h following the first injection of nZVI, but the rebound of the concentrations of these contaminants in groundwater has occurred within the next two weeks. However, application of biochar-nZVI greatly enhanced the removal of chlorinated solvents in groundwater over the longer period of 42 days. The enhanced removal of chlorinated solvents in groundwater by biochar-nZVI is mainly attributed to the synergistic effects of adsorption and reduction. The adsorption by biochar significantly reduced the level of chlorinated solvents in groundwater. Overall increases in ferrous iron and chloride concentrations after the injections indicated that the reduction has occurred during the removal of chlorinated solvents in groundwater. In summary, biochar-supported nZVI could be potentially used for the effective remediation of chlorinated solvents in groundwater.

Catalysis of hydrogen peroxide with Cu layered double hydrotalcite for the degradation of ethylbenzene.

A high catalytic system using Cu layered double hydrotalcite (Cu(II)-Mg(II)-Fe(III)LDHs) and hydrogen peroxide (H2O2) was developed for the degradation of ethylbenzene. It was identified that the degradation efficiency of ethylbenzene (0.08 mmol L-1) and TOC removal were 96.1% and 39.7% respectively in the presence of 0.1 g L-1 Cu(II)-Mg(II)-Fe(III)LDHs with (Cu2+ + Mg2+)/Fe3+ molar ratio of 5.0 and 0.16 mmol L-1 H2O2 in 6.0 h. Based on ESR and XPS data, hydroxyl radicals (•OH) were the predominant free radical specials generated from the catalytic decomposition of H2O2 for the degradation of ethylbenzene. The redox of Cu(II)/Cu(III) on the layered Cu(II)-Mg(II)-Fe(III)LDHs surface active sites accounted for the formation of •OH radicals and the cycle of Cu(II) in the Cu(II)-Mg(II)-Fe(III)LDHs/H2O2 system were proposed.

Enhanced reduction and adsorption of hexavalent chromium by palladium and silicon rich biochar supported nanoscale zero-valent iron.

The potential of silicon-rich biochar and Pd were evaluated for the enhanced removal of Cr(VI) in solution by nanoscale zero-valent iron (nZVI) composites. The composition and structures of the nZVI, RS700-supported nZVI, and Pd-doped samples were analyzed by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy before and after reaction with Cr(VI). The amount of Cr(VI) removed by nZVI-RS700-Pd was considerably greater than the removal by nZVI, nZVI-Pd, or nZVI-RS700. This was mainly due to the enhanced reduction and adsorption of Cr(VI) by silicon-rich biochar and Pd. Silicon and Pd promoted the reduction of Cr(VI) due to the Fe0 crystallinity in the nZVI structures. The significantly decreased removal of Cr(VI) by the silicon-removed sample (nZVI-RS700 (-Si)) further confirmed that silicon played a significant role in the removal of Cr(VI). Cr(VI) adsorption was enhanced by the dispersion and adsorption of RS700. Following the reaction of RS700-supported nZVI with Cr(VI), ferrous chromite (FeCr2O4) was observed on the nZVI-RS700 composite surface. The formation of FeCr2O4 can be attributed to the reduction of Cr(VI) by the nZVI and coprecipitation of chromium oxide with iron on the RS700 surface. Therefore, nZVI-RS700-Pd is a potential remediation reagent that can be used to effectively treat Cr(VI)-contaminated groundwater.

Enhanced removal of Cr(VI) by silicon rich biochar-supported nanoscale zero-valent iron.

Silicon-rich biochar-supported nanoscale zero-valent iron (nZVI) was studied to evaluate enhanced removal of hexavalent chromium (Cr(VI)) in solution. The compositional structures of the nZVI and biochar-supported nZVI were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectra before and after Cr(VI) reaction. The removal amount of Cr(VI) by nZVI-RS700 (rice straw pyrolyzed at 700 °C) was considerably greater than that by nZVI and other biochar-supported nZVI samples. Upon the silicon was removed from RS700 (nZVI-RS700(-Si)), a significant decreased removal of Cr(VI) was observed. It was revealed that nZVI supported by silicate particles of biochar and the promotion of iron oxidation by SiO2 both contribute to the enhanced Cr(VI) removal. We found that the reduction and adsorption both contributed to the removal of Cr(VI), ferrous chromite (FeCr2O4) was observed on the surface of the nZVI-RS700 composite. The formation of FeCr2O4 is attributed to the reduction of Cr(VI) by nZVI and the adsorption of chromium oxide with iron on the surface of RS700. Therefore, RS700-supported nZVI can be used as a potential remediation reagent to treat Cr(VI)-contaminated groundwater.