Shan-Li Wang

Reduction of Cr(VI) by Crop-Residue-Derived Black Carbon

Burning crop residues is a common postharvest practice on farmland, leading to the accumulation of black carbon (BC) in the soil. To understand the potential role of BC in immobilizing toxic Cr(VI) in soil, this study evaluated the Cr(VI) sorption kinetics at pH levels ranging from 3 to 7 and examined the reaction mechanism of Cr(VI) with BC derived from burning rice straw. The BC samples, after reacting with Cr(VI), were analyzed using Cr K-edge X-ray absorption spectroscopy. The results showed that Cr(VI) was sorbed and subsequently reduced to Cr(III), which was bound to the BC surface through surface complexation and precipitation. As indicated by the diffuse reflection infrared Fourier transform spectra, the phenolic groups of BC are the dominant drivers of Cr(VI) reduction, giving rise to carbonyl/carboxyl groups on the BC surface. The reaction rate of Cr(VI) with BC increased from 10(-3.62) to 10(-1.65) h(-1) as pH was decreased from 7 to 3 because Cr(VI) sorption and reduction both occur faster at low pH. These results suggest that BC derived from burning crop residue is an effective reductant for Cr(VI) and may play an important role in determining the fate of Cr(VI) in BC-rich farmland soils.

Cr(VI) Removal on Fungal Biomass of Neurospora crassa: the Importance of Dissolved Organic Carbons Derived from the Biomass to Cr(VI) Reduction

Interactions of toxic Cr(VI) with renewable biomaterials are considered an important pathway for Cr(VI) removal in ecosystems. Biomaterials are susceptible to dissolution, and their dissolved derivatives may provide an alternative to surface-involved pathway for scavenging of Cr(VI). In this study, dissolved organic carbon (DOC) derived from Neurospora crassa biomass was investigated. The proportion of Cr(VI) reduction by DOC to that on biomass was determined to evaluate the importance of DOC to Cr(VI) reduction. A rapid increase in DOC concentration from 145.6 to 193.7 mg L(-1) was observed when N. crassa-biomass was immersed in 0.01 M KCl solution at pH of 1-5, and polysaccharides, peptides, and glycoproteins with carboxyl, amide, and -NH functional groups, are the major compositions of DOC. On reaction of 96.2 microM Cr(VI) with N. crassa-biomass or DOC, it was estimated that DOC contributed approximately 53.8-59.5% of the total Cr(VI) reduction on biomass in the dark. Illumination enhanced Cr(VI) reduction via photo-oxidation of biomass/DOC under aeration conditions, which formed superoxide for Cr(VI) reduction. At pH 1, photoinduced Cr(VI) reduction by DOC proceeded more rapidly than reduction on the biomass surface. However, at pH >3, with a decrease in Cr(VI) reduction by DOC, photon-excited biomass may become an important electron source for Cr(VI) photoreduction.

Removal of hexavalent Cr by coconut coir and derived chars - The effect of surface functionality

The Cr(VI) removal by coconut coir (CC) and chars obtained at various pyrolysis temperatures were evaluated. Increasing the pyrolysis temperature resulted in an increased surface area of the chars, while the corresponding content of oxygen-containing functional groups of the chars decreased. The Cr(VI) removal by CC and CC-derived chars was primarily attributed to the reduction of Cr(VI) to Cr(III) by the materials and the extent and rate of the Cr(VI) reduction were determined by the oxygen-containing functional groups in the materials. The contribution of pure Cr(VI) adsorption to the overall Cr(VI) removal became relatively significant for the chars obtained at higher temperatures. Accordingly, to develop a cost-effective method for removing Cr(VI) from water, the original CC is more advantageous than the carbonaceous counterparts because no pyrolysis is required for the application and CC has a higher content of functional groups for reducing Cr(VI) to less toxic Cr(III).

Differential expression and regulation of iron‐regulated metal transporters in Arabidopsis halleri and Arabidopsis thaliana – the role in zinc tolerance

To avoid zinc (Zn) toxicity, plants have developed a Zn homeostasis mechanism to cope with Zn excess in the surrounding soil. In this report, we uncovered the difference of a cross-homeostasis system between iron (Fe) and Zn in dealing with Zn excess in the Zn hyperaccumulator Arabidopsis halleri ssp. gemmifera and nonhyperaccumulator Arabidopsis thaliana. Arabidopsis halleri shows low expression of the Fe acquisition and deficiency response-related genes IRT1 and IRT2 compared with A. thaliana. In A. thaliana, lowering the expression of IRT1 and IRT2 through the addition of excess Fe to the medium increases Zn tolerance. Excess Zn induces significant Fe deficiency in A. thaliana and reduces Fe accumulation in shoots. By contrast, the accumulation of Fe in shoots of A. halleri was stable under various Zn treatments. Root ferric chelate reductase (FRO) activity and expression of FIT are low in A. halleri compared with A. thaliana. Overexpressing a ZIP family member IRT3 in irt1-1, rescues the Fe-deficient phenotype. A fine-tuned Fe homeostasis mechanism in A. halleri maintains optimum Fe level by Zn-regulated ZIP transporters and prevents high Zn uptake through Fe-regulated metal transporters, and in part be responsible for Zn tolerance.

Hydration, expansion, structure, and dynamics of layered double hydroxides

Abstract Water-vapor sorption isotherms, relative humidity (RH) controlled powder X-ray diffraction (XRD) data, and new and previously published multi-nuclear NMR spectroscopic data for a wide range of layered double hydroxides (LDHs) provide greatly increased understanding of the effects of hydration state on the structure and dynamical behavior of interlayer and surface anions and the factors controlling the expansion behavior of this group of minerals. Li,Al and Mg,Al LDH phases containing SO42-, SeO42-, PO43-, HPO42-, MoO42-, ClO4- , SeO32-, CO32-, F-, Cl-, Br-, I-, OH-, and NO3- were examined. The phases studied can be grouped into three types based on basal spacing expansion, water sorption, and interlayer anion dynamics: Type 1, significantly expandable (1.5-3.0 Å); Type 2, slightly expandable (expansion <0.5 Å) and with significant interlayer water exchange; and Type 3, essentially non-expandable (0-0.2 Å) and with little interlayer water exchange. For Type 1, the fully expanded phases have a two-water layer structure, and the phase transition from one layer to two layers as determined by XRD consistently correlates with a significant step in the water sorption isotherm and with changes in the interlayer structure and dynamics as observed by NMR spectroscopy. For Type-2 phases, only one-water layer structures form, and the interlayer anions may undergo dynamical disordering with increasing RH, as observed by NMR. For both Types 1 and 2, the first water layer does not cause significant basal spacing expansion due to occupancy of vacant interstitial sites between the anions by the water molecules. For Type-3 phases, there is little interlayer water sorption because the interlayers are essentially closed due to the small size or planar shape of the anions and their strong electrostatic and hydrogen bonding interaction with the hydroxyl layers. RH has no effect on the structural environments and dynamics of the interlayer anions in this group.

Removal of hexavalent chromium from acidic aqueous solutions using rice straw-derived carbon

This study evaluates the removal of Cr(VI) from water by carbon derived from the burning of rice straw. Rice straw was burned in the air to obtain rice carbon (RC), and then the removal of Cr(VI) by RC was investigated under various pHs and ionic strengths. After the experiments, the oxidation state of Cr bound to RC was analyzed using X-ray photoelectron spectroscopy, which revealed that Cr bound to RC was predominately in the trivalent form. The results showed that upon reacting with RC, Cr(VI) was reduced to Cr(III), which was either adsorbed on RC or released back into solution. The extent and rate of Cr(VI) removal increased with decreasing solution pH because the Cr(VI) adsorption and the subsequent reduction of adsorbed Cr(VI) to Cr(III) both occur preferentially at low pH. The minimal effect of ionic strength on the rates of Cr(VI) removal and Cr(III) adsorption indicated specific interactions between Cr(VI)/Cr(III) and their surface binding sites on RC. These results suggest that rice straw-based carbon may be effectively used at low pH as a substitute for activated carbon for the treatment of Cr(VI) contaminated water.

Assignment of the structural OH stretching bands of gibbsite

Abstract Single-crystal Raman and FTIR methods have been combined to study the structural OH groups of gibbsite, Al(OH)3. According to factor group analysis, six unique OH stretching bands [ν(OH)] bands are expected to occur in both IR and Raman spectra. In this study, six ν(OH) bands were observed in both the Raman and IR spectra. Analysis of the gibbsite crystal structure reveals two distinct types of structural OH groups: interlayer and intralayer hydrogen-bonded OH groups. The ν(OH) bands corresponding to these two types of OH groups were clearly resolved using polarized single-crystal Raman spectroscopy. The interlayer hydrogen-bonded OH groups are oriented along the c axis of the crystal and are represented by three ν(OH) bands at 3433, 3370, and 3363 cm-1. In contrast, the intralayer hydrogen-bonded OH groups are oriented nearly parallel to the (001) face and are represented by the ν(OH) bands at 3623, 3526, and 3519 cm-1. Assignment of the ν(OH) bands was based, in part, upon the Lippincott and Schroeder one-dimensional (LS-1D) model of the hydrogen bond. Based upon the known geometry of each OH group, the LS-1D model was used to predict the ν(OH) frequencies corresponding to each OH group. Additional support for the band assignments was obtained by correlation between the single-crystal Raman band intensities and the OH bond orientations obtained from the crystal structure.

Biosorption of Cr(VI) by coconut coir: spectroscopic investigation on the reaction mechanism of Cr(VI) with lignocellulosic material.

In this study, the removal mechanism of Cr(VI) from water by coconut coir (CC) was investigated using X-ray photoelectron spectroscopy (XPS), Cr K-edge X-ray absorption near edge structure (XANES) and FTIR spectroscopy. The results showed that, upon reaction with CC at pH 3, Cr(VI) was reduced to Cr(III), which was either bound to CC or released back into solution. As revealed by the FTIR spectra of CC before and after reacting with Cr(VI), the phenolic methoxyl and hydroxyl groups of lignin in CC are the dominant drivers of Cr(VI) reduction, giving rise to carbonyl and carboxyl groups on CC. These functional groups can subsequently provide binding sites for Cr(III) resulting from Cr(VI) reduction. In conjunction with forming complexes with carbonyl and carboxyl groups, the formation of Cr(III) hydroxide precipitate could also readily occur as revealed by the linear combination fitting of the Cr K-edge XANES spectrum using a set of reference compounds. The phenolic groups in lignin are responsible for initiating Cr(VI) reduction, so lignocellulosic materials containing a higher amount of phenolic groups are expected to be more effective scavengers for removal of Cr(VI) from the environment.

Water-vapor adsorption and surface area measurement of poorly crystalline boehmite

Water-vapor adsorption on poorly crystalline boehmite (PCB) was studied using a gravimetric FTIR apparatus that measured FTIR spectra and water adsorption isotherms simultaneously. The intensity of the delta(HOH) band of adsorbed water changed linearly with water content and this linear relationship was used to determine the dry mass of the sample. Adsorption and desorption isotherms of PCB showed a Type IV isotherm. The BET(H2O) surface area of PCB was 514+/-36 m2/g. The mean crystallite dimensions of PCB were estimated to be 4.5 x 2.2 x 10.0 nm (dimensions along the a, b, and c axes, respectively) based on application of the Scherrer equation to powder diffraction data of PCB. A surface area value of 504+/-45 m2/g calculated using the mean crystallite dimensions was in good agreement with the BET(H2O) surface area. This work also demonstrated a method to determine surface areas for materials with minimal perturbation of their surface structure. In addition, the FTIR spectra of PCB were influenced by changes in water content. The delta(AlOH) band at 835 cm(-1) observed under dry conditions was assigned to the non-H-bonded surface OH groups. As the amount of adsorbed water increased, the intensity at 835 cm(-1) decreased and that at 890 and 965 cm(-1) increased. The 890- and 965-cm(-1) bands are assigned to surface OH groups H-bonded with adsorbed water.

Treatment of complex heavy metal wastewater using a multi-staged ferrite process

Complete removal of heavy metal from complex heavy-metal wastewater (CHMW) requires advanced technology. This study investigated the feasibility of a multi-staged ferrite process (MSFP) for treating CHMW, containing Cd, Cu, Pb, Cr, Zn, Ag, Hg, Ni, Sn and Mn. Our experimental results showed that most of the supernatants after conventional single-step ferrite process could conform to the effluent standard of Environmental Protection Administration in Taiwan. However, the sludge could not satisfy the toxicity characteristic leaching procedure (TCLP) limits due to high Cd, Cu, and Pb concentrations. The performance of MSFP in removing heavy metals from wastewater was subsequently investigated and the parameters of three treating steps in MSFP were optimized under 70°C and 90°C at pH 9, and 80°C at pH 10. After the three-staged procedures, all heavy metals in supernatant and sludge could fulfill the contamination levels regulated by law. In addition, the sludge generated from the MSFP was examined by XRD and forms a stable spinel structure, which could be effectively separated by external magnetic field.