Yuying Huang

Enhanced sequestration of Cr(VI) by nanoscale zero-valent iron supported on layered double hydroxide by batch and XAFS study.

Herein, the reduction of nanoscale zero-valent iron (NZVI) and adsorption of layered double hydroxides (LDH) to sequester Cr(VI) were well combined by the immobilization of NZVI onto LDH surface (NZVI/LDH). The characterization results revealed that LDH decreased NZVI aggregation and thus increased Cr(VI) sequestration. The batch results indicated that Cr(VI) sequestration by NZVI/LDH was higher than that of NZVI, and superior to the sum of reduction and adsorption. The LDH with good anion exchange property allowed the adsorption of Cr(VI), facilitating interfacial reaction by increasing the local concentration of Cr(VI) in the NZVI vicinity. X-ray absorption near edge structure (XANES) results indicated that Cr(VI) was almost completely reduced to Cr(III) by NZVI/LDH, but Cr(VI) was partly reduced to Cr(III) by NZVI with a trace of Cr(VI) adsorbed on corrosion products. The coordination environment of Cr from extended X-ray absorption fine structure (EXAFS) analysis revealed that LDH could be a good scavenger for the insoluble products produced during reaction. So, the insoluble products on NZVI could be reduced, and its reactivity could be maintained. These results demonstrated that NZVI/LDH exhibits multiple functionalities relevant to the remediation of Cr(VI)-contaminated sites.

Enhanced Removal of Uranium(VI) by Nanoscale Zerovalent Iron Supported on Na-Bentonite and an Investigation of Mechanism

The reductive removal of U(VI) by nanoscale zerovalent iron (NZVI) was enhanced by using Na(+)-saturated bentonite (Na-bent) as the support, and the mechanism for the enhanced removal were investigated comprehensively. Under the same experimental conditions, NZVI supported on the negatively charged Na-bent showed much higher removal efficiency (99.2%) of cationic U(VI) than either bare NZVI (48.3%) or NZVI supported on the positively charged bentonite (Al-bent) did. Subsequent experimental investigations revealed the unique roles of bentonite on enhancing the reactivity and reusability of NZVI. First, Na-bent can buffer the pH in reaction media, besides preventing NZVI from aggregation. Second, Na-bent promoted the mass transfer of U(VI) from solution to NZVI surface, leading to the enhanced removal efficiency. Third, the bentonite may transfer some insoluble reduction products away from the iron surface according to X-ray absorption fine structure (XAFS) study. Finally, Na-bent as the adsorbent to Fe(II) makes it more reactive with U(VI), which enhanced stoichiometrically the reduction capacity of NZVI besides accelerating the reaction rate.

X-ray absorption fine structure study of enhanced sequestration of U(VI) and Se(IV) by montmorillonite decorated with zero-valent iron nanoparticles

Herein, using Na-montmorillonite and Al-montmorillonite as templates, supported NZVI with superior reactivity, namely NZVI/Na-Mont and NZVI/Al-Mont, was synthesized and applied for enhanced sequestration of U(VI) and Se(IV). The results indicated that the negatively charged Na-Mont can effectively adsorb cationic U(VI), while the positively charged Al-Mont can adsorb anionic Se(IV), significantly enhancing the rate and extent of U(VI) and Se(IV) sequestration on NZVI due to the synergistic effect between adsorption and reduction. The inhibition effect of 1,10-phenanthroline demonstrated that surface-adsorbed Fe(II) on corrosion products and clay surfaces played an indispensable role in U(VI) and Se(IV) reduction, which was further confirmed by XPS identification. XANES analysis demonstrated that in the NZVI system, Na-Mont and Al-Mont promote the reductive transformation of U(VI) into U(IV), and Se(IV) into Se(0)/Se(−II), respectively. EXAFS analysis indicated the presence of Al/Si scattering for U(VI)-treated NZVI/Na-Mont and Se(IV)-treated NZVI/Al-Mont samples, revealing that Na-Mont and Al-Mont reacted as a scavenger for insoluble products like UO2 and FeSe, thereby, more reactive sites can be used for U(VI) and Se(IV) reduction. Our results suggested that the distinct structure of modified montmorillonite can be utilized for synthesizing supported NZVI to create properties compatible for enhanced enrichment of radionuclides, displaying potential application in nuclear waste management.

Cellular distribution of arsenic and other elements in hyperaccumulator Pteris nervosa and their relations to arsenic accumulation

Synchrotron radiation X-ray fluorescence spectroscopy (SRXRF) was used to study the cellular distributions of arsenic and other elements in root, petiole, pinna of a newly discovered arsenic hyperaccumulator,Pteris nervosa. It was shown that there was a trend inP. nervosa to transport arsenic from cortex tissue to vascular tissue in root, and keep arsenic in vascular during transportation in petiole, and transport arsenic from vascular tissue to adaxial cortex tissues in midrib of pinnae. More arsenic was accumulated in mesophyll than in epidermis in pinnae. The distributions of some elements, such as K, Ca, Mn, Fe, Cu, Zn, in petiole, midrib and pinna were similar to that of arsenic, indicating that those cations might cooperate with arsenic in those transportation processes; whereas the distributions of Cl and Br in pinna were the reverse of that of arsenic, indicating that those anions might compete with arsenic in pinna ofP. nervosa.

Ruthenium Nanoparticles Supported on CeO2 for Catalytic Permanganate Oxidation of Butylparaben

This study developed a heterogeneous catalytic permanganate oxidation system with ceria supported ruthenium, Ru/CeO2 (0.8‰ as Ru), as catalyst for the first time. The catalytic performance of Ru/CeO2 toward butylparaben (BP) oxidation by permanganate was strongly dependent on its dosage, pH, permanganate concentration and temperature. The presence of 1.0 g L(-1) Ru/CeO2 increased the oxidation rate of BP by permanganate at pH 4.0-8.0 by 3-96 times. The increase in Ru/CeO2 dosage led to a progressive enhancement in the oxidation rate of BP by permanganate at neutral pH. The XANES analysis revealed that (1) Ru was deposited on the surface of CeO2 as Ru(III); (2) Ru(III) was oxidized by permanganate to its higher oxidation state Ru(VI) and Ru(VII), which acted as the co-oxidants in BP oxidation; (3) Ru(VI) and Ru(VII) were reduced by BP to its initial state of Ru(III). Therefore, Ru/CeO2 acted as an electron shuttle in catalytic permanganate oxidation process. LC-MS/MS analysis implied that BP was initially attacked by permanganate or Ru(VI) and Ru(VII) at the aromatic ring, leading to the formation of various hydroxyl-substituted and ring-opening products. Ru/CeO2 could maintain its catalytic activity during the six successive runs. In conclusion, catalyzing permanganate oxidation with Ru/CeO2 is a promising technology for degrading phenolic pollutants in water treatment.

Simultaneous compartmentalization of lead and arsenic in co-hyperaccumulator Viola principis H. de Boiss : An application of SRXRF microprobe

The cellular distributions of Pb and As in the leaves of co-hyperaccumulator Viola principis H. de Boiss. were inspected by synchrotron X-ray fluorescence spectroscopy (SRXRF). The results revealed that Pb and As had similar compartmentalization patterns in the leaves. Both elements were enriched in the bundle sheath and the palisade mesophyll. In comparison with the sheath and the mesophyll, the vascular bundle and the epidermis contained lower levels of Pb and As. The palisade enrichment of Pb and As indicated that V. principis H. de Boiss. may have a special mechanism on detoxification of toxic metals within the mesophyll cells. Relative concentrations of both Pb and As in trichome bases were higher than those in trichome rays. The results of hierarchical cluster analysis and correlation analysis confirmed that the distribution of Pb was similar to that of As in the leaves, and their distribution patterns were different from the nutrient elements, such as K, Ca, Mn, Fe, Ni, Cu and Zn. In vivo cellular localization of Pb and As in the leaves provides insight into the physiological mechanisms of metal tolerance and hyperaccumulation in the hyperaccumulators.

Occurrence of bisphenol A in surface and drinking waters and its physicochemical removal technologies

Bisphenol A (BPA), an endocrine disrupting compound, has caused wide public concerns due to its wide occurrence in environment and harmful effects. BPA has been detected in many surface waters and drinking water with the maximum concentrations up to tens of μg·L−1. The physicochemical technology options in eliminating BPA can be divided into four categories: oxidation, advanced oxidation, adsorption and membrane filtration. Each removal option has its own limitation and merits in removing BPA. Oxidation and advanced oxidation generally can remove BPA efficiently while they also have some drawbacks, such as high cost, the generation of a variety of transformation products that are even more toxic than the parent compound and difficult to be mineralized. Only few advanced oxidation methods have been reported to be able to mineralize BPA completely. Therefore, it is important not only to identify the major initial transformation products but also to assess their estrogenic activity relative to the parent compounds when oxidation methods are employed to remove BPA. Without formation of harmful by-products, physical separation methods such as activated carbon adsorption and membrane processes are able to remove BPA in water effluents and thus have potential as BPA removal technologies. However, the necessary regeneration of activated carbon and the low BPA removal efficiency when the membrane became saturated may limit the application of activated carbon adsorption and membrane processes for BPA removal. Hybrid processes, e.g. combining adsorption and biologic process or combining membrane and oxidation process, which can achieve simultaneous physical separation and degradation of BPA, will be highly preferred in future.

Kinetics of selenite reduction by zero-valent iron

Zero-valent iron (ZVI) is an inexpensive agent that can remove many common environmental contaminants. The effects of dissolved oxygen (DO), pH, initial selenite concentration (Se(IV)), ZVI dosage and particle size as well as reaction temperature on Se(IV) removal by ZVI were systematically investigated in this study. Se(IV) removal by ZVI was more favored under oxic conditions with higher reaction rate than under anoxic conditions, ascribing to the promoted ZVI corrosion rate in the presence of DO. Moreover, Se(IV) removal by ZVI was enhanced with increasing ZVI dosage and reaction temperature but decreased with increasing pH and ZVI particle size. The removal rate of Se(IV) by ZVI experienced an increase and then a decrease with initial Se(IV) concentration ranging from 9.9 to 78.6mg L-1. To further describe the reaction rate, a pseudo-?rst-order kinetics was employed, and the calculated activation energy, by fitting the rate constants at different temperatures, was determined to be 32.86kJmol(-1). When fixing other conditions, good linear correlation could be observed between pseudo-first-order reaction rate constants (k(obs)) and ZVI dosage. Compared with other methods for Se(IV) removal reported in literatures, reduction by ZVI was considered a promising technique, which could rapidly and effectively eliminate Se(IV) from waters.

Catalyzing the oxidation of sulfamethoxazole by permanganate using molecular sieves supported ruthenium nanoparticles.

This study developed a heterogeneous catalytic permanganate oxidation system with three molecular sieves, i.e., nanosized ZSM-5 (ZSM-5A), microsized ZSM-5 (ZSM-5B) and MCM-41, supported ruthenium nanoparticles as catalyst, denoted as Ru/ZSM-5A, Ru/ZSM-5B and Ru/MCM-41, respectively. The presence of 0.5gL(-1) Ru/ZSM-5A, Ru/ZSM-5B and Ru/MCM-41 increased the oxidation rate of sulfamethoxazole (SMX) by permanganate at pH 7.0 by 27-1144 times. The catalytic performance of Ru catalysts toward SMX oxidation by permanganate was strongly dependent on Ru loading on the catalysts. The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses confirmed that Ru catalyst acted as an electron shuttle in catalytic permanganate oxidation process. Ru(III) deposited on the surface of catalysts was oxidized by permanganate to its higher oxidation state Ru(VII), which could work as a co-oxidant with permanganate to decompose SMX and was then reduced to its initial tri-valence. During the successive runs, Ru/ZSM-5A could not maintain its catalytic activity due to the deposition of MnO2, which was the reductive product of permanganate, onto the surface of Ru/ZSM-5A. Thus, the regeneration of partially deactivated Ru catalysts by reductant NH2OH⋅HCl or ascorbic acid was proposed. Ru/ZSM-5A regenerated by NH2OH⋅HCl displayed comparable catalytic ability to its virgin counterpart, while ascorbic acid could not completely remove the deposited MnO2. A trace amount of leaching of Ru into the reaction solution was also observed, which would be ameliorated by improving the preparation conditions in the future study.

Sorption of U(VI) on magnetic sepiolite investigated by batch and XANES techniques

Magnetic sepiolite was synthesized by chemical precipitation of Fe3+ and Fe2+ at sepiolite suspension. Removal kinetics of U(VI) on sepiolite and magnetic sepiolite can be well fitted by pseudo-second-order and pseudo-first-order kinetic models, respectively. At pHxa0<xa05.0, U(VI) removal on sepiolite significantly decreased with increasing ionic strength, whereas U(VI) removal on magnetic sepiolite was independent of ionic strength. The maximum removal capacity of sepiolite and magnetic sepiolite at pH 5.0 and 298xa0K calculated from Langmuir model were 28.17 and 74.63xa0mg/g, respectively. XANES spectra suggested that U(VI) was partly reduced to U(IV) at long-term conditions.