title: Fine structure characterization of zero-valent iron nanoparticles for decontamination of nitrites and nitrates in wastewater and groundwater.
abstract: The main objectives of the present study were to investigate the chemical reduction of nitrate or nitrite species by zero-valent iron nanoparticle (ZVIN) in aqueous solution and related reaction kinetics or mechanisms using fine structure characterization. This work also exemplifies the utilization of field emission-scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), and x-ray diffraction (XRD) to reveal the speciation and possible reaction pathway in a very complex adsorption and redox reaction process. Experimentally, ZVIN of this study was prepared by sodium borohydride reduction method at room temperature and ambient pressure. The morphology of as-synthesized ZVIN shows that the nearly ball and ultrafine particles ranged of 20-50 nm were observed with FE-SEM or TEM analysis. The kinetic model of nitrites or nitrates reductive reaction by ZVIN is proposed as a pseudo first-order kinetic equation. The nitrite and nitrate removal efficiencies using ZVIN were found 65-83% and 51-68%, respectively, based on three different initial concentrations. Based on the XRD pattern analyses, it is found that the quantitative relationship between nitrite and Fe(III) or Fe(II) is similar to the one between nitrate and Fe(III) in the ZVIN study. The possible reason is due to the faster nitrite reduction by ZVIN. In fact, the occurrence of the relative faster nitrite reductive reaction suggested that the passivation of the ZVIN have a significant contribution to iron corrosion. The extended x-ray absorption fine structure (EXAFS) or x-ray absorption near edge structure (XANES) spectra show that the nitrites or nitrates reduce to N2or NH3while oxidizing the ZVIN to Fe2O3or Fe3O4electrochemically. It is also very clear that decontamination of nitrate or nitrite species in groundwater via thein-situremediation with a ZVIN permeable reactive barrier would be environmentally attractive.
authors.affiliation: Department of Chemical Engineering & Materials Science/Fuel Cell Center, Yuan Ze University, Chung-Li City 320, Taiwan, Republic of China.
authors.forename: Kuen-Song
authors.initials: KS
authors.lastname: Lin
authors.affiliation: Civil and Environmental Engineering Department, University of Central Florida, Orlando, FL 32816, USA.
authors.forename: Ni-Bin
authors.initials: NB
authors.lastname: Chang
authors.affiliation: Department of Chemical Engineering & Materials Science/Fuel Cell Center, Yuan Ze University, Chung-Li City 320, Taiwan, Republic of China.
authors.forename: Tien-Deng
authors.initials: TD
authors.lastname: Chuang
keywords: XANES/EXAFS; chemical reduction; kinetics; nitrate; nitrite; zero-valent iron nanoparticles