Aqueous Ethanol modified Nanoscale Zerovalent Iron in Bromate Reduction: Synthesis, Characterization, and Reactivity

摘要

Nanoscale zerovalent iron (NZVI) was evaluated for the reduction of bromate that is a highly persistent and carcinogenic oxyhalid formed as an ozonation byproduct during oxidative disinfection in drinking water treatment. Solid-phase NZVI with different surface areas was controllably synthesized using a liquid phase reduction. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and a Brunauer-Emmett-Teller (BET) surface area and porosity analyzer were utilized to characterize particle size, surface morphology, surface area, and corrosion layers formed onto NZVI before and afterthe reduction of bromate. Surface area of synthesized NZVI was found to be influenced strongly by ethanol contents during synthesis with a maximum surface area of 67.51 ± 0.35 m~2/g in a 90% aqueous ethanol; additionally, capsule structures of NZVI with amorphous phase, in which tens of particles with diameters of 2-5 nm were packed into an iron oxide/hydroxide layer, were also synthesized using 100% ethanol as a solvent. Subsequent XRD and TEM results revealed that in a 20 min bromate reduction NZVI mostly converted to Fe_2O_3 and Fe_3O_4 corrosion products mixed with iron hydroxides. Compared to bromate reduction using microsized ZVI in a pseudo-first-order kinetic model, NZVI enhanced the reduction efficiency following a second-order kinetic model, with observed second-order rate constants (k_(obs)) of 2.57 × 10~(-4) to 2.19 × 10~(-3) μg~(-1) min~(-1)L Humic acid was found to be the most influencing factorto decrease NZVI reactivity in bromate reduction. However, the effect of sonication pretreatment showed that the bromate reduction efficiency could be enhanced by increasing the actual reactive surface area. Our results suggest that application of NZVI is a viable process for bromate reduction in water treatment.