Efficient Bromate And Atrazine Removal With Core-Shell Fe@Fe₂O₃ Nanowires

The rapid development of economy improved our life quality, however, it resulted in great damage to our environment. Developing efficient and environmental-friendly methods to remediate contaminated environment has been paid more and more attentions recently. Among numerous remediation methods, the utilization of zero-valent iron (ZVI) for pollutant remediation has attracted extensive attention in view of its abundance in earth’s crust, high reducibility and environmental compatibility. ZVI with high reducibility could remove pollutants to produce intermediates with low toxicity via reductive pathway, as well as active oxygen molecules in atmosphere to generate reactive oxygen species to degrade organic pollutants via oxidative routes. In this study, we prepared core-shell Fe@Fe2O3 nanowires, a kind of special nZVI, and we investigated the efficient bromate and atrazine removal with the nanowires and their mechanism.1. Bromate, as a byproduct during Advanced Oxidation Process (AOP), is a group 2B substance (possibly carcinogenic to humans) classified by the international Agency for Research on Cancer (IARC). In this study the removal of bromate with core-shell Fe@Fe2O3 nanowires was investigated at neutral pH. The intermediate, effect of surface bound Fe2+ and dissolved oxygen(DO) was investigated in this study. We demonstrated that bromate (BrO3-) with concentration of 1 mg·L-1 was reduced to bromide (Br-) nearly 100% with the core-shell Fe@Fe2O3 nanowires (CSFN) within 90 min. In contrast, bromate could not be removed by commercial iron powder. We investigated the bromine species and evaluated the bromine mass balance during the BrO3- reduction process, and it was found that BrO- species was an inevitable intermediate, followed by the final Br-species. Near 100% bromine recovery could be achieved, suggesting that the main bromine species are BrO3-, BrO-, Br-. In addition, we found the surface bound ferrous ions (Fe2+) on the core-shell Fe@Fe2O3 nanowires contribute 34% for the BrO3- reduction. The rate of bromate removal under Ar was 2.56 times higher than that under air condition. After the ·O2- and H2O2 was captured, the reduction rate decreased 82.4%、31.5%. Interestingly, when the ·OH was cleared, the removal of bromate enhanced 1.19 times than of that with no scavenger. X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopic (XPS) analyses further provided insight into the mechanism of bromate removal with core-shell Fe@Fe2O3 nanowires, and we deduced that the removal efficiency was highly dependent on the surface bound Fe2+ and the ROS species.2. Atrazine, a kind of herbicides, is widely used around the world and has a great influence on endocrine balance of animal and human beings. In this study Ni(Ⅱ) was added to Fe@Fe2O3/air system to change the regular degradation way of atrazine, and the result showed that the degradation rate of atrazine by Fe@Fe2O3/Ni(Ⅱ)/air system was 11.97 times than that by Fe@Fe2O3/air system. It was demonstrated that the first step of atrazine degradation was dechlorination, followed by dealkylation and the oxidation of side chain in the Fe@Fe2O3/Ni(II)/air system after analysis of the degradation intermediates. Control experiments results of CAAT and AAT degradation,’H NMR, and Raman spectra analysis of the intermediates suggested that the triazine ring of atrazine has been broken.