| The application of ozonation in drinking water deep treatment is widespread. But ozonation will generate a by-product—bromate when treating with water-containing bromide ion, which is carcinogenic. Bromate has been classified as a group2B or possible human carcinogen by the International Agency for Research on Cancer, and according to drinking water quality standards in china (GB5749-2006), the maximum contaminant level for bromate is10μg/L. Therefore it is urgent to study the removal of bromate in drinking water. Ordered mesoporous carbon (OMC) has an advantage of large surface area, high adsorbability, strong thermal stability and high resistance to hydrolysis with highly ordered mesoporous structure. OMC has a favorable adsorption of bromate without changing it into non-toxic substance.Nanoscale zero-valent iron has a merit of high reactivity, which leads to an effective removal of bromate. However, due to the high reducibility led itself easily oxidized and agglomeration, this decrease the reactivity and migration rate of Fe0. To overcome the above problems, we proposed to design novel supported Fe0composites using ordered mesoporous carbon as supports (Fe0/OMC). This can both guarantee the effective adsorption properties of OMC and maintain the reactivity of zero-valent iron, achieving the purpose of effective removal of bromate.Firstly, ordered OMC-Z particles were synthesized through simple hard-templating routes by using SBA-15as a template agent, sucrose as carbon precursor. Then, Fe0/OMC particles, with mesoporous structure and nanoscale iron particles in one were synthesized by using OMC as a template, ferrous sulfate as an iron source with the liquid phase reduction method. The resultant materials were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Nitrogen sorption/desorption and Zeta potential. Single factor (such as react time, dosage, bromate concentration, temperature and pH etc.) that may influence the bromate removal efficiency by both OMC and nano Fe0/OMC material was studied in detail. The results showed that:1. The as-synthesized OMC and nano Fe0/OMC materials possessed an ordered hexagonal mesoporous structure as SBA-15. The specific surface areas of OMC and nano Fe0/OMC materials were found to be1061m2/g and118m2/g, respectively. The specific surface area and pore volume have decreased after the loading.2. The results showed that bromate removal efficiency would increase with the increase of dosage of OMC and nano Fe0/OMC and the reaction time. The optimum bromate removal by OMC was observed over a wide initial pH range (5.0-10.0). While, nano Fe0/OMC composite has a good efficiency in acid condition when react with bromate. And alkaline conditions were unfavorable for bromate removal.3. Thermodynamics studies have shown that adsorption of bromate on OMC is spontaneous exothermic process, while temperature has little effect on bromate removal by nano Fe0/OMC material. The experimental data shows that the physical and chemical properties of OMC material after the loading have changed. Kinetic models were used to correlate the kinetic experimental data and the kinetic parameters reveal that the kinetic data of OMC and nano Fe0/OMC in bromate removal were well fitted to pseudo-second-order model. The linear correlation coefficients were0.994and0.999, respectively. According to the Weber and Morris model fitting, the intro-particle diffusion has in part controlled the reaction process during OMC and nano Fe0/OMC removing the bromate ion.4. The reaction of OMC and bromate was a purely physical adsorption process, without changing the valence of bromate. While, both oxidation-reduction process and adsorption process exist during nano Fe0/OMC react with bromate, in which the former process is dominant. |
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