Preparation And Characterization Of Silicate And Its Application In Catalytic Ozonation Of Chloronitrobenzenes In Water

In the traditional water treatment process, the trace organic pollutants in aqueous solution is difficult to be removed. Many strategies such as, adsorption, membrane seperation, bioaugmentation, zero-valent metal reduction and so on, have been carried out to solve the pollutants problem in aqueous solution. However, many drawbacks of these strategies such as low removal efficiency, high cost, make them difficult to be utilized in the practical water treatment. So, exploring new strategy in drinking water treatment to resolve trace organic pollutants problem in aqueous solution is necessary.Four kinds of common transitional metal silicate, prepared in laboratory, were used in the paper as ozone catalyst. Physical structure and surface properties of the four kinds of catalysts were characterized in the study. Static experiments and continuous flow experiments were conduct to study the catalytic activity of the four kinds of catalysts for ozonation of chloronitrobenzenes (CNBs). Then, the highest catalytic activity catalyst was used to study the catalytic properties in the catalytic oxidation of CNBs in aqueous solution.The catalysts prepared in the laboratory were iron silicate, manganese silicate, copper silicate and zinc silicate. TEM analysis shown that all of them contain many nano-sized oxide. Most materials have certain ability and capacity for the adsorption of gas, moreover, zinc silicate have the maximum adsorption capacity, followed by iron silicate, manganese silicate and copper silicate. FTIR analysis results shown that, hydroxyl groups was the mainly functional groups on the surface of the four catalysts. Zinc silicate has the maximum hydroxyl density. In addition, the zero charge of four catalysts are in the neutral range.Iron silicate, manganese silicate, zinc silicate, copper silicate exhibited good catalytic activity in the continuous flow experiments and static experiments. However, no matter in what process, the zinc silicate also exhibited highest catalytic activity. The adsorption capacity of four catalysts were very poor. After 24h adsorption, the CNBs removal efficiency were less than 5%. The pH stability of the four catalysts was well.The efficiency and affecting factors of zinc silicate catalytic ozonation of CNBs were studied in the preocesses of static experiments and continuous flow experiments, respectively. Experiment results showed that no matter in what process, the removal of CNBs increased with the increasing of initial concentration of ozone, catalyst dosage, water purity. In the static experiments, under the condition of ozone dosage 0.8mg/L, zinc silicate dosage 300mg/L, the initial concentration of CNBs was 200μg/L, the removal efficiency of CNBs in deionized water was best. However, in the continuous flow experiments, when the initial concentration of CNBs was 50μg/L, the removal efficiency of CNBs in tap water was best.Effect of Ca²⁺,Mg²⁺,Na⁺,K⁺ and NO3-on the catalytic ozonation of CNBs were very less. The removal efficiency of CNBs was decreased with the increase of the Cl- and PO43-. The ozonation of CNBs were slightly inhibited by the SO42-. For the HCO₃^- was the hydroxyl inhibitors, so in aqueous solution, it could inhibit the zinc silicate catalytic ozonation of CNBs. The ramoval efficiency of CNBs increased with the decrease concentration of humic acid, moreover, compared the process of static experiments in deionized water, the effect of HCO₃^- and humic acid were much less in the process of continuous flow experiments in tap water. With the increasing of the calcinated temperature, the catalytic activity of zinc silicate get weaker. After successive recycles, the catalytic activity of the zinc silicate kept stable.The mechanism of zinc silicate catalyzed ozonation of CNBs were carried out. Based on the tert-butanol inhibition test and ESR analysis, we conclused that in the process of zinc silicate catalytic oznation ,·OH was the activity species . The effect of anions concentration and solution pH on the catalytic ozonation confirmed that in the zinc silicate catalyzed ozonation of CNBs, hydroxyal groups which were on the surface of zinc silicate were the activity site.