【作者】 徐贞贞；

【导师】 陈忠林；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2009， 博士

【摘要】 传统的水处理工艺对水中的痕量有害有机污染物去除甚微,且这些有机物的在后续消毒过程中会引起消毒副产物的产生。化学氧化法是去除水中有机污染物的理想途径,但一般的氧化剂很难高效的氧化去除水中痕量的有机污染物。金属羟基氧化物催化臭氧氧化技术是强化臭氧氧化去除水中痕量有机污染物的新方向。掌握金属羟基氧化物催化臭氧氧化的基本规律,是寻找经济高效的水处理催化剂并正确应用催化臭氧氧化技术的基础。论文以实验室制备的六种过渡金属羟基氧化物作为催化剂,分别对它们进行了结构和表面性质的表征。通过考察各催化剂催化水中臭氧分解和氧化痕量对氯硝基苯(pCNB)的能力,筛选出催化活性较高的催化剂,并对其催化臭氧分解的机理进行了推测。最终探讨了催化剂的结构和表面性质对催化能力的影响。在单独臭氧氧化工艺中,水中痕量pCNB的去除效率随着臭氧浓度和水体纯净度的增加而增大,而与pCNB初始浓度成负相关性。羟基自由基的抑制剂和溶液pH值对臭氧氧化pCNB的反应影响显著。反应过程中,TOC的去除率比pCNB低50个百分点左右。实验中成功制备了羟基氧化锰(MnOOH)、羟基氧化铁(FeOOH)、羟基氧化钴(CoOOH)、羟基氧化镍(NiOOH)、羟基氧化铜(CuOOH)和羟基氧化锌(ZnOOH)六种过渡金属羟基氧化物,材料的单体大都具有纳米尺寸,对气体具有一定的吸附能力和容量。通过检测发现,催化剂表面主要含有羟基官能团,CuOOH的表面羟基含量较小,其他催化剂均含有丰富的表面羟基。各催化剂中构成羟基的氧种各不相同,ZnOOH、FeOOH和CoOOH中以化学吸附氧为主,MnOOH和CuOOH中所含的主要为晶格氧,而NiOOH中大多为表面吸附氧。ZnOOH、FeOOH和CoOOH具有较高的催化活性,可以使臭氧氧化去除pCNB的效率从55%分别提高至85%、92%和99%以上。而MnOOH、NiOOH和CuOOH没有表现出促进臭氧氧化降解pCNB的能力。催化过程中有微量的金属离子溶出,但均低于国标限值。分别研究了ZnOOH、FeOOH和CoOOH三种高效催化剂催化臭氧氧化pCNB的效能和反应过程的影响因素,结果表明:pCNB的去除率随臭氧浓度、催化剂投量和反应温度的提高而增大;反应体系对初始浓度为50μg/L和100μg/L的pCNB去除效率最高;随着水体纯净度的降低,催化剂促进pCNB降解的能力显著下降;NO3-、Na+和K+对催化臭氧氧化pCNB的影响可以忽略,水体硬度可以小幅度的促进催化臭氧氧化反应。一定浓度Cl-的存在可以使pCNB的去除率略有降低,SO42-具有一定的表面络合能力,使催化剂的催化能力有所下降,PO43-可以显著抑制催化体系中pCNB的去除;催化体系中pCNB去除率受水中HCO3-碱度的影响较大,抑制作用随HCO3-浓度的增加而增强;水体中微量腐殖酸对pCNB的去除基本没有影响,而高浓度腐殖酸则抑制pCNB的去除;催化剂随着烘制温度的升高其催化活性不断下降;催化剂多次使用后,仍可保持较好的催化能力。羟基氧化铁、羟基氧化钴和羟基氧化锌可以显著加速水中臭氧和pCNB的分解,分别使臭氧的一级分解速率常数提高了1.25倍、1.52倍和1.87倍,使pCNB的降解速率分别提高至单独臭氧氧化的2倍、3倍和9倍。叔丁醇可以大幅度的抑制催化反应中pCNB的降解,在三种催化反应体系中均检测到了羟基自由的产生,证明催化臭氧氧化工艺中pCNB的降解是以羟基自由基为主、臭氧分子为辅的氧化反应。催化剂在pH=6.5和7.5的中性溶液中催化能力最强。表面羟基是决定催化剂催化水中臭氧分解能力的关键因素,催化活性较高的羟基氧化物都具有较大的表面羟基密度。催化剂中的化学吸附氧是催化反应中的活性氧种,化学吸附氧上的结构羟基或表面吸附水中的氢离子形成的吸附羟基是反应的活性羟基,溶液中的臭氧分子在此类活性羟基上吸附并发生分解反应,生成高活性的·OH氧化物质。更多还原

【Abstract】 It is difficult for traditional water treatment process to remove trace concentration of organic pollutants, and then some disinfection by-products would be generated in the process of chlorination. Chemical oxidation has been considered to be an efficient way for the removal of organic pollutants in water, however, it is not so efficient in the destruction of recalcitrant organic pollutants. Research of metal hydroxides catalytic ozonation has recently received much attention. It is important to know the catalytic mechanism of metal hydroxides for the decomposition of ozone in water.Hydroxides of six transitional metals, prepared in laboratory, were used as catalysts in the paper. Some studies were carried out on the characterization of their structure and surface properties. The catalytic decomposition of ozone and p-chloronitrobenzene (pCNB) in water were investigated, and then some hydroxides with high catalytic activity were selected out and applied in the catalytic oxidation of trace concentration of pCNB. The mechanism of catalytic ozone decomposition was discussed. The role of the catalyst structure and surface hydroxyl in catalytic ozonation were finally summarized.In the solo ozone oxidation of pCNB, the removal efficiency gets better with increasing initial concentration of ozone and the water purity, but the initial concentration of pCNB has negative effects on its removal. Hydroxyl radical inhibitor and solution pH significantly affected the ozonation of pCNB. Removal of TOC was not so high as that of pCNB in the process, about 50 percentage points lower.The catalyst prepared in the laboratory were manganese hydroxide (MnOOH), iron hydroxide (FeOOH), cobalt hydroxide (CoOOH), nickel hydroxide (NiOOH), copper hydroxide (CuOOH) and zinc hydroxide (ZnOOH). Most materials have nano-sized monomers, all of them have certain ability and capacity for the adsorption of gas. Experimental results show that, the mainly functional groups on the catalyst surface was hydroxyl, all the hydroxides have abundant surface hydroxyl groups except CuOOH. Species of hydroxyl oxygen were found to be different in different hydroxides. Hydroxyl groups on the surface of ZnOOH, FeOOH and CoOOH mainly contain chemi-adsorbed oxygen, MnOOH and CuOOH have hydroxyl groups with the lattice oxygen, and the oxygen in NiOOH was identified as that in surface-adsorped hydroxyl groups.Iron hydroxide, cobalt hydroxide and zinc hydroxide present strong catalytic activity in the reaction. At reacting time of 20min, the catalytic removal of pCNB by FeOOH, CoOOH and ZnOOH in distilled water increases from 55% to 85%, 92% and 99%, respectively. Manganese hydroxide, copper hydroxide and nickel hydroxide hold no catalytic abilities in the ozonation of pCNB in this experiment. The dissolution of metal ions in the catalytic process can be ingnored, for the dissolved amount was much less than the limit in national standard.Efficiency and affecting factors of catalytic ozonation of pCNB by ZnOOH, FeOOH and CoOOH were investigated. Results show that, the removal of pCNB increased with the increasing reaction temperature, water purity, ozone concentration and catalyst dosage; the best removal efficiency of pCNB was obtained when the initial concentration of pCNB was 50μg/L and 100μg/L; effects of NO3-, Na+ and K+ on the catalytic ozonation of pCNB can be ignored, the degradation of pCNB were slightly promoted in the presence of Ca2+ and Mg2+, the ozonation of pCNB were slightly inhibited by high concentration of Cl-, the removal efficiency of pCNB decreased in the presence of SO42-, as hydroxyl inhibitors, PO43- and HCO3- can significantly inhibit the catalytic degradation of pCNB; the removal of pCNB decreased with the increasing concentration of humic acid; the catalytic ability of the catalyst get weaker with increasing the calcinated temperature; after five successive recycles, the catalyst remained stable in the catalytic ozonation of pCNB.Hydroxides of iron, cobalt and zinc can significantly speed up the decomposition of ozone and pCNB in water. Rate constant of ozone decomposition increased 1.25 times, 1.52 times and 1.87 times, respectively. The catalytic degradation rates of pCNB were 2 times, 3 times and 9 times higher as the solo ozonation. Tert-butanol can significantly inhibit the degradation of pCNB in these three catalytic reaction systems. Enhancements of hydroxyl free radicals were obtained in the catalyzed ozone decomposition by FeOOH, CoOOH and ZnOOH. So the catalytic oxidation of pCNB can be divided into two parts: main reaction with hydroxyl radicals and accessorial oxidation by ozone molecules. The optimal catalysis is achieved at solution pH=6.5 and pH=7.5.Surface hydroxyl groups were revealed to be important active sites on catalyst. Hydroxides, which show high catalytic activity in ozone decomposition, have abundant surface hydroxyl groups. Chemi-adsorbed oxygens were thought to be active oxygen species, hydroxyls formed on the adsorbed oxygen (structural hydroxyls or hydroxyls formed through adsorption of hydrogen ions in water) have the ability to catalyse ozone decomposition. Ozone molecules in water can be adsorbed on these active hydroxyls, then ozone decomposition with the production of·OH was promoted.更多还原