【作者】 杨婷；

【导师】 魏晓妹；

【作者基本信息】 西北农林科技大学 ， 水文学及水资源， 2013， 博士

【摘要】 水体中多种含氧酸盐污染物，给人体生命健康带来极大危害。硝酸盐是普遍存在于地下水中的一种典型的含氧酸盐污染物，过量摄入硝酸盐可引发高铁血红蛋白症和诱发癌症，目前仍没有较完善的地下水硝酸盐处理方法。纳米TiO₂光催化法是一种颇具应用前景的水处理方法，本文以纳米TiO₂光催化法为主要研究方法，选取Evonik P90为TiO₂催化剂，通过室内试验，探讨了以硝酸盐为主的含氧酸盐污染物的光催化还原去除。论文的主要结论包括以下几个方面：（1）制备了改性的P90/Ag光催化剂，与P90相比，P90/Ag具备更强的光催化活性，光照35min后，全部NO₃^-被还原为84.5%的N₂和15.5%的NH₄⁺。分析了溶液pH值、催化剂用量、初始硝酸盐浓度以及甲酸与硝酸盐摩尔比（IFNR）对硝酸盐光催化还原的影响。结果表明，酸性pH条件有利于硝酸盐的还原，催化剂用量为1g/L时硝酸盐去除速率最快，增加硝酸盐的初始浓度可以提高其绝对去除速率，而增加IFNR对提高光催化活性的效果不甚明显。试验结果为选用合适的光催化剂及寻求优化反应条件提供了试验依据。（2）基于光催化直接去除饮用水中硝酸盐存在的不足，提出了用离子交换与光催化还原相耦合去除地下水中硝酸盐的方法。试验结果表明，光催化还原法可以高效去除模拟盐水和真实离子交换废液中的硝酸盐，且处理后的废液可以重复利用于离子交换树脂的再生过程，认为离子交换与光催化还原耦合法是可行的。耦合法相比单一的离子交换法或光催化还原法，不仅可以降低处理和排放离子交换废液的高昂费用和节省NaCl的消耗，而且通过间接处理离子交换废液而不是地下水，可以最小化副产物（NO₂^-，NH₄⁺）对水质的二次污染，使处理后的地下水水质得到保证，从而为地下水中硝酸盐的去除提供了一条新途径。（3）在实验室研究的基础上，将试验规模放大70倍数，分析探讨了中试放大条件下硝酸盐的光催化去除效果。以PhotoCat@设备为中试反应器，清水中硝酸盐的光催化去除难以实现，而离子交换盐水中的NO₃^-以0.7mg-N/（L min）的速率被有效去除。由于PhotoCat@设备采用UV254低压汞灯为紫外光源，甲酸光解和光催化氧化的协同作用，使得甲酸和硝酸盐以接近1:1的比例共同去除得以实现。中试结果进一步展现了离子交换和光催化耦合法的应用潜力，为光催化去除硝酸盐的工业化应用提供了科学依据。（4）将纳米TiO₂光催化还原法拓展至溴酸盐等含氧酸盐的光催化去除，分别考查了含氧酸盐的光催化还原速率、反应动力学、还原产物以及与甲酸的共同去除效应。结果表明，光催化条件下，溴酸盐、氯酸盐、亚硝酸盐、重铬酸盐、碘酸盐和亚氯酸盐均得到了不同程度的去除，仅高氯酸盐不能被光催化去除。溴酸盐、氯酸盐和重铬酸盐分别被还原为单一的还原产物Br-、Cl-和Cr（III），可以实现与甲酸共同降解；而生成多种还原产物的含氧酸盐（如NO₃^-、NO₂^-）难以实现与甲酸的共同全部去除。含氧酸盐与甲酸共同降解的试验，为光催化直接去除饮用水中的含氧酸盐污染物和减少甲酸的二次污染提供了参考依据。（5）分组比较了光催化条件下各含氧酸盐的还原速率，结果表明，三种卤素含氧酸盐的光催化还原速率从大到小排序为IO₃^->BrO₃^->ClO₃，三种不同价态的含氯酸盐的光催化还原速率从大到小排序为ClO₂^->ClO₃^->ClO₄^-，酸性条件下各含氧酸盐的光催化反应速率从大到小排序为：BrO₃^->NO₂^->ClO₃^->NO₃^->Cr（VI），并从标准电极电势、原子半径、电子轨道排布式、电子亲和能和X-O键离解能等方面探讨了影响含氧酸盐还原速率的原因。更多还原

【Abstract】 Oxo-anions contaminants in water pose a great risk to human health. As a typicaloxo-anions contaminant, nitrate is prevalent in groundwater. Intake of excess nitrate maycause methemoglobinemia and cancer. So far there has been no perfect nitrate reductiontechnology for drinking water treatment. Photocatalysis is a promising technology for watertreatment. This study investigated the photocatalytic reduction of nitrate and other oxo-anionsthrough laboratory experiments mainly using photocatalysis with Evonik P90as the titaniumdioxide photocatalyst. The major conclusions of this work are presented as follows:（1） P90/Ag photocatalyst was synthesized, which showed higher photocatalytic activitythan P90. After35minutes of irradiation, nitrate was completely removed to84.5%N₂and15.5%NH₄⁺using P90/Ag. The influence of pH, catalyst dosage, initial nitrate concentrationand formic acid-to-nitrate molar ratio （IFNR） on photocatalytic nitrate reduction wasinvestigated. The results showed that acid condition was favorable for nitrate reduction;Nitrate removal was fastest at catalyst dosage of1g/L; Increasing the initial nitrateconcentration inhanced it’s absolute removal rate; Increasing IFNR did not significantlyincrease photocatalytic activity. Those results provided experimental support for choosing asuitable catalyst and seeking for optimized reaction condition.（2） Based on the shortcomings of direct photocatalytic nitrate reduction in drinking water,a technology that combining ion exchange with photocatalytic reduction was proposed toremove nitrate from groundwater. Experimental results showed that it was effective to removenitrate from synthetic and real ion exchange brines using photocatalytic reduction, and thetreated brine could be reused for regeneration of ion exchange resins. It is believed that ionexchange combined with photocatalytic reduction is a feasible way to remove nitrate.Compared with single ion exchange or photocatalysis, the combination technology can greatlydecrease the expense on brine discharge or treatment and save salt consumption, moreover, bytreating the ion exchange brine instead of groundwater, it can minimize the contamination ofgroundwater with side products（NO₂^-，NH₄⁺） and ensure the water quality. Therefore, Thiscombination technology can be a new approach for nitrate reduction from groundwater. （3） Based on laboratory research work, the scale of experiment was enlarged by70times,and photocatalytic nitrate reduction was examined under pilot scale condition usingPhotoCat@as the pilot scale photoreactor. The results showed that nitrate removal in nanopurewater was hard to achieve, while nitrate in ion exchange brine was effectively removed at arate of0.7mg-N/（L min）. Using UV254low pressure mercury lamp as the light source, bothphotolysis and photocatalytic oxidation of formic acid occurred, which made simultaneousremoval of formic acid and nitrate possible. Those results further testified the potential of thecombination of ion exchange and photocatalytic reduction, and provided scientific proof forindustrial application of photocatalytic nitrate reduction.（4） Expanding photocatalysis from removal of nitrate to bromate and other oxo-anions,this study investigated their photocatalytic removal activity, kinetics, by-products as well assimultaneous removal with formic acid. The results showed that bromate, chlorate, nitrite,dichromate, iodate and chlorite could be photocatalytically reduced, but perchlorate could notbe removed. Bromate, chlorate and dichromate were reduced to bromide, chloride andtrivalent chromium, respectively, and could be simultaneously removed with formic acid. Butfor those yielding multiple byproducts （e.g., NO₃^-、NO₂^-）, they were hardly simultaneouslyremoved with formic acid. The study of simultaneous removal of oxo-anions with formic acidprovided important reference for removal of oxo-anions contaminants directly from drinkingwater and minimization the secondary pollution of formic acid.（5） Photocatalytic removal rates of oxo-anions were compared. Halogen oxoanions weresorted as IO₃^->BrO₃^->ClO₃, and chlorates were sorted as ClO₂^->ClO₃^->ClO₄^-. Under acidiccondition, oxo-anions were sorted as BrO₃^->NO₂^->ClO₃^->NO₃^->Cr（VI）. The standardreduction potential, atomic radii, electron orbital configuration, electron affinity, and the bonddissociation energy were good indicators for the relative of reduction using photocatalysis.更多还原