饮用水中三种致癌无机酸根的去除

发布时间：2018-06-24 06:00

本文选题：Pd/Fe3_O_4 + 单分散　；参考：《中国科学技术大学》2013年博士论文

【摘要】：恶性肿瘤是当前严重影响人类健康、威胁人类生命的主要疾病之一。癌症与心脑血管疾病、意外事故一起,构成了当今世界的三大死亡原因。因此,世界卫生组织(WHO)把攻克癌症列为一项首要任务。我国卫生部近日公布的2005年城市居民死亡原因的第一位正是恶性肿瘤。近30年来,国内恶性肿瘤的发病率、死亡率呈明显上升趋势。预计在未来20-30年中,我国恶性肿瘤的发病率、死亡率都将呈现持续上升的趋势。越来越多的研究表明：大部分的癌症是由环境中的化学致癌因子造成的,而这些因子又广泛存在于地表水、地下水和经过处理的饮用水中。针对已经污染的水,我们必须进行治理。但是随着污染的加重,水中污染物种类和数量都在快速增加。面对越来越多的污染物,常规的水处理方法已经不能满足要求,因此需要我们提出新的方法,制备新的材料来应对新的挑战。我们选择了饮用水中常见的三种致癌无机酸根(硝酸根、溴酸根、砷酸根)做为研究对象,制备了新的材料、应用了新的方法对水中的这三种致癌无机酸根进行去除,取得了很好的效果。1.我们通过共沉淀法和氢气还原的方法成功制备Pd/Fe3O4催化剂,催化剂由四氧化三铁的纳米晶粒和负载于其表面的2nm的钯颗粒组成。运用TPR, XRD和XPS等手段证明了Pd/Fe3O4催化剂满足催化还原硝酸根的三个基本条件：具有可以激活H2的贵金属Pd;具有一个氧化还原电对Fe2+/Fe3+：Pd和氧化还原电对之间有比较强的相互作用。测试了催化剂还原硝酸根的能力,我们发现硝酸根的还原效率和催化剂中Pd的含量成正比,Pd含量越高催化活性越好。同时催化剂对亚硝酸根的催化活性要强于对硝酸根的活性。通过对反应后的Pd/Fe3O4催化剂的XRD和XPS表征,证明了Pd/Fe3O4在催化反应中确实起到了催化剂的作用。对不同条件下的反应进行了对比,并和文献报道中的双金属催化剂进行了比较,探讨了Pd/Fe3O4催化还原硝酸根的机理：硝酸根在Pd/Fe3O4催化剂和双金属对催化剂上的还原机理不同,在Pd/Fe3O4催化剂上,硝酸根首先在四氧化三铁的表面被还原为亚硝酸根：接着亚硝酸根在两个位置上被还原为铵根离子,一个是四氧化三铁表面,另一个是金属钯表面。反应机理的不同导致了反应产物的不同。通过催化剂的循环使用,确定了催化剂在使用过程中有失活现象的发生。催化剂的失活主要有两方面造成,第一是在催化剂使用过程中催化剂表面的二价铁离子被氧化成三价铁离子,这种失活现象可以通过氢气的还原恢复；另一个原因是在催化反应过程中催化剂中的钯和四氧化三铁之间的相互作用减弱,这种失活作用则不能恢复。 2.通过溶剂热和液相还原的方法制备了单分散的Pd/Fe3O4催化剂,该催化剂由单分散的四氧化三铁和负载于四氧化三铁上面的钯颗粒组成。催化剂的粒径在300～500nm之间,具有超顺磁性,饱和磁化强度可达70emu/go高的磁化强度使催化剂具有易从水中分离的优点,而超顺磁性可以保证外磁场撤出后不团聚,催化剂容易再分散到水中的优点。催化剂的单分散性使催化剂能很好的分散于水中,有效的减少了外传质对催化反应的影响：而Pd在催化剂表面的富集使得内传质的影响可以被忽略；这两点相互结合使得催化剂中的有效成分Pd得到了充分的利用,和其他商业催化剂相比具有更好的催化活性。通过对催化反应的测试,我们发现单分散Pd/Fe3O4催化剂具有很好的催化还原溴酸根的能力；水溶液中常见的阴离子如SO42-,Cl-以及NO3-离子对催化反应的影响不大,而碳酸氢根离子对反应的影响非常大。这是因为碳酸氢根在反应过程中被还原成甲酸,甲酸分解产生的一氧化碳使催化剂中毒所致。通过增加负载量可以从一定程度上解决碳酸氢根使催化剂失活的现象,Pd负载量增加到1wt%,催化剂受到碳酸氢根的影响减小。催化剂的循环试验表明单分散Pd/Fe3O4催化剂具有很好的循环利用性能,对于50ppb的溴酸根水溶液,Pd(1)/Fe3O4催化剂的循环利用次数可达100次以上,经过100次的循环仍然能在5min之内将50ppb的溴酸根降到0。高达100次循环利用次数使催化剂的成本大大降低,为该催化剂在实际生产中的应用奠定了基础。 3.采用溶胶凝胶和相分离的方法制备了具有双孔结构的二氧化硅块体材料,这种结构的特点是具有贯穿整个材料的大孔和位于氧化硅骨架上的中孔。贯穿的大孔可以提供水流的通道,减小传值的影响;介孔可以提供活性位,有利于纳米材料的负载和砷的吸附。通过改变反应温度和PEO的含量可在微米级范围内改变大孔的孔径,实验中我们发现：温度越高,大孔孔径越小：PEO含量越高,大孔孔径越大。通过改变溶剂置换过程中氨水的浓度、水热的温度及时问,可以在纳米范围内改变中孔的大小(6-23nm),氨水浓度越高,水热温度越高,时间越长,中孔的孔径越大。随着中孔孔径的增加,二氧化硅的比表面积下降。通过对负载方法的选择,我们选择了浸渍法负载氧化铈,浸渍法得到的吸附剂一次负载量可达到69wt%。当负载量增加到67wt%时出现大孔孔道阻塞的情况。当负载量小于67wt%时,氧化铈均匀负载于氧化硅的介孔孔道内。砷吸附动力学测试结果显示,三价砷的吸附速率比五价砷快,在低浓度时吸附剂吸附三价能力强于五价砷：在平衡浓度相同时,三价砷的饱和吸附量约为五价砷的两倍;pH对五价砷的吸附影响较大。流动实验表明本文中制备的双孔结构的吸附剂可以很好的去除水中的砷,当EBCT为4min时,三价砷和五价砷的穿透点分别为18000bv和12000bv,阳宗海水的穿透点为20000bv。双孔吸附剂脱附后的吸附剂性能有所下降,但是仍然保持了很好的砷吸附性能
[Abstract]:Cancer is one of the leading causes of human health and threatening human life . It is the first priority for cancer and cardiovascular and cerebrovascular diseases and accidents . In recent 30 years , the incidence and mortality rate of malignant tumors in China has been increasing . More and more studies have shown that most of the cancer is caused by chemical carcinogen factors in the environment . In the coming 20 - 30 years , the incidence and mortality of malignant tumors in China are rising rapidly .

Three kinds of carcinogenic mineral acids ( nitrate , bromate and arsenicum ) which are common in drinking water have been selected as the research objects , new materials have been prepared , and the new method has been applied to remove these three kinds of carcinogenic inorganic acid radicals in water . The Pd / Fe3O4 catalyst is successfully prepared by co - precipitation method and hydrogen reduction method .

The reduction efficiency of nitrate radical and the content of Pd in the catalyst were tested . The catalytic activity of Pd / Fe3O4 catalyst was higher than that of nitrate radical . The catalytic activity of Pd / Fe3O4 catalyst was proved by XRD and XPS .

The reaction between Pd / Fe3O4 and bimetallic catalysts was compared . The mechanism of Pd / Fe3O4 catalytic reduction of nitrate was discussed . On the Pd / Fe3O4 catalyst , the nitrate radical was reduced to nitrite ion on the surface of Pd / Fe3O4 catalyst .

the deactivation of the catalyst is mainly caused by two aspects , the first is that bivalent iron ions on the surface of the catalyst are oxidized into trivalent iron ions during the use of the catalyst , and the deactivation phenomenon can be recovered by reduction of hydrogen ;
Another reason is the reduction of the interaction between palladium and ferric oxide in the catalyst during the catalytic reaction , which cannot be recovered .

2 . A monodisperse Pd / Fe3O4 catalyst is prepared by means of solvent heat and liquid phase reduction . The catalyst is composed of monodisperse Fe3O4 and palladium particles supported on iron tetraoxide . The catalyst has the advantages of being easy to separate from water when the particle size of the catalyst is between 300 and 500 nm , and the super paramagnetism can ensure that the catalyst can be dispersed in water after the external magnetic field is withdrawn , and the influence of the external transmission quality on the catalytic reaction is effectively reduced : and the enrichment of Pd on the surface of the catalyst can be neglected ;
The combination of these two points enables the effective component Pd in the catalyst to be sufficiently utilized , and has better catalytic activity as compared to other commercial catalysts .

Through the catalytic reaction test , we find that monodisperse Pd / Fe3O4 catalyst has good catalytic reduction bromate ability ;
The common anions such as SO 2 - , Cl - and NO3 - ions in the aqueous solution have little influence on the catalytic reaction , and the influence of bicarbonate ions on the reaction is very large . This is because the bicarbonate is reduced to formic acid during the reaction , and the carbon monoxide produced by the decomposition of formic acid causes the poisoning of the catalyst . By increasing the loading amount , the phenomenon that the catalyst is deactivated can be solved to a certain extent , and the Pd loading is increased to 1 wt % , and the influence of the catalyst to the hydrogen carbonate is reduced .

The cycle test of the catalyst shows that the monodisperse Pd / Fe3O4 catalyst has good cyclic utilization performance , and the cycle utilization times of the Pd ( 1 ) / Fe3O4 catalyst can reach more than 100 times for 50 ppb bromate aqueous solution , and the cost of the catalyst can be greatly reduced after 100 cycles , so that the catalyst cost is greatly reduced , and the foundation is laid for the application of the catalyst in actual production .

3 . A silica block material with double pore structure is prepared by sol - gel and phase separation . The structure is characterized by a large hole penetrating the whole material and a middle hole on the silicon oxide skeleton .

By selecting the loading method , we chose the impregnation method to load cerium oxide , and the loading capacity of the adsorbent obtained by the impregnation method can reach 69wt % . When the loading amount is increased to 67 wt % , the large pore channel blockage occurs . When the loading amount is less than 67wt % , the cerium oxide is uniformly loaded in the mesoporous pore channel of the silicon oxide .

The results show that the adsorption rate of trivalent arsenic is faster than that of pentavalent arsenic . The adsorption capacity of trivalent arsenic is about twice that of pentavalent arsenic at low concentration . The adsorption of trivalent arsenic is about twice that of pentavalent arsenic when the equilibrium concentration is the same . The flow experiment shows that the adsorption of trivalent arsenic and pentavalent arsenic is 18000bv and 12000bv , respectively .
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU991.2

【参考文献】