新型石墨相氮化碳的制备及在环境有机污染物检测和处理中的应用

发布时间：2018-09-08 16:26

【摘要】：近年来,随着工业废水及生活污水等的排放,水质被大量的污染。美国国家环保局(USEPA)根据污染物的毒性、生物降解的可能性以及在水体中出现的几率等因素,规定需要优先控制的129种有毒物质,其中有机污染物有114种,这类有机污染物在水体中残留时间长,有蓄积性和剧毒性等,对人类有致毒、致癌的性能。由于它们在水环境中的痕量浓度,因此开发有效的分析技术以分析超痕量化合物是至关重要的。而有机污染物在生产和使用过程中进入环境水中达到一定浓度时,对农业、林业等会带来不可预估的破坏,也会影响人类和动植物的正常生活,因此人们不仅需要对环境水中的有机污染物进行检测,而且还需要对其进行吸附和降解处理。为了达到更好的富集、吸附和降解效果,所用到的材料通常需要比表面积大,易于分散,与目标分析物有较好的作用,处理速度快等特点。石墨相氮化碳(g-C_3N_4)对富集、吸附和降解有机芳香族化合物显示出巨大的潜力。g-C_3N_4的电子离域性质,赋予了它具有多种吸附机制,主要包括络合效应,氢键,氧化还原反应,π-π共轭效应,疏水效应,酸碱反应和静电相互作用等。然而,g-C_3N_4的分离过程中需要过滤或离心,这样的操作繁琐并且耗时。Fe_3O_4纳米粒子是最广泛使用的磁性材料之一,一方面它们具有较好的稳定性和较大的比表面积;另一方面,它们容易合成、聚集,易于固定在吸附剂表面上,并且不会有效地吸附分析物。因此,可以将Fe304固定在g-C_3N_4的表面上,以克服单独使用g-C_3N_4作为吸附剂时的不足。此外,g-C_3N_4还具有无毒和可见光响应(半导体带隙2.7eV),它的这种独特的结构决定了其在光催化领域的广泛应用。但是,普通g-C_3N_4的催化活性较小,可以通过增大其比表面积,这样有利于目标物与g-C_3N_4有更多的接触,从而提高g-C_3N_4的催化活性。因此本实验利用合成的新型大比表面积的天鹅绒状高分散性的V-g-C_3N_4/Fe304纳米复合材料对多氯联苯(PCBs)进行富集检测,对氯酚(CPs)进行吸附处理,最后合成不同比表面积的g-C_3N_4对氯酚进行光催化降解,以选出最佳光催化降解氯酚的材料。具体内容和结果如下:(1) V-g-C_3N_4/Fe_3O_4纳米复合材料的合成及在检测环境水中的多氯联苯的应用通过尿素的水辅助一步热缩合法制备天鹅绒状的石墨相氮化碳(V-g-C_3N_4),该合成方法简单、易于操作。将制备好的V-g-C_3N_4和Fe_3O_4通过化学共沉淀法制备V-g-C_3N_4/Fe_3O_4纳米复合材料。然后对材料进行热分析、元素分析、FT-IR、XRD、BET和TEM表征,结果表明此纳米复合材料成功合成。然后使用此纳米复合材料,对十种PCBs的混合溶液进行磁性固相萃取,在此过程中,利用响应曲面法(RSM)对影响固相萃取的因素,如温度、时间、pH值、盐度等进行优化。使用HPLC测定优化吸附条件和优化洗脱条件时的溶液,而使用GC-MS测定经过MSPE后的洗脱液,检测开发方法对四种实际水样中的PCBs富集的线性和检测限。实验结果表明,在最优条件下:本方法对PCBs具有较好的检测限(9.0×10~(-6)-5.8×10-5μg/mL,LOD,S/N=3)、精密度(0.02-3.7%,RSDs,n=3)和回收率(80.1-118.4%)。这项研究表明V-g-C_3N_4/Fe_3O_4可用于水样品中预处理和富集PCBs及其他含有碳基环结构的疏水性污染物。(2)V-g-C_3N_4/Fe_3O_4纳米复合材料作为吸附剂对水中的氯酚类化合物的吸附应用将所制备的V-g-C_3N_4/Fe304纳米复合材料用作吸附剂,对水中三种氯酚进行吸附处理,探究了氯酚初始浓度、吸附时间、盐度、溶液温度、溶液pH因素的影响,并且用响应曲面法对这些影响因素进一步优化,以选择出最佳吸附条件。利用HPLC进行分析,以评价此材料作为吸附剂时吸附氯酚类化合物的性能。实验结果表明,合成的V-g-C_3N_4/Fe_3O_4具有比表面积大,吸附速率快(30s)等优点,对氯酚类化合物吸附处理效果好。(3)不同比表面积的石墨相氮化碳纳米材料的合成及在可见光下快速光催化降解氯酚的应用通过三聚氰胺和尿素制备出不同比表面积的g-C_3N_4,在合成过程中,不必使用模板,有毒溶剂和昂贵的化学药品,然后对这些材料进行表征。本实验选择三种氯酚作为目标化合物,利用HPLC进行分析,以评价这些材料作为光催化剂的性能。还研究了一些影响光催化降解的关键因素,包括溶液的离子强度,pH和温度等,优化出光催化降解目标分析物的最佳条件,然后对材料重复利用。最后,在最佳条件下光催化降解氯酚,并用实时分析质谱(DART-MS)验证降解效果。结果表明,V-g-C_3N_4 (N2,3h)纳米材料对于CPs溶液的光催化降解效果是最好的,是由于此材料的大的比表面积和良好的分散性能导致。因此,该工作提供了一种高催化活性的光催化剂制备的方法,此催化剂在降解水中的氯酚和其他类似的非极性污染物方面具有潜在的应用价值。
[Abstract]:In recent years, with the discharge of industrial wastewater and domestic sewage, the water quality has been polluted by a large number of pollutants. Because of their trace concentrations in the water environment, it is very important to develop effective analytical techniques for the analysis of ultra-trace compounds. Agriculture, forestry and so on will bring unpredictable destruction, will also affect the normal life of human beings, animals and plants, so people not only need to detect organic pollutants in environmental water, but also need to be adsorbed and degraded. Graphite-phase carbon nitride (g-C_3N_4) shows great potential for enrichment, adsorption and degradation of organic aromatic compounds. The electron delocalization of g-C_3N_4 gives it a variety of adsorption mechanisms, including complexation effect, hydrogen bonding, oxidation and so on. However, the separation of g-C_3N_4 requires filtration or centrifugation, which is cumbersome and time-consuming. Fe_3O_4 nanoparticles are one of the most widely used magnetic materials. On the one hand, they have good stability and large specific surface area. Therefore, Fe304 can be fixed on the surface of g-C_3N_4 to overcome the shortcomings of using g-C_3N_4 as an adsorbent alone. In addition, g-C_3N_4 has non-toxic and visible light response (semiconductor band gap 2.7eV), which is unique. The structure of g-C_3N_4 determines its wide application in the field of photocatalysis. However, the catalytic activity of g-C_3N_4 is small, and the specific surface area of g-C_3N_4 can be increased by increasing the specific surface area of g-C_3N_4, which is beneficial for the target to have more contact with g-C_3N_4, thus improving the catalytic activity of g-C_3N_4. Polychlorinated biphenyls (PCBs) were enriched and detected by V-g-C_3N_4/Fe304 nanocomposites. Chlorophenols (CPs) were adsorbed by V-g-C_3N_4 nanocomposites. Finally, different specific surface areas of g-C_3N_4 were synthesized and photocatalytic degradation of chlorophenols was carried out to select the best materials for photocatalytic degradation of chlorophenols. Synthesis of V-g-C_3N_4 and Fe_3O_4 nanocomposites were prepared by water-assisted one-step pyrolysis of urea. The method was simple and easy to operate. The V-g-C_3N_4 and Fe_3O_4 nanocomposites were prepared by chemical co-precipitation method. The results of thermal analysis, elemental analysis, FT-IR, XRD, BET and TEM show that the nanocomposites were successfully synthesized. Then the magnetic solid-phase extraction of ten kinds of PCBs mixed solution was carried out using the nanocomposites. In this process, the response surface methodology (RSM) was used to analyze the factors affecting the solid-phase extraction, such as temperature, time, pH value, salinity and so on. The optimum conditions were determined by HPLC. The eluent after MSPE was determined by GC-MS. The linearity and detection limit of PCBs enrichment in four kinds of actual water samples were determined by GC-MS. The results showed that under the optimum conditions, the detection limit of PCBs was 9.0 (-6) - 5.8. The results show that V-g-C_3N_4/Fe_3O_4 nanocomposites can be used to pretreat and enrich PCBs and other hydrophobic pollutants containing carbon-based rings in water samples. The V-g-C_3N_4/Fe304 nanocomposites were used as adsorbents to adsorb three kinds of chlorophenols in water. The effects of initial concentration, adsorption time, salinity, solution temperature and pH on the adsorption of chlorophenols were investigated. The response surface methodology was used to optimize these factors in order to select the best adsorption conditions. The results showed that the synthesized V-g-C_3N_4/Fe_3O_4 had the advantages of large specific surface area, fast adsorption rate (30s) and good adsorption effect on chlorophenols. (3) Synthesis of graphite carbon nitride nanomaterials with different specific surface areas The application of rapid photocatalytic degradation of chlorophenols in visible light g-C_3N_4 with different specific surface area was prepared by melamine and urea. During the synthesis process, no templates, toxic solvents and expensive chemicals were used, and then these materials were characterized. Some Key Factors Affecting Photocatalytic degradation, such as ionic strength, pH and temperature of the solution, were studied to optimize the optimal conditions for photocatalytic degradation of target analytes, and then reuse the materials. Finally, photocatalytic degradation of chlorophenol was carried out under the optimal conditions and the real-time analysis was performed. The results showed that V-g-C_3N_4 (N2,3h) nano-material had the best photocatalytic degradation effect on CPs solution because of its large specific surface area and good dispersibility. Therefore, this work provided a method for preparing photocatalyst with high catalytic activity, which could degrade water. Chlorophenols and other similar non-polar pollutants have potential applications.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X52;O647.33

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