基于木质素制备多孔碳材料去除水中六价铬的研究

发布时间：2018-08-20 14:59

【摘要】：随着人口的不断增加和国民经济快速发展,我国水资源污染日趋严重。六价铬Cr(VI)作为第一类污染物,也是水污染五毒之一,普遍存在于工业污水中,工业上广泛用于电镀、制革、纺织印染等行业中。木质素是一种三维网状的可再生芳香基天然高聚物,在植物内含量仅次于纤维素,占植物体的15%-36%。而碱木素作为制浆造纸工业的副产品,产量大,利用率低,且对水环境有严重的污染。由于碱木素分子结构中含有多种活性基团,可对其化学改性制备功能材料,去除水中重金属离子。本研究利用碱木素中羟基、羧基、羰基等官能团,分别合成了多孔磁性碳吸附剂及Bi_2O_3负载的不同系列的光催化剂,用于去除水中六价铬Cr(VI)。具体工作主要分为以下三个方面:(1)利用球磨法引入聚乙烯亚胺中的氨基基团,并通过高温煅烧负载Fe3O4制备了多孔磁性碳材料吸附剂,提高了对六价铬Cr(VI)的吸附容量并实现了磁性分离。本实验以酸析提纯的碱木素为碳源,添加K_2CO_3、聚乙烯亚胺和Fe(NO_3)_3×5H_2O经球磨充分反应后高温煅烧,得到多孔磁性碳吸附剂。通过透射电镜、扫描电镜、傅里叶变换红外光谱、比表面测试和X射线光电子能谱等多种手段对多孔磁性碳吸附剂进行了表征。结果表明,木质素表面孔隙增多、比表面积增大,氨基基团和Fe3O4成功接枝到木质素表面。聚乙烯亚胺中的氨基基团能增强吸附剂对六价铬Cr(VI)的吸附作用,并能将毒性较高的六价铬Cr(VI)还原为毒性较低的三价铬Cr(III)。因此,多孔磁性碳材料不仅吸附了溶液中的六价铬Cr(VI),同时降低了溶液的毒性。溶液pH对吸附效果影响较大,在pH为2时最大吸附量可达到160 mg/g。(2)采用水热合成法成功制备了系列Bi_2O_3负载的碳光催化剂。首先,Bi~(3+)与聚乙烯吡咯烷酮(PVP)上的羰基氧通过配位结合形成胶粒,然后胶粒缓慢释放Bi~(3+)与木质素表面羟基基团反应形成Bi_2O_3负载的光催化材料。对所得产物通过透射电镜、扫描电镜、X射线粉末衍射、X射线光电子能谱和紫外-可见光谱进行了表征。结果表明,Bi_2O_3微球成功负载到木质素表面。可见光激发下,对不同浓度、不同pH的六价铬Cr(VI)溶液进行了光催化实验,实验证明光催化剂在pH=2时对六价铬Cr(VI)光催化降解性能最佳。制备的C@Bi_2O_3负载的系列光催化剂为下一步研究提供了思路。(3)为了进一步提高负载Bi_2O_3系列光催化剂的催化效果,通过球磨法和水热合成法制备了聚乙烯亚胺(PEI)修饰并负载α-Fe_2O_3-Bi_2O_3的复合木质素光催化材料。采用透射电镜、扫描电镜、X射线粉末衍射、X射线光电子能谱等表征多种手段对光催化材料进行表征。结果表明,木质素表面负载了α-Fe_2O_3-Bi_2O_3片层结构,对溶液中六价铬Cr(VI)的催化速率及催化效果高于Bi_2O_3负载的系列木质素光催化材料。这归因于α-Fe_2O_3促使光电子能快速迁移跃迁,提高了光电子空穴对的分离效果,增强了Bi_2O_3的催化活性。制备的C@α-Fe_2O_3-Bi_2O_3复合光催化材料实现了资源的循环利用,具有广阔的应用前景。
[Abstract]:With the increase of population and the rapid development of national economy, the pollution of water resources in China is becoming more and more serious. As the first kind of pollutant, hexavalent chromium chromium (VI) is also one of the five poisons of water pollution. It is widely found in industrial wastewater. It is widely used in electroplating, leather making, textile printing and dyeing industries. The content of natural polymers in plants is only inferior to cellulose, accounting for 15%-36% of the plant. As a by-product of pulp and paper industry, alkali lignin has high yield, low utilization rate and serious pollution to water environment. In this study, porous magnetic carbon adsorbents and different series of Bi_2O_3-supported photocatalysts were synthesized by using hydroxyl, carboxyl and carbonyl groups in alkali lignin to remove hexavalent chromium (VI) from water. Porous magnetic carbon adsorbents were prepared by calcining Fe_3O_4 loaded on Fe_3O_4 at high temperature, which improved the adsorption capacity of Cr(VI) and achieved magnetic separation.The porous magnetic carbon adsorbents were prepared by adding K_2CO_3, polyethylenimine and Fe(NO_3)_3 The porous magnetic carbon adsorbents were characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, specific surface testing and X-ray photoelectron spectroscopy. The adsorption of hexavalent chromium chromium (VI) on the adsorbent was enhanced and the toxic hexavalent chromium chromium (VI) was reduced to trivalent chromium (III) with lower toxicity. Therefore, the porous magnetic carbon materials not only adsorbed hexavalent chromium chromium (VI) in the solution, but also reduced the toxicity of the solution. A series of Bi_2O_3-loaded carbon photocatalysts were successfully prepared by hydrothermal synthesis. First, Bi~ (3+) and carbonyl oxygen on polyvinylpyrrolidone (PVP) were coordinated to form colloidal particles, and then the colloidal particles slowly released Bi~ (3+) and reacted with hydroxyl groups on the lignin surface to form Bi_2O_3-loaded photocatalytic materials. The materials were characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The results showed that Bi_2O_3 microspheres were successfully loaded on the surface of lignin. Under visible light excitation, the photocatalytic activity of hexavalent chromium Cr (VI) solution with different concentration and pH was studied. The photocatalyst was proved to be at pH=2. The photocatalytic degradation of hexavalent chromium chromium (VI) was the best. A series of C@Bi_2O_3-supported photocatalysts were prepared to provide ideas for further study. (3) In order to further improve the catalytic effect of Bi_2O_3-supported photocatalysts, polyethylenimine (PEI) modified and loaded with alpha-Fe_2O_3-Bi_2O_3 were prepared by ball milling and hydrothermal synthesis methods. Composite lignin photocatalytic materials were characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. The results showed that the catalytic rate and catalytic effect of hexavalent chromium Cr(VI) on lignin surface were higher than that on Bi_2O_3. This is attributed to the fact that alpha-Fe_2O_3 promotes the rapid migration and transition of photoelectron energy, improves the separation efficiency of photoelectron hole pairs, and enhances the catalytic activity of Bi_2O_3. The prepared C@alpha-Fe_2O_3-Bi_2O_3 composite photocatalyst realizes the recycling of resources and has broad application prospects.
【学位授予单位】：山东农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703;O643.36

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