仿生多孔二氧化钛合成及其光催化还原二氧化碳性能研究

发布时间：2018-05-22 19:13

本文选题：光催化还原CO_2 + 二氧化钛　；参考：《南京大学》2015年硕士论文

【摘要】：随着人口的增加和现代化与工业化进程的加快,世界各国对能源的需求愈来愈大,而经过数百年的过度开采和巨大消耗,作为人类社会主要能量来源的煤炭、石油和天然气等化石能源已经不可逆转地走向枯竭。而且,化石能源的大量燃烧造成大气中以CO2为主的温室气体急剧增加,破坏了自然界碳循环的平衡,导致全球气候变暖。近年来,受自然界绿色植物光合作用的启发,以CO：为原料,半导体材料为催化剂,在太阳光的照射下利用还原剂将CO2转化为含碳化合物的技术备受关注。该技术在降低大气中温室气体CO2的浓度的同时,生成的含碳化合物又能够缓解日益紧张的能源危机,实现了能源与环境的“双赢”。Ti02具有廉价、无毒、光稳定性好、容易制备等优点,被广泛地应用于光催化分解H20、光催化还原CO2和有机污染物降解。对C02的选择吸附性能差、光生电子-空穴复合几率高和光谱响应范围窄等因素限制了Ti02光催化CO2还原性能的提高。源于自然界绿色植物的光合作用的灵感,基于孔隙结构传统的硬模板和软模板合成方法,本文合成了分级多孔结构的Ti02海绵和MgO-TiO2复合材料,并应用于光催化还原CO2。主要研究内容如下：(1)以多孔藕粉凝胶为模板,将藕粉和Ti02的前驱物混合与水共热,共凝胶化形成多孔结构,在空气氛中煅烧将藕粉凝胶移除,合成了3D交联大孔/介孔结构的Ti02海绵。此方法将传统的硬模板法和软模板法有机地结合在一起,在获得模板的既定大孔结构的同时,交联围成大孔的薄壁表面形成大量的介孔。与同等条件下,不采用模板制得的参比Ti02样品相比,3D交联大孔/介孔结构的Ti02海绵光催化CO2还原为CH4的效率提升了2.6倍,原因为：(1)大孔结构有利于气体反应物和生成物的自由扩散；(2)入射光在孔隙结构中发生多步折射和散射,延长了光的传播路程,从而增强了样品的光吸收；(3)介孔结构增加了CO2在催化剂表面的吸附和反应活性位点。(2)以空心菜杆为模板,应用溶胶凝胶的方法,调节MgO的含量合成了系列仿生多孔结构的MgO-TiO2复合物。通过探究、比较不同含量MgO对复合物光催化C02还原为CH4效率的影响,结合催化剂的物理和化学性质的表征,证明MgO能够提高催化剂表面C02的化学吸附,活化C02分子,从而提高C02的光催化转化活性。虽然MgO的加入能够提高活性C02分子的含量,由于MgO为绝缘体材料,并且覆盖在Ti02颗粒表面,阻碍了光生电子向催化剂表面的迁移,一定程度上降低了催化剂的活性。因此,设计合成复合MgO的光催化剂时,要选择最佳复合量,本文实验结果证明：TiO2的MgO为最佳复合量为0.2 wt%。
[Abstract]:With the increase of population and the acceleration of modernization and industrialization, the demand for energy is increasing in all countries of the world. After hundreds of years of overexploitation and huge consumption, coal is the main source of energy for human society. Fossil fuels such as oil and natural gas have been irreversibly depleted. Moreover, the combustion of fossil energy causes a sharp increase of greenhouse gases dominated by CO2 in the atmosphere, which destroys the balance of the natural carbon cycle and results in global warming. In recent years, inspired by the photosynthesis of green plants in nature, the technology of conversion of CO2 to carbohydrates by reducing agent under the irradiation of sunlight, using CO: as raw material and semiconductor material as catalyst, has attracted much attention. While reducing the concentration of greenhouse gas CO2 in the atmosphere, the technology can also produce carbohydrates to alleviate the increasingly tense energy crisis and achieve a "win-win" between energy and the environment. Ti02 is cheap, non-toxic, and has good light stability. It is widely used in photocatalytic decomposition of H20, photocatalytic reduction of CO2 and degradation of organic pollutants. The poor selective adsorption of CO2, high photoelectron hole recombination probability and narrow spectral response limit the improvement of Ti02 photocatalytic CO2 reduction performance. Based on the traditional hard template and soft template synthesis method of pore structure, Ti02 sponge and MgO-TiO2 composite with graded porous structure were synthesized and applied to photocatalytic reduction of CO _ 2. The main research contents are as follows: (1) the porous lotus root powder gel is used as template, the precursor of lotus root powder and Ti02 is mixed with water to co-heat, the porous structure is formed by co-gelation, and the lotus root powder gel is removed by calcination in empty atmosphere. A 3D crosslinked Ti02 sponge with macroporous / mesoporous structure was synthesized. This method combines the traditional hard template method and the soft template method organically. While obtaining the established macroporous structure of the template, a large number of mesoporous cells are formed on the thin-walled surface of the cross-linked macroporous. Under the same conditions, the photocatalytic reduction of CO2 to CH4 by Ti02 sponge with 3D crosslinking macroporous / mesoporous structure was 2.6 times higher than that of the reference Ti02 without template. The reason is that the macroporous structure is advantageous to the free diffusion of gas reactants and products. The incident light refracts and scatters in the pore structure, which prolongs the distance of light propagation. Thus, the mesoporous structure of the sample was enhanced, and the adsorption and reaction activity sites of CO2 on the catalyst surface were increased. A series of bionic MgO-TiO2 complexes with porous structure were synthesized by adjusting the content of MgO. The effects of different MgO content on the efficiency of photocatalytic reduction of CO2 to CH4 were compared. It was proved that MgO could enhance the chemisorption of CO2 on the surface of the catalyst and activate CO2 molecule by combining with the characterization of the physical and chemical properties of the catalyst. Thus, the photocatalytic conversion activity of CO2 was improved. Although the addition of MgO can increase the content of active C02 molecule, because MgO is an insulator material and is covered on the surface of Ti02 particles, it hinders the migration of photogenerated electrons to the surface of the catalyst, thus reducing the activity of the catalyst to some extent. Therefore, when designing the photocatalyst for synthesizing composite MgO, we should choose the optimum compound amount. The experimental results show that the optimum compound amount of MgO is 0.2 wt.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ134.11;TQ426

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