【作者】 杨晓梅；

【导师】 薛屏；

【作者基本信息】 宁夏大学 ， 水资源利用与化学化工， 2021， 博士

【摘要】 随着社会经济的快速发展,不可再生化石能源的过度使用带来了一系列的能源、环境问题,受到了世界上越来越多国家的重视。以半导体为催化剂、利用太阳光驱动光(光电、光热)化学反应来产生清洁燃料或消除污染物是解决上述两大问题的重要策略,而高活性光催化材料及高效催化反应体系的设计和构筑是其中关键。镓基半导体具有导带电子轨道分布宽、光生电子理论迁移率高等特点,是一类潜在的新型光催化材料。设计合成高比表面积、孔隙丰富、可调骨架(尺寸、组成)的有序介孔镓基半导体可以有效增加反应位点数量、改善物质传输、促进光生电荷分离和表面反应并提高其催化性能,本论文率先对此进行了系统研究、合成了一系列有序介孔镓基半导体材料,并探索了其在光催化分解水产氢和光(热)催化一氧化碳氧化方面的应用,获得了显著增强的性能。采用熔融的硝酸锌和硝酸镓水合物为混合前驱体、有序介孔二氧化硅为硬模板,通过“无溶剂辅助渗透”纳米浇筑路线合成了一系列有序介孔镓酸锌材料,系统研究了二氧化硅硬模板的孔隙结构对所得介孔镓酸锌骨架尺寸、孔径大小的影响,获得了一种具有超细骨架(3～5 nm)、大介孔(11 nm)以及高表面积(～157 m2·g-1)的有序介孔镓酸锌材料,在紫外光照射下光催化分解水产氢速率可达2.72 mmol·h-1·g-1,是体相镓酸锌粒子的3.9倍(0.7 mmol·h-1·g-1),也优于其他普通介孔镓酸锌材料。采用类似的纳米浇筑路线并调控熔融混合前驱体的化学组成,合成了一系列铁、钴、镉等金属离子掺杂的有序介孔镓酸锌固溶体材料,发现适量镉离子掺杂可提高其光催化分解水产氢速率(4.36mmol·h-1·g-1),约为不掺杂介孔镓酸锌的1.6倍。采用次序纳米浇筑路线,先后将镓酸锌和硫化镉的前驱体渗透进入介孔氧化硅的孔道中,经高温固相反应、化学刻蚀氧化硅模板后,获得了一种有序介孔镓酸锌/硫化镉异质骨架复合材料,在可见光照射下光催化分解水产氢速率可达0.83 mmol·h-1·g-1。采用硝酸镓和其他硝酸盐的熔融水合物为混合前驱体,“无溶剂辅助渗透”纳米浇筑路线也被扩展到有序介孔镓酸铜、镓酸镍、镓酸钴的可控合成,系统研究了其骨架尺寸、化学组成、光谱吸收特性对光催化分解水产氢性能的影响,获得了一种具有超细骨架(3～5 nm)、大介孔(11 nm)以及高表面积(～170m2·g-1)的有序介孔镓酸镍,在紫外光照射下光催化分解水产氢速率可达1.97 mmol·h-1·g-1,优于其他普通介孔镓酸镍以及介孔镓酸钴和镓酸铜,但比介孔镓酸锌略低0.27倍。另外,所合成有序介孔镓基半导体材料在光(热)催化一氧化碳氧化去除方面的应用性能也被系统评估:介孔镓酸钴光热催化一氧化碳完全氧化所需温度(115℃)比单纯热催化一氧化碳完全氧化所需温度(200℃)降低了 85℃,表现出明显的光热协同性能;而单纯介孔镓酸锌的光热协同性能不显著,但通过原位光催化还原方法在其骨架表面沉积少量(1 wt%)贵金属铂后,光热催化一氧化碳完全氧化所需温度(90℃)比单纯热催化一氧化碳完全氧化所需温度(140℃)降低了 50℃,表现出明显的光热协同性能,且优于商业化铂碳催化材料。总之,本论文成功合成了一系列具有超细骨架、高比表面积的有序大介孔镓基半导体光催化材料,其在光催化分解水产氢和光(热)催化一氧化碳氧化去除等方面表现出显著增强的性能和较大的应用潜力,将为相关高效光催化材料的设计开发提供一定的借鉴作用。更多还原

【Abstract】 With the rapid development of society and economy,the excessive use of non-renewable fossil energy has brought a series of energy and environmental problems,which has attracted the attention of more and more countries in the world.It is a promising strategy for solving the above-mentioned two problems to produce clean fuel or eliminate pollutants through photochemical(photoelectronic,photothermal)reaction by utilizing semiconductors as catalysts and solar light as energy resource,where the design and construction of the highly active photocatalysts and efficient catalytic reaction system is the key point.Gallium-based semiconductor is viewed as a promising candidate for photocatalysts because of its wide conduction band electron orbital distribution and high theoretical mobility of photogenerated electrons.The design and synthesis of ordered mesoporous gallium based-semiconductors with high specific surface area,rich pores and adjustable(size and composition)frameworks is an important method to increase the number of active sites,improve mass transport,promote photogenerated charge separation and surface reaction,and improve their catalytic performance.In this thesis,a series of ordered mesoporous gallium-based semiconductor materials were synthesized and applied in photocatalytically splitting water to produce hydrogen and photocatalytic(photothermal)oxidation of carbon monoxide,exhibiting significantly enhanced performance.A series of ordered mesoporous zinc gallate materials were synthesized through the "solvent-free assisted infiltration" nanocasting route by using molten zinc nitrate and gallium nitrate hydrate as mixed precursors and ordered mesoporous silica as hard template.The effect of pore size and interconnectivity of mesoporous silica on the framework thickness and pore size of the resultant mesoporous zinc gallate were systematically investigated.An ordered mesoporous zinc gallate material with ultrathin framework(3～5 nm),large mesopore(11 nm)and high specific surface area(～157 m2·g-1)was obtained.Under UV irradiation,the rate of photocatalytically splitting water to produce hydrogen can reach 2.72 mmol·h-1·g-1,which is 3.9 times that of bulk zinc gallate particles(0.7 mmol·h-1·g-1),and is also better than other ordinary mesoporous zinc gallate materials.A series of ordered mesoporous zinc gallate solid solution materials with doping metal ions such as iron,cobalt,cadmium,were synthesized by using a similar nanocasting route and adjusting the chemical composition of molten mixed precursors.It was found that an appropriate amount of cadmium ion doping can increase the rate of photocatalytically splitting water to produce hydrogen(4.36 mmol·h-1·g-1),which is about 1.6 times that of pure mesoporous zinc gallate.An ordered mesoporous zinc gallate/cadmium sulfide composite was obtained by using the sequential nanocasting route,where the precursors of zinc gallate and cadmium sulfide were successively infiltrated into the pore of mesoporous silica.Under visible light irradiation,the rate of photocatalytically splitting water to produce hydrogen for ordered mesoporous zinc gallate/cadmium sulfide composite could reach 0.83 mmol·h-1·g-1.Using the molten hydrate of gallium nitrate and other nitrates as the mixed precursor,the "solventfree assisted infiltration" nanocasting route has also been extended to the synthesis of ordered mesoporous copper gallate,nickel gallate and cobalt gallate.The effect of the framework thickness,chemical composition and spectral absorption characteristics on the rate of photocatalytically splitting water to produce hydrogen were systematically investigated.An ordered mesoporous nickel gallate with ultrathin framework(3～5 nm),large mesopore(11 nm)and high specific surface area(～170 m2·g-1)was obtained and exhibited a higher rate of photocatalytically splitting water to produce hydrogen(1.97 mmol·h-1·g-1)under UV irradiation than those for mesoporous cobalt gallate and copper gallate,but slightly 0.27 times lower than that for mesoporous zinc gallate.In addition,the performance of these resultant ordered mesoporous gallium-based semiconductor materials used in photo(thermal)catalytic oxidation of carbon monoxide were also systematically evaluated.The temperature required for the complete oxidation of carbon monoxide over mesoporous cobalt gallate is 115 ℃ under the condition of both UV light irradiation and external heating and 200℃ under the condition of dark and only external heating respectively,showing the obvious synergistic effect of the photo and thermal energies.In the contrary,the synergistic effect of the photo and thermal energies over mesoporous zinc gallate for the catalytic oxidation of carbon monoxide is unobvious,unless loading a small amount of precious platinum by an in-situ photocatalytic deposition.Platinum-loaded mesoporous zinc gallate(1 wt%)exhibited a relative lower temperature(90℃)for the complete oxidation of carbon monoxide under the condition of both UV light irradiation and external heating than that(140℃)under the condition of dark and only external heating,which is superior over that for the commercial platinum/carbon catalyst.In summary,a series of ordered large-pore mesoporous gallium-based semiconductor photocatalysts with ultrathin frameworks and high specific surface area have been successfully synthesized in this thesis,which shows significantly enhanced performance and great application potential in photocatalytically splitting water to produce hydrogen and photocatalytic(photothermal)oxidation of carbon monoxide.This investigation will make some contribution in the design and development of advanced photocatalytic materials in future.更多还原