【作者】 孙净雪；

【导师】 陈刚；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2013， 博士

【摘要】 从太阳能多元化利用角度考虑，已经有许多种类的太阳能转化体系被广泛深入的研究和开发，光催化体系就是其中之一。通过光催化体系可以利用太阳能实现光解水制氢或光降解有机污染物。因此，如何获得高性能低成本的光催化材料引起人们的广泛重视。钽、钒酸盐光催化材料在光解水制氢及光降解有机污染物方面性能优异，具有重要的研究价值和实际应用前景。本论文利用简单的一步法设计合成了具有不同结构的钽、钒酸盐材料，通过系统的表征研究了不同因素对催化性能的影响，得到了一系列性能优异的光催化剂。采用固相法制备了具有烧绿石构型Bi_1.5ZnTa_1.5O₇（α-BZT）及Bi₂Zn_2/3Ta_4/3O₇（β-BZT）光催化材料，并通过Zn位Cu的掺杂进行了能带调控。在紫外光照射下，掺杂Cu的α-BZT催化活性相比于α-BZT提高了五倍。在可见光照射下，掺杂了Cu的催化剂在可见光下也表现出了较高的催化活性。通过基于密度泛函理论（DFT）的计算发现Cu掺杂导致催化剂能隙变窄的原因是在催化剂的导带和价带之间引入了由Cu3d轨道构成的杂质能级。进一步利用固相法制备了β-BZT并对其进行了Cu掺杂改性研究，发现0.01Cu掺杂后催化活性提高了近10倍，同时Cu掺杂后的β-BZT产生了可见光响应，表现出可见光分解水制氢性能。通过熔盐法制备了钽酸钠钾（NKT）系列单晶纳米立方催化剂，在牺牲剂甲醇存在的条件下，无需负载助催化剂，产氢活性高达19.9mmol·h^-1；在分解纯水制氢方面，NKT的产氢速率也高达2.51mmol·h^-1，较高的催化活性是因为Ta-O-Ta键的调控作用所致，但催化剂在分解纯水时氢氧并不按比例产生，且光稳定性较差。对NKT进行了B位Zr及Hf掺杂得到了单分散的纳米立方结构。将改性后的NKT用于分解纯水，最高产氢活性分别高达4.65mmol·h^-1和4.96mmol·h^-1，同时氢气和氧气的产生速率比值接近理论值（2:1），光稳定性也得到明显改善。利用熔盐法制备了钽酸钠锶（SNT）介晶光催化材料，比表面积最高达到40.6m²·g^-1，产氢速率最高可达27.5mmol·h^-1；在分解纯水的情况下，产氢和产氧速率分别可达4.89mmol·h^-1和1.25mmol·h^-1。高活性的原因主要是由于表面纳米台阶结构的存在，台阶的凸处可以作为产氢活性位，凹处可以作为产氧活性位。采用水热法制备了m-BiVO₄分级结构光催化剂，最佳制备工艺为pH=3条件下180℃水热反应6h。利用尿素作为模板剂制备了具有空心球状结构的m-BiVO₄分级结构催化剂，这种分级结构的构筑单元为m-BiVO₄的截角八面体，形成机制为气泡模板机制。空心球状结构的m-BiVO₄催化剂具有最优异的光催化性能。无需负载助催化剂，50min内可以在不添加双氧水的条件下降解超过80%的RhB，降解过程符合一级动力学方程，反应速率常数为0.035min^-1。空心球状结构的m-BiVO₄的降解机制为空穴降解，且在催化氧化异丙醇情况下具有较高的活性，同时催化剂具有优异的催化循环稳定性，循环4次后活性无明显降低。采用简单的一步熔盐法合成BiVO₄及BiVO₄/BiOCl光催化材料。利用LiNO₃/NaNO₃作为反应熔盐时的最佳熔盐与原料质量比为15:1，反应时间2h。制备的BiVO₄为片状结构，在未负载任何助催化剂条件下，50min对RhB的去除率可超过90%，降解过程符合一级动力学方程，反应速率常数为0.050min^-1。利用LiCl/KCl作为反应熔盐得到了BiVO₄/BiOCl异质结构，最佳熔盐与原料质量比为10:1，反应时间2h。BiVO₄/BiOCl呈现由纳米片组成的花状结构，纳米片的尺寸为200-500nm，厚度为5nm左右。HRTEM及元素面扫测试发现花状主体为BiOCl，BiVO₄以纳米晶的形式附着在片状结构上。催化剂30min对RhB的去除率超过了90%，反应速率常数相对于BiVO₄提高了60%。更多还原

【Abstract】 Various kinds of photon energy conversion systems have been extensivelystudied for solar energy utilization. In photocatalytic system, H2can be obtained andorganic pollutants can be decomposed by using sunlight. How to achievehigh-efficiency and low-cost phtocatalysts has attracted wide attention. Due to theiroutstanding performance in water splitting and photodegradation, tantalates andvanadates are considered to be suitable for basic research and practical application.In our study, several tantalates and vanadates materials have been synthesized viaone-step method. Series of tantalates and vanadates with excellent photocatalyticmaterials are obtained by studying the effects of conditions to their properties.Bi_1.5ZnTa_1.5O₇（α-BZT） and Bi₂Zn_2/3Ta_4/3O₇（β-BZT） with pyrochlore structureare synthesized by the solid state method and the band structure are adjusted bycooper doping in B site. Under UV light irradiation, the photocatalytic activity of Cudopped α-BZT is about5times higher than that of α-BZT. Under visible lightirradiation, Cu dopping in α-BZT makes it caplable of hydrogen generation. Themechanism is that the impure level forms revealed by Cu3d by DFT calculation.Furthermore, same effect is found for β-BZT. The activity of β-BZT is about10times higher than that of β-BZT.NKT nanocrystal is synthesized by the molten salt method. The rate ofhydrogen generation reaches up to19.9mmol·h^-1in the presence of CH3OH whilethe rate is2.51mmol·h^-1for pure water splitting. The high activity is due to thecontrol of Ta-O-Ta bond by A site adjustment. However, it is found that oxygenevolution rate is low and the ratio of hydrogen to oxygen deviats far from thedesired value of2:1. To improve the stability of the catalyst, tetravalent cations ofZr4+and Hf4+are doped. The as-synthesized NKZT and NKHT nanocrystals aremonodispersed and the rates of hydrogen generation reach up to4.65mmol·h^-1and4.96mmol·h^-1for pure water splitting. Furthermore, the ratio of hydrogen to oxygenis close to2:1with improved photostability.SNT mesocrystal is synthesized by the molten salt method, and the surface areais as high as to40.6m²·g^-1. The rate of hydrogen generation reaches up to27.5mmol·h^-1in the presence of CH3OH while the rates of hydrogen and oxygen is4.89mmol·h^-1and1.25mmol·h^-1for pure water splitting. The outstanding activity ismainly due to the enhanced charge separation facilited by the formation ofnanosteps. At the edges of the reduction sites, water can be efficiently reduced to H2and the grooves of the nanostep structure provide the catalytic active sites for O2formation. m-BiVO₄hierarchical structure is synthesized via the hydrothermal method andthe optimized conditions are pH=3, T=180℃andt=6h. Hollow monoclinic scheeliteBiVO₄spheres are facile synthesized by using urea as guiding surfactant. Theforming process consists of incorporation of bubble guiding, oriented attachmentand Ostwald ripening. The hollow spheres are built up with truncated octahedrons asconfirmed though theoretical calculation. It is found out that the m-BiVO₄withhollow structure shows the optimalizing activity and the reaction rate constantreaches up to0.035min^-1without H2O2as hydroxyl radicals donor. The degradationof RhB is attributed to intrinsically strong photo-oxidation ability rather thanphotosensitization and the synthesized samples also show efficient photocatalyticactivity for the degradation of2-propanol.Samples sbow high stability and durability,after four runs of RhB photodegradation, the photocatalytic ability of as-synthesizedm-BiVO₄did not show any loss.BiVO₄and BiVO₄/BiOCl phtocatalysts are synthesized via the one-step moltensalt method. The optimized conditions for LiNO₃/NaNO₃are w=15:1and t=2h. Theas-synthesized BiVO₄shows sheet-like morphology. Without cocatalyts loading,90%of RhB is removed in50min, and the photodegradation process agrees with thefirst order kinetics equation, the value of k is0.050min^-1. BiVO₄/BiOClheterostructure is obtained by using LiCl/KCl as molten salt and the optimizedconditions are w=10:1and reaction for t=2h. BiVO₄/BiOCl heterostructure showsthe morphology of flower-like which is built up of nanosheets. The size of nanosheetis200-500nm in diameter and5nm in thickness. HRTEM and element mappingshow that the body of nanosheet is BiOCl and BiVO₄exists as nanocrystal.90%ofRhB can be removed in30min and the value of k is60%higher that of BiVO₄. Theenhanced photocatalytic activity is due to high charge separation effect inducedheterojunctions.更多还原