【作者】 王旋；

【导师】 李洁； 吴争平；

【作者基本信息】 中南大学 ， 冶金物理化学， 2010， 硕士

【摘要】 本文通过固相烧结法和阳极氧化法分别制备了F、S非金属掺杂W03粉体光催化剂和具有结构与形貌差异的W03纳米多孔薄膜,并对其结构和光催化性能进行表征。非金属掺杂通过影响W03粉体光催化剂的W5+和氧空位含量以及晶粒尺寸等而改变其光吸收性能和电子传输性能,从而提高其光催化活性。在以Fe3+为牺牲剂的悬浮液体系中,非金属掺杂W03的光解水活性大幅提高。在紫外光照射下,掺杂前躯体浓度为1.0%的F掺杂WO3(F-WO3)和掺杂前躯体浓度为2.0%的S掺杂WO3(S-WO3)的12h平均析氧速率分别为102.1和99.9μmol·L-1·g-1·h-1,与纯W03的80.2μmol·L-1·g-1·h-1相比分别提高了27%和25%。在可见光照射下,虽然F-W03的光解水活性没有得到提高,但掺杂前躯体浓度为2.0%的S-W03的12h平均析氧速率却高达76.7μmol·L-1·g-1·h-1,与纯W03的48.9μmol·L-1·g-1·h-1相比提高了57%。致密和纳米多孔薄膜退火前后的化学组成均为W03。阳极氧化纳米多孔膜为无定形结构W03,退火后转化为(002)晶面优先生长的单斜晶系W03。退火移除了大量作为光生电荷复合中心的缺陷,故结晶W03薄膜与无定形结构相比,其电子传输性能和光解水活性得到显著地提高。在可见光照射下,纳米多孔W03薄膜(0.5% NaF、50 V、25℃、30min)的稳态光电流(1.6 V vs.Ag/AgCl)和最大光电转换效率分别为5.75 mA/cm2和1.68%,分别是结晶态致密W03薄膜的4.75倍和5.09倍。由于具有较大的比表面积,纳米多孔W03薄膜不仅能吸收更多的光照能量,也能与电解质更充分地接触,从而有利于电荷的分离与传递。因此,与致密薄膜相比,纳米多孔W03具有更小的界面电荷迁移电阻、更大的载流子浓度、更小的瞬态光电流谱动力学常数和更大的瞬态时间常数。此外,通过对电解质含氟浓度、电压、温度和反应时间等参数的调节可以控制产物形貌,从而改善其光解水活性。在本文中的最优化条件(0.5% NaF、50 V、15℃、60 min)下制备的纳米多孔薄膜产生的稳态光电流(1.6 V vs.Ag/AgCl)达到6.70 mA/cm2,是结晶态致密W03薄膜的5.54倍。更多还原

【Abstract】 F-doped WO3-x (F-WO3) and S-doped WO3-x (S-WO3) powder photocatalysts were prepared by solid-state annealing method, and nanoporous WO3 films with different structures and morphologies were prepared by anodization in neutral F--containing strong electrolytes. Structures and photocatalytic performance of samples were characterized.Photo absorption efficiency and electron transport propertise were influenced by doping, which changed grain size and the amount of W5+ and oxygen vacancies,and enhanced samples’ photocatalytic activity. In photocatalysts containing suspensions, using Fe3+ as sacrificial agent, the photocatalytic activities for water splitting were enhanced by nonmetal-doping. Under ultraviolet (UV) irradiation of 12 h, the highest average oxygen evolution rates obtained for F-WO3 (1.0%F precursor concentration) and S-WO3 (2.0%S precursor concentration) were 102.1 and 99.9μmol·L-1·g-1·h-1 compared with 80.2μmol·L-1·g-1·h-1 for WO3-x, respectively increased by 27% and 25%.Under 12 h of visible light (VIS) irradiation, the water splitting activities were inhibited by F-doping. However, the highest average oxygen evolution rate obtained for S-WO3 (2.0% S precursor concentration) was 102.1μmol·L-1·g-1·h-1 under VIS irradiation, which is 57% higher than 48.9μmol·L-1·g-1·h-1 for WO3-x.Before and after annealing, both compact and nanoporous films consist essentially of WO3.The as-anodized nanoporous films were amorphous and converted to a monoclinic phase with preferential orientation in the (002) planes after annealing. Annealing removed lots of lattice imperfection, which could serve as recombination centers of photoelectrons and holes.In this way, conductivities and water splitting activities of annealed films were enhanced significantly. Under visible light irradiation, the photocurrent density (at 1.6 V vs.Ag/AgCl) and maximum photoconversion efficiency generated by the annealed nanoporous film (0.5% NaF,50 V,25℃,30 min) were 5.75 mA/cm2 and 1.68%,respectively. These values were 4.75 and 5.09 times of that generated by annealed compact WO3 film. Due to the larger surface area, nanoporous WO3 films can not only absorb more light energy, but also contact fully with the electrolyte, which is conducive to charge separation and transfer. Compared with compact films, nanoporous WO3 has smaller interface charge transfer resistance, larger carrier concentration, smaller transient photocurrent kinetics constant and larger transient time constant. Moreover, morphologies of the samples could be controlled by adjusting fluoride concentration, voltage, reaction temperature and time, and thus improve the photocatalytic water splitting activity. Nanoporous films prepared under optimal conditons (0.5% NaF,50 V,15℃,60 min) can generate photocurrent of 6.70 mA/cm2(1.6 V vs.Ag/AgCl),5.54 times the value of annealed compact WO3 films.更多还原