新型可见光响应的InVO_4-Cu_2O-TiO_2三元纳米异质结:制备及其光催化性能（英文）

Novel visible-light-responding InVO_4-Cu_2O-TiO_2 ternary nanoheterostructure: Preparation and photocatalytic characteristics

由于日益严重的环境和能源危机,可见光催化剂的开发已成为当今最具挑战和紧迫的任务之一.将TiO_2和其它窄禁带半导体复合,已被证明是一种有效的可提高其可见光光催化性能的策略.Cu_2O是一种禁带宽度为2.0 eV的p型窄禁带半导体,InVO_4则是一种禁带宽度为2.0 eV的n型半导体,因它们可用于可见光光解水产氢和有机污染物的可见光降解而在过去的数年中引起了人们广泛的关注.但是纯的Cu_2O和InVO_4由于光生电子空穴对在其内部快速地复合,光催化活性通常都比较低.基于能带工程的策略本文设计了一种新型的可见光响应的InVO_4-Cu_2O-TiO_2三元纳米异质结,并通过普通的湿化学法进行制备:先通过水热法制备InVO_4,再通过溶胶-凝胶法制备InVO_4-TiO_2二元复合物,最后通过沉淀和还原过程制备得到InVO_4-Cu_2O-TiO_2三元纳米异质结.在10%InVO_4-40%Cu_2O-50%TiO_2三元纳米异质结的X-射线衍射谱中没有观察到明显的杂质峰;通过透射电子显微技术和高分辨透射电子显微技术观察到了它们之间异质结的形成,纳米颗粒的尺寸范围在5-20 nm;经紫外可见漫反射光谱估算得到10%InVO_4-40%Cu_2O-50%TiO_2的禁带宽度为2.78 e V,在可见光区域具有较强的吸收.以普通的9 W节能灯作为可见光光源光照甲基橙5 h后,纯的InVO_4,TiO_2和Cu_2O几乎没有光催化活性;10%InVO_4-90%TiO_2的光催化活性也很低,甲基橙降解率为8%;70%Cu_2O-30%TiO_2对甲基橙降解率达84%,但初始活性较低;10%InVO_4-40%Cu_2O-50%TiO_2对甲基橙降解率接近90%,并且循环使用6次后,其光催化活性的保持率还维持在90%以上,而50%Cu_2O-50%TiO_2光催化活性的保持率只有74%.经对使用过的10%InVO_4-40%Cu_2O-50%TiO_2进行X射线光电子能谱表征发现,存在一弱小的Cu(II)震动卫星峰,表明在InVO_4-Cu_2O-TiO_2的光催化过程中Cu_2O的光蚀并不严重.从能带工程的角度分析,InVO_4-Cu_2O-TiO_2三元纳米异质结具有优异的可见光催化性能的主要原因为:InVO_4的导带电极电位约为-0.5 e V(vs.SHE,下同),价带电位约为+1.5 e V,Cu_2O的分别约为-1.6和+0.4 e V,与TiO_2(导带和价带电极电位分别约为-0.23和+2.97 e V)相比,它们的导带位置更负,将它们组装成三元复合结构,可见光激发的导带电子就可能从InVO_4和Cu_2O的导带迁移到TiO_2的导带上去.同时,n型的TiO_2和InVO_4都与p型的Cu_2O形成p-n异质结,n型的TiO_2和InVO_4之间形成n-n异质结,由于p-n异质结中内电场的存在以及不同能级相互耦合,可进一步促进可见光激发的导带电子从InV O4和Cu_2O的导带迁移到TiO_2的导带上去,以及可见光激发的价带空穴从InVO_4的价带迁移到Cu_2O的价带上去,从而实现光生载流子空间上的有效分离.本文有望为新型可见光响应的半导体复合催化剂的设计和制备提供新的思路.

A novel visible-light-responding InVO4-Cu2O-TiO2 ternary nanoheterostructure was designed on the basis of the strategy of energy gap engineering and prepared through ordinary wet chemistry methods. The as-prepared nanoheterostructure was characterized by X-ray powder diffraction（XRD）, transmission electron microscopy（TEM）, high-resolution transmission electron microscopy（HRTEM） and diffuse reflectance ultraviolet-visible spectroscopy（UV-vis/DRS）. The TEM and HRTEM images of 10%InVO4-40%Cu2O-50%TiO2 confirm the formation of nanoheterostructures resulting from contact of the nanosized TiO2, Cu2O and InVO4 in the size of 5–20 nm in diameter. The InVO4-Cu2O-TiO2 nanoheterostructure, when compared with TiO2, Cu2O, InVO4, InVO4-TiO2 and Cu2O-TiO2, shows significant enhancement in the photocatalytic performance for the degradation of methyl orange（MO） under visible-light irradiation. With a 9 W energy-saving fluorescent lamp as the visible-light source, the MO degradation rate of 10%InVO4-40%Cu2O-50%TiO2 reaches close to 90% during 5 h, and the photocatalytic efficiency is maintained at over 90% after six cycles. This may be mainly ascribed to the matched bandgap configurations of TiO2, Cu2O and InVO4, and the formations of two p-n junctions by the p-type semiconductor Cu2O with the n-type semiconductors TiO2 and InVO4, all of which favor spatial photogenerated charge carrier separation. The X-ray photoelectron spectroscopy（XPS） characterization for the used 10%InVO4-40%Cu2O-50%TiO2 reveals that only a small shakeup satellite peak appears for Cu（II） species, implying bearable photocorrosion of Cu2O. This work could provide new insight into the design and preparation of novel visible-light-responding semiconductor composites.