【作者】 刘彬； 杨合情；

【Author】 Bin Liu;Heqing Yang;School of Materials Science and Engineering,Shaanxi Normal University;

【机构】 陕西师范大学材料科学与工程学院；

【摘要】 我们知道光催化在解决能源和环境问题中具有战略性地位[1a]。在光催化反应中电荷分离起着非常关键的作用,直接决定光催化反应的效率[1a]。然而,到目前为止,光生电荷分离机制不清楚,被认为是个黑匣子。最近,人们通过使用表面光电压和同步X射线光电子技术,研究了半导体纳米晶体晶面上光生电荷的分离过程[1b,1c]。不过,这些研究只关注具体一个晶面。基于ZnO光催化活性极性{001}晶面的原子结构,我们首次提出了Zn-ZnO(001)和O-ZnO(00-1)晶面间内电场促进光生电荷分离模式[2]。随后,发现CdS{001},CdSe{001},CoO{111},CdTe{111},NiO{111},Cu2Se{111},Cu2O{111},Cu2O/Cu2Se{111}和Ti O2{111}等光催化活性面也为极性晶面,并提出相关的光催化机理[3]。因此,我们认为所有极性晶面是光催化的活性晶面,所有光催化活性晶面具有极性结构。为此,建立了一个具有普遍意义的光生电荷分离理论:极性晶面间存在有内电场,这一内电场称为自发电场,在自发电场作用下,光生电荷分别向两个不同极性晶面迁移,在一个极性面发生电子还原反应,在另一个极性面发生空穴的氧化反应。最近,人们发现Ag+、PtCl62-的光还原与Mn2+光氧化反应分别选择性发生在AgI和PbTiO3 (001)和(00-1)不同极性晶面上[4],在具有[001]取向ZnO、BaTiO3薄膜以及[111]取向Ti O2薄膜和Cu2O/Cu2Se纳米线薄膜中观察到了整流与光伏效应[3d, 3e,5a, 5b],发现[111]极性方向生长的InP纳米线在电场作用下会沿电场方向排列组装[5c],这些工作充分证明了我们所提出的自发电场驱动的极性晶面间电荷分离理论。该理论有助于揭示铁电材料反常光伏效应的物理本质,为高性能光催化剂和新型光电器件的设计与制造提供指导。更多还原

【Abstract】 As we know, photocatalysis has attracted increasing attention as a potential strategy to address the energy shortage and environmental pollution issues [1 a]. Charge separation plays a very key role in the photocatalytic reaction, directly determine the efficiency of photocatalytic reactions [1 a]. However, the elaborate charge separation mechanism is not yet clear until now. Recently, separation of photoinduced charges on the exposed faces of semiconductor nanocrystals have been studied by using surface photovoltage techniques and synchronous illumination X-ray photoelectron spectroscopy [1 b,1 c]. However, the studies focus on a specific crystal facet, and atomic structures of reactive facets of the semiconductor catalysts have never been took into consideration. On the basis of atomic structure of ZnO photocatalytic reactive polar {001} planes, we present a photoproduced charge separation model under an internal electric field between positive Zn-ZnO(001) and negative O-ZnO(00-1) planes for the first time. Subsequently, CdS{001}, CdSe{001}, CoO{111}, CdTe{111} NiO{111}, Cu2 Se {111}, Cu2 O{111}, Cu2 O/Cu2 Se {111} and Ti O2 {111} photocatalytic activity crystal faects were also found to be polar crystal faces and proposed the corresponding photocatalytic mechanisms [3].Therefore, we believe that all the polar crystal faces are photocatalytic activity faects, and all the photocatalytic activity faects have polar structure. Thus, a general photogenerated charge separation theory between polar facets was established. The internal electric field between polar facets is named as spontaneous electric field(Es). Under the Es, the photogenerated charges migrate to two different polar crystal faects. The reduction reaction with electron and oxidation reaction with hole occur on the metallic and nonmetallic atom-terminated crystal faects, respectively. Recently, the photoreduction reaction of Ag+ and PtCl62-ions and the photooxidation reaction of Mn2+ ions were found to occur at the(001) and(00-1) polar crystal faces of AgI and PbTiO3 separately [4]. The photovoltaic and rectification effects were observed in [001] orientated ZnO and BaTiO3 films, [111] orientated TiO2 film and Cu2 O/Cu2 Se nanowire films [3 d,3 e,5 a,5 b]. The InP nanowires grown along [111] polar direction were found to assemble and align along electric field under an electric field [5 c]. These results fully prove the photogenerated charge separation theory between polar facets. The charge separation theory will be helpful to reveal the physical nature of abnormaousl photovoltaic effects in ferroelectric materials, and offer guidance to design and fabricate high efficiency photocatalysts and optoelectronic devices for light-electricity conversion.更多还原