Z-scheme奈米異質結構之製備與其光電化學水分解應用

Abstract

由於半導體奈米異質結構本身具有高度的複雜性，所以我們常利用奈米材料之間的協同增強作用表現出許多優異特性，而這些性質是無法由個別單一材料所觀察到的。尤其，由半導體-金屬-半導體所組成的Z-scheme奈米異質結構有著相當多進展，其中載子具有方向性的傳導大幅提升運用在光轉化時的氧化及還原能力。在此論文研究中，我們提出了由ZnO奈米棒為主體的Z-scheme奈米異質結構，並且將其運用於水分解系統中來研究光電化學性質。此樣品製備為先將Au奈米粒子接枝於ZnO奈米棒，再進一步藉由光沉積的方式，選擇性地在Au奈米粒子的表面沉積上一薄層的SnO2。在ZnO-Au-SnO2 Z-scheme奈米異質結構中，藉由Au奈米粒子改變材料間界面電荷的傳導，將SnO2導帶上的電子傳導至ZnO的價帶上。此載子具有方向性的傳導，使得被光激發的電子累積在ZnO的導帶，電洞則停留於SnO2的價帶，因此ZnO-Au-SnO2擁有足夠高的光催化氧化與還原能力。藉由時間解析螢光光譜和光電壓實驗的分析，載子的分離會因ZnO-Au-SnO2結構中Z-scheme電荷傳導的機制而顯著地提升，與未修飾ZnO、雙成份ZnO-Au與type-II ZnO-SnO2樣品相比，ZnO-Au-SnO2具有更好的載子分離及更高的氧化還原能力，故在光電化學水分解分析上有較優異的表現。由此研究可得知，Z-scheme奈米異質結構具有良好的載子分離及高氧化還原力等特性，使其可更有效率地運用在各種光轉化的過程中。

With the inherently high degree of complexity, semiconductor nanoheterostructures have exhibited superior synergistic properties that are difficult to acquire from their individual constituents. Particularly, great progress has been made in creating Z-scheme semiconductor-metal-semiconductor nanoheterostructures, in which the vectorial charge transfer scenario may increase the oxidizing and reducing powers for photoconversion applications. In this work, a ZnO nanorod-based Z-scheme nanoheterostrutcure system was proposed and realized for studying the photoelectrochemical properties in water splitting. The samples were prepared by selectively depositing a thin layer of SnO2 on the Au surface of Au nanoparticle-decorated ZnO nanorods using the photodeposition method. For Z-scheme ZnO-Au-SnO2 nanorods, the decorated Au may mediate interfacial charge transfer by promoting the electron transfer from the conduction band of SnO2 to the valence band of ZnO. This vectorial carrier transfer resulted in the situation that the photoexcited electrons accumulated at ZnO while the photogenerated holes remained at SnO2, rendering ZnO-Au-SnO2 sufficiently high redox powers. Time-resolved photoluminescence spectra and photovoltage analysis suggested that charge carrier separation was significantly improved in the ZnO-Au-SnO2 nanorods as a result of the Z-scheme charge transfer scenario. With the pronounced charge separation and sufficiently high redox powers, Z-scheme ZnO-Au-SnO2 nanorods performed much better in photoelectrochemical water splitting than pristine ZnO, two-component ZnO-Au and type-Ⅱ ZnO-SnO2 nanorods did. The demonstrations from this work may facilitate the use of Z-scheme nanoheterostructures in various photoconversion processes, in which the pronounced charge separation and high redox powers of Z-scheme charge transfer can be well employed.