Maijenburg A Wouter, Rodijk Eddy J B, Maas Michiel G, Ten Elshof Johan E
MESA+ Institute for Nanotechnology, University of Twente.
MESA+ Institute for Nanotechnology, University of Twente;
J Vis Exp. 2014 May 2(87):51547. doi: 10.3791/51547.
Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 µm were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.
具有光催化活性的纳米结构需要较大的比表面积，存在许多用于氧化和还原半反应的催化活性位点，以及快速的电子（空穴）扩散和电荷分离。纳米线呈现出适合满足这些要求的结构。通过分别在聚碳酸酯径迹蚀刻（PCTE）或阳极氧化铝（AAO）膜的孔内进行模板电沉积，制备了直径为200 nm、长度为6 - 20 µm的轴向分段Ag|ZnO和径向分段（同轴）TiO₂ - Ag纳米线。在光催化实验中，ZnO和TiO₂相充当光阳极，Ag充当阴极。连接两个电极无需外部电路，这是相对于传统光化学电池的一个关键优势。为了制备分段Ag|ZnO纳米线，在形成Ag段后更换Ag盐电解质，以形成附着在Ag段上的ZnO段。为了制备同轴TiO₂ - Ag纳米线，首先通过电化学诱导溶胶 - 凝胶法形成TiO₂凝胶。对形成的TiO₂凝胶进行干燥和热退火导致形成结晶TiO₂纳米管。随后在TiO₂纳米管内进行Ag电沉积步骤，从而形成同轴TiO₂ - Ag纳米线。由于在同一纳米线内n型半导体（ZnO或TiO₂）和金属（Ag）的结合，在各相之间的界面处形成了肖特基势垒。为了证明这些纳米线的光催化活性，将Ag|ZnO纳米线用于光催化实验，在该实验中，当紫外线照射分散在甲醇/水混合物中的纳米线时检测到H₂气体。照射17分钟后，从50 ml 80体积％的甲醇水溶液中约0.1 g Ag|ZnO纳米线的悬浮液中检测到约0.2体积％的H₂气体。
