Synthesis Of Cu2O-Based Nano-Heterostructures And Their Photocatalytic, Photoelectrochemical And Gas Sensing Properties

Cuprous oxide(Cu2O) is an environmentally friendly p-type metal oxide semiconductor with a direct band gap of ~2.1 eV and distinct excitonic properties at room temperature, which make it a promising candidate material for many applications, such as photoelectrolysis of water, photocatalysis, gas sensors, Li-ion batteries, solar cells, etc. ZnO nanostructures have been deeply studied in optoelectronic, photocatalytic and photochemical applications due to their variety of morphologies and the availability of simple and low cost synthesis process. In this dissertation, we prepared heterostructure nanomaterials by coupling Cu2 O with other metal semiconductor/metal nanostructures, such as 1D ZnO nanostructures and copper nanoparticles etc. The heterostructure can not only lead to a functional integration of the properties of both the components but also to novel interface effects and phenomena, for example tuning the light response in the visible region and accelerate the charge separation etc., which finally improves the photocatalytic, photovoltaic and gas sensing performances. The main work and results are summeriazed as follows.Large scale ZnO nanorod arrays(ZNAs) were grown on the indium-doped tin oxide(ITO) glass substrate by a novel and facile hydrothermal method at low temperature. Morphologies, crystalline and atomic structure, and room temperature photoluminescence(PL) of the as-prepared ZNAs were investigated. It is shown that the average diameter of ZnO nanorods(~500 nm) grown on the bare substrate is much bigger than that of nanorods grown on the ZnO-seed-coated substrate(~100 nm). ZNAs grown on ZnO-seed-coated substrate are highly aligned. All the as-grown Zn O nanorods have a very good crystallinity with hexagonal wurtzite structure and grow along the c-axis. Zinc metal spiral plays important roles for the growth of ZnO nanorods, which conduces to generate the additional growth unit of [Zn(OH)4]2-.Vertically aligned Cu2O/ZnO hetero-nanorod arrays were synthesized on indium-doped tin oxide(ITO) glass substrates using a simple hydrothermal method followed an electrodeposition process. Scanning electron microscopy(SEM) and high-resolution transmission electron microscopy(HRTEM) results show that Cu2 O nanoparticles conformably formed on the pre-grown ZnO single-crystalline nanorods. Compared to pure Cu2 O and pure ZnO nanorod arrays films, the Cu2O/ZnO hetero-nanorod arrays films exhibit an excellent improvement in photocatalytic applications under visible light irradiation. The increase of the electrodeposition time(amount) of Cu2 O helps to enhance the photocatalytic activities of the system until the Cu2 O nanoparticles nearly cover the entire periphery of the ZnO nanorods. The enhanced photocatalytic activity is attributed to better light scattering for the Cu2O/ZnO hetero-nanorod arrays structure and fast charge separation and transport within the heterojunctions of the Cu2O/ZnO.Cu2O quantum dots(QDs) decorated ZnO nanorod arrays(ZNAs) were fabricated using a facile hydrothermal method followed by a chemical bath deposition(CBD) process. The surface morphology, crystal structure and photovoltaic behaviors of the heterostructure films were investigated. The results indicate that the Cu2 O QDs decorated on the ZNAs can be as a good light absorber improving the visible spectral absorption. In addition the photo-induced electrons can easily transfer to ZnO, leading to an increase in the photovoltaic performance. When the number of CBD cycle was 10, an optimal photovoltaic performance could be obtained with a photocurrent of 3.21 mA/cm2, an open circuit photovoltage of 0.65 V and a conversion efficiency of 1.17% under the simulated sunlight illumination(AM 1.5G, 100 mW/cm2). Moreover, for improving the photovoltaic stability, a protective layer was prepared on the Cu2 O QDs by a simple process of heat treatment in ambient air at 100 ?C for 2h. The results demonstrate that the passive CuO layer could be an effective protective layer to increase the photovoltaic stability.Cu/Cu2 O nano-heterostructure hollow spheres with a submicron diameter(200~500 nm) were prepared by a microwave-assisted hydrothermal method using Cu(OAc)2·H2O, PVP and ascorbic acid solution as the precursors. The morphology of the products could evolve with the hydrothermal time from solid spheres to thick-shell hollow spheres, then to thin-shell hollow spheres, and finally to nanoparticles. Moreover, the content of Cu in the products could be controlled by adjusting the hydrothermal time. The spontaneous forming of the hollow structure spheres was found to result from the Ostwald ripening effect during the low temperature(100 °C) hydrothermal reaction process. The photocatalytic degradation activities on MO under visible-light irradiation and the gas sensing activities toward the oxidizing NO2 gas of the different Cu/Cu2 O nano-heterostructure hollow spheres were investigated. As a result, the Cu/Cu2 O nano-heterostructure hollow spheres obtained at the hydrothermal time of 30 min, with a rough/porous thin-shell structure and a Cu content of about 10.5 wt. %, exhibited the best photocatalytic and gas sensing performances compared with the others.