ZnO particles with rod and plate configurations were synthesized using a solvothermal method using zinc acetate and zinc chloride, respectively. The surface of the as-synthesized ZnO rods and plates were characterized using various analysis tools (XRD, XPS, photoluminescence, FE-SEM, HR-TEM, BET, and UV− vis) and their photocatalytic activities were examined for six different redox reactions. The surface areas and bandgaps of the two ZnO samples were nearly identical; however, XPS and photoluminescence (PL) studies showed that the rods and the plates have relatively pronounced oxygen vacancy and oxygen interstitial contributions, respectively. ZnO rods were found to be active for the decomposition of methylene blue and phenol, the production of OH radicals, and the generation of photocurrents, all of which are associated with single-electron transfer reactions. On the other hand, ZnO plates were more effective for the production of molecular hydrogen and hydrogen peroxide, both of which are initiated by two-electron transfer reactions. These single versus multiple charge transfers are discussed with regard to the roles of oxygen vacancies and oxygen interstitials, which are located near the conduction and the valence bands, respectively.

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For the fast and easy detection of carbon monoxide (CO) gas, it was necessary to develop a CO gas sensor to operate in low temperatures. Herein, a novel Cu/CuO-decorated ZnO hollow nanofiber was prepared with the electrospinning, calcination, and photodeposition methods. In the presence of 100 ppm CO gas, the Cu/CuO-photodeposited ZnO hollow nanofiber (Cu/CuO@ZnO HNF) showed twice higher sensitivity than that of pure ZnO nanofiber at a relatively low working temperature of 300 °C. The hollow structure and p–n junction between Cu/CuO and ZnO would be considered to contribute to the enhancement of sensitivity to CO gas at 300 °C due to the improved specific surface area and efficient electron transfer.

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