Development of photocatalytically active heterostructured MnO/ZnO and CuO/ZnO films via solution precursor plasma spray process

Abstract

Heterostructured ZnO photocatalysts for the degradation of organic pollutant are mainly synthesized by conventional chemical methods, suffering from long duration, multi-steps, and post-treatment of the powder-formed catalysts after usage. In this paper, Solution Precursor Plasma Spray (SPPS) process is demonstrated to be a fast and efficient method for the one-step preparation of MnO/ZnO and CuO/ZnO heterostructured films for photocatalytic applications. The ratios between MnO or CuO and ZnO materials in the films were easily adjusted by varying the molar ratio of Mn(OAc)2 or Cu(OAc)2 relative to Zn(OAc)2 during the SPPS synthesis. To optimize the microstructure of selected CuO/ZnO films, two alternative spraying patterns were also developed. The modified films (Cu20-ZnO-A and Cu20-ZnO-B) were partly composed of nanorods (NRs) instead of conventional irregular particles. The MnO/ZnO and CuO/ZnO films exhibit narrower bandgap than pure ZnO films. The photocatalytic performances of the ZnO based films were evaluated for the degradation of the Orange II dye. Cu20-ZnO and Cu20-ZnO-B films exhibit the highest degradation efficiency under UV light and visible light, respectively. For example, the SPPS deposited Cu20/ZnO films could almost remove 90% of Orange II within 3 h of UV light irradiation. Moreover, this study not only reveals that SPPS is of high potential for the deposition of heterostructured metal oxide films in rapid one-step, but also points out an efficient spraying strategy for adjusting the nanostructured morphologies in these films.