Solution precursor plasma spray process as an alternative rapid one-step route for the development of hierarchical ZnO films for improved photocatalytic degradation

The development of efficient photocatalytic hierarchical coral-like ZnO films via a relatively simple, efficient, rapid and single-step process is essential for industrial development. Herein, we report a novel method for directly synthesizing well-shaped ZnO nanorods (NRs) by Solution Precursor Plasma Spray (SPPS) process rather than conventional spherical/ellipsoidal particles. In the prepared ZnO-NRs films, the ZnO-NRs display an average diameter of 190 nm, and exhibit a preferential orientation growth along (002) plane compared to a reference ZnO films (called ZnO-P) containing spherical/ellipsoidal particles. ZnO-NRs films exhibit relative narrower bandgap (3.02 eV) probably due to the apparent non-equilibrium heating-cooling process and to the use of hydrogen in the SPPS method. Such ZnO-NRs films are capable of a quasi-quantitative (99%) decomposition of the Orange II dye within 150 min under Hg-Xe light irradiation, which is nearly 2.7 times of the reference sample ZnO-P (37% degradation). Besides, the ZnO-NRs films exhibit an excellent retention of performance (98.7% degradation in a second cycle). Moreover, these preliminary results demonstrate that SPPS process provides a promising alternative to conventional multi-step processes for the production of metal oxide photocatalytic films in practical applications.