Combination of chemical methods for obtaining ZnO films for application and reuse in photocatalysis: polymeric precursor and microwave-assisted hydrothermal methods

This paper evaluated the photocatalytic activity and reuse potential of ZnO films obtained by combining two chemical methods, polymeric precursor (PP) synthesis and microwave-assisted hydrothermal (HMW) synthesis, to remove Rhodamine B dye. This strategy is a promising route to photocatalyst synthesis, allowing easy control of deposition parameters and fast reactions. ZnO films had a hexagonal wurtzite structure and a typical bandgap of 3.3 eV, lower than that of the PP layer (3.9 eV). Films obtained by the PP method showed homogeneous structure and nanometric grain size (32 nm). The use of PP films as a seed layer for particle deposition by the HMW method resulted in films composed of spherical particles (25-137 nm) with an irregular surface. Films obtained after 10 min of PP-HMW reaction showed a less filled surface than those obtained after 30 min of reaction. The kinetic constant increased from 7 x 10-3 min-1 by the PP method to 9 x 10-3 min-1 by the HMW method. ZnO films obtained by the PP-HMW route had the best photocatalytic performance, achieving 67% dye degradation after 120 min of reaction. This result can be attributed to the presence of an interface between PP and HMW layers, which increases surface irregularity, consequently increasing contact between dye and semiconductor particles. The photocatalyst showed good reusability, achieving 56% dye degradation after five reuse cycles. These findings demonstrate the potential of combining PP and HMW methods to the of ZnO thin films.