Photocatalytic NOx oxidation over modified ZnO/TiO2 thin films

Pure ZnO and TiO2 coatings as well as composite ZnO/TiO2 coatings in various ratios were deposited on Quartz substrate via sol-gel method and dip coating technique. Porous ZnO/TiO2 films were created by modification of the precursor solutions with PEG 2000 and Pluronic F127 in order higher photocatalytic activity in NOx oxidation to be achieved. It was demonstrated that the pure TiO2 and ZnO films consisted of anatase TiO2 and wurtzite hexagonal ZnO, respectively. The ZnO/TiO2 films with initial solution ratio 1:1 and 2:1 had amorphous structure. The crystallinity of all the films increased upon modification. The UV-vis spectra showed that the addition of modifiers resulted in reduced transmittance for pure TiO2 and ZnO/TiO2 composite films with the phenomenon to be more prominent when Pluronic F127 was added. The TiO2 films exhibited smooth morphology, while the ZnO and the mixed oxides films became corrugated after modification. From the non-modified films, the pure TiO2 exhibited the highest photocatalytic activity in NOx oxidation and the presence of ZnO component led to deterioration of the activity. The modification of the films improved the photocatalytic performance especially when Pluronic F127 was used. The efficiency of the pure ZnO photocatalyst was significantly increased, while the porous Pluronic-modified ZnO/TiO2 film with 1:3 ratio demonstrated the greatest NOx oxidation among all the investigated films. The results were associated with the porous morphology of the films obtained by surface modification and coupling the TiO2 photocatalyst with second semiconductor ZnO in specific ratio. (C) 2014 Elsevier B.V. All rights reserved.