Synthesis of porous ZnO/TiO2 thin films with superhydrophilicity and photocatalytic activity via a template-free sol-gel method

Superhydrophilicity of TiO2 thin film under natural conditions is of great importance for antifogging and self-cleaning applications of glass products. Transparent superhydrophilic porous ZnO/TiO2 composite films were prepared on glass substrates using a template-free sol-gel method. The results indicated that the porous ZnO (10%)/TiO2 composite film possesses superhydrophilicity with water contact angle less than 5° without UV irradiation. Surface chemical composition of the films was characterized by X-ray photoelectron spectroscopy (XPS). The morphologies of the porous films were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The porous morphology, crystal structure and surface chemical composition were significantly affected by ZnO addition. The natural superhydrophilic performance was attributed to the synergistic effect of the porous structure and surface hydroxyl groups. Photocatalytic activities of the ZnO/TiO2 composites were also evaluated using methyl orange (MO) as a model pollutant, with 78.1% of MO degraded by ZnO (10%)/TiO2, which was higher than 49.3% obtained from pure TiO2.