Enhanced photocatalytic activity of TiO2 thin films on plasma-pretreated organic polymers

Abstract

Organic polymers are excellent substrates for photocatalytic applications of TiO2 thin films, which can be easily prepared by sol–gel synthesis followed by dip coating. However, the wettability of the hydrophobic surface of polymers should be improved. In this work, commercial poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA) and polystyrene (PS) were selected according to their high transmittance in the TiO2 activation range for the immobilization of the semiconductor. Low pressure (LPP) and atmospheric pressure (APP) plasma were used to modify the surface properties of the organic polymers to improve the affinity for TiO2 aqueous sols and solutions. The characterization of the materials was performed by atomic force microscopy (AFM), UV–Vis spectroscopy, and contact angle and surface tension measurements, employed to evaluate wettability of the samples. The effect of the power of discharge and treatment time on the induced surface properties was analyzed. LPP at 300 W during 600 s was found as adequate treatment to promote the hydrophilicity of all samples without damage to the bulk. The adhesion of TiO2 thin films on the polymers was improved with the plasma pre-treatment due to the generation of roughness and specific polar functional groups. Accordingly, the photocatalytic performance increased with respect to the non-treated substrates, reaching similar conversion values than the reference photocatalyst where glass, a hydrophilyc substrate, was used as support.