Chitosan films containing TiO2 nanoparticles modified with tungstophosphoric acid for the photobleaching of malachite green in solid￾gas interfaces upon different wavelengths

Abstract

Chitosan (CS) films containing visible light absorbing TiO2 nanoparticles modified with tungstophosphoric acid (TPA-TiO2) at different TPA-TiO2:CS ratios (10%, 20%, 30% and 40% (w/w) called CS/TPA-TiO2-10, CS/TPA-TiO2-20, CS/TPA-TiO2-30, and CS/TPA-TiO2-40 respectively) were prepared. Films were characterized by DRS, SEM-EDS, XRD, ATR-FT-IR, and contact angle (CA). Materials were evaluated in malachite green (MG) photobleaching solid-gas interface reactions upon different wavelengths. SEM-EDS micrographs showed that TPA-TiO2 nanoparticles were well dispersed through the CS film. According to ATR-FT-IR results, the interactions between TPA-TiO2 nanoparticles and the CS functional groups were weak. Regarding the MG photobleaching reactions, CS/TPA-TiO2-30 film showed the highest activity upon UV-A + visible irradiation, which was even higher than that of chitosan films containing the same amount of Evonik P-25 (CS/P25-30). It was also observed by DRS that the main absorption band of malachite green underwent a hypsochromic shifting caused by oxidative reactions of N-demethylation. On the other hand, at wavelengths higher than 450 nm (Vis-1), CS/TPA-TiO2-30 films showed a marked dye photobleaching. Finally, upon irradiation at wavelengths above 590 nm (Vis-2), a slight color fading was observed. These results revealed that CS/TPA-TiO2-30 films were efficient in the photobleaching of malachite green in solid-gas interfaces through an oxidative path by photocatalytic and photosensitized routes. CS/TPA-TiO2-30 films showed high stability and MG photobleaching capacity after 5 reuse cycles.