Self-cleaning and photodegradle PVDF separation membranes modified with self-assembled TiO₂-g-CS/CNTs particle

This work obtained separation membranes with UV-cleaning performance by adding TiO₂-g-CS/CNTs photocatalyst to the PVDF. The positively charged chitosan (CS) and negatively charged carboxylic carbon nanotube (CNTs-COOH) can be self-assembled into the bilayer structure on the surface of TiO₂ particles through electrostatic attraction. The presence of many hydrophilic groups in CS and CNTs-COOH significantly improves the hydrophilicity of TiO₂-g-CS/CNTs-PVDF membrane, and helps TiO₂ to be uniformly dispersed on the upper surface. TiO₂-g-CS/CNTs promote the change of pore structure and expand the flux of the modified membrane to 4.5 times that of pure PVDF. Zeta potential demonstrates that the TiO₂-g-CS particles successfully attracted CNTs in the PVDF matrix, and the membrane surface was still positively charged. Thus, the combined effect of the positively charged TiO₂-g-CS and the highly adsorbed CNTs enhanced the retention of the contaminants. More importantly, there is a charge transfer between the grafted CS and TiO₂ interface to obtain a broader light absorption band. The excitation carriers provided by CNTs significantly contribute to the photocatalytic performance after transfer between TiO₂ and CS; thus, TiO₂-g-CS/CNTs-PVDF produces higher photocatalytic activity for dye molecules (degradation rate > 97 %).