Comb Copolymer Templates for Interconnected, Hierarchically Porous TiO₂Nanoisland Photocatalytic Membranes

Pluronic block copolymers have been most widely used as templates for porous TiO2 photocatalytic structures, but small pores are formed, reducing water permeability. Herein, a comb copolymer, poly(glycidyl methacrylate)-co-poly(oxyethylene methacrylate) (PGMA-co-POEM; simply PGPO), was synthesized through free-radical polymerization and used as a template for hierarchically porous TiO2 (hp-TiO2) nanoislands on porous Al2O3 membranes via a sol-gel, spin-coating process. The PGPO comb copolymer exhibited self-assembled, microphase-separated morphology, leading to a mesoporous TiO2 architecture with superior interconnectivity. In situ epoxy-hydroxyl crosslinking and selective coordination of the TiO2 precursor to the hydrophilic chains of the PGPO copolymer resulted in the development of hp-TiO2 nanoislands. The layer-by-layer morphology ensured excellent photocatalytic ability for the degradation of contaminants associated with organic dye compounds upon UV irradiation (removal efficiency >90%). Organic fouling due to the dye compounds was further significantly reduced with the hp-TiO2 membrane (flux decline ∼10%) as compared to the case of a porous TiO2 (p-TiO2) membrane (removal efficiency ∼50%; flux decline ∼30%). Furthermore, the water permeability of hp-TiO2 nanoisland membranes was greater than those of membranes prepared using Pluronic P123, which is attributed to the self-assembly, microphase-separated structure and high molecular weight of the PGPO comb copolymer.