Comb Copolymer Templates for Interconnected, Hierarchically Porous TiO2 Nanoisland Photocatalytic Membranes

초록

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 similar to 10%) as compared to the case of a porous TiO2 (p-TiO2) membrane (removal efficiency similar to 50%; flux decline similar to 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.

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