Porous hollow TiO2 microparticles for photocatalysis: exploiting novel ABC triblock terpolymer templates synthesised in supercritical CO2

Abstract

Reversible addition–fragmentation chain transfer (RAFT) mediated dispersion polymerisation in supercritical carbon dioxide (scCO₂) is an efficient and green method for synthesising block copolymer microparticles with internal nanostructures. Here we report for the first time the synthesis of phase separated poly(methyl methacrylate-block-styrene-block-4-vinylpyridine) (PMMA-b-PS-b-P4VP) triblock terpolymer microparticles using a simple two-pot sequential synthesis procedure in scCO₂, with high monomer conversions and no purification steps. The microparticles, produced directly and without further processing, show a complex internal nanostructure, appearing as a “lamellar with spheres” [L + S(II)] type morphology. The P4VP block is then exploited as a structure-directing agent for the fabrication of TiO₂ microparticles. Through a simple and scalable sol–gel and calcination process we produce hollow TiO₂ microparticles with a mesoporous outer shell. When directly compared to porous TiO₂ particles fabricated using an equivalent PMMA-b-P4VP diblock copolymer, increased surface area and enhanced photocatalytic efficiencies are observed.