Porous hollow TiO 2 microparticles for photocatalysis: exploiting novel ABC triblock terpolymer templates synthesised in supercritical CO 2

Reversible addition–fragmentation chain transfer (RAFT) mediated dispersion polymerisation in supercritical carbon dioxide (scCO 2 ) 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 scCO 2 , 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 TiO 2 microparticles. Through a simple and scalable sol–gel and calcination process we produce hollow TiO 2 microparticles with a mesoporous outer shell. When directly compared to porous TiO 2 particles fabricated using an equivalent PMMA- b -P4VP diblock copolymer, increased surface area and enhanced photocatalytic efficiencies are observed.