Coassembly of metal and titanium dioxide nanocrystals directed by monolayered block copolymer inverse micelles for enhanced photocatalytic performance

Functional nanostructures of self-assembled block copolymers (BCPs) incorporated with various inorganic nanomaterials have received considerable attention on account of their many potential applications. Here we demonstrate the two-dimensional self-assembly of anisotropic titanium dioxide (TiO ₂) nanocrystals (NCs) and metal nanoparticles (NPs) directed by monolayered poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymer inverse micelles. The independent position-selective assembly of TiO ₂ NCs and silver nanoparticles (AgNPs) preferentially in the intermicelle corona regions and the core of micelles, respectively, for instance, was accomplished by spin-coating a mixture solution of PS-b-P4VP and ex situ synthesized TiO ₂ NCs, followed by the reduction of Ag salts coordinated in the cores of micelles into AgNPs. Hydrophobic TiO ₂ NCs with a diameter and length of approximately 3 nm and 20-30 nm, respectively, were preferentially sequestered in the intermicelle nonpolar PS corona regions energetically favorable with the minimum entropic packing penalty. Subsequent high-temperature annealing at 550 °C not only effectively removed the block copolymer but also transformed the TiO ₂ NCs into connected nanoparticles, thus leading to a two-dimensionally ordered TiO ₂ network in which AgNPs were also self-organized. The enhanced photocatalytic activity of the AgNP-decorated TiO ₂ networks by approximately 27 and 44 % over that of Ag-free TiO ₂ networks and randomly deposited TiO ₂ nanoparticles, respectively, was confirmed by the UV degradation property of methylene blue. Of micelles and metals: Coassembly of anisotropic TiO ₂ nanocrystals and Ag nanoparticles was achieved in the corona and core regions of monolayered block copolymer micelles, respectively (see figure). Thermal heating removed the block copolymer and the resulting TiO ₂ network nanostructure with Ag nanoparticles decorating its pores exhibited excellent photocatalytic performance.