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

摘要

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.