Block copolymer-templated BiFeO3 nanoarchitectures composed of phase-pure crystallites intermingled with a continuous mesoporosity: Effective visible-light photocatalysts?
Self-assembly, mesoporous, nanocrystalline, thin films, photocatalysis, multiferroic
Herein is reported the soft-templating synthesis of visible-light photoactive bismuth ferrite (BiFeO3) nanoarchitectures in the form of thin films using a poly(ethylene-co-butylene)-block-poly(ethylene oxide) diblock copolymer as the structure-directing agent. We establish that (1) the self-assembled materials employed in this work are highly crystalline after annealing at 550 °C in air and that (2) neither the bismuth-poor Bi2Fe4O9 phase nor other impurity phases are formed. We further show that there is a distinct restructuring of the high quality cubic pore network of amorphous BiFeO3 during crystallization. This restructuring leads to films with a unique architecture that is composed of anisotropic crystallites intermingled with a continuous mesoporosity. While this article focuses on the characterization of these novel materials by electron microscopy, krypton physisorption, grazing incidence small-angle X-ray scattering, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy, UV-vis and Raman spectroscopy, we also examine the photocatalytic properties and show the benefits of the combination of mesoporosity and nanocrystallinity. Templated BiFeO3 thin films (25% porosity) with a direct optical band gap at 2.9 eV exhibit a catalytic activity for the degradation of rhodamine B much better than that of nontemplated samples. We attribute this improvement to the nanoscale porosity, which provides for more available active sites on the photocatalyst.
Tsinghua University Press
Christian Reitz,Christian Suchomski,Christoph Weidmann,Torsten Brezesinski, Block copolymer-templated BiFeO3 nanoarchitectures composed of phase-pure crystallites intermingled with a continuous mesoporosity: Effective visible-light photocatalysts?. NanoRes.2011, 4(4): 414–424