Colloidal cubes for the enhanced degradation of organic dyes

The shape of cubic silica colloids is exploited to form close-packed structures, whereas the hollow core of the cubes may host functional substances. A proof-of-principle of this approach is presented for iron oxide particles (hematite, alpha-Fe2O3) confined inside silica cubes that display the ability to accelerate the degradation of the organic dyes methylene blue and rhodamine B in the presence of hydrogen peroxide (modified Fenton reaction). The silica coating does not impede the reaction, since degradation rates similar to those of bare hematite particles are observed. Moreover, the cubic colloids are still functional when densely packed onto a substrate. The degradation reaction is greatly enhanced by illumination with visible or UV light: the degradation time reduces by two orders of magnitude. Although the silica coating is damaged during the degradation reaction, the stability of the coating is improved by heat treatment of the cubes and by illumination.