Catalytic Degradation of Organic Molecules by Colloidal Hematite in a Silica Box via Fenton-like Reaction

Abstract

Fenton's reagent is the combination of ferrous ions and hydrogen peroxide and is commonly used for the degradation of organic molecules. The ferrous ions promote the formation of radicals from the hydrogen peroxide which degrade the organic molecules. In this research, colloidal hematite cubes are used as a source of iron ions. These cubes were synthesized according to an adjusted method of Sugimoto et al. and were coated with amorphous and porous silica, yielding colloidal hematite in a silica box. We find that in the presence of hydrogen peroxide these colloids accelerate the degradation of organic molecules in a fashion similar to Fenton's reagent. The degradation of the model organic molecules methylene blue and rhodamine B was followed by the eye and with UV-Vis spectroscopy to quantify the amount of remaining organic dye. Cubes immobilized on mica substrates were still able to accelerate the reaction, although the catalytic activity was less than for the cubes used in dispersed form. Unfortunately, not all the cubes remained on the support during the reaction. The adhesion was improved by thermally treating the substrates and it was observed that the silica shells were less brittle after the treatment. Nitrogen physisorption measurements were performed on the bare and silica coated hematite cubes to determine the surface area and pore sizes after etching the hematite core or the silica layer. Upon etching of the hematite core with hydrochloric acid the porosity of the hematite and the silica shell increased. A maximum in surface area for hematite during the etching with hydrochloric acid was not found.