Application of birnessite-type solids prepared by sol-gel and oxidation methods in photocatalytic degradation of 4-nitrophenol.

Potassium birnessites were prepared using two methods, sol-gel or oxidation. The solids were characterised by element chemical analysis, powder X-ray diffraction, FT-IR spectroscopy, thermal analyses, and nitrogen adsorption. The evolution of the properties as a function of the preparation method was discussed. The photocatalytic performance of these solids was preliminarily tested for the degradation of 4-nitrophenol. The degradation pathway and the nature of the by-products were investigated by mass spectrometry. The solids showed good catalytic behaviour, although their preparation must be improved, mainly concerning the calcination step involved in sol-gel synthesis, which led to the formation of Mn2O3 that worsened the catalytic behaviour.