Different Methods for Preparation of Active Sites in Kaolinite Surface and their Usability in Photocatalytic Processes

A relevant discovery of the last decade is the identification of the photochemical activity of the kaolinite-type minerals. The activity depends on several surface properties, such as mineral composition, morphology, lattice impurities and structural order. Preparation of the activated surface can be made by intercalation, exfoliation, mechanochemical activation, acid treatment, thermal treatment. The process of intercalation is a well-known way for a long while to produce delaminated and finally exfoliated structure from double-layered minerals. Coordination of octahedral Al atoms can be reduced by means of mechanochemical activation (i. e. dry grinding) and/or thermal treatment. The (hydrochloric) acid treatment alters not only the acid-base properties of the surface, but has effect on the mineral composition also. In this study the influence of the mentioned surface modification methods is shown on kaolins from different deposits with varying structural order, mineral and lattice impurities. The modified surface is investigated with thermal analysis (TG-DTG, CRTA), XRD, solid phase NMR and IR spectroscopic techniques. Photocatalytic activity is tested in liquid phase with oxalic acid test molecule during 365nm irradiation. Applying and combining various surface modification methods it is possible to enhance the natural kaolin-based materials in order to develop photocatalysts.