Photocatalytic properties of sodium decatungstate supported on sol–gel silica in the oxidation of glycerol

Photoexcitation of Na4W10O32 dissolved in water produces a powerful oxidizing reagent that is able to form hydroxyl radicals from water. OH• radicals formation has been demonstrated by EPR spintrapping technique using DMPO as spin trap. The photooxidation of glycerol occurs through its reaction with OH• radicals and is characterized by low selectivity and partial degradation of the substrate to CO2. Entrapment of Na4W10O32 inside a silica matrix by a sol–gel procedure gives a new heterogeneous photocatalyst characterized by the presence of micropores (7 and 13 A) and mesopores (30 A). Interaction between polyoxoanion and protonated silanol groups are strong and prevent any kind of leaching. The solid support affects the selectivity of the O2-assisted photooxidation process of glycerol. In particular, silica surface enhances alcohol adsorption improving its local concentration, so favouring its reaction with photogenerated OH• radicals that leads to glyceraldehyde and dihydroxyacetone. At the same time, carbon dioxide is not formed, thus indicating that it is possible to control the high oxidizing power of sodium decatungstate through its heterogenization on a suitable support.