Photocatalytic activity of thin films with selectively photofixed cocatalysts

Photocatalytic thin films find application in a number of priority technologies: for example, the destruction of organic pollutants in water or air (via photooxidation and photoreduction – to H2O and CO2) and self-cleaning surfaces; in photoelectrochemical cells for water splitting into "green" hydrogen (solar-to-hydrogen) or photoreduction of CO2 into useful products. They are most often based on wide-bandgap semiconductors (e.g., TiO2, ZnO, etc.), which, upon absorbing light energy, generate excited states (excitons) consisting of mobile photogenerated electrons and positively charged "holes". On the surface of the photocatalyst, these photogenerated charges can participate in redox processes with adsorbed molecules, leading to their chemical transformation and constituting the main mechanism of heterogeneous photocatalysis. 

A major problem in photocatalysis is the low quantum yield (the ratio of absorbed photons per unit area to successful chemical transformations on the surface), which in turn is mainly due to the recombination of photogenerated charges and the loss of most (>99%) of the absorbed light energy in the form of heat. A possible solution to this problem is the functionalization of the photocatalytic surface with cocatalysts – materials (most often noble metals or transition metal oxides) that, based on the formation of heterojunctions, accumulate only one of the two types of photogenerated charges, effectively separating the exciton, limiting the possibilities for recombination, and simultaneously promoting only oxidation or reduction reactions.