Graphitic carbon nitride thin films for light-induced photocatalysis in a slit geometry microreactor

A combination of a photocatalysis and a micro-flow technology provides a highly capable tool for the design and utilisation of functional thin films. Here, they are represented by graphitic carbon nitride films, potentially used for photo-oxidations in environmental chemistry or for hydrogen evolution by water splitting. The optimised synthesis involves a study of the role of monomers, solvents, calcination temperatures, particle size, etc., in respect of the achieved photocatalytic activity. Films were prepared from the mixture of milled powder catalysts and a binder, dried, and subjected to post-processing treatments (post annealing, plasma application). The intended functionality was assessed in two types of reactions, photo-oxidation of a fluorescent dye, Rhodamine B, and photo-oxidation of a common antibiotic, Tetracycline. The performance was compared for the bulk catalyst, and for the thin film. In either case, the same part of light spectrum, concentrations, and other conditions were applied. However, for the thin films, a special experimental setup was utilised. It had the appearance of a micro-flow apparatus designed as a slit geometry photo-microreactor. Comparison of the two different reaction systems revealed the advantages of the thin film catalyst, which was immobilised directly on the photo-microreactor wall. The specific rate constant was more than 50 times higher in this arrangement for both model reactants. In addition, thin films of g-C3N4 were stable and well adherent during the microreactor tests with the repetitive reaction cycles. Plasma treatment considerably increased the hydrophilicity of the dried thin films, which resulted in their substantially higher photoactivity. [Display omitted] •g-C3N4 films active in the Rhodamine B and Tetracycline photodegradation are shown.•The specific rate constant was 50x higher with g-C3N4 thin film compared to slurry.•Low-temperature plasma changed the hydrophobic g-C3N4 thin film to hydrophilic.•The g-C3N4 films showed stable photocatalytic activity after 6 reaction cycles.