Exploring next-generation X(NO3)Y (X = Na+, K+, Sr2+, Ag+; Y=1, 2) electrolytes for enhanced TiO2 nanotube hydrogen generation

The synthesis of high-efficiency TiO2 nanotube (TNT) layers is crucial for achieving photocatalytic caffeine degradation and H2 production. Herein, we successfully used next-generation fluoride-free nitrate-based X(NO3)Y, where X = Na+, K+, Sr2+, Ag+; Y = 1,2) electrolytes to prepare TNT layers via electrochemical anodisation. The prepared TNT layers (approximately 1 μm thick; 20–30 nm in diameter) underwent comprehensive characterisation, encompassing aspects of their morphology, structure, composition, as well as their photoelectrochemical and photocatalytic properties. The results demonstrated that the highest caffeine degradation efficiencies (k = 0.0354 min−1 and k = 0.0346 min−1) were achieved in K− and Ag-based electrolytes, respectively. Additionally, the H2 yields for the photocatalysts obtained after 4 h of irradiation ranged from 1791 to 1507 μmol/gcat. The use of a large surface area of the nanotubes (∼20 cm2), along with the absence of fluoride ions during anodisation, paves the way for potential industrial applications and provides a promising approach for the green synthesis of high-performance and environmentally friendly photocatalysts.