Several studies have shown that combining TiO₂ and Cu₂O enhances the photocatalytic activity of the material by generating a heterojunction capable of extending the light absorption in the visible and reducing the electron-hole recombination rate. Ball milling has been chosen as an alternative methodology for photocatalyst preparation, among the several techniques documented in the literature review. The results of a previously reported investigation enabled the identification of the most effective photocatalyst that can be prepared for hydrogen generation by combining Cu₂O and TiO₂ (i.e., 1%wt. Cu₂O in TiO₂ photocatalyst prepared by ball-milling method at 200 rpm and 1 min milling time). To optimize photocatalytic hydrogen generation in the presence of the greatest photocatalyst, the effects of (i) sacrificial species and their concentration, (ii) temperature, and (iii) pH of the system are taken into account, resulting in a light-to-chemical energy efficiency of 8% under the best-tested conditions. Last but not least, the possibility of using the present photocatalytic system under direct solar light irradiation is evaluated: the results indicate that nearly 60% of the hydrogen production recorded under sunlight can be attributed to the visible component of the solar spectrum, while the remaining 40% can be attributed to the UV component.

The existing literature survey reports rare and conflicting studies on the effect of the preparation method of metal-based semiconductor photocatalysts on structural/morphological features, electronic properties, and kinetics regulating the photocatalytic H₂ generation reaction. In this investigation, we compare the different copper/titania-based photocatalysts for H₂ generation synthesized via distinct methods (i.e., photodeposition and impregnation). Our study aims to establish a stringent correlation between physicochemical/electronic properties and photocatalytic performances for H₂ generation based on material characterization and kinetic modeling of the experimental outcomes. Estimating unknown kinetic parameters, such as charge recombination rate and quantum yield, suggests a mechanism regulating charge carrier lifetime depending on copper distribution on the TiO₂ surface. We demonstrate that H₂ generation photoefficiency recorded over impregnated Cu_xO_y/TiO₂ is related to an even distribution of Cu(0)/Cu(I) on TiO₂, and the formation of an Ohmic junction concertedly extended charge carrier lifetime and separation. The outcomes of the kinetic analysis and the related modeling investigation underpin photocatalyst physicochemical and electronic properties. Overall, the present study lays the groundwork for the future design of metal-based semiconductor photocatalysts with high photoefficiencies for H₂ evolution.

A combination of leaching and sacrificial photocatalytic deposition was proposed to recover palladium. The recycling of the photocatalyst resulted in a practical method for reducing wastes generated during the process.