Controlled growth of ultrasmall Cu₂O clusters on TiO₂ nanoparticles by atmospheric-pressure atomic layer deposition for enhanced photocatalytic activity

This work presents a gas-phase approach for the synthesis of Cu₂O/TiO₂ powder-based photocatalysts using atomic layer deposition (ALD). The process is carried out in a fluidized bed reactor working at atmospheric pressure using (trimethylvinylsilyl)-hexafluoroacetulacetonate copper(I) as the Cu-precursor and H₂O vapor as the oxidizer. The saturating regime of the chemical reactions and the linear growth of ALD are achieved. In combination with the unsaturated regime, the ALD approach enables the deposition of ultrasmall Cu₂O clusters with average diameters in the range of 1.3-2.0 nm, narrow particle size distributions and tunable Cu₂O loadings on P25 TiO₂ nanoparticles. The photocatalytic performance of Cu₂O/TiO₂ photocatalysts is investigated by the degradation of organic dyes, including Rhodamine B (RhB), methyl orange, and methylene blue; the results demonstrate that the surface modification of TiO₂ nanoparticles by Cu₂O nanoclusters significantly enhances the photocatalytic activity of TiO₂. This is attributed to the efficient charge transfer between Cu₂O and TiO₂ that reduces the charge recombination. The photocatalytic reaction mechanism is further investigated for the degradation of RhB, revealing the dominating role of holes, which contribute to both direct hole oxidation and indirect oxidation (i.e. via the formation of hydroxyl radicals). Our approach provides a fast, scalable and efficient process to deposit ultrasmall Cu₂O clusters in a controllable fashion for surface engineering and modification.