Molecular additive-driven control of Cu/Cu₂O nanoparticle growth on mesoporous silica for enhanced photocatalytic hydrogen production

Size-controlled cuprous oxide-based nanoparticles (NPs) are promising materials for enhancing visible-light-driven photocatalytic hydrogen production by increasing the number of Cu+ surface-active sites. This study investigates the role of molecular additives in the growth of Cu/Cu₂O NPs on mesoporous silica (m-SiO2) templates. The molecular additives, cetyltrimethylammonium bromide (CTAB), ascorbic acid (AA), and citric acid (CA) are analyzed for their ability to modify the zeta potential of m-SiO₂, facilitating the adsorption of Cu⁺ ions. The modified surface effectively controlled the interaction between Cu⁺ ions and the m-SiO₂ surface through the influence of molecular additives. The CTAB system facilitates a rapid nanoparticle (NP) growth rate and significant aggregation, thereby promoting Cu⁺ ion adsorption and subsequent larger NP formation. In contrast, CA provides better control over NPs formation, preventing aggregation through Cu²⁺ chelation and stabilizing it on the mesoporous voids of silica. Furthermore, the intensity ratio of metallic Cu to Cu₂O is the lowest value of 0.47 in the CA system, indicating a higher Cu₂O content compared to CTAB and AA systems. It was observed that the CTAB and AA systems are more favorable for the formation of metallic Cu in the NPs. As a result, the CA system achieves a 5-fold increase in hydrogen production rate under visible light compared to the CTAB system. These findings highlight the critical role of molecular additives in tailoring NPs growth and photocatalytic performance.