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 Cu²⁺ ions. The modified surface effectively controls the interaction between Cu²⁺ ions and the m-SiO₂ surface through the influence of molecular additives. The CTAB system facilitates a rapid nanoparticle (NP) growth and significant aggregation, thereby promoting the adsorption of Cu species and the subsequent formation of larger NPs. In contrast, CA provides better control over the formation of NPs, preventing aggregation through Cu²⁺ chelation and stabilizing the particles within the mesoporous voids of silica. Furthermore, the intensity ratio of metallic Cu to Cu₂O has the lowest value of 0.47 in the CA system, indicating a higher Cu₂O content compared to the CTAB and AA systems. CTAB and AA favor metallic Cu formation, while CA stabilizes Cu⁺ and promotes Cu₂O phase growth. As a result, the CA system achieves a 5-fold increase in the hydrogen production rate under visible light compared to the CTAB system. These findings highlight the critical role of molecular additives in tailoring NP growth and enhancing photocatalytic performance.