Cu2+/Cu+ pair mediated heterojunction in core-shell SiO2@Cu2GaBO5@TiO2 composite for enhanced photocatalytic methanol dehydrogenation for co-production of H2 and formaldehyde with nearly 100 % selectivity.

Co-production of hydrogen and formaldehyde by photocatalytic dehydrogenation of methanol is of great significance. However, it is still challenging for photocatalytic materials without precious metals to effectively obtain hydrogen and formaldehyde at room temperature with low concentration methanol driven by visible light. This work reported a photocatalytic composite material SiO2@Cu2GaBO5@TiO2 (SCGBT) prepared by a two-step hydrolysis-pyrolysis method. The SiO2@Cu2GaBO5@TiO2-550 (SCGBT-550) photocatalyst showed significantly enhanced photocatalytic activity for co-production of H2 and formaldehyde with the rate of hydrogen production and methanol oxidation to formaldehyde of 1524 μmol·g-1·h-1 and 1511 μmol·g-1·h-1 compared to pure-phase and other composite materials. The formaldehyde selectivity reached up to 99 %. The promising photocatalytic performance of SCGBT-550 can be attributed to the dual role of Cu ions from borate and the construction of heterojunction. The intimate interfacial contact and an internal electric field triggered an S-Scheme charge transfer process, which promotes the spatial separation of photogenerated charges. Cu ions serve as an electron transfer bridge and a hole oxidation active center, further improving the photocatalytic hydrogen production and formaldehyde selectivity. This catalyst design strategy not only paves the way for the efficient and stable borate reduction-oxidation catalysts, but also provides a new idea for the transformation of heterojunction electron transfer paths, and holds promise for achieving highly efficient hydrogen production and high-value chemical synthesis under mild conditions.