Novel hetero-bimetallic coordination polymer as a single source of highly dispersed Cu/Ni nanoparticles for efficient photocatalytic water splitting

A new strategy for depositing highly dispersed Cu and Ni nanoparticles on the surface of TiO₂ from a single source is demonstrated for photocatalytic hydrogen production. We used a newly synthesized cyanide-bridged hetero-bimetallic coordination polymer [{Cu^II(4,4′-dipy)₂}{Ni(CN)₄}]_n·0.7(C₂H₆O₂).1.6(H₂O) (CP-1) (4,4′-dipy = 1,3-di(4-pyridyl)propane) as a single-source precursor of Cu-Ni nanoparticles. The structure of CP-1 was established by single-crystal X-ray diffraction analysis; CP-1 crystallizes in the monoclinic space group C2/c with β = 111.67(3)°. CP-1/TiO₂ composites containing different weight percentages of CP-1 were achieved by hydrolyzing titanium isopropoxide in the presence of CP-1. Highly dispersed Cu and Ni nanoparticles were deposited on TiO₂ by the calcination of the CP-1/TiO₂ composites at different temperatures (420 °C, 470 °C and 520 °C) in air followed by reduction in H₂/Ar atmosphere at 470 °C for 2 h. XRD, DRS/UV-Vis, TEM, Cu/Ni 2p XPS, and photoluminescence spectroscopy demonstrated the presence of CuO/Cu⁰ and NiO/Ni⁰ as active co-catalysts on the surface of TiO₂. The 1 wt% Cu-Ni/TiO₂-470 photocatalyst showed the maximum H₂ production activity of 8.5 mmol h^-1 g^-1 in a glycerol/water mixture (20 vol%). The results are anticipated to direct the future development of efficient, low-cost and noble metal-free semiconductor photocatalysts for solar H₂ production.