Silica-supported Cu sub(2)O nanoparticles with tunable size for sustainable hydrogen generation

• Published in: Applied catalysis. B, Environmental Vol. 192; pp. 199 - 207
• Main Authors: Wanga Gang, van den Berg, Roy, de Mello Donega, Celso, de Jong, Krijn P, de Jongh, Petra E
• Format: Journal Article
• Language: English
• Published: 05.09.2016
• Subjects: CATALYSTS; COPPER OXIDE; Copper oxides; Crystallites; CUPROUS OXIDE; FABRICATION; HYDROGEN; Illumination; Light (illumination); Nanoparticles; OXIDES; PARTICLES; Quantum efficiency; SOLAR CELLS; Strategy; Synthesis; VALENCE
• ISSN: 0926-3373
• DOI: 10.1016/j.apcatb.2016.03.044

Cu sub(2)O is a p-type semiconductor which attracts much attention for application in photovoltaics, photocatalysis and solar water splitting. However, Cu sub(2)O is not intrinsically stable under illumination in aqueous solutions, and the edge of the valence band is not positive enough to provide sufficient overpotential for water oxidation. The stability and band edge position of nanostructured materials depend on crystallite size. In this paper, we describe a new strategy to vary the size of Cu sub(2)O nanoparticles using mesoporous silica supports. First, CuO nanoparticles were obtained via impregnation-drying-heating. The size of the nanoparticles was tuned by varying either the concentration of Cu precursor or the pore diameter of the supporting silica. Subsequently, the CuO was converted to Cu sub(2)O without particle growth by gas-phase reduction with carbon monoxide. The visible light absorption of these nanoparticles depended on the copper oxide phase and crystallite size, leading to a direct band gap energy of 2.60 eV for 2 nm Cu sub(2)O nanoparticles compared to 1.94 eV for macrocrystalline Cu sub(2)O. Our results highlight a new synthesis strategy for the preparation of metal-oxide nanoparticles with controlled sizes of 2-15 nm that are not directly accessible by alternative synthesis techniques. The as-obtained 15 nm Cu sub(2)O nanoparticles were used for H sub(2) evolution in a water-methanol mixture, the photocatalyst gave a H sub(2) evolution rate of 11.5 10 super(-3) mu mol min super(-1) which corresponded to an internal quantum efficiency of 15.8% and an overall quantum efficiency of 3.5% for light between 310 and 710 nm. Finally, the nanoparticles were stable during three hours of light illumination.