Synthesis of high efficient Cu/TiO₂ photocatalysts by grinding and their size-dependent photocatalytic hydrogen production

Highlights: • Cu nanodots were decorated on TiO₂ surface through ball milling method. • Its size distribution was investigated in water and ethanolic medium. • Photocurrent response and hydrogen evolution was improved. • Performance was found to be dependent on size of Cu nanodots. - Abstract: Recently, copper species have been extensively investigated to replace Pt as efficient co-catalysts for the evolution of H₂ due to their low cost and relatively high activity. Cu nanoparticles less than 5 nm are successfully decorated on TiO₂ surface in this work by an easy and mild milling process. These Cu nanoparticles are highly dispersed on TiO₂ when the loading amount of Cu is no more than 10 wt%. The sizes of Cu nanoparticles can be controlled by changing the milling environment and decrease in the order of Cu-ethanol > Cu-water > Cu nanoparticles obtained through drying milling. The highest and stable hydrogen generation can be realized on Cu/TiO₂ with 2.0 wt% Cu and sizes of Cu nanoparticles ranging from 2 to 4 nm, in which high and stable photocurrent confirms promoted photogenerated charge separation. Smaller Cu clusters are demonstrated to be detrimental to hydrogen evolution at same Cu content. High loading of Cu nanoparticles of 2–4 nm will benefit photogenerated electron-hole recombination and thus decrease the activity of Cu/TiO₂. The results here demonstrate the key roles of Cu cluster size in addition to Cu coverage on photocatalytic activity of Cu/TiO₂ composite photocatalysts.