The solution was then made up to 22.5 mL with double distilled water, and degassed for 30 minutes with N 2 under stirring (1000 RPM). 2.5 mL of a 1M aqueous NaBH 4 solution was then added dropwise, and the reaction proceeded for 30 minutes under continuous degassing. The resulting brown Cu 0 -SiO 2 particles were then washed 3x in degassed, double-distilled water (50mL), before making up the suspension to 150 mL with degassed, double-distlled water.