We report here on new photoreactive core-matrix reactive metal nanoparticles. Poly(methyl methacrylate)-capped aluminum nanoparticles (PMMA-Al NPs) were synthesized and demonstrated air stability on the order of 2 months. Upon exposure of the PMMA-Al NPs to UV radiation the composite reacts more rapidly to release H-2 gas from alkaline solution. FTIR spectroscopy indicates that the PMMA cap degrades under UV irradiation, exposing the reactive metal core. (C) 2013 Elsevier B. V. All rights reserved.