Polymer composite comprising metal based nanoparticles in a polymer matrix

A composite having a substrate and a plurality of core-shell nanoparticles. The substrate has microporosity, nanoporosity, or free volume and is a polymer matrix, a metal-organic framework, a micro-porous structure, or a nano-porous structure. The plurality of core-shell nanoparticles each has a core and at least one shell layer. The core is made from a decomposed product of a first precursor disposed in the microporosity, nanoporosity, or free volume of the substrate. The at least one shell layer is made from a decomposed product of a second precursor and is disposed on the core.