Abstract: The present invention discloses methods for producing a guest@nanoporous-host materials, and guest@nanoporous-host materials produced according to these methods. Methods according to the invention comprise steps of infiltrating a nanoporous host material with one or more reagents and a target guest precursor in a reaction environment such that a reaction occurs to form the target guest species within the pores of the nanoporous host material. The reagent comprise either a redox reagent and/or a pH modulator. By analysis of appropriate electrochemical potential-pH diagrams and careful selection of suitable reagents and control of process conditions to produce desired target guest particles from selected target guest precursors, the synthesis strategy to form the guests can be more flexible and versatile than known methods, because typically milder reaction conditions can be used than in such known methods.