The invention relates to composite adsorbent materials, and in particular, to highly porous carbon-based composite materials for the adsorption and stabilization of inorganic substances. The composite adsorbent material comprises a porous carbon carrier matrix and an adsorbent species, wherein the adsorbent species is precipitated within the pores of the carrier matrix. The invention extends to various uses of such adsorbent materials, for example in water purification, recovery of metals from waste streams and remediation applications, and where the adsorbant material is amended into soil, waste etc. for the purpose of breaking pollutant-receptor linkages.