Novel photoactive composites of cubic Cu2O nanoparticles with aluminosilicate geopolymers were prepared and their structure was shown by SEM/EDS and TEM. XRD, FTIR, Al-27 and Si-29 MAS NMR to consist of a well-reacted geopolymer matrix containing homogeneously dispersed Cu2O nanoparticles. Under dark conditions, both the geopolymer matrix and the composites were shown to adsorb a model organic compound (methylene blue, chosen for its colour stability at high pH) by a process which follows pseudo-first-order kinetics and can be described by Langmuir-type isotherms. At concentrations > 20 wt%, the oxide decreases the adsorption rate by blocking the active adsorption sites of the geopolymer. Under UV radiation, the composites remove the methylene blue by a combination of adsorption and photodegradation, without deterioration of the geopolymer structure or the photoactive Cu2O component, as evidenced by Cu-63 NQR spectroscopy, suggesting that these geopolymer composites should function as useful new materials for the removal of organic pollutants from water or the atmosphere.