▎ 摘　　要

NOVELTY - Preparing cobalt based double metal oxide loaded graphene quantum dots composite photocatalyst, comprises (i) dissolving predetermined amount of cobalt salt, oxo-acid salt of metal M, and urea in deionized water, ultrasonically stirring and mixing evenly to obtain mixed solution, transferring the mixed solution into reaction kettle, and reacting at 150-220℃ for 4- 8 hours, filtering, drying and grinding the precipitate obtained by suction filtration to obtain a powdery metal-cobalt-oxide precursor, adding the powdered precursor into tube furnace for calcination to obtain metal-cobalt-oxide compound, and (ii) mixing metal-cobalt-oxide compound obtained in the step (i) and carbon source small molecular substance to the certain proportion, transferring into polytetrafluoroethylene reaction kettle, reacting at 150-240℃ for 4-8 hours, performing suction filtration after finishing the reaction, drying and grinding the precipitate obtained by suction filtration. USE - The cobalt based double metal oxide supported graphene quantum dots composite photocatalyst is useful in decomposing water to produce hydrogen under visible light, degradation of organic pollutants under visible light., and catalytic reduction of carbon dioxide under visible light (all claimed). ADVANTAGE - The method: does not require the participation of a strong acid oxidant; does not requirepost-treatment e.g. dialysis to remove non-carbon impurities; is simple and easy to process; and environmentally friendly; and produces composite photocatalyst which has strong photocatalytic activity and stability. DETAILED DESCRIPTION - Preparing cobalt based double metal oxide loaded graphene quantum dots (GQDs) composite photocatalyst, comprises (i) dissolving predetermined amount of cobalt salt, oxo-acid salt of metal M, and urea in deionized water, ultrasonically stirring and mixing evenly to obtain mixed solution, transferring the mixed solution into reaction kettle, and reacting at 150-220℃ for 4- 8 hours, carrying out suction filtration, drying and grinding the precipitate obtained by suction filtration to obtain a powdery metal-cobalt-oxide (MCo2O4) precursor, adding the powdered MCo2O4 precursor into tube furnace for calcination to obtain metal-cobalt-oxide compound (MCo2O4), and (ii) mixing metal-cobalt-oxide compound (MCo2O4) obtained in the step (i) and carbon source small molecular substance to the certain proportion, transferring into polytetrafluoroethylene reaction kettle, reacting at 150-240℃ for 4-8 hours, performing suction filtration after finishing the reaction, drying and grinding the precipitate obtained by suction filtration to obtain powdery metal-cobalt-oxide/graphene quantum dots composite photocatalyst. metal M = nickel, iron or manganese. An INDEPENDENT CLAIM is also included for cobalt based double metal oxide loaded graphene quantum dots composite photocatalyst prepared by above method.