▎ 摘　　要

NOVELTY - Carbon nitride composite photocatalyst comprises a graphene carbon nitride nanosheet catalyst containing cyano groups and nitrogen vacancies, and phosphorus atoms and potassium atoms doped in the catalyst. USE - The carbon nitride composite photocatalyst is useful in the treatment of herbicide wastewater (claimed). ADVANTAGE - The carbon nitride composite photocatalyst has high photo-catalytic activity, good photo-catalytic stability, wide light response range, high herbicide removing rate, and good repeatability. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: preparation method a carbon nitride composite photocatalyst, comprising (1) mixing and grinding urea and potassium dihydrogen phosphate to obtain a precursor mixture, (2) carrying out thermal polycondensation reaction with precursor mixture, and obtaining carbon nitride composite photocatalyst precursor, and (3) calcining the carbon nitride composite photocatalyst precursor to obtain the carbon nitride composite photocatalyst; and treatment method for herbicide wastewater, comprising (a) mixing the carbon nitride composite photocatalyst with the herbicide wastewater under light-shielding conditions, and absorbing to obtain mixed solution II, and (b) subjecting the mixed solution II to photocatalytic reaction under the condition of visible light to obtain product.