A novel Ag_3PO_4–CaO composite photocatalyst with enhanced photocatalytic activity was synthesized and utilized for degradation of ammonia from aqueous solution under sunlight. Ag_3PO_4 was prepared by precipitation method, and the composite of Ag_3PO_4–CaO was prepared via impregnation method. Utilization of eggshell for CaO synthesis provided a cost-effective and environmental friendly way for the heterogeneous catalyst production. The as-prepared photocatalysts were characterized by FT-IR, FE-SEM, TEM,EDX, UV–vis and PL. Results show that the Ag_3PO_4–CaO samples have excellent photocatalytic performances in the wide visible-light region. The effect of operating parameters like the content of Ag_3PO_4 in composite, initial ammonia concentration, pH of solution, catalyst dosage and oxygen supply was investigated. The photocatalyst with 60 wt% content of Ag_3PO_4 had a high photocatalytic performance, because a low content of Ag_3PO_4 causes weak light absorption, and the excess amount of it results in serious electron–hole recombination due to the aggregation of Ag_3PO_4 particles. The maximum ammonia degradation(about 70%) was achieved in 340 mg/L of ammonia, pH 11, and 1.25 g/L of catalyst in the presence of pure oxygen. In comparison to Ag_3PO_4, 60 wt% Ag_3PO_4–CaO had a good stability and it could have been easily separated from the solution for recycling.
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