A method of making Cu—Ag3PO4 nanoparticles is provided. The method includes forming a mixture of at least one silver salt, at least one phosphate salt, and at least one copper (II) salt. The method further includes dissolving the mixture in water. The method further includes sonicating the mixture. The method further includes precipitating the Cu—Ag3PO4 nanoparticles or “nanoparticles”. The copper is present in the nanoparticles in an amount of 2 to 23 weight percent (wt. %) based on the total weight of the Cu—Ag3PO4. The nanoparticles of the present disclosure find application in treating cervical cancer, and colorectal cancer. The nanoparticles may also be used in photodegrading environmental pollutants.