Carbon-doped graphitic carbon nitride (g-C3N4) compositions are synthesized from the chemical precursors melamine, cyanuric acid and barbituric acid. Phosphorus-doped g-C3N4 compositions are synthesized from the chemical precursors melamine, cyanuric acid and etidronic acid. Carbon- and phosphorus-doped g-C3N4 compositions, when in the presence of UV or visible light, can be used in water treatment systems to photocatalytically degrade persistent organic micropollutants such as pharmaceuticals and personal care products (PPCPs), endocrine disrupting compounds (EDCs), pesticides, and herbicides. Carbon- and phosphorus-doped g-C3N4 compositions can also be applied to surfaces of household and public items to kill protozoa, eukaryotic parasites, algal pathogens, bacteria, fungi, prions, viruses, or other microorganisms, preventing the transfer thereof between users.