Boron carbon oxynitride (BCNO) nanoparticles as an efficient water purifier for dyes and antibiotics

The band structure of BCNO nanomaterials (with 20 at.% oxygen and 3.8–12.7 at.% carbon) was tuned during synthesis via a high-temperature solid-state reaction in ammonia by varying the molar ratio of boric acid to melamine in the precursors (1:0.1 (BCNO0.1), 1:0.5 (BCNO0.5), and 1:1 (BCNO1)). Carbon clusters were integrated into the h-BN matrix, forming embedded graphene-like domains. The increasing carbon content induced a transition from an indirect to a direct bandgap semiconductor, with band gaps of 3.95 eV (BCNO0.1) and 2.81 eV (BCNO1), respectively. BCNO0.1 produced reactive oxygen species (ROS) twice as intensely as BCNO1, and the addition of Methylene blue (MB) to the BCNO suspension further increased the ROS yield. BCNO0.1 exhibited high catalytic stability and effective photocatalytic activities of approximately 218 μmol·g −1 ·h −1 and 73 μmol·g −1 ·h −1 for MB and Congo red (CR) photodegradation, respectively. Superoxide radical anions ( − O 2 ) were the main reactive species generated through (i) direct BCNO0.1 photoexcitation, (ii) photolysis of MB in solution, and (iii) photoexcitation of MB adsorbed on the material surface. BCNO1 had almost five times lower photocatalytic activity but adsorbed almost twice as much MB as BCNO0.1 and BCNO0.5. The overall BCNO1 activity in removing tetracycline from aqueous solution was high (~800 μmol·g −1 ·h −1 ), sufficient to remove 1 mg of tetracycline from 50 mL of water within 1 h. DFT calculations showed that while oxygen doping has little effect on the electronic properties of h-BN, increasing the carbon content introduces additional bands and downshifts the conduction band minimum, resulting in band gap narrowing.