Seamless carbon nitride growth on bimetallic oxide for antibiotic residue degradation

Abstract

Emergence of antibiotic-resistant bacteria from overuse of antibiotics is a significant threat to human health. Photocatalysis utilizing semiconductors like graphitic carbon nitride (g-C₃N₄) is cost-effective for antibiotic degradation, however its efficiency is limited by rapid charge carrier recombination. This can be mitigated by forming heterojunctions with compatible semiconductors. Metal oxides, commonly employed for this purpose, are typically deposited on g-C₃N₄ surfaces, and often agglomerate, resulting in uneven distribution and reduced number of active-sites. Here we present a facile approach for in situ polymerization of g-C₃N₄ sheets onto bimetallic oxide surfaces, facilitating their seamless integration. CoNiO₂ was utilized as substrate for growth of g-C₃N₄, which improved crystallinity and surface area of g-C₃N₄-CoNiO₂ composite. Optimized g-C₃N₄-CoNiO₂-3% achieved a tetracycline degradation efficiency of 95.6%, markedly exceeding 61.3% degradation observed with pristine g-C₃N₄. Extended X-ray absorption fine structure spectroscopy confirmed synergistic interaction between CoNiO₂ and N-coordinating sites of g-C₃N₄ by interfacial Ni–N₂ bond, enhancing electron transport. This interaction is further evidenced by energy-resolved distribution of electron trap patterns from reversed double-beam photoacoustic spectroscopy, which reveal that while g-C₃N₄ displays significant electron trap density peaks around 2.7–2.9 eV. The g-C₃N₄-CoNiO₂ enhances this density, indicating formation of an electrical interface heterojunction that improves electron and hole migration across interfacial boundary. Electron spin resonance measurements confirmed that superoxide anion radicals and holes were main active species in promoting tetracycline degradation. Integration of g-C₃N₄ with bimetallic oxides enhances antibiotic degradation efficiency, presenting a promising and impactful strategy for environmental remediation.