Heterocyclic polymerization modified g-C3N4 nanotube with advanced charge separation for solar light driven degradation of ciprofloxacin

A novel heterocyclic polymerized g-C3N4 nanotube was prepared by thermal polycondensation using urea and 2,4,6-triaminopyrimidine (TAP). The TAP-polymerized g-C3N4 composite with 0.5 wt% TAP content showed the highest photocatalytic activity for ciprofloxacin (CIP) degradation under solar irradiation. The optimal composite derived from urea achieved ∼ 10.8 and ∼ 7.5 time of CIP degradation activity when compared with TAP-polymerized g-C3N4 derived from melamine and thiourea. The copolymerization of TAP molecules reduces the π electron defects in the g-C3N4 conjugated system thus accelerates the migration of photogenerated carriers. The doping of TAP in g-C3N4 reduces its band gap, which enhances the light absorption capacity and improves the utilization efficiency of visible light. The fluffy porous nanotube structure of the material endows it with unique surface morphology and excellent photoelectric characteristic. Electron spin resonance (ESR) and probe technology were used for qualitative or quantitative detection of free radicals in this work. Superoxide radicals (O2·-) played the major roles in the photodegradation of CIP. Recycling experiments displayed the high stability and activity of the modified materials, which is potentially applicable in practical engineering. Moreover, the photodegradation pathways and mechanisms of CIP were proposed and its toxicity evolution was assessed in this study. This work revealed the specific application of heterocyclic polymerization in modifying g-C3N4 material and provided unique insights for its application in photocatalytic degradation of antibiotic.