Integrated adsorptive and photocatalytic degradation of pharmaceutical micropollutant, ciprofloxacin employing biochar-ZnO composite photocatalysts

The expensive carbonaceous substrates including graphene, reduced graphene oxide, carbon nanotubes have been coupled with ZnO to improve the properties and photocatalytic performance of carbon based ZnO photocatalysts. To replace these expensive materials, biochar offers as a low-cost alternative to prepare biochar-based photocatalysts. In this study, Calotropis gigantea leaves derived biochar-ZnO (BC-ZnO) composites were synthesized to overcome the ZnO related problems (charge recombination, wider band gap, and poor visible light absorption). Different BC-ZnO (BCZ-1–3) composites were characterized to evaluate their intrinsic properties and composites were employed to degrade ciprofloxacin (CIP). BCZ-3 composite exhibited slower recombination of electron-hole pairs, lower band gap (2.97 eV), and better light absorption in visible region than ZnO. The enhanced adsorptive-photocatalytic degradation efficiency was attained up to 98.5% using BCZ-3 than BC (46.2%) and ZnO (41.4%). The O₂^∙- and OH^• radicals within BCZ-3 are dominant reactive species indulged in CIP photocatalytic degradation. BCZ-3 photocatalyst exhibits 80% degradation of CIP after four regeneration cycles. The maximum adsorption capacity was achieved 54.18 mg g⁻¹ for BCZ-3 than BC (46.20 mg g⁻¹) and ZnO (15.55 mg g⁻¹). The results show that BCZ-X composites can be used as stable, efficient, economical, and sustainable composite for the recovery of pharmaceutical wastewater.