Bandgap-engineered nitrogen plasma functionalized biochar-TiO₂ composite for enhanced antibiotic photodegradation

A nitrogen plasma-functionalized biochar-TiO₂ composite was engineered to enhance ciprofloxacin photodegradation by synergistically overcoming the inherent limitations of the wide bandgap and rapid charge recombination of TiO₂. Textile sludge-derived biochar, synthesized via pyrolysis, was integrated with sol-gel-prepared TiO₂ using the wet precipitation method. Subsequent AC plasma treatment achieved controlled nitrogen (N) doping without altering the crystalline structure. UV-vis DRS confirmed progressive bandgap narrowing from 3.10 eV (pristine TiO₂) to 2.90 eV (biochar-TiO₂) and further to 2.73 eV (plasma-doped composite), while EDX quantified effective N-incorporation (6.65 wt%) and XRD verified phase integrity. DLS analysis revealed reduced hydrodynamic diameters (90-106 nm) and suppressed agglomeration, which correlated with the hierarchical porosity observed in SEM, thereby enhancing reactive site accessibility. Photocatalytic evaluation across ciprofloxacin concentrations (10-50 mg L^-1) demonstrated exceptional performance; the plasma-doped composite achieved a 9-fold higher degradation rate (0.0196 min^-1 at 10 mg L^-1) than pristine TiO₂ and a 3-fold enhancement over non-plasma biochar-TiO₂. Remarkably, it maintained >40% superior efficiency at 50 mg L^-1 despite diffusion limitations. This enhancement is attributed to synergistic adsorption from the porous framework of biochar and bandgap-engineered reactive oxygen species (ROS) generation by plasma-induced Ti-O-N configurations. The proposed degradation mechanisms align with literature pathways involving decarboxylation and piperazine ring cleavage. The study establishes plasma-doped biochar-TiO₂ as an efficient photocatalyst for antibiotic remediation.