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

Abstract

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.