Optimization of photocatalytic degradation of sulfamethoxazole from wastewater using developed N-doped TiO2/biochar

• High levels of sulfamethoxazole in aquatic environments are causing adverse effects. • N-doped TiO 2 -biochar nanocomposite catalysts were successfully synthesized using the sol-gel method. • The maximum removal efficiency of sulfamethoxazole in synthetic wastewater reached 98.3 %. • The degradation efficiency for real pharmaceutical wastewater decreased to 89.3 %. • N-doped TiO 2 -biochar nanocomposites show promising potential for industrial-scale applications. This study introduces a novel N-doped TiO 2 /biochar nanocomposite aimed at enhancing the photocatalytic degradation of the antibiotic sulfamethoxazole (SMZ) in pharmaceutical effluent. Utilizing Response Surface Methodology (RSM), key operational parameters were optimized, achieving SMZ's impressive removal efficiency of 98.3 % from synthetic, and 86.6 % from actual wastewater samples. Characterization via X-ray diffraction (XRD) showed a predominant anatase phase, Diffuse Reflectance Spectroscopy (DRS) indicated a bandgap of 2.56 eV, and Fourier Transform Infrared Spectroscopy (FTIR) confirmed nitrogen doping. The optimization involved an agitation period of 95 min, a dosage of 1.5 g/L, a pH of approximately 5, and an SMZ concentration of 110 mg/L. RSM employed Central Composite Design (CCD) comprising four variables and 30 experimental runs to model and analyze degradation process. The quadratic model from RSM exhibited strong statistical significance ( p < 0.0001) with an R² value of 0.9998 and a non-significant lack of fit ( p = 0.3014), thereby confirming its validity. A close alignment with the pseudo-first-order reaction model was evidenced by a rate constant (k app ) of 0.0208 and an R² value of 0.991, consistent with the assumptions of the Langmuir-Hinshelwood model. Notably, this study successfully developed a highly durable nanocomposite (sustaining >6 cycles with <5 % efficiency loss), and displayed 1.58 times greater activity under visible light compared to pristine TiO 2 and effectively degraded 95 % of pharmaceutical residues within just 30 min, significantly surpassing the 64.2 % degradation rate of bare BC. This demonstrates the nanocomposite's potential as a scalable and energy-efficient solution for wastewater treatment.