Mn-Sb Co-doped SnO₂ nanoparticles as efficient photocatalysts for tetracycline degradation

The increasing presence of antibiotic contaminants such as tetracycline in aquatic environments poses a serious ecological and public health challenge, demanding efficient remediation strategies. In this work, Mn-Sb co-doped SnO₂ nanoparticles were synthesized using a cost-effective sol-gel method to enhance the photocatalytic performance of SnO₂. The Sb concentration was fixed at 4%, while Mn doping was varied from 0-8% to investigate its influence on structural, optical, and catalytic properties. Comprehensive characterization techniques including X-ray diffraction (XRD), Raman spectroscopy, FTIR, FESEM-EDS, UV-visible spectroscopy, X-ray photoelectron spectroscopy (XPS), and BET surface area analysis confirmed the successful incorporation of dopants into the SnO₂ lattice. Structural analysis revealed the formation of a tetragonal rutile phase with a reduction in crystallite size from 36.55 to 24.54 nm upon Mn doping. Optical studies showed band-gap modulation from 3.37 to 3.24 eV at moderate Mn concentrations, while higher doping levels caused band-gap widening due to the Burstein-Moss effect. BET analysis demonstrated an increase in surface area from 70.84 to 82.49 m² g^-1, while XPS results indicated an increased concentration of oxygen-vacancy defects that facilitate charge separation. Photocatalytic experiments for tetracycline degradation under Xe-lamp irradiation revealed that the optimally doped MATO4% catalyst achieved the highest degradation efficiency of 79.5% with a rate constant of 0.0125 min^-1. The enhanced photocatalytic performance is attributed to defect-induced charge separation, improved surface area, and optimized Mn doping. These findings highlight Mn-Sb co-doped SnO₂ as a promising photocatalyst for antibiotic pollutant remediation and provide insights into defect engineering strategies for improving photocatalytic materials.