Utilization of expired sulphadimidine in the fabrication of a metal free graphitic carbon nitride to photodegrade doxycycline in water: an experimental and statistical study

Doxycycline (DC) consumption increased greatly during the COVID-19 period, while sulphadimidine is being prescribed to treat fungal infections in both humans and livestock. When not required, these drugs are often improperly disposed off and dumped into water bodies, resulting in antimicrobial resistance and significant water contamination worldwide. Hence, to nullify two pollutants in a single strategy a nitrogen and sulphur co-incorporated graphitic carbon nitride (NSCN), metal free photocatalyst has been synthesized using expired sulphadimidine drug and melamine, which effectively degraded 98.3% of DC. However, pristine graphitic carbon nitride exhibited a degradation efficiency of only 41.1% towards DC under identical optimal conditions. The catalyst has been analyzed thoroughly using various characterization techniques. The incorporation of nitrogen and sulphur causes a shift in the energy band gap (E_g) from 2.7 eV to 1.8 eV, enhancing its potential as an efficient photocatalyst. Also BET (Brunauer-Emmett-Teller) exhibited an elevation in surface area of catalyst from 28 m²/g in pristine CN to 155.5 m²/g in NSCN after incorporation of N, and S. Batch studies exhibited that NSCN efficiently mitigates DC within 30 min from an aqueous solution at optimum parameters of catalyst dosage 10 mg, DC concentration of 20 mg/L, and obeys pseudo first-order kinetics.