Photocatalytic degradation of pharmaceutical compounds using ZnO and N-ZnO. • In the comparative analysis of Solar/ZnO and Solar/N-ZnO, N-doped catalyst exhibited a high degradation rate constant of ATM (0.0083 min −1 ), CXN (0.0136 min −1 ), and AMX (0.0073 min −1 ), which verified its superior photocatalytic performance under the sun light. • Solar/N-ZnO photocatalytic system enhances degradation efficiency (85–100%) over Solar/ZnO, attributed to N-doping, which improves visible light absorption and reduces charge carrier recombination. • Solar-driven systems achieved ∼85% lower capital cost and ∼28% lower treatment cost than UV/ZnO. Photocatalytic degradation of model pharmaceuticals compounds viz Acetaminophen (ATM), Ciprofloxacin (CXN), and Amoxicillin (AMX) were investigated using commercial ZnO and synthesised nitrogen-doped ZnO (N-ZnO) under UV and solar irradiation. The effect of major operating parameters such as pH (5–10), catalyst dosage (0.25–1 g/L), contact time (30–300 mins), and initial pollutant concentration (10–50 mg/L) was systematically investigated in batch mode. Under optimized conditions, pollutant degradation efficiencies reached 95% (ATM), 100% (CXN), and 100% (AMX) with UV/ZnO, while Solar/ZnO showed lower degradation (84%, 90%, and 78%, respectively). Solar/N-ZnO showed improved performance over Solar/ZnO with degradation efficiencies of 95% (ATM), 100% (CXN), and 85% (AMX). These performances were attained under distinct optimum operational conditions for each pollutant and system. For UV/ZnO, the optimum pH values were 6 (ATM), 6.3 (CXN), and 10 (AMX), with catalyst dosages of 0.5, 0.25, and 0.5 g/L, and contact times of 300, 240, and 180 min, respectively, at a constant pollutant concentration of 10 mg/L. Under Solar/ZnO, the optimum pH values were 7.3 (ATM), 8 (CXN), and 6.8 (AMX), with catalyst dosages of 1.0, 0.75, and 0.75 g/L, and contact times of 240, 300, and 300 min, respectively, for the same pollutant concentration (10 mg/L). Solar/N-ZnO showed optimum photocatalytic activity at pH 7.3 (ATM), 6.3 (CXN), and 6.8 (AMX), with catalyst dosages of 1.0, 0.5, and 0.5 g/L, and contact times of 300, 240, and 300 min, respectively, again maintaining a constant pollutant concentration of 10 mg/L. These optimized parameter combinations reflect the influence of catalyst modification and light source on photocatalytic efficiency across different pharmaceutical compounds. The results from the kinetic studies showed that the photocatalytic degradation of model pharmaceutical compounds followed pseudo first order reaction kinetics under all conditions. The higher rate constants was observed under UV/ZnO for CXN (k = 0.0232 min −1 ) and AMX (k = 0.0321 min −1 ). TOC studies demonstrated maximum mineralization under UV/ZnO with removal up to 78% for AMX, followed by Solar/N-ZnO 68% for CXN and 57% for AMX whereas Solar/ZnO showing the lowest mineralization of 55% for ATM, 60% for CXN and 45% for AMX. Economic analysis, based on defined scale assumptions and capital recovery methodology, indicated that solar-driven systems reduced capital costs by approximately 85% and treatment cost by about 28% compared to the UV/ZnO process.
Karthika et al. (Sun,) studied this question.