Characterization of the sulfur/oxygen-displacement synthesized Bi2S3/Bi2O3 nano catalyst and response surface methodology optimization of its photocatalytic performance toward ciprofloxacin

The coupled Bi₂S₃/Bi₂O₃ nano-scale catalyst was fabricated via a sulfur/oxygen-displacement procedure. The as-synthesized Bi₂O₃ and Bi₂S₃ NPs and the coupled catalyst were identified by SEM, XRD, UV–Vis diffuse reflectance spectroscopy (DRS), and FT-IR. Crystallite size determination with Williamson-Hall (WH) and Scherrer models gave values of 60, 51, and 63 nm (by WH model), and 50, 42, and 37 nm (by Scherrer model) for Bi₂S₃, Bi₂O_3, and Bi₂S₃/Bi₂O₃, respectively. Band gap energy of Bi₂S₃ and Bi₂O₃ calculated with DRS analysis is 2.46 and 3.1 eV. X-ray maps confirmed a relatively homogenous constituent elemental distribution throughout the catalyst. The pHpzc estimation for Bi₂S₃, Bi₂O_3, and Bi₂S₃/Bi₂O₃ gave values of 6.1, 6.9, and 6.4, respectively. In the initial photodegradation experiments, the boosted photocatalytic activity of Bi₂S₃/Bi₂O₃ was obtained toward ciprofloxacin (CIP). Thus, the simultaneous effects of the vital operating variables were investigated and optimized via a response surface methodology (RSM) approach. The RSM optimal run was defined at the experimental conditions of 12 mg/L CIP solution at pH 10, catalyst dose of 1 g/L, and illumination time of 110 min. The satisfactory correlation coefficient for the applicability of the second-order polynomial model to process the data was confirmed by a high R² value of 0.9994, which proves the agreement between the RSM predicted data and the experimental results. The process kinetics was well fitted to the pseudo-first-order Hinshelwood model. Catalyst stability was confirmed because no significant difference was observed in the photo degradation activity over four consecutive reusing cycles. After all, no significant difference was observed in the photodegradation activity over four reusing runs. In the scavenging agents study, the critical decreased activity by Na₂SO₄, as an electron scavenging agent, confirmed the highest relative role of the photoinduced electrons in CIP photodegradation by the binary catalyst used.