Functionalized SnO2 nanoparticles with gallic acid via green chemical approach for enhanced photocatalytic degradation of citalopram: synthesis, characterization and application to pharmaceutical wastewater treatment

Eco-friendly stannic oxide nanoparticles functionalized with gallic acid (SnO2/GA NP) were synthesized and employed as a novel photocatalyst for the degradation of citalopram, a commonly prescribed antidepressant drug. SnO2/GA NP were characterized using high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller measurements and X-ray diffraction. A validated RP-HPLC assay was developed to monitor citalopram concentration in the presence of its degradation products. Full factorial design (24) was conducted to investigate the effect of irradiation time, pH, SnO2/GA NP loading and initial citalopram concentration on the efficiency of the photodegradation process. Citalopram initial concentration was found to be the most significant parameter followed by irradiation time and pH, respectively. At optimum conditions, 88.43 ± 0.7% degradation of citalopram (25.00 µg/mL) was obtained in 1 h using UV light (1.01 mW/cm2). Citalopram kinetics of degradation followed pseudo-first order rate with Kobs and t0.5 of - 0.037 min-1 and 18.73 min, respectively. The optimized protocol was successfully applied for treatment of water samples collected during different cleaning validation cycles of citalopram production lines. The reusability of SnO2/GA NP was studied for 3 cycles without significant loss in activity. This approach would provide a green and economic alternative for pharmaceutical wastewater treatment of organic pollutants.

Conversion of "Waste Plastic" into Photocatalytic Nanofoams for Environmental Remediation

Plastic debris is a major environmental concern, and to find effective ways to reuse polystyrene (PS) presents major challenges. Here, it is demonstrated that polystyrene foams impregnated with SnO₂ are easily generated from plastic debris and can be applied to photocatalytic degradation of dyes. SnO₂ nanoparticles were synthesized by a polymeric precursor method, yielding specific surface areas of 15 m²/g after heat treatment to 700 °C. Crystallinity, size, and shape of the SnO₂ particles were assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), demonstrating the preparation of crystalline spherical nanoparticles with sizes around 20 nm. When incorporated into PS foams, which were generated using a thermally induced phase separation (TIPS) process, the specific surface area increased to 48 m²/g. These PS/SnO₂ nanofoams showed very good efficiency for photodegradation of rhodamine B, under UV irradiation, achieving up to 98.2% removal. In addition the PS/SnO₂ nanofoams are shown to retain photocatalytic activity for up to five reuse cycles.