Development of a novel photocatalyst for the degradation of antibiotics in aqueous medium

Abstract

Promising active pharmaceuticals like sulfamethoxazole (SFX), ciprofloxacin (CIP), and metronidazole (MNZ) are bio-persistent and toxic to nature. TiO2 based photocatalysis has been widely utilized in the last few decades to degrade persistent pollutants. Coupling TiO2 with transition metals/metal oxides (Ni, α-Fe2O3) may enhance the efficiency of TiO2. Therefore, this study aims to synthesize single (TiO2, NiO, α-Fe2O3), and composite (α-Fe2O3-TiO2, Ni-TiO2, Ni-α-Fe2O3, Ni-TiO2-α-Fe2O3) photocatalyst to evaluate performance in SFX, MNZ, and CIP degradation with optimization, and kinetics study of superior catalyst. The single and composites catalysts were synthesized by sol-gel, and impregnation method respectively. Characterization was done employing FTIR, SEM, EDS, and XRD. FTIR, validates the presence of respective M-O, and M-O-M bonds α-Fe2O3 (550 cm-1), NiO (435 cm-1), TiO2 (400−800 cm-1). SEM, and EDX show significant modification of the surface morphology, and elemental composition in the composite materials. XRD analysis depicted characteristics peak, and distinct crystallite size of the catalysts. pHpzc analysis shows the synthesized catalysts surface charge between 6.55-7.71. Photodegradation efficiencies were evaluated by degrading MNZ, SFX, and CIP under 21 mW/cm2 UV-254 nm irradiation in a batch reactor. NiO, α-Fe2O3, TiO2, Ni-TiO2, α-Fe2O3-TiO2, α-Fe2O3-Ni, and Ni-TiO2-α-Fe2O3 degrade about 51%, 56%, 59%, 61%, 63%, 64%, and 71% SFX respectively. Accordingly, Ni-TiO2-α-Fe2O3 shows superior photodegradation over CIP (64%), and MNZ (63%). From XRD analysis slightly deviated diffraction peak of both α-Fe2O3 (33.31°), and TiO2 (25.32°) with decreased peak intensity was observed in Ni-TiO2-α-Fe2O3. The average crystallite size decreases from 15.03 nm (TiO2), 45.74 nm (α-Fe2O3), 10.54 nm (NiO), to 9.16 nm in Ni-TiO2-α-Fe2O3. This may lead to the formation of heterojunction and defects in crystal lattice causing decrease of band gap (1.78 eV) and improves of photocatalytic property. Optimization of the reactor performance revealed that Ni-TiO2-α-Fe2O3 performs better at pH 3 for MNZ, and SFX and at pH 9 for CIP. The optimum antibiotic concentration, catalyst dosage, and H2O2 concentration were found to be 10 ppm, 0.25 g/L, and 50 ppm respectively. The kinetic study shows that pseudo-1st order reaction kinetics fits with experimental data. The competitive degradation of SFX, MNZ, and CIP mixture has shown comparatively lower degradation efficiency than single antibiotic. This research establishes Ni-TiO2-α-Fe2O3 composite as a promising photocatalyst for the degradation of persistent pollutant.