Efficient removal of oxytetracycline antibiotic from aqueous media using UV/g-C3N4/Fe3O4 photocatalytic process

Abstract

Residual pharmaceuticals in the environment are a class of emerging pollutants that endanger human health. Tetracycline's family, including oxytetracycline (OTC), are known as one of the most produced and consumed antibiotics worldwide. The g-C₃N₄/Fe₃O₄ nanocomposite with high level of catalytic efficiency features suitable performance in water/wastewater treatment. Therefore, in the present study, this nanocomposite was applied to remove the oxytetracycline from the aqueous environment. In this research study, g-C₃N₄/Fe₃O₄ nanocomposite (serving as catalyst) was initially synthesized by a simple hydrothermal method. The effect of key operating parameters such as initial solution pH, dose of catalyst, contact time and initial concentration of OTC in aqueous solutions was investigated under UV irradiation. In addition, COD and TOC tests, the kinetics and the effect of radical scavengers on the applied photocatalytic process were all evaluated. The maximum removal efficiency of OTC (99.8 %) was achieved under the following conditions: neutral solution pH 7; catalyst dose, 0.7 g/L; and an initial OTC concentration of 5 mg/L. The data showed that the kinetics of the reaction followed the first-order model with R² of 0.9755. The respective COD and TOC efficiency values for the applied photocatalytic process were determined to be 87 and 59 %, respectively. In addition, the lowest removal efficiency of OTC was observed in the presence of tert-butanol radical scavengers, and OH radicals played a main role. The UV/g-C₃N₄/Fe₃O₄ photocatalytic process proved to be highly efficient for the removal of OTC antibiotic and could be potentially applied for the removal of other pollutants from aqueous solutions.

Keywords: Antibiotic; Oxytetracycline; Photocatalyst; UV/g-C3N4/Fe3O4.

Fig. 1

Chemical structure of OTC.

Fig. 2

XRD patterns of Fe₃O₄, g-C₃N₄ and g-C₃N₄/Fe₃O₄ (a), FT-IR images of Fe₃O₄, g-C₃N₄ and g-C₃N₄/Fe₃O₄ (b).

Fig. 3

FE-SEM images of g-C₃N₄ (a and b) and g-C₃N₄/Fe₃O₄ (c and d).

Fig. 4

VSM analysis of g-C₃N₄/Fe₃O₄ nanocomposite.

Fig. 5

Effect of variation of pH of solution on the efficiency of the photocatalytic process (catalyst dose = 0.5 g/L, initial OTC concentration = 30 mg/L).

Fig. 6

Effect of catalyst dose on the efficiency of the photocatalytic process (pH = 7, and initial antibiotic concentration = 30 mg/L).

Fig. 7

Effect of initial concentration of OTC on the efficiency of the photocatalytic process (pH = 7, catalyst dose = 0.7 g/L).

Fig. 8

Effect of radical scavengers on the efficiency of the photocatalytic process (pH = 7, catalyst dose = 0.7 g/L, OTC concentration = 5 mg/L, scavenger concentration = 0.5 mmol/L and time = 60 min).

Fig. 9

Contribution of each component engaged in the degradation of efficiency of OTC under the optimum conditions (pH = 7, catalyst dose = 0.7 g/L, OTC concentration = 5 mg/L and time = 60 min).

Fig. 10

Efficiency of the photocatalytic process in OTC removal in real environmental samples (pH = 7, catalyst dose = 0.7 g/L, OTC concentration = 5 mg/L and time = 60 min).

Scheme 1

Illustration of the photocatalytic mechanism using Fe₃O₄/g-C₃N₄ catalyst for simultaneous OTC degradation: S-scheme heterojunction (a) and type-II heterojunction (b).