Gallic acid magnetic nanoparticles for photocatalytic degradation of meloxicam: synthesis, characterization and application to pharmaceutical wastewater treatment

Abstract

Environmentally friendly gallic acid coated magnetic nanoparticles (GA-MNP) have been synthesized and evaluated as a novel photocatalyst for degradation of meloxicam; a commonly prescribed nonsteroidal anti-inflammatory drug. The synthesized GA-MNP were characterized using transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and dynamic light scattering. Results showed the formation of core–shell MNP with a mean hydrodynamic diameter of 160.55 ± 5.02 nm and zeta potential of −42.4 ± 1.6 mV. A validated RP-HPLC stability-indicating assay was developed for monitoring of meloxicam concentration in the presence of its degradation products and for determination of the kinetics of degradation. Full factorial design (2⁴) was employed in order to investigate the effects of pH, irradiation time, GA-MNP loading and initial meloxicam concentration on the efficiency of the process. The irradiation time was found to be the most significant parameter followed by initial meloxicam concentration and GA-MNP loading, respectively. At the optimized conditions, increasing GA-MNP loading to 5.00 mg mL⁻¹ demonstrated superior photocatalytic activity when compared to bare MNP and TiO₂NP. Meloxicam degradation was found to follow pseudo first order rate kinetics with K_obs and t_0.5 of −0.0029 min⁻¹ and 239 min, respectively. The protocol was successfully applied for treatment of incurred water samples collected during various cleaning validation cycles. A percentage degradation of 89.10 ± 0.13% was achieved upon irradiation of samples containing 64.57 ± 0.09 µg mL⁻¹ with UV light (1012 µW cm⁻², 8 h) in the presence of 5 mg mL⁻¹ GA-MNP at pH 9.0 ± 0.05. It could be suggested that treatment of wastewaters collected during the cleaning validation of each pharmaceutical product, before pooling into the general waste pool, should improve the efficiency and economics of pharmaceutical wastewater treatment.