Effective photocatalytic degradation of sulfamethazine by CNTs/LaVO4 in suspension and dip coating modes

In this work, lanthanum vanadate (LaVO4) and carbon nanotubes (CNTs) have been synthesized to develop stable nanocomposites of CNTs/LaVO4 with mass ratios of 0.1% and 0.3%. The nanocomposites were employed to investigate the photocatalytic degradation of a sulphonamide antibiotic namely sulfamethazine (SMZ) in both suspension and dip coating modes. The characterization by high-resolution transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and Raman spectrometry revealed successful synthesis of the composites. Operating parameters (such as solution pH, catalyst dose and light intensity) were optimized by response surface methodology with a central composite design. Radical scavenging experiments indicated that hydroxyl radicals, holes and superoxide radicals contributed to the degradation of SMZ. In order to examine the treatment performance in the dip coating mode, CNTs/LaVO4 was immobilized on aluminum plates by polysiloxane. The reusability of immobilized CNTs/LaVO4 was evaluated in five consecutive runs revealing high stability of the composite after long periods of photocatalytic reaction. Furthermore, a possible degradation pathway was suggested based on a rigorous identification of the transformation products by mass spectrometry.