Tailored MXene-derived nano-heterostructure oxides for peroxymonosulfate activation in the treatment of municipal wastewaters

Abstract

Nowadays, in the field of environmental protection, a huge effort is focused on efficient and sustainable processes to treat wastewaters. The current study emphasizes the photocatalytic performance of TiNbO_x, a nano-heterostructure material derived from the oxidation of (Ti_0.75Nb_0.25)₂CT_x MXene. The TiNbO_x nano-heterostructure exhibited remarkable performance in the degradation of caffeine (CAF) and sulfamethoxazole (SMX) under UVA irradiation in the presence of peroxymonosulfate (PMS). Under optimal conditions, 0.2 g L⁻¹ of TiNbO_x, 0.5 mM PMS and 50 μM concentration of pollutants and natural pH of deionized water, we observed a complete degradation of SMX and 91% degradation of CAF. Scavenging studies provided evidence for the involvement of ˙OH and SO₄˙⁻ in the degradation of the pollutants, which was also supported by indirect techniques of electron paramagnetic resonance (EPR) spectroscopy. The degradation pathway of the pollutants was analyzed by liquid chromatography-mass spectrometry (LC-MS) and several mechanisms were suggested including hydroxylation and isoxazole ring-opening reactions. In addition, X-ray photoelectron spectroscopy (XPS) supported the proposed degradation mechanism. The reusability test underscored the high stability and efficiency of TiNbO_x. Moreover, the significance of this research was emphasized by conducting degradation studies in tap water (TW) and tertiary effluents of the wastewater (WW) treatment plant in Bratislava. Under optimal conditions, 49% and 30% CAF were degraded in TW and WW, respectively, after 12 hours of reaction. For SMX, 68% and 67% degradations were obtained in TW and WW, respectively.