Novel Nb4C3Tx-Co3O4 nanohybrid as AOP catalyst for potential quaternary treatment of wastewaters containing pharmaceuticals

The increasing occurrence of pharmaceutical residues in treated wastewaters, together with the emergence of MXene-based composites as novel and promising catalysts for advanced oxidation processes (AOP), motivates the development of more efficient and selective treatment technologies. In this study, a novel Nb 4 C 3 T x -Co 3 O 4 nanohybrid AOP catalyst was synthesized for peroxymonosulfate (PMS) activation under dark conditions to degrade four pharmaceutical pollutants including caffeine (CAF), ibuprofen (IBU), paracetamol (PAR), and sulfamethoxazole (SMX). Structural and morphological characterization confirmed successful integration of Co 3 O 4 nanoparticles onto the Nb 4 C 3 T x MXene surface. Under optimized conditions, complete degradation of the pharmaceuticals was obtained within 60 min, except for IBU, which required >100 min due to steric hindrance in its molecular structure, resulting in fewer sites available for attack by reactive species. The contribution of reactive species differs among the pharmaceutical where degradation of IBU and PAR was predominantly governed by sulfate radicals ( SO 4 • − ), contributing over 50% while CAF and SMX followed a degradation mechanism involving singlet oxygen ( 1 O 2 , up to 30%), SO 4 • − (20–40%) and OH • (20–40%). The AOP involved a redox-mediated PMS activation mechanism predominantly on Co and Nb surface sites. The Nb 4 C 3 T x -Co 3 O 4 catalyst exhibited robust performance in cocktail of pollutants and maintained high degradation efficiency, especially for SMX and PAR in tertiary effluents from wastewaters treatment plant (WWTP) collected in Bratislava. In addition, the chemical structure of degradation by-products was characterized by LC-MS analysis and a degradation mechanism was proposed. Colorimetric MTT assays of the treated waters showed no acute cytotoxicity from either the PhACs or their degradation products on short-term exposure. This study provides new insights into pollutant-specific oxidation mechanisms and reactive species profiles in PMS-based AOPs, establishing Nb 4 C 3 T x -Co 3 O 4 as a promising non-conventional catalyst for potential quaternary treatment in WWTP technology. Nb 4 C 3 T x -Co 3 O 4 activates PMS to generate ROS for rapid pharmaceutical degradation in wastewater effluents. • A novel Nb 4 C 3 T x -Co 3 O 4 composite catalyst was prepared via an ultrasonication method • Efficient degradation of 4 selected pharmaceuticals using PMS activation in the dark. • Ex-situ XPS and scavenging experiments confirmed the PMS activation mechanism. • Mechanistic insights revealed the pollutant-specific oxidation mechanism . • The catalyst showed relatively high efficiency and stability in WWTP tertiary effluents.