Photodegradation of an ammonium ionic liquid: spiking in urban wastewater and comparison with aromatic ionic liquids

Abstract

Ammonium ionic liquids are being extensively used in several applications, and hence, their effluent treatment is a significant cause of concern. Various Ag-doped SnO₂ nanoparticles (2%, 3% and 5% Ag–SnO₂) were developed and systematically characterized using advanced analytical instruments. Due to Ag doping in SnO₂, the optical bandgap was decreased from the original 3.92 to 3.05 eV. The crystalline NPs showed particle sizes in the range of 40–100 nm. All the synthesized NPs were subjected to degradation of an emerging quaternary ammonium ionic liquid (QAIL) pollutant, Aliquat 336, in the presence of UV-vis light. The sample aliquots were analyzed by a total organic carbon (TOC) analyzer and gas chromatography–mass spectrometry (GC-MS). The 5% Ag–SnO₂ catalyst (0.6 g L⁻¹) was able to degrade all the pollutants within 300 min. The essential parameters of photodegradation such as the catalyst concentration, wastewater pH and catalyst recycling were investigated. In a typical study, urban wastewater, which is also an emerging cause of concern, is spiked with the pollutant to evaluate other constituents' effects. It was observed that the proposed photocatalytic methodology could degrade all the pollutants with extended irradiation time. The detailed reaction kinetics with rate constants are presented. For the first time, based on the GC-MS study, the selected QAIL pollutant's degradation pathway is predicted. The original QAIL pollutant was sequentially degraded into CO₂ and H₂O through the intermediates dioctyl amine, primary amine and pentaldehyde. At the end, the degradation results of QAIL were compared with those of the other reported aromatic ILs.