Enhanced catalytic degradation performance of azo dyes based on Janus emulsification

Abstract

• Amphiphilic Janus nanosheets were used as carriers to achieve the integration of catalysts and solid emulsifiers for the degradation of azo dyes . • Bifunctional Janus-[BMIM][heteropolyanions] with phenyl side and ionic liquids side were fabricated via an anion-exchange reaction. • Compared with the traditional two-phase catalytic system, the emulsified catalytic degradation exhibited better performance on pollutant removal. • The mechanism of catalytic degradation for methyl orange based on Janus emulsification was investigated. • The Janus emulsion could be easily demulsified and exhibited excellent reusability. Amphiphilic Janus nanosheets with an asymmetric structure of non-polar phenyl side and polar ionic liquid side (1-Butyl-3-methylimidazolium chloride, [BMIM]Cl), denoted as Janus-[BMIM]Cl, were prepared and used as a carrier to achieve the integration of catalyst and emulsifier. Catalytic heteropolyanions (e.g., [PW 12 O 40 ] 3- , [PMo 12 O 40 ] 3- or [SiW 12 O 40 ] 4- ) were selectively decorated on the polar side induced by anion-exchange of [BMIM]Cl moieties, Janus catalysts (Janus-[BMIM][heteropolyanions]) were assembled and utilized as an open degradation platform for azo dyes such as methyl orange (MO). Morphology, structure, and properties were characterized by SEM, FT-IR, XPS, UV–Vis, Zeta potential, etc. The inbuilt amphipathy of Janus nanosheets endowed the decolorization process of dyes to perform in the emulsified system. The extremely increased interface coupled with the effective dispersion of catalysts at the interface synergistically improved the catalytic degradation performance. Compared with the decolorization catalyzed in a conventional immiscible system, the removal efficiency of MO achieved in the Janus emulsion greatly improved from 78.6 to 98.2% within 3 h. Besides, the Janus emulsion could be demulsified easily by centrifugation, and the degradation efficiency was still maintained at 93.7% after five cycles. These results provide valuable information for exploring and enriching the applications of Janus functional materials.