Pickering emulsions based on sustainable MIL-101(Fe)/CNC hybrid nanoparticles for effective photocatalytic degradation of aqueous dyes

The photocatalytic degradation of organic pollutants represents an efficacious, energy-conserving, and eco-friendly methodology. MIL-101 is a porous crystalline material composed of metal ions (or metal clusters) and organic linkers. As a prominent metal-organic framework material, MIL-101 exhibits remarkable thermal and chemical resilience, rendering it ideal for diverse applications encompassing gas storage, separation, and catalytic processes. However, its potency in the degradation of dye molecules is impeded by its innate hydrophobicity and predisposition to precipitate in aqueous solutions. In this study, MIL-101(Fe)/cellulose nanocrystal (CNC) hybrid nanoparticles (MCs) with high photocatalytic activity were prepared by in situ growth. Owing to their unique amphiphilicity and interfacial adsorption, the Pickering emulsions stabilised by MCs showed uniform particle size and stability. The MCs were uniformly adsorbed at the oil–water interface of the emulsion and dispersed in the water phase through a three-dimensional network with clusters. This facilitated complete contact of the MCs with pollutants, thereby significantly increasing the photocatalytic efficiency. The tuneable wettability of MIL-101(Fe) induced by CNCs considerably affected the stabilization and photocatalytic degradation performance. In the presence of 0.5 wt% CNCs, the MCs had a three-phase contact angle of 92°, resulting in the highest photocatalytic degradation rate and emulsion stability of the samples studied herein. An emulsion was produced with a constant emulsification index of 100% by using 0.4 wt% MCs and an oil-phase volume fraction of approximately 0.2. The MC-stabilised emulsion system exhibited high photocatalytic degradation efficiency for Rhodamine B. Moreover, the MCs could be recycled several times while ensuring a degradation efficiency within an acceptable range. Herein we introduce a new approach for improving and fabricating green, sustainable photocatalysts for the degradation of organic pollutants in aqueous systems.