Silica nanoparticles for real cutting emulsion separation: A morphology-driven perspective

This study addresses the challenge of recovering water from industrial exhausted emulsions (EE) from metal working treatments, designed for high stability and notoriously difficult to treat using conventional materials. Addressing this limitation, this study unravels as the wrinkle morphology of a material can enhance water recovery. A stable nano-emulsion with hydrodynamic diameters around 100 nm and a ζ-potential of −30 mV, was employed as a real system. Wrinkled mesoporous silica nanoparticles (WSNP), characterized by bimodal accessible pore size distribution, were compared with spherical non-porous (SNP), pseudo-spherical mesoporous silica nanoparticles (MSNP), featuring homogeneous pore network, and common sorbent materials, which work with high efficiency in model system reported in literature. Adsorption studies demonstrated the superior performance of WSNP, achieving a remarkable total organic carbon (TOC) removal efficiency (∼95%), higher than SNP, MSNP and commercial materials including hydrotalcite and carbon-based sorbents. Equilibrium adsorption data, modelled by the Freundlich isotherm, may indicate multilayer adsorption facilitated by WSNP's hierarchical pore structure. Mechanistic investigations revealed oil droplets adsorbing efficiently on the external surface and within the folds of WSNP, as evidenced by post-adsorption TEM imaging. Reusability tests confirmed stable performance over eight cycles, efficiency declining only after structural degradation of the wrinkled morphology. This study highlights WSNP as a novel and highly effective material for treating stable industrial emulsions, as a component of a three-dimensional system, providing proof of concept for the design of advanced sorbent materials for challenging wastewater applications.