Magnetically responsive Janus nanoparticles synthesized using cellulosic materials for enhanced phase separation in oily wastewaters and water-in-crude oil emulsions

A new class of magnetically responsive and interfacially active Janus (M−Janus) nanoparticles was designed and synthesized by sequential adsorption of cellulosic materials: hydrophobic ethyl cellulose (EC) and hydrophilic carboxymethyl cellulose (CMC) on the opposite sides of magnetite (Fe3O4) nanoparticles. The adsorption study using quartz crystal microbalance with dissipation (QCM-D) proved the concept of proposed synthesis of M−Janus nanoparticles. The adsorption of EC and CMC on magnetite nanoparticles was confirmed by zeta-potential measurements, thermogravimetric analysis (TGA), characterization using Fourier transform infrared spectroscopy (FTIR) and TEM. The surface wettabilities of the opposite sides on the M−Janus nanoparticles were investigated by measuring contact angles of nanoparticle surfaces deposited from the oil-water interfaces using the Langmuir-Blodgett method. SEM images revealed an excellent dispersion of M−Janus nanoparticles in both aqueous and organic phases. The results from the coalescence time and crumpling ratio measurement of particles-stabilized oil droplets along with the interfacial pressure-area isotherms demonstrated stronger interfacial activities of M−Janus nanoparticles and a stiffer interface with adsorbed M−Janus nanoparticles as compared with the interfaces stabilized by conventional interfacially-active nanoparticles. The microscopy images confirmed the deposition of M−Janus nanoparticles at the emulsion droplet surface during the phase separation process. The M−Janus nanoparticles not only exhibited excellent capability and high efficiency in separating emulsified water from water-in-crude oil emulsions and the oil from oily wastewaters under an external magnetic field, but also retained high interfacial activity and hence desirable separation efficiency after five-cycle applications. Because of the environmentally friendly and biodegradable cellulosic materials used in the synthesis, the M−Janus nanoparticle can achieve effective oil/water phase separation without causing further pollution to the continuous phase.