4.2 Article

Destructing surfactant network in nanoemulsions by positively charged magnetic nanorods to enhance oil-water separation

Journal

JOURNAL OF ENVIRONMENTAL SCIENCES
Volume 118, Issue -, Pages 112-121

Publisher

SCIENCE PRESS
DOI: 10.1016/j.jes.2021.08.039

Keywords

Nanoemulsions; Surface charge; Magnetic nanorods; Surfactant; Interfacial film; Oil-water separation

Funding

  1. National Natural Science Foundation of China [51978490]
  2. Natural Science Foundation of Shanghai [20ZDR1461200]
  3. Major Science and Technology Program for Water Pollution Control and Treatment, China [2017ZX07202003-02]

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A new approach is proposed to deal with high concentration surfactant stabilized waste nanoemulsions, achieving efficient oil-water separation and wastewater treatment by manipulating the surface charge and morphology of magnetic nanoparticles.
The separation of ultrafine oil droplets from wasted nanoemulsions stabilized with high concentration of surfactants is precondition for oil reuse and the safe discharge of effluent. However, the double barriers of the interfacial film and network structures formed by surfactants in nanoemulsions significantly impede the oil-water separation. To destroy these surfactant protective layers, we proposed a newly-developed polyethyleneimine micelle template approach to achieve simultaneous surface charge manipulation and morphology transformation of magnetic nanospheres to magnetic nanorods. The results revealed that positively charged magnetic nanospheres exhibited limited separation performance of nanoemulsions, with a maximum chemical oxygen demand (COD) removal of 50%, whereas magnetic nanorods achieved more than 95% COD removal in less than 30 s. The magnetic nanorods were also applicable to wasted nanoemulsions from different sources and exhibited excellent resistance to wide pH changes. Owing to their unique one-dimensional structure, the interfacial dispersion of magnetic nanorods was significantly promoted, leading to the efficient capture of surfactants and widespread destruction of both the interfacial film and network structure, which facilitated droplet merging into the oil phase. The easy-to prepare and easy-to-tune strategy in this study paves a feasible avenue to simultaneously tailor surface charge and morphology of magnetic nanoparticles, and reveals the huge potential of morphology manipulation for producing high-performance nanomaterials to be applied in complex interfacial interaction process. We believe that the newly-developed magnetic-nanorods significantly contribute to hazardous oily waste remediation and advances technology evolution toward problematic oil-pollution control. (c) 2022 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

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