Synthesis, characterization, and mechanism investigation of amphiphilic Fe3O4 magnetic nanocomposites for significant viscosity reduction of heavy oil

Fe 3 O 4 nanoparticles were coated with SiO 2 via the sol-gel method to obtain Fe 3 O 4 @SiO 2 nanoparticles. Optimal preparation conditions were identified as a molar ratio of Fe 3 O 4 : tetraethyl orthosilicate (TEOS): ammonia solution of 1:3:6. The surface of the resulting Fe 3 O 4 @SiO 2 nanoparticles (Fe 3 O 4 @SiO 2 -CN，MCNPs) was then functionalized with 3-aminopropyltriethoxysilane (APTES) and n-octyltriethoxysilane (OTES) to produce amphiphilic magnetic MCNPs. Characteristic peaks observed in the FTIR and XRD spectra, along with the core-shell structure revealed by TEM analysis, confirm the successful synthesis of the MCNPs, which exhibit a maximum magnetization of 33.82 emu·g −1 . MCNPs also exhibit excellent thermal stability (up to 300 ℃), dispersion stability, and amphiphilic properties (with a surface contact angle of 61.3°). Experimental results demonstrate that MCNPs possess an exceptional emulsifying capacity: 0.3 wt% MCNPs can reduce the oil-water interfacial tension from 26.9 mN·m −1 to 3.1 mN·m −1 , effectively enhancing the interfacial film strength and interfacial stability. Furthermore, MCNPs offer outstanding synergistic processing advantages throughout the entire workflow, including reducing viscosity, regulating emulsions and facilitating recovery. MCNPs achieve an efficiency of over 90 % in reducing viscosity for various types of heavy oil. After five consecutive recycling cycles, they achieve a recovery rate of 96.5 % and a viscosity reduction efficiency of 90.04 % (a 3.51 % decrease). Studies of the adsorption microscopic mechanism confirm that MCNPs can disrupt the internal structure of heavy oil, making it more susceptible to deformation and flow. The MCNPs then diffuse and adsorb at the oil-water interface, effectively reducing the oil-water interfacial tension and thereby lowering the viscosity of the heavy oil.