Synthesis and characterization of polycitric acid-functionalized MXene nanofluid for enhanced oil recovery

In this study, a polycitric acid-functionalized MXene (Ti 3 C 2 T x ) (F-MX) nanofluid was synthesized, characterized, and evaluated for enhanced oil recovery (EOR). MXene nanosheets were prepared via selective HF etching of the Ti 3 AlC 2 MAX phase and subsequently functionalized through in situ polymerization of citric acid, an environmentally friendly and naturally derived polymer. Characterization by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) confirmed successful exfoliation, interlayer expansion and surface functionalization of MXene nanosheets. The F-MX nanofluid exhibited excellent colloidal stability in both deionized water and brines containing up to 5–20 wt% NaCl for 3 months. Interfacial tension (IFT) measurements demonstrated reductions from 45.7 ± 0.27 mN/m in deionized (DI) water and 48.3 ± 0.25 mN/m in brine to 34.99 ± 0.28 mN/m and 38.96 ± 0.32 mN/m, respectively, at a concentration of 0.1 wt%. Wettability tests revealed a reduction in contact angle from 155.06° ± 0.42 to 129.06° ± 0.29 at concentration of 0.1 wt%, indicating wettability modification. Adsorption experiments revealed that the adsorption capacity was higher in DI water than in saline conditions as increasing ionic strength reduces adsorption through electrostatic screening effects. Micromodel flooding experiments showed a substantial improvement in oil recovery, from 21% with conventional brine injection to 59% with F-MX nanofluid injection. The results demonstrate that F-MX nanofluids significantly enhance oil recovery through combine effects of enhance colloidal stability, effective transport through porous media, interfacial tension reduction, wettability alteration and progressive mobilization of residual oil at the pore scale under saline conditions.