Synthesis and performance of APTES-silica nanofluid: Improvement of CO2 geological storage efficiency

This study aims to synthesize silica nanofluids (NFs) by modifying the surface of nanoparticles (NPs) with 3-aminopropyltriethoxysilane (APTES) to enhance the efficiency of CO 2 geological storage (CGS) and to prevent NPs aggregation under high-temperature (373.15 K) and high-salinity (200,000 ppm) conditions of deep saline aquifers. The dispersion stability of the NFs was assessed through visual observation, dynamic light scattering (DLS), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), and high salinity test (HST). Interfacial properties were measured to evaluate the CO 2 storage efficiency of the NFs. Visual observations confirmed the absence of precipitation across all tested concentrations at both room temperature (298.15 K) and high temperature. DLS measurements revealed that the average particle size ranged from 32.00 to 89.85 nm within the 0.01–5.0 wt% NP concentration range, consistent with the visual observation. TEM analysis showed that NFs with 0.05 wt% or more silica NPs maintained particle sizes below 100 nm at both 298.15 K and 373.15 K. Furthermore, HST demonstrated that the 0.05 wt% NFs remained stable when mixed with 200,000 ppm brine, exhibiting an average particle size of 53.47 nm under high-salinity conditions. Compared with seawater, the interfacial tension (IFT) and contact angle (CA) of the 0.05 wt% nanofluid were reduced by 27.01% and 41.43%, respectively. These findings indicate that silica NFs modified with APTES exhibit stable dispersion under harsh conditions, supporting their potential applicability as injection fluids for CO 2 storage in deep saline aquifers.