Facile and controllable synthesis of amino-modified carbon dots for efficient oil displacement

Zero-dimensional (OD) carbon dots exhibit excellent potential as a new oil-displacing agent for unconventional reservoir development. However, the difficulty in size/surface properties control and unclear mechanism hinder their further applications. In this study, amino-modified carbon dots (am-CDs) for oil displacement were facilely synthesized through the rapid polymerization of D-glucose (D-Glc) and 3-aminopropyltriethoxysilane (APTES). The size of am-CDs could be precisely controlled by the reaction condition and quenching achieved by adjusting the pH value to neutral. The surface amine groups endow am-CDs with excellent hydrophilicity and dispersion stability. The 0.30 wt.% nanofluid based on am-CDs with an average size of 2.6 ± 0.040 nm showed remarkable oil recovery efficiency (54.09%) without the addition of surfactant. The oil recovery efficiency of am-CDs is much higher than those of water flooding (30.25%), nano-SiO2 flooding (36.45%), and amino-free carbon dots (af-CDs) flooding (37.80%). Experimental and theoretical results reveal that am-CDs can be favorably adsorbed on the core surface to modulate the micro-scale wettability, changing the surface from oil-wet to relatively uniform water-wet. Meanwhile, am-CDs can effectively reduce the adhesion force between alkanes and sandstone surfaces, contributing to oil droplets peeling off and oil displacement. This study provides a new strategy for developing efficient carbon dots-based nanofluids for enhanced oil recovery.