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

Zero-dimensional(0D)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-SiO_(2) 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.