A Novel Carbon-Dot Surfactant to Fabricate Jammed Lamellae in Flue Gas Foams for Enhanced Oil Recovery with Concurrent CO2 Sequestration

Abstract Integrating flue gas reinjection for enhanced oil recovery with CO2 sequestration presents a dual-benefit strategy for fossil fuel emissions; however, severe gas fingering and poor foam stability under acidic, high-temperature, and saline conditions hinder its practical application. In this study, we pioneer the use of N,S-co-doped carbon dots (N,S-CDs), synthesized via a rapid one-step microwave route, as robust foam stabilizers for flue gas-based flooding and sequestration. The amphiphilic N,S-CDs, functionalized with amine and sulfonic acid groups, exhibit rapid interfacial adsorption, reducing surface tension to ∼20 mN/m. Under acidic flue gas conditions, protonation of amine groups enhances electrostatic repulsion and interfacial film elasticity, while sulfonic acid moieties confer exceptional thermal and salt resistance. In situ characterization further reveals that the N,S-CDs form a continuous jammed network within foam lamellae, effectively obstructing Plateau borders and suppressing liquid drainage. Microfluidic flooding experiments confirm that N,S-CDs-stabilized foam significantly mitigates gas fingering and ensures stable displacement in porous media, achieving high oil recovery efficiency (>60%) while maintaining substantial gas trapping capacity (>50%). This work introduces a sustainable carbon-based stabilization strategy that not only upgrades flue gas into a reusable flooding agent but also advances CO2 sequestration, aligning fossil fuel production with low-carbon circularity.