Chemical Engineering Journal

• Rapid, single step Continuous Hydrothermal Flow Synthesis (CHFS) of S-CQDs. • CHFS offers scale up industrialization. • S-CQDs have high stability in high salinity conditions. • S-CQDs have the ability to increase oil recovery from limestone in enhanced oil recovery (EOR). • Various models have been used to explain the mechanisms of EOR using S-CQDs. Currently, there is a paucity in the exploration and application of carbon-based nanomaterials for enhanced oil recovery. Carbon quantum dots (CQDs), 0D materials consisting of a graphitic core covered by an amorphous carbon framework, were produced from glucose and p -sulfonic acid calix[4]arene (SCX4) via Continuous Hydrothermal Flow Synthesis (CHFS), an environmentally benign synthetic approach. The S-functionalised carbon quantum dots (S-CQDs) demonstrated excellent colloidal stability in aqueous and brine solutions, low retention on sand surface, and impressive enhanced oil recovery (EOR) of 17% at very low concentrations of 0.01 wt%. The mechanisms proposed for CQDs in increasing oil sweeping efficiency involves altering the carbonate rocks wettability towards water wet, and creating temporary log-jamming, where the ultra-small particle size (1.7 ± 0.7 nm) allows S-CQDs to recover oil trapped in tight reservoirs. The synthesised S-CQDs also demonstrate photoluminescence, pH stability in the range of 3–11 and have excitation independent behaviour (300–360 nm) with an emission peak at 433 nm.

Continuous hydrothermal flow synthesis of S-functionalised carbon quantum dots for enhanced oil recovery