Low-cost preparation of temperature-resistant and salt-tolerant amphiphilic carbon dots from a nonionic surfactant and its application in enhanced oil recovery

Amphiphilic carbon dots (ACDs) were synthesized from nonionic surfactant alkyl glycosides with different alkyl chains by a low-cost method. Moreover, the surface activity of these ACDs (C6-ACDs, C10-ACDs, and C1214-ACDs) was investigated. These ACDs have similar surface tension curves as surfactants, and the surface activity of these ACDs also increases with the alkyl chain length of raw materials. Among these ACDs, C1214-ACDs have the lowest critical micelle concentration (CMC) of 40.00 mg/L, a fifth of the raw material (APG1214). The surface tension of C1214-ACDs is not easily affected by the change in pH. In addition, C1214-ACDs have excellent temperature-resistant and salt-tolerant properties. The interfacial tension of crude oil-water is reduced from 26.59 mN/m to 0.68 mN/m by C1214-ACDs. Furthermore, C1214-ACDs maintains high interfacial activity at cNaCl = 200 g/L and cCaCl2 = 50 g/L, reducing interfacial tension to 0.054 mN/m and 0.048 mN/m.C1214-ACDs have high oil removal efficiency. After treatment with APG1214, C6-ACDs, C10-ACDs, and C1214-ACDs, the area of the oil film is reduced by 51.0%, 46.6%, 56.2%, and 78.1%, respectively. Moreover, APG1214 and C1214-ACDs reduce the contact angle of water droplets from 107.4° to 60.5° and 45.6°, respectively, indicating the wettability alternation of C1214-ACDs is better than raw material APG1214. Finally, the oil displacement efficiency of C1214-ACDs is 16.6% in the presence of 85 g/L NaCl and 10 g/L CaCl2. Therefore, as temperature-resistant and salt-tolerant nanoparticles with an ultra-small size, ACDs have broad application prospects in enhancing oil recovery in high-temperature and high-salt reservoirs.