An experimental evaluation of green surfactants to stabilize silica nanofluids in saline conditions and its application in CO2 absorption

Abstract Conventionally, it has been established that the salt ions have the tendency to reduce the surface charge of nanoparticles (NPs) and render them unstable, regulating the stability of nanofluids in a saline environment has been an issue for a long time. To overcome this problem, our work presents the application of a novel green surfactant obtained from Fenugreek seeds of an anionic nature for use as a stabilizing agent for 0.1 wt% silica nanofluids prepared using in DI water. To prevent phase separation, it is imperative to stabilize silica nanofluid solution during their use for subsurface applications. Thus, salt tolerant nanofluids can be prepared and utilized for further applications in enhanced oil recovery and carbon storage etc. The surfactant was extracted from fenugreek seeds by using Soxhlet extraction technique. The liquid solution of extracted surfactant thus derived was dried in hot air oven in order to get the powdered surfactant. The results obtained from dynamic light scattering and zeta-potential, the use of the green surfactant, even in limited concentration (0.2 wt%) not only increases the stability of the nanofluid (from 2 to 12 h) but also lowers the influence of salt, if it is present in moderate concentration (up to 2 wt% NaCl). In addition, when 4 wt% NaCl is dissipated in the solution, the presence of surfactant allows the nanofluid to remain stable for up to 4 h. Furthermore, the surfactant-enriched silica NPs showed higher CO 2 absorption than conventional NPs due to higher surface area and better bubble breakage, paving the way for future field deployment of green-surfactant stabilized silica nanofluids for gas storage and enhanced oil recovery applications.