Environmentally friendly tea saponin foam detergents costabilized by GO-OH/SiO2 nanoparticles for removing radioactive surface contaminants

Currently, bare silica nanoparticles with low surface activity and weak stabilizing foam ability have restricted applicability in treating surface radioactive pollutants. To address potential issues with SiO2 as a foam stabilizer, a highly efficient foam stabilizer was fabricated by compounding silica with hydroxylated graphene oxide (GO -OH), which was prepared by hydrothermal modification of graphene oxide (GO). Then, an environmentally friendly foam detergent with high stability and high decontamination efficiency was developed using the natural surfactant tea saponin (TAS) as a foaming agent and a composite of silica and GO-OH (GO-OH/SiO2) as a foam stabilizer, which is named tea saponin foam detergent. For different types of surfactants, the structural and morphological characteristics of GO-OH, such as hydrophilic and surface oxygen groups, as well as the synergistic influence of GO-OH with SiO2 on foamability, foam stability, and detergency of the foam detergent, were studied. As a consequence, the TAS foam detergent has good stability with a drain half-life of 68 min. By hydrothermal modification of GO, the contact angle of water on GO-OH in air dropped to 63.2 degrees, which was lower than that (73.0 degrees) on GO. Furthermore, the hydrophilicity of GO-OH increased, and more oxygen-containing groups on GO-OH enhanced its absorption and enrichment of the radionuclide uranium and improved the decontamination rate of the TAS foam detergent. Moreover, when GO-OH was combined with SiO2, the dispersion and stability of SiO2 in the foam detergent improved, and the foam stability of the detergent subsequently further improved. Adding 2 wt% SiO2 and 0.1 wt% GO-OH to the detergent enhanced the foam drainage half-life of the detergent from 40 min to 68 min and improved the stability of the detergent by 70%. In addition, the synergistic action of GO-OH/SiO2 with TAS surfactant increased the liquid film thickness of the foam and the airflow resistance to support the weight-bearing capacity of the foam skeleton. As a result, it slowed the rate of foam disproportionation, reduced the bubble size, increased the bubble number, and finally improved the foam stability of the detergent. For simulated radioactive uranium pollutants on the surfaces of glass, stainless steel, and tiles, the foam detergent with the synergistic action of GO-OH/SiO2 and TAS surfactant had decontamination rates of 91.7%, 91.16% and 91.76%, respectively, which were 14.96%, 15.67% and 19.39% higher than that of TAS foam detergent without GO-OH/SiO2. The synergistic enhancement of GO-OH and SiO2 on foam stability and its adsorption and combination action with uranyl ions would be the main reasons to improve the detergency of the TAS foam detergent. Therefore, TAS foam detergent stabilized synergistically by GO-OH/SiO2 with high stability and efficient decontamination will be widely applied in nuclear emergencies and decommissioning decontamination of nuclear facilities.