The diversified mechanism of adsorption and electro-adsorption technologies by using Ti3AlC2 for removing fluoride

Fluoride is a common pollutant from nature, normal life, and production. Adsorption, electro-adsorption, and precipitation are dominant mechanisms corresponding to the adsorption and electro-adsorption technologies for removing fluoride. This paper presents Ti3AlC2 as an effective reagent for removing fluoride under acidic conditions. The adsorption mechanisms of adsorption and electro-adsorption were compared to sedimentation at pH 2 and 1, leading to a higher removal rate of adsorption by pH 2 than at pH 1. The adsorptive behavior of Ti3AlC2 with fluoride includes both multilayer sorption and chemisorption. Furthermore, the precipitation reaction induced a partial change of Ti3AlC2 to MXene. Notably, electro-adsorption was more effective rather than sedimentation at pH 1 in capacitive deionization technology. The Al adsorption sites made it easier to combine fluoride than Ti, and aluminum fluoride was easier to produce than titanium (III) fluoride. These adsorption and electro-adsorption experiments were carried out to elucidate and delineate the performance of Ti3AlC2 for removing fluoride. A molecular model of Ti3AlC2 was also built to calculate adsorption using the density functional theory. Hence, the Ti3AlC2 molecular model combined with XPS and other characterizations of materials provided an effective, easy-to-understand combinative mechanism for removing fluoride.