Clays are often envisaged as an alternative to activated carbon for wastewater pollutant adsorption. However, conclusive results have only been obtained for clays heavily chemically modified. In this study, a greener approach is proposed to improve the retention capacity of clays. It consists in mixing clay (C) with eggshell (ES) and calcine, and then exposing to gliding arc plasma (ESC-800/PL). The resulting materials were characterized by nitrogen physisorption, FTIR, XRD, TGA/DTG, and point of zero charge analyses. The preparation gives porous platelet agglomerates resulting from the kaolinite-metakaolinite transition, thereby increasing their internal specific surface area and capacity to retain pollutants. This granular distribution is kept stable by partial pozzolanic reactions avoiding deagglomeration. The specific surface area and total pore volume increased respectively from 14 m2 g-1 and 0.049 cm3 g-1 to 89 m2 g-1 and 0.061 cm3 g-1 leading to an enhanced removal efficiency of Fast Green and Orange G dyes from polluted water. The maximum adsorption capacity occurred at 298 K attaining values of 32.34 and 14.78 mg g-1 for OG and FG, respectively. The pH plays a crucial role in the maximum sorption of dyes, and the experimental data were successfully adjusted to pseudo-first-order kinetic and Liu isotherm model.
Keywords: Clay composite; Dye-adsorption; Eggshell; Metakaolin; Modified-clays; Plasma surface modification; Pozzolanic reaction.
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