Nitrogen doped residual carbon from gasification slag to enhance trifluoroacetate adsorption in groundwater: Experiments and calculations

Abstract

In this work, a nitrogen doped residual carbon (RCN) from gasification slag was prepared to adsorb trifluoroacetate (TFA) from groundwater. The physicochemical properties of the residual carbon variants were characterized using BET, SEM, XPS and Boehm titration techniques, which determines the porous structure and basic surface property of RCN. For all residual carbon variants, the TFA adsorption kinetics conform the pseudo-second-order model and isotherm data followed the Langmuir model. The RCN exhibited the highest TFA monolayer adsorption capacity of 24.8 mg/g. Thermodynamics study indicated that TFA adsorption onto these adsorbents was spontaneous and the increasing temperature is not conductive to TFA adsorption. During the rapid small scale column tests, the RCN offered 1390 bed volumes (BV) to 3 μg/L breakthrough which was >4 times higher than did the pristine residual carbon (290 BV). Moreover, the DFT calculations obtained the adsorption strength sequence of sulfate > TFA > nitrate onto nitrogen doped carbon, which manifested most unfavorable effect of sulfate on TFA adsorption. This research offers a theoretical and practice reference for the simultaneous gasification slag utilization and perfluorochemicals purification.