Activated carbon synthesized from biomass material using single-step KOH activation for adsorption of fluoride: Experimental and theoretical investigation

Abstract

Single-step potassium hydroxide synthesized activated carbon was prepared from Schima wallichii biomass by optimizing process parameters at different carbonization temperature (500 °C, 600 °C, 700 °C and 800 °C) and biomass to KOH impregnation ratio (1: 0, 1: 1, 1: 2 and 1: 3). The optimum condition for obtaining the best activation carbon was found to be at 600 °C and 1: 2 impregnation ratio with BET surface area, total pore volume, and pHzpc of 1,005.71m2g−1, 0.491 cm3g−1 and 6.11, respectively. SEM and XRD analysis revealed the ordering of the graphitic layer with more pores in the carbon matrix at optimized conditions. Batch adsorption experiments were run for fluoride adsorption and fitted, of which Langmuir isotherm model seems to be the best-fitted model with maximum adsorption capacity of 2.524mgg−1. Adsorption kinetics was elucidated best with the pseudo-second-order kinetic model. Theoretical calculations indicate that the adsorption of fluoride is favorable on edge site of both zig-zag and arm chair carbon models with chemisorption type of interaction. Fluoride uptake was found to be affected by the presence of co-ion in the order: $$\rm{CO_3^{2-}} >SO_4^{3-} >NO_3^{-} >Cl^-$$ .