Development of carbon adsorbents with high surface acidic and basic group contents from phosphoric acid activation of xylitol

Abstract

The present paper evaluated the feasibility of synthetizing activated carbons from xylitol with phosphoric acid activation at mild temperatures. Activation temperature (250–450 °C) and phosphoric acid to xylitol impregnation ratio (0.2–3 wt%) were varied during the synthesis of xylitol-based activated carbon, and the effects of these parameters on the textural and chemical properties of the final activated carbons were investigated by XRD, Raman, N₂ adsorption and desorption, SEM, XPS and Boehm's titration. The results of yield, XRD and Raman indicated that phosphoric acid activation enhanced the yields of activated carbons, and facilitated the formation of completely carbonized materials at low temperatures (around 250 °C) by comparing with charcoals derived from pyrolysis of xylitol. The porous structures of the activated carbons were developed after activation, and for each activation temperature, the carbons reached the maximum surface area at an impregnation ratio of 1.5. Due to the strong oxidizing radicals decomposed from phosphates, the produced carbons contain relatively high concentrations of acidic and basic surface groups. The total surface groups peaked at 6.08 mmol g⁻¹ for activated carbon obtained at an activation temperature of 350 °C and impregnation ratio of 1.5. The Ni(II) adsorption capacity of the activated carbons was 4 to 7 folds that of the charcoals.