Preparation and evaluation of activated carbons from lotus stalk with trimethyl phosphate and tributyl phosphate activation for lead removal

The present research explored the feasibility of preparation of activated carbons from lotus stalks (LS) by trimethyl phosphate (TMP) and tributyl phosphate (TBP) activations (producing AC-TMP and AC-TBP) and compared their physiochemical and Pb(II) adsorptive properties with the activated carbon (AC-PPA) obtained from phosphoric acid (PPA) activation of LS. The carbons were characterized by N2 adsorption/desorption, Boehm's titration, FTIR and XPS. Physical and chemical analysis results indicated that activations with TMP and TBP dramatically enhanced the SBET and concentrations of O-containing surface functional groups of the AC-TMP and AC-TBP compared to the carbon (LS-C) derived from pyrolysis of LS. AC-TMP and AC-TBP displayed much less SBET than AC-PPA, but they contained much higher acidic groups on their surfaces. The Pb(II) adsorption capacities of the carbons were also investigated at different contact times, pHs, ionic strengths and initial Pb(II) concentrations. The adsorption equilibrium data of the carbons were well fitted to the Freundlich model. The maximum Pb(II) adsorption capacities of AC-TMP (240.6 mg/g) and AC-TBP (229.1 mg/g) were much higher than that of AC-PPA (139.0 mg/g), resulting from their higher content of O-containing functional groups that could adsorb more Pb(II) species by electrostatic attraction, cation exchange and surface complexation.