Preparation of activated carbon from lotus stalks with the mixture of phosphoric acid and pentaerythritol impregnation and its application for Ni(II) sorption

Activated carbons were prepared from lotus stalks impregnated with H3PO4 solution or the H3PO4 solution mixed with pentaerythritol (PER), producing AC and AC-PER. The results of thermogravimetric analysis and SEM suggested that PER enhanced the depolymerization of lignocelluloses and the degree of cross-linked structure in activation process. The physicochemical properties of AC and AC-PER were characterized by N2 adsorption/desorption, Boehm’s titration, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). AC exhibited much higher values of the BET surface area (1418.78 m2/g) and total pore volume (1.253 cm3/g) than that of AC-PER (342.67 cm2/g and 0.273 cm3/g). Nevertheless, the results of FTIR, Boehm’s titration and XPS showed that AC-PER contained much more surface oxygen-containing functional groups. The sorption equilibrium data for Ni(II) sorption onto the carbons agreed well with the Langmuir model. The maximum sorption capacity derived from Langmuir model was 0.5800 mmol/g for AC and 0.9184 mmol/g for AC-PER (I = 0 mM). Based on the results of sorption studies, FTIR and XPS analysis, several possible mechanisms for these sorption systems were elaborated further. Cation exchange, electrostatic attraction and surface complexation were likely important mechanisms for Ni(II) sorption onto the carbons.

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► PER was especially used as “cross-linking agent” to produce activated carbon.
► The surface physical and chemical properties of AC and AC-PER were investigated.
► AC-PER contained much more surface acidic functional groups than AC.
► Ni(II) removal on AC-PER was much higher than that on AC.
► XPS and FTIR analysis were used to investigate the Ni(II) sorption mechanisms.