Enhancement of Ni(II) removal by urea-modified activated carbon derived from Pennisetum alopecuroides with phosphoric acid activation

• Pennisetum alopecuroides as a new precursor first using one-step activation to produce activated carbons.
• Urea was employed to modify the activated carbons by phosphoric acid activation.
• The modified activated carbon was for improving its Ni(II) removal from aqueous solutions.
• The Ni(II) sorption mainly depended on the surface chemistry of the carbons.

Urea was employed to modify activated carbons by phosphoric acid activation from a new precursor: Pennisetum alopecuroides. The urea-modified activated carbon was used to improve the adsorption of Ni(II) from aqueous solutions. The original activated carbon (PAC) and urea-modified activated carbon (PUAC) were characterized by N2 adsorption/desorption, elemental analysis, Boehm's titration and X-ray photoelectron spectroscopy (XPS) analysis. The Ni(II) removal capabilities of PAC and PUAC were evaluated by batch sorption experiments. The results of N2 adsorption/desorption demonstrated that the BET surface areas and total pore volumes of PAC (1108 m2/g and 1.469 cm3/g) were larger than those of PUAC (1060 m2/g and 1.226 cm3/g). Nevertheless, the results of elemental analysis, Boehm's titration and XPS showed that PUACs contained more surface nitrogen-containing functional groups than PAC. The sorption studies revealed that PUACs showed higher sorption capacities for Ni(II) than PAC. The equilibrium data for PAC and PUACs were best fitted by the Langmuir model. The results showed that Ni(II) uptake increased when the initial pH was increased and the ionic strength of the solution was decreased. The main mechanisms for the sorption of Ni(II) onto the carbons were cation exchange, electrostatic attraction and surface complexation.

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