Sorption heavy metal ions by activated carbons with well-developed microporosity and amino groups derived from Phragmites australis by ammonium phosphates activation

• Three APs were new activated agents using one-step activation to produce activated carbons.
• AC–APs contained much more basic groups and nitrogen content than AC–PPA.
• AC–APs showed much higher Ni(II), Cu(II) and Cd(II) sorption capacities than AC–PPA.
• The metal ions sorption mainly depended on the surface chemistry of the carbons.

Activated carbons (ACs) were prepared from Phragmites australis impregnated with phosphoric acid (PPA) and ammonium phosphates (APs). APs include triammonium phosphate (TAP), diammonium phosphate (DAP), and monoammonium phosphate (MAP). The activation process of ACs was simulated by thermo-gravimetric analysis. The physicochemical properties of AC–PPA and AC–APs were systematically examined by N2 adsorption/desorption, elemental analysis, Boehm's titration, and XPS. AC–PPA exhibited much higher values of the BET surface area (894.5 m2/g) and total pore volume (1.108 cm3/g) than that of AC–APs (< 500 cm2/g and < 0.3 cm3/g), but less Smic/SBET (29.3%) and Vmic/Vtot (14.9%) of AC–PPA than that of AC–APs (> 60% and >50%). Nevertheless, the results of elemental analysis, Boehm's titration, and XPS showed that AC–APs contained much more surface nitrogen-containing functional groups. The sorption equilibrium data for heavy metal ions Ni(II), Cu(II), and Cd(II)) sorption onto the carbons was analyzed by the Langmuir and Freundlich model. The differences of the carbons in the physicochemical and adsorption properties suggested that AC–APs exhibited higher heavy metal ions sorption capacities than AC–PPA due to well-developed microporosity and abundant amino groups.

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