Preparation and evaluation of activated carbon with different polycondensed phosphorus oxyacids (H3PO4, H4P2O7, H6P4O13 and C6H18O24P6) activation employing mushroom roots as precursor

• Mushroom roots (MR) were used as raw materials to prepare activated carbons.
• H3PO4, H4P2O7, H6P4O13 and C6H18O24P6 were employed as activating agents.
• H4P2O7, H6P4O13 and C6H18O24P6 activation generated more surface acidic groups.
• MRAC-C6H16O24P6 had the largest surface area and micropore volume.

Orthophosphoric acid (H3PO4), pyrophosphoric acid (H4P2O7), polyphosphoric acid (H6P4O13) and phytic acid (C6H18O24P6) were specially employed as activating agents to produce activated carbons from mushroom roots (MR). Thermogravimetric studies of MR after these phosphorus oxyacids (POA) impregnation indicated the thermal degradation of MR was greatly influenced by different polycondensed POA. The prepared activated carbons were characterized by N2 adsorption/desorption isotherms, Fourier-transform infrared spectroscopy (FTIR) and Boehm's titration. The surface area of the carbons was similar but the characteristics of pore volume were different. MRAC-C6H16O24P6 owned the largest surface area and micropore volume. MRAC-H3PO4, MRAC-H4P2O7 and MRAC-H6P4O13 presented a similar micropore volume. MRAC-H6P4O13 exhibited a comparatively narrow mesopore distribution around 4 nm. Boehm's titration results indicated that MRAC-C6H16O24P6, MRAC-H6P4O13 and MRAC-H4P2O7 had much more acidic functionalities than MRAC-H3PO4. MRAC-C6H18O24P6 had the highest amount of total acidic surface groups (4.02 mmol/g). Batched sorption studies were also performed to compare adsorptive properties of the carbons toward methylene blue (MB). The sorption capacity of MB follows an order of MRAC-C6H16O24P6 ≈ MRAC-H6P4O13 > MRAC-H4P2O7 > MRAC-H3PO4, which may be assigned to the different pore structures and chemical properties.