Effect of bifunctional acid on the porosity improvement of biomass-derived activated carbon for methylene blue adsorption

Activated carbon (AC) with high specific surface area was prepared by using bifunctional H3PO4 agent, which led to dehydrating and activation effects through hydrothermal pretreatment and subsequent pyrolysis process. N2 adsorption and desorption isotherms of AC showed a high BET surface area of 2434 m2 g−1 and a total volume of pores (VT) of 2.0447 m3 g−1 for AC. The morphology and the chemical components of hydrochar and AC were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, which indicated that H3PO4 was benefitting for the formation of porous structure of AC. Subsequently, the effect of H3PO4 in hydrothermal pretreatment and activation process was investigated by comparative experiments. The removal and adsorption of methylene blue (MB) dye with different concentrations onto the AC were studied. The monolayer equilibrium adsorption capacity was 644 mg g−1, showing that AC has good adsorption qualities for methylene blue (MB). The adsorption balance data of MB on AC was best fitted to the Redlich-Peterson model. The adsorption kinetic data fit better to the pseudo-first-order model at low MB concentration, and the pseudo-second-order and Elovich models fit better when the MB concentration was rising.