Hierarchical porous activated carbon from waste Zanthoxylum bungeanum branches by modified H3PO4 activation for toluene removal in air

Activated carbon adsorbents were prepared by chemical activation with waste Zanthoxylum bungeanum branches as raw materials and H3PO4/H2SO4 as composite activator under different dosages of the auxiliary activator H2SO4. The prepared samples were characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area test, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The adsorption/desorption performances of low concentration toluene in the air were evaluated, and its reusability was evaluated by the adsorption/desorption cycle. Adsorption results were fitted using the quasi-first, quasi-second, and Bangham models. The adsorption properties of activated carbon adsorbent for toluene in the air show a "volcanic-type change trend" with the increase of H2SO4 dosage. The toluene adsorption properties of the prepared activated carbon adsorbents from high to low are as follows: BAC02 > BAC05 > BAC01 > BAC10 > BAC00. When the mass fraction of auxiliary activator H2SO4 was 2.0%, the adsorption amount of toluene on the prepared BAC02 activated carbon adsorbent increased by 51%, reaching 511 mg/g. After thermal desorption at 200℃, the adsorption performance of toluene was regenerated. The adsorption process of toluene conforms to the quasi-first-order model and Bangham model. The whole adsorption process can be divided into three stages: outer surface adsorption, intra-channel diffusion, and adsorption equilibrium. The addition amount of H2SO4 significantly affected the specific surface area, pore volume, and pore size distribution of the prepared activated carbon adsorbent.