Activated carbon with high mesopore ratio derived from waste Zanthoxylum bungeanum branches by KNO3 assisted H3PO4 staged activation for toluene adsorption

Abstract

Abstract Waste Zanthoxylum bungeanum branches were used to prepare activated carbon adsorbents with high mesopore ratio by H3PO4 staged activation method with adding KNO3 additive. The prepared activated carbon adsorbents were characterized by SEM, BET, FT-IR, and XRD. The adsorption properties of the prepared activated carbon adsorbents were evaluated by the toluene adsorption/desorption in air. The quasi-first-order, quasi-second-order, and Bangham models were used to fit the obtained toluene adsorption results. The oxidative etching of KNO3 additive improved the pore-forming ability of the H3PO4 activator to enhance the activation pore-forming effects of the selected biomass raw material. The secondary pore-forming effects of K atoms promoted the effective expansion of the pore diameter in the activated carbon preparation process to prepare activated carbon adsorbents with high mesopore proportion. The specific surface area and mesopore proportion of the activated carbon adsorbents prepared by adding KNO3 additive exceeded 1100 m2/g and 71.0%, respectively, and the toluene adsorption capacity exceeded 370.0 mg/g. The rich mesopore structures can effectively reduce the toluene mass transfer resistance, which can promote the corresponding activated carbon adsorbent to be regenerated by low-temperature (40 °C) thermal desorption. The toluene adsorption on the prepared activated carbon adsorbents include surface adsorption and diffusion in pore strucutres, and the toluene adsorption mechanism is more consistent with the Bangham kinetic model.