Pyrolyzing spent coffee ground to biochar treated with H3PO4 for the efficient removal of 2,4-dichlorophenoxyacetic acid herbicide: adsorptive behaviors and mechanism

Abstract

In this work, the adsorptive behavior of H3PO4-activated spent coffee ground (SCG) biochar (P-SCGB) were assessed for the removal of the 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide from aqueous solutions. P-SCGB was produced via pyrolysis carbonization at 300 °C for 2 h and impregnated with H3PO4 as a pretreatment. The characteristics of the biochar were implemented through the FTIR, SEM, XPS, XRD, N2 adsorption/desorption curves and point of zero charge, which demonstrated that P-SCGB had a typical structure of amorphous materials and presented porous structure. It was found that the greatest removal efficiency of the 2,4-D occurs at pH 2 and adsorbent dosage of 0.75 g L−1. The experimental adsorption data fitted well with the Elovich kinetic model and Freundlich isotherm model. Adsorption results indicated the maximum 2,4-D adsorption capacity of P-SCGB reached 323.76 mg g−1, which was higher than most of 2,4-D adsorptive study. The thermodynamic behavior pointed to be exothermic and the magnitude of the adsorption enthalpy was in agreement with chemical adsorption. The reusability of adsorbent was also studied. Besides, our work also investigated and revealed the multiple mechanisms for 2,4-D adsorption. Over all, the study promoted the development of biochar preparation which act as an alternative adsorbent and its high adsorption uptake is proved to be beneficial for the advanced treatment of 2,4-D herbicide.