Effects of NaOH Activation on Adsorptive Removal of Herbicides by Biochars Prepared from Ground Coffee Residues

Abstract

In this study, the adsorption of herbicides using ground coffee residue biochars without (GCRB) and with NaOH activation (GCRB-N) was compared to provide deeper insights into their adsorption behaviors and mechanisms. The physicochemical characteristics of GCRB and GCRB-N were analyzed using Brunauer–Emmett–Teller surface area, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction and the effects of pH, temperature, ionic strength, and humic acids on the adsorption of herbicides were identified. Moreover, the adsorption kinetics and isotherms were studied. The specific surface area and total pore volume of GCRB-N (405.33 m²/g and 0.293 cm³/g) were greater than those of GCRB (3.83 m²/g and 0.014 cm³/g). The GCBR-N could more effectively remove the herbicides (Q_e,exp of Alachlor = 122.71 μmol/g, Q_e,exp of Diuron = 166.42 μmol/g, and Q_e,exp of Simazine = 99.16 μmol/g) than GCRB (Q_e,exp of Alachlor = 11.74 μmol/g, Q_e,exp of Diuron = 9.95 μmol/g, and Q_e,exp of Simazine = 6.53 μmol/g). These results suggested that chemical activation with NaOH might be a promising option to make the GCRB more practical and effective for removing herbicides in the aqueous solutions.