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.

This study examined differences in the adsorption kinetics, isotherms, and thermodynamics of the dyes (methyl orange and fast green FCF) by pristine (M–biochar) and chemical activated mandarin peel biochars (MN–biochar and MZ–biochar). The specific surface area (1085.0 m²/g) and pore volume (0.194 cm³/g) of MZ-biochar much higher than those of the M–biochar (specific surface area = 8.5 m²/g, pore volume = 0.016 cm³/g) and MN–biochar (specific surface area = 181.1 m²/g, pore volume = 0.031 cm³/g). The equilibrium adsorption capacities (mg/g) of MO and FG using M–biochar (MO = 0.95, FG = 0.78) MN–biochar (MO = 2.52, FG = 2.13), and MZ–biochar (MO = 16.27, FG = 12.44) have well-matched the pseudo-second-order model (R² ≥ 0.952) compared with the pseudo-first-order model (R² ≥ 0.008). Furthermore, the better explanation of the adsorption behavior of dyes by the Freundlich isotherm model (R² ≥ 0.978) than the Langmuir isotherm model (R² ≥ 0.881) supports the assumption that the multilayer adsorption governed the adsorption of dyes using mandarin peel biochars. The adsorptions of dyes were significantly dependent on the solution pH and temperature since the electrostatic and spontaneous endothermic reactions governed their removal using the pristine and chemical activated mandarin peel biochars.

This study explored the effects of peanut shell biochar (PSB) on the adsorption capacities of fungicides with and without successive chemical modifications, using KMnO₄ and KOH (PSB_OX-A), in order to provide a valuable understanding of their adsorption mechanisms and behaviors. To this end, the physicochemical properties of PSB and PSB_OX-A were examined by using the Brunauer–Emmett–Teller method, Fourier transform infrared spectroscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer. The effects of temperature, ionic strength, and humic acids on the adsorption of fungicides, using PSB and PSB_OX-A, were estimated through batch experiments. Furthermore, adsorption kinetics, isotherms, and thermodynamics were studied. The maximum adsorption capacities of fungicides by PSB_OX-A were estimated to be more notable (Q_max of carbendazim = 531.2 μmol g⁻¹, Q_max of pyrimethanil = 467.7 μmol g⁻¹, and Q_max of tebuconazole = 495.1 μmol g⁻¹) than PSB (Q_max of carbendazim = 92.6 μmol g⁻¹, Q_max of pyrimethanil = 61.7 μmol g⁻¹, and Q_max of tebuconazole = 66.7 μmol g⁻¹). These findings suggest that successive chemical modification using KMnO₄ and KOH could potentially be used to effectively fabricate PSB to remove fungicides in water-treatment processes.