Adsorption Characteristics of Methylene Blue onto Biochar Derived from Lavender Straws

The first lavender straws derived biochar (LBC) capable of adsorbing methylene blue (MB) was created using this well-known agricultural waste (lavender straw, LS). Using the scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), the physicochemical characteristics of LBC were investigated. On MB adsorption by LBC, the effects of various adsorption dosages, initial pH, adsorption times, initial mass concentrations, and temperatures were examined. The maximum theoretical adsorption capacity was 305.27 mg·g−1 under the conditions of a dosage of 1.0 g·L−1, beginning pH of 8.0, adsorption period of 360 min, and temperature of 318 K. The Redlich-Peterson isotherm adsorption model and the pseudo-second-order model both have \({R}^{2}\) values that are high enough to provide good fits for the MB adsorption process. The adsorption of MB by LBC was a process of spontaneous, endothermic, entropy-increasing process. The mechanism between LBC and MB involved electrostatic interaction, pore filling, hydrogen bonding, complexation, π-π and n-π interaction, etc. The adsorption capacity of LBC was more than 200 mg·g−1 after five cycles of regeneration. Overall, the LBC showed good adsorption efficiency and reusability, thereby suggesting its potential to serve as an efficient MB adsorbent for wastewater treatment.