Biochars from wood biomass as effective methylene blue adsorbents

Abstract

Forest waste is a significant ecological and economic problem, requiring effective solutions that will not only reduce its quantity but also contribute to the protection of the natural environment. This research paper focuses on the use of sawdust from mixed trees, as one of the main forest wastes, for production of biochars characterized by adsorption properties. Sawdust, a by-product of the wood industry, has a porous structure, which makes it an attractive precursor to biochar. Using pyrolysis technology and hydrothermal activation under various conditions, sawdust was transformed into biochars with a developed specific surface area. The studies proved that the parameters of the pyrolysis process have a significant impact on the structural, surface and adsorption properties of biochars. The materials were characterized based on the results of N<sub>2</sub> adsorption, scanning electron microscopy SEM/EDS, thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Raman spectroscopy. The surface characterization was made using the Boehm titration and pH<sub>pzc</sub> determination. The sorption capacity of methylene blue (MB) was studied. It was stated, that the obtained materials were characterized by a large specific surface area (227.5 – 1019 m<sup>2</sup>/g), the micro/mesoporous structure and the large pores volume (0.106 – 0.784 cm<sup>3</sup>/g). The surface oxygen functionalities allowed for large adsorption of MB. The adsorption process follows the Langmuir theory (qm,cal from 357.1 to 434.8 mg/g) and can be described using the kinetic pseudo-second-order model (R<sup>2</sup> = 0.99). The obtained biochars showed high adsorption capacity of methylene blue impurities which indicates their significant potential for use in water purification.