Preparation of Lignin-based Mesoporous Biochar Nano- and Microparticles, and Their Adsorption Properties for Hexavalent Chromium

The removal performance and mechanism of Cr(VI) from aqueous solution was studied for a novel micro-nano particle kraft lignin biochar (BC) pyrolyzed at 400 to 700 degrees C. The physicochemical properties of BC were determined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and N-2 adsorption-desorption isotherms. The results illustrated that the BC had irregular micro- and nanoparticles with abundant pore structure and high BET surface area (111.1 m(2)/g). The FT-IR results showed that the lower pyrolysis temperature resulted in more oxygen-containing functional groups. The Cr(VI) adsorption capacity decreased with the pyrolysis temperature increasing from 400 to 700 degrees C, and the maximum percentage removal of Cr(VI) for BC obtained at 400 degrees C was 100% at pH 2, which suggested that the removal efficiency was mainly dependent on functional groups. Kinetic analysis demonstrated that Cr(VI) adsorption on BC fit well to the pseudo-second-order kinetic model. The adsorption data was well fitted with the Langmuir isotherm models, and the maximum adsorption capacity was 37.2 mg/g at 298K. The BC could be reused twice with Cr(VI) removal of 63.91% and was suitable for Cr(VI) contaminated waste-water treatment.