Enhanced methylene blue adsorption onto activated reed-derived biochar by tannic acid

This study investigated the effect of tannic acid (TA) on the adsorption efficiency of activated biochar (ABC) prepared from reed biomass regarding the removal of methylene blue (MB) from aqueous solution. The structure and chemical properties of the obtained ABC adsorbent were characterized by XRD, FTIR, N2 adsorption-desorption isotherms, and scanning electron microscopy. After the HNO3 activation of the original biochar (BC), the well-developed porous surface structure of ABC was observed with a considerable increase in the specific surface area. The adsorption behavior of MB onto ABC was determined with the presence of TA (pre-loading versus co-introduction with solute). Results demonstrated that the removal of MB was promoted in the presence of TA solutions with pH ranging from 4.0 to 8.0, and an increase of the initial concentration of TA (from 10 to 50 mg/L) caused a more pronounced promotion effect. The adsorption of MB onto ABC followed the Elovich kinetic model, suggesting a heterogeneous multilayer adsorption process. The adsorption data were best described by the Sips isotherm model, showing a maximum adsorption amount of 77.35 mg/g in the presence of TA, which was much higher than many reported adsorbents. The adsorption mechanism appeared to be related to electrostatic interaction, hydrogen bonding, ion exchange, n-π/π-π interaction, etc. Findings of the present work highlighted the positive effect of TA on the adsorptive removal of MB by ABC, and were also beneficial for developing reed-derived biochar as an engineered absorbent for removal of toxic dyes from aqueous solution.