Hierarchically porous tobacco midrib-based biochar prepared by a simple dual-templating approach for highly efficient Rhodamine B removal

High volatile matter contents in the feedstock could promote the development of porous structures and the reactivity of biochar. Herein, tobacco midrib with high volatile matter contents was used to prepare biochar by a dual-templating approach with mild activators (K2C2O4·H2O, CaCO3). The characterizations of textural properties indicated that tobacco midrib-based biochar possessed numerous meso-, micro-, and macro-pores, specific surface area reached 1841.9 m2 g−1. As a dye adsorbent, the adsorption capacity of this biochar towards Rhodamine B reached 588.7 mg g−1. After recycling 5 times, it still retained over 90% of its initial adsorption capacity. Moreover, thermodynamic parameters assessed with full vańt Hoff equation confirmed that dye molecules replace water molecules connected on biochar surface during the adsorption according to negative heat capacity change (-3.9 kJ mol−1 K−1), ΔH0 (–22.1 kJ mol−1) and ΔS0 (0.3 kJ mol−1) revealed that the adsorption process of Rh B by TMB was exothermic and the disorder of the solid–liquid interface increased. Overall, this research provides a mild and effective approach to modifying biochar from special tissue of agriculture waste and an insight into the process of dye adsorption on biochar from thermodynamics.