One-step template-free pyrolysis for biochar: Biomass organs control porosity and high-performance for methylene blue...

Biomass containing inorganic ingredients can be converted into highly porous biochar via in-situ activation and templating process. Here, N-doped biochar is obtained by pyrolysis of spinach organs for efficient dye removal, using methylene blue (MB) as a model dye, and pyrolysis temperature plays a critical role in determining both porosity and N-species within biochar. Significantly, leaf biochar (LC-900) as pyrolyzed at 900 °C shows surface areas of 1263 m²/g larger than that of biochar from stem and root, indicating a dependence on the biomass organ source. Adsorptive MB behavior can be analyzed by Langmuir and pseudo-second-order kinetic models with a maximum amount up to 1048.0 mg/g at 25 °C for LC-900, surpassing majorities of ever reported biochar in free of extra activator. High porosity with suitable mesopores and N-species are prerequisites in biochar with excellent MB removal ability, involving mechanisms of pore-filling, H-bonding, electrostatic and π-π stackings. Pyrolyzed biochar from spinach organs especially for LC-900 shows great potential as highly efficient adsorbent towards dyeing water treatment.