Na related nanowhisker-containing biochar obtained from self-catalyzation and functionalization of papermaking black liquor lignin with superior heavy metal immobilization capability.

In this study, papermaking black liquor lignin (ULG) was directly used to produce biochar through pyrolysis. It was found that ULG has a high ash content (15.38 %), primarily consisting of Na-related minerals. During pyrolysis, the ash can reduce the activation energy of ULG (by over 6 kJ/mol), promote the development of pore structures, and enhance the graphitization of the resulting biochar through self-catalyzation. Additionally, the Na-related minerals form abundant nanowhiskers on the surface of biochar during pyrolysis, mainly composed of NaCO and NaPO, achieving self-functionalization, particularly in biochar produced at 700 °C (ULG-700). In the adsorption process, these nanowhiskers on the surface of ULG-700 act as efficient active adsorption sites. The theoretical maximum adsorption capacity for Cd(II) and Zn(II) by ULG-700 at room temperature is 639.71 and 161.27 mg/g, respectively. This study suggests that ULG can be developed as a low-cost and high-efficient heavy metal adsorbent.