Bi-Activation Engineering of Lignin-Derived Porous Carbon Adsorbent for Highly Efficient Water Purification

Organic contaminants have become a major concern in current environmental policies. Biochar is often used to absorb pollutants due to its large surface area, wide availability, and cost-effectiveness. Lignin, a byproduct of the pulp and paper industry, is an ideal precursor for biochar due to its abundance, sustainability, and high carbon content. Bi-activation engineering of alkali lignin during the carbonized process by combining potassium carbonate and melamine to produce porous carbon with more micro–mesoporous structure was proposed. Melamine reacts with the carbon matrix during the activation process, creating new alkaline compounds and releasing more gas, resulting in the formation of more micropores and mesopores. Adjusting the ratio of potassium carbonate to melamine can optimize the micro–mesoporous structure of porous carbon materials. In this regard, a nitrogen-doped three-dimensional porous carbon (ALNC-2-1) with a specific surface area of up to 3522 m2 g–1 was synthesized for the adsorption of methylene blue and tetracycline hydrochloride in wastewater; the largest adsorption capacities were 1364 and 1682 mg g–1, respectively. The adsorption process was found to follow the pseudo-second-order kinetic model and was attributed to electrostatic interaction, pore filling, hydrogen bonding, and π–π interaction. Moreover, ALNC demonstrated high removal rates for organic pollutants and excellent regeneration performance, thus making it a promising material for practical wastewater treatment.