Nitrogen-Doped Lignin-Derived Porous Carbon Spheres for Efficient Adsorption of Tetracycline Hydrochloride

Tetracycline hydrochloride (TC), as an emerging pollutant that poses a threat to the aquatic environment, adsorption technology is a highly promising treatment method. In order to further enhance the adsorption performance, optimization strategies should focus on the modification of adsorbent materials and the regulation of adsorption process conditions. In this study, lignin nanospheres (LNS) were employed as the precursor to successfully synthesize nitrogen-doped lignin-based porous carbon spheres (NCLS-2-0.5) through a simple one-step synthesis method. The resulting material exhibited excellent structural characteristics, characterized by an elevated specific surface area of 2371 m²/g and a well-developed porous structure. The total pore volume measured 1.117 cm³/g, with microporosity comprising 83.58% of the pore architecture. Experimental results demonstrated that NCLS-2-0.5 possessed outstanding adsorption capacity for TC, with a maximum adsorption capacity reaching 1105.9 mg/g. More importantly, after five consecutive adsorption–desorption cycles, the material maintained a removal efficiency of 84.4%, indicating good stability and regenerability. Mechanistic studies revealed that the adsorption process was driven by multiple interactions, including pore filling, electrostatic interaction, hydrogen bonding, and π–π interaction. This study demonstrates a viable approach for the effective elimination of TC from aqueous systems, while simultaneously advancing lignin valorization strategies for high-value applications.