Sulfur self-doped hierarchical porous carbon materials synthesized by one-pot method for efficient adsorption of thallium(I)

In this work, sulfur self-doped hierarchical porous carbons (KLC-X-Y) were fabricated via one-pot method using inexpensive sodium lignosulphonate as carbon and sulfur source and potassium hydroxide (KOH) as activator. Through detailed analysis, it was found that the carbonization temperature and KOH addition exhibited significant effects on the porosity, phase composition, functional groups and morphology of KLC-X-Y. Among them, KLC-700–2 possessed a hierarchical porous structure, high specific surface area (851.3 m²·g⁻¹), large pore volume (0.53 cm³·g⁻¹), appropriate pore size distribution (D = 2.49 nm), and abundant oxygen- (COOH and OH) and sulfur-containing (SO₃H and SH) functional groups. Notably, the synthesized KLC-700–2 displayed excellent adsorption performance for Tl(I) with a maximum adsorption amount of 523.7 mg·g⁻¹. After five consecutive adsorption–desorption processes, the adsorption amount of Tl(Ⅰ) by KLC-700–2 decreased slightly, which still reached 85.6 % of the initial adsorption amount, and its own structural properties didn’t change significantly, indicating that KLC-700–2 had good stability and reusability. The adsorption process of Tl(Ⅰ) on KLC-700–2 was verified to be spontaneous and endothermic, and conformed to the pseudo second order and Langmuir models by adsorption kinetic, isotherm, and thermodynamic studies. By comparing the physicochemical properties of KLC-700–2 before and after adsorption of Tl(I), it was confirmed that the adsorption of Tl(Ⅰ) on KLC-700–2 was co-controlled by chemical and physical adsorption, including ion exchange, precipitation reaction, surface complexation, pore filling and electrostatic attraction.