Facile fabrication of poly(tricholorotriazine-tannic acid) nanosphere and its rapid removal feature towards lead ions

The presence of Pb²⁺ in water systems poses potential dangers to the environment and public health, and developing efficient adsorbents is a feasible solution to the predicament. Herein, a cross-linked poly(tricholorotriazine-tannic acid) (TCA) nanosphere has been facilely prepared through one-step precipitation polymerization. The microstructure of TCA was well analyzed by TEM, SEM, FT-IR, XRD, TGA and N₂ sorption and its adsorption performance for aqueous Pb²⁺ was systematically evaluated. Results showed that TCA owned a hard spherical structure with size of about 250 nm and specific surface area of 22.3 m² g⁻¹. The adsorption capacity of TCA for Pb²⁺ in 50 mg L⁻¹ lead nitrate solution could be up to 136.3 mg g⁻¹ at pH = 5 and 298 K. The adsorption rate is extremely fast, completing 91% of the equilibrium adsorption capacity within one minute. After five cycles of adsorption-desorption, the TCA nanospheres still maintained a high adsorption capacity of 109 mg g⁻¹ for Pb²⁺. Adsorption kinetics and isotherm analysis suggested that the removal of Pb²⁺ by TCA followed the pseudo-second-order dynamics model and the Langmuir isotherm model. Thermodynamic parameters revealed that the Pb²⁺ removal process was spontaneous and endothermic in nature. The plausible removal mechanism could be attributed to coordination, chemical bonding and ion exchange between TCA and Pb²⁺.