Cu(II) removal from water by trimercapto-s-triazine trisodium salt modified alkaline lignin

To overcome the poor removal ability of alkaline lignin (AL) toward heavy metals, trimercapto-s-triazine trisodium salt (TMT) was selected as the modifying agent to introduce reaction groups. The Fourier transform infrared (FT-IR) spectra and the scanning electron microscopy (SEM) suggested that -SNa, C-N, and C = N groups were successfully introduced. Copper (II) was applied to evaluate the uptake performance of the adsorbent (AL-TMT). Adsorbent dosage and solution pH were taken into account to study their effects in the batch experiments. The pseudo-second-order dynamics and Langmuir models better described the experimental data. Nitrogen (N) and carbon (C) functional groups in thiotriazinone carried by AL-TMT were determined to be the primary uptake sites through X-ray photoelectron spectroscopy (XPS), FT-IR, and electrostatic potential (ESP). The selective experiments of AL-TMT toward Cd(II), Cu(II), Pb(II), Zn(II), Co(II), and Mg(II) were performed. It showed that AL-TMT possessed better adsorption selectivity toward Cu(II) than others. Furthermore, the density functional theory (DFT) calculations of thiotriazinone in AL-TMT also exhibited the lowest binding energy toward Cu than toward others. This work may provide a theoretical basis to facilitate the extraction of specific heavy metals from water or wastewater by using such modified alkaline lignin.