Tartaric acid modified nitrogen-doped hydrothermal carbon for germanium recovery and DFT calculation

The efficient recovery of germanium from complex secondary resources is a significant challenge in resource sustainability. In this study, a tartaric acid-functionalized nitrogen-doped hydrochar (NPB-TA) was synthesized for selective germanium (Ge) capture from aqueous solutions containing other metal ions. Adsorption experiments demonstrated that NPB-TA can be used in germanium solutions of varying pH and concentration, achieving a saturated adsorption capacity of 112.23 mg/g at pH = 3. The adsorption process was found to be in accordance with the Langmuir isotherm and pseudo-second-order kinetic models, indicating monolayer adsorption and chemisorption as the dominant mechanisms. Moreover, NPB-TA exhibited superior selectivity toward Ge (IV) even in binary systems with competing ions. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Density functional theory calculations were applied to elucidate the adsorption mechanism. The mechanism involves synergistic coordination between Ge (IV) and surface-bound -OH/-COOH groups, with amino groups facilitating the formation of stable chelating rings containing C-O-Ge/C-N-Ge bonds. This study demonstrates that tartaric acid-modified N-doped biosorbent has potential for the selective recovery of germanium from aqueous solution.