An anionic metal-organic framework decorated with tartaric acid for enhanced adsorption of indium ions

Adsorption and recovery of indium (In) ions is highly important for the sustainable use of this valuable metal resource. This work reports the synthesis of a novel metal-organic framework (MOF) adsorbent, MOF-808-TA (TA, tartaric acid). The introduction of TA molecules was achieved through a post-synthesis exchange of TA and acetic acid that is initially in the clusters of MOF-808. MOF-808-TA exhibits a larger adsorption amount for In(III) ions (173.3 mg g-1) than the unmodified MOF-808 (57.5 mg g-1). Meanwhile, adsorption equilibrium time is 1-120 min at the concentration range of 0.2-40 mg L-1. Further experiments show that MOF-808-TA owns still a high removal ratio for In(III) ions upon the presence of some metal ions. Moreover, MOF-808-TA can be well regenerated with a slight loss of adsorption capacity after five adsorption-desorption cycles. X-ray photoelectron spectrometry (XPS), Fourier transform infrared (FTIR) spectroscopy, and density functional theory (DFT) calculation unveil the synergic chelation contribution of the aliphatic hydroxyl and carboxyl groups from TA molecules. Also, the use of TA leads to the formation of the negative charge property of MOF-808-TA, which induces an electrostatic interaction towards cationic In(III) ions. This work indicates the high potential of MOF808-TA for the removal of In(III) ions from aqueous solutions.