Tetrazine-functionalized UiO-68 for highly selective Au(III) recovery from acidic solutions

A tetrazine-functionalized zirconium MOF, UiO-68-TZDC (isostructural with UiO-68-TPDC), is constructed through a one-pot solvothermal synthesis for the selective recovery of Au(III) from acidic chloride media, using UiO-68-TPDC as a tetrazine-free, isostructural counterpart. The obtained crystalline materials possess good thermal stability. UiO-68-TZDC shows a saturated Au(III) uptake of 404.4 mg g^-1, which is significantly higher than that of UiO-68-TPDC (114.5 mg g^-1), and comparable or superior to many reported N- and S-functionalized Zr-MOFs. The adsorption kinetics follow the pseudo-second-order model with multi-stage intraparticle diffusion, indicating combined control by chemisorption and diffusion. UiO-68-TZDC displays pronounced selectivity for Au(III) over Fe(III) and Cu(II) and retains more than 70% of its initial capacity after several adsorption-desorption cycles. Structural and spectroscopic analyses reveal the formation of crystalline Au⁰ domains and surface Au(III) and Au(I) species, directly indicating a partial reduction process driven by the electron-rich tetrazine linker, as evidenced by significant shifts in the electronic states of the nitrogen sites. These results support a cooperative "preconcentration-coordination-reduction" mechanism and demonstrate that tetrazine linker engineering in robust UiO-68 frameworks is an effective strategy for developing high-performance adsorbents for Au(III) recovery from acidic gold-containing waste streams.