Open/Closed Cage Silsesquioxane-based Thioamide-bridged Hybrid Networks with Unexpected Adsorption Abilities and Selectivity for Au (III)

The design and preparation of multifunctional adsorbents for highly selective recovery and reuse of gold-containing waste are of paramount importance for resources re-utilization and environmental protection. Two different kinds of thioamide-bridged silsesquioxane-based adsorbents; open cage PCS-STOH and closed cage PCS-ST, were synthesized by crosslinking reaction of thiocarbonohydrazide with octa(3-chloropropyl) silsesquioxane (SQ-Cl8) in the presence or absence of NaHCO3, respectively. Compared to PCS-ST (670 mg g−1), PCS-STOH can absorb 1720 mg g−1 of Au (III). Moreover, PCS-STOH can reduce Au (III) concentrations from ppm levels (12 mg L-1) to ppb levels (0.001 mg L-1). Adsorption behaviors were systematically studied at various pHs, ion concentrations, temperatures and contact times. Besides, PCS-ST and PCS-STOH show excellent selectivity in extracting Au (III) from competing ions as well as e-waste. The adsorption mechanism may be attributed to oxidation–reduction, coordination and electrostatic interactions between adsorbents and Au (III). Importantly, the Au (III) loaded PCS-STOH and PCS-ST can act as heterogeneous catalysts to transform 4-nitrophenol to 4-aminophenol. This work provides a strategy for preparing open/closed cage silsesquioxane-based thioamide-functionalized hybrid networks. Facile and low-cost synthetic procedure make it very promising to be industrialized and be of great use in the field of selective recovery of gold ions.