Porous polyisothiocyanurates for selective palladium recovery and heterogeneous catalysis

Summary

Palladium is an indispensable metal due to its wide range of industrial applications. Pd refining, however, is an extremely energy-intensive process with a serious environmental impact. Thus, the selective recovery of Pd from secondary sources is rather important. In this direction, solid sorbents are promising candidates owing to their reusability. Here, we report the synthesis of porous polyisothiocyanurates through the trimerization of 1,4-phenyldiisothiocyanate under ionothermal conditions, named covalent isothiocyanurate frameworks (CITCFs), bearing in situ generated thiourea moieties as binding sites for Pd. High surface area of CICTFs, 1,589 m² g⁻¹, along with the presence of abundant sulfur atoms within a hierarchically porous network, enabled an exceptional Pd(II) uptake capacity of 909 mg g⁻¹, fast adsorption kinetics, stable uptake over a wide pH range, and selective Pd(II) recovery from wastewater conditions. Moreover, the reduction of recovered Pd(II) within the polymer network led to highly efficient heterogeneous catalysis for the Suzuki-Miyaura cross-coupling reaction.