AIE-derived fluorescent silsesquioxane-based hybrid aerogel for light-enhanced gold recovery

Abstract

In this work, two aggregation-induced emission (AIE)-active organic fluorescent monomers (TPV, TPC) were synthesized by Knoevenagel reaction of 2,2′-([1,1′-biphenyl]-4,4′-diyl)diacetonitrile with benzaldehyde and 4-bromobenzaldehyde, respectively. Subsequently, two fluorescent hybrid porous polymers with semiconductor performance (PCS-TPV, PCS-TPC) were prepared successfully by connecting octavinyl silsesquioxane (OVS) with TPV and TPC through Friedel-Crafts reaction and Heck coupling, respectively. Among them, PCS-TPV with a hyper-crosslinked structure offered a specific surface area of up to 1165 m² g⁻¹; PCS-TPC was the first AIE-derived fluorescent hybrid silsesquioxane-based semiconductor polymer with 3-D conjugated structure. Compared with PCS-TPV, PCS-TPC exhibited stronger visible light absorption, higher fluorescent performance and quantum yield due to its high AIE-active unit content. Besides, PCS-TPC exhibited a remarkable gold recovery capacity (Q_m = 2728 mg g⁻¹) when exposed to visible light irradiation. Adsorption mechanism revealed that the photoelectrons produced by PCS-TPC under visible light irradiation reduced all adsorbed Au(III) to Au(I) and Au(0). Furthermore, a hybrid aerogel was prepared through physical blending of PCS-TPC with chitosan, overcoming the limitation that insoluble powder was difficult to process and recycle. This work provided a very efficient, sustainable, and industrially feasible way for gold recovery in e-waste.