Efficient and Rapid Extraction of Gold from E-Waste via Tailoring the Skeleton Environment of Covalent Organic Framework

The recovery and repurposing of noble metal from electronic waste has attracted significant attention due to the tremendous benefits to the economy and environment but is of great challenge. Herein, a two-dimensional oxygen-rich COF material, named TbDa-COF, was fabricated via integrating 1,3,5-tris(4-formylphenyl)benzene (TFPB) and oxygen-rich 3,3'-dihydroxybenzidine (DHB) into a π-conjugated framework. TbDa-COF permits selective gold recovery through local coordination and electrostatic interaction, which is then followed via in situ reduction to form gold nanoparticles (AuNPs) within its skeleton. The experiment results exhibited satisfactory selectivity and favorable capture capacity (247.1 mg g^-1), which is attributed to the favored crystallinity, numerous active functional moieties in DHB, and the efficient reduction of gold via hydroxyl groups. Meanwhile, the characterization results demonstrated that gold nanoparticles were evenly enriched and localized on the skeleton of TbDa-COF, which exhibits excellent catalytic activity in the reduction of 4-nitrophenol (90.9%) and rhodamine B (99.3%) with NaBH₄. More importantly, the strong anchoring ability between AuNPs and oxygen-rich units over the skeleton enhances the binding of AuNPs with TbDa-COF to maintain the preferred stability and easily reuse without loss of the catalytic property. The design of novel COF materials with specific functional units will open a new frontier on the recovery and reuse of noble metals; but also the composite has various potential developments in the fields of catalysis and optoelectronics.