Recovery of precious metals from e-waste was of great economic and environmental significance. Herein, the spherical covalent organic frameworks (COF-V) were constructed by the Schiff base reaction between 1, 3, 5-tris (4-aminophenyl) benzene and 2, 5-divinylterephthalaldehyde, followed by post-synthetic modification using mono-(6-mercapto-6-deoxy)-β-cyclodextrin (S-β-CD) and dithiothreitol (DTT) for recovery of gold from e-waste. Multi-farious microscopic and spectroscopic techniques were used to explore the micromorphology and elemental composition of all the materials. Meanwhile, the response surface method was used to optimize the experimental parameters to improve the adsorption performance of Au(III). The functionalized spherical COFs exhibited excellent Au(III) adsorption abilities with maximum adsorption capacities of 652.6 mg/g and 820.8 mg/g for COF-V-DTT and COF-V-S-β-CD, respectively. The impressive properties were due to the synergistic adsorption effect of the grafted hydroxyl and sulfhydryl groups in appropriately sized ordered pores. The spectral analysis demonstrated that Au(III) was firstly adsorbed on the adsorbents by coupling with the S atom, and then in situ reduced to Au(0) by hydroxyl groups. Moreover, two COFs materials also exhibited an excellent selectivity in the actual gold-containing waste liquid. Thus, this study would provide an efficient and economical way to recovery Au(III) from wastewater. 

Post-synthetically functionalized covalent organic frameworks for highly efficient recovery of gold from leaching liquor of electronic waste

Sustainable cutting-edge techniques for gold valorization from electronic wastes

Recovering gold from unconventional sources, such as electronic waste, offers significant environmental and economic benefits. Exploiting materials and methods with high efficiency and selectivity is demanding. Herein, we reported a novel light-enhanced Au(III) recovery process using a porphyrin-based metal–organic framework (PCN-224). Our results showed that PCN-224 exhibited a remarkable Au(III) recovery capacity of up to 2613 mg/g when exposed to visible light irradiation, which was 3 times higher than that in the dark. Furthermore, light irradiation also improved the Au selectivity of PCN-224 against coexisting ions, including Zn2+, Mg2+, Cd2+, Ni2+, Hg2+, Cu2+, Pb2+, Al3+, and Fe3+. Based on characterization and kinetic analysis, an adsorption–reduction mechanism was proposed for the light-enhanced Au recovery, and porphyrin linkers played an essential role as active sites for both adsorption and reduction. To further protect the porphyrin linkers in PCN-224, acetic acid was introduced as a representative electron donor molecule in electronic waste, which could further enhance the Au(III) recovery capacity to 4946 mg/g. In addition, we demonstrated that PCN-224 and its light-enhanced feature also performed effectively in the actual leaching solution of waste electrical and electronic equipment, and the framework was successfully reused for at least six cycles. Overall, our discoveries could inspire the design of more outstanding materials and the artful use of clean energy to recover precious metals while minimizing the environmental impact. 

Selective and Light-Enhanced Au(III) Recovery by a Porphyrin-Based Metal–Organic Framework: Performance and Underlying Mechanisms

A robust aerogel incorporated with phthalocyanine-based porous organic polymers for highly efficient gold extraction

Effective and selective recovery of gold from e-waste is highly desired from the viewpoint of economics and environment, but remains a challenge. Herein, by combining the advantages of high porosity and abundant pyridine cations units, a cationic covalent triazine framework (CTF) was employed for gold recovery from e-waste. Impressively, the prepared iCTF-BPM (BPM = 1,4-bis(4-cyanopyridinium-l-methylene)-benzene·2Br-) exhibits excellent adsorption capacity of 1836 mg g−1, super-fast adsorption kinetics, and outstanding cycle stability. Especially, the recovery efficiency of Au of up to 99 % can be achieved within 1 min. More importantly, iCTF-BPM enables highly selective recovery of gold from the actual leaching solution of e-waste in the presence of high-concentration interfering ions (including Cu, Ni, and Zn), with more than 98 % of the gold removed within 1 min and over 99 % within 5 min. X-ray photoelectron spectroscopy and density functional theory calculations corroborate that the efficient gold adsorption of iCTF-BPM can be attributed to the synergy of electrostatic interaction, selective reduction, conjugation effect, and hydrogen-bond interactions between pyridine cation sites and AuCl4- ions. 

A robust cationic covalent triazine framework-based nanotrap for fast and efficient recovery of gold from electronic waste

Efficient and Selective Gold Recovery from E-Waste by Simple and Easily Synthesized Covalent Organic Framework

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Efficient and Selective Gold Recovery from E-Waste by Simple and Easily Synthesized Covalent Organic Framework