Covalent Organic Framework Isomers for Photoenhanced Gold Recovery from E-Waste with High Efficiency and Selectivity

Gold recovery from electronic wastewater (e-waste) has attracted more and more attention because of the rapid increase of electronic waste, which is also significant for the economy and the environment. However, it remains a great challenge to design stable adsorbents for selective gold recovery from e-waste with large capacity and fast adsorption rate. Herein, three covalent organic framework (COF) isomers adopting different layer stacking models (named Tp-BTD-AA, Tp-BTD-AB, and Tp-BTD-ABC) were employed for gold adsorption. Interestingly, the adsorption rates and uptake amount of these COF isomers for gold were improved markedly under the irradiation of visible light. After optimizing the pH of aqueous solutions and the wavelength of the light source, Tp-BTD-AA exhibits the highest gold capacity of 3.0946 g/g at pH 5 and under irradiation with 460 nm light. The adsorption procedure conformed to the pseudo-second-order kinetic and Langmuir models. Moreover, Tp-BTD-AA showed high adsorption selectivity to gold and good recyclability, which could be used as a potential adsorbing material for the adsorption of gold from e-waste.