Ionic covalent organic frameworks with precisely engineered pyridinic nitrogen sites for light-driven gold recovery

Gold is a strategically important and technologically indispensable metal underpinning applications in electronics, catalysis, medicine and energy technologies. However, its naturally accessible abundance is exceedingly limited, necessitating the exploration of alternative resource streams-particularly electronic waste. Meanwhile, the escalating generation of gold-containing electronic waste also underscores the urgent need for efficient and sustainable recycling technologies. Here, we report the synthesis of two ionic covalent organic frameworks (ICOFs) incorporating distinct bipyridinium units via a one-step quaternization strategy. These photoactive cationic sites can act as effective coulombic traps for [AuCl₄]^- and also promote sustained charge separation under illumination, thereby enabling in situ photoreduction of Au(iii). As a result, both of the synthesized ICOFs exhibit outstanding gold adsorption performance, with capacities exceeding 2800 mg g^-1. Notably, ICOF-36BPy achieves an ultrahigh gold uptake capacity of 3854 mg g^-1, representing a 10.91-fold enhancement over that of its neutral parent COF under dark conditions. Density functional theory calculations further reveal that strengthened coulombic interactions between nitrogen-containing cationic sites and [AuCl₄]^- markedly accelerate adsorption kinetics, whereas sustained photoinduced charge separation in ICOF-36BPy constitutes a critical mechanism enabling efficient Au(iii) reduction.