Sunlight-boosted recovery of precious metal ions from E-waste using tannin-grafted mesoporous silica

The escalating demand and dwindling reserves of precious metals request efficient recycling techniques from electron waste. Addressing this need, we introduce a new method utilizing tannin-grafted mesoporous silica for the sunlight-boosted recovery of precious metals. Our strategy leverages the inherent photoreactivity of tannins, enabling metal–ligand complexation and plasmonic enhancement of chemical reduction. The result is a marked increase in the adsorption capacity and the high selectivity towards precious metal ions in electronic waste. Our robust covalent bonding approach concentrated tannic acids onto silica at a high density (500,000 per square micrometer), which significantly boosted the adsorption of gold ions up to an 11-fold increase, even amidst a mixture of nine other metal species. Impressively, we achieved a maximum adsorption capacity of 68.4 mmol per gram, equivalent to 13.4 g of gold per gram of adsorbent. Also, the adsorption rates for platinum and palladium ions were enhanced by 2.6 and 3.0 times, respectively. The underlying mechanism includes the visible-light-driven plasmonic hot electron transfer that affords nearly perfect selectivity for gold ions (approximately 99%). These findings not only advance the field of metal recovery from electronic waste but also offer an environmentally benign and cost-effective solution that harnesses renewable solar energy.