Constructing yolk-shelled magnetic carbon with controllable cavities and multiple sites for efficient acteoside adsorption

Acteoside (ACT) is a natural product with diverse pharmacological activities and commonly coexists with the structurally similar echinacoside (ECH) in Cistanche tubulosa . Obtaining high-purity ACT requires separating it from the structurally similar ECH, which remains challenging. In this study, yolk-shelled magnetic carbon (YSMC) adsorbents with controllable cavities and multiple sites were developed via a sacrificial-template method for the efficient adsorption of ACT. The controllable cavity between the Fe 3 O 4 core and the carbon shell was achieved by regulating carbonization temperatures. The YSMC adsorbents were synthesized at different temperatures and denoted as YSMC-500, YSMC-700, and YSMC-900, with cavity volume proportions of 52.4 ± 1.4%, 91.3 ± 0.5%, and 70.8 ± 0.8%, respectively. Among them, YSMC-700, which combined the largest cavity volume with the highest specific surface area and pore volume, exhibited a high adsorption capacity of 253.24 mg/g and a selectivity of 2.19 toward ACT over ECH under the optimized adsorption conditions. Its large cavity may have facilitated mass transport and provided abundant accommodation space for ACT, while the well-matched mesoporous structure promoted the pore-filling effect and improved the utilization of adsorption sites. In addition, hydroxyl groups, Fe–OH groups, and ether groups provided multiple sites for ACT binding through hydrogen bonding interactions. Moreover, the magnetic adsorbent was easily separated and maintained 87.5% of its capacity after eight cycles, demonstrating good reusability. These findings demonstrate that combining controllable cavities with multiple sites is an effective strategy for developing advanced adsorbents for separating large bioactive ingredients from natural products.