Application of lanthanum-modified silk fibroin/polyvinyl alcohol film for highly selective defluoridation in brick tea infusion.

To mitigate the risk associated with water-soluble fluoride in tea and to have less influence on the contents of tea infusion, a highly selective lanthanum modified silk fibroin (SF) and polyvinyl alcohol (PVA) composite film (SF/PVA-La) was prepared to remove fluoride from brick tea infusion. Notably, SF/PVA-La could remove about 48 % of the fluoride from in brick tea infusion within 30 min. Importantly, the reduction in total tea polyphenols in brick tea did not exceed 10 %, and the reduction in caffeine was only 0.4 %. In addition, the Langmuir model revealed a maximum fluoride adsorption capacity of 9.15 mg/g for SF/PVA-La in brick tea infusion. Both FTIR and XPS analyses confirmed that SF/PVA-La engages in electrostatic adsorption of fluoride ions, with ion exchange occurring between the hydroxyl groups on its surface and the fluoride ions. These findings underscore the potential of SF/PVA-La as an effective material for selective fluoride removal from brick tea infusions.