Metal ion adsorption using silk fibroin-coated polypropylene filters

Abstract

Heavy metals from industrial manufacturing wastewater can contaminate ground and surface water sources. Current wastewater treatment methods to remove these metals involve liquid separation processes which are energy intensive and expensive. Removal of these heavy metals though adsorption processes provides an alternative processing method which is less labor and energy intensive. In this thesis, adsorption of Cu (II) and Zn (II) metal ions were investigated using silk fibroin-coated nonwoven polypropylene filters. As a strong biopolymer that can be utilized as a coating for any substrate, silk fibroin contains electron-rich functional groups that serve as potential active sites for metal cation adsorption. Batch adsorption studies were conducted for the initial metal ion concentration and time effects on adsorption for a metal ion concentration range of 200-2400 ppm in aqueous solution. Filter adsorption followed a Langmuir model, with uncoated filter adsorption capacities changing from 67.5 to 50.8 mg/g and 66.8 to 83.5 mg/g for silk fibroin coated filters with Cu (II) and Zn (II) adsorption, respectively. Silk-coated filters exhibit an adsorption efficiency below 10% for copper and zinc, suggesting this silk fibroin coating requires further functionalization to remove metals down to the ppb range concentration required for wastewater discharge into the environment.