An Effective Mercury Ion Adsorbent Based on a Mixed-Matrix Polyvinylidene Fluoride Membrane with Excellent Hydrophilicity and High Mechanical Strength

Abstract

Improving the hydrophilicity and mechanical strength of membranes in water treatment applications remains challenging. In this study, modified vermiculite (VT-M) and a hydrophilic polyvinylpyrrolidone (PVP) were introduced into a polyethyleneimine-functionalized polyvinylidene fluoride composite membrane (PVDF/PEI) to prepare a comprehensively modified mixed-matrix PVDF composite membrane adsorbent that exhibited high mechanical strength and excellent hydrophilicity. The modified composite membrane featured good tensile properties, with a maximum tensile strength of 2.093 MPa, which was 2.5 times that of the PVDF/PEI membrane. After 7 s, the water contact angle of the composite membrane decreased to 0°, leading to significantly improved hydrophilicity. The modified composite membrane exhibited excellent adsorption selectivity for mercury ions, with a fitted maximum adsorption capacity of 807 mg/g. In a mixed-metal ion solution, the selectivity of the membrane for Hg(II) ions was 1.2 × 105 times that for Cd(II) ions. The adsorption mechanism of Hg(II) ions involved chelation, electrostatic attraction, and crystal growth processes. The present work suggests the great potential of mixed-matrix PVDF composite materials in the remediation of mercury-polluted water environments.