Development and Characterization of Membranes with PVA Containing Silver Particles: A Study of the Addition and Stability

Abstract

Developing technologies for the reduction of biofouling and enhancement of membrane functionality and durability are challenging but critical for the advancement of water purification processes. Silver (Ag) is often used in the process of purification due to its anti-fouling properties; however, the leaching of this metal from a filtration membrane significantly reduces its effectiveness. Our study was designed to integrate the positive characteristics of poly vinyl alcohol (PVA) with the controlled incorporation of nano-scale silver ions across the membrane. This approach was designed with three goals in mind: (1) to improve antifouling activity; (2) to prevent leaching of the metal; and (3) to extend the durability of the functionalized membrane. The fabrication method we used was a modified version of manual coating in combination with sufficient pressure to ensure impregnation and proper blending of PVA with cellulose acetate. We then used the spin coater to enhance the cross-linking reaction, which improved membrane durability. Our results indicate that PVA acts as a reducing agent of Ag⁺ to Ag⁰ using X-ray photoelectron spectroscopy analysis and demonstrate that the metal retention was increased by more than 90% using PVA in combination with ultraviolet-photo-irradiated Ag+ reduced to Ag⁰. The Ag⁺ ions have sp hybrid orbitals, which accept lone pairs of electrons from a hydroxyl oxygen atom, and the covalent binding of silver to the hydroxyl groups of PVA enhanced retention. In fact, membranes with reduced Ag displayed a more effective attachment of Ag and a more efficient eradication of E. coli growth. Compared to pristine membranes, bovine serum albumin (BSA) flux increased by 8% after the initial addition of Ag and by 17% following ultraviolet irradiation and reduction of Ag, whereas BSA rejection increased by 10% and 11%, respectively. The implementation of this hybrid method for modifying commercial membranes could lead to significant savings due to increased metal retention and membrane effectiveness. These enhancements would ultimately increase the membrane's longevity and reduce the cost/benefit ratio.

Keywords: biofouling; poly(vinyl) alcohol; silver particles; ultrafiltration.

Figure 1

FTIR spectra of the top (coated) and bottom (uncoated) sides of the poly vinyl alcohol (PVA)-Ag membrane.

Figure 2

SEM micrograph of (A) PVA-Ag cross-section; (B) PVA-Ag top (coated) surface.

Figure 3

Atomic composition (at %) of the top (coated) surface of a PVA-Ag membrane as determined by EDS.

Figure 4

XPS silver 3D region overlay of membrane exposure and non-exposure to UV.

Figure 5

XPS oxygen (1s) spectrum of membranes (A) without UV exposure and (B) with UV exposure.

Figure 6

Before and after filtration XPS Spectra of (A) PVA-Ag and (B) PVA-UV.

Figure 7

Equilibrium Solution Content (ESC) of control and affinity membranes in water at room temperature.

Figure 8

PWF of unfunctionalized and functionalized membranes.

Figure 9

Flux measurements and bovine serum albumin (BSA) rejection of membranes crosslinked with 2.5% GA.