Open-air plasma treatment of polypropylene fabrics for enhanced metal oxide nanoparticle adhesion: the effect of oxide acid–base character

Abstract

Methods to attach metal oxide nanoparticles (MONPs) to inert supports such as polymers, fabrics and membranes, are important for applications that include filtration, lithium-ion battery separators, and photocatalysis. In the present study, a high-throughput method that consists of open-air plasma treatment of polypropylene (PP) knitted fabric, followed by spray-coating with ethanolic colloidal suspensions of various MONPs, has been investigated. X-ray photoelectron spectroscopy (XPS) indicates that open-air plasma treatment forms surface hydroxyl, carbonyl and carboxylic acid groups. The water contact angle of similarly treated spin-coated PP films decreases to 80°, compared to 97° for untreated PP. XPS and field emission scanning electron microscopy (FE-SEM) of plasma-treated and untreated controls spray-coated with MONPs, rinsed, and ultrasonicated in ethanol show that plasma treatment leads to enhanced particle adhesion. MONPs that act as weak Lewis acids, such as ZnO, MgO and In₂O₃, essentially completely coat the fibers, while more acidic MONPS, such as CeO₂, SiO_x, SnO₂, TiO₂, and WO₃, adhere relatively poorly, even on plasma-treated fabric. Metal oxide coverage, determined by XPS, inversely correlates with the polarizing power of the cation in the metal oxide. It is hypothesized that the metal oxide hydroxyl groups play a key role in adhesion, with strong Lewis acid MONPs exhibiting weaker hydrogen bonding to the polar functional groups (e.g., carbonyl groups) of the plasma-treated PP. Photocatalytic application of this method of attaching nanoparticles is demonstrated by ultraviolet light-induced decomposition of methyl paraoxon by ZnO-functionalized PP.