Tailoring the surface properties of porous zeolite constructs using plasma processing

Abstract

Zeolites are widely used in adsorption, catalysis, and gas separations; however, the relative effectiveness of these applications is inherently impacted by material surface properties. Plasma modification presents an ideal methodology to address these issues, as it has an extensive parameter range and the potential to create tailored surface functionalities. Here, zeolite modification via plasma processing was investigated, along with the fabrication of different zeolite constructs (i.e., native zeolites, pellets and electrospun fibers). Water contact angle goniometry was employed to evaluate surface wettability, noting that untreated zeolites are nominally hydrophilic. We explored the use of fluorocarbon and H2O(v) inductively coupled plasmas to tune the resulting wettability of microporous NaX zeolites over a range of operating conditions. Specifically, after C3F8 plasma exposure, contact angles ranging from 123.9 to 138.2° were measured, depending on plasma treatment parameters. Formation of a fluorocarbon film was verified via X-ray photoelectron spectroscopy and scanning electron microscopy analyses. C2F6 and H2O(v) plasma exposure increased water absorption rates, as a consequence of surface etching and functionalization, respectively. Optical emission spectroscopy was used to probe gas-phase species, gleaning how the material intrinsically changes the plasma environment. Our studies revealed correlations between gas-phase spectroscopic analyses, the gas-surface interface, and the resulting plasma modified surface properties, ultimately leading to improved plasma processes.