Plasma Surface Modified TiO₂ Nanoparticles: Improved Photocatalytic Oxidation of Gaseous m-Xylene

Abstract

Titanium dioxide (TiO(2)) is a preferred catalyst for photocatalytic oxidation of many air pollutants. In an effort to enhance its photocatalytic activity, TiO(2) was modified by pulsed plasma treatment. In this work, TiO(2) nanoparticles, coated on a glass plate, were treated with a plasma discharge of hexafluoropropylene oxide (HFPO) gas. By appropriate adjustment of discharge conditions, it was discovered that the TiO(2) particles can be either directly fluorinated (Ti-F) or coated with thin perfluorocarbon films (C-F). Specifically, under relatively high power input, the plasma deposition process favored direct surface fluorination. The extent of Ti-F formation increased with increasing power input. In contrast, at lower average power inputs, perfluorocarbon films are deposited on the surface of the TiO(2) particles. The plasma surface modified TiO(2) nanoparticles were subsequently employed as catalysts in the photocatalytic oxidation of m-xylene in air, as carried out inside a batch reactor with closed loop constant gas circulation. Both types of modified TiO(2) were significantly more catalytically active than that of the unmodified particles. For example, the rate constant of m-xylene degradation was increased from 0.012 min(-1) with untreated TiO(2) to 0.074 min(-1) with fluorinated TiO(2). Although it is not possible to provide unequivocal reasons for this increased photocatalytic activity, it is noted that the plasma surface treatment converted the TiO(2) from hydrophilic to highly hydrophobic, which would provide more facile catalyst adsorption of the xylene from the flowing air. Also, based on literature reports, the use of fluorinated TiO(2) reduces electron-hole recombination rates, thus increasing the photocatalytic activity.

Conformal Encapsulation of Three-Dimensional, Bioresorbable Polymeric Scaffolds Using Plasma-Enhanced Chemical Vapor Deposition

“…In one report on pulsed HFPO film deposition, Sumitsawan et al claim that HFPO film thickness varied linearly over treatment times ranging from 5 to 60 min. 34 Our group has previously reported constant deposition rates for HFPO depositions for treatment times up to 2 h, but most of these depositions were performed much further downstream from the plasma glow than in the present study. 29 The only report of a similar, self-limiting FC PECVD system, to our knowledge, is that of a C 2 F 6 /CF 4 system, where deposition rate decreased as a function of treatment time.…”

Fluorine-Doped Iron Oxide Nanomaterials by Plasma Enhanced-CVD: An XPS Study

“…The main one, located at 284.8 eV (45.6% of the total C content), is assigned to adventitious contamination (Refs. [15][16][17][18], whereas the one located at 286.3 eV (24.0% of the total C content) can be attributed to the presence of adsorbed carbonates arising from air exposure (Refs. [16][17][18].…”

“…[15][16][17][18], whereas the one located at 286.3 eV (24.0% of the total C content) can be attributed to the presence of adsorbed carbonates arising from air exposure (Refs. [16][17][18]. The two bands at 289.0 and 292.6 eV (17.3% and 13.1% of the total C amount, respectively) can be ascribed to CF and CF 2 species (Refs.…”

“…The main one, located at 684.5 eV (53.8% of the total F content), is related to lattice fluorine species (Refs. 2, 10, [16][17][18]20) whereas the second one at BE = 688.3 eV can be attributed to C-F x moieties (Refs. 2, [16][17][18], in line with data pertaining to the C 1s peak (see Accession #1248-02).…”

“…2, 10, [16][17][18]20) whereas the second one at BE = 688.3 eV can be attributed to C-F x moieties (Refs. 2, [16][17][18], in line with data pertaining to the C 1s peak (see Accession #1248-02). Interestingly, while the latter component completely disappeared after 10 min Ar + sputtering, lattice F was still present after erosion.…”