Tungsten Oxide Coatings from the Aerosol-Assisted Chemical Vapor Deposition of W(OAr)₆ (Ar = C₆H₅, C₆H₄F-4, C₆H₃F₂-3,4); Photocatalytically Active γ-WO₃ Films

Abstract

Tungsten hexaaryloxide complexes of formula W(OAr) 6 (Ar ) C 6 H 5 , 1; C 6 H 4 F-4, 2; C 6 H 3 F 2 -3,4, 3) have been synthesized by the reaction of W(O)Cl 4 and ArOH in 22-28% yield. The complexes were characterized by 1 H, 13 C, 19 F, and 183 W NMR (1, δ ) -474.8; 2, δ ) -416.3; 3, δ ) -446.3), melting point (1, 95 °C; 2, 101 °C; 3, 105 °C), IR, microanalysis, and singlecrystal X-ray diffraction (octahedral coordination). Aerosol-assisted chemical vapor deposition of W(OAr) 6 using acetone and toluene solvents and substrate temperatures from 300 to 500 °C produced blue tungsten oxide films on glass substrates. The films were analyzed by glancing angle powder diffraction and shown to be amorphous at 300 °C, but consisted of crystalline WO 3-x at higher deposition temperature. Annealing the films from 1 at 550 °C in air for 30 min produced yellow γ-WO 3 with preferred growth in the [020] direction. Raman analysis of the as-formed films showed WO 3-x with evidence for W V -W VI paired ions. Annealed samples produced Raman patterns for γ-WO 3 (807, 715, 273, and 133 cm -1 ). The films were adhesive to the substrate, conformal, passed the Scotch tape test, and gave good coverage. Typical growth rates were 20-50 nm min -1 . SEM showed uniform films consistent with an island growth mechanism. Energy dispersive analysis confirmed the presence of only tungsten and oxygen. XPS showed that the as-formed films were WO 3-x (x ≈ 0.22) with binding energy shifts for W 4f 5/2 at 37.2 and 4f 7/2 34.4 eV and for oxygen 1s at 532.6 eV. The as-formed films had an absorption maxima at 320-360 nm (dependent on film thickness) and an onset for absorption at 400 nm. Reflectance/transmission measurements produced interference fringes that enabled a calculation of film thickness. In general the films showed good transmission from 500 to 1000 nm (60%) and some reflectivity (ca. 20%) over the same region. After annealing, the absorption edge was pushed more into the visible and the films showed evidence for some scattering associated with haze. The blue WO 3-x films showed negligible photocatalytic activity. The annealed, yellow WO 3 films were active photocatalysts and readily destroyed an overlayer of stearic acid.

Atmospheric pressure chemical vapour deposition of WO3 thin films from a volatile fluorinated tungsten oxo‐alkoxide precursor, W(O)(OCH2CF3)4

“…6 −474.8 ppm. [12] The EI mass spectrum of 1 showed no parent molecular ion. 6 present, but in the absence of any evidence in the 183 W NMR that this is the case, it it likely they are artefacts of the EI methodology.…”

“…W(CO) 6 , [9] W(CO) 4 (PR 3 ) 2 (R = OEt) or W(η 3 -C 3 H 4 ) 4 , [10] but compounds with a direct W-O bond have advantages as they may act as single-sources (SSP), delivering both elements of the final film in one go. Although the use of polytungstates in an aerosol-assisted delivery route has recently been reported by Parkin, [11] more emphasis has been placed on the use of tungsten alkoxides W(OR) 6 (R = C 6 H 5 , C 6 H 4 F-4, C 6 H 3 F 2 -3,4) [12] and oxo-alkoxides [W(O)(OR) 4 , R = Et, Pr i , Bu t , CH 2 Bu t ] [13,14] in this regard. However, to our knowledge the only example of such precursors which can be used at atmospheric pressure (AP), a significant advantage for large scale industrial coatings, has been using W(OEt) x (x = 5, 6).…”

Structural and optical properties of visible active photocatalytic WO3 thin films prepared by reactive dc magnetron sputtering

“…[9][10][11] PC oxidation for indoor air purification and self-cleaning is today considered in several applications in the built environment. 12,13 Recently, WO 3 has drawn attention because of its high efficiency in PC activity under daylight illumination [14][15][16][17] and its ability to photodegrade a wide range of environmental pollutants. 16,18,19 Nano-WO 3 is reported to have much higher PC activity compared to bulk WO 3 photoelectrodes.…”

Growth mechanism of planar or nanorod structured tungsten oxide thin films deposited via aerosol assisted chemical vapour deposition (AACVD)

“…Tungsten oxide thin films with planar or NR structure have been previously deposited by AACVD [13][14][15].…”