Carbon-Doped TiO₂ and Carbon, Tungsten-Codoped TiO₂ through Sol–Gel Processes in the Presence of Melamine Borate: Reflections through Photocatalysis

Abstract

A series of C-doped, W-doped, and C,W-codoped TiO2 samples have been prepared using modified sol–gel techniques. Reproducible inexpensive C-doping arises from the presence of melamine borate in a sol–gel mixture, whereas W-doping is from the addition of tungstic acid to the sol. The materials have been characterized using elemental analysis, N2 physisorption (BET), thermogravimetric analysis, X-ray diffraction, Raman, X-ray photoelectron, UV–vis spectroscopies, and photocatalytic activity measurements. Doping C and W independently results in an increased absorbance in the visible region of the spectrum with a synergistic effect in increased absorbance when both elements are codoped. The increased visible-light absorbance of the W-doped or codoped materials is not reflected in photocatalytic activity. Visible-light-induced photocatalytic activity of C-doped material was superior to that of an undoped catalyst, paving the way for its application under only visible-light irradiation conditions. A significant fraction of the spectral red shift commonly observed with doped catalysts might be due to the formation of color centers as a result of defects associated with oxygen vacancies, and bandgap-related narrowing or intragap localization of dopant levels are not the only factors responsible for enhanced visible-light absorption in doped photocatalysts. Furthermore, bandgap narrowing through increases in the energy of the valence band may actually decrease photo-oxidation activity through a curtailment of one route of oxidation.

Wheat bran valorisation: Towards photocatalytic nanomaterials for benzyl alcohol photo-oxidation

“…The difference in the fitting peak for Ti2p of 454.5 eV and 458.3 eV is potentially resulted from the presence of CeTieO bond in the TiO 2 lattice that the electronegativity of C (2.55) is lower than that of O (3.44) which results in more electron-rich in TieO bond and further affects the difference in binding energy. This may also indicate the lattice distortion due to the presence of C atom (Neville et al, 2012), as similarly observed in the XPS spectra of other Ti-Bran catalysts. Ti content (Table 1) was also quantified via ICP/MS and was found to be in the range of 8e40 wt% of the final materials in the Ti-Bran samples after partial removal of the organics from wheat bran.…”

“…Co-doping of C and N Yang et al, 2008), metal and non-metal co-doping (Neville et al, 2012;Shen et al, 2008; were reported to render materials with high visible light response.…”

Codoping titanium dioxide nanowires with tungsten and carbon for enhanced photoelectrochemical performance

“…30 To our best knowledge, there is no direct experimental demonstration on the effect of codoping TiO 2 for PEC application because of the lack of suitable doping methods for donor (metallic) dopants. Previous methods of doping TiO 2 with metallic donors typically introduced the dopants during the synthesis stage of TiO 2 with methods, such as sol-gel 23,26,31 , hydrothermal 32 , sputtering 27 and solution combustion 33 . All these in-situ doping methods change the crystallinity/morphology compared with undoped TiO 2 , preventing the isolation of the doping effect from crystallinity/morphology effects on the PEC performance.…”

A brief review of co-doping

“…(W + C) codoped TiO 2 synthesized by Neville et al [109] and by Xiao et al [110], and (N + V) co-doped TiO 2 synthesized by Xu et al [111], also exhibited similar red-shifts of the absorption edge. Improving the catalytic activity by (W + C) co-doping is inconclusive, and Xiao et al demonstrated an increased photocatalytic activity with (W + C) co-doping compared to the undoped case [110], while the opposite was observed by Neville et al [109]. The presence of elemental C and Ti-O-C bonding [102,108] suggests that doped C mostly remains in its elemental phase, with only a relatively minor amount incorporated into TiO 2 in the form of interstitial or anion substitutional defects.…”

“…The deviation was attributed to the low concentration of dopant and N 2 adsorption on the surface [102]. (W + C) codoped TiO 2 synthesized by Neville et al [109] and by Xiao et al [110], and (N + V) co-doped TiO 2 synthesized by Xu et al [111], also exhibited similar red-shifts of the absorption edge. Improving the catalytic activity by (W + C) co-doping is inconclusive, and Xiao et al demonstrated an increased photocatalytic activity with (W + C) co-doping compared to the undoped case [110], while the opposite was observed by Neville et al [109].…”