Visible Light Absorption by Various Titanium Dioxide Specimens

Abstract

A set of heat-induced and photoinduced absorption spectra of various compositions of Degussa P25 TiO2 and different polymers has been examined. The spectra are described as the sum of overlapping absorption bands (ABs) with maxima at 2.90 eV (427 nm, AB1), 2.55 eV (486 nm, AB2), and 2.05 eV (604 nm, AB3); the spectra correlate entirely with the experimentally observed absorption spectra after the reduction of TiO2. Absorption spectra of visible-light-active TiO2 photocatalysts reported recently in the literature have also been analyzed. Relatively narrow absorption spectra are very similar and independent of the method of photocatalyst preparation. The average absorption spectrum can be described reasonably well by the sum of the two absorption bands AB1 and AB2. It is argued that visible light activation of TiO2 specimens (anion-doped or otherwise) implicates defects associated with oxygen vacancies that give rise to color centers displaying these absorption bands and not to a narrowing of the original band gap of TiO2 (EBG approximately 3.2 eV, anatase) through mixing of dopant and oxygen states, as has been suggested recently in the literature.

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

“…shown by Kuznetsov and Serpone [25,62]. In the present study, the XPS data shows clearly that doping definitely occurs in the TiO 2 lattice.…”

Solid-State 13C NMR Characterization of Carbon-Modified TiO2

“…[34][35][36][37] Main group doping increases visible absorption by creating narrow, localized bands of orbitals within the band gap, as well as by promoting other defects of the TiO 2 lattice. [38][39][40][41][42][43][44][45] For example, nitrogen doping of TiO 2 has been correlated to an increase in oxygen vacancies, which are believed to be involved with the observed increased visible light activity. 39,41,44,45 Among the most promising materials is carbon-doped TiO 2 , 24,26-33,46-52 hereafter called C-TiO 2 .…”

Photosensitised Degradation of Organic Dyes by Visible Light Using Riboflavin Adsorbed on the Surface of TiO2Nanotubes

“…Thus, after absorption of the photon and electronic excitation, the injection of an electron into the conduction band of the semiconductor is possible, leading to the formation of radical species with high oxidant power. The sensitisation of semiconductors has been widely studied in the past in the development of photoelectrochemical solar cells, 10,11 electronic devices, 12,13 heterogeneous photocatalysis, 3,[14][15][16] and recently many efforts have been made in the production of a visible light photocatalyst to produce hydrogen through water splitting using sensitiser dyes. [17][18][19][20][21][22] The efficiency of those processes depends on the properties of the sensitisers, semiconductor and their interaction under photoexcitation.…”