Correlation between the non-stoichiometry of titanium dioxide and its photoelectrochemical behaviour

Abstract

TiOz (rutile) has been reduced in well-defined conditions to give n-type TiOzhx semiconductors in which both the nature and concentration of the defects attributed to reduction are known. The influence of the value of x in TiOz-x on the efficiency of such a material when used as a photoanode is very marked and, in particular, there exists a value of x for which this efficiency is a maximum. The influence of x on the electrochemical behaviour of Ti02-, is only noticeable for electrodes whose active surface has been previously mechanically polished. Finally the broadening of the absorption spectrum towards the visible as x increases can be attributed to the existence of deep acceptor levels which are excited by the light, giving free holes that can be involved in the OH-oxidation process.

The photoelectrocatalytic oxidation of aqueous nitrophenol using a novel reactor

“…The thickness W of the depletion layer varies as [15] (V)V f ) 1/2 where V is the potential at the conduction band edge, and V f is the flat band potential. Photons of sufficient energy to excite electrons across the band gap are absorbed to a depth 1/a where a is the absorption coefficient of the incident light at the wavelength of interest.…”

“…As shown in Figure 1, providing that the electrolyte concentration exceeds the dopant density, the application of a positive potential to an n-type TiO 2 photoanode generates an electric field within the semiconductor [13][14][15]. The thickness W of the depletion layer varies as [15] (V)V f ) 1/2 where V is the potential at the conduction band edge, and V f is the flat band potential.…”

A review of TiO2 nanoparticles

“…The differences in photoactivity derive from the change in the diffusion length of the minority carriers [76]. For optimal e -/h + separation, the magnitude of the potential drop across the space-charge layer should not fall below 0.2 V [77]. The dopant content directly influences the rate of e -/h + recombination by the equation: W = (2 εε o V s /eN d ), where W is the thickness of the space-charge layer, ε is the static dielectric constant of the semiconductor, ε o is the static dielectric constant in a vacuum, V s is the surface potential, N d is the number of dopant donor atoms, and e is the electron charge [78].…”

“…Electron transfer from one of these levels to the conduction band requires lower photon energy than in the situation of an unmodified semiconductor. TiO 2 has been doped with many different transition metals [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86]. Grätzel et al [73] studied the effect of doping TiO 2 with transition metals such as Fe, V, and Mo by electron paramagnetic resonance.…”

Is methylene blue an appropriate substrate for a photocatalytic activity test? A study with visible-light responsive titania

“…Current efforts have been focused on their modification to extend the wavelength of photoabsorption towards the visible region that matches the solar spectrum or indoor illumination. Attempts have been made along this line on doping with transition metals [3,4] and metal complexes [5], semiconductor coupling [6,7], and hydrogen reduction [8,9]. Doping with non-metallic elements such as nitrogen [10][11][12][13][14][15], fluorine [16], carbon [17][18][19], boron [20], sulfur [21][22][23], or their mixture [24][25][26], has also been tested.…”