Photoelectrochemical Behavior of Alizarin Modified TiO₂ Films

Abstract

Photocurrent voltage curves obtained under visible light excitation of alizarin molecules chemisorbed to nanoporous TiO 2 films show both anodic and cathodic currents. The potential at which the sign reversal occurs depends on the electrolyte pH, the presence of acceptors, and the dye coverage, but as a general rule, it occurs at potentials ca. 600-700 mV more positive than the flat band potential. Negative photocurrents are accounted by efficient electron discharge to the electrolyte mediated by the ligand. Cathodic photocurrents are only observed at pH values higher than ca. 4.0 and go through a maximum at intermediate alizarin loadings. This phenomenon is ascribed to the progressive reparation of surface states by alizarin which hampers carrier transport through the TiO 2 matrix and decreases electron discharge to the electrolyte solution.

Hybrid Semiconducting Materials: New Perspectives for Molecular‐Scale Information Processing

“…Surface-engineered wide-band-gap semiconductors can be also regarded as more advanced logic devices based on the combination of a few simple logic gates. TiO 2 modified with redox-amphoteric organic chromophores such as folic acid (FA@TiO 2 ) [182], (CA@TiO 2 ) [170], or alizarin [183] are the best examples of such materials, which are capable of performing more complex information processing. In these cases, the photocurrent polarity strongly depends on photoelectrode potential.…”

TiO2–anthraquinone hybrids: from quantum-chemical design to functional materials

“…[2][3][4] Most of these materials reported to date are based, with some exceptions, [5][6][7][8][9] on titanium dioxide. 1,[10][11][12][13][14][15][16][17][18][19][20][21][22] Its surface is usually modified with inorganic, organometallic or organic species with desired optical and electrochemical reactivity. First of all the modifier itself should absorb visible light or be engaged in chromogenic interaction with titanium(IV) ions.…”

“…All these compounds are stable and easily available from both synthetic and natural sources, therefore they are compatible with the concept of green chemistry, however the application of organic solvents during the synthesis of dye-semiconductor hybrids cannot be avoided. Alizarin itself is a well-known photosensitizer of TiO 2 16,[30][31][32][33][34][35][36][37][38][39][40] and a preliminary report on quinizarin can also be found. 17 1 is a molecule composed of the central quinone ring, the catechol ring on the one side and the benzene ring on the opposite side.…”

Coordination chemistry for information acquisition and processing

“…For the first group the photocurrent switching effect was observed mainly for unmodified oxide semiconductors such as bismuth orthovanadate, 30,31 BixLa1−xVO4 solid solutions (x between 0.23 and 0.93), 9 lead molybdate, 10 V-VI-VII semiconductors: bismuth oxyiodide, 7,11 bismuth oxynitrate 12 and antimony sulfoiodide 13 as well as cadmium sulphide 14,15 and lead sulphide. 16 For unmodified semiconductors, the observation of the switching effect is possible only for sufficiently low potential barrier Ebi at the solid-liquid junctionthis may be achieved by the reduction in grain sizes of the semiconductor and the decrease in the doping level, 17 TiO2 pentacyanoferrates(II), L=H2O, NH3, thiamine, thiodiethanol, thiodipropanol, thiodiacetic acid, thiodipropionic acid, thiodipropionitrile, 1,3-dithiane, 1,3-dithiolene, thiamine 23,24 TiO2 Alizarin 25,26 TiO2 dihydroxyanthraquinones 25 TiO2 alizarin complexone 27 TiO2 Ferrocene CrO4 2-, CrO3F - 32 CdS Prussian Blue 8 CdS Fullerene-oligothiophene 33 When considering the examples presented in Table 1 we may formulate some general principles that must be met in order to observe the PEPS effect. The most obvious is the illumination of a semiconducting system within its absorption range in order to generate an electron-hole pair (except for the scenario in which a sensitisation of a semiconductor occurs).…”