PHOTOELECTRIC BEHAVIOR OF HYDROXOALUMINIUMTRICARBOXYMONOAMIDE PHTHALOCYANINE ADSORBED ON TiO2

HERNÁN B. RODRÍGUEZ; YÉSICA DI LORIO; MARTA I. LITTER; MARÍA A. GRELA; ENRIQUE SAN ROMÁN

La Serena, Chile

Otro; X Encuentro Latinoamericano de Fotoquímica y Fotobiología (X-ELAFOT); 2010

Recently, we have tested the capability of hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc) adsorbed on TiO2 Degussa P-25 for the photocatalytic reduction of Cr(VI) under visible irradiation in the presence of 4-chlorophenol as sacrificial electron donor. It was demonstrated that a very rapid reduction to Cr(III) is possible in spite of the aggregation of AlTCPc on the surface of TiO2. In order to elucidate the role of aggregates in charge injection, the photoelectric behavior of AlTCPc adsorbed on a TiO2 electrode is studied in this work. Nanocrystalline TiO2 electrodes were prepared from Degussa P-25. The powder was milled with a small amount of water and acetylacetone for a long time in order to lower the degree of aggregation and stabilized with Tween 80. Films were obtained extending the white viscous paste over ITO electrodes, drying at 100 ºC for 1 h and heating at 500 ºC for 30 min. AlTCPc was adsorbed onto the modified electrodes from dimethylsulfoxide (DMSO) and characterized through total reflectance and diffuse transmittance measurements to obtain the absorption spectrum. The circuit was closed using a SnO2-graphite counter-electrode and a thin layer of 0.5 M KI - 0.05 M I2 in ethyleneglycol as the electrolyte. Photocurrents were measured either directly or using modulation techniques under irradiation in the red (AlTCPc Q-band) as a function of the applied potential and dye loading. Absorption spectra do not depend on dye loading and suggest a high aggregation degree as found in Degussa P-25 suspensions, whereas photocurrent spectra do not depend on  the applied potential and dye loading and resemble the absorption spectrum of the monomeric dye in DMSO. These results show that the species responsible for the charge injection is the monomeric AlTCPc. Slow response times (~ 0.6 s) and a large increase of photocurrent on electrodes previously illuminated at open circuit for different time intervals are observed. The origin of the photoelectric response is analyzed and discussed.