Fabrication and properties of porphyrin nano- and micro-particles with novel morphology

Abstract

New types of porphyrin nano- and micro-particles composed of J- and H-heteroaggregates were prepared by electrostatic self-assembly of two oppositely charged porphyrins, tetrakis(4-trimethylammoniophenyl)porphyrin (H 2TAPP 4+) and tetrakis(4-sulfonatophenyl)porphyrin cobalt(II) (CoTPPS 4-), in aqueous solutions. Transmission electron microscopy (TEM) images showed novel morphology and size distribution of porphyrin particles fabricated under different experimental conditions. The assembly process of the nano- and micro-particles was monitored by UV-Vis spectra. Fluorescence spectra and UV-Vis spectra provided optical information on the formation of the nano- and micro-particles. Cyclic voltammograms of the porphyrin particles indicated that the electron gain and loss of the H 2TAPP 4+ ion were restrained, and the electron transfer of the CoTPPS 4- ion was promoted in the J- and H-type porphyrin heteroaggregates within the particles. The stability and constitution of the nano- and micro-particles were confirmed by UV-light irradiation, heat-treatment, and pH and ionic strength changes. Photoelectrochemical measurements showed that the photoelectron transfer of TiO 2 modified with the particles was more efficient than that of TiO 2 sensitized by either monomers. The photoelectronic and photocatalytic properties of the products indicated that the pyramidal or spherical configuration of the nano- and micro-particles was favorable for the absorption and transfer of the energy. It can be found that TiO 2 sensitized by the porphyrin nano- and micro-particles exhibits significant improvement in energy conversion and photocatalytic activity with reference to pure TiO 2.