Preparation And Photoelectric Properties Of Meso-tetra (4-N, N, N-trimethylanilinium) Porphyrin/graphene Oxide Composite Materials

In recent years, in order to greatly develop and use solar energy, scientists have studied many artificial photosynthesis system. Porphyrin group is the ideal part to provide electronic for electron donors-receptor (D-A) system. Porphyrin with conjugate system of macrocyclic π electron delocalization, and it could reduce the energy deference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), therefore porphyrin has the spectral response in a wide range, especially in the visible light region has a higher quantum yields. Graphene is a novel two-demensional (2-D) material, has excellent physical and chemical properties. Oxidized graphene consists of covalently bonded carbon atoms and contains some oxygen functional groups e.g. hydroxyl, carboxyl groups, and epoxide on their basal planes and edges and make it soluble in water. Based on the superior of structure and photoelectric properties of porphyrin and GO, combined porphyrin and GO to form electron donor-electron acceptor system, realized the effective electron transfer between the two, and it has very important application value in the field of photoelectric conversion materials. The preparation methods of grapheme-porphyrin complexes are covalent bonding and non-covalent bonding, due to non covalently bonding can remain the unique electronic properties and structure characteristics of graphene and porphyrin not destroyed, and non-covalent complexes are more similar to natural system and can be used to mimic the natural photosynthetic system, so we chose a non-covalent bonding way to achieve the composition of porphyrin and GO in aqueous solutions, study spectral properties and the photoelectric conversion properties, as follows:In this study, a common water-soluble cationic porphyrins meso-tetra (4-trimethylammonium-yl) porphyrin (TTAP) under the condition of protonated (pH= 2.0) and non-protonated (pH= 7.0) conditions was reacted with GO in aqueous solution. The reaction product was observed by transmission electron microscopy porphyrins accumulate in the surface of GO to form a distinct folds. Raman spectrum, FTIR spectrum, UV-vis absorption spectrum and fluorescence spectrum showed TTAP accumulate on the surface of GO sheets by π-π stacking and electrostatic interactions, and they formed TTAP/GO hybrids through non-covalent binding. Dropped and coated the complex onto the ITO conductive glass electrode, then measured photoelectrochemical response of the modified electrode, the study found that there is a stable and reversible photocurrent and photovoltage while lighting, indicated that porphyrin/GO hybrid materials have potential applications in the field of photoelectric conversion value, and speculated the mechanism of donor-acceptor electron transfer. UV-vis absorption spectrum and Benesi-Hildebrand equation were used to obtain the binding constants between TTAP and GO, the value were 2.38×103 L/mol (pH=2.0) and 3.68×104 L/mol (pH=7.0), respectively. The result indicated that under the condition of pH=7.0, the binding force between TTAP and GO was greater. Time resolved fluorescence spectrum showed that luminescent characteristics of porphyrin molecules could quench by GO, and there was electron transfer and delivery between the two.Ascorbic acid is a common biochemical reagents and often used as an electron donor in biochemical reactions, so this paper used uv-vis absorption spectroscopy, fluorescence spectroscopy and photoelectrochemistry measurement methods to study spectrum and photoelectric conversion properties in the presence of ascorbic acid porphyrin/graphene oxide hybrids. The results showed that in the presence of ascorbic acid the maximum absorption peak intensity of TTAP/GO system increased, and enhanced the ability of absorbing light. At the same time, fluorescence quenching increased from 94% to 96%, indicated that the deactivation process of the excited photoelectron transferred from porphyrin to graphene oxide was accelerated. Photoelectrochemical measurements indicated that ascorbic acid involved in the photoinduced electron transfer process of porphyrin/graphene oxide system, and played a role in electron transfer. We put forward the possible model of ascorbic acid involved in photoelectron transfer in porphyrin/graphene oxide nanohybrid system.