Currently I am studying about photocatalysis experiment of TiO2 in degrading Rhodamine B dye solution. For the condition I am using 2 condition setup which use the TiO2 in its powdered form directly into the solution and the other ones makes the TiO2 deposited in a membrane of PES that was LbL assembled with ionic PAH and PSS. I got a hypsochromic in the colloidal and no hypsochromic in membrane state. Anyone have a clue what might cause this? I know that TiO2 indeed having 2 kind of reaction when photosensitized with Rhodamine B but the results of the membrane setup reaction is not acting as I expected
The hypsochromic shift is due to the N-deethylation process and it takes place when the TiO2 is sensitized with Rhodamine B under visible light irradiation. The other mechanism is chromophore destruction which results in solution decolorization. But - the pH can influence degradation mechanism strongly. When Rhodamine cannot adsorb via amino groups on photocatalyst surface due to the electrostatic repulsion - the electron transfer and sensitization cannot be efficient, thus the deethylation is supressed. Therefore you can see different behavior of the dye on spectra. I recommend you to measure pH of your solution and measure the zeta potential of both your photocatalysts in this pH because it really has strong influence on the mechanism.
Please find also these papers - I hope they will help you:
Article pH-Control of the Photocatalytic Degradation Mechanism of Rh...
Article Understanding the Role of Silver Nanostructures and Graphene...
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