Photocatalytic Properties of Tetraphenylporphyrins Immobilized on Calcium Alginate Aerogels

Alexey V Krivandin,Anna B Solovieva,Peter S Timashev,Darya D Lovskaya,Svetlana L Kotova,Natalia V Menshutina,Alexander S Kopylov,Marina A Savko,Ilya V Shershnev,Artyom E Lebedev,Tatiana S Zarkhina

doi:10.1038/s41598-017-12945-9

Abstract

We have prepared photocatalytic systems based on tetraphenylporphyrins (TPP) immobilized on calcium alginate solid gels in the conditions of thermal drying on air (xerogel), freeze drying in vacuum (cryogel) and supercritical drying in the supercritical carbon dioxide (scCO2) medium (aerogel). As a test reaction to measure the prepared systems’ efficiency, we studied tryptophan photooxidation in the aqueous medium. We have demonstrated that the systems with aerogel as a carrier exhibited the highest photocatalytic efficiency. In that case, the rate constant for the test substrate (tryptophan) oxidation exceeds the corresponding rate constants of similar systems based on xerogel and cryogel by more than 5 times. Moreover, the aerogel-based photocatalytic systems demonstrated enhanced functional stability and a possibility of multiple use of such a catalyst in tryptophan oxidation. Based on the data of small-angle X-ray scattering and thermooxidative destruction, we have made a conclusion about the relationship between the high photocatalytic activity of aerogel-immobilized TPP and formation of a developed porous aerogel structure in the conditions of drying in the scCO2 medium, which is stabilized due to formation of additional complex bonds of calcium ions with fragments of glycoside rings.

Highlights

Aerogel (AEG) is a unique 3D-arranged nanostructured highly porous material with a low density (0.003– 0.35 g/cm3), high area of the inner surface, pore sizes of an order of several nanometers[2,3]
We have shown that the most active catalytic systems are formed by TPP immobilization on aerogels, with the activity of the prepared systems preserved during repeated use in a model process of tryptophan photooxidation in the aqueous medium
The basic result of our study on the prepared systems’ photocatalytic activity in the tryptophan oxidation consists in the finding of the highest activity of the AEG/TPP system as compared to the systems based on porphyrins immobilized on xero- and cryogels

Summary

Introduction

Aerogel (AEG) is a unique 3D-arranged nanostructured highly porous material with a low density (0.003– 0.35 g/cm3), high area of the inner surface (up to 1000 m2/g), pore sizes of an order of several nanometers[2,3]. We have prepared such systems by immobilization of tetraphenylporphyrin (TPP) and its derivatives, as most active photosensitizers of singlet oxygen generation, on solid calcium alginate gels.

Results

Conclusion