Anthocyanins Immobilization on Titania Nanotubes and Its Characterization through Cyclic Voltammetry: Preliminary Results
Authors: Martinez-Pacheco Mariana , Lozada-Ramirez Jose Daniel , Ortega-Regules Ana , Cerro-Lopez Monica 
Published: February 2020

Titania nanotubes grown on titanium through the electrochemical anodization are an attractive nanostructure due to their applicability in areas such as photocatalysis, dye-sensitized solar cells, sensors, etc. Nanotubes functionalization with nanoparticles or different molecules is becoming a common practice that can either aid or enhance their performance in a variety of applications. Dyes have been used in solar cells and photocatalysis to sensitize the semiconductor and, biological dyes such as anthocyanins have been tested for these purposes due to their low cost and environmentally friendly nature (1).
In this work, titania nanotubes electrodes were functionalized with anthocyanins in order to test their performance as sensitizers for photoelectrocatalytic purposes. Anthocyanins alcoholic extract has been obtained from hibiscus flower (Hibiscus sabdariffa L) and immobilized on titania nanotubes (TiO2 Nts ) grown from 2 cm2 titania plates (TiO2 Nts/Ti) by anodization at 30 V in a glycerol:water (2:1) solution containing sodium fluoride and sodium sulfate. Anthocyanins immobilization was achieved through immersion for 48 h of the TiO2/Ti plates in the alcoholic extract at O°C. The antioxidant activity from both, the as-extracted and the immobilized, anthocyanins was tested by the ABTS assay. This essay showed that a 1:100 dilution from the extract had an antioxidant activity of 550 μTrolox while the immobilized anthocyanins had a higher antioxidant activity of 699 μTrolox (2).
Electrochemical techniques have gained importance in the study of nanostructured materials especially in the field of surface characterization. Within this work, cyclic voltammetry was used to determine surface characteristics from the bare TiO2 nanotubes and from the nanotubes functionalized with anthocyanins. Through cyclic voltammetry in a pH 7.00 1.0 M buffer phosphate it was possible to confirm TiO2 Nts functionalization with anthocyanins as it can be seen from the change in the voltamperogram´s shape for the bare nanotubes and after functionalization with anthocyanins (Figure 1). Cyclic voltammetry on anthocyanins-TiO2-Nts electrode showed two oxidation peaks at -0.390 V and -0.096 V (vs. mercurous sulfate electrode) which can be attributed to the delphinidin-3-O-glucoside (3), the main anthocyanin found in Hibiscus sabdariffa L (4). Complementary results concerning these electrodes performance will be presented at the conference.

References

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Janeiro, P., Oliveira-Brett, A. M. 2007. Redox behavior of anthocyanins present in Vitis vinifera L. Electroanalysis. 19(17): 1779-1786.

Galicia-Flores, L. A., Salinas-Moreno, Y., Espinoza- García, B. M. y Sánchez-Feria, C. 2008. Caracterización fisicoquímica y actividad antioxidante de extractos de jamaica (Hibiscus sabdariffa L) nacional e importada. Revista Chapingo Serie Horticultura. 14(2):121-129.

Figure 1