Effect of acidity on the energy level of curcumin dye extracted from Curcuma longa L.

The purpose of this research is to investigate the effect of acidity on the energy level of curcumin dye. The natural dye, curcumin, was synthesized from Curcuma longa L. using a simple extraction technique. The purification of curcumin dye was conducted in a column of chromatography and its characteristics were studied. Next, the purified curcumin dye was added by benzoic acids until various acidities of 3.0, 3.5, 4.0, 4.5, and 5.0. The absorbance spectra and the functionality groups found in the dyes were detected by ultraviolet-visible spectroscopy and Fourier-transform infrared spectroscopy, respectively. Meanwhile, the energy level of the dyes, E_HOMO and E_LUMO was measured by cyclic voltammetry. The best energy level of curcumin dye was achieved at pH 3.5 where E_red = −0.37V, E_LUMO = −4.28 eV, E_ox = 1.15V, E_HOMO = −5.83 eV, and E_{band gap} = 1.55 eV. Therefore, the purified curcumin dye added by benzoic acid was promising for sensitizing the dye-sensitized solar cells.