Absorption spectra of dyes and the dyes adsorbed onto the TiO2 surface
The UV–Vis absorption spectra of the dye and the dye after adsorbed onto TiO2 surface are shown in Figs. 1 and 2, respectively,for the dye obtained from the fruits of ivy gourd and flowers of
red frangipani. The photographic images of collected fruits of ivy gourd and flowers of red frangipani are shown as insets in Figs. 1 and 2, respectively. A clear difference in the absorption characteristics is observed between the extracts obtained from fruits of ivy gourd and flowers of red frangipani. The ivy gourd fruit extract shows broad absorption level between 400 and 550 nm with doublet absorption maxima at 458 and 480 nm and shoulder peaks at around 425 and 520 nm as shown in Fig. 1. Ivy gourd is identified to be rich in b-carotene as reported earlier [16,20]. The absorption peaks observed in the present investigation for fruit extract of ivy gourd agrees with the absorption spectra of b-carotene as reported in literature [21,22].
No significant shift was observed in the absorption spectrum of ivy gourd fruit extract adsorbed onto TiO2 surface as shown in Fig. 1. This may be due to the absence of binding groups such as hydroxyl or carboxylic groups in b-carotene.
The UV–Vis absorption spectrum for the flowers of red frangipani extract shown in Fig. 2 reveals the absorption between 450 and 600 nm with absorption maxima at 530 nm. Recent investigations indicated that anthocyanins are responsible for the attractive colors of the flowers of red frangipani with absorption maxima at 520 nm [17]. High-resolution liquid chromatography–mass spectrometry (LC–MS) investigations on the extract of red frangipani
flower indicates signals of molecular ions (M+) at m/z 611 and 449 as shown in Fig. 3, which agrees well with the earlier high resolution liquid chromatography–electrospray mass spectrometry (ESI+/TOF) studies [17]. Byamukama et al. predicted that the molecular ion observed at m/z 611.1581 corresponds to cyanidin 3-O-b-(200-glucopyranosyl-O-b-galactopyranoside) with the empirical formula C27H31O16 and the molecular ion observed at m/z 449.1068 corresponds to cyanidin-3-O-b-galactopyranoside with the empirical formula C21H21O11 [17].
The absorption spectrum for the red frangipani extract adsorbed on TiO2 surface shown in Fig. 2 is broader and exhibit a clear red shift of the absorption peak from 530 to 562 nm. This
red shift indicates that extracts are well adsorbed onto TiO2 surface and may increase the absorption of light by the TiO2 particles in the visible region due to the binding of anthocyanins present in the extract to the oxide surface [8,23].