# Sustainable Organic Dyes from Winemaking Lees for Photoelectrochemical Dye-Sensitized Solar Cells
## 2 Materials and Methods
### Characterization Techniques  
Nitrogen physisorption at -196 \({}^{\circ}\)C with an ASAP 2010 Micrometrics sportometer characterized the textural properties of titanium dioxide. The samples (about 0.1 g) were treated first at 130 \({}^{\circ}\)C for 12 h at 0.67 Pa and then at RT for 2 h at 1 \(\times\) 10\({}^{-4}\) Pa. The well-known BET equation was applied and the specific pore volume (V\({}_{\text{s}}\)) was calculated at P/P\({}_{0}\) = 0.98 to determine the specific surface areas. The pore size distribution was calculated according to the BJH method. X-Ray Diffraction (XRD) was used to determine the crystalline phases of titania, by using a Philips X'Pert system (Bragg-Brentano parafocusing geometry) with a nickel-filtered Cu K\(\alpha_{1}\) radiation at 0.154 nm. The samples (disc shaped pressed powders) were analyzed before and after calcination. The anatase and rutile crystallite average size was determined on XRD peak broadening by the Scherrer equation (line width of the anatase (101) reflection at 20 = 25.3\({}^{\circ}\) and rutile (110) reflection at 20 = 27.4\({}^{\circ}\)):  
\[\tau=\frac{K\,\lambda}{\beta\,\cos\Theta} \tag{1}\]  
where \(\tau\) is the crystallite size, \(K\) the shape factor, \(\lambda\) is the X-ray wavelength for Cu K\(\alpha_{1}\) radiation, \(\beta\) is the line broadening at FWHM, and \(\Theta\) is the Bragg's angle. To obtain the anatase/rutile weight fraction, the following equation [28] was used:  
\[Anatase\,(\%)=\frac{100}{\left(1+1,265\,\frac{I_{R}}{I_{A}}\right)} \tag{2}\]  
where \(I_{A}\) and \(I_{R}\) are the peak intensities of the (101) and (110) reflections for anatase and rutile, respectively. Field-Emission-Gun Scanning Electron Microscopy (FEG-SEM) Zeiss with cutting-edge electro-optical design was used to study the size and morphology of the nanoparticles. Diffuse Reflectance Spectroscopy (DRS) determined the band gap of titania. The spectra were collected with a Perkin Lambda 35 UV-Vis spectrophotometer. Band gap energy, E\({}_{\text{g}}\), thoroughly determined the absorption coefficient \(\alpha\) value (m\({}^{-1}\)) from a plot of (\(\alpha\)hv)\({}^{0.5}\) versus photon energy (hv), where h is the Planck's constant and v is the frequency (s\({}^{-1}\)). The intercept of the tangent to the absorption curves was used to estimate the band gap (E\({}_{\text{g}}\)) value. The dye extraction process was monitored by an Agilent 8453 UV-Vis spectrophotometer, following the absorbance at the maximum of UV-Vis spectrum, after water dilution. Dye solutions were characterized by various methods to determine the concentrations of anthocyanins, catechins, tannins, polyphenols, and color intensity. Anthocyanins that were extracted from winemaking lees were determined by the procedure of [PERSON] (1965) [29] with the bisulphite bleaching as anthocyanins form colorless compound with the bisulphite ion, thus transferring from the red colored flavylium cation to a non-colored form. The catechins were determined according to the method proposed by [PERSON] et al. [30], while using DAC (4-(dimethylamino)cinnamaldehyde). The assay was performed using a chromogen reagent of 1.0 g DAC dissolved in 250 mL of 37% HCI and 750 mL methanol. To 1 mL of 1:25 (v/v) diluted sample, 5 mL of DAC solution were added and, after 5 minutes, the maximum value of absorption at 640 nm was measured against a blank that was prepared by substituting sample with 1 mL of 10% ethanol. Tannins characterization was carried out following the Weinges and Nader method [31]: the sample was diluted fifty times and 2 mL of solution was added to a tube containing 6 mL of acidized butyl alcohol prepared by dissolving 150 mg Fe(SO\({}_{4}\)) in 500 mL of 1-butanol and 500 mL of HCI 37%. Half of this solution was put in an oven at 100 \({}^{\circ}\)C for 30 minutes. After cooling, the optical density was measured at 550 nm for both solutions against water.