Enhanced Optical Properties of ZnO-TiO₂ Films Through Co-Sensitization with Multiple Natural Dyes

The ZnO-TiO₂ films were co-sensitized with single, double, and triple natural dyes, leading to distinct effects on the optical properties. ZnO (wurtzite) and TiO₂ (anatase) were prepared from commercial powders and the XRD results revealed that the crystallite size is 158 and 443 nm, respectively. The UV absorbance of ZnO powder shows significant peaks at wavelengths of 255 and 345 nm, with a band gap energy of 3.07 eV. Meanwhile, TiO₂ powder exhibits a maximum peak at 325 nm and possesses a band gap energy of 3.16 eV. The extraction of natural dyes (Moringa oleifera, Biancaea sappan, Matricaria chamomilla, Rosa, and Chrysanthemum) was carried out using a cost-effective and simple method involving immersion in ethanol for 2 × 24 h followed by filtration. FTIR test results show the presence of O–H, C–H, C=C, and C–O functional groups. The results of coating the ZnO-TiO₂ film with natural dyes show that the UV spectrum peaks are higher than the visible light wavelength. Co-sensitization of double natural dyes demonstrated different effects on the ZnO-TiO₂ film, i.e., achieved panchromatic absorption mainly in the UV wavelength spectrum.