The relation between structural, optical, and electronic properties of composite CuO/ZnO in supporting photocatalytic performance

Phase transformation, structural and optical properties of ZnO/ CuO composite for various milling times were studied by means of X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy, respectively. The refractive index (n), extinction coefficient (k), dielectric function, energy- loss function (Im(-1/(epsilon)), and optical absorption coefficient were determined from the quantitative analysis of FTIR spectra by applying Kramers-Kronig relation. Density of states (DOS) was analyzed using Quantum ESPRESSO package. For milling time up to 12 h, crystalline phase is dominant and for > 12 h, phase transformation changed from crystalline to amorphous. The crystallite size shows a decrease with increasing the milling time due to Zn and Cu atoms spreading each other and producing the individual crystalline structure. For 20 h milling time, it shows the minimum distance (Delta) between two optical phonon modes due to the enlarging lattice. For various milling time, the density of states (DOS) is similar for each composite due to the crystalline phase (%) for composites also similar. The best degradation percentage is 96.8% and only 30 min irradiation time for sample 1 h milling. For milling 20 h up to 52 h, the degradation decreases from 93.10% to 78.5% and up again to 91.5% for 56 h milling which the trend is opposite with longitudinal optical phonon mode. This study shows powerful method for determining optical properties from FTIR spectra and effective way to investigate the transformation phase and structural properties from XRD spectra of CuO/ZnO composite.