Gas adsorption properties of complex copper oxides

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Highly epitaxial films of CuFeO2 and CuFe0.75Ga0.25O2 were grown by pulsed laserdeposition (PLD) from stoichiometric targets over Al2O3 (001) substrate undercontrolled partial pressure of oxygen as carrier gas. Resulting films were highly orientedin c-axis direction.Structural properties of samples were characterized by X-Ray Diffraction (XRD), Raman spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), optical transmittance and diffuse reflectance. This characterization techniques confirmed the rhombohedral Delafossite crystal structure for both kind of samples and CuFe0.75Ga0.25O2 samples were formed by an alloy between CuFeO2 and CuGaO2 Delafossite materials. Using optical transmittance and diffuse reflectance, the optical transitions were estimated by using theTauc method. Direct optical transitions were measured at 1.28±0.02 eV and 2.20±0.05eV for pure CuFeO2 samples and for CuFe0.75Ga0.25O2 were measured at 1.50±0.04 eVand 2.30±0.09 eV, plots showed another higher transition near 3 eV but due to technical limitations this gap cannot be clearly determined. Adsorption of CO2 and H2O was studied via thermal programmed desorption technique. In both films Copper and Iron were present at the surface, and consequently formed part of the surface-gas interface. X-ray photoelectron data indicated that CO2 is adsorbed preferentially at copper sites forming a similar coordination to CuCO3. The energy for desorption of CO2 and H2O was estimated to be 1.0±0.8 eV/molecule for CuFeO2 and0.7±0.4 eV/molecule for CuFe0.75Ga0.25O2. Also, it was possible to correlate second order desorption with a CO2 reduction reaction. Copper Delafossite materials studied in this work showed some catalytic activity in good agreement with the literature. Future work in this field would involve synthesis of a wider variety of CuFe1-xGaxO2 samples in order to get a better idea of the influence ofiron substitution for gallium in the Delafossite structure. Also, for a better understanding of the relationship between adsorption properties and catalytic behavior some futurework regarding electrical and electrochemical properties is proposed
Tesis (Doctor in Physics)--Pontificia Universidad Católica de Chile, 2017