Mg-Containing Zn₃O₃ Structures for Detection of CO₂: A DFT Study on CHEM Effects of SERS and Electronic Properties

Surface-enhanced Raman spectra (SERS) and electronic-structure-based properties are important tools for investigation of the molecular sensing ability of nanoparticles. The present computational study is intended to explore the sensing ability of Zn₃O₃ and Mg-containing Zn₃O₃ structures for CO₂ molecules by CHEM effects of the SERS technique. Geometries of CO₂-adsorbed Zn₃O₃, Zn₂MgO₃ (Mg as a substitutional impurity), and Zn₃O₃Mg (Mg as an interstitial impurity) structures are modeled using the B3LYP/6-31G(d,p) level of density functional theory. The Mg site of the Zn₂MgO₃ and Zn₃O₃Mg structures is preferential for the adsorption of CO₂. The observed energy trends are supported by geometrical analysis, molecular orbital interactions, redshifts in CO₂ vibrational modes, and topological properties. Raman activity enhancement of the CO₂ symmetric vibrational mode is significant when the molecule is adsorbed at the Mg site of Zn₃O₃Mg. The observed Raman activity enhancement is supported by SERS spectra obtained from anharmonic calculations carried out on B3LYP/6-31G(d,p) geometries and substantiated by a larger change in the polarizability with energy corresponding to the symmetric vibrational mode of CO₂. The TDDFT calculations, frequency-dependent polarizabilities, and charge transfer interactions show that Zn₃O₃Mg is a good substrate for sensing of CO₂, with visible wavelengths, by resonance Raman effect. The trends with adsorption energy, Raman activity, and excited state properties are also substantiated by B3LYP/6-311+G(d,p) calculations.