Enhancement of the CO2 Sensing/Capture through High Cationic Charge in M-ZrO2 (Li+, Mg2+, or Co3+): Experimental and Theoretical Studies

Abstract

The capture and storage of CO₂ are of growing interest in atmospheric science since greenhouse gas emission has to be reduced considerably in the near future. The present paper deals with the doping of cations on ZrO₂, i.e., M-ZrO₂ (M = Li⁺, Mg²⁺, or Co³⁺), defecting the crystalline planes for the adsorption of carbon dioxide. The samples were prepared by the sol-gel method and characterized completely by different analytical methods. The deposition of metal ions on ZrO₂ (whose crystalline phases: monoclinic and tetragonal are transformed into a single-phase such as tetragonal for LiZrO₂ and cubic for MgZrO₂ or CoZrO₂) shows a complete disappearance of the XRD monoclinic signal, and it is consistent with HRTEM lattice fringes: 2.957 nm for ZrO₂ (101, tetragonal/monoclinic), 3.018 nm for tetragonal LiZrO₂, 2.940 nm for cubic MgZrO₂, and 1.526 nm for cubic CoZrO₂. The samples are thermally stable, resulting an average size of ∼5.0-15 nm. The surface of LiZrO₂ creates the oxygen deficiency, while for Mg²⁺ (0.089 nm), since the size of the atom is relatively greater than that of Zr⁴⁺ (0.084 nm), the replacement of Zr⁴⁺ by Mg²⁺ in sublattice is difficult; thus, a decrease of the lattice constant was noticed. Since the high band gap energy (ΔE > 5.0 eV) is suitable for CO₂ adsorption, the samples were employed for the selective detection/capture of CO₂ by using electrochemical impedance spectroscopy (EIS) and direct current resistance (DCR), showing that CoZrO₂ is capable of CO₂ capture about 75%. If M⁺ ions are deposited within the ZrO₂ matrix, then the charge imbalance allows CO₂ to interact with the oxygen species to form CO₃^2- which produces a high resistance (21.04 × 10⁶ (Ω, Ohm)). The adsorption of CO₂ with the samples was also theoretically studied showing that the interaction of CO₂ with MgZrO₂ and CoZrO₂ is more feasible than with LiZrO₂, subscribing to the experimental data. The temperature effect (273 to 573 K) for the interaction of CO₂ with CoZrO₂ was also studied by the docking method and observed the cubic structure is more stable at high temperatures as compared to the monoclinic geometry. Thus, CO₂ would preferably interact with ZrO₂^c (E_RS = -19.29 kJ/mol) than for ZrO₂^m (22.4 J/mmol (ZrO₂^c = cubic; ZrO₂^m = monoclinic).

Keywords: DFT studies; ZrO2; capture/sensing of CO2; crystal phase change; metal doping.