ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Characterization and application of the hetero-system LaCoO₃/ZnO for degradation of Orange II under solar light

A. Ouatizerga, G. Rekhila, S. Mirad, and M. Trari

URMPE Research Unity of Materials, Processes and Environment, Faculty of Technology, M. Bougara University, Boumerdes, Algeria

E-mail: rekhilagharib@gmail.com

Received: 16 February 2023  Accepted: 11 April 2023

Abstract:

LaCoO₃ elaborated by nitrate route was characterized physically and electrochemically to be applied in the Orange II (OII) oxidation upon solar light. The X-ray diffraction (XRD), SEM analysis and electrical conductivity were undertaken. The diffractogram showed that the single phase is completed at 850 °C and the oxide crystallizes in a distorted perovskite structure. The peak at 643 cm⁻¹ in the attenuated total reflection (ATR) spectrum confirmed the purity of the phase. The forbidden band (1.35 eV), determined from the diffuse reflectance, is assigned to Co³⁺: d-d transition in a low spin configuration (3d⁶, E_5/2) in conformity with the black color of the oxide. The field-dependent magnetization was measured at 300 K in the range ± 25 kOe, and the perovskite exhibits a low magnetism with a saturation magnetization (0.28 emu/g) confirming the low spin state Co³⁺. The thermal variation of the conductivity is characteristic of non-degenerate behavior and a hole mobility of 10⁻² cm² V⁻¹ s⁻¹ and an activation energy of 0.11 eV. The latter is different from that obtained from the thermo-power, a signature of a conduction mechanism by small polaron hopping. LaCoO₃ is chemically stable above pH 5; an exchange current density of 40 μA cm⁻², a polarization resistance of 1.92 kΩ cm² and a corrosion potential of 0.99 V_SCE were obtained at pH ~ 7 (Na₂SO₄, 0.1 M). Curiously and unlike the perovskites, the variation of the inverse of the square of the capacitance as a function of potential (C⁻²− E) indicates p type behavior with a flat band potential of 0.30 V_SCE and holes density of 1.97 × 10¹⁷ cm⁻³. The conduction band (− 0.94 V_SCE), made up of Co³⁺: 3d orbital, enables the formation of the radical O₂^•−, and as application, the oxide was successfully experimented for the oxidation of OII upon solar irradiation. The hetero-junction p-LaCoO₃/n-ZnO enhances considerably the photo-activity, due to the facile transfer of electrons with an abatement of 86% at neutral pH. The oxidation follows a first-order kinetic with a half photocatalytic life of 23 min.

Keywords: Perovskite LaCoO3; Semiconductor; Photo-electrochemical; Orange II; ZnO; Solar light

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-023-02830-3

Chemical Papers 77 (9) 4935–4942 (2023)