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

Physical and photo-electrochemical properties of NiCr₂O₄/ZnO: application to the photo-oxidation of OII under solar light

S. Mirad, G. Rekhila, Y. Azoudj, and M. Trari

Laboratory of Storage and Valorization of Renewable Energies, Faculty of Chemistry, USTHB, Algiers, Algeria

E-mail: rekhilagharib@gmail.com

Received: 15 April 2024  Accepted: 23 July 2024

Abstract:

The photoelectrochemical characterization of the spinel NiCr₂O₄ synthetized by sol gel route was investigated. The thermal analysis showed that the single phase is formed above 530 °C as confirmed by X-ray diffraction. The direct optical transition (1.79 eV), determined from the diffuse reflectance, is assigned to the lifting degeneracy of Cr³⁺: 3d³ orbital octahedrally bonded to O²⁻ ions. Field-dependent magnetization, measured at 300 K in the range (± 20 kOe), shows a maximum magnetization of ~ 0.16 emu/g with no saturation and a weak coercivity of 67 Oe. The thermal variation of the electrical conductivity indicates localized 3d-electrons and the data are fitted by a low lattice-polaron hopping with an activation energy of 0.17 eV, characteristic of a semiconducting behavior. A flat band potential (E_fb) of − 0.23 V_SCE with p-type nature was deduced from the variation of the capacitance (C⁻²) on the potential (E) of the junction NiCr₂O₄/Na₂SO₄. The p-type conduction is corroborated by the positive thermo-power (S_300K = 123 µV K⁻¹), supporting the non-degenerate semi-conductivity. The electron transfer from the conduction band (− 1.85 V_SCE) to dissolved oxygen is predicted from the potential diagram, constructed from the physic-chemical properties; this allows the oxidation of Orange II (O II) upon solar light. Similarly, ZnO enhanced the photoactivity by 68% with loading the spinel as sensitizer. O II is mineralized by O₂^•− radicals at pH ~ 7 within 1 h on the heterosystem NiCr₂O₄ (60%)/ZnO for O II concentration of 20 mg L⁻¹. The removal color obeys a pseudo first order kinetic with a rate constant of 0.023 min⁻¹ (t_1/2 = 23 min).

Keywords: Spinel NiCr2O4; Magnetism; Photoelectrochemical; Orange II; Photocatalysis; Solar light

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-024-03626-9

Chemical Papers 78 (13) 7623–7631 (2024)