K α1 spectrometer

The investigation of the binding energy and ionization states of the existing atoms of the ZnO/MgO/Cr₂O₃ NFs were evaluated by XPS analysis performed on a K-α1 spectrometer (Thermo scientific, K-α1 1066) with an excitation radiation source (A1 Kα1, beam spot size = 300.0 μm, pass energy = 200.0 eV, pressure ∼ 10–8 torr). The photosensitivity and existing functional groups of the synthesized ZnO/MgO/Cr₂O₃ NFs were evaluated by the application of UV-Vis (Thermo Scientific) and FTIR (Thermo Scientific NICOLET iS50, Madison, WI, USA) spectroscopic analysis. The structural morphology and elemental compositions (shape, size, and structure) of the synthesized ZnO/MgO/Cr₂O₃ NFs were inspected by FESEM (JEOL, JSM-7600F, Japan) furnished with EDS. The phase crystallinity of the nanomaterial is an important measurable characteristic, and it is able to determine the unit cell dimension. Therefore, the phase crystallinity was studied by powder X-ray diffraction. The N₂ adsorption–desorption isotherms were carried out by the 3Flex analyzer (Micromeritics, USA) at 77.0 K. The specific surface area (SBET) was calculated using multi-point adsorption data from the linear segment of the N₂ adsorption isotherms using BET theory. Finally, the electrochemical detection was performed by a Keithley electrometer (USA).

The following instruments and methods were used to complete the characterization, electrode preparation, and sensor application of the NPs. To investigate the photosensitivity of the calcined ZnO/NiO/MnO₂ NPs, a 300 UV/visible spectrophotometer (Thermo Scientific) was implemented to measure the UV-vis spectra, and a NICOLET iS50 FTIR spectrometer (Madison, WI, USA) was used in the range of 400–4000 cm⁻¹ to identify the functional groups. The oxidation states and binding energies of species were measured by X-ray photoelectron spectroscopic (XPS) analysis using a Kα1 spectrometer (Thermo Scientific, Kα 1066). Beside this, the morphology of the prepared ZnO/NiO/MnO₂ NPs was inspected by field emission scanning electron microscopy (FESEM, JEOL, JSM-7600, Japan), and the respective elemental analysis was executed by energy dispersive X-ray spectroscopy (EDS, JEOL, Japan). Moreover, the crystallinity of synthesized NPs was analyzed by X-ray diffraction. Electrochemical investigations were carried out using an electrometer (651-Keithley Electrometer, USA).