Axis ultra instrument

GO was characterized by transmission electron microscopy (TEM, JEM-200CX, JEOL, Japan), AFM (SPM-9600, Shimadzu, Japan), and Raman spectroscopy (Renishaw Invia Plus laser Raman spectrometer, Renishaw, UK). Zeta potential analyzed by the Nano Zetasizer using a dynamic light scattering (DLS) technique. To perform AFM measurement, a few drops of the GO suspension was pipetted on Si substrates, and then the substrates were air-dried and placed under the AFM tip for morphology analysis. Elemental composition analysis was carried out by XPS (AXIS Ultra instrument, Kratos, UK).

The surface characteristics of the BiVO₄-n electrodes were investigated by field-emission scanning electron microscopy (FESEM, Zeiss Merlin, Germany). Surface roughness analysis was carried out by atomic force microscopy (AFM, Agilent 5400SPM, Agilent Technologies, USA), at scan areas of 2.0 × 2.0 μm and 5.0 × 5.0 μm for all samples. Powdered X-ray diffraction (XRD, Bruker D8 Advance diffractometer, USA, using Cu Kα radiation, λ = 1.5418 Å) was used to characterize the crystallinity of the samples. All samples were analyzed by XRD in the range of 15–70° at a scan rate of 0.5° min⁻¹; the crystal sizes of the BiVO₄-n were estimated with the Scherrer formula.^{32 (link)} The diffuse reflectance UV-Vis absorption spectra of the samples were recorded with a spectrophotometer (UV 2550, Shimadzu, Japan), with fine BaSO₄ powder as a reference. In thermal gravimetric analysis (TGA, NETZSCH, Germany),100 μL precursor was vacuum-dried for 5 h prior to the measurements. X-ray photoelectron spectroscopy (XPS) results were collected by an Axis Ultra instrument (Kratos Analytical) under ultrahigh vacuum (<10⁻⁸ torr) and by using a monochromatic Al Kα X-ray source. The adventitious carbon 1s peak was calibrated at 285 eV and used as an internal standard to compensate for any charging effects.

For the XPS measurement, the same concentrations (750 mg/L) of GO/CFGOs aqueous dispersion were prepared. Then, 0.09 g cement and 60 g GO/CFGOs aqueous dispersion was added into a beaker flask. For the pure cement sample, 0.09 g cement was added in 60 g water. The mixture was vibrated in the oven-controlled crystal oscillator at room temperature for 5 h. Finally, the mixture was vacuum filtered. The filter cake can be used to test the adsorption layer thickness of GO/CFGOs on the surface of cement. The XPS analysis was carried out on an AXIS–Ultra instrument from Kratos Analytical (Manchester, UK) using monochromatic Al Ka radiation (225 W, 15 mA, 15 kV) and low–energy electron flooding for charge compensation. To compensate for surface charges effects, binding energies were calibrated using C1s hydrocarbon peak at 284.80 eV.

X-ray photoelectron
spectroscopy (XPS) measurements were carried out using a Kratos AXIS
ULTRA instrument with a monochromatic Al Kα X-ray source (1486.6
eV) at 12 kV anode potential (120 W) and 10 mA emission current.

The microtubes were grounded to powder for XRD and XPS analyses. In addition, a standard undoped n-type ZnO substrate was employed as the control sample for the XPS analysis. The XRD used Cu-Kα1 (λ = 1.5418 Å) radiation generated at 36 KV/20 mA at a scanning speed of 0.02° min⁻¹ in the range of 20°–80°. The XRD date was indexed by hexagonal wurtzite-type ZnO (JCPDS No. 80-0074). The XPS data were acquired by an AXIS-Ultra instrument from Kratos Analytical with monochromatic Al Kα radiation (225 W, 15 mA, and 15 KV) and low-energy electron flooding for charge compensation. In order to compensate to surface charges, binding energies were calibrated using C_1s hydrocarbon peak at 284.80 eV.

The morphologies electrodes were characterized by scanning electron microscopy (SEM, FEI, Quanta 600). The crystalline structure of the samples was analyzed by X-ray diffraction (XRD) (Bruker D8 Discover diffractometer, using Cu Kα radiation (1.540598 Å)). The chemical compositions and status were analyzed by X-ray Photoelectron Spectroscopy (XPS) with an Axis Ultra instrument (Kratos Analytical) under ultrahigh vacuum (<10⁻⁸ torr) and by using a monochromatic Al Kα X-ray source. The adventitious carbon 1 s peak was calibrated at 284.8 eV and used as an internal standard to compensate for any charging effects.