Nexsa spectrometer

The structure and morphology of the samples were characterised by a wide range of analytical techniques. The size and microstructure of samples were studied by transmission electron microscope (FEI Titan Themis 300: X-FEG 300 kV S/TEM). A software ‘ImageJ (1.46r)’ was used to measure the particle size from TEM images. X-ray photoelectron spectroscopy (XPS) was used to analyse the surface elemental composition on a Thermo Scientific NEXSA spectrometer. Samples were analysed using a micro focused monochromatic Al X-ray source (72 W) over an area of approximately 400 µm. Data were recorded at pass energies of 200 eV for survey scans and 50 eV for high resolution scan with 1 eV and 0.1 eV step sizes, respectively. Raman spectra were obtained through a Renishaw plus Raman spectrometer using 532 nm laser excitation. Fourier transform infrared (FTIR) spectra were recorded on a Bio-Rad FTIR spectrometer (Cary 630 FTIR, Agilent Technologies) using Diamond ATR.KBr tip. The pH of the samples was monitored with the help of pH meter (Mettler Toledo, FiveEasy pH meter). The absorption and fluorescence spectra were recorded on Shimadzu UV-1800 spectrophotometer and Shimadzu RF-6000 spectrofluorophotometer, respectively.

The measurement was performed on a Thermo Fisher Scientific NEXSA spectrometer. The samples were analysed using a micro-focused monochromatic Al X-ray source (72 W) over an area of approximately 400 microns. Data were recorded at the pass energies of 200 eV for survey scans (1.0 eV step) and 50 eV for the high-resolution scans (0.1 eV step). Charge neutralisation of the sample was achieved using a combination of both low energy electrons and argon ions. C 1s electron at 284.8 eV was used as the standard reference to calibrate the photoelectron energy shift. XPS spectra in Ce 3d region from 840 to 940 eV was collected and fitted to identify the ratio of Ce in different oxidation states. Data analysis were performed on the CasaXPS software (version: 2.3.18PR1.0).

X-ray photoelectron spectroscopy (XPS) analysis was carried out using a Nexsa spectrometer (Thermo Scientific, Sunnyvale, USA) equipped with a monochromatic, micro-focused, low-power Al Ka X-ray source (photon energy: 1486.6 eV). High-resolution spectra were acquired at a pass energy of 50 eV. The source power was typically 72 W. The measurements had been carried out under ultra-high-vacuum conditions, at a base pressure of 5 × 10⁻¹⁰ torr (and no higher than 3 × 10⁻⁹ torr). The obtained spectra were analyzed and deconvoluted using Vision software (Kratos). Overlapping signals were analyzed after deconvolution into Gaussian/Lorentzian-shaped components.