Phi 5000 versa probe 2 spectrometer

X-ray photoelectron spectroscopy was performed on a PHI 5000 Versa Probe II spectrometer (ULVAC-PHI, Inc., USA). The excitation source was monochromatized Al Kα radiation (hν = 1486.6 eV), with power of 50 W and beam diameter of 200 µm. We used a charge neutralization system because a slight electrostatic charge was observed, which distorted the spectra. Atomic concentrations were determined from survey spectra using the relative elemental sensitivity factors of the C1s, O1s, N1s, and S2p lines. The binding energies, Eb, of photoelectronic lines were determined from high-resolution spectra, taken at an analyzer transmission energy of 23.5 eV and a collection density of 0.2 eV/step. The binding energy scale, Eb, was calibrated for Au4f—83.96 eV—and Cu2p3—932.62 eV. The Eb scale was corrected for the first peak in the C1s spectrum (with the lowest Eb value of 284.7 eV), since the samples contain a large number of carbon atoms in aromatic fragments—the presence in the C1s spectrum with Eb peak in the region of 291 eV, the so-called shake-up satellite representing sp2 carbon bonds.

Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were obtained using a JEOL JEM-2100 microscope (JEOL, Japan) at an acceleration voltage of 80 kV or 200 kV, respectively. X-ray diffraction (XRD) characterizations were obtained using a Bruker D8 Advance diffractometer with a copper Ka (k = 0.154056 nm) radiation source. X-ray photoelectronspectroscopy (XPS) measurements were obtained using a PHI5000 Versaprobe-II spectrometer (ULVAC-PHI, Japan) with a monochromatic Al Ka (1486.6 eV) source. The UV absorption spectra were obtained with a UV-6300 spectrophotometer (Mapada instruments Ltd., Shanghai, China). The photoluminescence spectra were obtained using an FS5 spectrophotometer (Edinburgh instruments Ltd., Livingston, UK). The fluorescence images were obtained with an upright fluorescence microscope (i203 type, Chongqing UOP, Chongqing, China) and an Eclipse Ni-U (Nikon Ltd., Tokyo, Japan) fluorescence microscope. Fourier-transform Infrared Spectrometer (FTIR, Thermo Fisher Scientific Ltd., Waltham, MA, USA) was employed to carried out IR spectra. Atomic force microscope (AFM, Dimension Icon, Bruker Co. Ltd., USA) was used to obtain AFM images. The particle size distribution and zeta potential were studied by dynamic light scattering (DLS) using Malvern Zetasizer (Malvern Instruments Ltd., Malverm, UK).