Escalab 250 high performance electron spectrometer

p-Phenylenediamine (p-PDA) and (3-aminopropyl)trimethoxysilane (APTMS) were purchased from Aldrich. Sodium citrate, NaOH, H₂SO₄, ethanol and all the metal salts were supplied by Sinopharm Chemical Reagent Company, Ltd (Shanghai, China). All chemicals were used as received without further purification unless otherwise specified. Ultrapure water (18.2 MΩ cm) was prepared with a Millipore water purification system.
The structure and morphology were examined using a JEOL 2010 transmission electron microscope. Fluorescence spectra were recorded with a Cary Eclipse fluorescent spectrophotometer. The UV–visible absorption spectra were obtained with a Shimadzu UV-2550 spectrometer. Fourier transform infrared (FT-IR) spectra were obtained with a Thermo Fisher Nicolet iS10 FT-IR spectrometer. X-ray photoelectron spectroscopy (XPS) measurements were carried out with a Thermo ESCALAB 250 high performance electron spectrometer with Al Kα (1486.6 eV) radiation. Fluorescent photos were taken under an AGL-9406 portable UV lamp (365 nm) by a Canon 350 D digital camera.