2.3. Characterization

A powder X-ray diffractometer (XRD, Bruker D8-Advance, Germany) was used to characterize the crystal structure of as-synthesized samples. A field-emission scanning electron microscope (FE-SEM, Hitachi, Tokyo, Japan) with an energy dispersive X-ray spectroscopy (EDS) was used to characterize the morphologies and elemental analyses of samples. The microstructures of the samples were further measured on the transmission electron microscopy (TEM, FEI Tecnai G20, Hillsboro, OR, USA), operating at 200 kV. The X-ray photoelectron spectroscopy (XPS) measurement was carried out by using an Escalab 250Xi system with a Al Kα radiation source (1486.6 eV). Fourier transform infrared (FT-IR) spectra were recorded on a FTIR spectrometer (Thermo Fisher Nicolet 6700, Waltham, MA, USA) using the standard KBr disk method. The UV-Vis diffuse reflectance spectra (UV-Vis DRS, Puxi TU-1901, Beijing, China) of the as-prepared photocatalysts were measured with a UV-Vis spectrometer (Puxi TU-1901, Beijing, China), in the range of 230–750 nm, using BaSO₄ as a reference.