*2.3. Characterization*

The crystalline structure of the samples was analyzed by a Rigaku D/Max 2500 powder diffractometer (XRD) (Tokyo, Japan) with Cu Kα radiation (λ = 1.5406 Å). The morphology of the as-prepared samples was characterized by field-emission scanning electron microscopy (FESEM, FEI SIRION 200, Hillsboro, OR, USA), and transmission electron microscopy (TEM, Philips Tecnai 20 G2 S-TWIN, Hillsboro, OR, USA). X-ray photoelectron spectroscopy (XPS) data of the samples were determined with a K-Alpha 1063 electron spectrometer from Thermo Fisher Scientific (East Grinstead, West Sussex, UK) using 72W Al Kα radiation. Infrared spectroscopy analysis (IR) of the samples was performed on an AVATAR360 IR analyzer (Madison, WI, USA). UV-vis diffuse reflectance spectra (UV-vis) were measured with a Specord 200 UV spectrophotometer (Schönwalde-Glien, Germany).
