fig2

Figure 2. Physicochemical characterizations. (A) XRD patterns of the mesoporous Nb₂O₅ microspheres before and after calcination; (B) Nitrogen adsorption-desorption isotherms; and (C) pore size distribution curve of the mesoporous Nb₂O₅ microspheres; (D) Raman spectrum of the mesoporous Nb₂O₅ microspheres; High-resolution XPS spectra of (E) Nb 3d, and (F) O 1s; (G-J) EDS images of the mesoporous Nb₂O₅ microspheres. XRD: X-ray diffraction; XPS: X-ray photoelectron spectra; EDS: energy dispersive X-ray spectrometry.