fig3

Figure 3. Porosity regulation. (A-E) SEM images of the mesoporous Nb₂O₅ microspheres after calcination at varied temperatures from 500 to 700 °C in air. Scale bars in (A-E) are all 200 nm; (F) Planar structural illustrations of the mesopores accumulated from Nb₂O₅ grains. The d_pore stands for the mesopore size and the d_grain is grain size; (G) XRD patterns; (H) nitrogen adsorption-desorption isotherms and (I) pore size distribution curves of the mesoporous Nb₂O₅ samples calcined in air at different temperatures from 500 to 700 °C; (J) Plots of variations for mesopore and grain size versus calcination temperature. SEM: Scanning electron microscopy; XRD: X-ray diffraction.