X-ray diffraction (XRD) patterns and average crystal size were
collected with Bruker axs, D8 Advance. N2 adsorption and desorption
isotherms were obtained at 77 K using a volumetric
adsorption apparatus (Nova2000 series, Chromatech). The pore
structures were estimated according to the Brunauer–Emmett Teller
(BET) method.