(HRTEM, JEM-2100). Thermogravimetric analysis (TGA) was carried out to monitor the mass loss of products at a heating rate of 10 C min 1 from 25 to 700 C under an air atmosphere
(Mettler Toledo, TGA/SDTA851e). N2 adsorption–desorption isotherms were measured on a QuadraSorb SI apparatus at 77 K.The surface areas were calculated by the Brunauer–Emmett–Teller (BET) method, and the pore size distribution was calcu-lated from the desorption branch using the Barrett–Joyner–Halenda (BJH) theory.