MBG was prepared by a modified sol–gel method, as shown in Figure 1 . In detail, cetyltrimethylammonium bromide (3.6 g) and trimethylamine (0.12 mL) were added into 100 mL of distilled water and stirred for 1 h at 50 °C. Subsequently, tetrahydrate calcium nitrate (3.39 g) was added to the above solution to obtain an aqueous solution. After mixing 5 mL of tetraethyl orthosilicate and 20 mL of cyclohexane by sonication, the mixture was slowly added to the obtained aqueous solution for 12 h under stirring. After centrifugation at 3000 rpm, a white precipitate was collected. Subsequently, the MBG was obtained by cleaning the white precipitate with distilled water, drying at 80 °C for 20 h and calcining at 650 °C for 3 h. All reagents were provided by Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China).
The morphology and microstructure of the synthesized MBG were studied utilizing transmission electron microscopy (TEM, Tecnai G-20, FEI, Hillsboro, OR, USA) equipped with an energy dispersive spectrometer (EDS, Oxford Inca Energy 350, Oxford Instruments, Abingdon, UK) at 200 kV. The phase structure analysis of MBG was conducted using an X-ray diffractometer (XRD, Bruker, D8 Advance, Berlin, Germany) with Cu Kα radiation and at a step size of 5°/min. The surface area and pore size distribution were evaluated using the nitrogen adsorption–desorption technique at 77 K.
The morphology and microstructure of the synthesized MBG were studied utilizing transmission electron microscopy (TEM, Tecnai G-20, FEI, Hillsboro, OR, USA) equipped with an energy dispersive spectrometer (EDS, Oxford Inca Energy 350, Oxford Instruments, Abingdon, UK) at 200 kV. The phase structure analysis of MBG was conducted using an X-ray diffractometer (XRD, Bruker, D8 Advance, Berlin, Germany) with Cu Kα radiation and at a step size of 5°/min. The surface area and pore size distribution were evaluated using the nitrogen adsorption–desorption technique at 77 K.