Synthesis of spherical mesoporous silica materials by pseudomorphic transformation of silica fume and its Pb2+ removal properties

• Silica fumes as silica source (parent spheres).
• An inexpensive and convenient preparation process of spherical mesoporous silica.
• Providing a foundation on the optimal control of scale-up production for the materials.
• The materials exhibit high Pb2+ adsorption capacity.

Spherical mesoporous silica material (SMSM) was hydrothermally synthesized using cetyltrimethylammonium bromide (CTAB) as the template agent and silica fume as the silica source. High-quality SMSMs were successfully prepared by pseudomorphic transformation. The structure and morphology of the SMSMs are investigated by X-ray diffraction, N2 sorption/desorption, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses. The effects of synthetic parameters, such as crystallization time, crystallization temperature, n(NaOH)/n(SiO2) molar ratio, and n(CTAB)/n(SiO2) molar ratio, are quantitatively investigated. The optimal synthetic conditions for high-quality SMSMs are a crystallization time of 48 h, crystallization temperature of 363 K, n(NaOH)/n(SiO2) molar ratio of 0.2–0.3, and n(CTAB)/n(SiO2) molar ratio of 0.15. The qualities of Si–OH are tested by NaOH titration and IR. The results of the both methods confirm that the amount of Si–OH in SMSM is higher than silica fume. Furthermore, SMSMs are employed as effective adsorbents for removing Pb2+ from the static, competitive and column experiments. The capacity for Pb2+ removal demonstrates great improvement.

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