Synthesis of Mesoporous Calcium Silicate by Ultrasonic-Assisted Template Method and Evaluation of Its Adsorption Characteristics for Cd(II)

Mesoporous calcium silicate (MCS) was prepared from calcium nitrate and sodium silicate by ultrasonic-assisted template method. The effects of different templates (sodium dodecyl sulfate, cetyl trimethyl ammonium bromide, P123, and cetyl trimethyl ammonium bromide-tetramethyl ammonium hydroxide) on the pore size and surface topography of MCS were investigated. Calcium silicate synthesized was characterized by X-ray diffraction, scanning electron microscopy, the Brunauer-Emmett-Teller method, and Fourier transform infrared spectroscopy. The adsorption performances of the MCS synthesized for Cd2+ were also investigated. Results showed that the MCS synthesized using cetyl trimethyl ammonium bromide as template under ultrasonic treatment acquired a mesoporous slit-pore structure with a specific surface area of 244.32 m(2) g(-1) and pore size (DBJH) of 11.2 nm. MCS showed extremely high adsorption capacity for Cd2+ at pH 5.0-7.5, and the adsorption capacity for Cd2+ was 509.91 mg g(-1) at 293 K, which was much higher than those of the adsorbents in literature. The equilibrium adsorption data of MCS for Cd2+ all fitted the Langmuir and Redlich-Peterson models, and more closely with the Redlich-Peterson model. The adsorption of MCS toward Cd2+ was a spontaneous endothermic reaction driven by increased entropy involving both physical and chemical modes. The adsorption of MCS for Cd2+ was better described by the pseudo-second-order model than by the pseudo-first-order model, with an activation energy of 13.4327 kJ mol(-1). Thus, it is evident that MCS can be a promising excellent adsorbent for the treatment of Cd2+-containing wastewater.