Ordered Mesoporous Silica Preparation, Characterization And Application

Preparation, functionalization and application of highly ordered mesoporous silica HOM-5 (Ia3|-d) were investigated in this paper. HOM-5 with three-dimensional (3D) and gyroidal bicontinuous meso-structures, was fabricated under acidic condition via a direct-templating synthesis. Primary lyotropic liquid crystal mesophase of triblock copolymer P123 was used as template. In order to remove hazardous ions such as Cr(VI) and Pb²⁺ from water, HOM-5 as-synthesized was functionalized with organosiloxane precursors (TM-551 and TM-580) subsequently. Materials named H/NN-HOM-5 and SH-HOM-5 with functional groups thiol- and amine- were prepared, which had adsorption ability of objective ions in aqueous solution. 3D cubic structures of the samples were affirmed by small X-ray diffraction (SXRD) and high-resolution transmission electron microscopy (HRTEM). HOM-5 as-synthesized was hydrothermal stable, which endowed this material with good functional capability. Materials after functionalization retained initial space groups of Ia3|-d , and constant lattice parameter was increased from 207.09A (HOM-5) to 215.61A(H/NN-HOM-5) and 213.89A(SH-HOM-5). FT-IR and EDS were adopted for composition and element analysis, which indicated that a certain amount of functional groups were grafed to HOM-5.The sulfur and nitrogen contents were 2.73mmol/g and 1.03mmol/g, respectively. Silanol groups were decreased while the Si-O-Si groups were increased in functionalized materials. Results of nitrogen-adsorption/desorption measurements showed that the obtained HOM-5 had a most concentrative pore diameter of 57.9A, which decreased to 52.6A(H/NN-HOM-5) and 51.7A(SH-HOM-5), while the thick walls was increased from 151.7A to 157.6A(H/NN-HOM-5) and 157.0A(SH-HOM-5) after functionalization. The modified pseudo-second-order equation is applied to sorption kinetics. Experiments showed that adsorption of Cr(VI) on H/NN-HOM-5 fitted the Langmuir isotherms. The adsorption capability increased greatly after functionalization, with the maximum loading 2.264mmol/g of Cr(VI) on H/NN-HOM-5.Stoichiometric ratios of Cr(VI)/N=0.83 have been observed. Distribution coefficient reached 51910.1mL/g in the case of an initial solution concentration of 20mg/L.Adsorbents that functionalized with thiol- groups had efficient competitive adsorption ability for Pb²⁺ from an mixed-metal solution containing Pb²⁺:Cu²⁺ or Cd²⁺=1:5(the molar ratio).The ratio of distribution coefficient were Kd'Pb²⁺/Kd'Cu²⁺= 13.1 and Kd'Pb²⁺/Kd'Cd²⁺= 9.2, respectively. The mesoporous silica HOM-5 was characterized with large pore size, thick walls and...