Formation Mechanism Of Mesoporous Silica Research Articles

Insight into the role of anions in the formation of mesoporous silicates

Cationic surfactants can form micellar structures in solution and the condensation of silicate around these micellar structures results in the inorganic/organic mesostructured composites. Anions other than silicates in the solution were believed to be located closely to the headgroup of the cationic surfactant micelle and thus affected the effective headgroup area, a component of the surfactant packing parameter g (g = V/a0l, where V is the chain volume, a0 is the effective headgroup area, and l is the chain length). In the presence of H2SO4, HCl, HBr, and HNO3, the surfactant cetyltriethylammonium bromide (CTEABr) directed the well-ordered mesophases of three-dimensional (3D) hexagonal P63/mmc, cubic Pm3‾n, 2D hexagonal p6mm, and cubic Ia3‾d, respectively. The diversity of the mesophases from CTEABr was attributed to the anion tuning of the effective headgroup area of CTEA+ in surfactant packing parameter g by closely located anions of SO42−, Cl−, Br−, and NO3− with various radii and hydratability. In this work, we discovered that part of Cl−, Br−, and NO3− can penetrate into the micellar system of CTEA+, which may increase the chain volume V of CTEA+ to some degree. The distance of anions to the center of the micelle, determined by the liquid 1H NMR analyses, was in the order of SO42− > Cl− > Br− > NO3−, which is consistent with the Hofmeister series. The deeper penetration of anions into the micelle may lead to the larger chain volume V and surfactant packing parameter g. Such insight into the location of anions in micellar system provided us a new picture on the formation mechanism of mesoporous silica and other mesostructured materials in solution.

Preparation of Mesoporous Silica from Electrolytic Manganese Slags by Using Amino-Ended Hyperbranched Polyamide as Template

Large quantities of waste slags are produced during the preparation of electrical manganese, causing serious pollution to the environment. The recycling and utilization of electrolytic manganese slags (EMS) is a serious challenge to the industry. Here, we report the utilization of EMS in preparation of high-performance mesoporous silica using amino-ended hyperbranched polyamide (AEHPA) as template. The effects of AEHPA content and molecular weight on properties of mesoporous silica, including the specific surface area, pore diameter, pore volume, size and distribution, have been investigated. Based on 0.3 wt% AEHPA-2 during preparing silica, the specific surface area, pore volume and pore diameter of the produced amorphous mesoporous silica are 451.34 m2•g-1, 0.824 cm3•g-1 and 7.09 nm, respectively, showing remarkable improvements over the silica without AEHPA with specific surface area (271.05 m2•g-1), pore volume (1.167 cm3•g-1) and pore diameter (17.43 nm). The formation mechanism of mesoporous silica ...

The use of in situ and ex situ techniques for the study of the formation mechanism of mesoporous silica formed with non-ionic triblock copolymers

Since the discovery of the mesoporous silica material templated by ionic surfactants and the subsequent development of materials templated by non-ionic surfactants and polymers, for example SBA-15, there has been a continuous research effort towards understanding their formation. In situ methodologies, such as Small Angle X-ray Scattering (SAXS), Small Angle Neutron Scattering (SANS), spectroscopic techniques like NMR and EPR, and ex situ methodologies such as electron microscopy techniques (SEM, TEM and cryo-TEM) are powerful and important tools in the investigation of the mechanism by which these materials form. The need for a fundamental understanding of the systems is of academic concern and of great importance when developing materials for applications. In this tutorial review we aim to give the reader a comprehensive overview on the development of the field over the years and an introduction to the experimental in situ and ex situ techniques that have been used.

Synthesis and characterization of mesoporous silica using new gemini surfactants as templates in neutral pH conditions

Abstract A series of MSU-x wormlike mesoporous silica samples were synthesized using a new type of gemini surfactants [C n H2 n +1N+(CH3)2–CO2–(CH2)4–CO2–N+(CH3)2C n H2 n +1] ·2 Br (n = 12, 14, 16) at circumneutral pH and characterized using Fourier transform infrared spectroscopy, thermo gravimetric analysis, X-ray diffraction, N2 adsorption-desorption and scanning electron microscopy. The MSU-x samples have high surface area and thick pore walls. The pore structure remained after treatment in boiling water for 72 h, which has hardly been reported among mesoporous materials synthesized under mild conditions. The effects of synthesis temperature, aging time and concentration of surfactant on the mesoporous structure were investigated. Based on these, a formation mechanism of mesoporous silica using the new gemini surfactant was proposed.