Preparation And Characterization Of Mesoporous Silica/polyamide Reverse Osmosis Composite Membranes

Reverse osmosis has become one of the most economical techniques in the desalination of seawater and brackish water. However, the high energy consumption, low selectivity, fouling-prone and membrane flux limited of the current reverse osmosis membrane make the cost of obtaining fresh water through reverse osmosis technology was high. It is necessary to study and prepare the advanced composite membranes with high water permeability, selectivity and low energy consumption. Compared to traditional molecular sieve, mesoporous materials have large pore size and large amount of hydroxyl on the surface. Thus, mesoporous silica could be easily modified by incorporating organic functional groups. Mesoporous silica spheres and amino-functionalized mesoporous silica spheres were synthesized in this work. The synthesized mesoporous spherical particles were dispersed into the composite membrane in order to improve the performance of the membrane.Mono-dispersed mesoporous silica spheres with different particle size were synthesized using alkyl trimethyl ammonium chloride (CTAC) as template, tetraethyl orthosilicate(TEOS)as silica source and methanol as co-solvent under basic condition by hydrothermal method. The influence of the concentration of CTAC and TEOS, the methanol ratio and the temperature was investigated. The results indicated that the mono-dispersed mesoporous silica spheres with the uniform particle size were prepared with 0.024mol/L of CTAC,0.0096mol/L of TEOS and 0.5 of methanol ratio at 25℃.And the synthesized mono-dispersed spherical silica has ordered hexagonal mesoporous structure, uniform pore size distribution and high surface area.Amino-functionalized mono-dispersed mesoporous silica spheres were synthesized by co-condensation of 3-aminopropyltriethoxysilane (APTES) and tetraethyl orthosilicate using cation surfactant as template with the aid of the co-solvent under basic condition. The amino-functionalized mono-dispersed spherical particles were successfully synthesized with less than 15% of APTES.The results showed that amino groups were successfully incorporated into the mesoporous silica surface, and the synthesized amino-functionalized mono-dispersed spherical silica has larger pore size and higher surface area.The synthesized mesoporous silica and amino-functionalized mesoporous silica spherical particles were dispersed into the composite membrane to improve the water permeability. The surface, cross-section structure and composition of membrane were characterized by scanning electron microscope and energy dispersing spectra. The scanning electron micrograph displayed that the surface of the reverse osmosis membranes appeared the apparent structure of peaks and valleys, and spherical paticles were visible on the membrane surface. Also, energy dispersing spectra analysis confirmed that the mesoporous silica and the amino-functionalized mesoprous silica particles were successfully incorporated into the film layer.