Preparation And Preliminary Applications Of Polymer-titania Nanocomposite Membrane

Recently, it has been focused on the fabrication and application of organic-inorganic composite membranes, owing to its combining the advantages of traditional organic and inorganic membrane. TiO₂ has a high chemical stability, light corrosion and photocatalytic activity, strong scattering ability, absorption of UV light, and sterilization. When incorporated into Polymer matrix, TiO₂ can increase the thermal stability, mechanical strength and permeability of composite membrane. The characteristic properties of TiO₂ can be reflected in the hybrid membrane. Therefore, polymer-TiO₂ hybrid membranes have been attracted wide spread concern.Currently, organic-inorganic hybrid membranes are usually prepared by physical or chemical methods. Green synthesis method is becoming a challenging task with the growing concern on environmental protection.In this article, a pure biological method was used to one pot synthesizing bacterial cellulose-TiO₂ composite membrane at the first time. It provides a good green synthesis strategy. The effect of morphology and structure of TiO₂ on the separation property and the preliminary application of hybrid membranes were explored.First, Acetobacter was used as a multi-reactor to one pot synthesizing bacterial cllulose(BC)-TiO₂ nanocomoposite. The formation mechanism and preliminary application of BC-TiO₂ nanocomposite are explored, and characterized by X-ray diffraction, X-ray Photoelectron Spectroscopy, scanning electron microscope, and transmission electron microscopy. BC-TiO₂ nanocomposite was fabricated by adding the precursor titanium(IV) bis(ammonium lactato) dihydroxide into the culture medium. The results show that three dimensional bacterial cellulose membrane is composed of 60-120nm cellulose fibril. The introduction of TiO₂ does not change the microstructure of the membrane. TiO₂ nanoparticles with size of 30-50nm are main embedded in the bacterial cellulose network, the content of it can reach 4wt%. Acetobacter synthesize bacterial cellulose and mineralize TiO₂ simultaneously. Cell wall/membrane plays an important role in the mineralization of TiO₂. Similarly, when sodium silicate or silicic acid added into the culture medium, BC-SiO₂ nanocomposite membranes were synthesized. It shows that the biological method has some versatility. Secondly, in order to enhance the TiO₂ nanoparticles content in the BC-TiO₂ membrane, BC-TiO₂ nanocomposite membrane are fabricated by in situ method. The growth of Acetobacter is not affect by adding TiO₂ gel particles into the culture medium, and the microstructure of the nanocomposite membrane does not change. TiO₂ nanoparticles are mainly embedded in the bacterial cellulose network, the content of it can reach up to 7.1wt%. It is supposed that the suspended TiO₂ in the culture medium are wrapped into the network when the bacterial cellulose are synthesized, and finally formed a nanocomposite membrane.Third, in order to study the impact of the morphology and structure on the properties of composite membrane, Titanate nanotubes(TNTs) with layered structure synthesized by the hydrothermal method were incorporated into a chitosan matrix to fabricate organic-inorganic hybrid membranes. The strong hydrogen bond of surface -OH groups of TNTs with -OH or -NH₂ groups of chitosan chains facilitated the dispersion of TNTs, and rendered these hybrid membranes of lower methanol crossover and higher mechanical strength. Particularly, CS-TNTs-15 displayed the highest mechanical strength of 85.0 MPa, low methanol permeability of 0.497×10^-6 cm2·s^-1, and proton conductivity of 0.0151 S·cm^-1, which had the potential for DMFC applications.