4. Fabrication of pH-responsive membranes

Intended for the pre-synthesis of pH-responsive polyacrylamide zirconium titanosilicate (PAm-ZTS) membranes, liquid titanium(IV)chloride (98%), TiCl4, 189.68 [g/mol], 1.728 g/cm3 (20C), and zirconium(IV)oxychloride octahydrate powder (>99.5%), ZrOCl2.8H2O, 321.26752 [g/mol], 1.91 g/cm3 (20C), pH value ~1 (50 g/l, H2O, 20C), were picked up from Merck Chemicals, Darmstadt, Germany, while Sigma-Aldrich tetraethyl orthosilicate (C2H5O)4Si 208.33 [g/mol], 0.93 g/cm3 (20C), USA was used.

Because of the immense difference between the traditional organic polymers and the corresponding inorganics in their natures and due to strong aggregation of the nanofillers, polymer-inorganic nanocomposite PAm-ZTS membranes cannot be prepared by common schemes such as melt blending and roller mixing. The most frequently secondhand synthesis techniques in the production of nanocomposite membranes can be allocated as three categories [20].

The sol-gel method, the former category secondhand preparation procedure, in which organic monomers, oligomers, or polymers and inorganic nanoparticle precursors are well balanced in solution. The inorganic pioneers were mixed together by gradual addition of tetraethyl orthosilicate, dissolved in equal volumes of bidistilled water and ethyl alcohol with vigorous stirring to zirconium oxychloride octahydrate and titanium tetrachloride solutions, previously dissolved in concentrated hydrochloric acid. The total components are instantly hydrolyzed in an appropriate quantity of water, following to condensation into well-dispersed nanoparticles in the polyacrylamide polymer skeleton with different mole fractions. The reactions' conditions are moderate; usually room temperature, an ordinary atmospheric pressure, and the concentrations of organic and inorganic components are easy to control over the solution. Additionally, the precursor ingredients, as organic and inorganic ingredients could be dispersed in nanometer level in the membranes, and thus the formed membranes are homogeneous. Other techniques as solution mixing and in situ polymerization are used.
