Fundamental studies of a new hybrid (inorganic–organic) positively charged membrane. II. Membrane preparation via alcoholysis reaction and amination processes of silicone and titanate coupling agents

A series of novel inorganic–organic hybrid positively charged membranes were prepared by coupling of 3-glycidoxypropyltrimethoxysilane (GPTMS) and mixed GPTMS/Ti(O-n-C4H9)4 in n-butyl alcohol (BuOH) solution at various temperatures and then followed quaternary amination with trimethyl amine (TMA). The synthesized membranes were characterized by IEC, streaming potential, pure water flux, FT-IR, TGA measurements as well as SEM observations. It was exhibited that anion exchange capacities (IECs) of the membranes decreased with increasing curing temperature within a range of (1.4–3.1) × 10−2 mequiv. cm−2 coated for one time and (3.5–4.6) × 10−2 mequiv. cm−2 coated for two times. The positive charge of the membranes was approved by these IEC values as well as FT-IR spectrum of step products and streaming potential values. The thermal stability was tested by TGA analysis and showed that the membranes doped with titanium could undergo a curing temperature up to 300 °C. Pure water flux showed that they decreased with increasing curing temperature, the composition of precursor and dip-coating times, respectively. SEM observations indicated that the membranes became thicker and denser with increasing content of titanium, but excessive Ti-content would decrease the stability of Sisingle bondOsingle bondTi bonds in the membranes.