Preparation And Properties Of Calcium Alginate - Based Hydrogel Filtration Membrane

A free-standing CaAlg/PAM hydrogel membrane was synthesized through the polymerization of acrylamide and Ca2+ crosslinking. The membranes were characterized by SEM, FTIR and TG. BSA solution and yeast suspension were used to investigate its anti-fouling performance. Brilliant Blue G250 dye rejection demonstrated the potential applications of this material as nano-filtration membrane. However, due to the complex process of fabricating CaAlg/PAM hydrogel membrane and the casting solution was too viscous to remove bubbles, which may lead to membrane defects. Therefore, the main work may focus on talking about pure CaAlg hydrogel filtration membrane in the following chapters.Then, Calcium alginate (CaAlg) hydrogel filtration membrane was prepared by ion crosslinking using polyethylene glycol (PEG) as the pore-forming agent. The CaAlg filtration membrane was characterized by SEM, FTIR and TG. The mechanical behavior of the membrane was also evaluated. Concentrations of sodium alginate (NaAlg) and PEG on the pure water flux (PWF) and filtration properties of lysozyme (Lyz) solutions were investigated. Results showed that the PWF increased with an increase in the pressure initially, and then reached a stable value. The CaAlg filtration membrane in lower NaAlg concentration and higher PEG concentration had higher flux. While filtering BSA solution and oil-water emulsion, CaAlg filtration membranes exhibited good anti-fouling properties. While PEG was used as rejection objects, the rejection of PEG reached above 90% when the molecular weight (Mw) of PEG in feed solution was larger than the pore-forming agent PEG for preparing the membranes. The CaAlg filtration membrane prepared using PEG400 as the pore-forming agent could reject almost 100% Brilliant Blue G250 (Mw=854.02 Da), and 99.5% Congo Red (Mw=696.68 Da).While using urea as pore-forming agent, the CaAlg hydrogel membrane can be served as nano-filtration membrane. The flux of bovine serum albumin (BSA) solutions was 97.65% of the pure water flux (PWF). After three consecutive BSA filtrations, the flux recovery rate still reached 91.3% after washing by 1 wt.% CaCl2 solution, indicating that the membrane having excellent anti-fouling properties. The water contact angle of the nano-filtration membrane reached nearly zero within 2 seconds. The removal rate of the membrane reached over 99.5% within 120 min when 20 mg/L Cd2+ was used. For the single ion solution of Pb2+, Cu2+ and Cd2+, the nano-filtration membrane can achieve a high removal rate, which is above 99%. while it comes to mixed heavy metal ions of Pb2+, Cu2+ and Cd2+, various removal rates were observed for different ions, and the removal rates followed the order of Pb2+> Cu2+> Cd2+, which was surprisingly consistency with the crosslinking interaction sequence between those three metal cations and NaAlg. And there is a good reason to believe that the effect of removal of ions was not mainly dependent on retention, but competitive adsorption or ions exchange between the heavy metal ions and Ca2+in membrane matrix. To verify the above assumption, Energy Dispersive Spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were used to detect the distribution of ions in the membrane matrix. The removal of heavy metal ions mainly depends on the adsorption effect and ion exchange with Ca2+ in membrane matrix.By adding Kaolin powder in CaAlg hydrogel matrix, Kaolin/calcium alginate (K/CaAlg) composite hydrogel film was successfully prepared. The interactions between Kaolin powder and gel matrix were characterized by Fourier transform infrared spectra (FTIR) and thermo gravimetric analysis (TGA). The CaAlg hydrogel film provided a suitable carrier for Kaolin powder in the adsorption of dyes. On the other hand, the adsorption capacity of the composite film was enhanced by the incorporation of Kaolin powder. The adsorption kinetics and isotherms of the K/CaAlg composite films were investigated by using different dyes. Moreover, the reusing results in dye adsorption demonstrated the composite film has good regeneration properties.