A study on surface modified nanofiltration membranes with high permeability and stability

Nanofiltration is a newer method of membrane filtration processes. This method is usually used to separate particles from waters that have small amounts of dissolved solids; such as surface water and fresh underground water. The purpose of this method is to remove polyvalent cations and to remove prefabricated disinfectants such as natural and synthetic organic materials. The application of nanofiltration in food industries such as dairy industries is expanding widely. In these industries, nanofiltration is used for the partial removal of minerals (monovalent ions). High performance membranes circumventing the global water scarcity are emerging from exquisite nanofabrication but the materials preparation complexity and permeability stability remain challenges. We report here that both the permeability and antibacterial property of piperzine-trimesoyl chloride (PIP-TMC) polyamide nanofiltration membranes were improved through simple surface modification by a strong electrolyte monomer bearing a multiple of amines and quaternary ammonium (Quaternized diaminoethylpiperzine, QAEP). The new monomer reacts effectively with residual acyl chloride groups on pristine membranes, bringing about the synergy of improved hydrophilicity with surface microstructures that facilitates high way path for transmembrane transportation of water molecules. The PIP-TMC-QAEP membrane exhibit high salt rejection (RNa۲SO۴ = ۹۷.۸%, RMgSO۴ = ۹۴.۲%), coupled with high permeate flux (۹۶ L m-۲ h-۱, feed: ۱ g L-۱ Na۲SO۴, ۶ bar) that is ۳ times as high as that of the PIP-TMC membranes. Meanwhile the membrane features a high salt selectivity (۳۰) in processing NaCl/Na۲SO۴ mixed solution (۱۰ g L-۱), coupled with satisfactory performances against fouling and biofouling and elongated continuous operation time (۱۲ days).

Keywords:

Nanofiltration , Surface modification , Polyamide membrane , Quaternary ammonium , Antibacterial