Preparation and characterization of low-pressure nanofiltration membranes and the application in the separation process of dye molecules

Low-pressure nanofiltratioin (NF) membranes were prepared with hydroxyl groups ended hyperbranched polyester (HPE) using polysulfone (PSf) ultrafiltration membrane as the porous support. The prepared membranes are characterized using Fourier transforms infrared spectrometry, scanning electro microscopy, atom force microscopy, X-ray photoelectron spectroscopy and water contact angle. The results indicated that the crosslinked HPE formed a uniform, ultra-thin and active layer on PSf support. Water permeability and salt rejection of the membranes were measured at the trans-membrane pressures as low as 0.3 MPa. NF membranes exhibited high enhancement in water permeability while maintaining high rejection of salts. The rejections of the nanofiltration membrane to Rhodamine B and Xylenol orange were 100 and 98.4%, respectively. The study indicated that these NF membranes could be applied to separate small organic molecules.