Poly(vinyl butyral)/zeolitic imidazole framework-8/poly(vinyl alcohol) thin-film nanocomposite nanofiltration membrane: synthesis and characterization

Abstract

Zeolitic imidazole framework-8 (ZIF-8) was synthesized and its structure was investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffractometry methods. Poly(vinyl butyral) (PVB)/ZIF-8 nanocomposite membranes as substrate were prepared with different percentages of ZIF-8 nanoparticles. Then, a thin layer of poly(vinyl alcohol) was created by coating method and cross-linked with glutaraldehyde (GA). As a result, thin-film nanocomposite (TFN) nanofiltration membranes were obtained. The TFN membranes were characterized by SEM, FTIR, atomic force microscopy, and contact angle measurement. The effects of incorporating ZIF-8 on membrane performance were investigated. As amount of ZIF-8 in the substrate was increased, water flux increased due to increasing porosity, and because of increasing hydrophilicity and negative charge of membrane surface fouling decreased. Thereby, the TFN membrane with ZIF-8 at 3% showed the highest water flux and the least fouling because of increasing porosity. As the concentration of PVA solution and GA was increased, the flux decreased and rejection increased. The PVB/(ZIF-8 3%) substrate membrane with PVA (1%) and GA (5%) cured at the temperature of 100 °C for 30 min resulted in the optimum balance of flux and rejection. For TFN membranes prepared under optimum conditions, the average rejection of Congo red dye was 98% and pure water flux was about 195 L/m2 h.