Influence of hexagonal boron nitride nanosheets as the additives on the characteristics and performance of PVDF for air gap membrane distillation

In this study, composite membranes were fabricated through embedment of hexagonal boron nitride (h-BN) in the polyvinylidene fluoride (PVDF). Exfoliated h-BN nanosheets were characterized by transmission electron microscope (TEM). Then, different concentrations of h-BN were incorporated into PVDF to explore their impacts on the membrane performance. Various analyses comprising Fourier transform-infrared spectroscopy (FT-IR), energy dispersive X-ray (EDS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were applied to identify the membrane characteristics. The composite membrane properties including thermal and mechanical stability, liquid entry pressure (LEP), hydrophobicity, flux, and salt rejection were also investigated. Results showed that PVDF/h-BN membranes compared with PVDF had higher roughness, hydrophobicity, flux, and salt rejection. Applying operating temperature at 80 degrees C, M2 (contained 0.5 wt% h-BN) as the best membrane indicated flux of 7.1 kg/m(2).h (43% increase compared to PVDF) and 99% salt rejection during 60 h continuous desalination process. These improvements in desalination performance were due to increase in pore size, porosity, and van-der-waals interactions between water and h-BN atoms that facilitated fast transport of water through membrane. Moreover, polar nature of B-N bonds in h-BN induced high affinity with water that contributed to the selective separation of water through passing from the h-BN nanochannels.