Hydrophobic silica sand ceramic hollow fiber membrane for desalination via direct contact membrane distillation

A porous hollow fibre ceramic membrane derived from a low-cost natural material (silica sand) and fabricated by combine phase inversion and sintering technique followed by fluoroalkylsilane (FAS17) grafting to improve its hydrophobicity is reported in this study. Prior to the subjection of the silica sand ceramic hollow fibre membrane (SSCHFM) to a desalination performance test via direct contact membrane distillation (DCMD), characterization studies were performed on the SSCHFM before and after grafting using different characterization techniques, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), 3-points bending, water liquid entry pressure (LEPw), and water contact angle measurement. Mercury porosimetry analysis (MIP) was also used to determine the pore size distribution and porosity of the SSCHFM. The grafting process caused an increasing of the contact angle from 0° to 142.5° ± 2.0, and LEPw value of (2.6 ± 0.4 bar) was achieved. AFM images showed an increment in the surface roughness of the grafted SSCHFM from 0.305 µm to 0.375 μm, with a slight decrease in the average pore size and porosity from 0.17 µm and 17% to 0.12 µm and 14.7% respectively. After the grafting process, the performance of the membrane in DCMD was evaluated on a salt solution for 32 h at different NaCl concentrations (8,16, 24, 32 and 40) g/L, feed flow rates and feed temperatures. The results showed a decrease in the permeate flux at increasing feed concentration, but the reverse was at higher feed flow rates and feed temperatures. The surface-modified membrane recorded a water flux value of 35 kg/m2.h and 100% salt rejection. The results indicate that the hydrophobic hollow fibre ceramic membranes derived from silica sand have significant potential to be developed for membrane distillation application in water purification and reclamation.