Deposition of synthesized zirconium-based metal organic framework on ceramic hollow fibre for forward osmosis desalination

Abstract

This study was aimed to develop zirconium (Zr)-based metal organic framework (MOF) ceramic membrane that can be used for forward osmosis (FO) desalination. As the first step, ceramic substrate surface was first modified with zirconium dioxide (ZrO2) using sol-gel Pechini’s method to provide active seeds that can favour MOF nucleation. Using this modified substrate, a series of solvothermal synthesis conditions were tested to build the FO applicable membrane. In the unmodulated procedure, only sample synthesized at 220°C with 0.3 M and 16 h gave positive water flux. Field emission scanning electron microscopy (FESEM) and themogravimetric analysis (TGA) results have shown that the non-uniform coverage and defect frameworks of MIL-140B (Materials of Institute Lavoisier –MIL) on the substrate layer was the cause to this problem. Hence, to tune the defect, modulated synthesis was introduced. Increment in modulator amount by increasing precursor concentration from 0.58 M to 2.32 M had successfully lowered the percentage of defect framework from 26.03% to 16.87%. Despite this framework enhancement, FO test result of this sample still displayed worse performance than the previous synthesis due to its high tendency of agglomeration. Loosely joint particles that formed during agglomeration at high temperature synthesis were easily brushed off during FO test. Therefore, lower synthesis temperature of 120°C and longer synthesis time of 24 h was employed in the next procedure to allow slow nucleation process that can form better connected crystals. Instead of MIL-140B, UiO-66-NDC (University of Oslo – UiO) framework was found at 2? = 10.36° and the crystal shape appeared in octahedron. Even with this reformatted crystal shape, the FO performance result still could not be in positive value. Therefore, the UiO-66-NDC membrane active layer was polymerised with fluorinated polymer as the last resort. Integration between this polymer and UiO-66-NDC had successfully treated the membrane defects by building new bonds inside the framework as proven by FESEM, atomic force microscopy, xray diffraction, Fourier-transform infrared spectroscopy and TGA results. With better connected crystals, smoother deposition layer and perfect frameworks, FO performance of all UiO-66-NDC samples finally gave positive water flux results and the highest value was 16.189 L/m2.h. Its lowest reverse solute flux achieved was 0.003 L/m2.h with sodium chloride rejection of up to 80 % which is definitely better than the previous study. Therefore, polymer-synthesized UiO-66-NDC on ceramic hollow fibre can definitely serve as an excellent FO membrane option that can be used in the desalination process.