Zirconium based metal organic framework deposited onto modified alumina hollow fiber for humic acid removal

Abstract

Membrane technology using alumina hollow fiber (AHF) deposited with zirconium-based metal-organic framework (MOF) known as UiO-66 serves as a great option for humic acid (HA) removal present in water systems. The main limitation for growing UiO-66 on AHF is the difficulty to develop a well-continuous and defect-free UiO-66 layer onto AHF due to its abundant micropores and tubular configuration, resulting in low stability and poor HA rejection. There are three objectives of this study which are i) to study the single deposition and second deposition of UiO-66 membrane onto AHF using in-situ solvothermal synthesis, ii) to examine the surface modification of AHF with coat seeding sol-gel zirconium nanoparticles prepared using sol-gel Pechini method prior to the growth of UiO-66 membrane and iii) to investigate the effectiveness of membrane samples prepared using single deposition UiO-66, second deposition of UiO-66 and UiO-66 deposited onto AHF modified by zirconium nanoparticles for the removal of HA. Four main phases involved in this study which are i) preparation of AHF using spinning based phase inversion and sintering technique, ii) deposition of UiO-66 membrane onto AHF using single and second deposition techniques under controlled parameters, iii) deposition of UiO-66 membrane onto AHF modified with zirconium nanoparticles prepared using sol-gel Pechini method and iv) HA removal studies using cross-flow filtration. The AHF, UiO-66 particles, and the developed UiO-66 membrane on AHF were characterized based on their physicochemical properties. All prepared samples were further tested for pure water flux test and HA removal test. For the single deposition technique, no UiO-66 membrane layer was observed where the UiO-66 solution was diffused within AHF’s micropores. The UiO-66 membrane was successfully formed after the second deposition of UiO-66 and after coat-seeding with zirconium nanoparticles in the range of 1.5 µm to 11 µm thickness. The UiO-66 and zirconium particles acted as an anchor site for UiO-66 deposition by enhancing the adhesion and provided full coverage of the UiO-66 membrane onto AHF. It was found that the pure water fluxes for all prepared samples reduced ranging from 13.00 to 163.88 L m-1 h-1 as compared to pristine AHF’s pure water flux of 259.67 L m-1 h-1. These reductions of water flux were due to the presence of UiO-66 particles and zirconium nanoparticles on the entire surface of the AHF that increased the mass transfer resistance of water permeation across the membranes. Study on HA removal using UiO-66 membrane revealed that the prepared samples showed excellent performance of HA removal with 99 % rejection and satisfied solute fluxes ranging from 3.16 to 68.37 L m-1 h-1. The high removal of HA can be explained by similar negative charge between UiO-66 particles and HA molecules which created charge repulsion between the surface of the membrane and the HA. This study concluded that UiO-66 membrane had been successfully deposited onto modified AHF with zirconium nanoparticles. Results from this study provided solutions on the difficulty of synthesizing well-developed, defect-free and well-continuous of UiO-66 membrane onto AHF with excellent HA rejection, moderate solute flux of UiO-66 membrane onto AHF.