Development of Novel Functionalized Polydopamine-Enabled Mixed Matrix Membranes for Wastewater Treatment Application

  • Roqaya Abbas Ismail

Student thesis: Doctoral Thesis

Abstract

In this dissertation, three types of polydopamine (PDA)-based nanohybrid fillers were synthesized and explored for the first time as additive materials in Poly (ether sulfone) (PES) membrane to enhance its antibacterial & antifouling activity against several organic and inorganic foulants. The successful synthesis of the nanohybrid fillers and the modified membranes was confirmed by utilizing set of tools such as x-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Raman, attenuated total reflectance-fourier-transform infrared spectroscopy (ATR-FTIR), thermogravimetric Analyzer (TGA), atomic force microscopy (AFM), zeta (ζ) potential and contact angle measurements. The surface morphology, charge and hydrophilicity of the membranes were tuned upon integrating the nanohybrid fillers which affected their overall separation performance. In the first part of this study, a new quaternized polydopamine anchored reduced graphene oxide (QSiPD-rGO) nanohybrid was prepared through a one-step mussel-inspired tailoring of GO using a quaternized silica precursor and dopamine. The QSiPD-rGO was applied for the first time as a nanofiller, at a significant loading rate of up to 8 wt%, to manufacture positively charged, high flux, fouling resistant and antibacterial hybrid ultrafiltration (UF) membranes, via non-solvent induced phase separation (NIPS). Consequently, pure water flux significantly increased, reaching ~ 270 L m−2h−1 (at 1 bar) for PMQ4 with 6 wt% QSiPD-rGO loading. This was 94% higher than the corresponding flux of pristine membrane (139 L m−2h−1, at 1 bar). The hybrid membranes also showed superior fouling resistance during the UF of 500 ppm bovine serum albumin (BSA) solution. The BSA rejection rate of the hybrid membranes was very high and uncompromised by their high flux, exceeding 98% for PMQ4. Additionally, a remarkable antibacterial activity (against E. Coli.) of the membranes was induced by the nanohybrid, with a strong correlation between this activity and QSiPD-rGO loading. In the second part of this study, a quaternized polydopamine (QSiPD) nanohybrid was synthesized by the condensation reaction between the silicon hydroxyl moieties of the hydrolyzed QSiP and hydroxyl moieties of PDA and applied as an additive in PES membrane via NIPS technique. The QSiPD nanohybrid was used to prepare UF membranes at a loading percentage up to 8 wt.% and loose nanofiltration (NF) membranes at a loading percentage up to 20 wt.%. The water flux of the composite membrane incorporated with 4 wt.% of QSiPD nanohybrid (UF4) was reported to be as high as ~402 L m−2h−1. The antifouling activity of the hybrid ultrafiltration membranes was assessed using BSA solution of 50 ppm, and the hybrid membranes have exhibited superior antifouling activity with a rejection rate of ~99% in UF4 membrane, uncompromised by its high flux. It was also observed that increasing the QSiPD content from 0 to 4 wt.% reduced the irreversible fouling (Rir) from 33% to 0.4% in UF4 membrane, proving a relatively high fouling resistance against BSA protein. Besides, the loose nanofiltration composite membranes were used to separate four single salt solutions and congo red dye. The hybrid nanofiltration membranes showed high rejection rate of several salt solutions in the order of Na2SO4 (67%) > NaCl (47%) > MgSO4 (46%) > CaCl2(45%) for the membrane NF15 and an outstanding rejection of congo red dye (>99.9%). Furthermore, the hybrid UF and loose NF membranes have showed an improved antibacterial activity against E. coli reflected by the reduction in the number of attached bacterial cells on the surface of the modified membranes. In the final part of this study, a novel zwitterionic PDA-based nanohybrid (ZrSiPD) was successfully synthesized via simultaneously alkaline hydrolysis of zwitterionic silica precursor (ZrSiP) and oxidative polymerization of dopamine monomers followed by condensation reaction. The obtained ZrSiPD nanohybrid was applied as a nanofiller to improve the water permeability and antifouling property of PES ultrafiltration process. The ZrSiPD nanohybrid was utilized to fabricate membranes at different loading percentages up to 8 wt.% via NIPS method. The significant improvement in the modified membrane's surface properties (hydrophilicity, surface charge, and pore structures) have remarkably enhanced their antifouling properties against humic acid (HA) foulant. The water flux of the ZrM8 hybrid membrane was reported to be around 473 L m−2h−1. The antifouling activity was evaluated using HA solution of 50 ppm, and the modified membranes have experienced an enhanced rejection rate of 91%. ZrM4 membrane was shown to be the least susceptible membrane to HA fouling, and almost 98% FRR value certifies an outstanding elimination of poorly adhered HA layer from the surface of ZrM4. Rir values of all hybrid membranes were lower than pristine membrane, with the minimal Rir value observed in ZrM4 with 1.64%. Based on the above results, we believe that these modified membranes have promising potential in enhancing the performance of PES UF systems for a variety of separation and treatment applications.
Date of AwardMay 2022
Original languageAmerican English

Keywords

  • Antifouling; nanofiltration; nanohybrid; polydopamine; ultrafiltration.

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