Author: Wan, Zhishang
Title: Advancing nanocomposite membranes for water treatment : mechanistic understanding of nanofiller incorporation and development of aerosol-assisted nanoengineering approaches
Advisors: Jiang, Yi (CEE)
Li, Xiangdong (CEE)
Degree: Ph.D.
Year: 2023
Subject: Water -- Purification -- Membrane filtration
Membrane separation
Membrane filters
Hong Kong Polytechnic University -- Dissertations
Department: Department of Civil and Environmental Engineering
Pages: xiv, 224 pages : color illustrations
Language: English
Abstract: Nanocomposite membranes, i.e., a new class of membranes prepared by incorporating functional nanomaterials in a membrane matrix (nanofillers) or into the membrane surface, have attracted significant attention due to their improved performance and multifunctionalities compared with traditional polymeric membranes. To further advance such membranes for water treatment, the role of nanofillers in enhancing membrane performance needs to be understood. Furthermore, the incorporation of nanomaterials into the membrane surface layer maximizes material benefits for performance enhancement. Therefore, it is desired to develop innovative surface nanoengineering approaches. To address these knowledge/technical gaps, this thesis unravels preparation-structure-performance relationships of nanofiller-incorporated membranes through experimental and meta-analysis studies, and develops two simple yet robust aerosol-assisted membrane surface nanoengineering approaches.
This thesis firstly studies the effects of two carbon nanofillers (i.e., graphene oxide (GO) and carboxylic carbon nanotube (c-CNT)) and establishes a coherent understanding of the preparation-structure-performance relationships of such nanofiller-incorporated ultrafiltration (UF) membranes. Through experiments, this thesis reveals that the morphological factor, as a result of nanoparticle properties, is an important factor to consider during membrane preparation (i.e., nonsolvent-induced phase separation (NIPS)). A meta-analysis of data from 121 publications is further conducted. The results show 1D or 2D nanofillers (e.g., CNT, SBA-15, or GO) usually have lower optimum mass loadings than 3D nanofillers (e.g., TiO2, SiO2, and ZnO), primarily because 3D nanofillers have lower specific surface area. For performance, high nanofiller hydrophilicity and concentration of nanofillers into the membrane surface layer improve both membrane separation and antifouling performance. In addition, incorporation of nanofillers increases membrane mechanical strength because nanofillers themselves have excellent mechanical properties and serve as physical cross-linkages between polymer chains.
To localize nanomaterials on the membrane surface, this thesis develops a rapid surface nanoengineering approach that couples electrospray and polymeric solvent bonding. Successful stabilization of Ag NPs via interfacial polymeric bonding occurs under the conditions of large material contact area, high material compatibility, and proper temperature (22°C) and polymer-to-solvent ratio (3-5%). Ag NPs (0.02% of the whole membrane) are stabilized on the membrane surface within minutes. The resultant membrane shows markedly improved catalytic and antimicrobial (anti-biofouling) performance and maintained rejection. The surface nanoengineering approach is further modified to incorporate c-CNTs of ultra-high loadings into the membrane surface layer during spray-assisted NIPS. Membrane formation is influenced by thermodynamic, kinetic, and morphological factors. The introduction of c-CNTs in the surface layer overall acts as a barrier for solvent-nonsolvent exchange, which contributes to even higher kinetic hindrance compared to that in conventional NIPS. The as-prepared membrane structure and performance coincide well with the proposed membrane formation mechanisms. Through optimization, membranes with the highest c-CNT loading (11%) are prepared, showing decreased water permeability (36% reduction) but much improved bovine serum albumin rejection (>30% enhancement), flux recovery ratio (>10% enhancement), and tensile strength (>80% increase).
In summary, this thesis identifies and solves key issues that currently impede the advancement of nanocomposite membranes. The knowledge obtained will guide the rational design and scalable incorporation of nanomaterials and thus accelerate their applications in water treatment membranes.
Rights: All rights reserved
Access: open access

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