Functional Mussel-inspired Coatings with Applications in Wastewater Treatment
Creators: Yang, Wenshuai
Publisher: name: University of Alberta Library
Year: 2022

<p>In marine bio-systems, robust mussel adhesion is achieved by the formation of a “bio-glue” layer between byssal plaque and substrates. By mimicking this mussel adhesion strategy, many mussel-inspired coatings have been designed for various environmental applications due to their high surface affinity. Nevertheless, it still remains a challenge to integrate different functionalities into these developed mussel-inspired coatings to fulfill the specific requirements of different water treatment processes. Moreover, current understanding of the underlying molecular interaction mechanism in the mussel-inspired coating assembly process is limited. In this thesis, different functional mussel-inspired coatings for eliminating organic pollutants or separating oily contaminants from water are designed and the corresponding molecular interactions in the coating assembly process are also investigated. <br>
Water contamination by organic pollutants poses a serious threat to human health. Most catalysts developed for organic pollutants removal generally suffer from low catalytic efficiency. Herein, in the first work, silver nanoparticles (Ag NPs) functionalized magnetic graphene oxide (MGO) was synthesized with the assistance of a tannic acid (TA)/Fe3+ coating. The as-prepared nano-catalyst showed excellent catalytic reduction performance towards different organic pollutants. Specifically, the catalytic rate constant for methylene blue (model dye) removal was up to 0.054 s−1, which was about ten times faster than most reported catalysts. It was also found that the as-prepared nanocomposite showed outstanding removal efficiency of Escherichia coli (E. coli) and can be easily regenerated through magnetic separation, indicating its potential in various environmental applications.<br>
Oily wastewater generated during the oil refining process is regarded as one of the most hazardous wastes, severely affecting the local water resources. The membrane materials designed for oil/water separation generally suffer from surface fouling issues due to the undesired deposition of oily contaminants on the membrane surface. Thus, in the second project, an antifouling cellulose nanocrystal (CNC) coating was designed by anchoring CNCs onto substrates using a mussel-inspired adhesive layer composed of tannic acid/polyethylenimine/vanadium (TA/PEI/V). The underlying nano-mechanics in the coating process were investigated by applying the atomic force microscope (AFM) colloidal probe technique. The super hydrophilic CNCs coating showed a water contact angle of ~8° and exhibited outstanding antifouling properties towards oil contamination, protein adsorption, and cell attachment. The CNCs coating also maintained its structural integrity and wettability after cyclic friction tests. Moreover, the CNCs-coated membrane showed high water permeation flux (~ 6000 L m−2 h−1 bar-1) and remarkable self-cleaning properties in the oil-in-water (O/W) emulsion separation process, demonstrating its great potential in oily wastewater purification. <br>
Polyethylene glycol (PEG) has been widely applied in the fabrication of antifouling membranes for O/W emulsion separation due to its strong surface hydration property. However, most reported PEG coatings were fabricated by anchoring the PEG polymer chains onto substrates via weak and unstable non-covalent bonds, resulting in PEG coatings that easily detached from substrates. Therefore, in the third project, a durable PEG coating was fabricated by covalently anchoring the poly(ethylene glycol) diglycidyl ether (PEGDE) polymer onto the levodopa/polyethyleneimine (LP)-coated substrate. The PEGDE/LP coating showed outstanding stability and maintained its wettability under harsh solution conditions (acid/alkaline/salt). Moreover, the PEGDE/LP coating showed superior antifouling properties towards different kinds of proteins such as bovine serum albumin (BSA). The antifouling mechanism of PEGDE/LP coating was investigated by directly measuring the interaction forces between the PEGDE/LP coating and BSA using the surface forces apparatus (SFA). Moreover, the PEGDE/LP-coated membrane could remove more than 99% O/W emulsion with enhanced water flux, indicating the outstanding performance of PEGDE/LP coating for O/W emulsion separation.<br>
In this thesis, three novel functional coatings are developed by integrating different functionalities into mussel-inspired coatings for wastewater treatment. Moreover, the molecular interaction mechanisms during the coating assembly process are investigated. This work not only expands the application of functional mussel-inspired coatings in wastewater treatment processes but also gives new insight into the precise designing of functional coatings with tunable properties for a broad range of engineering and environmental applications.</p>