Abstract
Marine biofouling is a process that fouling substances or organisms accumulate unexpectedly on the surface, which presents major challenges for marine industries and leads to substantial economic losses and energy consumption. Traditional antifouling strategies rely on coatings containing metal and organic based biocides, while effective, these coatings pose significant environmental and biological risks. With tributyltin (TBT) being banned worldwide, the development of sustainable, non-toxic, and environmentally friendly alternatives is urgent.In this project, two coatings based on capsaicin mimetics and two coatings based on metal-organic frameworks (MOF) materials were developed by coupling antifouling agent release strategy and superhydrophobic self-cleaning strategy, respectively. The formulation and structure of the coatings were optimized to improve their antifouling and anti-corrosion performance and service life. A capsaicin mimic N-(4-hydroxy-3-methoxy-benzyl)-acrylamide (HMBA) was synthesized and immobilized with silica nanoparticles, further modified with fluorosilane. Subsequently, a multi-layer superhydrophobic antifouling coating was prepared by spraying precursor solutions of different concentrations.
A high contact angle of 164° and a low rolling angle of 6° was obtained. Significant reduction in adhesion rates of proteins, polysaccharides, and algae was achieved by the superhydrophobic surface, which was only 11.9%, 8.7%, and 3.3%, respectively. In terms of seawater corrosion, its corrosion current was decreased by four orders of magnitude. The addition of capsaicin achieved an antibacterial capability of 96.6% and 99.9% against E. coli and S. aureus, respectively. Even if the superhydrophobic structure fails, the release of capsaicin can still provide protection for the surface, demonstrating the effectiveness of the dual insurance strategy. HMBA molecule contains phenolic hydroxyl groups, to investigate its potential application in designable antifouling benzoxazine coating, two different amines and HMBA were used to synthesize two benzoxazines HMBA-APTES (HA) and HMBA-FFA (HF). After thermal polymerization, the coating exhibited excellent resistance to chloride ion corrosion. The quaternary ammonium group was introduced into the benzoxazine monomer through iodomethane, and the P(HFI) coating showed antibacterial rates of 93.8%, 96.4%, 99.9%, and 99.9% against E. coli, S. aureus, P. aeruginosa, and B. subtilis, respectively, and effectively reduced the adhesion of algae, but the increase in ionization degree led to an increase in surface porosity and a significant decrease in corrosion resistance.
MOF materials are excellent carriers for drug release and can be used for sustained release of antifouling agents to improve the service life of coatings. Amino groups functionalized NH2-ZIF-8 nanoparticles were prepared and loaded with the epoxidation antifouling agent BITEP to get NH2-ZIF-8@BITEP (ZB) antifouling particles. ZB coating was prepared by embedding these nanoparticles into epoxy resin. ZIF-8 can respond to local pH changes caused by microorganisms or corrosion to degrade and release trace amounts of antifouling agents, achieving contact sterilization against E. coli and S. aureus. ZB20 coating can reduce the formation of bacterial biofilm and hinder the adhesion of algae, demonstrating significant antifouling ability. It was shown that the degradation of ZIF-8 can also form a protective layer with corrosion products, slowing down further corrosion and improving the corrosion resistance of the coating.
ZIF-8 nanoparticles are also used as fillers to construct fluorine free superhydrophobic antifouling coatings together with polydimethylsiloxane (PDMS) to avoid the harm of fluorine-containing reagents to the environment. In order to improve poor strength of PDMS, chalcone is polymerized with PDMS and crosslinked under ultraviolet light to enhance the mechanical strength and adhesion of the coating. The antifouling agent BITEP was added to prepare chalcone-ZIF-8@BITEP (CZB) coating. The contact angle test shows that the CZB4 coating has a contact angle higher than 162°, and its superhydrophobicity significantly reduces the adhesion of fouling organisms. After co-culturing with diatoms for 21 days, only 0.09% of the surface of CZB4 coating adhered, and CZB4 coating also has excellent corrosion resistance after salt spray testing. Even if the superhydrophobic barrier fails, ZIF-8 can still serve as a safety barrier to release antifouling agents. CZB4 showed bactericidal rates of 89.0% and 93.9% against E. coli and S. aureus, respectively, further improving the service life of the coating.
Overall, this study proposed 4 types of multifunctional antifouling coatings based on the use of capsaicin mimetics and MOF nanoparticles. Through the coupling of various antifouling strategies such as superhydrophobicity, antifouling agent release, and quaternary ammonium sterilization, the antifouling performance and anti-corrosion ability of the coatings have been improved, providing potential advancements for the development of marine antifouling coatings.
However, there are also many issues with this study, such as insufficient testing of antifouling performance and insufficient duration of sea experiments. In the future, various anti fouling strategies such as slippery liquid fused porous surfaces (SLIPS) and self-degradation can be combined to develop more efficient and environmentally friendly multifunctional marine anti fouling coatings.
| Date of Award | 18 Jul 2026 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Hao Chen (Supervisor), Hua Li (Supervisor) & Ming Li (Supervisor) |
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