Surface plasma Ag-decorated Bi₅O₇I microspheres uniformly distributed on a zwitterionic fluorinated polymer with superfunctional antifouling property

Highlights

• A novel Bi₅O₇I/Ag/ zwitterionic fluorinated polymer composite film is prepared.

• Ternary synergy contributed to the excellent antifouling performance.

• The ABZFP films are expected to be long-lasting and eco-friendly coatings.

Abstract

A novel superfunctional antifouling film composed of surface plasma Ag-decorated three-dimensional Bi₅O₇I flower-like microspheres incorporated in a zwitterionic fluorinated polymer (ZFP) fabricated is reported. The Bi₅O₇I/Ag/ZFP (ABZFP) composite film exhibits excellent diatom anti-adhesion performance and high antibacterial rates for Escherichia coli and Staphylococcus aureus of up to 99.62 % and 99.78 %, respectively. This is ascribed to the combination of photothermal catalysis, ion release, and hydration. On the one hand, as a semiconductor, Bi₅O₇I/Ag, is excited and generates reactive oxygen species (e.g., O₂ and OH) under visible light irradiation, and it also possesses good capability for photothermal catalytic antifouling. On the other hand, release of Ag⁺ and Bi³⁺ and the hydration layer formed by the resin provide antifouling capability, and thus the ABZFP films are expected to be long-lasting and environmentally friendly antifouling coatings. Thus, the multiple synergistic mechanism of the ABZFP composite film shows promise for potential application in marine antifouling.

Introduction

Biofouling or fouling is a naturally occurring phenomenon caused by accumulation, settlement, and rapid colonization of marine organisms (e.g., bacteria, algae, and mollusks) on submerged surfaces, including ship hulls, pipelines, oil platforms, and ocean sensors, in marine environments [[1], [2], [3]]. This causes serious problems, particularly for marine industries, because of deterioration of surfaces, increased roughness, higher fuel usage, and loss of vessel speed [4,5]. Historically, toxic release has been used to combat marine biofouling, but it causes severe ecological damage. Thus, there is an urgent need for new antifouling strategies that are more environmental friendly but effective controlling adhesion of fouling communities [6,7].

Recently, the photocatalytic antifouling technique, an economical, effective, and environmentally photooxidation process, has attracted much attention because it uses solar energy and has low toxicity [8,9]. This approach is considered to be a promising technique for marine engineering materials [10,11]. When semiconductor materials are irradiated by visible light, reactive oxygen species (ROS), such as e⁻, h⁺, OH, and O₂⁻, are produced, and they play important roles in photocatalytic systems [12,13]. Many types of semiconductor materials, such as TiO₂, C₃N₄, and ZnO, are considered to be suitable photocatalysts for widespread application because of their high activity, stability, and low cost [[14], [15], [16], [17]]. TiO₂ is the most widely used photocatalyst because of its low cost, good stability, and environmental friendly characteristics. However, its band-gap energy of 3.2 eV means that TiO₂ can only absorb a small fraction of solar energy (<4%) [18,19]. To achieve sufficient utilization of solar energy, novel photocatalysts driven by visible light have attracted considerable attention. Bismuth oxyhalides (BiOX, X = Cl, Br, and I) are a group of V–VI–VII ternary compound semiconductors with layered configurations composed of [Bi₂O₂] layers, and they have recently shown low recombination rate of electron–hole pairs and remarkable photocatalytic activity [[20], [21], [22]]. Among the bismuth oxyhalides, BiOI has been extensively investigated because of its visible light absorption range and suitable band-gap energy, and it has attracted extensive research interest in the field of photocatalysis [23,24]. Unfortunately, because of some deficiencies, such as unsatisfactory charge separation and utilization efficiency, the low light absorption efficiency of BiOI greatly limits its further applications. A series of optimized strategies have been explored to overcome these intrinsic deficiencies, such as crystal face exposure, ion doping, and heterojunction construction [[25], [26], [27]]. Recently, a bismuth-rich strategy has been reported to be effective for improving the photocatalytic efficiency of bismuth oxyhalides, and Bi₅O₇I possesses a more positively positioned valence band edge and generates more photoholes than other bismuth oxyhalides (such as BiOI, Bi₄O₅I₂ and Bi₂O₃) [28,29].

It has been reported that some metals (including Ag and Pt) deposited on the surface of photocatalysts act as an electron mediator and also exhibit plasmon-enhanced light harvesting and charge separation [29,30]. Ag nanoparticles are commonly used as an effective co-catalyst and active sites on the surface of semiconductors, because Ag has low cost and excellent ability for absorbing visible light owing to surface plasmon resonance [31,32]. However, released Ag ions can change the permeability of the cytomembrane and denature proteins in biofouling organisms, which cause the fouling organisms to lose their bioactivity [33,34].

Photoexcitation of semiconductors can also generate heat, which have higher initial carrier temperature than the lattice temperature. Some nanoparticles containing Au, Ag, and Bi have been reported as photothermal materials based on their light absorption to exhibit a photothermal response [[35], [36], [37]]. Therefore, the Ag plasmon-enhanced Bi₅O₇I composite can act as a photothermal agent for antifouling applications.

Zwitterionic polymers have also attracted considerable attention as promising antifouling materials owing to their high hydrophilicity and environmental stability. They contain equal numbers of opposite charges within each repeat unit, resulting in a net medium charge but a high density of local charge [38,39]. This locally highly charged feature causes a significant hydration layer on the surface of the zwitterionic polymer by electrostatic interactions. Although zwitterionic polymers exhibit effective antifouling properties, many defects still exist [40]. Modification of zwitterionic polymer surfaces with nanoparticles is a common strategy to improve the resistance to adhesion [41].

In this study, we prepared Bi₅O₇I/Ag/zwitterionic fluorinated polymer (ZFP) (ABZFP) composite films consisting of a flower-like Bi₅O₇I structure, plasma-enhanced Ag co-catalyst, and ZFP for the first time. Their crystal structures, chemical compositions, chemical valences, and morphologies were then investigated. Their antifouling activities and photocatalytic activities under visible light irradiation were also investigated. In addition to the individual function of each component, the combination of Ag, Bi₅O₇I, and ZFP realized synergistic ion release, photothermal catalysis, and the hydration effect to improve the antifouling activity. These results may open a new route for marine antifouling.