In Situ Reduction of Silver Nanoparticles/Urushiol-Based Polybenzoxazine Composite Coatings with Enhanced Antimicrobial and Antifouling Performances

Abstract

Marine anti-fouling coatings represent an efficient approach to prevent and control the marine biofouling. However, a significant amount of antifouling agent is added to improve the static antifouling performance of the coatings, which leads to an issue whereby static antifouling performance conflicts with eco-friendly traits. Herein, this work reports an in situ reduction synthesis of silver nanoparticles (AgNPs) within polymers to produce composite coatings, aiming to solve the aforementioned issue. Firstly, urushiol-based benzoxazine monomers were synthesized by the Mannich reaction, using an eco-friendly natural product urushiol and n-octylamine and paraformaldehyde as the reactants. Additionally, AgNPs were obtained through the employment of free radicals formed by phenolic hydroxyl groups in the urushiol-based benzoxazine monomers, achieved by the in situ reduction of silver nitrate in benzoxazine. Then, the urushiol-based benzoxazine/AgNPs composite coatings were prepared by the thermosetting method. AgNPs exhibit broad-spectrum and highly efficient antimicrobial properties, with a low risk to human health and a minimal environmental impact. The composite coating containing a small amount of AgNPs (≤1 wt%) exhibits effective inhibition against various types of bacteria and marine microalgae in static immersion, thereby displaying outstanding antifouling properties. This organic polymer and inorganic nanoparticle composite marine antifouling coating, with its simple preparation method and eco-friendliness, presents an effective solution to the conflict between static antifouling effectiveness and environmental sustainability in marine antifouling coatings.

Keywords: AgNPs; environmentally friendly; in situ reduction; static antifouling; urushiol-based benzoxazine.

Figure 1

(a) Collection of raw lacquer and chemical structure of urushiol, (b) synthetic route of urushiol-based benzoxazine, (c) preparation of UOB/AgNPs composites and UOHP/AgNPs composite coatings.

Figure 2

(a) Mechanism of free radical formulation in the structure of urushiol and preparation of AgNPs by in situ reduction, (b) UV-vis spectra of UOB solution and UOB/AgNP composites, (c) ATR-FTIR spectra of UOB and UOB/AgNP composites.

Figure 3

(a) XRD patterns of UOHP coating and UOHP/AgNP composite coatings, (b) XPS survey of UOHP coating and UOHP/AgNP composite coatings, (c) XPS high resolution Ag 3d spectra of UOHP/AgNP composite coatings.

Figure 4

EDS analysis of surface chemical composition and mapping of (a) UOHP, (b) UOHP-0.05%AgNPs, (c) UOHP-0.1%AgNPs, (d) UOHP-0.5%AgNPs and (e) UOHP-1.0%AgNPs composite coatings. The information displayed at the bottom of each single image is as follows: MAG: 10,000×, HV: 10 kV, WD: 10.9 mm, and scale bar is 2 μm.

Figure 5

HR-TEM images of UOHP-1.0%Ag composite coating at different magnification scales (a–d), (e) element mapping of AgNPs, (f) EDS analysis of UOHP-1.0%Ag composite coating.

Figure 6

(a) TGA and (b) DTG curves of UOHP and UOHP/AgNP composite coatings.

Figure 7

The WCA and SFE of UOHP and UOHP/AgNP composite coatings.

Figure 8

Digital photographs of antibacterial test towards typical (a) Gram-negative bacteria E. coli, (b) Gram-positive bacteria S. aureus, marine bacterial (c) V. alginolyticus and (d) Bacillus sp. after 24 h of incubation on (i) BG, (ii) UOHP, (iii) UOHP-0.05%AgNPs, (iv) UOHP-0.1%AgNPs, (v) UOHP-0.5%AgNPs and (vi) UOHP-1.0%AgNPs. (e) The inhibition efficiency of UOHP and UOHP/AgNP composite coatings relative to BG towards E. coli and S. aureus, V. alginolyticus and Bacillus sp.

Figure 9

Adhesion of bacteria (a) E. coli, (b) S. aureus (c) marine bacterial V. alginolyticus and (d) Bacillus sp. after 24 h of incubation period on surface of (i) BG, (ii) UOHP, (iii) UOHP-0.05%AgNP, (iv) UOHP-0.1%AgNP, (v) UOHP-0.5%AgNP and (vi) UOHP-1.0%AgNP composite coatings by FE-SEM images (the scale bars are 5 μm).

Figure 10

Fluorescent photographs of (a) N. closterium, (b) P. tricornutum and (c) D. zhan-jiangensis adhesion after 5 days of cultivation time on (i) BG, (ii) UOHP, (iii) UOHP-0.05%AgNPs, (iv) UOHP-0.1%AgNPs, (v) UOHP-0.5%AgNPs and (vi) UOHP-1.0%AgNPs composite coatings (the scale bars are 100 μm), (d) statistical chart showing algal density in examined fields by ImageJ 1.52a software, (e) antifouling mechanism of UOHP/AgNP composite coatings.