Environmentally benign fouling release metallosurfactant coatings; evaluation of surface properties, leaching rate, biocorrosion resistance and durability

Abstract

Biofouling is the biggest issue that impair the success of marine infrastructure. The biofilm forming aerobic bacteria Pseudomonas aeruginosa present in sea water causes considerable environmental and economic losses by initiating microbially induced corrosion. Concerning the importance of fouling release coatings, we are aimed to fabricate non-toxic metallosurfactants (MS) coating on carbon steel to mitigate growth and adhesion of biofilm and consequent corrosive reactions on its surface. As the toxic ion release from fouling-release metallic coatings have deleterious effect on the aquatic eco-system therefore the MS coatings with slow release of metal ions can be a greener approach in this field. Here, we report the surface modification of CS with self-assembly of a series of MS viz. MC42H76N2Cl4, where M = Co, Ni and Cu. The MS under study is a complex of an anti-corrosive surfactant ligand cetyl pyridinium chloride (CPC) and transition metal salts in a stoichiometry of 2:1 (CPC: M). For surface modification, a cost-effective sol–gel technique was adopted. The coatings were characterized by Fourier Transform Infra-Red Spectroscopy (FT-IR), Atomic force microscopy (AFM), Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The chemical composition of coatings reveals the presence of anti-bacterial metal ions present in mixed oxidation state causing the variable rate of their leaching in sea water media (M1942). The quantification of metal ions leached from metallosurfactant coating after immersing in M1942 media was done using inductively coupled plasma-mass spectrometry (ICP-MS). The ICP-MS data shows 19.86 ng/mL release of Cu ions from coating after 21 days of immersion which advocates its slow-release nature. The corrosion activities of sea water salts and marine bacteria Pseudomonas aeruginosa on bare and modified CS substrates was extensively studied by employing standard electrochemical tests like potentiodynamic and potentiostatic polarisation, Electrochemical Impedance Spectroscopy (EIS). The potentiodynamic polarisation test shows the coatings exhibit corrosion inhibition efficiency up to 93.5%. The coatings remained intact even after polarisation at +0.7 V in sea water media. Atomic force microscopy (AFM) and Scanning Electron Microscopy (SEM) was conducted to check corrosion morphology and biofilm characteristics. The DEAD/LIVE test of biofilm displays a higher ratio of dead bacteria on modified surface as compared to bare which demonstrate the antibacterial character of coatings. The results obtained from various corrosion tests reveal this strategy can be used to develop long term and eco-friendly anti-fouling coatings.