Fouling can occur as the result of the growth of bacteria, algae, or mollusks in harbor facilities, on boat hulls, and aquaculture netting. The resulting damage and consequential costs can be significant and is estimated to be equivalent to $200 billion annually in the shipping industry alone. To address this problem, chemists at Johannes Gutenberg University Mainz (JGU) (Mainz, Germany) developed an environmentally friendly method to reliably hinder hazardous seawater fouling that is effective and affordable.
Protective coatings applied to vessels usually contain copper-based biocides, which may harm the environment and become ineffective due to resistance developed by organisms. To find an alternative, a JGU research team simulated a defense mechanism employed by algae, and established that cerium dioxide (CeO2) nanoparticles can effectively prevent fouling. This discovery could lead to the production of new protective coatings that are much less environmentally harmful than antifouling coatings in use now.
Marine algae utilize secondary metabolic products that provide a form of chemical defense against microorganisms and predators. These halogenated secondary metabolites specifically prevent bacterial biofilms, other algae, and even barnacles from becoming attached to and developing on larger formations of algae, sponges, and other creatures. This natural defense process has been mimicked by the research team using CeO2 nanoparticles. “Field tests have shown that cerium dioxide is an ecologically acceptable alternative to cuprite, a substance that is used as a biocide together with copper thiocyanate and copper pyridine at concentrations of up to 50 percent in antifouling coatings,” explains Wolfgang Tremel, a professor with JGU’s Institute of Inorganic Chemistry and Analytical Chemistry. Such copper compounds are toxic and accumulate in the environment, which motivated some countries, such as Canada and Denmark, to impose strict limitations on the use of copper-based antifouling coatings.
“What we have here is an environmentally compatible component of a new generation of antifouling coatings that simulate the natural defense systems employed by marine organisms. What is important is that it is effective not only under laboratory conditions but also when actually used in the aquatic environment,” says doctoral student Karoline Herget. Steel panels with CeO2 coatings were exposed to seawater for weeks on end without becoming covered by bacteria, algae, mollusks, or barnacles. Reference samples with conventional water-based coatings developed massive fouling over the same time period.
Biofilms are around virtually everywhere. They are present in drinking water pipes and clarification plants, in ground water, water filtration and cooling systems, etc. The main problem with combating these biofilms using biocides and antibiotics is the risk of the organisms developing resistance to the biocides. This drawback, the researchers say, could be effectively circumvented in an ecologically acceptable manner by applying surface coatings of CeO2 particles. They note this innovative technique has potential for applications such as ship and exterior coatings, roof coverings, outdoor textiles, polymer membranes used for desalination, aquaculture enclosures, and many plastic components.
The research project was undertaken in cooperation with BASF and the results have been published in the journal Advanced Materials. For additional information, visit uni-mainz.de.