Indole-functionalized polythiourethane/tetrapodal shaped ZnO nanocomposites for eco-friendly marine biofouling control

Antifouling coatings for marine use are a widely employed method for controlling the settlement and growth of unwanted aquatic organisms on surfaces. In this study, indole derivative N-(1H-5-bromo indole-3-ylmethyl) acrylamide (BIAM)-functionalized polythiourethane (PTU)/tetrapodal shaped zinc oxide (t-ZnO) nanocomposites (PTU/BIAM/t-ZnO) were synthesized through a Friedel–Crafts Alkylation reaction, thiol-ene click reaction and polyaddition reaction. Nanocomposites' surface characteristics, such as surface free energy, chemical composition, and surface morphology were investigated here. The mechanical characteristics and antifouling properties of the coating materials were also considered. These nanocomposites exhibited not only superior mechanical properties, due to the presence of both PTU and t-ZnO, but also promising antifouling properties owing to the incorporation of BIAM on their surfaces. The adhesion strength of the nanocomposites increased from 0.26 MPa to 0.68 MPa due to the incorporation of t-ZnO particles. Benefiting from the PTU matrix, the tensile strength of nanocomposite can reach over 57 MPa. The PTU/BIAM/t-ZnO nanocomposites demonstrated improved algae resistance and marine antifouling performance compared to the reference PTU/t-ZnO nanocomposite without indole derivative. The PTU/BIAM/t-ZnO nanocomposites exhibit resistance to fouling organisms due to the synergistic effect of the easy-to-clean characteristic of the PTU/t-ZnO and the reduction of the polar component of the surface free energy resulting from the inclusion of indole derivative BIAM on the surface. This, in turn, reduces the interaction between fouling organisms and the material surface. Furthermore, BIAM interferes with the homeostasis of cellular calcium ions, thereby hindering the attachment of fouling organisms. Under the combined action of PTU, BIAM, and t-ZnO, the synergistic effect of good antifouling properties, environmental compatibility, good mechanical properties and strong adhesion to the substrate was achieved.