Superhydrophobic Nano-Engineered Zinc Oxide/Titanium Dioxide-Phosphate-Based Coatings with Photocatalytic and Anticorrosive Properties

Abstract

The proposed coatings are based on the application of composite films incorporating hydrophobic materials over the hierarchically arranged self-assembled ZnO/TiO2 nanoparticle-based composites chemically fused to the substrate using phosphate chemistry mechanisms, ultimately providing the micro- and nano-scale bumps on the surface. This approach enables biomimicry of a “Lotus effect,” creating durable multi-scale surface roughness enhancing hydrophobic, anticorrosive, photocatalytic, and antimicrobial properties (XPAC). In addition, the superhydrophobic properties help to repel the respiratory droplets, thus minimizing the ability of pathogens to linger on surfaces and facilitate cleaning procedures.The photocatalytic reactions take place on the TiO2 and ZnO components of the coatings, allow the deactivation of pathogens on the surface, and introduce the antimicrobial properties of the system. Systems containing titania were capable of decomposing 99.2% of organic pollutants within 60 minutes under UV light exposure. Application of the two-layer surface treatment surpasses corrosion current density 253-fold, increases polarization resistance of the coating system 232-fold, and inhibits corrosion by 99.6%, showing excellent anticorrosive effectiveness. Neutron microscope and goniometer wetting characterizations proved the creation of stable over- and superhydrophobic surfaces. The friction behavior of coated with different formulations steel samples were compared to uncoated steel substrates through tribological characterization. The coefficient of friction of uncoated metal substrates, ranging from 0.221 to 0.269, and the two-layer hydrophobic coatings, ranging from 0.234 to 0.273, indicated that the coating systems confer hydrophobic properties to the substrates without a notable change in the friction behavior. Correlations between surface wetting, friction behavior, and average roughness were drawn. It was demonstrated that enhancement of surface roughness allows the formation of a superhydrophobic system capable of creating effective water barriers on the surface with contact angles exceeding 150°, which remain effective even after relatively extensive surface damage. Combining these value-added features in robust coatings enables to overperform the limitations intrinsic to existing products. Forming a stable non-homogenous interface with a stable hydrophobic response achieved with proposed coatings suggests that these coatings can find wide applications in industry.