Ultrastable Porous Covalent Organic Framework Assembled Carbon Nanotube as a Novel Nanocontainer for Anti-Corrosion Coatings: Experimental and Computational Studies.

Abstract

Covalent organic frameworks (COFs) have been proposed as a wholly organic architecture sharing high crystallinity, porosity, and tuneability. Moreover, they exhibit highly stable structures against harsh chemical environments, including boiling water, strong acids and bases, and oxidation and reduction conditions, making them good candidates for extreme conditions. For the first time, a porous COF structure based on terephthalaldehyde and melamine was synthesized and employed as a novel nanocontainer for hosting corrosion inhibitors to provide a coating with superior active/passive anti-corrosion properties. In this study, the multi-walled carbon nanotube was utilized as a platform for growing COF (CC) to improve the coating's barrier and thermo-mechanical properties. The zinc cations were loaded into the CC structure (called CCZ) as one of the most promising inhibitors for mild steel. The COF-based nanoparticles' characterization was done by Fourier transform infrared, Raman, X-ray diffraction, thermogravimetric analysis, Brunauer-Emmett-Teller, field emission scanning electron microscopy, and transmission electron microscopy (TEM) techniques. Moreover, the Density functional theory modeling and molecular dynamics simulation quantitatively highlighted the adsorption propensity of the investigated COF structures onto the oxidized CNT-based nanostructures and the interactions of epoxy with these nanostructures. The CCZ nanoparticles (NPs) showed 75% inhibition efficiency in saline solution and 418 ppm zinc ions release after 24 h at acidic pH. The CCZ/EP coating revealed the smart release of inhibitor for 24 h and represented excellent barrier properties after 9 weeks of immersion in saline solution. In terms of mechanical properties, the elastic modulus values derived from the dynamic mechanical thermal analyzer were enhanced by 107 and 137% in CC/EP and CCZ/EP samples compared to the neat epoxy. Furthermore, the yield stress and breakpoint elongation were strengthened by 102 and 63% for the CC/EP sample, respectively. Finally, the highest pull-off adhesion strength in dry (8.53 MPa) and wet (2.7 MPa) conditions, along with the lowest adhesion loss (68.3%), was related to the CCZ/EP sample.