Growth of nano-porous covalent organic frameworks on graphenic carbon hollow spheres; towards designing advanced multi-functional nanocomposites

For the first time, melamine-based covalent organic frameworks (COFs) were synthesized in situ on the graphenic shells of carbon hollow spheres (CHSs) for achieving a hybrid nanomaterial with unique thermo-mechanical characteristics. To improve the thermal stability of CHS-COF nanostructures (NSs), Zn²⁺/sodium L-glutamate (ZG) inorganic-organic complexes were loaded in their porosities and interior spaces (denoted as ZG@CHS-COF). The fabricated epoxy nanocomposites illustrated enhanced thermo-mechanical and UV-shielding properties. The tensile strength of the epoxy coatings, filled with CHS-COF and ZG@CHS-COF NSs, increased by 185 and 168 %, respectively, compared to the blank epoxy. DMTA results revealed that the glass transition temperature (T_g) of the epoxy, filled with CHS-COF and ZG@CHS-COF NSs increased around 2.1 and 8.1 °C, respectively. Also, the lower height of tan(δ) peaks (HTP) in the presence of CHS-COF and ZG@CHS-COF NSs illustrated their better interactions with epoxy chains. The highest ash content (≈46.3 %) and superior thermal durability were acquired in the presence of ZG@CHS-COF NSs. TEM results confirmed the better dispersion and distribution of ZG@CHS-COF NSs than CHS ones. The ZG@CHS-COF-filled epoxy coating led to a 71 % reduction in color changes (ΔE) after 3 weeks of UV irradiation.