Thermal Conductivity of a 2D Covalent Organic Framework and Its Enhancement Using Fullerene 3D Self-Assembly: a Molecular Dynamics Simulation

Covalent organic frameworks (COFs) have attracted growing interest for their potential applications in gas storage and separation. However, the extremely low thermal conductivity is one of the biggest stumbling blocks of practicality of COFs. In this regard, a simulation based on an equilibrium molecular dynamic method is first employed to study the thermal conductivity of two-dimensional COF-1, which is on the order of 1 W/(m·K) and 0.01 W/(m·K) in the XY and Z direction, respectively. Furthermore, a newly reported nanopatterning C60@COF-1 composite material is predicted to have a huge boost in thermal conductivity with an order of magnitude of 10 W/(m·K). Within the temperature range of 200–500 K, the thermal conductivities of COF-1 and its three dimensional counterpart decrease as temperature increases. The energy transfer and localization of COF-1 are analyzed by the phonon density of states and overlap energy between different atom types to find out the barrier to heat transfer. Theoretical analysis of the vibrational density of states and the phonon mode participation ratio shows that the addition of C60 contributes a greatly activated phonon vibration in the low-frequency mode and a better match between different atoms, and as a result, a tenfold increase occurred in the thermal conductivity of C60@COF-1 prior to that of COF-1.