In this work, high pressure selective CO2/CH4 adsorption over functionalized covalent triazine based frameworks (CTF-NH) have been reported at high-pressure (1�20 bar) and different temperatures. The findings revealed that the successive incorporation of amine functionalities to the CTF leads to the enhancement of CO2 and CH4 adsorption capacities by 94.99 and 3.69, respectively. The CO2 and CH4 adsorption capacities decreased with rising temperatures. The selectivity of CO2/CH4 was improved from 2.745 to 5.145. The different adsorption isotherms showed good fitting agreement with the experimentally acquired data with a lower value (AARE and R2) approaching to 1. The isotherm analysis exhibited that the adsorption is heterogeneous and satisfactory under these conditions. Dubinin-Radushkevich (D-R) isotherm analysis showed that the physisorption is dominant, with adsorption energy of less than 20 kJ/mol. Finally, thermodynamic properties revealed that at lower temperatures, the adsorption phenomenon is satisfactory, physical in nature, and exhibiting less disorder and randomness. © 2020 Elsevier Ltd