Highly selective CO2/C2H2 separation with porous g-C9N7 nanosheets by charge and strain engineering

Efficient CO2/C2H2 separation at ambient conditions is an essential but challenging process owing to their similar molecular sizes and physical properties. In this work, a novel approach of charge/strain-regulated gas capture and separation was proposed, which offered the advantages of reversibility and controllable kinetics. Highly selective CO2 separation from CO2/C2H2 with porous g-C9N7 nanosheets were demonstrated with varying charge densities and strains using molecular dynamics (MD) simulations and first-principle density function theory (DFT) calculations. The remarkable CO2 permeance up to 5.85 × 107 GPU can be achieved by charge engineering. Under the condition of tensile strain, a controllable CO2 separation performance was exhibited, whose CO2 permeance increased with increasing the applied strain. The maximum permeance was 3.44 × 107 GPU with 9% strained g-C9N7 membrane. More interestingly, a promising approach combining the charge regulation with strain engineering was explored to investigate the synergistic effect. Under conditions of 2 e- charge and 3% tensile strain on g-C9N7 membrane, the CO2 permeance reached 4.24 × 107 GPU, which was 1.6 times of CO2 permeability when only 2 e- was added and 10 times of CO2 permeance when only 3% strain was added. Additionally, the energy barrier of CO2 decreased with the increasing degree of regulation (charge and strain engineering) on the g-C9N7 membrane, indicating that the g-C9N7 membrane can be served as an excellent candidate for CO2/C2H2 separation. These results provide useful guidance for developing advanced materials and applying new regulation techniques to realize highly tunable and selective CO2/C2H2 separation.