Effect of graphitic carbon nitride anisotropy on water transport performance: Insights from molecular dynamics simulations

The transport efficiency of water molecules on two-dimensional (2D) nanomaterial surfaces is intrinsically linked to the structural configuration of their migration pathways. Identifying the optimal transport orientation of anisotropic nanochannels is beneficial for improving the performance of nanofluidic devices. In this work, we simultaneously investigated the spontaneous and pressure-driven water transport behavior within graphitic carbon nitride (g-C3N4) nanochannels with different orientations via molecular dynamics simulations. It was found that within g-C3N4 nanochannels of different orientations, water molecules exhibited distinct spreading patterns. The molecular details revealed that water molecules within g-C3N4 nanochannels are prone to migrate along a "natural defect-half structural unit-natural defect" pathway in the absence of external pressure. However, an orientation that enables water molecules to spread more quickly does not guarantee a higher water conduction rate. The g-C3N4 nanochannels have low water conduction efficiency when the major pathway is not oriented in the same direction as the pressure gradient. Adjusting the orientation of the g-C3N4 nanochannel could increase its water flow rate by 17.9%. This work theoretically highlights the distinction between the spreading process and the water conduction process. We believed that identifying the optimal orientation of 2D membranes can better aid in developing novel nanofluidic devices.