Abstract:  Defects, whether intentionally created or inadvertently formed, are ubiquitous in all materials, including two-dimensional (2D) materials. Nevertheless, not much is known as to how these defects form, what topologies of defects are more likely to form, and how the defect topology affects the performance of 2D materials in various applications. Our group has been working to combine quantum-mechanical density functional theory (DFT) calculations with classical molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations to understand the formation of nanopores in 2D materials and their effects on molecular and ion transport on and through these materials.

In this talk, I will discuss the combined use of DFT, KMC, and chemical graph theory to predict nanopore shapes in graphene in excellent agreement with microscopy images. I will introduce the use of gradient-boosted machine learning strategies, coupled with structural features of nanopores, to predict the probabilities and formation times of arbitrary nanopore shapes in graphene. I will also explain how defects influence water slippage on the surfaces of 2D materials, showing via MD simulations, that the water slip length increases threefold on hexagonal boron nitride (hBN) in the presence of certain vacancy defects. Moreover, I will show that the presence of surface roughness in hBN, but not that of vacancy defects, can explain the experimentally observed water contact angle and slip length on hBN. Finally, I will discuss the adverse impacts of grain boundaries and surface charge on the salt rejection capability and water permeation rate of nanoporous hBN membranes. Overall, the multi-scale simulations presented in this talk will help understand and advance the controlled synthesis of nanoporous 2D materials and their applications in nanofluidics and membrane separations.

Bio: Ananth Govind Rajan is currently an Assistant Professor in the Department of Chemical Engineering at the Indian Institute of Science (IISc), Bengaluru. He obtained his B.Tech. degree from the Indian Institute of Technology (IIT) Delhi and his M.S. and Ph.D. degrees from the Massachusetts Institute of Technology (MIT).