research topic

Recently, graphene, a carbon-based two-dimensional substance, has been considered an ideal membrane material for liquid and gas separation because of its atomic thickness and extraordinary mechanical strength. Based on this outlook, concepts for graphene-based membranes (nanoporous graphene, stacked graphene, and mixed matrix graphene-based membranes), have recently been suggested. Beyond graphene, other 2D nanomaterials such as MXenes and MoS2, have also been spotlighted as novel membrane materials. However, due to several technological and economic challenges, it has been also shown that the practical application of graphene (or other 2D nanomaterials)-based membranes is not straightforward. Our research aims at overcoming a number of key challenges for the practical implementation of graphene- and other nanomaterial-based membranes into liquid and gas separation systems.

Recently, forward osmosis (FO), which uses natural osmotic pressure as a driving force to desalinate, has been recognized as a low-energy next-generation desalination technology. FO exhibits practical hurdles such as non-sufficient water flux in practical terms and low system stability due to its inborn nature of non-pressure- driven membrane processes. In our group, the FO process has been studied to address important findings in practical terms.

A bioelectrochemical system (BES) is a versatile electrochemical device capable of simultaneously recovering energy from organic waste and treating wastewater. Membrane-based technologies for water/wastewater treatment and energy production, such as electrodialysis, forward osmosis, reverse electrodialysis, and ultrafiltration, have been integrated into BESs to improve their performance.

Membrane-based technology is a simple and energy-efficient process since it uses only gas diffusion rate differences to separate the gases, and no phase changes and intermittent cycles are involved. However, one of the drawbacks of membrane-based technology is that the produced gas purity and production scale remain insufficient to match that of cryogenic distillation and adsorption. Particularly, polymeric membranes suffer from a permeability-selectivity trade-off which limits their separation performances. To address this challenge, various nanomaterial fillers have been incorporated into polymer matrices to realize mixed matrix membranes (MMMs). The fillers should possess a high capacity to adjust the gas transport and physicochemical properties of the MMMs.

One- and two-dimensional nanomaterials such as carbon nanotubes, graphenes, and MXenes have the catalytic ability and high electrical conductivity that can be leveraged for membrane application, by endowing membranes with electrically conductive and electrochemically catalytic capabilities. This smarter and more versatile membrane platform possessing these electrical and electrochemical functions is referred to as an electrically responsive membrane (ERM). With the assistance of external power, ERMs can conduct additional capabilities that conventional membranes cannot perform. In previous studies, it was demonstrated that electrically responsive membranes can be used for mitigating membrane fouling, monitoring membrane fouling propensity, self-cleaning, electrochemically oxidizing organic contaminants, controlling permeability and selectivity, energy recovery, and controlling membrane wettability.