Paper Title
The Composition of a Few Layers of Transition Metal Dichalcogenidesnanosheets Influences the Separation Mechanism of High Permeance Hydrogen Selective Laminar Membranes

Abstract
Simultaneous exfoliation and functionalization of transition metal dichalcogenides (TMDs) nanosheets in membrane applications is fascinating. The chemical composition of two-dimensional TMDs influences nanosheet stacking in laminar membrane and alters the gas separation behavior of the stacked layer, yet little is known about this phenomenon. In this study, tannic acid (TA) is employed for membrane preparation in order to perform a simple, an environmentally friendly aqueous exfoliation of TMDs. Because of its aphiphilicnature the TA not only served as a negatively charged surfactant, but it also adhered to delaminated nanosheets of TMDs, enabling for effective delamination of the bulk TMDs. The microstructure of WSe2, MoSe2, and MoS2 laminar membranes was studied using X-ray diffraction and positron annihilation spectroscopy in order to correlate membrane microstructure and interlayer spacing with gas transport mechanisms. The ability of the developed membranes to separate H2/CO2 exceeds Robeson`s upper bound. The major gas transport mode of the membranes flips from molecular sieving to Knudsen diffusion when the transition metal tungsten is replaced with molybdenum. The chalcogen atom change, on the other hand, has no effect on the gas transport mechanism. Our experimental finding pave the way for membranes to be developed for industrial applications including H2 refinement and CO2 removal. Keywords - Transition Metal Dichalcogenides, Exfoliation of 2D Nanosheets, Tannic Acid, Microstructure Analysis, H2 Selective Membrane.