Fabrication Of Large-area High-quality Single-layered Nanoporous Graphene And Its Nanofiltration Performance Study

Monolayer graphene,a sp²-bonded allotrope of carbon arranged in a two-dimensional lattice,exhibits extraordinary imperviousness and mechanical properties in its pristine form,making it an ideal material for separation applications.Recent proof-of-principle experiments have shown the performance of graphene in certain applications,such as ultrafast gas/liquid separation,molecular sensing and DNA sequencing,far exceeds the state-of-the-art.In these applications high quality graphene has to be suspended,which due to limitations of current fabrication techniques restricts the accessible size to tens of microns.Most attempts to support the graphene sheets are based upon introducing pores in the substrate onto which the graphene has been deposited or transferred,such as masking and etching of copper or photoresist.The complexity of this process prevents mass-production.Other attempts to fabricate large area suspended graphene membranes have been based on adhering CVD grown graphene sheets onto prefabricated porous supporting layers.However,in addition to inevitable lattice defects occurring during CVD growth the transfer process introduces further defects such as pinholes or cracks that are due to microscopic mismatches between the graphene and the supporting substrate.Although these defects can be sealed,they still are prone to failure in pressurized membrane applications such as filtration.Techniques for scalable fabrication of robust high quality suspended graphene sheets are still lacking,which prevents their commercialization for practical applications that are based on 2D membranes.We develop a scalable in-situ,phase-inversion casting technique to create 63 cm² high-quality single-layered perforated graphene membranes for ultrafast nanofiltration that can operate at pressures up to 50 bar.The work includes three major parts:1.In-situ fabrication of porous substrate on graphene by phase inversion,which realizes ultra-high single-layer graphene coverage on porous substrate?defect area less than 0.003%?.2.Sealing of defects in the graphene membrane by filtration of nanoparticles in the certain range of sizes.The flux of pure water at 50 bar is less than the detection limit of 0.5 L·M^-2·H^-1.3.Using ion bombardment followed by acidic potassium permanganate etching to create nanopores with less than 1 nm in diameter in the single-layered graphene.The graphene membrane obtained by the technique above is stable at a pressure of at least 50 bar without break.The membrane has a 5 to 10 folds increase in flux compared to existing commercial nanofiltration membranes.This result demonstrates the feasibility of our technique for creating robust scalable high quality graphene membranes for a host of separation applications,such as molecular separation,parallel DNA sequencing,molecular sensors or hydrogen fuel cells.