Atomically Thin Graphene for a Membrane-Based Total Organic Carbon Analyzer

Stability is a vitally important criterion to measure the effectiveness of a membrane, especially in the engineering fields. Although polymeric membranes are widely used, stability problems frequently arise in long-term applications. Two-dimensional atomically thin materials, especially graphene, have aroused wide interest from membrane science due to the excellent physical and chemical properties and, most importantly, the ability to simultaneously achieve high selectivity and high permeability. However, defects are generated in the growth and transfer process, impairing the desired properties and resulting in unstable performance of graphene membranes. Therefore, overcoming the negative effects from defects is urgent for their applications. Here, we report a facile route to produce stability-enhanced double-layer graphene membranes and provide an application paradigm of graphene in a membrane-based precision instrument, the membrane-based total organic carbon (TOC) analyzer. The first layer and the second layer of graphene were respectively transferred onto the polymer substrate through phase inversion and heat pressing methods. Then, Ar plasma was employed to accurately create high-density (10(11)-10(12) cm(-2)) nanopores in the graphene lattice. The obtained double-layer graphene membranes could function normally in the TOC analyzer with a higher precision (signal linear correlation R-2 of 99.64%) than the polymeric membranes (99.16% for poly(vinylidene fluoride) and 99.33% for Teflon). Furthermore, the stability of double-layer graphene was evidently better (RSD (relative standard deviation) of 1.93%) than that of the single-layer graphene membrane (3.12%) in the continuous measurement for 7 days. Moreover, the stability-enhanced double-layer graphene membranes could work properly for more than 30 days (RSD of 2.50%), which have potential to satisfy the industry standards. Therefore, our work not only provides a solution to enhance the stability of membranes, which is significant in engineering fields, but also bridges the gap between the "proof-of-concept" in the laboratory and the application of graphene in membrane-based precision instruments.