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

Abstract

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 (1011–1012 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.

Bioinspired Large‐Area Atomically‐Thin Graphene Membranes

“…Such obvious difference could translate to a breakage pressure of 10 bar for the graphene layer, indicating a 2 to 26 times improvement compared to state‐of‐the‐art graphene membranes ( Figure a), and demonstrating that the GCM can withstand higher pressure for practical application. [ 28,32,35,36,38–41,50,51 ]…”

“…Finally, a double-layer graphene composite membrane was obtained after repeating the above hot-pressing and etching processes for this structure. As elaborated elsewhere, plasma etching induced nanopores in the double-layer graphene surface at 10 Pa of argon atmosphere with 50 W of power for 40 s. [51] Structural Characterization: The graphene-Cu foil samples after heat treatment were analyzed by optical microscopy (LV100ND, NIKON, Japan) to evaluate the quality of the graphene film, which was easy to identify the oxidized area of copper foil not covered by graphene. [36] The SEM images were obtained by FEI Quattro S (Thermo Fisher Scientific, USA) at an accelerating voltage of 5.0 kV.…”

“…Analysis of mechanical performance. The comparisons of breakage pressure a), stress-strength-stiffness b), and strain c) of this work with literature studies [28,32,35,36,[38][39][40][41]50,51]. d) Optical images of the GCM under different conditions of bending.…”

“…These results indicated the successful and cost-effective fabrication of large-area GCMs with high coverage and negligible defects, which is critical for practical application. [28,32,35,36,[38][39][40][41]50,51] d) Optical images of the GCM under different conditions of bending. e) Photographs of the GCM before and after bending.…”

“…Such obvious difference could translate to a breakage pressure of 10 bar for the graphene layer, indicating a 2 to 26 times improvement compared to state-of-the-art graphene membranes (Figure 3a), and demonstrating that the GCM can withstand higher pressure for practical application. [28,32,35,36,[38][39][40][41]50,51] The tensile tests were performed on the membranes to study the tensile performance of the GCMs, as shown in Figure 3b (inset). As a result, the fracture stress, fracture strength, and tensile stiffness are 33.3 MPa, 33.3 N, and 35011 N m −1 , respectively (Figure S4, Supporting Information), [21] up to 17, 67, and 94 times higher than other graphene-based membranes (Figure 3b).…”