Pyrenebutyric acid-assisted room-temperature synthesis of large-size monolayer graphene oxide with high mechanical strength

Graphene oxide (GO) has received great attention for its potential applications. The formation of large-size GO is favoured for its high mechanical properties and low structural defects. Improved Hummers' method is a commonly used method for GO synthesis. However, the production of large-size GO is often limited by the inevitable GO fragmentation caused by excessive oxidation and mechanical exfoliation. Here, we discovered that adding 1-pyrenebutyric acid (1-PBA) during the pre-treatment of graphite with sulfuric acid protects graphite from excessive oxidation and facilitates its self-exfoliation. Consequently, 99% monolayer GO with an average lateral size of 116 μm was obtained without external forces. Furthermore, X-ray photoelectron spectroscopy and Raman analyses showed that the large-size GO synthesized in the presence of 1-PBA has a high C/O ratio of 3.62 and low Raman I _D/I _G ratio of 0.83, so it has low structural defects. A mechanism of 1-PBA during GO synthesis was proposed. Moreover, we investigated the mechanical property of GO synthesized with 1-PBA and how the lateral size of GO affects the mechanical properties of GO films. Our results showed that the LGO film displayed the highest tensile strength (127 MPa) due to a denser, more aligned and compact structure than other GO films.