Direct writing of graphene patterns and devices may significantly facilitate the application of graphene-based flexible electronics. In terms of scalability and cost efficiency, inkjet printing is very competitive over other existing directwriting methods. However, it has been challenging to obtain highly stable and clog-free graphene-based ink. Here, we report an alternative and highly efficient technique to directly print a reducing reagent on graphene oxide film to form conductive graphene patterns. By this "inkjet reduction" method, without using any other microfabrication technique, conductive graphene patterns and devices for various applications are obtained. The ionic nature of the reductant ink makes it clog-free and stable for continuous and large-area printing. The method shows self-limited reduction feature, which enables electrical conductivity of graphene patterns to be tuned within 5 orders of magnitude, reaching as high as 8, 000 S·m^–1. Furthermore, this method can be extended to produce noble metal/graphene composite patterns. The devices, including transistors, biosensors, and surfaceenhanced Raman scattering substrates, demonstrate excellent functionalities. This work provides a new strategy to prepare large-area graphene-based devices that is low-cost and highly efficient, promising to advance research on graphenebased flexible electronics.

An inkjet-printed graphene film is of great importance for next-generation flexible, low cost and high performance electronic devices. However, due to the limitation of the inkjet printing process, the electrical conductivity of inkjet-printed graphene films is limited to ~10 S·cm^–1, and achieving a high conductivity of the printed graphene films remains a big challenge. Here, we develop a "weak oxidation–vigorous exfoliation" strategy to tailor graphene oxide (GO) for meeting all the requirements of highly conductive inkjet-printed graphene films, including a more intact carbon plane and suitable size. The π-conjugated structure of the resulting graphene has been restored to a high degree, and its printed films show an ultrahigh conductivity of ~420 S·cm^–1, which is tens of times higher than previously reported results, suggesting that, aside from developing a highly efficient reduction method, tuning the GO structure could be an alternative way to produce high quality graphene sheets. Using inkjet-printed graphene patterns as source/drain/gate electrodes, and semiconducting single-walled carbon nanotubes (SWCNTs) as channels, we fabricated an all-carbon field effect transistor which shows excellent performance (an on/off ratio of ~10⁴ and a mobility of ~8 cm²·V^–1·s^–1) compared to previously reported CNT-based transistors, promising the use of nanocarbon materials, graphene and SWCNTs in printed electronics, especially where high performance and flexibility are needed.

We report a facile approach to synthesize narrow and long graphene nanoribbons (GNRs) by sonochemically cutting chemically derived graphene sheets (GSs). The yield of GNRs can reach ~5 wt% of the starting GSs. The resulting GNRs are several micrometers in length, with ~75% being single-layer, and ~40% being narrower than 20 nm in width. A chemical tailoring mechanism involving oxygen-unzipping of GSs under sonochemical conditions is proposed on the basis of experimental observations and previously reported theoretical calculations; it is suggested that the formation and distribution of line faults on graphite oxide and GSs play crucial roles in the formation of GNRs. These results open up the possibilities of the large-scale synthesis and various technological applications of GNRs.