This paper, written by researchers from Xi'an Jiaotong University and others, discusses Salt and water co-assisted exfoliation of graphite in organic solvent for efficient and large scale production of high-quality graphene. The paper is published in an important journal < Journal of Colloid and Interface Science >. IF：5.091.

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Graphene has attracted enormous attention due to its unique physical properties and attractive applications in many fields. However, it is an ongoing challenge to develop a facile and low-cost method for the large scale preparation of high-quality graphene (HQGr). In this work, we have developed an improved liquid-phase exfoliation method to mass produce HQGr. This method is quite simple but efficient by exfoliation of graphite in organic solvent with the co-assistance of sodium citrate and water. Remarkably, the concentration of as-exfoliated HQGr was as high as 0.71 mg/mL under optimal conditions, while the oxygen content in HQGr was only 2.39%. After annealing at 500 °C for 2 h in argon atmosphere, the mean conductivity of annealed HQGr was as high as 1.4 × 104 S m1. Therefore, this facile method for liquid-phase exfoliation of graphite has excellent potential in the industrial-scale production of HQGr for numerous applications in energy storage, optical and electronic fields.

In summary, we have developed an improved liquid-phase exfoliation method for the large scale preparation of HQGr in organic solvents with the co-assistance of citrate salt and deionized water. The effects of alkali metal species, solvent type and the volume ratio of NMP/water in co-solvent on the exfoliation efficiency of graphite were studied systematically. This simple but effective method significantly improved the exfoliation efficiency of graphite in organic solvent. The obtained concentration of the as-prepared HQGr was as high as 0.71 mg mL-1 in NMP/water co-solvent (4:1 V/V) with the addition of sodium citrate and sonication (1000 W) for 4 h. Specifically, the atomic oxygen content was only 2.39%, exhibiting the superior quality of the obtained graphene nanosheets. The procedure was extremely fast, suitable for scale-up, and free of polluting byproducts. Therefore, the proposed method is potentially suitable for the industrial production of HQGr for numerous applications in optical and electronic fields, such as anode material of lithium ion batteries.

In a typical procedure, natural graphite powder (0.5 g), citrates (1 g), organic solvent (40 mL), and deionized water (10 mL) were mixed in a 150-mL beaker. Then, the mixture was sonicated for 4 h at room temperature using an XH-600US intelligent ultrasonic cell disrupter (1000 W, 25 KHz, Beijing Xiang Hu Science and Technology Development Co., Ltd) with a 5-min break for every 10 min of operation. After exfoliation, the dispersion was centrifuged at 3000 rpm for 5 min to remove any non-exfoliated graphite. The HQGr dispersion was stored for later use.