A research team led by the National University of Singapore (NUS) has developed an economical and industrially viable strategy to produce graphene. The new technique addresses the long-standing challenge of an efficient process for large-scale production of graphene, and paves the way for sustainable synthesis of the material.

Graphene is a two-dimensional material with a honeycomb structure of only one atom thick. Graphene exhibits unique electronic properties that can potentially be employed for a wide range of applications such as touch screens, conductive inks and fast-charging batteries. The difficulty to produce high-quality graphene affordably on a large scale, however, continues to pose hindrance to its widespread adoption by industries.

The conventional method of producing graphene utilizes sound energy or shearing forces to exfoliate graphene layers from graphite, and then disperses the layers in large amounts of organic solvent. As insufficient solvent causes the graphene layers to reattach themselves back into graphite, yielding one kilogram of graphene currently requires at least one tonne of organic solvent, making the method costly and environmentally unfriendly.

The NUS-led development research team, on the other hand, uses up to 50 times less solvent. This is achieved by exfoliating pre-treated graphite under a highly alkaline condition to trigger flocculation, a process in which the graphene layers continuously cluster together to form graphene slurry without having to increase the volume of solvent. The method also introduces electrostatic repulsive forces between the graphene layers and prevents them from reattaching themselves.

Preparation of ultra-high concentration graphene in water. a) Conventional liquid-phase exfoliation in which graphene flakes are peeled off from graphite and dispersed in an organic solvent, yielding low concentration dispersion in low yield because of the limited stability of the dispersion. b) New non-dispersion strategy for graphene production in water. Pretreated graphite is exfoliated by high-rate shearing and subsequently flocculated in alkaline water, producing graphene slurry on a large scale (100 g), high yield (82.5 wt%), and ultra-high concentration (50 mg mL−1). c) Comparison of concentration, yield, and production scale of non-dispersion strategy with other liquid-phase exfoliation strategies (shearing, ultrasonic, microwave, and chemical intercalation-assisted exfoliation). Dong et al. Click to enlarge.

The resulting graphene slurry be easily separated into monolayers when required or stored away for months. The slurry can also be used directly to 3D-print conductive graphene aerogels, an ultra-lightweight sponge-like material that can be used to remove oil spill in the sea.

The research was conducted in collaboration with Fudan University and the findings were published in an open-access paper in Nature Communications.

Resources

• Lei Dong, Zhongxin Chen, Xiaoxu Zhao, Jianhua Ma, Shan Lin, Mengxiong Li, Yang Bao, Leiqiang Chu, Kai Leng, Hongbin Lu & Kian Ping Loh (2018) “A non-dispersion strategy for large-scale production of ultra-high concentration graphene slurries in water” Nature Communications volume 9, Article number: 76 doi: 10.1038/s41467-017-02580-3