Novel insights into graphene-based sustainable liquid lubricant additives: A comprehensive review

Graphene's derivatives such as graphene oxide (GO) and reduced graphene oxide (r-GO) are emerging classes of 2-D material, which have been widely used in different applications such as biosciences, energy storage, electronics, chemistry, and other fields due to its unique chemical, electronic and optical characteristics. In tribological applications, GO/r-GO is also discovered to be one of the most promising lubricating additives. It has been proved that lubricating contacting surfaces with lubricant containing GO/r-GO materials as additives exhibited superior anti-frictional and anti-wear performances, which result in energy savings, low carbon emissions and less wear and tear of mechanical components. This review article discusses the current tribological research progress, applications and lubrication advantages of GO/r-GO as additives for a wide range of liquid lubricants. Other important aspects such as thermo-physical and dispersion stability of GO/r-GO-based lubricants have also been summarized in detail. In addition, possible lubrication mechanisms of GO/r-GO nanomaterials have been reviewed. Furthermore, perspectives on challenges and future research directions have been discussed based on past research investigations at the end.