4. Conclusions and outlook
In recent years, tremendous effort has been invested in the synthesis and application of 2D GO sheets [81,82]. With respect to photocatalytic properties, the primary advantages of GO include its substantial solubility and processibility, high surface area and abundance of inexpensive source material. Furthermore, the fact that physicochemical properties of GO can be tailored to facilitate specific photocatalytic applications by simple chemical modifi- cations, makes this material even more intriguing. Despite the promising results obtained so far, the study of 2D GO sheets in the field of photocatalysis is still in its infancy and further developments are needed. Much work remains to be done in facilitating the practical applications of GO materials and broadening the scope of their photocatalytic applications in the near future. Firstly, a clearer understanding on the nature of GO catalytic active sites and the accountability of specific functional groups in the opening of bandgap is necessary. Rigorous theoretical simulations and modeling techniques are imperative to pave the way for the development of highly efficient and durable GO photocatalysts. In addition, studies on the optimization of structure and morphology of GO with respect to its photocatalytic activity and stability remain scarce. To address this, the development of standard tools and testing protocols is essentialto validate both ofthese aspects in the photocatalysis scene. Furthermore, the underlying mechanisms of the photocatalytic enhancement of GO must also be fully understood. This will rely on extensive research into the mechanistic details of photocatalytic reactions as well as a complete determination of electron transport characteristics on the GO sheets. Another major challenge is to develop a synthetic route that precisely tunes the characteristics of GO materials. As discussed in this paper, the properties of GO are dependent on numerous parameters such as size, number of layers and embedded functionalities ofthe graphene sheets. Hence,the rationale design of GO will not only favor the adjustment of redox potential and the enhancement of light harvesting, but also the interaction between the GO photocatalyst and target reactant molecules.
