Understanding solvothermal reductive reactions of graphene oxide in boron and ammonia solutions

Graphene has several favourable characteristics for both current and prospective applications. However, there are some economic issues emanating from the current methods of graphene synthesis and the need for high dispersibility in most potential applications. Reduced graphene oxide (RGO) is a suitable alternative that addresses these shortfalls. The synthesis of RGO via graphene oxide (GO) is leading to a quest for effective and 'greener' reduction protocols that simultaneously tune physicochemical properties for specific applications. Herein the study and comparison of the effects of electrophilic (empty orbitals on boron in boric anhydride) and nucleophilic (lone pairs on nitrogen in ammonia) solutions in solvothermal reduction of GO are presented. The study provides a better interpretation of the defect intensity, from Raman spectroscopy analysis, in relation to the conductivity of RGO. The highest increase in the C/O ratio from 2.48 (GO) to 11.36 (NRGO) suggests that ammonia displays the most reductive effect. Nucleophilic attack of carbon atoms within the oxygen functionalities of GO possibly enhanced reduction. Hydrothermal, and solvothermal reduction in electrophilic and nucleophilic solutions improved conductivity by two, three and five orders of magnitude relative to pristine GO, respectively. The sheet resistance, carrier concentration, and mobility of the superior NRGO were 93 ohm cm, 3.51 x 10(18) cm(-3) and 0.02 cm(2) V-1 s(-1), respectively. The solvent properties are dynamic in both the solvothermal reduction of GO and electronic property tailoring of RGO. The current work paves the way for future, cost-effective, facile reduction and doping protocols that tailor the physicochemical properties of graphene derivatives from the solvent nature. This is a practical economic approach that solves conductivity issues of GO whilst avoiding the use of toxic chemicals and high temperatures toward effective electronic devices.

Automated summary

Graphene has favorable characteristics, but there are economic issues with current synthesis methods. Reduced graphene oxide (RGO) is a suitable alternative that addresses these issues. This study compares the effects of different reduction protocols on RGO synthesis and provides a better understanding of defect intensity and conductivity. Solvothermal reduction using nucleophilic solutions, particularly ammonia, shows the most reductive effect and enhances the reduction process. Solvent properties play a dynamic role in solvothermal reduction and electronic property tailoring of RGO. This research provides a cost-effective and practical approach to solve conductivity issues and tailor the physicochemical properties of graphene derivatives.