Green Solvents for the Liquid Phase Exfoliation Production of Graphene: The Promising Case of Cyrene

Abstract

The liquid phase exfoliation (LPE) of graphite has allowed to produce graphene materials on a large scale and at a reasonable cost. By this method, stable dispersions, inks and liquid suspensions containing atomic-thick graphene flakes with tailored concentrations can be produced, opening up applications in a wide range of cutting-edge technologies such as functional coatings, printed and flexible electronics, and composites. However, currently established LPE techniques raise several health and environmental risks, since unsafe and toxic solvents (such as NMP, DMF, and DMSO) are often regarded as the most effective liquid media for the process. Therefore, it appears necessary to unlock eco-friendly and sustainable methods for the production of graphene at an industrial scale. This review focuses on the latest developments in terms of green solvents for LPE production of graphene. We highlight the use of a new green solvent, Cyrene, and its performance when compared to conventional solvents.

Self-Assembled p–n Homojunction in SnS2 Nanosheets for Enhanced Visible Light-Driven Photocatalysis

“…Compared to these processes, we have used water (surface tension ∼72 kJ/m 2 ) as a "green solvent" for SnS 2 dispersion. 29 Prolonged aqueous washing through centrifugation at a high rpm (10,000 rpm in our case) provides a shear force upon the stacked nanosheets and separates them. The p−n homojunction is formed due to the sulfur vacancies (V S ) that promote the fractional conversion of Sn 4+ to Sn 2+ to maintain charge neutrality.…”

“…This approach is simpler and greener than conventional mechanical or chemical methods of layer separation. The mechanical process of layer exfoliation is achieved by the use of adhesive tape, sonication, ball milling, etc. − Layer exfoliation using adhesive tape is time-consuming and clumsy. Ultrasonication produces few-layered nanosheets, but prolonged sonication may degrade the solvent quality and compromise stable material dispersion.…”

Effects of Green Solvents and Surfactants on the Characteristics of Few-Layer Graphene Produced by Dual-Frequency Ultrasonic Liquid Phase Exfoliation Technique

“…The average size of the initial GP particles was about 70 μm as per manufacturer's specification. Green chemicals such as ethanol (99.9% absolute grade) from Merck Life Science UK, dodecylbenzene sulfonic acid sodium salt (SDBS) and cholic acid sodium salt (SC) from Fisher Scientific were used as the eco-friendly [19] solvent and surfactants, respectively, mixed with pure deionized water (DIW) supplied by Lab Unlimited Carl Stuart group. The choice of the surfactants was based on the literature survey [18,20,[28][29][30][31] and their concentration was adopted to our dual frequency ULPE process based on the yield measured after each exfoliation session.…”

“…For the last decade the LPE users were challenged by the difficulties in removing harsh chemicals in the graphene production [16]. Green solvents and surfactants came into focus of LPE graphene manufacturers [9,[17][18][19]. Water is not typically considered as an effective dispersant for exfoliation nor as a good stabiliser due to the mismatch in water and graphene Hansen solubility parameters [20], surface tension [21] and high graphite hydrophobicity [22].…”

Does Green Exfoliation of Graphene Produce More Biocompatible Structures?

“…Although all these methods effectively produce high-quality graphene, they are expensive and require chemical compounds, which are usually hazardous and harm the environment and human health. Thus, efforts have been made into the development of more eco-friendly methods for the exfoliation of graphene that employ the use of green solvents and stabilizers instead of chemical compounds [ 16 , 17 ].…”