der Waals force present in between stacked layers of bulk material. These intercalated

compounds can be exfoliated by a modest sonication technique to mono- or few-layer

sheets. In the majority of cases, hydrogen gas is produced due to a reaction between

intercalated ions and water, which further promotes exfoliation. Through these methods,

a high yield of 2D materials can be achieved [38]. Therefore, liquid exfoliation via ion

intercalation is suitable to synthesize 2D materials for bioelectronics. Furthermore, the

electrochemical ion intercalation method has been effectively employed to prepare a

variety of 2D materials [38]. Figure 3.8 shows the schematic representation of 2D gra­

phene synthesis through electrochemical assisted liquid exfoliation of graphite. In this

method, electrochemical force and ions for intercalation act as the driving force [39]. The

metallic foils coated with bulk material act as a cathode, while Li foils (intercalating ion)

act as anodes. Under the applied voltage, the layered bulk material is intercalated with Li,

and intercalated material is obtained on the electrodes. Afterward, the electrodes with

intercalated material are washed and the obtained suspension was sonicated for ex­

foliation. Later, exfoliated material is centrifuged to obtain mono- or few-layered 2D

material. This approach has many benefits such as high yield, flexibility in various con­

ditions, and ecofriendly in nature. However, complexity and irreversibility are the two

major drawbacks that restrict the widespread use of electrochemical intercalation.

Moreover, liquid exfoliation by cation or anion exchange is also utilized to synthesize

2D materials. Layered metal oxides and metal phosphorus trichalcogenides are fre­

quently exfoliated through cation exchange [40]. In the process, the layered metal oxide is

immersed in an acidic medium. This resulted in H⁺ cation exchange and the formation of

FIGURE 3.7

Liquid exfoliation of graphite via sonication to obtain graphene. Adapted with permission [ 36]. Copyright

(2018) Elsevier.

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Bioelectronics