Exploring intercalation compounds of two dimensional (2D) MoS2
Creators: name: Wang, Yichao
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340301
subject: Inorganic materials (incl. nanomaterials)
classificationCode: 401605
subject: Functional materials
classificationCode: 401807
subject: Nanomaterials

description: In chemistry, intercalation by definition is a process that induces insertion of a molecule or ions into crystals with layered structures. The research regarding intercalation chemistry in layered transition metal dichalcogenides (TMDs) was initiated 40 years ago. However, the recent emergence of exfoliated planar two dimensional (2D) TMDs has brought fresh research curiosity to this area.<br><br>As a key member of the 2D TMDs family, 2D molybdenum disulphide (MoS2), has recently attracted significant attention owing to its unique electronic and optical properties. 2D MoS2 provides a good foundation to form planar intercalation compounds in a host–guest structure, which greatly changes its physicochemical properties. <br><br>In this PhD thesis, the author focuses on the intercalation compounds of 2D MoS2 nanoflakes and their optical and electronic properties. Using these compounds, the author shows how the photoluminescence (PL) can be actively controlled, how to obtain plasmon resonances in near visible light range, how to implement this material in biosystems and how to reduce its hydrogen evolution reaction (HER) overpotential. Based on the strategies and investigations by the author, the PhD project was conducted in four distinct stages that each resulted in novel outcomes.<br><br>In the first stage, the author used an electrochemical approach to actively control the PL of liquid-phase-exfoliated 2D MoS2 nanoflakes via manipulating the amount of intercalated ions including Li+, Na+, and K+ into and out of the 2D crystal structure. It was revealed that this controlled intercalation allowed for large PL modulations, short response and recovery times, as well as excellent reversibility.<br><br>In the second stage, the author used the outcome of the work presented in Chapter 2 for the demonstration of plasmonic resonances in intercalation compounds of 2D MoS2. The results showed that the plasmon resonances in the visible and near UV wavelength ranges can be achieved. It was also revealed that the generated plasmon resonances can be controlled by doping level of 2D flakes. The system also exhibited a biosensing capability which was tested using a model protein.<br><br>In the third stage, the author used the concept developed in Chapter 2 and demonstrated the ion exchanges in enzymatic activities and cell viability. The results showed that the intercalation of 2D MoS2 was enabled in enzymatic activities via an external applied voltage. The intercalation of ions in viable cells occurred in the presence of the intrinsic cell membrane potential.<br><br>In the final stage, the author investigated enhanced HER performance based on the intercalation compounds of 2D MoS2. The author observed a notable improvement of HER activity for samples prepared under light illumination in the presence of Li+ containing solution.<br><br>In summary, the author believes that the outcomes of this PhD research provide an in-depth knowledge of intercalation compounds for 2D MoS2. The author also believes that this study has contributed significantly towards practical applications of intercalation compounds in optical and electric areas.