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Fundamental Studies of Optical Properties and Electrocatalytic Properties of Nanomaterials Carbon and Nano Dots (CNDs) and 2D Transition Metal Dichalcogenides (TMDs)

CP 114
Speaker(s) / Presenter(s):
Nadeesha Kothalawala

Nanomaterials are widely used in a variety of applications such as opto-electronics, energy production and storage, and bio-medical applications due to their unique optical, catalytic, electronic, and mechanical properties. Most of the nanomaterials offer a plethora of modifications in their structure, composition, morphology, and dimensionality that can lead to the manipulation of their physiochemical properties. Thus, this dissertation presents insight into two types of compelling nanomaterials: carbon nanodots (CNDs) and transition metal dichalcogenides (TMDs), investigating their optical and electrocatalytic properties respectively.   Carbon nanodots (CNDs) are a promising class of photoluminescent nanomaterials that hold a significant potential in many optoelectronic applications. The photoluminescence behavior of CNDs highly depends on their structure and chemical composition. The complexity of the structure and chemical composition of CNDs makes it difficult to uncover the origin and behavior of the photoluminescence of these materials. Hence, this work first provides fundamental insight into the photoluminescence of low-oxygen-content CNDs derived from polycyclic aromatic hydrocarbon pyrene. In this study, the formation of bright emitting molecular fluorophore was identified through a rigorous separation scheme using column chromatography and solvent-induced extraction. Further, the distinct structure and optical properties of the molecular fluorophore  and CNDs were identified using different structural and morphological characterization techniques and bulk fluorescence measurements.  Transition metal dichalcogenides (TMDs) are another intriguing class of nanomaterials that are abundant and cost-effective alternatives to expensive and precious electrocatalysts for various electrochemical reactions. 

TMDs can be modified by changing their phase and dimensionality, and their layered nature makes them suitable for heterostructures. Consequently, TMD nanostructures have gained attention as electrocatalysts for hydrogen evolution reactions (HER) due to the increasing demand for low-cost green hydrogen production. Thus, secondly, a greener and reliable top-down synthesis approach for producing highly exfoliated ultrathin crystalline WS2 nanosheets using a modified liquid phase exfoliation is presented in this work. The ultrathin pristine WS2 nanosheets showed a promising electrochemical activity for HER, and the correlation between the structure and the electrocatalytic activity was carried out through Operando Raman spectro-electrochemical measurements. Further, TMD nanostructures are excellent candidates to use as support materials for metal single atom catalysis (SACs). Pt single atom catalysts (SACs) supported on transition metal dichalcogenides (TMDs) are promising electrocatalysts in the green hydrogen production by proton exchange membrane (PEM) water electrolysis. Hence, thirdly this study presents a novel and a convenient synthesis of Pt SACs and clusters supported on WS2 (Pt/WS2) using photonic curing, with improved efficiency for hydrogen evolution reaction (HER). This catalyst design constitutes enhanced atomic utilization, higher number of accessible active sites and catalytic activity modulation of Pt through electronic metal support interactions (EMSI). This work as a whole provides insight on the fundamental aspects of intricate properties of two types of nanomaterials in unveiling the correlation between structure, properties, and application.