Advancing borophene synthesis and functionalization for tailored applications

<p dir="ltr">Borophene is a novel two-dimensional (2D) material with great electronic mobility, strong mechanical properties, and high chemical reactivity that has drawn a lot of interest from researchers in fields including electronics, energy storage, catalysis, and beyond. However, the scalability of synthesis, structure control, and functionalization have hindered its extensive use and integration. This thesis responds to these critical challenges in full by exploring two novel synthetic pathways to borophene, cryo-exfoliation, and intercalation exfoliation, and exploring the nanoarchitectonics of borophene through microwave-assisted doping.</p><p dir="ltr">The thesis starts with Chapter 1, an introductory chapter that places borophene within the broader background of 2D materials that have revolutionized the field of materials science by offering unique quantum confinement effects and exceptional properties not attainable in bulk materials. This chapter investigates how 2D materials, especially borophene, have changed prospects in photonics, electronics, and energy technologies. It highlights the special mechanical flexibility, electrical mobility, and chemical reactivity of borophene above other Xenes, which identify it as a very intriguing prospect for upcoming usage. In addition, the chapter highlights the urgent need to address current challenges related to synthesis and functionalization to balance borophene’s theoretical potential with its practical applications.</p><p dir="ltr">An in-depth examination is presented in Chapter 2, which analyzes borophene’s physical and chemical properties as well as existing synthesis approaches, highlighting their intrinsic limitations. Traditional approaches, including molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), yield high-quality borophene but are faced with limitations, including scalability problems, high expenses, and complicated procedures. Likewise, liquid-phase synthesis techniques are limited by oxidation issues and variable structure outputs. These limitations highlight the necessity to advance other innovative synthetic strategies. The need for ecologically friendly synthetic routes that are scalable, reproducible, and economical is high from an application point of view.</p><p dir="ltr">Cryo-exfoliation, detailed in Chapter 3, introduces a new, scalable, and cost-effective technique. This approach gently sonicates boron crystals after fast freezing them under liquid nitrogen. This produces the exfoliation of borophene sheets while minimizing oxidation. This environmentally friendly method helps borophene to be synthesised sustainably. It is simple to operate, generates high chemical phase purity borophene without oxidation, and can be scaled for more general use. Raman spectroscopy and atomic force microscopy (AFM) confirmed the structural integrity and chemical purity of the generated borophene. Still, if technology is to move forward, problems with layer thickness and lateral size fluctuation have to be fixed.</p><p dir="ltr">Chapter 4 describes solvothermal treatment with lithium (Li⁺) and potassium (K⁺) ions intercalation exfoliation method—which uses these ions intercalated between boron layers. These intercalants reduce the interlayer coupling in boron crystals, therefore enabling effective exfoliation following mechanical agitation. Excellent scalability, high yield, cost-effectiveness, and chemical phase purity made this novel approach a strong contender for mass borophene synthesis. Strong structural integrity and consistent yields were shown by comprehensive characterization; yet, comparable to cryo-exfoliation, tighter control over the number of layers and lateral size is needed. Intercalation exfoliation offers a safer and more efficient alternative to traditional liquid-phase methods by removing the necessity for toxic chemicals.</p><p dir="ltr">The microwave-doping method, explained in Chapter 5, is a novel avenue for the substitute doping of borophene and, hence, its functional enhancement. Using dopants comprising sulfur and iron, this method achieves the doping of borophene's lattice structure under controlled microwave irradiation. Targeted and quick heating of microwaves allows one to precisely dope with the lowest defect development. Clearly, the improvement in specific capacitance and activity in hydrogen evolution processes (HER) illustrates how much this complete strategy enhances the catalytic and electrochemical properties of borophene. Structural characterization by high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) attested to the successful incorporation of the dopant and the retention of structural integrity. Though microwave-assisted doping is efficient and suppresses defects, its scalability is limited, with scope for potential future development. A relative comparison of these three approaches reveals the advantages and limitations of each. Cryo-exfoliation and intercalation exfoliation emerge as being scalable and low-cost, and hence amenable to large-scale borophene production. Contrarily, the microwave-assisted doping technique provides unparalleled accuracy in borophene nanoarchitectonics, which allows for property tuning of the material towards specific desired applications. This thesis shows that these approaches provide a route for borophene synthesis and material optimization since they solve several problems related to current techniques.</p><p dir="ltr">The outcomes of this work not only show the potential of scale synthesis and functionalizing borophene but also provide the basis for the following studies. Future research subjects could include co-doping techniques to increase functionality, synthesis condition optimization, and borophene integration into composite materials. Emphasizing its applicability in the domains of electronics, energy storage, catalysis, molecular sensing, non-volatile memory, and biomedicine, this thesis also helps borophene go from a theoretical material to a building block in developing breakthroughs.</p>