METAL-ARENE DRIVEN NEW SYNTHETIC APPROACH TO MULTIFUNCTIONAL INTERMETALLIC COMPOUNDS

Abstract

Intermetallic compounds have attracted considerable attention in the field of thermoelectricity, superconductivity, ferromagnetism, water splitting, and catalysis. However, these compounds as nanomaterials have gained enormous attention in these applications. Due to the fine control over synthetic conditions, the bottom-up approach has proven to be more advantageous than the top-down approach for the synthesis of intermetallic nanomaterials. Liquid phase synthesis is the best choice among bottom-up approaches for the synthesis of intermetallic nanomaterials/nanostructures. Current research has made significant progress in wet-chemical approaches for monometallic and binary intermetallic phases. However, producing ternary intermetallic nanoparticles reliably has been challenging due to various obstacles, such as differential reduction rates of metal cations, prevention of agglomeration, and removal of surfactants or supports. The primary objective of this thesis is to design and develop a new wet-chemical synthetic approach for the synthesis of binary and ternary intermetallic nanoparticles in an ordered phase with fine control over the particle size distribution and morphology, and to explore new applications. To achieve this goal, the current thesis explores the metal-arene driven reduction approach to synthesize highly crystalline binary and ternary intermetallic ordered nanoparticles. The methodology involves the reduction of metal cations in a strong reducing agent, sodium naphthalenide, followed by refluxing or sintering to obtain the desired binary or ternary intermetallic nanoparticles. The general methodology developed in this thesis can provide a new direction for the synthesis of intermetallic nanoparticles with controlled morphology and size distribution. The present study investigates the synthesis of binary intermetallic compounds CoSb, FeSb, and NiSb using the sodium naphthalenide reduction approach. These compounds were compared with the simple reduction and polyol method, revealing that FeSb could only be synthesized by metal-arene driven reduction approach. The study confirms the superiority of the sodium naphthalenide approach over the other methods. The impact of synthetic conditions/parameters on the preparation of these antimonides was also investigated. Moreover, FeSb nanoparticles of particle size ~2-3 nm was prepared using the sodium naphthalenide approach followed by refluxing. The study also provides a comprehensive analysis of the effect of particle size on the catalytic reduction of p-nitrophenol. The results suggest that FeSb nanoparticles with the least refluxing time exhibit excellent catalytic activity compared to other reported non-noble metal-based compounds. Furthermore, ternary intermetallic stoichiometric CoFeSn nanoparticles were successfully synthesized using the sodium naphthalenide driven reduction approach. The prepared CoFeSn nanoparticles were highly crystalline and in pure hexagonal phase, with a narrow size distribution. The impact of the precursor was comprehensively studied, and the CoFeSn nanoparticles exhibited excellent electrocatalytic activity towards hydrogen evolution reaction compared to other reported non-noble metal-based compounds. The study was further expanded to explore the reliability of the synthesis methodology towards more ternary intermetallic stoichiometric FeNiSn, CoNiSn, and CoNiSb. All the ternary samples prepared showed different morphologies in the nano-scale utilizing the same methodology. Thus, the present study suggests that pure-phase binary or ternary ordered intermetallic nanoparticles could also be prepared using this generic methodology.