Bimetallic Nanostructures with Noble (Ag & Au) and Earth Abundant (Cu & Sn) Metals and their Catalytic & Photocatalytic Applications

Abstract

Noble metal nanoparticles in catalysis have attracted great deal of attention in recent years. Among them, Au and Ag nanoparticles have shown great potential due to their unique properties associated at the nanoscale. However, the main demerit of these nanoparticles is their high cost. One best way to minimize this problem is to alloy them with cheap and earth abundant metals such as Cu and Sn to form bimetallic nanoparticles. Bimetallic nanoparticles are interesting as they offer the ability to tune the activity, stability, and selectivity during the reaction. Keeping this in mind, this thesis is broadly focused on two objectives; (1) Synthesis of Cu-based bimetallic nanoparticle catalyst Cu-M (M=Ag and Au) for catalytic applications, and (2) Synthesis of Sn-based bimetallic nanoparticle Sn-M (M=Ag and Au) for photocatalytic applications. Each project has different studies associated with the main objective of the design of bimetallic nanoparticles via mixing of noble metals with earth abundant metals. In the catalysis project, emphasis was given using bimetallic nanoparticles for the synthesis of biologically important fine chemicals. As no literature(s) were available demonstrating the efficiency of bimetallic nanoparticles for fine chemical syntheses, the first project involved the synthesis, characterization and catalytic activity of Ag-Cu bimetallic alloy nanoparticle for fine chemical synthesis such as β-enaminones and β enaminoesters (RSC Advances, 2016, 6, 49923). To best of our knowledge, for the first time, use bimetallic nanoparticles as an efficient catalyst for the synthesis of fine chemicals was explored. After the successful demonstration of metallic alloy nanoparticles for fine chemical synthesis, the efficiency of other bimetallic architecture; e.g. core-shell structure towards fine chemical synthesis was worth exploring. Core-shell nanoparticles are important in catalysis as they can minimize the amount of precious metals as well as increase the stability of oxidation prone material by keeping it in the core. Therefore, in the second objective, for the first time we documented the synthesis of fine chemical such as octahydroquinazolinones using Cu@Ag core-shell nanoparticles (Manuscript Submitted). Cu@Ag core-shell nanoparticle showed higher activity in comparison to alloy and monometallic nanoparticles. In both the previous work, higher catalytic activity was attributed to the possible synergistic effect between individual metal nanoparticles. This intrigued us to theoretically study the synergistic effect in a bimetallic system. To comprehensively study, the role of support was taken into consideration along with metal nanoparticle (Au-Cu nanoparticle on rGO support). In this objective, for the first time, we have documented a detailed combined density functional theory (DFT) calculation of a nanoparticle-rGO hybrid to study the possible synergistic effects between Au-Cu nanoparticles and rGO support and its effect on the enhanced catalytic activity (Applied Catalysis A: General, 2017, 538, 107). In the end we have shown an efficient waste management strategy for the treatment of polluted water using red mud as suitable solid adsorbent. In addition to our exploration of using Cu-based bimetallic nanoparticles for catalytic applications, this thesis was also focused on demonstrating Sn-based bimetallic system for photocatalytic degradation of toxic organic pollutants. As there were dearths of literatures exploring Sn-based bimetallic system for photocatalytic applications, as a proof-of-concept, bimetallic Ag-Sn nanoparticles on TiO2 support was utilized as an efficient photocatalyst for degradation of methylene blue dye under visible light irradiation (Nano, 2015, 10, 1550059). Following our successful foray into documenting the photocatalytic application of any Sn-based bimetallic system as photocatalyst, we attempted to explore other Sn-based bimetallic system for photocatalysis. In the last objective, bimetallic Au-Sn nanoparticles on ZnO was chosen efficient photocatalyst for the degradation of a series of toxic phenolic derivatives and rhodamine B dye (manuscript submitted),. In this work, attempts were made to increase the porosity of the support material by using room temperature imidazolium ionic liquid as solvent and combustion method as synthetic route. All the above bimetallic nanocatalysts were thoroughly characterized using various analytical techniques such as UV-vis, FTIR, flouroscence, ICP-OES, Raman, N2 adsorption-desorption study, XPS, SEM, HRTEM, EDS mapping/line scan and photoelectrochemical measurements. All the bimetallic nanocatalysts presented in this thesis proved to be stable, efficient and recyclable system for reactions of biological and environmental significance