Towards the Rational Design of Surface Modified Metal Oxide Nanorod-based Catalysts for Efficient Synthesis of Biologically Important Molecules

Abstract

Metal oxide nanostructures are widely used in various fields such as environmental, biological, electronic, super capacitor, battery, sensing, and catalysis. Among various classes of metal oxide nanostructures, metal oxide nanorods possess particular importance because of their significant physical and chemical properties. In particular, they are potential material for catalysis due to their high surface to volume ratios, shape anisotropy, high coordination domain and also superior electronic properties. However, pristine nanorods have significant stability and leaching issues and hence, surface modifications of these nanorods are of greater scientific interest. Various approaches like compositional effect (decorating on suitable support and varying the acidity), electronic effect (nanoparticle decoration), morphological effect (varying the shapes and crystal planes), etc have proven to be some of the most preferred approaches while using such metal oxide nanostructures in catalysis. Keeping these in mind, the overall objectives of my PhD work was to modify the metal oxide nanorods (WO3, MnO2, Fe2O3 and CeO2) and use them as potential heterogeneous catalysts for efficient synthesis of biologically important molecules like amino alkyl napthol, bisamides, Quinoline, Coumarin, and Pyran. Broadly, the effect of acidity (WO3), the decoration of different nanoparticles (Au, Ag, and Pt on MnO2, Fe2O3 and CeO2), morphology (twin sphere vs. nanorods of Fe2O3) and metal-support interaction on the overall catalytic activity have been thoroughly investigated. Each chapter of this thesis has different studies associated with the main objective of design of highly active and stable metal oxide nanorod-based hybrid catalyst materials. In the first part, it documents the use of acidic WO3 supported on GO for efficient synthesis of Quinoline and derivatives. This work has been published in New Journal of Chemistry, 2022, 46, 4850-4863. Envisioning the importance of metal nanoparticle decoration on a nanorod-based system, in the second objective, gold nanoparticles were decorated on GO-MnO2 nanohybrid and used it as highly active, stable, and recyclable catalyst for synthesis of Bisamides and Betti bases. This work has been published in Molecular Catalysis, 2019, 474, 110415. From the previous objective, decoration of nanoparticles generally increased the activity of material. This could be due to surface defects (oxygen vacancy) and electronic effect (redox potential value). With an eye to see such effects of metal oxide nanorods in the synthesis of biologically important molecule, the third objective involves the detailed studies of such effects in a GO-CeO2 Pt system during the synthesis of Pyran and its derivatives. The final objective documents the morphology and crystal face effect of Fe2O3 (twin sphere vs. nanorods) in the synthesis of Coumarin. All the materials presented in this thesis proved to be stable, efficient, and recyclable system for the above applications, which are of significant biological importance.