When materials approach the size of few nanometers, they show properties which are significantly different from their bulk counterpart. Such unique/improved properties make them potential candidate for several emerging applications. At the reduced dimension, controlling the shape of nanocrystals provides an effective way to tune several material properties. In this regard, wet chemical synthesis has been established as the ultimate route to synthesize nanocrystals at ultra-small dimensions with excellent control over the morphology. However, the use of surfactant poses a barrier into efficient realization of its application as it requires a clean interface for better performance. Exercise of available cleaning protocols to clean the surface often leads to coarsening of the nanoparticles due to their inherent high surface curvature. For anisotropic nanomaterials, rounding of the shape is an additional problem. Anchoring nanomaterials onto substrates provides an easy way to impart stability. In this thesis, ultrathin Au nanowires, that are inherently unstable, have been shown to grow over a wide variety of substrates by in-situ functionalization. Use of nanomaterials as device component holds promise into miniaturization of electronics. But device fabrication in such cases require manipulation of nanomaterials with enhanced control. Dielectrophoresis offers an easy way to assemble nanomaterials in between contact pads and hence evolved as a promising tool to fabricate device with a good level of precision. Herein, directed assembly of ultrathin Au nanowires by dielectrophoresis, has been shown as an efficient strategy to fabricate devices based on the wires. Combining more than one nanocrystal, to form a heterostructure, often has the advantage of synergism and/or multifunctionality. Therefore, synthesis of heterostructure is highly useful in enhancing and/or adding functionalities to nanomaterials. There are several routes available in literature for synthesis of heterostructures. Newer strategies are being evolved to further improve performance in an application specific way. In that regard, a good understanding of mechanism of formation is crucial to form the desired product with the required functionality. For example, Au due to high electron affinity has been known to undergo reduction rather than cation exchange with chalcogenides. In this thesis, it has been shown that the final product depends on the delicate balance of reaction conditions and the system under study using CdS-Au as the model system. In yet another case, PdO nanotubes have been shown to form, on reaction of PdCl2 with ZnO at higher starting ratio of the precursors. In-situ generation of HCl provides an effective handle for tuning of the product from the commonly expected hybrid to hollow. Graphene has evolved as a wonder material due to its wide range of practical applications. Its superior conductivity with high flexibility has made it an important material in the field of nanoelectronics. In this thesis, an interesting case of packed crumpled graphene has been shown to sense a wide variety of strain/pressure which has applications in day to day life. The study reported in the thesis is organized as follows: Chapter 1 presents a general introduction to nanomaterials followed by the review of the available strategies to synthesize various 1D nanomaterials. Subsequently, a section on the classification of hybrid followed by the different synthetic protocols adopted in literature to synthesize them, have been provided. A review on the available methodologies for directed assembly of nanomaterials has been presented. Chapter 2 provides a summary of the materials synthesized and the techniques used for characterization of the materials. A brief description of all the synthetic strategy adopted has been provided. The basic principle of all the characterization techniques used, has been explained. A section explaining the principle of dielectrophoresis has also been presented. Chapter 3 presents a general method to grow ultrathin Au nanowires over a variety of substrates with different nature, topography and rigidity/flexibility. Ultrathin nanowires of Au (~2 nm in diameter) are potentially useful for various catalytic, plasmonic and device applications. Extreme fragility on polar solvent cleaning was a limitation in realizing the applications. Direct growth onto substrate was an alternative but poor interfacial energy of Au with most commercial substrates lead to poor coverage. In this chapter, in-situ functionalization of the substrates have been shown to improve Au nucleation dramatically which lead to growth of dense, networked nanowires over large area. Catalysis and lithography-free device fabrication has been demonstrated. Using the same concept of functionalization, SiO2 coating of the nanowires have been shown. A comparative study of thermal stability of these ultrafine Au nanowires in the uncoated and coated form, has been presented. Chapter 4 demonstrates an ultrafast device fabrication strategy with Au nanowires using dielectrophoresis. While dense growth of Au nanowires is beneficial for some applications, it is not so for some others. For example, miniaturization of electronics require large number of devices in a small area. Therefore, there is a need for methods to manipulate nanowires so as to place them in the desired location for successful fabrication of device with them. In this chapter, dielectrophoresis has been used for assembling nanowires in between and at the sides of the contact pads. Alignment under different conditions lead to an understanding of the forces. Fabrication of a large number of devices in a single experiment has been demonstrated. Chapter 5 presents a simple route to synthesize CdS-Au2Sx hybrid as a result of cation-exchange predominantly. Au due to high electron affinity has been shown in literature to undergo reduction rather than cation exchange with CdS. In this chapter, it has been shown that cation exchange may be a dominant product. The competition between cation exchange and reduction in the case of CdS-Au system has been studied using EDS, XRD, XPS and TEM. Thermodynamic calculation along with kinetic analysis show that the process may depend on a delicate balance of reaction conditions and the system under study. The methodology adopted, is general and may be applied to other systems. Chapter 6 presents an one pot, ultrafast microwave route to synthesize PdO hollow/hybrid nanomaterials. The common strategy to synthesize hollow nanomaterials had been by nucleation of the shell material on the core and subsequent dissolution of the core. In this chapter, a one step method to synthesize hollow PdO nanotubes, using ZnO nanorods as sacrificial template, has been shown. By tuning the ratio of the PdCl2 (PdO precursor) to ZnO, ZnO-PdO hybrid could be obtained using the same method. The PdO nanotubes synthesized could be converted to Pd nanotubes by NaBH4 treatment. Study of thermal stability of the PdO nanotubes has been carried out. Chapter 7 demonstrates a simple strategy to sense a variety of strain/pressure with taped crumpled graphene. Detection of ultralow strain (10-3) with high gauge factor is challenging and poorly addressed in literature. Taped crumpled graphene has been shown to detect such low strain with high gauge factor (> 4000). An ultra-fast switching time of 20.4 ms has been documented in detection of dynamic strain of frequency 49 Hz. An excellent cyclic stability for >7000 cycles has been demonstrated. The same device could be used to detect gentle pressure pulses with consistency. Slight modification of the device configuration enabled detection of high pressure. Simplicity of the device fabrication allowed fabrication of the device onto stick labels which could be pasted on any surface, for instance, floor. Hard pressing, stamping with feet and hammering shocks do not alter the base resistance of the device, indicating that it is extremely robust. Sealed arrangement of the graphene allowed operation of the device under water in detection of water pressure. Presence of trapped air underneath the tape enabled detection of air pressure both below and above atmospheric pressure.

Catalysis using nanostructures has been a topic of substantial interest for fundamental studies and for practical applications in energy and environmental sectors. The growing demand for production of energy and in the cleaning of polluting hazardous vehicles/industrial wastes has led to several studies in catalysis. Despite the substantial growth of heterogeneous catalytic technologies in last decade, they are still far from reaching their full potential in terms of efficiency, selectivity as well as durability. It is often difficult to simultaneously tackle all the mentioned issues with single component catalysts. Most of these challenges are being overcome with heterostructures/supported hybrid catalysts by modifying their interfaces. The properties of heterostructures hybrids arises not only from the individual contributions of the individual components but also from strong synergetic effect arising from the interface. Engineering the interfaces provides pathways to promote the catalytic performance and hence has been explored. In this regard, we have focused on the progress in investigating the active interfaces that affect the performance of metal oxide-metal, semiconductor-metal and coupled semiconductor nanocatalyst hybrids. We explored a wide spectrum of their applications in photo catalytic, electrocatalytic as well as gas-phase reactions and highlighted the importance of the interface for overall performance. The entire study reported in the thesis is organized as follows: Chapter 1 is a general introduction of hybrid nanocatalyst and their role in wide spectra of catalytic reactions in photo/electro catalysis as well as gas-phase reactions. This chapter describes the motivation behind modulating the interface between two or more nanostructures to obtain multifunctional nanocatalysts. Nan catalysts to achieve high throughput with active interfaces are elaborated while indicating the role of morphology, internal induced state, charge transfer, geometric, support, as well as electronic effect for enhanced performance. Motivation behind specific nanocatalyst hybrid, synthesis routes as well as characterization techniques are detailed in the respective chapters. Specific details for different hybrids are described in the following chapters. Chapter 2 describes the synthesis of high dense ultrathin Au wires on ZnO nanorods for electrocatalytic oxidation of ethanol, where the prerequisite step is the formation of amine-modified support. Oleylamine modification not only serves to anchor Au nanowires on ZnO but also passivates surface defects of ZnO, which in turn enhances the photocurrent. In addition to the stability, the support induces electronic effect on Au nanowires, which facilitates redox process at low potential. Most importantly, the support promotes the activity of Au nanowires upon photoirradiation, and thus leading to synergy between electro and photooxidation current. This is of immense importance for photofuel cell technologies. Moreover, the method enabled the first time electrocatalysis on these nanowires that revealed ultrathin nanowires are potentially interesting systems for catalysis applications provided they are stabilized by a suitable support. Chapter 3 deals with the growth of ultrathin Au nanowires on metal oxide (TiO2) coupled with graphene hybrid support in order to overcome the low conductivity of metal oxide. Oleylamine, used for growth of Au nanowires simultaneously functionalizes the support and leads to room temperature GO reduction. With respect to catalytic activity, we also synthesized the binary counterparts (rGO/Au, TiO2/Au ultrathin nanowires) to delineate the contribution of each of the components to the overall electrocatalytic oxidation of ethanol. Comparative analysis of photo and electrocatalytic activity between the different binary and ternary hybrids provides interesting information. Both, electronic effect of TiO2 and electrical conductivity of rGO add their specific beneficial to the nanowires, leading to superior ternary system. Chapter 4 rGO supported ultrathin Au nanowires exhibits high electrocatalytic performance for oxidation of borohydride with a lower onset potential compared to rGO/Au nanoparticles. Electrochemical impedance spectroscopy measurements display abnormal inductive behavior of the synthesized hybrids, indicative of Au surface reactivation. DFT calculations indicate that the origin of the high activity stems from the shift in the position of the Au d-band center. Chapter 5 Different aspect ratio ZnO nanostructures are obtained by varying the solvothermal reaction time. We observed a direct correlation between observed photocatalytic activity, measured photocurrent and length of the ZnO nanorods. Furthermore, photoresponse of the high aspect ratio ZnO nanorods are improved by attaching Au nanoparticles, intimate contact of two components leads to band bending. Thus, the synthesized ZnO/Au heterostructure favors for prominent separation of photogenerated charge carriers. Chapter 6 TiO2 and PbO/TiO2 hybrids are synthesized via non–hydrolytic sol–gel combustion method. Hybrid exhibits higher photocatalytic activity for the degradation of dye than TiO2. The estimated photogenerated species reveals that the origin of enhanced activity stems from the direct oxidization of dye via photogenerated hole rather than radicals. The semiconductors are matched based on their band edge positions, for the formation of energetic radicals to degrade the pollutants. Based on this study, we infer that semiconductors should not neglected (for example Si) based on calculated mismatch of their valence band edges position for photooxidation reaction via radicals. Chapter 7 describes the Pd dopant associated band engineering, a strategy for tuning the optoelectronic properties of ZnO towards enhanced photocatalytic activity. Incorporated Pd heterocation induces internal energy states within the ZnO band gap. The created energy level leads to trends mismatch between photocatalytic activity and measured photocurrent. Formed energy level arrests the photogenerated electrons, which make them not contribute for the photocurrent generation. Hence, the isolated photogenerated hole efficiently oxidizes the pollutants through hydroxyl radicals, and thus leads to enhanced photocatalytic activity. Chapter 8 employed Pd-substituted zinc stannate for CO oxidation as heterogeneous catalyst for the first time. Compared with SnO2 support, zinc stannate based materials exhibits abnormal sudden light-off profiles at selective temperatures. On the basis of DRIFT studies under relevant conditions, we find that the initially formed product gets adsorbed over the catalyst surface. It leads to the accumulation of carbonates as a consequence, both lattice oxygen mobility and further CO interactions are disabled. As soon as Sn redox nature dominates over the accumulated carbonates, this leads to sudden release of lattice oxygen, and thus leads to a sudden full conversion. Therefore, choosing the suitable support material greatly influences the nature of the light-off CO oxidation profile. Chapter 9 Although, reducible oxide supported gold nanostructures exhibits the highest CO oxidation activity; they still suffer from problems such as limited selectivity towards CO in the presence of H2. Both ex-situ and in-situ experiments demonstrate that, Au nanoparticles supported on Zn2SnO4 matrix selectively oxidizes CO. DRIFT experiments revealed that the involvement of OH groups leads to the formation of hydroxycarbonyl under PROX conditions. Chapter 10 This chapter discusses the conclusions for the previous chapters and highlights the possibilities for future scope for the developed nanocatalysts hybrids for energy and environmental applications.