Advanced Nanomaterial Composites for Enhanced Photocatalysis and Sensing

Abstract

Recent advances in nanostructuring techniques have contributed to the field of plasmonics. In current research, plasmonic plays an important role in sensing, including surface enhanced Raman spectroscopy (SERS). The fabrication of platforms for optical sensing has traditionally been carried out using costly techniques requiring specialized equipment. These techniques require precious metals, which have limitations in biocompatibility, high environmental impact, cost, and availability. Semiconductors are used in SERS since they provide enhanced Raman signals through their unique optical and electronic properties, allowing for tunability and reproducibility. Their stability and compatibility with various technologies render them valuable substrates for highly sensitive molecular analysis. Furthermore, their additional benefits include cost-effectiveness, recyclability, self-cleaning properties, and flexibility, which make them suitable for potential integration with other technologies. Even though semiconductor-based SERS have been the subject of numerous promising studies, current state-of-the-art designs are largely restricted due to their lower signal enhancements. New designs for SERS substrates are crucial to overcome some limitations and improve the performance of SERS. Existing designs may have limitations in terms of sensitivity, reproducibility, scalability, or compatibility with specific molecules or applications. The aim of the thesis is to investigate the combination of semiconductors and plasmonic nanomaterials in order to develop new designs implementing simple, cost-effective, and environmentally friendly strategies. The combination of plasmonic nanomaterials with semiconductors has great potential for sensing and photocatalysis. This thesis is divided into nine chapters: In Chapter 1, a brief description of Raman scattering and molecular dynamics is presented, as well as Raman-active modes selected based on vibration spectra, light-driven electronics. In the following section, examples are provided of how Raman spectroscopy is used in modern research. Following this, a brief overview of SERS is provided, including electromagnetic and chemical enhancements as well as effects related to wettability. Lastly, the chapter discusses photocatalysis mechanisms and applications, such as chemical oxidation reactions and self-cleaning photocatalysis. Chapter 2 provides an overview of the primary strategies which can be utilized in the design of optical sensing platforms for SERS. Several material classes are discussed as well as their properties that make them useful for chemical detection. First, the primary processes involved in the production of platforms fabricated from precious metals will be briefly reviewed. This method will also be discussed in terms of its advantages and disadvantages. In the following section, alternative semiconductor materials are examined; these materials have the advantage of being biocompatible and easy to fabricate. Several subgroups of semiconductor materials that have been demonstrated to be effective at enhancing optical signals are discussed following an introduction to the two primary categories of semiconductor materials - organic and inorganic. In Chapter 3, a brief overview is presented of the major spectroscopy and microscopy techniques utilized to explore the optical properties and morphology of the manufactured substrates investigated in this thesis, along with the methods utilized to analyze the data. The analysis methodology and experimental specifics of how the measurements were conducted are described in some depth in the text, which presents the overall ideas underlying the analysis. In Chapter 4, investigate the photocatalytic potential of transition metal chalcogenides (TMCs) cadmium sulfide (CdS) when coupled with plasmonic nanostructures. The synthesis of dimercaptoazobenzene (DMAB) from p-amino thiophenol (PATP) was demonstrated by the super bandgap irradiation of a silver nanowire (Ag NWs) and cadmium sulfide composite for PATP. For plasmonic photocatalysis applications, our findings indicate that cadmium sulfide can serve as an alternative to semiconductors, such as titanium dioxide. In Chapter 5 a combination of conducting polymers such as P3HT (poly-3-hexylthiophene) and PcBm (phenyl-C61-butyric acid methyl ester) with plasmonic nanomaterials is demonstrated to enhance Raman scattering spectroscopy signals up to five-fold and to support the oxidation of target molecules by supporting the charge transfer. The purpose of this chapter is to demonstrate how conducting polymers can be used as semiconductor platforms for the development of plasmonic catalysis and sensing techniques. Chapter 6 describes the development of nanocomposites consisting of metals and organic conducting semiconductors, which have the potential to provide a flexible, lightweight platform for plasmon-based sensing. The purpose of this chapter is to demonstrate the use of super band-gap irradiation to provide plasmon excitation and irradiation to remove analytes from a polymer-plasmonic composite based upon the conducting polymers P3HT and PCBM, as well as to support plasmon-enhanced spectroscopic detection. Our research demonstrates that such a polymer-plasmonic composite is an effective self-cleaning system for use as a reusable optical sensing substrate. In Chapter 7, plasmon active metal nanostructures and semiconductors are described as nanocomposites that support catalytic activity. As discussed in this chapter, transition metal dichalcogenides such as MoS2 when combined with metal oxides such as ZnO have the potential to control charge states in plasmonic nanomaterials. The objective of Chapter 7 is to demonstrate the possibility of controlling plasmonic reactions through the careful selection of semiconductors. In Chapter 8, we present a framework consisting of silver nanoparticles (Ag NPs) on Mg-doped lithium niobate surface. The activation of charge transfer processes on this substrate under white light irradiation is demonstrated to support the oxidation of compounds such as p-amino thiophenol. The purpose of this chapter is to highlight the use of doped lithium niobate materials as semiconductor platforms for plasmonic catalysis. Conclusions and future work are discussed in Chapter 9.