Preface

It gives us immense pleasure to introduce this book called *Gold Nanoparticles— Reaching New Heights*, based on the state of the art of gold nanoparticles (AuNPs) with their outstanding and potential applications. The book deals with the advanced nanotechnological aspects of synthesis, characterization, development, and potential optical and biological applications of AuNP materials. Discussion of these aspects develops through the fundamental and applied experimental routes using conventional methods via the interaction of AuNPs and finally brings together both scientific and technological worlds. Basically, AuNPs have undoubtedly achieved many accomplishments in a conventional sense and have taken new directions from preparation to practical applications in research and development in different areas of science and technology. New paths and emerging frontiers branch out from time to time from this advanced nanotechnology stage of low nanodimensional AuNPs. Advances in AuNPs with instrumentation for evaluating the structural model in aqueous or non-aqueous phases now enable us to understand quite broadly almost all the events that take place with gold AuNPs at least at the nano level.

In this book, authors Gavino et al. focus on the design of colorimetric sensors and probes due to their interesting photophysical properties. In this approach, the surface plasmon resonance (SPR) band is sensitive to the proximity of other nanoparticles and thus analyte-triggered aggregation of AuNPs results in an important bathochromic shift of the SPR band and a change in the color of the solution from red to blue due to interparticle surface plasmon coupling. The selectivity of AuNPbased sensors towards different analytes depends on the recognition properties of the molecules attached to the surface of the nanoparticles. Finally, a selection of biologically active molecules is considered as analytes: neurotransmitters, nerve agents, pesticides, and carboxylates of biological interest. Taking into account the interesting photophysical properties of AuNPs, their easy functionalization, the use of aqueous solutions, and detection using the naked eye, they conclude that the red or blue question will continue to be ever present in the molecular sensing field.

Qureshi et al. also approach the higher catalytic activity being observed for AuNPs supported on reducible metal oxides such as TiO2, CO3O4, CeO2, and Fe2O3. Here, they study in detail CO oxidation catalyzed by mono- and bimetallic AuNPs over various silica supports. Finally, it is true to say that silica-supported gold nanocatalysts are becoming a hot topic of research for CO oxidation; conversely, there are still many challenges ahead for the improvement of silica-supported gold nanocatalysts to fulfill the main necessities of any catalyst such as an easy and low-cost synthesis method, high activity, selectivity, and greater stability at lower temperatures. Furthermore, they conclud that the proof of identity for active gold species is still a challenging task for CO oxidation reactions catalyzed by gold.

Briggs et al. approach nanoparticle interactions with energetic neutrons, photons, and charged particles that can cause structural damage ranging from single atom displacement events to bulk morphological changes. Due to the diminutive length

scales and prodigious surface-to-volume ratios of AuNPs, radiation damage effects are typically dominated by sputtering and surface interactions and can vary drastically from bulk behavior and classical models. Here, they report on contemporary experimental and computational modeling efforts that have contributed to the current understanding of how ionizing radiation environments affect the structure and properties of AuNPs. Finally, the future potential for elucidating the active mechanisms in AuNPs exposed to ionizing radiation and the subsequent ability to predictively model the radiation stability and ion beam modification parameters are discussed in his chapter.

Sivakumar et al. develop a promising technique for photodegradation of various hazardous chemicals that are encountered in waste waters. Here, they investigate the performance of various semiconductors. The anatase phase of TiO2 affords the best compromise between catalytic performance and stability in aqueous medium. Apart from many positive attributes of TiO2, the main drawbacks associated with this catalyst are (1) large band gap (*E*g > 3.2 eV), which can be excited only by UV light, and (2) recombination of excitons. Dye sensitization, coupling of semiconductors, transitional metal doping, etc., are some methods to shift the optical response from UV to the visible spectral range. They also introduce another important approach to shift the optical response of TiO2 from UV to the visible spectral range, i.e., by doping of noble metals with TiO2. Here, they research nanoparticles of different noble metals such as Ag, Au, and Pt deposited on synthesized TiO2, characterized by using various instrumental techniques such as XRD, TEM, FT-IR, BET, UV-Vis, and AAS and subjected to the degradation of textile dyes, namely TAZ, RY-17, and RB-5 under both UV and visible irradiations. Reaction conditions such as catalyst concentration, dye concentration, pH, irradiation time, light intensity, and additives were optimized for complete decolorization and are discussed in detail in this chapter.

Chen and Shon review intriguing catalytic studies that are accomplished by employing a variety of catalysts such as metal complexes, supported materials, supported metal complexes, and nanosized materials for polyene hydrogenation. Additionally, unsupported colloidal nanoparticle catalysts, which exhibit excellent activity and selectivity toward polyene hydrogenation, are introduced. The high activity of colloidal metal nanoparticle catalysts often allows reactions to be completed under mild conditions at atmospheric pressure and at room temperature. The important fundamental understandings of the influence of chemical environments (solvents, ligands, dopants, etc.) and compositions (metal complexes, metals, alloys, etc.) towards the catalytic activity and selectivity of various catalysts in homogeneous, heterogeneous, and semi-heterogeneous conditions are discussed. Systematic evaluation is also discussed in this review chapter, which paves the way to further develop chemo-, regio-, and stereoselective catalysts for polyene hydrogenation.

Finally, Puszkiel discusses hydride-forming binary as well as complex materials for their potential hydrogen storage properties, which possess high volumetric and gravimetric hydrogen capacities. Tuning the kinetic behavior of these hydrideforming materials involves different approaches and their combinations are discussed in this chapter. Herein, basic concepts of the chemical reaction for hydride compound formation/decomposition, thermodynamics, kinetics, and applied strategies to enhance the kinetic behavior of hydride compounds and systems are comprehensively described and discussed.

**V**

This work aims to bridge the gap between undergraduates, graduates, and scientists in applied AuNPs as well as modified colloidal gold particles to initiate researchers to study in as straightforward a way as possible and to introduce them to the opportunities offered by applied science and technological fields. We worked unswervingly to complete this work with the help of IntechOpen Open Access publisher. We hope that this contribution will further enhance applied AuNPs in nano- and bioscience, especially in bringing new entrants into the applied and hybrid AuNP science and technology fields and help scientists to forward and develop their own

**Mohammed Rahman and Abdullah Mohammed Asiri**

King Abdulaziz University, Kingdom of Saudi Arabia

fields of specialization.

This work aims to bridge the gap between undergraduates, graduates, and scientists in applied AuNPs as well as modified colloidal gold particles to initiate researchers to study in as straightforward a way as possible and to introduce them to the opportunities offered by applied science and technological fields. We worked unswervingly to complete this work with the help of IntechOpen Open Access publisher. We hope that this contribution will further enhance applied AuNPs in nano- and bioscience, especially in bringing new entrants into the applied and hybrid AuNP science and technology fields and help scientists to forward and develop their own fields of specialization.
