Synthesis and Applications of Semiconductor Nanostructures

Semiconductor nanostructures show different properties compared to their bulk counterparts due to quantum confinement effects and enhanced surface-to-volume ratio with the reduction in particle size on nanoscale dimensions. This chapter introduces the nanomaterials, especially semiconductor nanostructures of various morphologies, quantum nanostructures (quantum dots, quantum wires and quantum wells) along with conventional 3D nanostructures. The present time is the introductory era of nanoscience and nanotechnology; synthesis of highly monodisperse nanostructures for device applications is a challenge for researchers and technocrats. This chapter discusses at length fascinatingly the bottom-up and top-down synthesis approaches along with the commonly used nanomaterial synthesis techniques, such as mechanical milling, lithography, electrospinning, template synthesis, chemical precipitation, sol-gel method, hydrothermal/solvothermal method, laser ablation, and other vapour processing methods.

Semiconductor Nanostructures (SCNSs) are of great interest due to their excellent optical and electronic properties. As a result of their unique properties, semiconductor nanostructures have found applications in several fields, including optoelectronics, solar energy conversion, photocatalysis, and sensing. SCNSs show promising prospects in photocatalytic and sensing applications. Photocatalytic application of SCNSs provides potential solutions for environmental remediation and energy generation. Several strategies have been developed to achieve high efficiency for photocatalytic processes using semiconductor nanostructures. Efforts have also been made to achieve high sensitivities in sensing applications using SCNSs. In the present chapter, the photocatalysis activity of semiconductor nanostructures has been discussed along with the photocatalytic mechanism and strategies for enhancing photocatalytic efficiency. Several applications of semiconductor photocatalysis in wastewater treatment, hydrogen production, and air purification are cited in recent literature. The sensing applications of semiconductor nanostructures have also been discussed, including their use as chemical sensors, gas sensors, and biosensors.

Tailoring the electronic, surface and morphological properties alter the catalytic properties of the material(s), specifically at the nanoscale. In the past years, a plethora of research has been reported to find sustainable and eco-friendly catalysts for environmental pollution remediation. In this direction, titania nanoparticles have been intensively explored to check their potential for photocatalytic removal of various pollutants. In the current scenario, where the growing population needs to feed on an everyday basis, abundant pesticides indiscriminately are being used to increase crop yield, thus causing environmental pollution and ecological imbalance. In order to remove these environmental pollutants along with the polycyclic aromatic hydrocarbons (PAHs) that are formed by incomplete combustion of crop residue or any other organic matter have been studied, and the results reported for these two categories of pollutants are summarized in this chapter.

Several metals have been reported to possess antimicrobial properties. Out of these metal nanoparticles, some semiconductor nanoparticles are expectant solutions to the pathogenic activities of microorganisms. Many studies have proved that these nano-sized particles are effective against several Gram-positive as well as Gram-negative pathogenic bacteria. Different types of nanoparticles are synthesized from different metals, and according to their size, they show effective responses against the target microorganisms. The exact mechanism of the antimicrobial effect has not been confirmed, but some supposed methods have been described. These particles also help to decrease antibiotic pollution as the hefty use of antibiotics can bring drastic changes in the environment and livings beings in the form of side effects. 

Metal-organic frameworks (MOFs) are structurally complex structures constructed from inorganic and organic components. MOFs are highly ordered porous structures with special characteristics, such as high thermal stability, tunable surface properties, and large surface area. The MOFs demonstrate a wider range of potential applications in adsorption, gas storage, catalysis, drug delivery and sensing. As a result, the research in the area of MOFs is experiencing rapid growth. Considering the promising prospects of MOFs, this chapter presents an overview of the general synthesis and characterization methods for MOFs. Besides, the applications of MOFs in adsorption, sensing, and catalysis are also highlighted.

Metal-organic frameworks (MOFs), due to their high porosity, enhanced surface area, rich topology, diverse structures and controllable chemical structures, have recently emerged as an exciting class of porous crystalline materials. The integration of nanostructures with MOFs generates MOF composites with synergistic properties and functions, attracting the broad application prospect. In this chapter, the primary strategies guiding the design of these materials, including MOFs, are described as host materials that contain and stabilize guest nanoparticles. A detailed discussion about the recent progress of nanostructure-impregnated MOFs based on diverse photocatalytic (e.g., environmental remediation, oxidation of alcohols, CO2 reduction, and H2 generation) and sensing (organic pollutants, gaseous pollutants, and heavy metal ions) applications has been provided. With a deeper knowledge of nanostructure-impregnated MOFs, this book chapter will provide better guidance for the rational design of high-performance MOF-based materials and is likely to shed new light on future research in this promising field.

Metal-organic framework (MOF) is a class of materials, which is formed by combining metal/inorganic and organic linkers, resulting in the formation of a framework with high surface area and permanent porosity. The freedom to vary inorganic and organic linkers stimulated the synthesis of thousands of MOF structures, for their utility in various applications. The presence of high porosity, high surface area and high free volume made these materials a perfect choice among the class of solid adsorbents. The metal nodes, tunable pore, versatile structure and functionalized surface allow various types of chemical interactions, viz. electrostatic interactions, π complexation, H-bonding, coordination bonding, van der Waals interactions, hydrophobic/hydrophilic interactions. All these features made MOF a customizable material to be utilized for targeted applications. This chapter involves a discussion about the usage of versatile MOFs in smart applications, such as gas storage, gas separation and drug delivery, along with a brief discussion about the synthesis of MOFs.

Hematite is an n-type semiconductor, and its semiconducting properties can further be improved by nano-structuring and doping. In several optoelectronic devices, such as thermoelectric and solar cells, both n- and p-type semiconductors are required. The p-type hematite can be synthesized by doping cations, such as Ni2+, Mg2+, Cu2+, and Mn2+. Furthermore, hematite is a weak ferromagnetic material, and its magnetic properties vary with the size of nanoparticles, doping of cations as well as doping concentration. This chapter discusses various properties of nanostructured nickel-doped hematite. As nickel is a ferromagnetic divalent dopant with a high magnetic moment, its doping in hematite together with nano-structuring shows a large variation in both electrical and magnetic properties in nickel.

The application of various nanoparticles and nanotechnology in cosmetics and pharmaceuticals is an interesting area of research and development. The use of nanotechnology has also emerged as an important tool for gene manipulations, diagnosis of several diseases along with improvement in treatment efficacy. This chapter has emphasized the use of nano-materials in cosmetics and pharmaceuticals globally with associated legislation in different countries. More than 100 different products have been listed and discussed with their uses in different fields along with associated concerns. 

In today’s fast-moving scenario, nanotechnology has already spread its wings to nanocosmetics and nanomedicines due to the wide range of physical and chemical properties associated with nanoparticles. Different types of nanoparticles, like nanoliposomes, fullerenes, solid lipid nanoparticles etc., have made their entrance into the nanocosmetic industry. However, the safety concern of nanoparticles has forced the cosmetic industry to limit their applications. The pharmaceutical industry has explored the benefits of nanotechnology; it has developed dendrimers, micelles, drug conjugates, metallic nanoparticles etc. The brief explanation of these nanoparticles provides a salient glimpse of why they are used in nano pharmaceutical and medicinal chemistry. • Metallic nanoparticles: Used for drug delivery, cancer treatment, and also in biosensors. • Nano-liposomes: Bio-compatible and possess entrapment efficiency. • Nano-emulsions: Used for controlled delivery of bioactive materials. 

Superparamagnetic iron oxide nanoparticles have attracted attention due to their compatibility with various biomedical applications. The quantum confinement and increased surface area to volume ratio of the nanostructures alter their magnetic properties. There are several bottom-up techniques to synthesize superparamagnetic iron oxide nanoparticles; however, they offer certain limitations, like the existence of a secondary phase. The reaction parameters can be controlled to form pure-phase nanoparticles to increase their scope of applications in the field of medicine. Moreover, different applications demand different surface coatings of iron oxide nanoparticles.

The study of the physical and structural properties of rare-earth doped borate glasses is discussed in this chapter. The glasses have been synthesized using the conventional melt quenching technique. X-ray diffractometer has been used to determine the amorphous nature of the prepared glass samples. Upon closer inspection of the XRD patterns, it is observed that the peak width changes, which indicates that the increase in the concentration of rare earth induces a localized devitrification of the prepared glasses around the rare earth. To investigate the structural dependence on the chemical composition of the manufactured glass, various parameters were determined. The molecular vibrations and rotations related to covalent bonds found in the glasses were studied using the infrared spectrum. 

Carbon nanotubes (CNTs) composed of sp2 carbon units oriented as one rolled-up graphene have provided exceptional advances in the design of chemical sensors for environmental and health monitoring. The remarkable properties of CNTs, such as high active surface area, chemical inertness, high strength, high electrical conductivity, excellent thermal stability, and low charge-transfer resistance, have made them a potential candidate for the detection of various explosive, combustible, and toxic gases, such as hydrogen sulfide (H2S), nitrogen oxides (NOx ), ozone (O3 ), and halogens (Br2 , Cl2 , and I2 ). However, CNT-based sensor shows issues like low sensitivity and slow response/recovery time due to minimum charge transfer between the pristine CNTs and target analytes. The functionalization of CNTs with metal oxides, noble metal nanoparticles, and organic semiconductors not only improves the gas sensing parameters but also enhances their selectivity toward a particular type of target analyte due to the better charge transfer between the composite and gas analytes. This book chapter focuses on the ways to create CNT-based sensors exhibiting selective responses to different target analytes, future developments in the field of chemical sensors, and the viewpoint of their commercialization. 

Graphene has been an interesting material for scientists and engineers by virtue of its remarkable properties. It has unique electronic properties with zero bandgap at the Dirac point. The absence of bandgap in graphene limits its application in electronics. The formation of graphene nanoribbons and substitutional doping of graphene are the methods to manipulate the geometric and hence electronic structure of graphene. Starting from the geometric and electronic properties of graphene, this chapter involves a discussion on the geometric and electronic structure of graphene nanoribbons and substitutionally doped graphene systems based on first principles studies.

In this chapter, different structural, electronic and magnetic properties of strained graphene nanoribbons are examined. All the calculations are performed by using density functional theory. Compressive stress along a nanoribbon's longer axis and tensile stress at the midpoint and perpendicular to the nanoribbon's plane are studied. There are remarkable changes in the structures, including the formation of nanoripples in the ribbons. The shape and size of the ribbons lead to variation in their electronic and magnetic properties. Strained nanoribbons show tunable magnetic properties that can be used for developing magnetic nano-switches.