Nanomaterials: Properties, Synthesis, Characterizations, and Toxicities

MOHIT AGARWAL,1 RAJESH SINGH TOMAR,1 R. K. SINGH,2 ANIL KUMAR MEENA,2 and ANURAG JYOTIL*

  • 1 Amity Institute of Biotechnology, Amity University Madhya Pradesh, Maharajpura, Gwalior - 474 005, India
  • 2Division of Toxicology, CSIR-Central Drug Research Institute, Jankipuram Extension, Lucknow - 22 6031, India
  • *Corresponding author. E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

ABSTRACT

This chapter represents a detailed overview of properties, synthesis, characterization, and toxicities related to nanoparticles (NPs). NPs are minute particles of 1-100 mn in size, and they are just a link between bulk materials and atomic or molecular structures. As compared to conventional bulk particles, nanomaterials exhibit different unique properties. They can be classified into different classes based on its properties, shapes, or sizes. NPs possess unique physical and chemical properties due to their high surface area and nanoscale size. Their optical properties are reported to be dependent on the size, which imparts different colors due to absorption in the visible region. Generally, NPs already exist in nature; natural sources of NPs in the atmosphere are volcanic eruptions, minerals such as clay and mica, natural colloids include blood and milk. The main approaches for NPs synthesis are either bottom-up or top-down approach, and various synthesis procedures include: physical, chemical, biological, and green synthesis. To understand the possible potential of NPs, a deeper knowledge of their synthesis and characterization is needed. Characterization is done by using a variety of different techniques. Nanoparticle characterization can be preliminarily done by UV-visible spectroscopy, and after preliminary confirmation, it can be done as needy, by using FTIR, ТЕМ, XRD. Metallic NPs are reported to be so rigid and stable than their degradation is not easily achievable, which can lead to several toxicities. Toxicity can refer to the effect on a cell (cytotoxicity), gene (genotoxicity), an organ (e.g., renal or liver toxicity), or the whole organism and an estimate of how much of a substance causes a kind of harm.

INTRODUCTION: AN OVERVIEW

Nanotechnology is defined as any technology that utilizes nanomaterials, which are in the range from 1-100 mn. To know the world of nanotechnology, one should have knowledge about the units of measures involved. A nanometer (mn) is one-billionth of a meter and is still very large if we compare it to the atomic scale. For instance, cells are our nature’s nanoma- chines [5]. Bulk materials possess continuous physical properties, and the same is applied to macro-sized material, but when they reach to nano-scale properties changes. Actually, these basically depend on the size and are different from the properties of bulk at macro scales. Nanomaterials have been found to have novel physical and chemical properties with respect to their large size counterparts. Also, the unique magnetic, electrical, optical, physicochemical properties of NPs arise due to its higher surface area to volume ratio.

UNIQUE CHARACTERISTICS/PROPERTIES OF NANOMATERIALS

Nanotechnology is a prominent area of science that is being explored in different field biotechnological, pharmacological, and in applied sciences. NPs are minute particles of 1-100 mn in size. They are just a link between bulk materials and atomic or molecular structures. NPs exhibit different properties when compared to conventional bulk particles. NPs have special optical properties as they can confine their electrons and also can perform better quantum effect due to the presence of surface plasmon resonance (SPR) [11, 14]. Color, NPs are of different colors, varying on metal salt utilized, on reducing and the capping agent being utilized. It has been reported that when gold materials are converted to nanomaterials, they turn into red color. Gold nanoparticles (AuNPs) interaction with light is vigorously governed by the particle sizes of the materials. The melting point also changes; it drastically falls down when the particle size reaches to nanoscale [24]. NPs possess mechanical vigor as compared to conventional counterparts. It is one or two times higher in magnitude than that of in bulk. Conversion of materials into nanoscale increases crystal perfection or reduction of defects, which would result in the enhancement of mechanical vigor. In general, the hardness of metals increases linearly with an increase of grain size. The electrical property also changes. By this, special property NPs can enhance crystal perfection. In integration, a reduction in particle size below a critical dimension, i.e., electron de Broglie wavelength would result in a modified electronic structure with a wide and discrete bandgap. It also shows good catalytic activity due to the immense surface, NPs composed of transition element exhibit intriguing catalytic properties. In special cases, catalysis may be enhanced and more concrete by embellishing these particles with gold or platinum clusters. In magnetic NPs, the energy may be that minute that the vector of magnetization fluctuates thermally called superparamagnetism. Physically contacting superparamagnetic particles is losing this special property by interaction, except the particles are kept at a distance. A consequential property of NPs is to compose suspensions. At elevated temperatures, especially, NPs possess the property of diffusion. NPs are generally based on their dimensionality. ID nanomaterials, i.e., they are typically thin films or surface coatings, computer chips, and hard coatings on eyeglasses. These have been utilized in electronics, chemistry, and engineering. 2D nanomaterials include 2D nanostructured films, with nanostructures firmly affixed to a substrate, or nanopore filters. Asbestos fibers are an example of 2D NPs, and 3D nanomaterials, these include thin films deposited under atomic- scale porosity and colloids.

NANOPARTICLES (NPS)BASED MATERIAL

NATURAL NANOMATERIALS

Natural nanomaterials means it belongs to the natural world without any anthropogenic modification or processing and should have a veiy unique property due to its inherent nanostructure. Natural sources of NPs in the atmosphere are volcanic eruptions [20]. There are many natural materials to which common peoples are familiar with their unique properties and composition. One of the best examples is the Lotus rolling activity for water droplets and dust removal. The nanostructure of this plant is responsible for its unique property and ability to self-clean. Exactly, for this reason, this plant is considered a sign of purity. Its leaves have a very outstanding property that it’s totally repelling water because of its superhydrophobic nature. The basic mechanism behind is dragging the dirt away from the surface of the plant by rolling off water droplets. This mechanism is known as the self-cleansing action of lotus; due to this, the plant is resistant to dirt. This property was first investigated by Wilhelm Barthlott and published a paper describing the lotus effect (Figure 9.1).

Assuming lotus flower with water droplets removing dirt by the rolling mechanism

FIGURE 9.1 Assuming lotus flower with water droplets removing dirt by the rolling mechanism.

In nature, there are various outstanding phenomenon which can easily be shortlisted under natural nanomaterials phenomenon’s which are:

  • 1. NPs from natural erosion and volcanic activity.
  • 2. Minerals such as clay and mica are the types of layered silicates that are characterized by a fine 2D ciystal structure. Naturally occurring clay includes montmorillonite (MMT).
  • 3. Natural colloids include blood, and milk is the best liquid colloid occurs naturally, fog, mist, and smog are aerosol type, while gelatin is gel type.

4. Materials like shells, corals, bones, skin, claws, feathers, horns, hair, etc. Some of these are made up of largely of very flexible protein, and some of these are formed with a polymer [6].

VARIOUS METALLIC NANOPARTICLES (NPS)

During the last decades, the biosynthesis of metallic NPs, such as zinc, silver, and AuNPs have received more attention.

ZINC OXIDE NANOPARTICLES (NPS)

Zinc oxide is listed as generally recognized as safe (GRAS) by U.S. Food and Drug Administration (FDA) (21CFR 182.8991). It is most commonly used as a food additive in the fortification of cereal-based food due to its antimicrobial property. It is also used in food can packing, meat, fish, and corn to preserve color. It is also famous for various applications such as photo-catalyst, optical material, cosmetics, UV absorber, and Gas sensor. While nano ranged of zinc oxide has more pronounced antibacterial activity than that of bulk, due to its large surface to volume ratio, which provides better binding with pathogens. Also, recent studies have shown selective toxicity to bacteria and minimal effect on human cells [16]. The bactericidal mechanism of ZnO NPs is complex and still under investigation [7].

SILVER NANOPARTICLES (AGNPs)

It is well known from ancient times that silver has a strong antimicrobial property [3]. To increase the antimicrobial effect of silver, it has to be converted into the nanoscale, as the size is reduced, surface area to volume ratio increases [1]. Silver nanoparticles (AgNPs) size of 10-100 nm has a strong bactericidal property [2, 4]. A broad range of nanosilver has been emerged. A more than thirteen hundred manufacture throughout the world are investing to develop nanotechnology-based products for the commercial market and more than 300 products made up of nanosilver. The world is growing well in nanotechnology, with an increase of 25% annually, about 3 trillion dollars by 2020 [18].

GOLD NANOPARTICLES (AUNPs)

Presently, the biosynthesis of gold nanoparticles (AuNPs) is an active research area. Syntheses of the gold nanoparticle by using biological as well as chemical approaches are well established. In this study, the biosynthesis of GNPs using lemongrass is well established. Although the mentioned plant, i.e., lemongrass study was earlier investigated, but it is by using AgNPs [9], but still there is no data available for the synthesis of GNPs by using lemongrass. The main objective of the present study is to develop a clean, non-toxic, and eco-friendly method for obtaining GNPs.

VARIOUS REDUCING AND CAPPING AGENT

Reducing agent is the chemical compound which performs reduction reaction. Typically reducing agents are used in the synthesis of metallic NPs. They generally reduce metal salts into pure metals. The amount of reducing agent required in a typical reaction is normally decided by the quantity of metal salt at the starting point. For example, sodium borohy- dride, amino acids, СТАВ, ascorbic acid, etc., are reducing agents. While tri-sodium Citrate is reducing as well as a capping agent to prevent the binding. A capping agent is used for the stabilization of NPs is strongly absorbed monolayer of organic molecules. Particles can be functionalized using capping agents to impart useful properties. A capping agent can be polymerized to form a functional polymer and used to protect the surface of materials. Also, the capping agents like dendrimers, even clay particles protect the NPs from aggregation, and chemical reaction, for example, hydrobenzamide, citrate, polyvinyl pyrrolidone (PVP), mercaptoethanol, and thiourea is also a capping agent (Table 9.1).

TABLE 9.1 Precursors, Reducing Agent Polymeric Stabilizer’s Used for Nanoparticles Synthesis

Sr.

No.

Category

Salt Used

1

Precursors

Metal salt: Zinc acetate, copper sulfate, silver nitrate, auric chloride, etc.

2

Reducing Agent

Sodium citrate, citric acid, ascorbic acid, glucose, plants extract, etc.

3

(Polymeric) Stabilizer

PVP, PVA, plants extract, glucose etc.

 
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