Plant Mediated Synthesis of Metal Nanoparticles

Green Nanoparticles: An Introduction

Savita Ahlawat¹, *, Nirantak Kumar¹

¹ Department of Chemistry, School of Basic and Applied Sciences, IEC University, Baddi, Solan, H.P., India

Abstract

This chapter elaborates the basic introduction of nanoparticles obtained from different sources. This includes the information regarding different types of nanoparticles, methods of synthesis and important principles of green chemistry etc. along with all these parameters this chapter emphasize on production of environmental friendly green nanoparticles by using different parts of the plants such as stem, bark, leaves, root, flower, seed and fruit etc. Clear information can be gathered from the chapter regarding appropriate parameters and precautions to be taken while synthesis of green and sustainable materials with wide ranges of applications which includes essential industries like food, cosmetics, pharmaceuticals etc. Brief introduction has also been mentioned here about the various characterization techniques adopted for identification and monitoring of green nanoparticles.

Keywords: Applications, Green nanoparticles, Nanoparticles, Synthesis.

* Corresponding author Savita Ahlawat: Department of Chemistry, School of Basic and Applied Sciences, IEC University, Baddi, Solan, H.P., India; E-mail: savitaahlawat905@gmail.com

1. Introduction

Nanotechnology is science, engineering, and technology carried out at the Nano-scale, which ranges from up to 100 nm. Richards Feynman is the pioneer of nanotechnology. The study of incredibly small objects is known as nanoscience or nanotechnology, and it has applications in all other scientific domains, including chemistry, biology, physics, material science, and engineering. Richard Feynman proposed the theory and notion behind nanotechnology and nanoscience in a discussion on There is Plenty of Room at the Bottom at a meeting on December 29, 1959. Professor Norio Taniguchi coined the term nanotechnology. The ability to observe and control individual atoms and molecules is at the heart of nanotechnology and nanoscience. Atoms contribute to everything on Earth, especially the food we consume, the clothes we put on, buildings, houses, and our bodies. However, atoms are so minuscule that they are invisible to the naked eye.

The microscope, which is used in the school science lab, can also observe the infection. In the early 1980s, the microscope required to examine the thing at the Nano size was invented. Scientists possessed the necessary tools at the time, such as the scanning tunneling microscopy (STM) and the atomic force microscope (AFM). Today's scientists and engineers are discovering a wide range of ways to purposefully create materials at the Nano size in order to benefit from them. Nanotechnology is a small solution to big problems. As it is the rule of nature that a thing with advantages has disadvantages too (Fig. 1).

Fig. (1))

Nanotechnology's benefits and drawbacks.

2. Types of nanotechnology

There are many forms of nanotechnology, which are explained below. These forms depend upon different techniques for the formation of nanoparticles.

2.1. Descending (Top-down)

This is the most frequent trend, especially in the electronic field. The structure is miniature at the nanometer scale from 1 to 100 nanometers.

2.2. Ascending (Bottom-up)

This is a mounting or self-assembly process that allows you to build a larger mechanism than you started with (you start with a Nanometric structure- a molecule) [1].

2.3. Dry Nanotechnology

It is utilized to make structures that do not work with humidity out of coal, silicon, inorganic materials, metals, and semiconductors.

2.4. Wet Nanotechnology

Based on biological systems found in watery environments. It is concerned with genetic material, the membrane, enzymes, and other cellular components.

2.5. Green Nanotechnology

This branch of nanotechnology deals with the concept of green chemistry and green engineering. It refers to the utilization of plant products. It consumes less energy and fuel. NPs synthesized by biological methods are more valuable and preferred over Physicochemical methods. Physico-chemical methods require a large amount of investment, which may allow the use of toxic solvents and the production of hazardous substances at the end of the process. Whereas in chemical methods, the use of more than one chemical species may lead to toxicity, which also harms human health and the environment. NPs synthesized from green synthesis have different approaches to synthesis.

3. What is a nanoparticle?

Nanoparticles are materials with diameters ranging from 1 to 100 nm. They fall in the transition zone between the molecule and their bulk counterparts [2, 3]. Because of their small size, they feature unique physiochemical qualities such as enormous surface area, high energy, and quantum confinement [4-6]. Since they have their very large scale specific surface area, high surface energy, and quantum confinement [7], they exhibit numerous unique properties (optical, magnetic, electrical, and so on). Because of their unique physiochemical properties, nanoparticles have a wide range of uses, including medicine [8], cosmetics [9], electronics [10], the food business [11], and the chemical industry [12]. Nanoparticles exhibit a wide range of chemical and morphological features [13].

3.1. Types of Nanoparticles

Nanoparticles come in a variety of forms, including metallic, metal oxide-based, alloy-based, magnetic, and others, which are addressed further below:

3.1.1. Metallic Nanoparticles

These are nano metals with nanoscopic dimensions (between 1-100nm). The existence of metallic nanoparticles in solution was first recognized by Faraday in 1857 [14], and Mie published a quantum description of the color-changing behavior of nanoparticles in solution in 1908 [15]. The following are some essential characteristics of metallic nanoparticles:

A high surface area-to-volume ratio

High surface energy

Particular electrical structure

Plasmon stimulation

Quantum confinement

There are numerous varieties of metallic nanoparticles that have been created, the most common of which are silver, gold [16], copper [17], palladium [18], and platinum [19]. Because of its unique anti-bacterial characteristics, silver is a commonly preferred nanoparticle and can be easily converted from monovalent silver into metallic silver [20]. Silver shows a higher tendency towards the plasmon excitation [21]. It also shows a wide range of applications in various fields like medicine [22], textiles [23], water treatment [24], and catalysis [25].

3.1.2. Metal Oxide Nanoparticle

These nanoparticles are created by connecting metal centers with Oxo (M-O-M) or hydroxo (M-OH-M) bridges, resulting in metal-Oxo or metal-hydroxo polymers in solution [26].

3.1.3. Alloy Nanoparticles

These are the alloy nanoparticles that are formed by combining different elements, and they show metallic properties. The synergic effect enhances the specific properties of alloy nanoparticles [27]. Their physical and chemical qualities are modifiable by varying the composition, atomic order, and size of the clusters [28]. Nano alloy has different properties than the bulk which leads to a number of properties in different fields such as electronics, engineering, and catalysis [29].

3.1.4. Magnetic Nanoparticles

These nanoparticles are made up of two parts: a magnetic component (such as iron, nickel, or cobalt) and a chemical component with a specified functionality [30]. Because of the magnetic component, these magnetic nanoparticles may be easily manipulated [31]. They exhibit a range of magnetic properties and are hence used in catalysis [32], medical diagnosis [33] and tissue-specific targeting [34].

4. Principles of green chemistry

There are twelve major concepts that support the use of green chemistry in the synthesis of green nanoparticles [35]:

4.1. Prevention

Necessary steps should be taken to avoid the formation of waste products during and after synthesis.

4.2. Atom Economy

The synthesis components must be turned into the end product without the production of extra materials.

4.3. Safer Solvent

Use of auxiliary chemicals and solvents should be avoided.

4.4. Less Risky Chemical Synthesis

Synthesis procedures that need materials with low or no toxicity to the environment should be used.

4.5. Utilization of Renewable Feedstocks

The feedstock must be renewable, with minimal depletion.

4.6. Catalysis

Catalysis agents should be used as stoichiometric agents.

4.7. Creating Safer Chemicals

Chemicals should be designed to perform a certain function with minimum harmful environmental effects.

4.8. Avoid Derivatives

If feasible, avoid derivatives such as protecting or deprotecting groups and blocking agents.

4.9. Degradation Design

Chemicals should be chosen so that they degrade into non-toxic derivatives at the conclusion of synthesis.

4.10. Real-time Analysis for Pollution Prevention

Toxic chemical synthesis should be monitored in real-time.

4.11. Design for Energy Efficiency

The usage of energy for synthesis should be kept to a minimum.

4.12. Inherently Safer Chemistry for Accident Prevention

Synthetic agents should be chosen with care to avoid potentially dangerous mishaps.

5. Nanoparticles produced by using parts of plants

Previously, the biosynthesis of AgNPs utilizing medicinal herbs was reported [36]. These medical plant extracts are advantageous because they are cost-effective, energy-efficient, and safeguard human and environmental health. Such approaches promote healthier workplaces and, as a result, are acceptable in all aspects of AgNP synthesis. Azadirachta indica (A. indica) is a medicinal plant that is used to cure a variety of ailments. Because of the presence of terpenoids and flavanones, which enable the stabilization of AgNPs, A. indica extract is useful for the synthesis of AgNPs. Many investigations have previously reported AgNP production utilizing A. indica leaf extract [37]. To the best of our knowledge, AgNP biosynthesis using A.indica fruit extract has only been studied once.

5.1. Fruit

Natural bioactive compounds found in fruit extracts have been shown to have great medicinal potential [38-40]. Consumption of fruit and its products not only improves individuals' health but also lowers their risk of various diseases such as age-related muscular degeneration, aging, cardiovascular diseases, cancer, cataracts of the eye, compromised immune system, gastrointestinal disorders, hypertension, and high cholesterol [41]. They are high in dietary fibers, minerals (calcium, iron, magnesium, and potassium), vitamins (ascorbic acid, folic acid, and vitamin A), and phytochemicals and antioxidants. Fruit-derived nanoparticles have been shown to have antimicrobial, anticancer, antioxidant, and catalytic properties. Carotenoids are plant pigments that give fruits their red, yellow, and orange colors [42]. Various animal and human research have demonstrated that lycopene has anti-inflammatory properties [43-46]. Citrus fruits and berries are high in flavonoids.

Fruits rich in anthocyanins, ascorbic acid, phenolic compounds, flavonoids, saccharides, and other vitamins include blueberries, blackberries, grapes, Citrullus lanatus, Terminalia arjuna, and Funica granatum [47]. Citrus medica Linn's juice, Capparis spinosa whole fruit, and Fragaria ananassa whole fruit are utilized to produce copper oxide nanoparticles, which have an advantage over biological techniques.

5.2. Root

Silver nanoparticles can be manufactured using the plant root of Morinda citrifolia, which belongs to the Rubiaceae family and has long been used in traditional medicine to cure a variety of diseases such as Atherosclerosis [48], hypertension [49], colic [50], and diarrhea [51]. The principal elements present in the roots of M. citrifolia are isoflavonoids, flavonoids, proteins, alkaloids, terpenoids, carbohydrates, and proteins present in the plant, which act as a stabilizing and reducing agent in the creation of silver nanoparticles. Damnacanthal, an anthraquinone derivative of M. citrifolia, has a cytotoxic effect against breast cancer cells. It also has antifungal efficacy against Candida albicans and anti-tuberculosis activity against Mycobacterium tuberculosis [52, 53].

5.3. Flower

Trifolium pratense flower extract was also used to create zinc oxide nanoparticles. T. pratense is a member of the Leguminosae family and contains anthocyanins, phenolic acid, and a trace of tannins. Carotene, essential oils, and vitamins C and E are all present. T. pratense possesses a high concentration of estrogenic isoflavones. These isoflavones have cardiovascular, skin, and bone-protecting properties [54].

5.4. Leaf

Extraction of plant leaf extracts such as tea leaves [55] or tree and shrub leaves is carried out [56]. When opposed to traditional methods, the utilization of these extracts offers various advantages. The polyphenolic matrix can operate as a capping agent, preventing early oxidation of the iron nanoparticles, and it can be employed as a source of nutrients and microbes for a possible bioremediation activity after chemical treatment.

5.5. Seed

The aqueous seed extract of Jatropha curcas, a tree of major economic value, can be used to create nanoparticles. Because of the presence of 40-50% oil from seed, it has been identified as a possible biodiesel crop. This, through a chemical or lipid-mediated esterification process, can be transformed into biodiesel. Jatropha seed kernels yield 40-60% oil as a valuable end product. It has 47% crude fat, 25% crude protein, 10% crude fiber, 5% moisture, and 8% carbohydrates [57-59].

5.6. Bark

The bark of Pinus eldarica contains a high concentration of phenolic compounds, which have significant antioxidant properties. The goal of this project was to create silver nanoparticles. Pinus bark was employed as a reducing agent in the creation of silver nanoparticles. The bark of the medicinal plant Syzygium cumini is used to reduce blood pressure and gingivitis [60]. Phytochemical substances found in the plant include phenols, tannins, alkaloids, glycosides, amino acids, and flavones [61]. The bark extract is used to create silver nanoparticles that have antibacterial properties against bacteria such as E. coli, Staphylococcus aureus, Pseudomonas aeruginosa, Azotobacter cerococcid, and Bacillus licheniformis.

Table 1 Different parts of various plants used to synthesize nanoparticles with variable shapes, sizes, and morphology.

Table 1 Plant sources of nanoparticles.

6. Green nanoparticles

Green chemistry is a collection of concepts that reduce