ZnO nnaoparticles have unique physical and chemical properties which make them an essential component in the different substances and devices from pharmaceuitical to the agriculture, industries, ceramics, tyres, paints, daily usages and many electronic and optoelectrioncs devices (Rakzimaska et al., 2014).
1.8.1. Medical uses
Zinx oxide plays a vital and effective role in central nervous suystem (CNS) and even durin the process of disease developments via meditating neuron excitability and discharge of nurotransmitters. It has been revealed that ZnO is effective too much in the function of many tissues and cells, natural enggineering of cells and biocompatibilty (Osmond et al., 2010).
1.8.2. Agriculture uses
ZnO nanoprticles have vital role in the production of valable crops and seeds. These nanoparticels are better to increase the palnt growth. Nanoparticles in different concentrations are treated with seeds in oreder to enhance seed vigour and germination. These nanoparticles are better sources to increase the stem and root geowth (Prasad et al., 2012).
1.9. Synthesis of nanoparticels
The synthesis of nanomaterials is a challenging task toady with the control size and structure which is very much significant for the application of nanopatucels in different areas such as catalysis, medicine, elctronis and industry. The nanosynteis methodologies are devied broadly inti two catagoriess “top down” and “bottom up”. A heavy masive solid is divede into the small masses which result into the nanosvale materials in the firet case. While in bottom up process the material is condensed from atomic or molecular level in form of gaseous and solution form to grnerate the nanosize materials. However the later approcah is mostly choosen for this purpose. The scematic diagram is shown in Fig 1.2 showin the relation of two aproaches.
Figure 1.2: Schematic of Bottom-up and Top-down approaches
Plenty of methods have been discussed on the ltieratur which are the bottom up appraoch teilding the nanoparticels in controlled manners. some of them are given below (Gao et al., 2007).
1.9.1. Sol-gel method
It is a wet chemical based process used for the fabrication of nanoparticles. The collidol suspension and gelation in case of the evaluation of complex to the sol formed in the liquid phase called gel. Mostly metal salts and alkoxides are used as precursors and process of hydrolysis of condensation takes place further times. This process has many benefits to be used as it is low temperature, cost effective, and facile that controls the byproducts and the concentration of the dopants including dyes or rare earth products even at a very small level. On the other hand the required elements can be added to any point required during process and finally gives the dispersion of synthesized particles. The agglomeration and growth of the particles results in the form of thick gels. However the above reaction depends upon many factors such as pH vales, time, temperature, concentration and catalysts. It is easy to control the size, structure and other properties of synthesized particles by controlling the above mentioned parameters. After the reaction process the required Nano powder, Nano rods or thin films can be synthesized depending upon the deposition and drying technique. Such nanomaterial synthesized by sol-gel has wide range of applications in plenty of fields such as paints, plastic, ceramics, industries, pharmaceutical, medical and optics. This method is divided into two categories, the alkoxides and non-alkoxide routes. In non-alkoxide, the inorganic salts are used while extra efforts are required to remove other inorganic ions and compounds. On the other hand metal oxides are used in alkoxides route. Many reaches revealed the preparation of NPs by sol-gel method (Gao et al., 2007).
1.9.2. Hydrothermal method
There is no use of the organic solvents and other supplements due to which this reaction process becomes more simple and economic and environment friendly. The process is performed in and autoclave and substance is heated up to 100-300 degree temperature for few days. The crystal nuclei are formed when the hot substance is cooled down slowly and then grow. This process has various advantages as it is carried out at low temperature. The crystal of many shapes and different dimensions can be formed by controlled manners. This is done by controlling the concentration of initial product, temperature and time duration of reaction. This process has many techniques of synthesizing particles such as aqueous solution at high temperature and high pressure.
Fig 1.3: Experimental setup for hydrothermal synthesis
It is termed as single crystal process that synthesis the single crystal depending upon the temperature and hot water solution of substance at high pressure (Salahuddin et al., 2015).