Biogenic synthesis of metal nanoparticle of various shape and size using microorganisms and plant tissues extracts. This method of biosynthesis is very simple, requiring less time and energy in comparison to the physical and chemical methods with predictable mechanisms. The other advantages of biological methods are the availability of a vast array of biological resources, a decreased time requirement, high density, stability, and the ready-to-soluble as-prepared nanoparticles in water [ ].
Therefore, biogenic synthesis of metal NPs unwraps up enomorus opportunities for the use of biodegradable or waste materials. At the nanoscale, particle-particle interactions are either dominated by weak Vander Waals forces, stronger polar and electrostatic interactions or covalent interactions. Characterization of nanoparticles is vital part of determination of the phase purity, shape, size, morphology, electronic transition plasmonic character, atomic environment and surface charge, etc.
Optical analysis techniques such as Fourier transform infrared FTIR spectroscopy, fluorescence correlation spectroscopy FCS, diffusion coefficients, hydrodynamic radii, average concentrations, and kinetic chemical reaction , X-ray diffraction XRD for phase purity with crystal parameters and particle size , diffuse light scattering DLS can probe the size distribution of small particles , UV-Vis spectroscopy band gap, particle size electronic interaction , XPS X-ray photon spectroscopy, surface environment of elemental arrangement , Raman spectroscopy it provides submicron spatial resolution average size and size distribution through analysis of the spectral line broadening and shift , nuclear magnetic resonance NMR can detect structure, compositions, diffusivity of nanomaterials, dynamic interaction of species under investigation , small-angle X-ray scattering SAXS; from 0.
Above analysis can be used to determine the properties of nanomaterials such as the size distribution, dispersibility, average particle diameter, charge affect the physical stability and the in vivo distribution of the nanoparticles. Few of above are discussed below. The crystalline structure, size, and shape of the unit cell and the crystallite size of a material can be determined using X-ray diffraction spectroscopy XRD.
In this technique the whole sample is analyzed by scanning with a focused fine beam of electrons and electrostatic or electromagnetic lenses to generate images of much higher resolution. Surface morphology of the sample is determined by the help of the secondary electrons emitted from the sample surface.
In TEM analysis, an incident beam of electrons is transmitted through an ultra-thin sample which interacts with the sample and transforms into unscattered electrons, elastically scattered electrons, or inelastically scattered electrons. The scattered or unscattered electrons are focused by a series of electromagnetic lenses and then projected on a screen to generate a electron diffraction, amplitude-contrast image, a phase-contrast image, or a shadow image of varying darkness according to the density of unscattered electron.
Transmission electron microscopy techniques can provide direct imaging, diffraction and spectroscopic information, chemical composition, either simultaneously or in a serial manner, of the specimen with an atomic or a sub-nanometer spatial resolution. High-resolution TEM imaging, when combined with nanodiffraction, scanning tunneling microscopy STM , atomic resolution electron energy-loss spectroscopy, and nanometer resolution X-ray energy dispersive spectroscopy techniques, is critical to the fundamental studies of importance to nanoscience and nanotechnology.
Different surface structures can be obtained from various synthesis routes. Surface morphology of the nano-structural features of silver are examined using above electron microscopic techniques.
A sharp scanning tip, an xyz-piezo scanner controlling the lateral and vertical movement of the tip, a coarse control unit positioning the tip close to the sample within the tunneling range, a vibration isolation stage and feedback regulation electronics are the basic parts of the STM instrumentation.
Its working on the generic principle for, i. The AFM can investigate the size, shape, structure, sorption, dispersion, and aggregation of nanomaterials. One of the principal advantages of this nondestructive technique is that it felicitates the imaging of the non-conducting samples without any specific pretreatment and without causing appreciable harm to the surface.
The major drawbacks of this technique is i the size of the cantilever tip is generally larger than the dimensions of the nanomaterials to be examined that led to unfavorable overestimation of the lateral dimensions of the samples [ , ], ii AFM also lacks the capability of the detecting or locating specific molecules; however, this disadvantage has been eliminated by recent progress in single-molecule force spectroscopy with an AFM cantilever tip carrying a ligand.
In looking to the better understanding of the atomic processes in solids, their emerging demand for new imaging, diffraction and spectroscopy methods with high-spatial resolution. That demand has been reinforced by the growing interest of human being in nanomaterials. Although, the transmission electron microscopy TEM can provide the structural information with excellent spatial resolution down to atomic dimensions through high-resolution TEM imaging and electron diffraction technique, electron energy-loss spectroscopy offers unique possibilities for the nanoscale thin materials plasmonic analysis.
Due to the broad range of inelastic interactions of the high energy electrons with the specimen atoms, ranging from phonon interactions to ionization processes, EELS and their combination with TEM offers the facility to map the elemental composition of a specimen for studying the physical and chemical properties of a wide range of biological and non-biological materials. Moreover, the energy distribution of all the inelastically scattered electrons provides the information [ ] about the local environment of the atomic electrons for the universal dispersions of surface plasmons in flat nanostructures, [ ] 3D distribution of the surface plasmons around a metal nanoparticle [ ] and exotic nanostructures are shown in Figure 15 [ ].
EELS data and corresponding electrodynamic calculation for rod.
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In decades past, synthesis of silver nanostructures has been an active research area because of their excellent optical properties such as surface-enhanced Raman scattering SERS and surface plasmonic resonance, which strongly depend on size, shape, and composition, and can be checked by the help of the optical analyses like XPS and UV-Visible spectroscopy analysis.
Although, the change in color of precursor silver ion to silver nanoparticles was visually observed, the absorption measurements were carried out using UV-Visible spectrophotometer to check the stability of silver nanoparticles.
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Effect of shape and size on optical properties of the silver nanoparticle is reflected by Figure UV-Vis spectroscopy also used for particle size determination of silver nanoparticles, using Mie scattering theory. SERS can be employed as a sensitive and selective technique for identification of molecules. Strong electromagnetic fields are generated due to the localized surface plasmon resonance LSPR of nano-noble metals, when they are exposed to visible light.
If the Raman scatterer is placed near these intensified electromagnetic fields of nano-noble metals, the induced-dipole increases that results in the increase of intensity of the inelastic scattering. Similar relations can hold-good for the extinction and scattering cross sections of the nanoparticle. If the extinction and scattering cross sections of the nanoparticle at resonant wavelengths are maximized, it represents the spectroscopic signature of exciting the LSPR.
A SER spectrum also provides the accurate information about molecular structure and the local environment in condensed phases than any other electronic spectroscopy technique.
SEM images of a self-assembled dimmer of flower-like silver mesoparticles along with their corresponding Raman images at the axis parallel to the dimer axis of the detected particles with high SERS quality . Metal nanocatalysts of different shapes and sizes like quantum dots, nanotubes, nanofibres, nanolithographs, self-assemble processing devices, nanoparticles, and nanofibres, have immense significance. They have bright future in broad research areas of high-tech applications in the field of information of storage, computing, medical and biotechnology, energy, sensors, photonics, communication, and smart materials.
The size and shape of the nanometal is a critical criteria to target-specific applications that may be achieved by keeping size distribution as narrow as possible. Nanometals has enormous potential to serve all facets of life for building big future from small things, as they acquire the goodness of both homogeneous and heterogeneous catalysts. At present, the pretty command over the morphologies of silver nanoparticles has received immense attention of researchers due to their considerable budding applications in almost all fields.
In the present context, they have attracted the interest of the people due to their unique physical, chemical, and biological properties in compared to their massive counterparts. Silver nanoparticles are also studied by material scientists who investigate their integration into other materials in order to obtain enhanced properties, for example, in solar cells where silver nanoparticles are used as plasmonic light traps. These properties make them valuable in other applications such as catalyst [ , ], inks, microelectronics, medical, imaging, health products, and waste management.
This makes nanofibres excellent materials for use in filtration [ ]. It includes the share of different facets of life, i. Out of the versatile applications of nanosilver in diverse phases of life, few are discussed below. The photothermal heating killed the cancer cells while leaving the surrounding healthy tissue unharmed.
Silver nanotechnology, emerging as a fast growing technology in the field of orthopedics due to its antimicrobial properties. Therefore, silver nanoparticles can be used in orthopedic applications such as trauma implants, tumor prostheses, bone cement, and hydroxyapatite coatings to prevent the biofilm formation.
Bio film formation is a major source of morbidity in orthopedic surgery. The promising results with in vitro and in vivo studies of the use of AgNPs in this field reduce the risk of infection in an effective and biocompatible manner [ ]. Silver nanoparticles are already utilized for various applications in areas such as food supplements, food packaging, and functional food ingredients. To protect the food from dust, gases O 2 , CO 2 , light, pathogens, moisture nanocomposite LDPE films containing Ag and ZnO nanoparticles packaging, would be a safer, inert; cheaper to produce, easy to dispose and reuse-way.
In recent years, one of the most important applications of the AgNPs has been observed in catalysis of chemical reactions.
Nanosilver of different shapes and sizes catalyzed many organic transformations such as cyclization, Michael addition, alkylation, alkynylation, oxidation, cross-coupling reaction, A 3 -coupling reaction, reduction, Friedal-crafts, Diel-Alder reaction, and many more [ ]. Researchers are fascinated to silver nanoparticles, since it has enabled unprecedented or low selective transformations to highly reactive and chemoselective catalysis for various nanosilver-catalyzed reactions.
For example, kinetically difficult reduction of p-nitrophenol is not possible even in presence of strong reducing agent NaBH 4 and month long aging. But, by the addition of AgNPs in the same reaction mixture, it made the reaction possible by formation of the p-aminophenol [ ]. Studies in this field, revealed the strong potential of nanosilver catalysis in the total synthesis of natural products and pharmaceutical molecules [ ]. Bioaerosols are airborne biological origins such as viruses, bacteria, fungi, which are capable of causing infectious, allergenic, or toxigenic diseases.
Large quantities of these bioaerosols were accumulated on the filters of heating, ventilating, and air-conditioning HVAC systems [ ]. It often resulted in the low quality of indoor air. These pathogens generate mycotoxins which are dangerous to human health.
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To reduce the microbial growth in air filters, Ag-deposited-activated carbon filters ACF were effectively used for the removal of bioaerosols. Studies supported that the silver nanoparticle AgNP can work as an excellent antiviral, antimicrobial, and disinfectant agents. The results obtained showed that silver nanoparticles in surface water, ground water, and brackish water are stable.
However, in seawater conditions, AgNP tend to aggregate.
The comparison of AgNP-impregnated ceramic water filters and ceramic filters impregnated with silver nitrate was made. The results showed that AgNP-impregnated ceramic water filters are more appropriate for this application due to the lesser amount of silver desorbed compared with silver nitrate-treated filters without disturbing the water chemistry conditions and performance of the filters.
Quaternary ammonium functionalized silsesquioxanes-treated ceramic water filter desorbed less from the filters and achieved higher bacteria removal than the filters impregnated with AgNP. This indicates that the quaternary ammonium functionalized silsesquioxanes compound could be considered as a substitute for silver nanoparticles due to its lower price and higher performance [ ]. Nanosilver products such as beauty soap, hair shampoo and conditioner, body cleanser, tooth brush, sanitizer, facial masksheets, skin care line, makeupline, wetwipes, disinfectant spray, wash and laundry detergent, etc.
Silver nanoparticles can also be incorporated in manufacturing of the toothpaste or oral care gels. The nanoproduct can also be used in dyeing of cosmetic foundations, eye shadows, powders, lipsticks, inks, varnishes, or eyebrow pencils. According to Ha et al. A soap with silver nanoparticles as one of the ingredients was prepared; and in , the method for its preparation was patented [ ]. Nia had used the silver nanoparticles to improve the plant growth of the plants citrus fruits, grains, and oleaceae trees [ ]. Silver nanoparticles-treated structure of textile materials [ ] were used for antimicrobal activities protected clothing.
Materials at nano-level may induce some specific physical or chemical interactions with their environment. As a result, they perform exceptional changes in the properties like conductivity, reactivity, and optical sensitivity, in comparison to their massive counterparts, which may enhance the processes such as dissolution, redox reactions, or the generation of reactive oxygen species ROS.
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These processes may be accompanied by biological effects that would not be produced by larger particles of the same chemical composition. The nanomaterials are responsible for the possible undesirable interactions with biological systems and the environment which might generate toxicity. Therefore, there is an urgent requirement to establish the principles, procure the test procedures to ensure safe manufacture and commercial use of nanomaterials [ ] to stop the uncontrolled release of nanoparticles to the environment through waste disposal, and to incorporate the nanowaste and nanotoxicology in the waste management.
Thus, the bioaccumulation and toxicity of the nanoparticles may become important environmental issues. Although the amount of the nanoparticles in commercial products are lower than those present in soluble form but the toxicity resulting from their intrinsic nature e.