Authors: Sandhya Sanand1, Kishor U Tribhuvan1, Sandeep Kumar 2, Anshika Tyagi1
1 ICAR - National Research Centre on Plant Biotechnology, New Delhi – 110012.
2 ICMR - National Institute of Virology, Pune – 411021.
Summary
Nanotechnology is an emerging area having plethora of applications from house hold to industry. Nanostructured materials (NSMs) have unique length scale in the order of 1-10 nm. These NSMs need to be characterized extensively, before they can be put to use. This article briefly explains regarding classification and various methods of characterization for nanomaterials.
Definition:
Nanotechnology has been defined by the US National Nanotechnology Initiative (NNI) as understanding and control of matter at dimensions of roughly 1-100 nm, where unique phenomena enable novel applications (NNI, 2007). As per European commission “Nanomaterial” means a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1-100 nm.
NSMs include nanoparticles, nanofilms, and nanocomposites. Most of them are synthesized or produced using a ‘bottoms up’ approach in order to develop specific structural and functional features. The result is normally a highly ordered, monodispersed particle sample with a large surface area.
Classification of nanostructured materials (NSMs)
The idea of classification of NSMs was first given by Gleiter in 1995 and further described by Skorokhod in 2000. Consequently, Pokropivny and Skorokhod stated an improved classification outline for NSMs which comprises all the 0D, 1D, 2D and 3D NSMs.
Based on their structure, NSMs can be classified as follows:
1. Zero dimension (0D): no dimension nanomaterials which are spheres or clusters think out as point-like particles and it includes oxides, metal, semiconductor, fullerene uniform particles arrays (quantum dots), heterogeneous particles arrays, core–shell quantum dots, onions, hollow spheres and Nano lenses etc.
2. One dimension (1D): at least one dimension in range of 100 nm and it includes nanofibers, nanowires, nanorods and nanotubes etc.
3. Two dimensions (2D): have two dimensions outside of the nanometric size range. It includes monolayer, multilayer, self-assembled, and plates etc.
4. Three dimensions (3D): nanomaterials are nanophase materials of equiaxed nanometer-sized grains and it includes nanocomposite nanohybrids, micro and mesoporous hybrid, nanometer-sized grains.
Fig1. Classification of nanomaterials based on their structure
Bulk nanomaterials are larger objects made from structures having well-identified domains with an average size less than 100 nm, for instance the grain size in ceramics. Every class of the materials has unique chemical and physical properties as compared to their bulk materials and this characteristic is due to small size and high surface area.
Characterization
Characterization is a process in which physiochemical property of materials are queried and measured. It is the first and foremost process in the area of nanotechnology followed by synthesis, which is required for better understanding of materials and of course to ensure the kind of nanomaterial we need. It has been reported earlier that behavior of nanomaterials is influenced by the surrounding environment e.g., the medium in which they dispersed which makes certain in the physiochemical properties or in reactivity of materials. So, it’s pertinent to study their composition, solubility and other factors like temperature, pH, salt concentration etc. These aspects modulate their overall reactivity and hence should be assessed after synthesis and prior to use. Recently, several characterization techniques have been introduced. From basic optical microscopy to arrival of the electron microscope and secondary ion mass spectrometry in the 20th century, these new techniques have transformed the characterization area. The imaging and analysis of molecular structures and chemical compositions on much smaller scales than was earlier possible, has led to increased knowledge and understanding of different classes of nanomaterials. Various techniques that are being used for the characterization of nanomaterials include dynamic light scattering (DLS), X Ray Diffraction (XRD), field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscope (XPS), Small angle X-ray scattering (SAXS), and infrared transform absorption spectrometer (FTIR).
Characterization may be broadly classified into two methods:
a. Physical characterization - means to characterize the physical property of nanomaterial viz, particle size, surface area, there state etc.
b. Chemical characterization - means to characterize the chemical information viz, chemical composition, molecular structure, surface chemistry, reactivity etc.
| Physical property | Methods |
| Size | DLS, TEM, NTA |
| Surface morphology | SEM, AFM, STM |
| State (aggregation / agglomeration) | EM, SLS, DLS, CPS, SMPS, Laser diffraction |
| Crystallinity | XRD |
| Surface area and porosity | BET isotherm |
| Surface charge | Zeta Potential, Laser doppler anemometry |
| Chemical property | Methods |
| Molecular structure | FTIR, EDS, SAXS |
| Chemical composition | FTIR, NMR, EDS, ICP-MS, XRF |
| Degree of purity | EDX |
| Elemental analysis | ICP-MS, ICP-OES, AAS |
| Organic compound analysis | LC-MS |
| Surface chemistry | XPS |
NSMs are being developed for a wide range of products and applications including drug delivery, diagnostics, regulated release systems, and medical instruments. The characterization of these materials is challenging as it require next generation analytical techniques operated by skilled analysts.
The difficulty that these nanostructured materials present during characterization significantly impacts the applied aspects of nanotechnology. Inadequate and insufficient characterization can have serious adverse effects on understanding and applicability of these nanomaterials especially in reference to public health and environment. These materials need to be characterized extensively with due consideration to their physical, chemical properties and their interactions with biomolecules before being put to use.
Abbreviations
AAS- Atomic absorption spectroscopy, AFM- Atomic force microscopy, BET- Brunauer, Emmett and Teller, CPS- Centrifugal Particle Sedimentation, EDS- Energy dispersive X-ray spectroscopy, FTIR- Fourier transformed infrared spectroscopy, ICP- MS- Inductively coupled plasma mass spectrometry, ICP- OES- Inductively coupled plasma optical spectroscopy, LC-MS- liquid chromatography mass spectrometry, NMR- Nuclear magnetic resonance spectroscopy, NTA- Neutron Tracking analysis, SAX- Small Angle X-ray scattering, SLS- Static light scattering, SMPS- Scanning Mobility Particle Size, STM- Scanning electron microscopy, TEM- Transmission electron microscopy, XPS-X -ray photoelectron spectroscopy, XRD- X- Ray diffraction, XRF- X-Ray Fluorescence Analysis.
References:
Gleiter H. Nanostructured materials: basic concepts and microstructure. Acta Materialia2000; 48:1.
Skorokhod V, Ragulya A, Uvarova I. Physico-chemical kinetics in nanostructured systems. Kyiv: Academperiodica; 2001. p. 180.
Pokropivny VV, Skorokhod VV. Classification of nanostructure by dimensionality and concept of surface engeenring in nanomaterial science. Mater Sci Eng C 2007; 27:990.
ISO/TR13014:2012 “Nanotechnologies-Guidance on physico-chemical characterization of engineered nanoscale materials for toxicologic assessment”References (if any)
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