Synthesis of Nanomaterials: Bottom-up and Top-down Approach

Table of Contents

The synthesis of nanomaterials is the foremost step in nanotechnology research and development. Nanomaterials synthesis generally refers to the preparation of nanometer scale dimension materials.

The method for synthesizing nanomaterials can vary depending on the type of nanomaterial, from a straightforward “mix and cook” method to a complex nanofabrication method incorporating clean room tools. Shape, purity, yield, size distribution (whether nanodispersed or a mixture of different sizes), surface modifications, and requirements for downstream analysis are just a few of the variables that influence the method chosen for the synthesis of nanomaterials. Industrial-scale manufacture and small-scale laboratory synthesis may require various approaches.

Some of the major challenges in the synthesis of nanomaterials include the synthesis of nanodispersed particles, size and shape control, reproducibility, large-scale synthesis, and synthesis of complex structures.

Synthesis of Nanomaterials

Depending on the approach of assembling atoms, ions, or molecules, splitting up bulk materials, generation of the raw materials, and protocol of nanoparticle synthesis, there are various kinds of nanoparticle synthesis approaches Broadly, nanoparticle synthesis can be classified into two categories:

  • Bottom up approach
  • Top down approach
synthesis of nanomaterials

Bottom up approach

In this approach, nanostructures are assembled from the smaller starting materials such as atoms, molecules, or clusters. Short-range forces like van der Waals forces, electrostatic forces, and different interatomic or intermolecular forces cause these atoms or molecules to coalesce into nanometer-sized particles. The bottom up technique is mostly used in the chemical synthesis of nanoparticles. The key advantages of bottom up approach are the generation of a wide range of nanoparticles with very small to large scale sizes, and a more homogenous particle size distribution. Generally, bottom-up methods are most attractive for both laboratory and industrial-scale nanomaterial synthesis due to the controllability in size and properties of materials via proper control of the reaction conditions.

Some of the bottom up approaches for the synthesis of nanomaterials are:

  • Sol-Gel method
  • Physical vapor deposition
  • Chemical vapor deposition
  • Molecular beam epitaxy
  • Spray conversion processing
  • Wet chemical synthesis
  • Self-assembly, and so on.

Top down approach

Size reduction techniques such as top-down or physical procedures are used to produce nanostructured material from big bulk material. The ability to synthesize huge quantities of materials is one benefit of the top down approach. However, this method makes it difficult to control shape and size. Instead of producing nanoparticles, this approach is typically useful in the synthesis of nanostructured bulk materials.

Some of the top down approaches for the synthesis of nanomaterials are:

  • Mechanical alloying
  • Equal channel angular pressing
  • High pressure torsion
  • Nanofabrication and nanolithography, and so on.

The bottom-up and top-down approach can be schematically represented as:

image 28
Figure source: K. Habiba et al., 2014

Top down vs Bottom up approach

The difference between top down and bottom up approach are discussed below:

Bottom upTop down
DefinitionFormation of nanostructured materials from the assembly of smaller starting materials such as atoms, molecules, or clusters.Formation of nanostructured materials from a large bulk material via size reduction methods.
Size
distribution
Relatively homogenous, have control over shape and size.Mostly heterogeneous, difficult to control shape and size
Scale of synthesisSmall scaleLarge scale
Methods of synthesisHomogenous and heterogeneous nucleation, chemical precipitations, vapor deposition, spray pyrolysis, and so on.Grinding, dissolution, milling, and so on

Nanomaterial synthesis video

References

  • Paramasivam G, Palem VV, Sundaram T, Sundaram V, Kishore SC, Bellucci S. Nanomaterials: Synthesis and Applications in Theranostics. Nanomaterials (Basel). 2021 Nov 28;11(12):3228. doi: 10.3390/nano11123228. PMID: 34947577; PMCID: PMC8705396.
  • Nadeem Baig, Irshad Kammakakam, and Wail Falathabe. Nanomaterials: a review of synthesis methods, properties, recent progress, and challenges. Materials Advances, 2021, 2, 1821-1871. doi: 10.1039/D0MA00807A 
  • Khan, F.A. (2020). Synthesis of Nanomaterials: Methods & Technology. In: Khan, F. (eds) Applications of Nanomaterials in Human Health. Springer, Singapore. https://doi.org/10.1007/978-981-15-4802-4_2
synthesis of nanomaterials

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