How do I synthesize nanomaterials

How are nanomaterials made?

There are basically two options available for the synthesis of nanomaterials. On the one hand the top-down technique and on the other hand the bottom-up technique.

Top-down technique

By grinding, etching or other mechanical processing, larger pieces of a substance are processed into nanoscale structures. This approach is particularly widespread in physics, physical technology, electronics (small transistors and conductor tracks on computer chips) and in medical and biological analysis processes (biochips).

Bottom-up technique

In this technique, the structure of nanoparticles is synthesized from atomic or molecular building blocks. The bottom-up technique is particularly used in chemistry and biology.

During the synthesis, either the so-called "self assembly" (the atoms or molecules arrange themselves independently in a certain structure) or the individual positions are given to the atoms or molecules in the so-called "positional assembly" from the outside. “Self assembly” can be observed, for example, with carbon atoms that arrange themselves to form carbon nanotubes (CNT). “Positional assembly”, on the other hand, is very complex, which is why it is not yet used industrially.

Sol-gel process

In the sol-gel process, a nanoscale substance is evenly distributed in another substance. By heating or by adding a catalyst, the particles grow to a critical size. With special chemical interventions, the growth can be stopped in certain phases. The resulting particles have a defined size, the surface of which can be further chemically changed. This can provide protection against clumping, for example, or certain solubility properties can be established. By subsequently removing part of the solvent, a gel is created in which all nanoparticles are connected to one another. These gels have different properties than the individual nanoparticles. For example, they can conduct electricity.

Gas phase synthesis

Gas, liquids or solids are introduced as starting materials into a gas flow and passed through a hot zone. For this purpose, liquids are vaporized or atomized into droplets and solids into particles.

Further atoms and molecules attach to the resulting primary particles, as a result of which the primary particles grow into precursor particles. Finally, the nanomaterials are formed from several precursor particles.

Advantages over the sol-gel process can lie in the cleaner particle surface. In addition, there are almost no by-products. Reaction conditions such as pressure, temperature and residence time can be controlled very well in the hot zone. This allows the size and shape of the particles to be precisely defined. It is possible to measure the particle size during the synthesis and to sort out nanoparticles with the desired size.