CERION NANOMATERIALS BLOG | JULY 16, 2021
Nanomaterial Synthesis Methods: Pros, Cons and Economics
Article by: Andrew Zane, Ph.D., Senior Scientist, Cerion Nanomaterials

The use of nanomaterials in commercial products has grown exponentially over the past decade. Manufacturers, including those in industry, life sciences and the defense market, are taking advantage of the countless benefits that nanomaterials can provide when incorporated into their products and production systems. The capability of companies to enhance and differentiate their products in a crowded marketplace has been driving a significant increase in the number of commercial products utilizing nanomaterials today, and that number is just getting bigger.

Different nanomaterials provide diverse benefits and specific attributes when integrated into products or applied to production systems. Everyday items, such as screens on cell phones and laptops, are being made more user-friendly by the application of nanomaterial-based coatings with high refractive indexes, which render the screens anti-reflective and less tiring on the eyes of the user. Another of many examples – and particularly significant during the current Coronavirus pandemic – is in healthcare and medical products. Today, the antimicrobial and anti-viral benefits achieved by incorporating nanomaterials as a coating on textiles and fibers are stimulating heightened market demand. Nanomaterials can be tailored to specific requirements and many diverse use cases, their common characteristic being that they are nanoscale and therefore possess unique properties when compared with bulk materials.

Despite their multiple diverse properties and many potential uses, companies often find it challenging to successfully incorporate nanomaterials into their products and systems for a number of reasons. Typically, companies find that building the in-house capability to design and manufacture nanomaterials can be too time-consuming and costly, in both equipment and knowledge acquisition. This ultimately raises concerns that nanomaterial production could take the focus away from their core product development. Alternatively, some companies have purchased off-the-shelf nanomaterials (catalogue-style) to integrate into their products – often unsuccessfully. Just as end-products are precisely engineered for performance and use, nanomaterials need to be precisely engineered into the right particle shapes and sizes to ensure optimal integration, and to achieve the desired improvements in product performance.

Enter Cerion. We use our technical expertise and over a decade of experience developing and applying different synthetic techniques (detailed below), to determine the best ways of producing ideal, customized nanoparticles for optimal performance and seamless integration into our clients’ products and processes. We do this by identifying the optimal synthesis method for you and your business – balancing practicality, cost and customizability to give you the best possible results.

Nanomaterial Synthesis Methods

For nanomaterials, there are two main classes of synthesis methods, called ‘top-down’ and ‘bottom-up.’ Top-down methods, such as milling, take bulk materials and break them down in size. The alternative, bottom-up methods use chemical processes to build nanomaterials from scratch. Many synthesis methods fall into the bottom-up category and involve the nucleation of seed particles from atoms in solution, which can then be grown in a controlled manner to the desired size, and with narrow size distributions. Some of the more common nanomaterial synthesis methods are outlined in detail below (all being bottom-up processes except high energy milling).

Plasma and Flame Pyrolysis
Pyrolysis is often the first method that many researchers try when looking for a nanomaterial that fits their system. Companies that attempt this first for themselves – and find it doesn’t work as planned – then come to Cerion for help and advice.

Unlike many synthesis methods where the reaction takes place in a liquid, plasma and flame pyrolysis are methods that initiate a reaction in the gas phase. By volume of nanomaterial produced, flame pyrolysis is typically one of the least expensive synthesis methods, while plasma pyrolysis is significantly more expensive.

Of the different fabrication methods, plasma and flame pyrolysis both have the least amount of flexibility when it comes to the design, design precision and customization of the nanoparticle. As a result, this method is rarely employed except for high-volume manufacturing where technical specifications are of limited importance.

Using this method, it is difficult to control the size of the nanoparticles created, and many particles also show a strong tendency to aggregate. Due to aggregation of the nanoparticles within the bulk powder, surface functionalization can be challenging to impossible. This restricts the ability to create quality nanoparticle dispersions that have a high degree of monodispersity. Surface functionalization, when required, must be done with post-processing. The ability to control other nanoparticle design aspects, such as composition and morphology, or to create complex structures such as alloys and doped structure are very limited.
Despite the overall low cost of material production, the high start-up costs – mainly from the purchase of expensive essential equipment – make plasma and flame pyrolysis an unworkable solution for most product applications. Nevertheless, if you can tolerate a high degree of variation for your nanoparticle specification and have very low-cost requirement, there are instruments available on the market that make this method a viable option for some.


Precipitation

If you need a high degree of precise control over nanoparticle size and non-size related attributes, one go-to option is precipitation. Using this wet-chemical method, precursor solutions quickly develop into small nuclei of the desired nanomaterial. These nuclei can then be grown to the chosen size via a longer growth phase. Precipitation methods allow for good control over the size and shape of nanoparticles, with high levels of monodispersity and a low degree of aggregation. This degree of control also allows for a seemingly infinite variety of techniques to customize the material such as creating homogeneous alloys, core-shell systems, and various other morphologies and compositions.

Precipitation methods typically use relatively low temperatures and industrially available solvents, enabling structural modifications to the nanoparticles to be made with much greater ease than other methods. For example, surface functionalization through the addition of organic ligands can make the nanoparticles more compatible with a wide variety of solvent systems, with the ligands being carefully selected to fit the intended application. These ‘capping agents’ can stabilize the nanoparticles and inhibit over-growth of the particle’s size, while also preventing aggregation of the particles. Some common examples of surface functionalization include the cross-linking of polymers, adding receptors onto nanoparticles for biological targeting, as well as improving the stability of nanoparticles in solvent systems with which they would otherwise be incompatible.

One aspect of precipitation methods to consider is that any unreacted precursors and synthesized by-products must be removed from the reaction by washing and filtering. This is often a delicate process, as the nanoparticles may aggregate during the process. If not done correctly, additional costs arise from increases in equipment and personnel time, and potentially the need for additional raw materials. Cerion’s years of experience and expertise can benefit you here, as our knowledge of how to best approach these challenges helps to keep the costs down and the processes streamlined.

Precipitation is a worthwhile method when a high degree of customization and design precision is required. This is particularly the case when specific compositions, particle sizes, size distributions, monodispersity and/or surface functionalization are required. The costs associated with precipitation methods are driven by the particle specifications and the formula that is designed to achieve them. A diverse number of metal, metal oxide and even ceramic nanomaterials can be manufactured cost-effectively using this approach.


Solvothermal/Hydrothermal Synthesis

If standard precipitation is determined not to be the ideal technical or cost approach, then the next go-to method tends to be thermal synthesis – either hydrothermal or solvothermal.

Thermal methods are similar to precipitation, with the main difference being that the reaction takes place in a sealed reactor under high temperatures and pressure. Hydrothermal reactions are performed in water and solvothermal reactions take place in any solvent other than water. The simple change to a higher reaction temperature and pressure enables nanoparticle sizes, shapes and crystal phases to be synthesized that may not be possible with a standard precipitation method. Like precipitation, this method requires washing and filtering to remove unreacted by-products.

One of the main drawbacks of thermal synthesis, particularly when scaling up, is that complex and expensive synthesis reactors are needed, leading to higher costs. These costs can be offset if an existing reactor can be adapted – provided it won’t contaminate the reaction.

Hydrothermal and solvothermal methods are typically used when the desired properties cannot be achieved using standard precipitation methods. While it is a more complex method than precipitation, at times it can offer benefits for customization, however, this comes at an increased cost due to the requirement of specialized equipment.

Thermal Reduction
Thermal reduction is used at Cerion for synthesis and processing, resulting in much sought-after product features especially for applications requiring high strength, wear resistance and stability in extreme conditions. Our proprietary synthesis method enables significant control over composition, particle size and distribution, leading to efficient and economical production of custom designed, high-performance nanomaterials.

Metals, oxides, ceramics and carbide nanomaterials are synthesized in furnaces at high temperature in atmospheres of oxygen and other gases. Products can be processed into a variety different forms – including powders, slurries and suspensions.

While many of Cerion’s techniques for this synthesis remain proprietary, it represents a significant paradigm shift in the way certain nanomaterials are manufactured, making previously difficult to achieve design specifications within reach. Equally as important, it has opened up new opportunities to access certain previously high-cost nanomaterials at a significantly lower cost.

High-energy Milling

Standard milling methods have been widely utilized on an industrial level for many decades and remain popular for making micron and sub-micron sized ceramic, metal and metal oxide materials. However, it is very difficult to break bulk materials down to the nanoscale using standard milling methods. Often, in the cases where it is possible, the processing costs are too high for it to be commercially feasible. There is also very limited control over certain aspects of the nanomaterial such as size. Size distributions can be hundreds of nanometers or more from the target particle size. Additionally, the ability to modify a particle’s composition is equally limited.

Cerion has been pioneering new high-energy milling methods which allow nanoparticles and nanostructured grains to be produced at manufacturing volumes never previously thought possible. We achieve this by inputting high kinetic energy into a bulk material, under a variety of different operating conditions including but not limited to power, time, temperature, inert conditions and gaseous atmospheres.

High-energy milling is not a replacement for other synthesis methods when very tight design precision is a requirement. It can be an expensive method during the start-up phase but is a good fit with many types of metals and oxides. Unlike standard milling, high-energy milling methods have also been successful in producing enhanced ceramics such as boron carbide, tungsten carbide, and alumina nanomaterials.

The Cerion Approach

For more than a decade, Cerion has been helping companies obtain the exact nanomaterial to match the performance, the price and the integration method appropriate to their products and systems.

We work closely with our clients to strike a balance between the level of customization required, the desired budget, and the cost of each synthesis method – enabling nanomaterials to be both economical and accessible to a larger cross-section of industry.

When a customer first approaches Cerion to secure a material with a specific particle composition that is otherwise not commercially available, our in-house team works to identify the synthesis approach that will meet both technical and cost requirements. The ability to balance these different aspects relies on our creativity and flexibility to tailor the product to your exact needs. Our capability to do this, and our capacity to support customers from their product development phase through to scale up and manufacturing, comes from over 15 years of developing and delivering nanomaterials for our customers. Our experience in this area provides surety that Cerion will provide the right recommendation on the best synthesis method for you, which will yield the best technical outcome, at the best cost, versus any other provider in the market.

Beyond Design:

Cerion uses a phased development approach that effectively transitions custom nanomaterials from applied research through scale-up and manufacturing.
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