Industrial Scale Production of Nanoparticles

Interview conducted by Will SoutterDec 10 2014

In this interview, James Murray from MetNano talks about their unique, patented process for producing high quality silver colloids and nanoparticles, scalable to industrial volumes.

Can you give a brief introduction to your large-scale nanoparticle products?

MetNano Limited (MNL) is a new company set up to exploit unique patented processes for making metallic nanoparticles and colloids. Our current off-the-shelf products are stock solutions of highly stable aqueous silver colloids, manufactured via a chemical process. We use PI reactors, rather than batch reactors, so the process is scalable from litre to tonnage scale with high quality, highly uniform products.

The scalability we offer results in significant cost reductions for our customers, as well as surety of supply and control over the material parameters. The high stability of the colloid also means that the product can be stored for very long periods of time – up to 3-5 years without agglomeration.

This means that we can ship the products over very long distances, and it also means that customers can bulk order colloid and store it for as long as they need to, with no requirement to implement “just-in-time” (JIT).

Unlike many colloids on the market, MNL silver colloids are metallic as opposed to ionic, and do not contain any additional stabilisation molecules – our aqueous silver colloids quite simply only contain silver and water. The lack of ethylene glycol and other stabilisers is a real bonus for product formulators, especially in the medical market, where additional ingredients could cause issues.

This property could also boost performance in antimicrobial applications, as it has been found that metallic silver outperforms ionic silver in this area. Metallic nanosilver is an optimal solution requiring a lower loading level (10-30mg/kg fabric), and providing better antimicrobial activity and a lower release rate when subjected to repeat washing than other forms.

As well as the stock solutions, we also offer consultancy and bespoke manufacturing for specific needs, including a range of different metals, concentrations and particle sizes. The scalable nature of our process makes us very flexible in this regard, so we can work with almost any specialist requirements that customers might have for their colloid or nanoparticle materials.

Silver colloids produced using MetNano's scalable process

How was the large-scale process developed?

The process was first developed at the University of Lincoln, with the aim of making colloids for use in SERS. SERS is an analytical technique whereby a chemical binds to a metal, changing the spectrophotometric properties of the chemical in the process.

Gold colloid is the most common material used for SERS – it is known that silver performs better, but until the development of our process it has been more unstable and difficult to make.

So once the process had been developed to make from millilitres to tonnage scale of very high quality silver colloid for use in SERS, BHR Group contributed their process intensification expertise to the table, to scale up the process from litres to tonnage scale. The project resulted in the formation of MetNano Ltd., the first company to industrialize the chemical method of silver colloid synthesis.

What are the main applications you are targeting with the silver nanoparticle products?

The main applications are analytical techniques like SERS, which the product was originally developed for, and also immunoassays in immunodiagnostics – another technique where colloidal gold is typically used, conjugated to an antibody. MNL’s silver colloid is a direct replacement in these techniques, with improved performance and reduced cost.

As I mentioned, silver is also antimicrobial, and a number of antibacterial products have appeared on the market in the last few years. Our material is ideal for coatings, paints, or impregnations, particularly as use of these products grows and larger volumes are required.

Another key application for silver is in high end electronic circuits, and in metallization for photovoltaic cells. Conductive inks and pastes based on silver nanoparticles are used in these industries now, generally manufactured by grinding or ablation.  We are exploring routes to provide the high particle concentrations required for these applications.

Another area which is enabled by our capacity to finely control the parameters of the process is in security. We can make a material for incorporation into anti-counterfeiting inks or added into paper which have a very unique particle size distribution, with a very narrow and specific range. This is incredibly difficult to reproduce, but quite easy to check using a microscope or a relatively simple instrument.

It is also possible to harness the ideas behind SERS in this area – a conjugating dye can be used which is very hard to detect unless you know exactly what you are looking for, but very clearly detectable if you do. This is ideal for counterfeit detection, and this is something we have been consulting on, although we can’t share any further details of the project.

Is the process limited to producing silver nanoparticles, or can you work with other materials?

The process is not limited to silver, but that is our first product. Other materials we are testing include, palladium, copper, aluminium and zinc. We can currently work with any of these on request as part of a bespoke project, but we could also look at producing these as off-the-shelf products.

The next products will most likely be reformulations of our silver nanoparticles for solutions, pastes and powders rather than colloids. The silver pastes would be analogous to those used in electronics. Beyond that, we will be looking at zinc, copper, and some of the more delicate nano-metals that are hard to produce.

Silver is our first product as it is one of the hardest materials to produce stable nanoparticles of, so it’s the material we can offer the greatest cost savings for. The next metals will need to be the ones where we can offer similar cost savings and performance benefits at scale.

Moving on from simple nano-metals, we will also be looking at amalgams – not just mixed powders, but particles where each particle is composed of, say, 50% gold and 50% silver. These can have really unique electrical, anti-microbial and optical properties.

Electron microscope image of silver nanoparticles from MetNano

What are the applications for these other nano-metals, like nickel and copper?

Most of these metals would basically be used as cheaper alternatives to silver, in a similar set of applications. For electronics in particular, where silver is the “holy grail” of performance, metals like copper or iron could be used as acceptable, lower performance alternatives for lower-value markets.

There a number of metals, like platinum, palladium, nickel, and rhenium, which are used as catalysts in the chemical industry – bulk production of nanocatalysts is another growing area that we are looking to move into. We have the potential to produce these metals upon demand, and we would be looking to scale up in the future to manufacture them in large quantities.

How have your customers responded to the initiative so far?

The feedback from our customers has been very positive - they see the cost reduction and assured uniformity as transformative for the move from small scale technical development to large scale product manufacture.

Our capabilities will allow them to consider product placements which would previously not have been considered – we have removed many of the limits of price and availability which would otherwise prevent scaled-up manufacturing.

How will this impact the use of nanomaterials in products and industrial applications?

We anticipate that the MNL technology will be highly disruptive in the field of nano-metals and metal colloids in that for the first time industry and academia can access scalable amounts of nano-products at a significant price reduction to what is already on the market, with the certainty that the product has been made to high QA and QC standards.

How will MNL look to expand its operations in the future?

One big possibility that we are looking at would be to put the colloid process on our clients’ premises, operating under license. This would be a big shift for the market, and it’s a completely unique proposition.

For our larger clients working on bulk materials like antimicrobial paint, there would be huge efficiency benefits – rather than us making tonnage quantities of colloid and shipping it to them, we would provide a package allowing direct injection into their product, made on demand and under their control.

This could be a crucial proposition for really high volume manufacturers in batteries or photovoltaics, as they would have full control over the product specification, and would not need to rely on external suppliers.

Fundamentally, we are looking to be able to tailor the product to the client’s needs. Whether a client needs many different millilitre scale samples, or 50 gallon drums, we want to be able to provide that.

At the moment, the market does not provide significant tonnage quantities of nanoparticles, due to the batch manufacturing processes. With our process, we will be able to open that up offer the whole range of scales, from the smallest to the largest, all whilst maintaining very high product quality.