Nanoparticles and other nanomaterials are essential components of cutting-edge science and technology, including photochemistry, energy conversion, and medicine. New research suggests that automating nanomaterial synthesis can reduce the environmental footprint of these advanced materials while at the same time improving quality and scalability.
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New Research in Automated Nanomaterial Synthesis
The groundbreaking paper, “Towards automation of the polyol process for the synthesis of silver nanoparticles” makes the argument for automated synthesis to enable the manufacturing of colloids with properties that are precisely tunable and – crucially for industrial nanomaterial synthesis – reproducible.
The study, which was published in the journal Scientific Reports in 2022, could have a significant impact in various fields of science, as the metal nanoparticles its authors synthesized are used at the forefront in photochemistry, energy conversion, and medicine.
The interdisciplinary team behind the paper – materials researchers, nanotechnology specialists, and chemical engineers from Germany’s Federal Institute for Materials Research and Testing (BAM), Max Planck Institute of Colloids and Interfaces, and Humboldt-Universität zu Berlin’s Department of Chemistry – focused their research on silver nanoparticle synthesis.
Silver was a suitable test candidate for the automated synthesis method because, while it is one of the more commonly used nanoparticles due to its antibacterial properties and sensing and catalysis applications, it is difficult to produce in well-defined products. The obstacles to this are silver’s high polydispersity: it is difficult to precisely control or tune silver nanoparticles’ sizes.
Responding to this challenge, the German researchers developed an automatic approach for on-demand silver nanoparticle synthesis. The method enables fabricators to synthesize silver nanoparticles between 3 and 5 nm, employing a modified polyol process.
To test their results, the team employed small-angle X-ray scattering, dynamic light scattering, and a number of other investigations. All results showed that the new automated synthesis method is suitable for yielding reproducible and tunable properties in synthetic colloids.
Synthetic nanomaterials are made with shapes or structural components that measure between 0.1 and 100 nm – or 0.1 to 100 billionths of a meter. The metal nanoparticles that the present research focuses on find numerous applications in research, medicine, and technology contexts.
Synthesis methods for nanoparticles have to provide a high degree of control over the nanoparticles’ size, shape, and polydispersity while limiting the effects of aggregation or agglomeration (ensuring an even distribution). They also need to take into account the rheological properties of nanoparticle dispersions and the long-term stability of the solution.
Challenges with synthesizing nanoparticles include reproducibility and colloidal stability. These challenges mean there are limited nanoparticle-based references available, despite calls for such materials from environmental, health, and safety concerns for a number of years.
For example, gold nanoparticles are ubiquitous in nanotechnology due to their straightforward synthesis requirements, distinct size regulation, and ability to realize predictable nanoparticle sizes and dispersion.
But, despite a high demand due to silver’s well-known antibacterial properties and use in catalysis, photochemistry, sensing, and optoelectronics, silver nanoparticles remain difficult to synthesize with available methods.
One available method is based on a polyol process. Here, silver nanoparticles are formed by reducing silver ions in the presence of polyacrylic acid in hot ethylene glycol. The ethylene glycol acts as both a reducing agent and a solvent.
This method is considered important because it stabilizes nanoparticles in a water-based solution by adjusting the solution’s pH balance to 10, creating a negatively charged shell that means particles can remain unchanged in the suspension for over six months.
As a result, the nanoparticles produced make good candidates for reference materials. Reference materials are used in nanomaterial synthesis to quantify the size, distribution, and concentration of nanoparticles in doped materials.
Reference materials need to be made in bulk and able to remain stable for a long period of time in storage to be useful. The adapted polyol process described above can achieve these requirements, although it is not best suited for the task.
Speeding Up Nanomaterial Synthesis with Automation
To develop reference materials like silver nanoparticles faster, researchers focused on developing an automated platform for rapid on-demand synthesis.
An automated platform could avoid the need for bulk quantities and long-term stability by offering required reference materials to researchers at minimal cost and without excessive lead-in times.
It would also enable targeted testing of nanomaterials’ physicochemical properties and a shorter development cycle before arriving at the desired properties.
To achieve this, the German scientists developed an automated silver nanoparticle synthesis method with the polyol process producing a colloidally stable silver.
They deployed the so-called “Chemputer” for the first time in the field of inorganic chemistry. The Chemputer is an automated platform that was developed by the Cronin group to execute multi-step, solution-based organic synthesis and purification tasks.
The Chemputer works in a batch mode with common laboratory items like heaters and glassware connected to a backbone made out of HPLC selection valves and syringe pumps. Liquid solutions are transferred across the backbone and manipulated along its various modules in different ways.
Every operation is controlled with a software script, which ensures a high rate of reproducibility. The accompanying software also makes it easy to adjust the synthesis conditions as required and documents all changes in the reaction log file.
References and Further Reading
Calderón-Jiménez, B. et al. (2017). Silver nanoparticles: Technological advances, societal impacts, and metrological challenges. Frontiers in Chemistry. doi.org/10.3389/fchem.2017.00006.
Dong, H. et al. (2015). Polyol synthesis of nanoparticles: Status and options regarding metals, oxides, chalcogenides, and non-metal elements. Green Chemistry. doi.org/10.1039/C5GC00943J.
Kaabipour, S., and S. Hemmati (2021). A review on the green and sustainable synthesis of silver nanoparticles and one-dimensional silver nanostructures. Beilstein Journal of Nanotechnology. doi.org/10.3762/bjnano.12.9.
Wolf, J.B., et al. (2022). Towards automation of the polyol process for the synthesis of silver nanoparticles. Scientific Reports. doi.org/10.1038/s41598-022-09774-w.
You, H., and J. Fang (2016). Particle-mediated nucleation and growth of solution-synthesized metal nanocrystals: A new story beyond the LaMer curve. Nano Today. doi.org/10.1016/j.nantod.2016.04.003.