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Content archived on 2024-06-18

Development of a microfluidic platform to produce nanomaterials and assessment on new nanotechnology applications

Final Report Summary - PLATFORM2NANO (Development of a microfluidic platform to produce nanomaterials and assessment on new nanotechnology applications)

The long-term goal of Platform2nano is to develop a microfluidic platform that enables the continuous synthesis of nanomaterials under well-defined and pre-determined properties in higher yields than conventional reactors, as well as facing the restrictions of small-scale batch reactors.

The reasons behind this project are the following:

- Batch-to-batch variations and polydispersity in the resulting nanoparticles from the same batch reactor.

- Synthesis of monodisperse nanomaterials requires an excellent control on mixing and synthesis variables such as synthesis time and temperature.

- Many labour-intensive post-synthesis purification steps (i.e. dialysis, sedimentation, centrifugation, size-exclusion chromatography, etc.) are needed when using common chemical methods for the synthesis of nanoparticles because the non-homogenous production.

- Microfluidics design aims to maximize the reaction performance, which typically means achieving the highest efficiency towards the desired output product.

- The small reaction volumes of microfluidic reactors, combined with the high heat and mass transfer rates enable reactions to be performed under more aggressive conditions with higher yields than can typically be achieved with conventional batch reactors.

- Nanomedicine, energy, catalysis and nanocomposite applications of nanoparticles are highly demanded nowadays. Therefore, large-scale quantities of those materials prepared following low-cost continuous synthesis methods are needed.

- Microfluidic reactors enable to run chemical reactions at extreme conditions, while safer confining potentially toxic, high reactive starting materials, which could become important for the synthesis of novel nanostructured materials.

This project has established different continuous synthetic approaches based on the microfluidics and wet-chemistry to produce nanomaterials on demand with tunable properties. A wide variety of nanomaterials has been produced, comprising different types of magnetic nanoparticles, gold nanostructures, sub-nanometer noble metal particles, polymeric nanoparticles and hybrid nanostructures. The nanomaterials produced have at least the same quality as the nanomaterials obtained with conventional batch reactors, but the synthesis yield and shape selectivity were increased. These facts enable to increase the productivity and consider a feasible translation from lab to mass scale production. The produced nanomaterials were tested in some promising fields such as catalysis, energy, nanomedicine or nanocomposites, obtaining remarkable results.

The most remarkable achievements of Platform2nano can be summarized as follows:

- A variety of microreactors has been selected to be use in the synthesis of nanomaterials dispersed in aqueous and organic phases. Polymer and glass microreactors were selected to carry out synthesis of nanomaterials at low temperature. This type of reactors are very versatile because it is relatively easy to modify the residence time and provide good optical access. On the other hand, a stainless-steel plate microreactors have been designed to withstand high temperature and pressure conditions and then be used in the synthesis of nanomaterials whose chemical precursors require high temperature to decompose.

- Several types of nanomaterials have been successfully synthesized using microfluidics. One of the most important targets in this project was discovering how to produce high-value nanomaterials under an excellent control of shape and size. It can be highlighted that the scope of nanomaterials proposed in this project was never produced using the microfluidic technology. A complex nanostructure made of gold, a hollow gold nanoparticle, was produced in a continuous approach using three microfluidic stages in a time scale of 6 minutes: 1) Synthesis of Co nanoparticles as template 2) Replacing the Co by Au and generate a hollow structure 3) Surface functionalization to improve the biocompatibility. In addition, a new stage was implemented to sterilize the nanoparticles with UV light. To go further, the microfluidic reactor was scaled-up to increase 10 fold the production rate. Then, it has been designed a platform to produce on demand hollow gold nanoparticles which were functionalised with PEG ligands and sterilized. According to it, the as made nanoparticles could be directly used in any biomedical applications. These nanoparticles have very interesting optical properties because their surface plasmon absorption occurs at the “water window”. Then, it enables that these nanoparticles could be applied in any photothermal therapy. The production rate achieved using the microreactor was not able to be achieved by a conventional batch-type reactor. Furthermore the synthesis reproducibility achieved in the microreactor was considerably better than with batch reactor-type.

- This project has reported for the first time the synthesis of metallic-organic-frameworks (MOFs) nanoparticles, describing an excellent control on size just by tuning the synthesis time. A segmented flow was selected as the proper flow pattern because the fluid segmentation into slugs of several nanolitres enables an excellent control on MOFs nanoparticle growth in ultrafast residence times.

- Gas segmented flow-based microreactors were used for the continuous production of faceted nanocrystals. Flow segmentation was proposed as a versatile tool to manipulate the reduction kinetics and control the growth of faceted nanostructures; tuning the size and shape. Switching the gas from oxygen to carbon monoxide or hydrogen permits the adjustment in nanostructure growth from 1D (nanorods) to 2D (nanosheets) or 3D (prisms). CO is a key factor in the formation of metal nanostructures due to: 1) The gas segmentation improves the mixing and enables an excellent control at the nucleation and growth stages, 2) It is a stabilizing agent that could preferentially be adsorbed on certain facets to promote the anisotropic growth of nanostructures, 3) It is a reducing agent

- Polymeric nanoparticles were also produced to encapsulated biomolecules. Assessment of different types of microreactors was accomplished in order to get polymeric nanoparticles with a particle size distribution as narrow as possible and with a high encapsulation efficiency of several types of drugs. Computational fluid dynamic was considered to elucidate the best conditions to promote a homogenous formation of emulsions. Single and double emulsions were produced in continuous flow with a productivity as high as 10 g/h.

- A wide variety of the produced nanomaterials in Platform2nano was applied in catalysis, biomedicine and energy process, obtaining remarkable results.

Finally, Platform2nano has fostered the use of microfluidics to design and produce nanomaterials that were previously reported, facing productivity scale-up and reproducibility. The impact of Platform2nano in the scientific community was of merit, establishing a high number of collaborations, participating in international conferences and publishing in high impact journals.