Periodic Reporting for period 4 - NOC2D (Nucleation of Organic Crystals onto 2D materials)
Periodo di rendicontazione: 2020-03-01 al 2022-01-31
The formation of crystalline solids from liquid-phase precursor is a central idea in materials chemistry. Organic crystal structures can be found in a large number of products, including food, explosives, pigments and pharmaceuticals. Control of molecular assembly is therefore a fundamental problem for both research and industry and it involves substantial scientific and economic challenges. For example, polymorphism is crucial for drug manufacturers because the crystal structure, morphology and size, can all affect the stability, efficacy and production cost of the drug. Therefore, it is essential to achieve a deeper understanding on the molecular processes happening at the early stage of crystallization. Although important results have been obtained, our understanding on how a crystal of organic molecules nucleates on a surface is still poor. To go beyond state-of-the art we need techniques able to probe rare nucleation events with nanoscale resolution and very high sensitivity, providing direct insights on the structure of the nuclei and their interaction with the environment.
The aim of NOC2D is to use 2D crystals to open new horizons in the understanding of nucleation of organic crystals by using a multi-disciplinary approach, which combines chemical engineering, material chemistry, graphene physics and sensors technology. The conclusions from each WP of the project are the following:
i) Graphene, a single layer of graphite, has been successfully used as advanced surface template or as impurity during crystallization. Polymorph selectivity is demonstrated by tailoring carefully the surface chemistry of graphene. Our results show that ad hoc designed graphene additives could be used in crystal engineering to achieve polymorphic selectivity and screening, which are of fundamental importance in many industrial processes.
ii) Sensors technologies, commonly used for biosensing, have been successfully used to monitor the crystallization process, from pre-nucleation to final crystal formation, as well as to quantify molecular mass transport during nucleation. This technology is very attractive to study crystallization because it can be easily extended to more complex systems, i.e. organic molecules, inorganic molecules and macromolecules that are soluble in water (although experimental conditions may need to be optimized for each case).
iii) Raman spectroscopy was successfully used to study graphene nanoribbons with well controlled structures, produced by bottom-up approaches. We demonstrated that although the Raman spectrum shows more complex features, as compared to the one of graphene or carbon nanotubes, this technique still provides quantitative information on the quality of the edges and their functionalization type. Raman spectroscopy has been also successfully used to study crystallization of glycine in situ, demonstrating that crystals do grow first by forming some sort of beta-disordered assembly, which quickly turns into (the stable) alpha-glycine.
The aim of NOC2D is to use 2D crystals to open new horizons in the understanding of nucleation of organic crystals by using a multi-disciplinary approach, which combines chemical engineering, material chemistry, graphene physics and sensors technology. The conclusions from each WP of the project are the following:
i) Graphene, a single layer of graphite, has been successfully used as advanced surface template or as impurity during crystallization. Polymorph selectivity is demonstrated by tailoring carefully the surface chemistry of graphene. Our results show that ad hoc designed graphene additives could be used in crystal engineering to achieve polymorphic selectivity and screening, which are of fundamental importance in many industrial processes.
ii) Sensors technologies, commonly used for biosensing, have been successfully used to monitor the crystallization process, from pre-nucleation to final crystal formation, as well as to quantify molecular mass transport during nucleation. This technology is very attractive to study crystallization because it can be easily extended to more complex systems, i.e. organic molecules, inorganic molecules and macromolecules that are soluble in water (although experimental conditions may need to be optimized for each case).
iii) Raman spectroscopy was successfully used to study graphene nanoribbons with well controlled structures, produced by bottom-up approaches. We demonstrated that although the Raman spectrum shows more complex features, as compared to the one of graphene or carbon nanotubes, this technique still provides quantitative information on the quality of the edges and their functionalization type. Raman spectroscopy has been also successfully used to study crystallization of glycine in situ, demonstrating that crystals do grow first by forming some sort of beta-disordered assembly, which quickly turns into (the stable) alpha-glycine.
A crystallisation protocol was designed (sample set-up, control environmental conditions, concentration, volume , etc) using silicon as a reference substrate and glycine, as reference molecule. Glycine was selected because it has been widely used and its polymorphs can be easily distinguished by Raman spectroscopy. Both homogeneous and heterogenous nucleations were investigated.
-homogeneous nucleation was studied by performing acoustic levitation of graphene droplets. We observed formation of a liquid marble under specific conditions. The manuscript is currently ready to be submitted.
-heterogeneous nucleation was performed using graphene as impurity or surface. We show that graphene induces the preferential crystallization of the metastable α-polymorph compared to the unstable β-form at the contact region of an evaporating droplet. Computer modeling indicates the presence of a small amount of oxidized moieties on graphene to be responsible for the increased stabilization of the α-form. Our results show that the ability to finely tune the surface properties of graphene makes this material very attractive for polymorph screening. This work was published in ACS Nano 2020, 14, 8, 10394 and presented at Chem2D Mat conference in Dresden in 2019 and at the workshop: from 2Dto3D in 2021, Free University of Brussels.
-heterogenous nucleation was studied using different types of electrical readouts. First, an interdigitated electrode sensor has been used to monitor in real-time the crystallization process. We show that from the electrical signal, it is possible to easily and precisely extract the induction time and the supersaturation ratio. We observed characteristic fluctuations in the current after the induction time, which could be ascribed to the molecular assembly dynamics. The results were published in Nanoscale Horiz., 2021, 6, 468-473. In a second work, we demonstrated that electrolyte-gated organic field-effect transistors (EGOFETs) are able to monitor in real-time the crystallization process in an evaporating droplet. The high sensitivity of these devices at the solid–liquid interface, through the electrical double layer and signal amplification, enables the quantification of changes in solute concentration over time and the transport rate of molecules at the solid–liquid interface during crystallization. Our results show that EGOFETs offer a highly sensitive and powerful, yet simple approach to investigate the molecular dynamics of compounds crystallizing from water. The results were published in Nano Lett. 2022, 22, 7, 2643.
- we performed detailed Raman characterization of various types of graphene nanoribbons (GNRs), made by bottom up approach, showing that the low-energy region, especially in the presence of bulky functional groups, is populated by several modes, so a single radial breathing-like mode cannot be identified. However, we observed characteristic dispersions of the G and D peaks, which offer further insight into the GNR structure and functionalization, by making Raman spectroscopy a crucial tool for the characterization of these nanostructures. The results were published in Phys Rev B,100, 045406 (2019) and in JACS, 142, 18293 (2020); 139, 16454 (2017).
- we performed Raman characterization of graphene produced by electro-chemical exfoliation under different conditions showing that one can finely tune the surface chemistry of the material. The work was published in Nano Letters, 20 (5), 3411 (2020). The results were also used to develop a device based on this type of graphene, which has been funded with a ERC PoC.
- we developed a new way to deposit molecules on a surface, called the blow coating. The results are published in ACS Omega, 4, 11657 (2019).
-homogeneous nucleation was studied by performing acoustic levitation of graphene droplets. We observed formation of a liquid marble under specific conditions. The manuscript is currently ready to be submitted.
-heterogeneous nucleation was performed using graphene as impurity or surface. We show that graphene induces the preferential crystallization of the metastable α-polymorph compared to the unstable β-form at the contact region of an evaporating droplet. Computer modeling indicates the presence of a small amount of oxidized moieties on graphene to be responsible for the increased stabilization of the α-form. Our results show that the ability to finely tune the surface properties of graphene makes this material very attractive for polymorph screening. This work was published in ACS Nano 2020, 14, 8, 10394 and presented at Chem2D Mat conference in Dresden in 2019 and at the workshop: from 2Dto3D in 2021, Free University of Brussels.
-heterogenous nucleation was studied using different types of electrical readouts. First, an interdigitated electrode sensor has been used to monitor in real-time the crystallization process. We show that from the electrical signal, it is possible to easily and precisely extract the induction time and the supersaturation ratio. We observed characteristic fluctuations in the current after the induction time, which could be ascribed to the molecular assembly dynamics. The results were published in Nanoscale Horiz., 2021, 6, 468-473. In a second work, we demonstrated that electrolyte-gated organic field-effect transistors (EGOFETs) are able to monitor in real-time the crystallization process in an evaporating droplet. The high sensitivity of these devices at the solid–liquid interface, through the electrical double layer and signal amplification, enables the quantification of changes in solute concentration over time and the transport rate of molecules at the solid–liquid interface during crystallization. Our results show that EGOFETs offer a highly sensitive and powerful, yet simple approach to investigate the molecular dynamics of compounds crystallizing from water. The results were published in Nano Lett. 2022, 22, 7, 2643.
- we performed detailed Raman characterization of various types of graphene nanoribbons (GNRs), made by bottom up approach, showing that the low-energy region, especially in the presence of bulky functional groups, is populated by several modes, so a single radial breathing-like mode cannot be identified. However, we observed characteristic dispersions of the G and D peaks, which offer further insight into the GNR structure and functionalization, by making Raman spectroscopy a crucial tool for the characterization of these nanostructures. The results were published in Phys Rev B,100, 045406 (2019) and in JACS, 142, 18293 (2020); 139, 16454 (2017).
- we performed Raman characterization of graphene produced by electro-chemical exfoliation under different conditions showing that one can finely tune the surface chemistry of the material. The work was published in Nano Letters, 20 (5), 3411 (2020). The results were also used to develop a device based on this type of graphene, which has been funded with a ERC PoC.
- we developed a new way to deposit molecules on a surface, called the blow coating. The results are published in ACS Omega, 4, 11657 (2019).
There are no previous works looking at crystallisation on/with graphene, so all results obtained are currently beyond state of art.