Passivation by Ultimate Ligand-Surface Activation Rationalized by NMR
Lead Research Organisation:
UNIVERSITY OF MANCHESTER
Department Name: Chem Eng and Analytical Science
Abstract
Dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy has proven in recent years to be a powerful technique for the characterization of challenging solid materials and their interfaces. Substantially increased sensitivity of NMR experiments becomes possible through DNP, where the large polarization of unpaired electron spins is transferred to the desired nuclei. For inorganic nanoparticles (NPs) surrounded with sources of unpaired electrons, known as polarizing agents, polarization transfers are mainly to their surfaces. Therefore, surface selectivity, in addition to increased sensitivity, is achieved and this can be used to study the surface chemistry of NPs. The capping of NPs with inorganic ligands (ILs), rather than conventional organic ligands, has been proposed to improve charge carrier lifetime in solids composed of assemblies of NPs, usually termed colloidal quantum dot solids (CQDSs). Substantial increases in transport properties and method versatility have led researchers to explore many types of IL to improve the mobility of charge carriers. However, gaining a detailed understanding of the surface chemistry of IL-capped NPs remains a challenging task and is thus still lacking. This project aims to correlate the surface chemistry and interfaces of ligand-capped CQDSs with their performance. Surface characterization of IL-capped NPs will be carried out by advanced DNP-enhanced solid-state NMR spectroscopy. Photoluminescence and conductivity measurements will indicate the effect on charge carrier lifetimes in assembled CQDSs. Therefore, the proposed research will result in a breakthrough atomic-level understanding of how IL choice and surface chemistry influences charge transport and will lead to a generalized method for achieving single-crystal-grade mobility values in CQDSs.
People |
ORCID iD |
| Ran Abutbul (Principal Investigator / Fellow) |
Publications
Abutbul RE
(2026)
Am I Still IL? Evolution of CdS Nanocrystals from Inorganic Ligand Exchange.
in Journal of the American Chemical Society
Buckingham MA
(2025)
Passivation, phase, and morphology control of CdS nanocrystals probed using fluorinated aromatic amines and solid-state NMR spectroscopy.
in Nanoscale advances
Ouzrour Z
(2025)
HCl-assisted fabrication of metal-organic framework UiO-66(Zr) for affordable gas capture
in Materials Advances
| Description | This research generated several important advances in understanding and designing nanomaterials, particularly semiconductor nanocrystals used in optoelectronic devices. First, it produced significant new knowledge by demonstrating that inorganic ligand coatings on nanocrystals are not chemically static after they are applied, as widely assumed, but instead evolve over time through ligand-specific transformation pathways. The work showed that certain inorganic ligands can cause degradation by extracting metal ions from the nanocrystal surface and forming new metal-salt domains, while other inorganic ligands produce chemically stable but ionically dynamic interfaces, improving surface passivation. This overturns the prevailing "static surface" model and establishes that long-term performance depends strongly on the chemical identity of the ligand and associated counterions. Second, the project delivered a methodological advance by establishing multinuclear solid-state NMR spectroscopy as a powerful tool for probing nanocrystal surfaces at atomic resolution over extended timescales. By combining measurements of multiple nuclei (including hydrogen, cadmium, phosphorus, sodium, and tin) with microscopy and optical spectroscopy, the researchers were able to directly observe ligand binding modes, counterion behaviour, and surface restructuring processes that are difficult or impossible to detect using conventional techniques. This methodological framework represents an improved research capability that can be applied broadly across the science of nanomaterials. Third, the work identified important new design principles and resources for device development by linking specific surface chemistries to electronic and optical behaviour. The study showed that different ligand treatments create distinct distributions of electronic trap states, modify recombination dynamics, and influence charge transport, thereby providing practical guidance for selecting inorganic ligand systems for photovoltaics, LEDs, sensors, and catalytic applications. These insights effectively create a knowledge resource for rational engineering of nanocrystal interfaces. Finally, the research opened up new questions and directions by revealing the central role of counterions, residual organic ligands, hydration, and redox processes in determining surface stability and functionality. The discovery that mobile ions or slow chemical transformations can dominate long-term behaviour highlights previously underexplored mechanisms that must now be considered in nanocrystal device design and stability studies. Together, these outcomes significantly advance both fundamental understanding and applied capability in the field of functional nanomaterials. |
| Exploitation Route | The outcomes of this work can be taken forward through both academic research and industrial technology development. In academia, researchers working on semiconductor nanocrystals, quantum dots, catalysis, and functional nanomaterials can apply the multinuclear solid-state NMR methodology demonstrated here to investigate surface chemistry evolution in other material systems. The findings also provide a framework for studying counterion dynamics, ligand stability, and ageing processes, opening opportunities for collaborations between chemists, materials scientists, spectroscopists, and device physicists. In non-academic contexts, companies developing nanocrystal-based technologies such as displays, photovoltaics, photodetectors, and sensors can use the insights to improve material stability, device lifetime, and manufacturing reproducibility. For example, ligand selection strategies identified in this work could guide industrial surface treatments to minimise degradation or optimise charge transport. Instrument manufacturers and specialist analytical facilities may also build on the methodological advances by expanding NMR-based characterisation services for nanomaterials. Overall, the research provides both practical design guidance and advanced analytical approaches that can be adopted by academic groups, industrial R&D teams, and national research facilities to accelerate the development of stable, high-performance nanocrystal technologies. |
| Sectors | Chemicals Electronics Energy Manufacturing including Industrial Biotechology |
| Title | Am I still IL? Evolution of CdS Nanocrystals from Inorganic Ligand Exchange |
| Description | Ligand exchange has become the standard route for modifying the surface chemistry of colloidal nanocrystals (NCs), providing a mechanism to tailor their optoelectronic properties, solubility, and chemical functionalization. This enables NCs to be deployed in myriad applications where the surface-solution interface is key to performance or process compatibility. Ligand-passivated surfaces are generally considered stable and chemically inert, with incoming ligands assumed to fully replace native ones. Here, we demonstrate that inorganic ligand shells on CdS NCs are dynamic, chemically evolving over time, with transformation pathways strongly dependent on ligand identity. This is evaluated for representative oxoanions (o-phosphoric acid), chalcogenides (Na2Se, Se2-), and metal-chalcogenides (thiostannate). Using multinuclear (1H, 13C, 23Na, 31P, 113Cd, 119Sn) solid-state NMR spectroscopy and electron microscopy, we show that: (i) surface-bound phosphates reorganize over time into cadmium phosphate domains, degrading NC quality; (ii) polyselenide ligands remain chemically stable, but their associated Na+ counter-ions exhibit dynamics that may suppress charge transport; and (iii) partial oxidation of thiostannate ligands to SnO2 occurs, along with surface reconstruction, which improves NC passivation. Across all systems studied, residual oleylamine is detected. These findings reveal that inorganic ligand exchange does not necessarily yield chemically uniform or stable surfaces. Instead, each ligand class exhibits distinct behavior, ranging from surface degradation (phosphates), to stable yet dynamic interfaces (selenides), to hydrophilic and partially oxidized surfaces (thiostannates). This challenges the static-surface model and positions multinuclear solid-state NMR spectroscopy as a key tool for designing future functional materials. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2025 |
| Provided To Others? | Yes |
| Impact | This dataset was used in the associated journal article of the same title. |
| URL | https://figshare.manchester.ac.uk/articles/dataset/Am_I_still_IL_Evolution_of_CdS_Nanocrystals_from_... |
| Title | Passivation, phase, and morphology control of CdS nanocrystals using fluorinated aromatic amines |
| Description | Nanocrystals are widely explored for a range of medical, imaging, sensing, and energy conversion applications. CdS nanocrystals have been reported as excellent photocatalysts, with thin film CdS also highly important in photovoltaic devices. To maximise catalytic activity of nanocrystals, control over phase, facet, and morphology are vital. Here, CdS nanocrystals were synthesised by the solvothermal decomposition of a Cd xanthate single source precursor. To attempt to control CdS nanocrystal surfaces and morphology, the solvent used in the nanocrystal synthesis was altered from pure trioctylphosphine oxide (TOPO) to a mixed TOPO:fluorinated aromatic amine (either 3-fluorobenzyl amine (3-FlBzAm) or 3-fluoroaniline (3-FlAn)), which also provides a sensitive NMR-active probe moiety (mono-fluorinated capping ligands on the CdS nanocrystal surface). Powder X-ray diffraction found that the CdS nanocrystals synthesised from TOPO:3-FlAn solvent mixtures were predominantly cubic whilst the TOPO:3-FlBzAm synthesised nanocrystals were predominantly hexagonal. Raman spectroscopy identified hexagonal CdS in all samples, indicating a likely mixture of phases in at least some of the synthesised systems. Solid-state NMR of 113Cd, 19F, 13C, and 1H was employed to investigate the local Cd environments, surface ligands, and ligand interactions. This showed there was a mixture of CdS phases present in all samples and that surfaces were capped with TOPO:fluorinated aromatic amine mixtures, but also that there was a stronger binding affinity of 3-FlBzAm compared with 3-FlAn on the CdS surface. This work highlights that fluorinated aromatic amines can be used to passivate NC surfaces and also control NC properties through their influence during NC growth. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2024 |
| Provided To Others? | Yes |
| Impact | Accessible data under FAIR principles. |
| URL | https://figshare.manchester.ac.uk/articles/dataset/Passivation_phase_and_morphology_control_of_CdS_n... |
| Description | Design, synthesis, and characterisation of inorganic nanocrystals |
| Organisation | University of Manchester |
| Country | United Kingdom |
| Sector | Academic/University |
| PI Contribution | Guided the design, synthesis, and characterisation of inorganic nanocrystals |
| Collaborator Contribution | Worked together for the design, synthesis, and characterisation of inorganic nanocrystals |
| Impact | This collaboration is multi-disciplinary with chemical engineers, chemists, materials scientists working together to design, produce, and characterise nanocrystals. Outputs: 1. Passivation, phase, and morphology control of CdS nanocrystals probed using fluorinated aromatic amines and solid-state NMR spectroscopy. Buckingham, M. A.; Crawford, R.; Li, Y.; Abutbul, R. E.; Han, B.; Hazledine, K.; Cartmell, S.; Walton, A.; Eggeman, A. S.; Lewis, D. J.; and Lee, D. Nanoscale Advances,10.1039.D4NA00564C. 2025. 2. Am I Still IL? Evolution of CdS Nanocrystals from Inorganic Ligand Exchange. Abutbul, R. E.; Maddox, C.; Binks, D. J.; Lewis, D. J.; and Lee, D. Journal of the American Chemical Society, 148(3): 3420-3432. 2025. |
| Start Year | 2024 |