Julio Chacón

During his PhD he was funded by the Austrian Science Foundation (FWF) and the OEAD Amadeus Program. He graduated in November 2013 with a thesis entitled: “Theory and Spectroscopy on functionalized graphene and GICs”. In May 2014 he was awarded a DRS Posdoctoral Fellowship at Freie Universität Berlin, Germany, and spent two years and a half in Berlin working on a project related to in-situ graphene and carbon nanotubes doping and characterization under inert and high-vacuum conditions.

In September 2016 Julio joined Yachay Tech University in Ecuador as an Assistant Professor where he is the heard of Nanotechnology in the School of Physical Sciences and Nanotechnology and Coordinator of the Master degree in Applied Physics. Since the pandemic, Julio started a new line of research combining the use of spectroscopic techniques to characterize and analize supramolecular interactions in biomolecules and carbon-nanostructures that will be the topic he is presenting to us today.

Revealing supramolecular interactions between Biomolecules and Carbon Nanostructures employing spectroscopic techniques.

School of Physical Sciences and Nanotechnology, Yachay Tech University
Hda. San José SN y Proyecto Yachay, 100119 Urcuquí, Ecuador

jchacon@yachaytech.edu.ec

Over the past few years, Chemistry, Physics, and Biotechnology have merged together in order to develop novel methods for studying supramolecular surface interactions between carbon nanostructures and biomolecular systems and diverse functional groups. Raman spectroscopy combined with X-ray photoelectron spectroscopy (XPS) have become together the tools of choice to analyze these supramolecular interactions, doping, and functionalization, especially in carbon-based nanostructures. However, much less is known about the physicochemical interaction existing between biomolecular systems and carbon nanostructures. During this presentation I will try to convince you about the existence of a near-universal Raman response where charge transfer governs the electrochemical activation of carbon nanomaterials when exposed to potassium undergoing an electron doping (n-type doping) process. [1]–[3] More recently, we have disclosed inherent interactions between biopolymers such as chitosan and DNA inhibiting the fluorescence effects of the biomolecule, and enhancing the Raman response of the bio-composite under the presence of pristine graphene. Our results from XPS confirm the presence of the biomolecule on graphene, and our Raman analysis reveals a strong electrostatic surface interaction between the biomolecule and the graphene. In summary, our results confirm that supramolecular interactions in carbon nanostructures are strongly governed by synergistic electrostatic effects that be categorized in three main important results of interest for Material science community: i) When carbon nanostructures (SWCNTs, [2] MWCTs, [4] carbon nano-onions, [3] graphite, [1] graphene, [5] and carbon nanoribbons [6]) are exposed to high level of charge transfer, the doping induces a shift in the Fermi energy level that triggers a shift in the G-line of the sample and deactivates some resonance Raman. ii) In single-walled carbon nanotubes there exists a trend where the RBM vibrational mode down-shifts along the doping process depending on their diameter and chirality as a general behavior in SWCNTs [2] iii) Functional groups can be clearly identified and assigned by means of a fine Raman spectroscopic deconvolution analysis and micro-XPS spectroscopy. For instance, when a moiety attaches to the surface of the carbon-nanostructure, it forms a sp3 functional site that activates additional Raman active bands appear becoming the fingerprint of functionalization without damaging the crystallinity of the nanostructure as confirmed by the sp2-sp3 C1s components. [3], [7], [8] Finally, this novel metrology can be extended to non-carbon nanostructures, revealing unprecedented and novel results that could drive a new systematic procedure towards the implementation of Raman spectroscopy and XPS to trace controlled synthesis of functional nanostructured materials for optoelectronics, batteries, and specialized biosensing devices.

References

J. C. Chacón-Torres, L. Wirtz, and T. Pichler, “Raman spectroscopy of graphite intercalation compounds: Charge transfer, strain, and electron-phonon coupling in graphene layers,” Phys. Status Solidi B Basic Res., vol. 251, no. 12, pp. 2337–2355, Dec. 2014.
[2] C. Kröckel et al., “Understanding the Electron-Doping Mechanism in Potassium-Intercalated Single-Walled Carbon Nanotubes,” J. Am. Chem. Soc., vol. 142, no. 5, pp. 2327–2337, Feb. 2020.
[3] M. E. Pérez-Ojeda et al., “Carbon nano-onions: Potassium intercalation and reductive covalent functionalization,” J. Am. Chem. Soc., vol. 143, no. 45, pp. 18997–19007, Nov. 2021.
[4] J. C. Chacón-Torres et al., “Potassium intercalated multiwalled carbon nanotubes,” Carbon N. Y., vol. 105, no. Supplement C, pp. 90–95, Aug. 2016.
[5] R. Podila, J. Chacón-Torres, J. T. Spear, T. Pichler, P. Ayala, and A. M. Rao, “Spectroscopic investigation of nitrogen doped graphene,” Appl. Phys. Lett., vol. 101, no. 12, p. 123108, Sep. 2012.
[6] J. Jakovac, L. Marušić, D. Andrade-Guevara, J. C. Chacón-Torres, and V. Despoja, “Infra-Red Active Dirac Plasmon Serie in Potassium Doped-Graphene (KC8) Nanoribbons Array on Al2O3 Substrate,” Materials , vol. 14, no. 15, Jul. 2021, doi: 10.3390/ma14154256.
[7] G. Abellán et al., “Exploring the Formation of Black Phosphorus Intercalation Compounds with Alkali Metals,” Angew. Chem. Int. Ed Engl., Oct. 2017, doi: 10.1002/anie.201707462.
[8] J. C. Chacón-Torres, L. Wirtz, and T. Pichler, “Manifestation of charged and strained graphene layers in the Raman response of graphite intercalation compounds,” ACS Nano, vol. 7, no. 10, pp. 9249–9259, Oct. 2013.