Think Outside the Lab: Modeling Graphene Quantum Dots in Pandemic Times

Abstract

A computational laboratory experiment is carried out to investigate the size-, geometry-, and chemistry-dependent properties of small molecules known as polycyclic aromatic hydrocarbons (PAHs) at the Facultad de Ingeniería (Universidad Nacional de La Plata, UNLP), Buenos Aires, Argentina. This computational research was adapted for upper-division undergraduate and initial graduate education levels. Due to the adverse circumstances of the pandemic, students were challenged to perform theoretical calculations on a regular computer at home. They were able to model PAH molecules similar to graphene quantum dots (GQDs) and learn how to use various open and freely available softwares, including visual molecular dynamics (VMD), Avogadro, nanoHUB.org, and ORCA. Through these computational tools, students designed PAHs of various sizes, geometries, and functional groups in order to study some of their optoelectronic properties. They simulated UV–vis absorbance spectra based on changes in size, geometry, and chemistry at the edges of the GQDs. Students then calculated the energy of the HOMO–LUMO gap and compared using three different methods included in ORCA corresponding to Hartree–Fock (H–F) approximation, density functional theory (DFT), and time-dependent DFT (TD-DFT). Finally, based on the results obtained, students propose the construction of more efficient solar devices by tuning the size and geometry of GQDs.

Efficient generation of highly crystalline carbon quantum dots via electrooxidation of ethanol for rapid photodegradation of organic dyes

“…In addition, secondary bands corresponding to benzo-e-pyrene (∼330 nm) and benzo-ghi-perylene (∼265 nm and ∼374 nm) are also observed. The absorbance bands simulated here for coronene (∼285 nm) falls within PAHs reported by our group 23 as well as UV-vis experiments performed by Patterson 36 and Fetzer. 37 Moreover, pyrene-like molecules observed experimentally at 335, 38 345, 25 and 360 nm coincide with our simulations.…”

“…26 Computational tools have been also utilized to describe the optical properties of PAHs that may change with their specific structure or chemistry. 23,[27][28][29] For instance, Peng Chen and coworkers studied how the emission properties of alike-GQDs change with size, edge configuration, functional groups, and addition of heteroatoms. 28 Also, Zhang and co-workers employed time-dependent DFT (TD-DFT) to chemisorb five different types of oxygen-containing groups to the basal plane of graphene dots.…”

“…27 Another example is Melia et al who simulated linear- and hexagonal-shaped PAHs and demonstrated distinct absorption bands based on the number of benzene units and aspect ratio. 23 Despite the significant progress made in the field, characterizing the optical properties of carbon-based nanostructures, by considering the complex interplay between their constituents, remains uncertain.…”

How to Characterize 4–90 nm Size Gold Nanospheres with Experimental and Simulated UV–Vis and a Single SEM Image

“…This group primarily focused on the synthesis of various NP sizes and how the size-dependent optical properties change when altering the NP size. Incorporation of simulations and theoretical calculations to experiments is crucial nowadays because they can predict/analyze given physical-chemical behaviors. − For instance, via simulations it has been determined the size- and shape-dependence on stability, absorption of light in carbon nanostructures, and overall optical properties in Ag nanoparticles . Simulations have also been applied in a wide range of fields that include environmental issues, pharmaceutical companies, and chemical laboratories .…”

Toward Strong Near‐Infrared Absorption/Emission from Carbon Dots in Aqueous Media through Solvothermal Fusion of Large Conjugated Perylene Derivatives with Post‐Surface Engineering

“…Based on theoretical calculations, increasing the diameter of the conjugated sp 2 domain to ≈2 nm could tune its bandgap to the NIR region. [ 12 ] Reported CDs are usually synthesized from non‐ or low‐conjugated molecules through dehydration and carbonization processes. [ 13 ] Although their particle sizes can be much larger than 2 nm, their main absorption bands are always observed in the UV or visible regions, indicating smaller conjugated sp 2 domains in the carbon cores.…”