This study assesses the pedagogical benefits obtained by students, teachers, and a sponsor through the development of a computational chemistry research project on interactions between carbon materials and gases. Achievements, challenges, and opportunities are identified, emphasizing the mastery of transferable and technical skills throughout the four-year-long project. Engineering thesis students formed the teamwork. We highlight the implementation of the servers and software which are necessary to apply computational chemistry as a methodological tool. The subject of air pollution is also examined by performing a multidisciplinary analysis that determines potential areas for future applications and the impact of the computational analyses performed. It is concluded that there is development of training abilities in complex scientific-technological areas for both undergraduate and graduate students in a geographically isolated context that may limit performance.
Intrinsic reaction coordinate (IRC) data regarding the interactions of water with a carbene-like active site located at the edge of a polyaromatic hydrocarbon [, , ] has been obtained using density functional theory (DFT) and the 6-31g(d) basis set as implemented in the Gaussian 16 software . The data is presented as two videos (frontal and lateral mechanism views) combining four consecutive IRC calculations corresponding to the four different transition states presented on “https://doi.org/10.1016/j.carbon.2020.01.011”  (Figure 6, side approach). These videos provide powerful insights on two key aspects: a) the rotational process that occurs during water adsorption and b) the hydrogen gas desorption process during water gasification of carbons.
Reactions of carbon and oxygen containing molecules, such as O2, NO, H2O and CO2, are ubiquitous on earth and the universe. Through ab initio calculations, we study the reactions of H2O and CO2 with small graphene clusters containing armchair edges, both H- and non-H terminated, and compare with studies of zigzag carbon edges interacting with oxygen-containing molecules. Our results highlight the differences between armchair and zigzag sites and our mechanistic comparisons regarding carbon reactions with H2O and CO2, identify similarities and differences on their reactivity. In the case of H2O, adsorption is favored over armchair sites exhibiting no rotational process and the H2 desorption step is favored over zigzag sites. Regarding the CO2 reaction, chemisorption is favored on zigzag sites. Several adsorption mechanisms lead to the formation of lactone groups as the most stable structures. A specific armchair CO desorption path for stable functional groups exists, agreeing with experimental reports, and thus completing our explanations for this reaction, previously limited to zigzag sites. Finally, the reaction over armchair sites leads to direct formation of pentagonal rings, without an active site deactivation process and with low activation energies. This deeper understanding provides further possibilities for improving the control of carbon-oxygen reactions. https://doi.org/10.1016/j.carbon.2022.02.048 For a limited time, this article can be downloaded here: https://authors.elsevier.com/a/1eqOk1zUASAMu
This paper explores the reactivity differences for H2 adsorption/desorption processes at both edges and surfaces of curved and non-curved carbon materials. It was presented as an oral presentation at the Carbon 2019 conference, and the paper can be found on: http://carbon2019.org/wp-content/uploads/2019/07/246-oyarzun.pdf
This is a preprint of an article in press. To see the finished article please visit: https://doi.org/10.1016/j.carbon.2020.01.011 Free full article until May 27: https://authors.elsevier.com/a/1asaP1zUALh1L
Aiming to better understand the reactivity of graphene-based materials, the present work employs density functional theory that provides detailed information about spin-density distributions for single and contiguous pairs of carbene-like active sites. In order to examine the extent to which different models, methodologies, and approximations affect the outcome, our calculations employ the AIMPRO, QuantumEspresso and Gaussian program packages. Models are in the form of polycyclic aromatic hydrocarbons (PAHs) and graphene nanoribbons (GNRs), both isolated and within supercells with periodic boundary conditions. Benchmarking calculations for the phenyl radical and cation are also presented. General agreement is found among the methods and also with previous studies. A significant electron spin polarization (spin density >1.096 electron spin) on the active sites is seen in both periodic and cluster systems, but it tends to be lower for GNRs than graphene clusters. The effect of the functional seems to be much more important than the position of singularities at the edges of the GNRs. Finally, we show the interactions and effects on spin density when a single site lies at the edge of a bilayer GNR, where bonding between layers may occur under specific circumstances.
H2O and CO2 reactions with graphene are of great interest in the energy industry as well as in materials related applications. Although the reactions may seem straightforward, their mechanistic details deserve further scrutiny, especially regarding to the reactants adsorption and products desorption steps. In this study we use quantum chemistry on zigzag actives sites to present thermodynamics and kinetics of the relevant mechanistic steps, and compare them with the previously studied NO and O2 reactions (Oyarzún 2016). Their differences and similarities are reviewed within the scope of oxygen transfer reactions for carbon materials. The mechanistic analysis of the water reaction results differ from the usually accepted mechanism, including dissociative adsorption instead of a concerted adsorption step with simultaneous H2 desorption. Additionally, a surface rearrangement for desorption of products is proposed, which may account for the inhibition process. In the case of CO2, inhibition mechanisms are also analysed. The results allow us to propose the participation of a surface or extended-edge effect on the inhibition process, which may account for experimental facts such as the hexagonal pits seen for the H2O and graphene reaction, in contrast to the circular ones seen for the CO2 and graphene reaction (Yang 1983). (1) Oyarzún, A.M., A.J.A. Salgado-Casanova, X. García and L.R. Radovic, Carbon, 2016. 99: 472-484. (2) Yang, R.T. and C. Wong, Journal of Catalysis, 1983. 82: 245-251.
The reaction of carbon materials with nitric oxide has gained increasing importance for both fundamental and practical reasons. The removal of NOx from stationary and mobile sources, smog reduction and the development of new NO sensors represent a few examples. In previous studies, we used computational chemistry to calculate thermochemical and kinetic information, and proposed a reaction route that connects the reactants and products through the N2O intermediate. In contrast, the present work proposes a reinterpretation of the mentioned kinetic results, and finds a different reaction mechanism may connect reactants and products through the NO2 intermediate. Hitherto overlooked experimental evidence seen during NO chemisorption on cellulosic chars (DeGroot, 1991) appears to agree with this mechanism proposal and shows that further studies are required to both: a) clarify the role of the NO2 as an intermediate in the NO-carbon reaction and b) analyze the potential use of this reaction path to transform NO into N2 and O2. The latter involves the use of carbon as a catalyst in a key reaction mechanism, which supposes a mayor challenge for NOx remediation for environmental purposes.