Effect of Nitrogen Doping on the CO₂ Adsorption Behavior in Nanoporous Carbon Structures: A Molecular Simulation Study

Nitrogen (N) doping is considered an effective design strategy to improve CO₂ adsorption in carbon materials. However, experimental quantification of such an effect is riddled with difficulties, due to the practical complexity involved in experiments to control more than one parameter, especially at the nanoscale level. Here, we use molecular simulations to clarify the role of N doping on the CO₂ uptake and the CO₂/N₂ selectivity in representative carbon pore architectures (slit and disordered carbon structures) at 298 K. Our results indicate that N doping shows a marginal improvement on the CO₂ uptake, although it can improve the CO₂/N₂ selectivity. CO₂ uptake and CO₂/N₂ selectivity are predominantly controlled by the pore architecture as well as ultra-micropores; the tendency of linear CO₂ molecules to lie flat on the carbon surface favors the CO₂ uptake in slit pore architectures rather than disordered carbon pore structures. We also demonstrated through molecular simulations that the N doping effect may be difficult to exemplify experimentally if the material has a disordered pore architecture and complex surface chemistry (such as the presence of other functional groups)

Strain and Orientation Modulated Bandgaps and Effective Masses of Phosphorene Nanoribbons

Passivated phosphorene nanoribbons, armchair (a-PNR), diagonal (d-PNR), and zigzag (z-PNR), were investigated using density functional theory. Z-PNRs demonstrate the greatest quantum size effect, tuning the bandgap from 1.4 to 2.6 eV when the width is reduced from 26 to 6 Å. Strain effectively tunes charge carrier transport, leading to a sudden increase in electron effective mass at +8% strain for a-PNRs or hole effective mass at +3% strain for z-PNRs, differentiating the (<i>m</i>_h^*/<i>m</i>_e^*) ratio by an order of magnitude in each case. Straining of d-PNRs results in a direct to indirect band gap transition at either −7% or +5% strain and therein creates degenerate energy valleys with potential applications for valleytronics and/or photocatalysis

Preferential Pt Nanocluster Seeding at Grain Boundary Dislocations in Polycrystalline Monolayer MoS₂

We show that Pt nanoclusters preferentially nucleate along the grain boundaries (GBs) in polycrystalline MoS₂ monolayer films, with dislocations acting as the seed site. Atomic resolution studies by aberration-corrected annular dark-field scanning transmission electron microscopy reveal periodic spacing of Pt nanoclusters with dependence on GB tilt angles and random spacings for the antiphase boundaries (<i>i.e.</i>, 60°). Individual Pt atoms are imaged within the dislocation core sections of the GB region, with various positions observed, including both the substitutional sites of Mo and the hollow center of the octahedral ring. The evolution from single atoms or small few atom clusters to nanosized particles of Pt is examined at the atomic level to gain a deep understanding of the pathways of Pt seed nucleation and growth at the GB. Density functional theory calculations confirm the energetic advantage of trapping Pt at dislocations on both the antiphase boundary and the small-angle GB rather than on the pristine lattice. The selective decoration of GBs by Pt nanoparticles also has a beneficial use to easily identify GB areas during microscopic-scale observations and track long-range nanoscale variances of GBs with spatial detail not easy to achieve using other methods. We show that GBs have nanoscale meandering across micron-scale distances with no strong preference for specific lattice directions across macroscopic ranges