Catalytic conversion of hazardous gases can solve many of the environmental problems caused by them. We performed a density functional theory (DFT) study with the Perdew−Burke−Ernzerhof (PBE) functional to investigate the CO oxidation by using N 2 O as an oxidizing agent over an iron-embedded graphene (Fe-Graphene) catalyst. The N 2 O molecule was first decomposed on the Fe site yielding the N 2 molecule and an Fe−O intermediate, which was an active species for the CO oxidation. The activation energy for the N 2 O decomposition step was predicted to be 8 kcal/mol. According to the population analysis, the graphene acted as both the electron withdrawing and donating support to assist the charge transfer between the Fe atom and the probe molecules, which are important for the reaction. The reaction was found to be less facile when the Fe site was first covered by the CO which has a higher adsorption energy than that of the N 2 O (−10.0 vs −33.6 kcal/mol). The reaction proceeded via a concerted transition structure and required an activation energy of 19.2 kcal/mol when the CO was prior adsorbed. Thus, control of the adsorbing molecules over Fe-Graphene might be a key factor for the activity of the catalyst. With the higher catalytic activities of Fe-embedded graphene compared to other typical catalysts, this may open new avenues in searching for oxidation of CO at an economical cost.

Small semiconductor structures often exhibit "telegraph noise". If the number of charge carriers is small, then spontaneous changes in the number of carriers can lead to abrupt switching between two or more discrete levels, leading to burst noise or popcorn noise in transistors. We have observed similar behavior in the fluorescence of organic semiconductor nanoparticles, where typical carrier populations are often less than ∼10 carriers per nanoparticle. Spontaneous changes in the number of charges results in abrupt switching between 2 or more fluorescence intensity levels, because the charges act as highly efficient fluorescence quenchers. The equilibrium number of charges is determined by competition between a photodriven ionization process and spontaneous recombination. Doping with redox-active molecules also affects the balance. Nanoparticles of the conjugated polymer PFBT doped with the fullerene derivative PCBM, rapidly establish a fluctuating steady-state population of tens of hole polaron charge carriers, sufficient to nearly completely suppress nanoparticle fluorescence. However, fluctuations in the number of charges lead to occasional bursts of fluorescence. This spontaneous photoswitching phenomenon can be exploited for superresolution imaging. The repeated, spontaneous generation of short, intense bursts of fluorescence photons results in a localization precision of ∼0.6 nm, about 4 times better than typical resolution obtained by localization of dye molecules.

We propose a new mechanism for the bimolecular healing of the vacancy defect in single-walled carbon nanotubes (SWCNTs). The mechanism is of particular importance to avoid the errors often encountered in the electronic properties of carbon nanotubes. Using density functional theory (DFT) calculations with the Perdew−Burke−Ernzerhof (PBE) functional, we investigate the reaction mechanism of the healing process of the monatomic vacancy defect in the (8, 0) SWCNT via carbon monoxide disproportionation. It is found that the proposed mechanism is theoretically possible and it has the following advantages: (1) The activation energy is only 9.37 kcal·mol−1 for the 4-membered-ring-opening step at high CO concentrations; (2) no catalyst is needed, and thus no purification step is needed to remove the catalyst; (3) the CO can be used as a reactant; (4) no oxygen byproduct is found; and (5) there is a high selectivity of CO for vacancy defect sites. Our finding establishes that a CNT with a vacancy defect, as it is generally obtained from the syntheses or from uses as a nanomaterial device, can be healed completely and resumes its function as a perfect CNT displaying the original electronic properties.

We present super-resolution (∼2 nm spatial resolution per frame, 1 ms time resolution) tracking of single charge carriers in nanoparticles of the conjugated polymer PFBT. The motion of the charge carrier is determined from fluctuations in the centroid position of the particle fluorescence spot arising from fluorescence quenching by the polaron. A single polaron is observed to hop between a few sites, consistent with dispersive charge transport in a disordered energy landscape. In some shorter segments of the trajectory, there is repeated hopping between two sites, whereas for longer segments and full trajectories, random walk-like behavior consistent with multiple sites is observed. The hopping times range from a few milliseconds to seconds, following a power law distribution, while the hopping distances range from 2 to 5 nm, roughly following an exponential distribution. From the polaron hopping time distribution, we estimate a barrier height of 430–570 meV, with a nearest-neighbor distribution ranging from 2 to 5 nm, consistent with the presence of deep traps often associated with structural or chemical defects.