First-Principles Study of Crown Ether and Crown Ether-Li Complex Interactions with Graphene

Adsorption of molecules on graphene is a promising route to achieve novel functionalizations, which can lead to new devices. Density functional theory is used to calculate stabilities, electronic structures, charge transfer, and work function for a crown-4 ether (CE) molecule and a CE–Li (or CE–Li⁺) complex adsorbed on graphene. For a single CE on graphene, the adsorption distance is large with small adsorption energies, regardless of the relative lateral location of the CE. Because CE interacts weakly with graphene, the charge transfer between the CE and graphene is negligibly small. When Li and Li⁺ are incorporated, the adsorption energies significantly increase. Simultaneously, an <i>n</i>-type doping of graphene is introduced by a considerable amount of charge transfer in CE–Li adsorbed system. In all of the investigated systems, the linear dispersion of the p_<i>z</i> band in graphene at the Dirac point is well-preserved; however, the work function of graphene is effectively modulated in the range of 3.69 to 5.09 eV due to the charge transfer and the charge redistribution by the adsorption of CE–Li and CE–Li⁺ (or CE), respectively. These results provide graphene doping and work function modulation without compromising graphene’s intrinsic electronic property for device applications using CE-based complexes

Phonon Resonance Catalysis in NO Oxidation on Mn-Based Mullite

A phonon is the medium a bulk material used to exchange energy with the environment and is thus crucial for heterogeneous catalysis. However, a physical correlation between phonons and catalytic processes has not been established yet. Herein, by combining various in situ characterization techniques, we discovered the intrinsic correlations between phonon modes and the vibrations of reactant intermediates during NO oxidation on the mullite catalyst YMn2O5. It was found that the active phonon modes (350 (Ag(5)) and 670 cm–1 (B1g(12))) are strongly correlated with the vibrational frequencies of the adsorbed −O2 and −O–NO2 intermediates. The resulting resonance will transfer the superposed energy (nℏω) of the high-energy phonons to reactants one by one via the unit energy (ℏω) and then increase the vibrational amplitude along the reaction direction, contributing to the increase in the entropy of the surface reactants and thus the reduction of the Gibbs energy of activation. Phonon resonance catalysis (PRCAT) was thus proposed based on this discovery. This work provides insights into the bidirectional selection of catalysts and precise chemical reactions by matching catalyst phonons with reactant vibrational frequencies

Schottky Barrier Height of Pd/MoS₂ Contact by Large Area Photoemission Spectroscopy

MoS₂, as a model transition metal dichalcogenide, is viewed as a potential channel material in future nanoelectronic and optoelectronic devices. Minimizing the contact resistance of the metal/MoS₂ junction is critical to realizing the potential of MoS₂-based devices. In this work, the Schottky barrier height (SBH) and the band structure of high work function Pd metal on MoS₂ have been studied by <i>in situ</i> X-ray photoelectron spectroscopy (XPS). The analytical spot diameter of the XPS spectrometer is about 400 μm, and the XPS signal is proportional to the detection area, so the influence of defect-mediated parallel conduction paths on the SBH does not affect the measurement. The charge redistribution by Pd on MoS₂ is detected by XPS characterization, which gives insight into metal contact physics to MoS₂ and suggests that interface engineering is necessary to lower the contact resistance for the future generation electronic applications

Formaldehyde Decomposition from −20 °C to Room Temperature on a Mn–Mullite YMn₂O₅ Catalyst

Large ambient temperature changes (−20–>25 °C) bring great challenges to the purification of the indoor pollutant formaldehyde. Within such a large ambient temperature range, we herein report a manganese-based strategy, that is, a mullite catalyst (YMn2O5) + ozone, to efficiently remove the formaldehyde pollution. At −20 °C, the formaldehyde removal efficiency reaches 62% under the condition of 60,000 mL gcat–1 h–1. As the reaction temperature is increased to −5 °C, formaldehyde and ozone are completely converted into CO2, H2O, and O2, respectively. Such a remarkable performance was ascribed to the highly reactive oxygen species generated by ozone on the YMn2O5 surface based on the low temperature-programed desorption measurements. The in situ infrared spectra showed the intermediate product carboxyl group (−COOH) to be the key species. Based on the superior performance, we built a consumable-free air purifier equipped with mullite-coated ceramics. In the simulated indoor condition (25 °C and 30% relative humidity), the equipment can effectively decompose formaldehyde (150 m3 h–1) without producing secondary pollutants, rivaling a commercial removal efficiency. This work provides an air purification route based on the mullite catalyst + ozone to remove formaldehyde in an ambient temperature range (−20–>25 °C)

Differentiating Plasmon-Enhanced Chemical Reactions on AgPd Hollow Nanoplates through Surface-Enhanced Raman Spectroscopy

Plasmonic photocatalysis demonstrates great potential for efficiently harnessing light energy. However, the underlying mechanisms remain enigmatic due to the transient nature of the reaction processes. Typically, plasmonic photocatalysis relies on the excitation of surface plasmon resonance (SPR) in plasmonic materials, such as metal nanoparticles, leading to the generation of high-energy or “hot electrons”, albeit accompanied by photothermal heating or Joule effect. The ability of hot electrons to participate in chemical reactions is one of the key mechanisms, underlying the enhanced photocatalytic activity observed in plasmonic photocatalysis. Interestingly, surface-enhanced Raman scattering (SERS) spectroscopy allows the analysis of chemical reactions driven by hot electrons, as both SERS and hot electrons stem from the decay of SPR and occur at the hot spots. Herein, we propose a highly efficient SERS substrate based on cellulose paper loaded with either Ag nanoplates (Ag NPs) or AgPd hollow nanoplates (AgPd HNPs) for the in situ monitoring of C–C homocoupling reactions. The data analysis allowed us to disentangle the impact of hot electrons and the Joule effect on plasmon-enhanced photocatalysis. Computational simulations revealed an increase in the rate of excitation of hot carriers from single/isolated AgPd HNPs to an in-plane with a vertical stacking assembly, suggesting its promise as a photocatalyst under broadband light. In addition, the results suggest that the incorporation of Pd into an alloy with plasmonic properties may enhance its catalytic performance under light irradiation due to the collection of plasmon-excitation-induced hot electrons. This work has demonstrated the performance-oriented synthesis of hybrid nanostructures, providing a unique route to uncover the mechanism of plasmon-enhanced photocatalysis