The Journal of Physical Chemistry C
ISSN / EISSN : 1932-7447 / 1932-7455
Published by: American Chemical Society (ACS) (10.1021)
Total articles ≅ 46,761
Latest articles in this journal
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c01438
Single CdSe/CdS quantum dots have been embedded into a polymer (poly(methyl methacrylate), PMMA) nanoparticle of about 50 nm diameter. The influence of external electric AC fields on photoluminescence blinking dynamics has been investigated as a function of field strengths up to 800 kV cm–1 and field frequencies up to 5 kHz. Detailed blinking analysis is carried out by truncated power laws. They are interpreted within the framework of the electric field dependent dielectric response of the PMMA nanoparticle acting as the quantum dots local nanoenvironment. Subsequent to the creation of an exciton, the hole is eventually trapped at the QD interface and the electron is ejected into PMMA, creating a local dipolar reaction field. A competition between electric field induced polarization and electric dipole orientation of the reaction field modifies trap depths for charges and thus blinking dynamics. The frequency dependence of blinking indicates a broad distribution of electric dipolar relaxation times centered at 100 ms. To account for such a relaxation in PMMA at room temperature, we propose a close relation to the β-relaxation of PMMA.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c02246
Barium distannide (BaSn2), a potential precursor for stannene, is predicted to be a topological insulator. However, little is known about BaSn2 as the material is extremely air-sensitive. Here we present, for the first time, characterization of BaSn2 by scanning/transmission electron microscopy. We use advanced imaging and spectroscopy techniques to show disproportionation of BaSn2 particles into β-Sn + BaxSny. X-ray diffraction analysis confirms that this disproportionation is driven by exposure to a low-pressure environment.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c04195
Construction of inverse oxide/metal model catalyst with specific chemical composition and interfacial structure is essential for clarifying their structure–performance relationship. This work describes the structural evolution of Mn–Au surface alloy and two-dimensional manganese oxide (MnOx) islands on Au(111) surface under different treatment conditions. By employing near-ambient pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy, we can obtain four different MnOx structures. Among them, double-layer square lattice Mn3O4(001) and monolayer parallelogram-shaped Mn3O4 are prepared by postannealing Mn–Au surface alloy in “oxygen-poor” and “oxygen-rich” regimes, respectively. Annealing the monolayer parallelogram-shaped Mn3O4 in vacuum to 700 K produces a double-layer structure consisting of Mn3O4 top layer and MnO(111) bottom layer, while double-layer MnO(111) is formed after annealing in vacuum to 800 K. Our study lays the foundation for exploring the catalytic properties of inverse manganese oxide/metal model catalysts.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c02550
In recent times, perovskite oxide based photovoltaic devices have attracted lots of attention. Here we report the effect of light illumination on the transport properties of a two-dimensional electron gas formed at the recently discovered conducting interface of EuO and KTaO3. We have seen that lowering the carrier density increases the photoresponse in this system. In room temperature the photoresponse consists of two processes. However, at low temperature it is not only governed by a single process; in addition, the response rate becomes several orders of magnitude faster. At the same time the magnitude of the photoresponse is also larger at low temperature. Our observation suggests an interplay between carrier and phonon dynamics determines the photoresponse and should be investigated theoretically in detail to design future photoresponsive cells.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c04572
The impedance of diffusion is an important tool to investigate a wide variety of systems, including electrochemical devices such as Li-ion batteries, porous electrodes, and solar cells. The classical impedance model for diffusion in a thin layer with a blocking boundary contains two separate regimes: Warburg diffusion at high frequency and capacitive charging at low frequency. Here, we provide a physical criterion for the transition between these two regimes, as the point of closest approach between early- and late-time approximations of the exact diffusion current. The resulting frequency is (π2/2)ωd with respect to the natural frequency ωd = Dn/L2, with Dn being the diffusion constant and L being the thickness of the layer.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c03260
A new design strategy for the development of bifunctional electrocatalysts capable of catalyzing both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) is proposed. In this strategy, the MnOx lattice is doped with either electropositive (Sr, Ba) or electronegative (Bi, Pb) elements that results in the coincorporation of electron-rich donor (Mn2+) and electron-poor acceptor (Mn4+) defects in the same parent (Mn3+) lattice. These defects effectively catalyze the reduction (ORR) and oxidation (OER) processes on the same electrode surface. This study is based on the results of a previous study on Mn2O3 that showed Mn2+ and Mn4+ as the active sites for ORR and OER processes, respectively. Our results show that BiMnOx is the most promising bifunctional catalyst with OER/ORR activities that are comparable to the individual activities of state-of-the-art commercial Pt or RuO2 catalysts. Stability tests show the catalyst to be stable for more than 3 h of continuous OER or ORR polarization. This work provides a pathway for the individual tuning of defects to control electrocatalytic activities, which opens up new possibilities for the rational design of many perovskite-based oxides.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c03585
The recently synthesized two-dimensional (2D) MoSi2N4 material with a proper band gap and excellent environmental stability promises potential optoelectronic applications. On the basis of first-principles calculations and electron–phonon interaction theory, we systematically analyze the structural, optical, carrier distribution and transport, and photocatalytic water-splitting properties of pristine and strained MoSi2N4 monolayers. They are all found to be dynamically stable. Their optical absorption efficiencies are very high for photon energy larger than the respective band gap. Surprisingly, the optical absorption coefficient of tensile MoSi2N4 is as large as 106 cm–1 across 300–880 nm. To the best of our knowledge, this is the best among optoelectronic materials in the visible region. In addition, compressive strain results in spatial separation of photogenerated electrons and holes, which is beneficial for increasing their separation rates. Transport properties indicate that the lifetime and mean free path (MFP) of photogenerated electrons and holes are, respectively, on the scale of several femtoseconds and within 1.5 nm. Tensile strain notably increases them, becoming comparable to conventional semiconductor Si. Finally, pristine and strained MoSi2N4 monolayers are predicated to be able to photooxidize and photoreduce H2O with proper band edges and H2O adsorption capacities. These systematic characterizations not only deepen understanding of the physical and optoelectronic properties of MoSi2N4 but also indicate promising applications of MoSi2N4 in electronics, optoelectronics, and photocatalytic water splitting.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c05531
Clathrate structures are sustained by a host lattice formed by hydrogen-bonding water molecules, which encapsulates guest molecules. Up to now, all water molecules in the host lattice are considered ice-like crystallized. Here, we discovered the occurrence of “liquid-like” water molecules and the resulting defects in (polar) tetrahydrofuran clathrates by liquid-state 1H NMR experiments. The liquid-like water molecules start occurring at 271 K, well below the apparent dissociation point (277 K) of the clathrate matrix, via extracting water molecules from the host lattice by host–guest H-bonding. We found an intriguing two-stage dissociation of the clathrate: Partial dissociation at 271 K converting one-third of water molecules into liquid-like followed by complete dissociation at 277 K. The clathrate structure is molecularly heterogeneous in the region between 271 K and 277 K. No liquid-like water exists in (nonpolar) cyclopentane clathrates. This work uncovers the essentiality of host–guest interaction for clathrate structures and the ability to tune their stability using polar molecules.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c04092
Compartmentalizing reagents within small droplets is promising for highly efficient conversion and simplified procedures in many biphasic chemical reactions. In this work, surface nanodroplets (i.e., less than 100 nm in their maximal height) were employed to quantitatively understand the size effect on the chemical reaction rate of droplets. In our systems, a surface-active reactant in pure or binary nanodroplets reacted with the reactant in the bulk flow. Meanwhile, the product was removed from the droplet surface. The shrinkage rate of the nanodroplets was characterized by analyzing the lateral size as a function of time, where the droplet size was solely determined by the chemical reaction rate under a given flow condition for the transport of the reactant and the product. We found that the overall kinetics increases rapidly with the decrease in droplet’s lateral radius R, as dR/dt ∼ R–2. The faster increase in the concentration of the product in smaller droplets contributes to accelerating reaction kinetics. The enhancement of reaction rates from small droplet sizes was further confirmed when a nonreactive compound was present inside the droplets without reducing the concentrations of the reactant and the product on the droplet surface. The results of our study improve the understanding of chemical kinetics with droplets. Our findings highlight the effectiveness of small droplets for the design and control of enhanced chemical reactions in a broad range of applications.
The Journal of Physical Chemistry C; doi:10.1021/acs.jpcc.1c02357
The prospect of aqueous polyethyleneimine-capped CdS quantum dots (QDs), in toxic metal-ion sensing, has been explored. Pb2+ binds strongly to the surface of the QDs facilitating ultrafast electron transfer. As a result, severe (∼90%) PL quenching is observed. Hot electron transfer plays an important role in the quenching process, as is elucidated by anticorrelation between the magnitude of ground-state bleach of the QDs and the concentration of Pb2+ ions, as well as the concurrent decrease in bleach rise time. A second major contribution is from electron transfer from conduction band edge, with a rate constant of 1.45 × 1011 s–1. Selectivity in this “turn-off” sensing process is governed by the exergonicity, quality of QD surface, nature of capping ligand, and its metal-ion binding properties. Engineering these factors is crucial for the development of QD-based selective and efficient metal-ion sensors.