Confining Sulfur Species in Cathodes of Lithium–Sulfur Batteries: Insight into Nonpolar and Polar Matrix Surfaces

To alleviate the polysulfides shuttle effect in lithium–sulfur batteries (LSBs), the use of a functionalized carbon matrix with a polar surface has been widely reported to chemically bind the soluble polysulfides. However, whether and how such a polar carbon surface affects the overall cathode performance, particularly the initial discharge corresponding to the reduction of cyclooctasulfur (S₈), has not caught enough attention. By combining polar and nonpolar carbon matrix surfaces in different configurations through sandwiching sulfur species between two carbon matrix membranes, we found cells with dramatically different performance. The discharge process at different states, particularly the charge-transfer resistances corresponding to nonpolar S₈ and polar polysulfide intermediates and the final Li₂S, were investigated. The experimental results, further supported by first-principles density functional theory calculations, indicate that the adsorption energy and barrier for electron transfer together affect the electrochemical performance of LSBs, and therefore, a rational design that combines polar and nonpolar surfaces should be adopted

Comparing Graphene-TiO₂ Nanowire and Graphene-TiO₂ Nanoparticle Composite Photocatalysts

We demonstrate that uniform dispersion of TiO₂ on graphene is critical for the photocatalytic effect of the composite. The hydrothermal method was employed to synthesize TiO₂ nanowires (NW) and then fabricate graphene-TiO₂ nanowire nanocomposite (GNW). Graphene oxide (GO) reduction to graphene and hybridization between TiO₂ NWs and graphene by forming chemical bonding was achieved in a one-step hydrothermal process. Graphene-TiO₂ nanoparticle (NP) nanocomposite (GNP) was also synthesized. Photocatalytic performance and related properties of NP, NW, GNP, and GNW were comparatively studied. It was found that by incorporation of graphene, GNP and GNW have higher performance than their counterparts. More importantly, it was found that NWs, in comparison with NPs, have more uniform dispersion on graphene with less agglomeration, resulting in more direct contact between TiO₂ and graphene, and hence further improved electron–hole pairs (EHPs) separation and transportation. The adsorbability of GNW is also found to be higher than GNP. The result reveals that the relative photocatalytic activity of GNW is much higher than GNP and pure NWs or NPs

Rationally Designed Porous MnO_<i>x</i>–FeO_<i>x</i> Nanoneedles for Low-Temperature Selective Catalytic Reduction of NO_<i>x</i> by NH₃

In this work, a novel porous nanoneedlelike MnO_<i>x</i>–FeO_<i>x</i> catalyst (MnO_<i>x</i>–FeO_<i>x</i> nanoneedles) was developed for the first time by rationally heat-treating metal–organic frameworks including MnFe precursor synthesized by hydrothermal method. A counterpart catalyst (MnO_<i>x</i>–FeO_<i>x</i> nanoparticles) without porous nanoneedle structure was also prepared by a similar procedure for comparison. The two catalysts were systematically characterized by scanning and transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, ammonia temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT), and their catalytic activities were evaluated by selective catalytic reduction (SCR) of NO_<i>x</i> by NH₃. The results showed that the rationally designed MnO_<i>x</i>–FeO_<i>x</i> nanoneedles presented outstanding low-temperature NH₃-SCR activity (100% NO_<i>x</i> conversion in a wide temperature window from 120 to 240 °C), high selectivity for N₂ (nearly 100% N₂ selectivity from 60 to 240 °C), and excellent water resistance and stability in comparison with the counterpart MnO_<i>x</i>–FeO_<i>x</i> nanoparticles. The reasons can be attributed not only to the unique porous nanoneedle structure but also to the uniform distribution of MnO_<i>x</i> and FeO_<i>x</i>. More importantly, the desired Mn⁴⁺/Mn^<i>n</i>+ and O_α/(O_α + O_β) ratios, as well as rich redox sites and abundant strong acid sites on the surface of the porous MnO_<i>x</i>–FeO_<i>x</i> nanoneedles, also contribute to these excellent performances. In situ DRIFT suggested that the NH₃-SCR of NO over MnO_<i>x</i>–FeO_<i>x</i> nanoneedles follows both Eley–Rideal and Langmuir–Hinshelwood mechanisms

Highly Efficient Photocatalyst Based on a CdS Quantum Dots/ZnO Nanosheets 0D/2D Heterojunction for Hydrogen Evolution from Water Splitting

A novel CdS/ZnO heterojunction constructed of zero-dimensional (0D) CdS quantum dots (QDs) and two-dimensional (2D) ZnO nanosheets (NSs) was rationally designed for the first time. The 2D ZnO NSs were assembled into ZnO microflowers (MFs) via an ultrasonic-assisted hydrothermal procedure (100 °C, 12 h) in the presence of a NaOH solution (0.06 M), and CdS QDs were deposited on both sides of every ZnO NS in situ by using the successive ionic-layer absorption and reaction method. It was found that the ultrasonic treatment played an important role in the generation of ZnO NSs, while NaOH was responsible to the assembly of a flower-like structure. The obtained CdS/ZnO 0D/2D heterostructures exhibited remarkably enhanced photocatalytic activity for hydrogen evolution from water splitting in comparison with other CdS/ZnO heterostructures with different dimensional combinations such as 2D/2D, 0D/three-dimensional (3D), and 3D/0D. Among them, CdS/ZnO-12 (12 deposition cycles of CdS QDs) exhibited the highest hydrogen evolution rate of 22.12 mmol/g/h, which was 13 and 138 times higher than those of single CdS (1.68 mmol/g/h) and ZnO (0.16 mmol/g/h), respectively. The enhanced photocatalytic activity can be attributed to several positive factors, such as the formation of a Z-scheme photocatalytic system, the tiny size effect of 0D CdS QDs and 2D ZnO NSs, and the intimate contact between CdS QDs and ZnO NSs. The formation of a Z-scheme photocatalytic system remarkably promoted the separation and migration of photogenerated electron–hole pairs. The tiny size effect effectively decreased the recombination probability of electrons and holes. The intimate contact between the two semiconductors efficiently reduced the migration resistance of photogenerated carriers. Furthermore, CdS/ZnO-12 also presented excellent stability for photocatalytic hydrogen evolution without any decay within five cycles in 25 h

Development of Multifunctional Nanoencapsulated <i>trans</i>-Resveratrol/Chitosan Nutraceutical Edible Coating for Strawberry Preservation

Phytochemical nanoencapsulation for nutrient delivery and edible coatings for perishable food preservation are two emerging technologies. Leveraging the strong antimicrobial function of phytochemical nutrients, we propose convergent research to integrate the two technologies by embedding phytochemical-encapsulated nanoparticles in an edible coating on fresh fruits to achieve multiple functions. In particular, we report the study of an edible coating on strawberries that is composited of trans-resveratrol (R)-encapsulated nanoparticles (RNPs) embedded in a chitosan (CS) matrix. The biodegradable and biocompatible RNPs significantly increased the aqueous solubility of R by 150-fold and bioavailability by 3.5-fold after oral administration. Our results demonstrated the abilities of the RNP-embedded CS edible coating to diminish dehydration, prevent nutrient loss, inhibit microbe growth, increase nutraceutical value, preserve strawberry quality, and extend shelf life during storage at both 22 and 4 °C. Such a phytochemical nanoencapsulation-based edible coating is promising for the dual purposes of enhancing nutrient delivery and preserving perishable foods

Polarization and Dielectric Study of Methylammonium Lead Iodide Thin Film to Reveal its Nonferroelectric Nature under Solar Cell Operating Conditions

Researchers have debated whether methylammonium lead iodide (MAPbI₃), with a perovskite crystal structure, is ferroelectric and therefore contributes to the current–voltage hysteresis commonly observed in hybrid perovskite solar cells (PSCs). We thoroughly investigated temperature-dependent polarization, dielectric, and impedance spectroscopies, and we found no evidence of ferroelectric effect in a MAPbI₃ thin film at normal operating conditions. Therefore, the effect does not contribute to the hysteresis in PSCs, whereas the large component of ionic migration observed may play a critical role. Our temperature-based polarization and dielectric studies find that MAPbI₃ exhibits different electrical behaviors below and above ca. 45 °C, suggesting a phase transition around this temperature. In particular, we report the activation energies of ionic migration for the two phases and temperature-dependent permittivity of MAPbI₃. This study contributes to the understanding of the material properties and device performance of hybrid perovskites

An example image including FSD (a), QISS (b), and CE-MRA (c) from which the SNR, CNR, and vessel sharpness were derived.

<p>The circles drawn in the cross-section of arterial segments (yellow circles) and the adjacent tissue (red circles) indicated the representative ROIs for the calculation of signal intensity of arterial blood and tissue, respectively. The circles drawn in the background (green circles) indicated the representative large air ROI for the calculation of noise. The line drawn perpendicularly to the vessel wall indicated the representative user-selected line for the calculation of vessel sharpness.</p

Comparison of image quality of three calf arterial segments for NCE-MRA in 26 patients with diabetes.

<p>^aWilcoxon signed rank test.</p><p>Comparison of image quality of three calf arterial segments for NCE-MRA in 26 patients with diabetes.</p

The number of different kinds of artifacts for NCE-MRA in 26 patients with diabetes.

<p>The number of different kinds of artifacts for NCE-MRA in 26 patients with diabetes.</p

Comparison of the time efficiency of SNR (SNR _eff) and CNR (CNR _eff) between QISS and FSD with only dark and bright blood scan (a, b) or adding the phase-contrast and m1-scout scan (c, d)) in three arterial segments of the calf.

<p>Each column represents average measurements and error is shown as standard deviation. Asterisks indicated significant difference (P < 0.05). SNR: signal-to-noise ratio; CNR: contrast-to-noise ratio; QISS: quiescent-interval single-shot; FSD: flow-sensitive dephasing.</p