Radiative Cooling Face Mask

Radiative cooling is a zero energy consumption surface cooling technology, which appears to be a viable option for the development of radiative cooling face masks. After the COVID-19 pandemic, face masks have become crucial protective equipment in our daily lives, protecting from inhalation of fine particulate matter (PM) and also viruses. However, wearing conventional face masks for a long time is very unpleasant due to swelter on the face, especially in the outdoor sunlight environment. In this study, a radiative cooling polymer-based composite material (PCM) face mask has been designed and demonstrated experimentally to enhance the wearing comfort of the users including protection from PM and viruses. With a single layer of the silver nanoparticle coating, a PCM face mask has high efficiency to block sunlight by reducing solar transmittance and emit radiation by higher IR emissivity. Additionally, outdoor measurements with a simulated skin under the sun was carried out, and the PCM face mask showed a notable 4 °C cooling impact in comparison to the bare mask

Understanding the Conduction Mechanism of the Protonic Conductor CsH₂PO₄ by Solid-State NMR Spectroscopy

Local dynamics and hydrogen bonding in CsH₂PO₄ have been investigated by ¹H, ²H, and ³¹P solid-state NMR spectroscopy to help provide a detailed understanding of proton conduction in the paraelectric phase. Two distinct environments are observed by ¹H and ²H NMR, and their chemical shifts (¹H) and quadrupolar coupling constants (²H) are consistent with one strong and one slightly weaker H-bonding environment. Two different protonic motions are detected by variable-temperature ¹H MAS NMR and <i>T</i>₁ spin–lattice relaxation time measurements in the paraelectric phase, which we assign to librational and long-range translational motions. An activation energy of 0.70 ± 0.07 eV is extracted for the latter motion; that of the librational motion is much lower. ³¹P NMR line shapes are measured under MAS and static conditions, and spin–lattice relaxation time measurements have been performed as a function of temperature. Although the ³¹P line shape is sensitive to the protonic motion, the reorientation of the phosphate ions does not lead to a significant change in the ³¹P CSA tensor. Rapid protonic motion and rotation of the phosphate ions is seen in the superprotonic phase, as probed by the <i>T</i>₁ measurements along with considerable line narrowing of both the ¹H and the ³¹P NMR signals

Revealing Local Dynamics of the Protonic Conductor CsH(PO₃H) by Solid-State NMR Spectroscopy and First-Principles Calculations

A joint study incorporating multinuclear solid-state NMR spectroscopy and first-principles calculations has been performed to investigate the local structure and dynamics of the protonic conductor CsH­(PO₃H) in the paraelectric phase. The existence of the superprotonic phase (>137 °C) is clearly confirmed by NMR, in good agreement with the literature. The variable-temperature ¹H, ²H, and ³¹P NMR data further reveal a distribution of motional correlation times, with isotropic rotation of the phosphite ion being observed below the superprotonic phase transition for a small but gradually increasing subset of anions. This isotropic rotation is associated with fast local protonic motion, with the distribution of correlation times being tentatively assigned to internal defects or surface adsorbed H₂O. The phosphite ion dynamics of the majority slower subset of phosphite ions is quantified through analysis of variable-temperature ¹⁷O spectra recorded from 34 to 150 °C, by considering a model for the pseudo <i>C</i>₃ rotation of the phosphite ion around the P–H bond axis below the phase transformation. An extracted activation energy of 0.24 ± 0.08 eV (23 ± 8 kJ mol^–1) for this model was obtained, much lower than that reported from proton conductivity measurements, implying that no strong correlation exists between long-range protonic motion and <i>C</i>₃ rotations of the phosphite. We conclude that proton conduction in CsH­(PO₃H) in the paraelectric phase is governed by the activation energy for exchange between donor and acceptor oxygen sites, rotation of the phosphite units, and the lack of isotropic rotation of the phosphite ion. Surprisingly, coalescence of ¹⁷O NMR resonances, as would be expected for rapid isotropic reorientations of all phosphite groups, is not observed above the transition. Potential reasons for this are discussed

Probing Oxide-Ion Mobility in the Mixed Ionic–Electronic Conductor La₂NiO_4+δ by Solid-State ¹⁷O MAS NMR Spectroscopy

While solid-state NMR spectroscopic techniques have helped clarify the local structure and dynamics of ionic conductors, similar studies of mixed ionic–electronic conductors (MIECs) have been hampered by the paramagnetic behavior of these systems. Here we report high-resolution ¹⁷O (<i>I</i> = 5/2) solid-state NMR spectra of the mixed-conducting solid oxide fuel cell (SOFC) cathode material La₂NiO_4+δ, a paramagnetic transition-metal oxide. Three distinct oxygen environments (equatorial, axial, and interstitial) can be assigned on the basis of hyperfine (Fermi contact) shifts and quadrupolar nutation behavior, aided by results from periodic DFT calculations. Distinct structural distortions among the axial sites, arising from the nonstoichiometric incorporation of interstitial oxygen, can be resolved by advanced magic angle turning and phase-adjusted sideband separation (MATPASS) NMR experiments. Finally, variable-temperature spectra reveal the onset of rapid interstitial oxide motion and exchange with axial sites at ∼130 °C, associated with the reported orthorhombic-to-tetragonal phase transition of La₂NiO_4+δ. From the variable-temperature spectra, we develop a model of oxide-ion dynamics on the spectral time scale that accounts for motional differences of all distinct oxygen sites. Though we treat La₂NiO_4+δ as a model system for a combined paramagnetic ¹⁷O NMR and DFT methodology, the approach presented herein should prove applicable to MIECs and other functionally important paramagnetic oxides

Adsorption Behavior of Dyestuffs on Hollow Activated Carbon Fiber from Biomass

<div><p>This study focuses on the adsorption behavior of typical dyestuffs (methylene blue and reactive black 5) on hollow activated carbon fibers (ACFs) obtained from Kapok- and Hasuo-seed based biomass. It was found that the adsorption of dyestuffs on ACFs increased with increasing pH and temperature. In addition, the Hasuo-seed based ACFs showed higher adsorption capacities than the Kapok-seed based ACFs for dyestuffs. It was also determined from the adsorption energy distribution results that the ACFs are having energetically heterogeneous surfaces. The results clearly indicated that the prepared ACF in this study could efficiently remove dyes dissolved in water.</p></div

The Effect of Water on Quinone Redox Mediators in Nonaqueous Li‑O₂ Batteries

The parasitic reactions associated with reduced oxygen species and the difficulty in achieving the high theoretical capacity have been major issues plaguing development of practical nonaqueous Li-O₂ batteries. We hereby address the above issues by exploring the synergistic effect of 2,5-di-<i>tert</i>-butyl-1,4-benzoquinone and H₂O on the oxygen chemistry in a nonaqueous Li-O₂ battery. Water stabilizes the quinone monoanion and dianion, shifting the reduction potentials of the quinone and monoanion to more positive values (vs Li/Li⁺). When water and the quinone are used together in a (largely) nonaqueous Li-O₂ battery, the cell discharge operates via a two-electron oxygen reduction reaction to form Li₂O₂, with the battery discharge voltage, rate, and capacity all being considerably increased and fewer side reactions being detected. Li₂O₂ crystals can grow up to 30 μm, more than an order of magnitude larger than cases with the quinone alone or without any additives, suggesting that water is essential to promoting a solution dominated process with the quinone on discharging. The catalytic reduction of O₂ by the quinone monoanion is predominantly responsible for the attractive features mentioned above. Water stabilizes the quinone monoanion via hydrogen-bond formation and by coordination of the Li⁺ ions, and it also helps increase the solvation, concentration, lifetime, and diffusion length of reduced oxygen species that dictate the discharge voltage, rate, and capacity of the battery. When a redox mediator is also used to aid the charging process, a high-power, high energy density, rechargeable Li-O₂ battery is obtained