Reaction between Pyridine and CH₃NH₃PbI₃: Surface-Confined Reaction or Bulk Transformation?

Pyridine molecules have been used to passivate surface Pb²⁺ sites of CH₃NH₃PbI₃, to recrystallize CH₃NH₃PbI₃, and to bleach CH₃NH₃PbI₃. However, these results contradict each other, as recrystallization and optical-bleach require transformation of bulk CH₃NH₃PbI₃, but surface passivation demands the confinement of the reaction at the surface region. The underlying mechanism for these seemly contradicting results is not yet understood. In this paper, we show, at 25 °C, partial pressure of pyridine vapor is a determining factor for its reaction behaviors with CH₃NH₃PbI₃: one can modify the surface region of CH₃NH₃PbI₃ by using pyridine vapor of pressure 1.15 torr or lower but can transform the whole bulk CH₃NH₃PbI₃ film with a pyridine vapor of 1.3 torr or higher. Our result is the first demonstration that the reaction modes, i.e., surface-confined reaction and bulk transformation, are very sensitive to the partial pressure of under-saturated pyridine vapor. Despite the different reaction behaviors, it is interesting that in all pressure ranges, pyridinium ion is a main product from the reaction between pyridine and CH₃NH₃PbI₃. The bulk transformation is due to the formation of a liquid-like film, which increases the mobility of species to catalyze the reaction between pyridine and CH₃NH₃PbI₃. It is important to note 1.3 torr is much smaller than the saturated vapor pressure of pyridine (20 torr at 25 °C). These findings provide a guidance in applying pyridine and other amines to functionalize and transform CH₃NH₃PbI₃ and other hybrid halide perovskites. It also highlights the critical role of fundamental studies in controllably modifying CH₃NH₃PbI₃

Probe Decomposition of Methylammonium Lead Iodide Perovskite in N₂ and O₂ by in Situ Infrared Spectroscopy

Packaging methylammonium lead iodide perovskite (MAPbI₃)-based solar cells with N₂ or dry air is a promising solution for its application in outdoor photovoltaics. However, the effect of N₂ and O₂ on the decomposition chemistry and kinetics of MAPbI₃ is not yet well-understood. With in situ Fourier transform infrared spectroscopy measurements, we show that the effective activation energy for the degradation of MAPbI₃ in N₂ is ∼120 kJ/mol. The decomposition of MAPbI₃ is greatly accelerated by exposure to O₂ in the dark. As a result of the synergistic effect between O₂ and a HeNe laser (633 nm), the degradation rate is further increased with photon flux. This synergistic effect reduces the effective activation energy of degradation of MAPbI₃ to ∼50 kJ/mol. The solid decomposition products after annealing in N₂ and O₂ at 150 °C or below do not have absorbance between 650 and 4000 cm^–1

Interface-Mediated Synthesis of Transition-Metal (Mn, Co, and Ni) Hydroxide Nanoplates

We report a general and efficient strategy to produce monodisperse transition-metal (Mn, Co, and Ni) hydroxide nanoplates with tunable composition through the interface-mediated growth process. It is worth noting that, using common nitrates as the precursors, the as-obtained nanoplates were prepared under hydrothermal conditions. Moreover, the possible formation mechanism of the transition-metal hydroxide nanoplates has also been investigated. Subsequently, the resulting transition-metal hydroxides can be eventually transformed into transition-metal oxide nanoplates and lithium-ion intercalation materials through solid-state reactions, respectively. Furthermore, the electrochemical properties of the resulting nanomaterials have also been discussed in detail. This protocol may be easily extended to fabricate many other metal hydroxide and oxide nanomaterials

Energy Upconversion in Lanthanide-Doped Core/Porous-Shell Nanoparticles

Here, we report upconversion nanoparticles with a core/porous-shell structure in which bulk emission and nanoemission are simultaneously observed. The activated porous shell can efficiently tune the bulk emission but has negligible influence on the nanoemission

Synthesis of phosphatidylcholine in rats with oleic acid-induced pulmonary edema and effect of exogenous pulmonary surfactant on its <i>De Novo</i> synthesis

<div><p>In mammals, oleic acid (OA) induces pulmonary edema (PE), which can initiate acute lung injury (ALI) and lead to acute respiratory distress syndrome (ARDS). Pulmonary surfactant (PS) plays a key role in a broad range of treatments for ARDS. The aim of the present investigation was to assess changes in the synthesis of phosphatidylcholine (PC) from choline and determine the effect of exogenous PS on its <i>de novo</i> synthesis in rats with OA-induced PE. Experimental rats were randomized into three groups, including a control group, OA-induced PE group, and OA-induced group treated with exogenous PS (OA-PS). Twenty-four rats were sacrificed 4 h after induction of the OA model, and tissue was examined by light and electron microscopy to assess the severity of ALI using an established scoring system at the end of the experiment. After 15 μCi ³H-choline chloride was injected intravenously, eight rats in each group were sacrificed at 4, 8, and 16 h. The radioactivity of ³H incorporated into total phospholipid (TPL) and desaturated phosphatidylcholine (DSPC) was measured in bronchoalveolar lavage fluid (BALF) and lung tissue (LT) using a liquid scintillation counter and was expressed as counts per minute (CPM). Results showed that TPL, DSPC, and the ratio of DSPC/total protein (TP) in lung tissue decreased 4 h after challenge with OA, but the levels recovered after 8 and 16 h. At 8 h after injection, ³H-TPL and ³H-DSPC radioactivity in the lungs reached its peak. Importantly, ³H-DSPC CPM were significantly lower in the PS treatment group (LT: Control: 62327 ± 9108; OA-PE: 97315 ± 10083; OA-PS: 45127 ± 10034, <i>P</i> < 0.05; BALF: Control: 7771 ± 1768; OA-PE: 8097 ± 1799; OA-PE: 3651 ± 1027, <i>P</i> < 0.05). Furthermore, DSPC secretory rate (SR) in the lungs was significantly lower in the PS treatment group at 4 h after injection (Control: 0.014 ± 0.003; OA-PE: 0.011 ± 0.004; OA-PS: 0.023 ± 0.006, <i>P</i> < 0.05). Therefore, we hypothesize that exogenous PS treatments may adversely affect endogenous <i>de novo</i> synthetic and secretory phospholipid pathways via feedback inhibition. This novel finding reveals the specific involvement of exogenous PS in endogenous synthetic and secretory phospholipid pathways during the treatment of ARDS. This information improves our understanding of how PS treatment is beneficial against ARDS and opens new opportunities for expanding its use.</p></div

Nanoscale Coating of LiMO₂ (M = Ni, Co, Mn) Nanobelts with Li⁺‑Conductive Li₂TiO₃: Toward Better Rate Capabilities for Li-Ion Batteries

By using a novel coating approach based on the reaction between MC₂O₄·<i>x</i>H₂O and Ti­(OC₄H₉)₄, a series of nanoscale Li₂TiO₃-coated LiMO₂ nanobelts with varied Ni, Co, and Mn contents was prepared for the first time. The complete, thin Li₂TiO₃ coating layer strongly adheres to the host material and has a 3D diffusion path for Li⁺ ions. It is doped with Ni²⁺ and Co³⁺ ions in addition to Ti⁴⁺ in LiMO₂, both of which were found to favor Li⁺-ion transfer at the interface. As a result, the coated nanobelts show improved rate, cycling, and thermal capabilities when used as the cathode for Li-ion battery

Changes in TPL and DSPC in lung tissue.

<p>Changes in TPL and DSPC in lung tissue.</p

Alveolar structure and schematic design of isotope tracing.

<p>³H-labeled methyl chloride choline is involved in surfactant phospholipid synthesis of alveolar type II cells. The level of ³H in phospholipids was monitored to detect the amount originating from endogenous phospholipid synthesis. The radioactivity of TPL and DSPC in BALF and LT indicates the total content of ³H-labeled choline chloride incorporated into TPL and DSPC, which reflects the newly synthesized TPL and DSPC and the body’s ability to synthesize PC. The secretory rate of TPL was expressed as the ratio of radioactivity in BALF and the whole lung (BALF+LT). The secretory rates of TPL and DSPC indicate the ability of alveolar type II epithelial cells to secrete PC into the alveolar space.</p

Electron microscopy observations of pulmonary surfactant layer (PSL) and vascular endothelial cells.

<p>A and D: Normal control group, B and E: OA-PE group, C and F: OA-PS treatment group. A, B, C: PSL; D, E, F: vascular endothelial cells.</p

Changes in ³H-TPL and ³H-DSPC levels in LT and BALF.

<p>A: Changes in ³H-TPL and ³H-DSPC levels in LT. B: Changes in ³H-TPL and ³H-DSPC levels in BALF. C: Changes in TPL SR and DSPC SR.</p