Photooxidation of polystyrene by O2 and N2O

Strips of polystyrene held in a flowing O₂ or N₂O atmosphere have been exposed to 240-600 nm radiation. The extent of photooxidation has been followed by x-ray photoelectron spectroscopy (XPS). Although N₂O is a more reactive gas than O₂, it produces a less oxidized polymer surface. This surprising observation can be correlated to the photochemistry occurring at the gas/polystyrene interface. © 1992 John Wiley & Sons, Inc.     

O2 reduction to H2O by the multicopper oxidases

In nature the four electron reduction of O2 to H2O is carried out by Cytochrome c oxidase (CcO) and the multicopper oxidases (MCOs). In the former, Cytochrome c provides electrons for pumping protons to produce a gradient for ATP synthesis, while in the MCOs the function is the oxidation of substrates, either organic or metal ions. In the MCOs the reduction of O2 is carried out at a trinuclear Cu cluster (TNC). Oxygen intermediates have been trapped which exhibit unique spectroscopic features that reflect novel geometric and electronic structures. These intermediates have both intact and cleaved O-O bonds, allowing the reductive cleavage of the O-O bond to be studied in detail both experimentally and computationally. These studies show that the topology of the TNC provides a unique geometric and electronic structure particularly suited to carry out this key reaction in nature.     

Direct Synthesis of H2O2 by a H2/O2 Fuel Cell

Direct synthesis of H₂O₂ solutions by a fuel cell method was reviewed. The fuel cell reactor of [O₂, gas-diffusion cathode electrolyte solutions Nafion membrane electrolyte solutions gas-diffusion anode, H₂] is very effective for formation of H₂O₂. The three-phase boundary (O₂(g)–electrode(s)–electrolyte(l)) in the gas-diffusion cathode is essential for efficient formation of H₂O₂. Fast diffusion processes of O₂ to the active surface and of H₂O₂ to the bulk electrolyte solutions are essential for H₂O₂ accumulation. The maxima H₂O₂ concentrations of 1.2 M (3.5 wt%) and 2.4 M (7.0 wt%) were accomplished by the heat-treated Mn-OEP/AC electrocatalyst with H₂SO₄ electrolyte and by the VGCF electrocatalyst with NaOH electrolyte, respectively, under short circuit conditions.     

Hyperthermal reactions of O and O2 with a hydrocarbon surface: direct C-C bond breakage by O and H-atom abstraction by O2

A C-C bond-breaking reaction has been observed when a beam containing hyperthermal oxygen was directed at a continuously refreshed saturated hydrocarbon liquid (squalane) surface. The dynamics of this C-C bond-breaking reaction have been investigated by monitoring time-of-flight and angular distributions of the volatile product, OCH3 or H2CO. The primary product is believed to be the methoxy radical, OCH3, but if this radical is highly internally excited, then it may undergo secondary dissociation to form formaldehyde, H2CO. Either the primary or the secondary product may scatter directly into the gas phase before thermal equilibrium with the surface is reached, or they may become trapped on the surface and desorb in thermal equilibrium with the surface. Direct, single-collision scattering events that produce a C-C bond-breaking product are described with a kinematic picture that allows the determination of the effective surface mass encountered by an incident O atom, the atom-surface collision energy in the center-of-mass frame, and the fraction of the center-of-mass collision energy that goes into translation of the scattered gaseous product and the recoiling surface fragment. The dynamical behavior of the C-C bond-breaking reaction is compared with that of the H-atom abstraction reaction, which was the subject of an earlier study. Another reaction, H-atom abstraction by O2 (which is present in the hyperthermal beam), has also been observed, and the dynamics of this reaction are compared with the inelastic scattering dynamics of O2 and the dynamics of H-atom abstraction by O. The dynamics involving direct inelastic and reactive scattering of O2 are also described in terms of a kinematic picture where the incident O2 molecule is viewed as interacting with a local region of the surface.     

Steady-state photocatalytic epoxidation of propene by O2 over V2O5SiO2 photocatalysts

A silica-supported, lowly loaded vanadium oxide (V2O5/SiO2) photocatalyst promotes the photocatalytic epoxidation of propene with O2 at steady state in a flow reactor system. Very little deep oxidation of propene into CO2 takes place over V2O5/SiO2, in contrast to the results obtained over a TiO2 photocatalyst in which total oxidation is the main path. With each loading, the sums of the selectivities into propene oxide (PO) and propanal (PA) at steady state were almost the same. The monomeric VO4 tetrahedral species dispersed on SiO2 yield PO under UV irradiation. The less dispersed vanadium oxide species on SiO2 promote the isomerization of PO into PA. We utilized a flow reactor system in which the short contact time reduced the isomerization and resultant decomposition of PO over the catalyst surface.     

Solar-to-H2O2 Catalyzed by Covalent Organic Frameworks

Benefiting from the excellent structural tunability, robust framework, ultrahigh porosity, and rich active sites, covalent organic frameworks (COFs) are widely recognized as promising photocatalysts in chemical conversions, and emerged in the hydrogen peroxide (H₂O₂) photosynthesis in 2020. H₂O₂, serving as an environmental-friendly oxidant and a promising liquid fuel, has attracted increasing researchers to explore its potential. Over the past few years, numerous COFs-based photocatalysts are developed with encouraging achievements in H₂O₂ production, whereas no comprehensive review articles exist to summarize this specific and significant area. Herein we provide a systematic overview of the advances and challenges of COFs in photocatalytic H₂O₂ production. We first introduce the priorities of COFs in H₂O₂ photosynthesis. Then, various strategies to improve COFs photocatalytic efficiency are discussed. The perspective and outlook for future advances of COFs in this emerging field are finally offered. This timely review will pave the way for the development of highly efficient COFs photocatalysts for practical production of value-added chemicals not limited to H₂O₂.     

酮-过氧化氢体系对烯烃的环氧化

过氧化酮是优良的烯烃环氧化试剂,可将烯烃氧化成环氧化物。在这些反应中,所用的氧化剂都是过硫酸氢钾或商品Oxone^[1-6]。用其它氧化剂与酮生成过氧化酮使烯烃环氧化的报道很少^[7,8],只有一例是使用过氧化氢作氧化剂的,但其只研究了一种酮与过氧化氢对烯烃的环氧化^[8]。本文使用价格便宜,且没有污染的过氧化氢取代Oxone,与酮反应形成的过氧化酮使烯烃环氧化,并首次研究了一系列酮化合物与过氧化氢组成的催化体系对烯烃的环氧化反应,考察了各种酮的催化活性。     

Sm2O3改性对S2O2-8/ZrO2-SiO2固体超强酸催化剂性能的影响

硫酸促进型固体超强酸催化剂具有极强的酸性,制备简单,在酯化、烷基化、酰基化等有机反应中催化活性高,可重复使用,对设备腐蚀小,环境友好,是一类具有广阔应用前景的新型绿色催化材料,已成为固体超强酸研究的热点之一。然而,目前该类催化剂使用成本高、比表面小、含硫基团容易流失、稳定性差,阻碍了其在工业上的推广和应用。为了探索和改善其催化性能,近年来多组分氧化物的固体超强酸开始引起人们的关注。     

非均匀成核法表面包覆氧化铝的尖晶石LiMn2O4研究

采用高温固相法合成尖晶石LiMn2O4,以非均匀成核方式对其进行包覆氧化铝的表面处理.通过XRD、SEM、粒度分析等技术对表面处理前后的LiMn2O4进行表征,分析了表面处理前后LiMn2O4物理特性的变化,并结合电化学性能测试,研究了表面处理工艺对LiMn2O4电化学容量与循环性能的影响.未经表面处理的LiMn2O4在1 C倍率下初期放电容量为86.5 mA•h•g－1,50次循环充放电后容量衰减26.3％.表面包覆0.5％、1％(w)氧化铝的LiMn2O4在1 C倍率下的初期放电容量分别为96.0、80.1 mA•h•g－1,经过50次循环后,容量分别降低7.0％、5.6％.实验结果表明,表面处理后的LiMn2O4循环性能显著提高,而且随着氧化物含量的增加,循环性能增强,但放电容量降低.     

Loss of CH2O and H2O by stepwise mechanisms in mass spectrometry

Experimental evidence demonstrating reversible hydrogen transfer between specific positions in the molecular ions of anisole and o-toluic acid suggests stepwise mechanisms for the loss of CH₂O and H₂O, respectively. Added support for a stepwise mechanism for the loss of CH₂O is found in the mass spectra of pyridine and quinoline analogues.     

O2/n2-separation by polymer-bound cobalt complexes

Facilitated or complexation-mediated transport of oxygen in the solid membrane containing a fixed carrier was described, by using the polymer-bound cobalt Schiff's base chelate (CoS) and cobaltporphyrin (CoP). α³ β-Substituted cobaltporphyrin derivatives were synthesized: The oxygen-binding reaction to cobalt was affected by the cavity structure on porphyrin, i.e., unbulky amido-substituted groups such as acetylamido- and acrylamido-substituents enhanced oxygen-binding and -dissociation rate constant or provided an oxygen-binding pathway. Oxygen transport through the membranes of these polymer-bound CoP derivatives was selectively augmented due to the rapid and reversible oxygen-binding. Diffusion constants via the fixed CoPs correlated to the characteristics of oxygen-binding reaction.     

Temperature-programmed reduction of V2O5 and coprecipitated V2O5−TiO2 by hydrogen

Temperature-programmed reductions (TPR) with H₂ of both pure V₂O₅ and coprecipitated V₂O₅?TiO₂ systems with different titanium concentrations was performed. The original and the reduced samples following each TPR step were characterized by X-ray diffraction, Fourier transform infrared analysis and scanning electron microscopy. Within the temperature range in which TPR analysis was carried out (100–600°C) the V₂O₅ phase was reduced in two or three steps, while no variation in the TiO₂ phase (anatase or rutile) was observed. In the first reduction step only superficial reduction of the oxides was detected. In the following steps, the H₂ reacted with oxygen atoms of the V=O and V?O?V bonds. This led to important changes in the structure and morphology of the system. The experimental evidence allowed the conclusion that titanium stabilizes certain phases of vanadium oxides in which vanadium appears as V(+4) or as a mixture of V(+4) and V(+5). Moreover, when moderate and high titanium concentrations were used, the reduction temperature of the bulk V₂O₅ decreased markedly.     

Preparation of Cr2O3-Al2O3 Solid Solutions by Reactive Magnetron Sputtering

 (Al,Cr)₂O₃ layers were deposited on cemented carbide insert tips at a substrate temperature of 500 °C by means of reactive magnetron sputtering. An Al target was sputtered in RF mode and a Cr target in DC mode simultaneously in an oxygen/argon plasma. The influence of the Al and Cr sputter power and of the oxygen partial pressure on composition and structure of the (Al,Cr)₂O₃ layers as well as on the binding states of their components were investigated. Special attention was paid to the interpretation of the O ls and O-KLL fine structure and peak shifts. For the binary phases γ-Al₂O₃ and Cr₂O₃, a good agreement with literature values was observed in each case. In case of the ternary phases a continuous shift of the energetic position of the O1s peak, the O-KL₂₃L₂₃ transition and the modified Auger parameter α ′ of oxygen between the two binary phases γ-Al₂O₃ and Cr₂O₃ could be detected, indicating a wide range of solid solubility between Al₂O₃ and Cr₂O₃. As revealed by grazing incidence X-ray diffraction, the crystallinity of the ternary phases is less pronounced as compared to the binaries and increases with increasing oxygen flow rate.     

Thermal Decomposition of CF3C(O)O2NO2, CClF2C(O)O2NO2, CCl2FC(O)O2NO2, and CCl3C(O)O2NO2

Haloacetyl, peroxynitrates are intermediates in the atmospheric degradation of a number of haloethanes. In this work, thermal decomposition rate constants of CF₃C(O)O₂NO₂, CClF₂C(O)O₂NO₂, CCl₂FC(O)O₂NO₂, and CCl₃C(O)O₂NO₂ have been determined in a temperature controlled 420 l reaction chamber. Peroxynitrates (RO₂NO₂) were prepared in situ by photolysis of RH/Cl₂/O₂/NO₂/N₂ mixtures (R = CF₃CO, CClF₂CO, CCl₂FCO, and CCl₃CO). Thermal decomposition was initiated by addition of NO, and relative RO₂NO₂ concentrations were measured as a function of time by long-path IR absorption using an FTIR spectrometer. First-order decomposition rate constants were determined at atmospheric pressure (M = N₂) as a function of temperature and, in the case of CF₃C(O)O₂NO₂ and CCl₃C(O)O₂NO₂, also as a function of total pressure. Extrapolation of the measured rate constants to the temperatures and pressures of the upper troposphere yields thermal lifetimes of several thousands of years for all of these peroxynitrates. Thus, the chloro(fluoro)acetyl peroxynitrates may play a role as temporary reservoirs of Cl, their lifetimes in the upper troposphere being limited by their (unknown) photolysis rates. Results on the thermal decomposition of CClF₂CH₂O₂NO₂ and CCl₂FCH₂O₂NO₂ are also reported, showing that the atmospheric lifetimes of these peroxynitrates are very short in the lower troposphere and increase to a maximum of several days close to the tropopause. The ratio of the rate constants for the reactions of CF₃C(O)O₂ radicals with NO₂ and NO was determined to be 0.64 ± 0.13 (2σ) at 315 K and a total pressure of 1000 mbar (M = N₂). © 1994 John Wiley & Sons, Inc.     

复合光催化材料H3PW122O40/Ta2O5光催化降解染料的研究

采用溶胶-凝胶法制备了半导体型金属氧化物Ta2O5,并通过浸渍法与杂多酸H,PW12O40复合,获得了纳米复合光催化材料H3PW12O40/Ta2O5.通过1CP-AES、FT-lR、N2吸附、Tc等手段对其组成、结构及其表面物理化学性质进行了表征,并在可见光下考察了该复合材料对可溶性染料罗丹明B和亚甲基蓝的光催化活性.实验结果表明,该复合材料存可见光下有较好的光催化活性,其中,H3PW12O40/Ta2O5在180min内对亚甲基蓝的光催化降解转化率达到78%.     

Photoelectrochemical properties of Fe2O3-Nb2O5 films prepared by sol-gel method

Fe2O3-Nb2O5 coating films of various Nb/(Fe + Nb) mole ratios were prepared on nesa silica glass substrates from Fe(NO3)3.9H2O - NbCl5 - CH3(CH2)2CH2OH - CH3COOH solutions by the sol-gel method. The photoanodic properties were studied in a three-electrode cell with an aqueous buffer solution of pH = 7 as the supporting electrolyte. The crystalline phases identified were alpha-Fe2O3 (Nb/(Fe + Nb) = 0), alpha-Fe2O3 + FeNbO4 (Nb/(Fe + Nb) = 0.25), FeNbO4 (Nb/(Fe + Nb) = 0.5), FeNbO4 + Nb2O5 (Nb/(Fe + Nb) = 0.75), and Nb2O5 (Nb/(Fe + Nb) = 1). When the Nb/(Fe + Nb) mole ratio increased from 0 to 0.25, the crystalline phases changed from alpha-Fe2O3 to alpha-Fe2O3 + FeNbO4, the photoanodic current under white light illumination increased, and the photoanodic current under monochromatized light illumination increased in both visible and ultraviolet regions. When the Nb/(Fe + Nb) ratio increased over 0.25, the crystalline phases changed to FeNbO4, FeNbO4 + Nb2O5, or Nb2O5, and the photoanodic current decreased. The sample consisting of alpha-Fe2O3 and FeNbO4 (Nb/(Fe + Nb) = 0.25) exhibited photoresponse extending to 600 nm and an IPCE of 18% at a wavelength of 325 nm.