Pathway of oxygen incorporation from O2 in TiO2 photocatalytic hydroxylation of aromatics: oxygen isotope labeling studies

The hydroxylation process is the primary, and even the rate-determining step of the photocatalytic degradation of aromatic compounds. To make clear the hydroxylation pathway of aromatics, the TiO(2) photocatalytic hydroxylation of several model substrates, such as benzoic acid, benzene, nitrobenzene, and benzonitrile, has been studied by an oxygen-isotope-labeling method, which can definitively assign the origin of the O atoms (from oxidant O(2) or solvent H(2)O) in the hydroxyl groups of the hydroxylated products. It is found that the oxygen source of the hydroxylated products depends markedly on the reaction conditions. The percentage of the products with O(2)-derived hydroxyl O atoms increases with the irradiation time, while it decreases with the increase of substrate concentration. More intriguingly, when photogenerated valence-band holes (h(vb)(+)) are removed, nearly all the O atoms (>97?%) in the hydroxyl groups of the hydroxylated products of benzoic acid come from O(2), whereas the scavenging of conduction-band electrons (e(cb)(-)) makes almost all the hydroxyl O atoms (>95?%) originate from solvent H(2)O. In the photocatalytic oxidation system with benzoic acid and benzene coexisting in the same dispersion, the percentage of O(2)-derived hydroxyl O atoms in the hydroxylated products of strongly adsorbed benzoic acid (ca. 30?%) is much less than in that of weakly adsorbed benzene (phenol) (>60?%). Such dependences provide unique clues to uncover the photocatalytic hydroxylation pathway. Our experiments show that the main O(2)-incorporation pathway involves the reduction of O(2) by e(cb)(-) and the subsequent formation of free (?)OH via H(2)O(2), which was usually overlooked in the past photocatalytic studies. Moreover, in the hydroxylation initiated by h(vb)(+), unlike the conventional mechanism, the O atom in O(2) cannot incorporate into the product through the direct coupling between molecular O(2) and the substrate-based radicals.     

Boron-assisted growth of silica nanowire arrays and silica microflowers for bendable capacitor application

Aligned-long silica nanowire arrays and microflowers were synthesized with boron as catalyst. Besides that parallel plate capacitors were fabricated using the silica nanowire mat as a dielectric. Their frequency response and mechanical properties were investigated.     

Photooxidation of dibenzothiophene and 4,6-dimethyldibenzothiophene sensitized by N-methylquinolinium tetrafluoborate: mechanism and intermediates investigation

Photooxidation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) sensitized by N-methylquinolinium tetrafluoborate (NMQ(+)BF4-) has been investigated in O2-saturated acetonitrile solutions. Nearly 100% oxidation of DBT and DMDBT was observed, and the oxidized products are predominantly composed of sulfoxides and sulfones, which are formed via photoinduced electron transfer (ET). Such ET processes were studied with fluorescence quenching of NMQ+, time-resolved transient absorption measurement, and ESR experiments. The fluorescence of NMQ+ is efficiently quenched by DBT and DMDBT via diffusion-controlled processes, with bimolecular quenching constants of 1.6 x 10(10) M(-1) s(-1) for DBT and 2.3 x 10(10) M(-1) s(-1) for DMDBT. The electron-transfer nature of the quenching is evidenced by the transient absorption measurement of the neutral radical NMQ*, which is formed by electron transfer from the substrates (DBT or DMDBT) to the excited singlet state of NMQ+. The ESR spectra of the superoxide radical anion (O2*-) trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in the photooxygenation of DBT and DMDBT as well as their sulfoxides manifest that O2 traps an electron from NMQ* to form O2*-. The fact that the formation of sulfoxides and sulfones is greatly suppressed in the presence of benzoquinone (BQ), an efficient electron trap for NMQ* and O2*-, further indicates an ET process in the photooxidation of DBT and DMDBT. As inferred from the control experiments, the role of singlet oxygen (1O2) in the photooxidation is negligible. The intermediates responsible for the formation of sulfoxides and sulfones have been examined in detail.     

Efficient degradation of toxic organic pollutants with Ni2O3/TiO(2-x)Bx under visible irradiation

To promote efficient use of solar energy, many studies have focused on the modification of TiO2 to extend its spectral response to visible region. Here we report a combined modification of TiO2 by two components: the nonmetal element boron and the metal oxide Ni2O3. The photocatalyst presents high photocatalytic activity in the visible region, which can efficiently degrade and mineralize toxic organic pollutants such as trichlorophenol (TCP), 2,4-dichlorophenol (2,4-DCP), and sodium benzoate. The dechlorination and mineralization results indicate the photocatalytic pathway via visible light excitation. The study demonstrates that the modification of TiO2 both to extend its spectral response to the visible region and to improve its catalytic efficiency can be achieved by doping with boron, a nonmetal, and Ni2O3, a metal oxide.     

SHIELD程序靶设计的实用化及其在W靶参数设计中的应用

将GEANT3.21中的几何设计和图示技术移植到SHIELD程序中,并在此基础上对几种具有复杂构造的W靶进行参数设计的初步研究.     

基于几何级数展开的鬼波压制方法

海上拖缆地震数据采集,检波器位于海平面以下,由于海平面的反射作用,检波器接收到的除了上行的一次波,还包括下行的鬼波,因为一次波和鬼波的干涉作用,导致地震信号的有效频带变窄,分辨率降低。为了恢复信号的有效频带,需要进行鬼波压制的宽频处理。该文提出了一种基于逆鬼波算子几何级数展开的鬼波压制技术。几何级数的每一项都是一个波场传播算子,级数的叠加可以实现鬼波的压制,通过对几何级数的截断,可以得到只含上行波的反射信号。数值算例证明了该文方法的有效性,因为波场延拓算子在频率波数域进行,借助快速傅里叶变换,该文方法的效率很高。     

Detoxification mechanisms of a combination of Semen Strychni and Radix Glycyrrhizae: A comparative analyses of differences in toxicokinetics and tissue distribution after oral administration of Semen Strychni-Radix Glycyrrhizae decoction

To evaluate the detoxification effect of a combination of Radix Glycyrrhizae (GU) and Semen Strychni (SN) from toxicokinetics and drug tissue distribution perspectives, decoctions of processed SN and codecoction of SN and GU (SGN) were prepared, and an HPLC-ESI-MS/MS method was developed to monitor the severe exposure level in 1-month toxicokinetics and tissue distribution experiments to detect brucine and strychnine in rats. The toxicokinetic characteristics and tissue distribution before and after the addition of GU were analyzed. The method was successfully applied to evaluate the toxicokinetics and tissue distribution before and after the combination of SN and GU. The results show that GU decreased the blood concentration of toxic components in SN, and a double peak was observed in the drug time curve. The results of tissue distribution show that a combination of GU and SN significantly decreased the accumulation of toxic substances in metabolic organs and accelerated the clearance of toxic substances in the brain. These results provide a reference for the toxicity reduction mechanism of GU combined with SN.     

Understanding interactions between poly(styrene-co-sodium styrene sulfonate) and single-walled carbon nanotubes

Understanding formation mechanisms of hybrids of carbon nanotubes (CNTs) wrapped by polymers and their interactions is critical in modifying solubility of CNTs in aqueous solution and developing new nanotube-based polymer materials. In the present work, we investigate the structural details of poly(styrene-co-sodium styrene sulfonate) (PSS) wrapping around the CNT and the interactions between the PSS chain and the CNT using molecular dynamics (MD) simulations. The fraction of sulfonated groups significantly influences the wrapping conformations of the PSS chain. Due to limited time scale in the MD simulations, two different initial conformations of the chains are introduced to explore the effect of the initial state on the wrapping behavior. When the chains initially wrap around the CNT in a perfect helix manner, more compact pseudo-helical conformations are obtained. For initial straight line arrangement of the chain monomers, the chains adopt looser wrapping conformations. The free-energy analysis and binding interaction of the PSS chain on the CNT surface take a glance on the relationship between the conformational transition of the chain and the energy evolution.