离子刻蚀法制备具有高效催化性能的m-Bi2O4/BiOCl p-n异质结催化剂

光催化技术作为一种绿色的环境修复方法而备受关注,它直接利用太阳光作为能源,可有效地降解有机污染物.铋系化合物具有化学稳定性强、抑制光腐蚀、无毒和来源广泛等优点,被认为是一种环境友好的光催化剂,广泛用于降解染料、苯酚和其他有机污染物.BiOCl具有独特的内部结构,可形成内电场促进电子和空穴的移动,抑制其复合.但是BiOCl本身带隙能过大,只能被紫外光激发,对光的利用率较低,限制了其在环境治理中的应用.近两年来发现,m-Bi2O4带隙能小,可吸收大波长的可见光,催化性能好.为充分发挥m-Bi2O4的优异性质,改善BiOCl的性能,本文将BiOCl与m-Bi2O4复合制得新型催化剂,降低催化剂的带隙能,增强对光的吸收,提高量子效率,促进光生载流子的分离,抑制电子-空穴复合,从而提高催化剂性能,加速降解反应进程.本文通过离子刻蚀法制备具有p-n异质结的m-Bi2O4/BiOCl复合催化剂,通过调节HCl的加入量制得不同比例的催化剂,并考察了其在可见光下催化降解MO(甲基橙)的性能.结果表明,m-Bi2O4/BiOCl复合催化剂在可见光下表现出优异的光催化降解MO和四环素的性能,反应10内min可降解95％的MO,反应150 min内四环素的降解率为85.5％;该复合催化剂对MO和四环素的光降解效率分别是纯BiOCl的52.3和4.9倍.活性自由基捕获实验表明,空穴在光催化降解过程中起最主要的作用,其次是超氧自由基,羟基自由基对降解反应也起到一定的作用.采用XRD,SEM,EDS,TEM,SAED,FT-IR,Raman,XPS,BET,UV-vis和光电流等表征方法分析了催化剂的结构、形貌、化学组成、元素价态、孔结构、带隙能、光学性质和载流子复合效率.结果表明,与BiOCl的斜四方体相比,m-Bi2O4/BiOCl复合催化剂呈现纳米片状结构,氯离子进入晶格的内部,颜色也由BiOCl原来的深褐色变为黄色.m-Bi2O4/BiOCl为介孔结构,比表面积为112.90 m2/g,其吸收波长红移,由紫外光扩展至可见光区域,带隙能也由3.2降低为1.87 eV,能带弯曲形成p-n异质结,提高了电子-空穴的转移效率,抑制其复合;m-Bi2O4/BiOCl的光电流密度高于m-Bi2O4和BiOCl,电子-空穴的分离效率更高,因而其催化性能更优越.     

Applications of the channel flow cell for UV-visible spectroelectrochemical studies. Part 2: Transient signals

The use of the channel flow cell for ultraviolet-visible (UV-vis) spectroelectrochemical experiments has been developed to determine the diffusion coefficients of electrogenerated species by means of monitoring the transient absorbance response resulting from a potential step at a working electrode immediately upstream of the incident spectrophotometric beam. The technique is applied to measure the diffusion coefficient of tris(4-bromophenyl)amine (TBPA) radical cation in acetonitrile at 25°C. It is shown that the diffusion coefficient of electrogenerated TBPA radical cation (1.64 ± 0.02 × 10⁻⁵ cm² s⁻¹) is very close to that of the parent molecule (1.57 ± 0.03 × 10⁻⁵ cm² s⁻¹).     

Enantiomer separations by capillary GC on modified gyclodextrins

Three new chiral selectors, 6-tert-butyldimethylsilyl-2,3-diethyl-a-cyclodextrin, 6-tert-butyldimethylsilyl-2,3-diethyl- and dipropyl-β-cyclodextrin (TBDE-α-CD, TBDE-β-CD, TBDP-β-CD) were synthesized and tested as chiral stationary phases in capillary gas chromatography. TBDE-β-CD in particular showed a high enan-tioselectivity for test chiral compounds due to good solubility in a polar polysiloxane (OV-1701). Enantioselectivity obtained with TBDE-β-CD was compared with that of 6-tert-butyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrin (TBDM-β-CD). Better enantiose-lectivity was obtained with TBDE-P-CD than with TBDM-β-CD for the test chiral compounds studied. This is probably due to greater effect of the increased hydrophobicity of TBDE-β-CD which favors inclusion of the analytes than the effect of increased steric hindrance. With TBDP-β-CD the less polar lactones are well separated due most likely to increased hydrophobicity of the propyl groups while the more polar are not well resolved. For TBDP-β-CD it is likely that the unfavorable steric hindrance is predominant over the favorable hydrophobicity of the propyl groups, thus hindering the formation of inclusion complexes of the alcohols with TBDP-β-CD. TBDE-α-CD was also a valuable chiral selector for the separation of small chiral molecules such as simple secondary alcohols and nitro-substituted alcohols.     

Conformation and absolute configuration of nocathiacin I determined by NMR spectroscopy and chiral capillary electrophoresis

Nocathiacin I (BMS-249524) is a highly cross-linked thiazolyl peptide that displays potent activity against Gram-positive bacteria, including a number of antibiotic-resistant strains. This natural product contains 10 chiral centers. NMR studies have been performed to characterize the solution structure of nocathiacin I. A uniformly 13C,15N-labeled sample was used to obtain NMR assignments. Restrained simulated annealing calculations were performed by using accurately determined NOE distance restraints. All of the chiral centers were allowed to float during the simulated annealing protocol. Two clusters of structures were obtained that satisfy the NOE restraints very well and that are reasonably consistent with vicinal J-coupling constants. Within each cluster, all 10 chiral centers are uniquely defined. The two clusters are effectively mirror images of each other: all chiral centers that have the R(S) configuration in one cluster have the S(R) configuration in the other. The single threonine residue in nocathiacin I was subsequently determined to be l-threonine by chiral capillary electrophoresis, allowing the absolute configurations of all 10 chiral centers to be defined.     

“手”望相助，志虑忠“醇”

Through three stories about alcohol antiseptics, "hand" messengers, characters of the article find the best choice of alcohol, and method of application. This article introduces proper ways to use alcohol antiseptics in daily life from the following three aspects. The ethanol and propanol can be used, the best concentration for daily use is 70%, and the optimal use of alcohols is considered under different circumstances.     

Synthesis of (Alkynyl)phenyl Porphyrins by Palladium Catalysed Cross Coupling Reactions

meso-para and meso-meta-(phenyltriflate)tritolyl porphyrins and the zinc complexes are coupled with alkynyl stannanes or terminal alkynes with palladium catalyst to give the meso-para and meta(m-alkynylphenyl)tritolylylkphenyl porphyrins as well as the zinc complex in good yields.