仿生多孔 MgO-TiO2合成及其光催化 CO2还原性能

研究表明, MgO能够活化吸附在其表面的 CO2分子,促进 HCO3–的生成,而在 H原子存在的条件下, HCO3–为 CO2光催化还原为碳氢化合物和 CO的活性中间体. CO2为对称的直线型分子,在化学反应中表现出极高的稳定性,成为阻碍人工光合作用发展的重要因素.在设计新型光催化剂时,复合 MgO可能会有效提高催化剂的活性.绿色植物的叶片结构或茎中存在大量尺寸不一的多孔结构,以利于植物生命活动(包括光合作用和呼吸作用)过程中气体的有效扩散和水分、营养物质的运输. TiO2因其良好的化学稳定性、无毒且成本低廉,在人工光合成领域得到广泛的研究.因此,本文以空心菜杆为模板, TiO2为主体催化剂,应用溶胶-凝胶法,通过调节 MgO的含量合成了一系列仿生多孔结构的 MgO-TiO2复合物.
　　样品的 X射线衍射、X射线光电子能谱和高分辨透射镜表征结果证明,生物模板空心菜杆在550oC下煅烧5 h之后可被完全移除,且 MgNO3分解为 MgO,生成 TiO2-MgO复合物.从扫描电镜中可观察到,以空心菜杆为模板合成的 MgO-TiO2,模板的空心管状结构得以保持,在长度和宽度上有一定程度的皱缩.横截面和纵截面图说明样品很好地复制了空心菜杆的导管和筛管组成的多孔结构.同时N2吸附-脱附结果表明,样品中存在3–5 nm的介孔结构.同时我们发现,由于 MgO的加入,0.05% MgO-TiO2复合物的比表面积比 TiO2减少了18%,之后随着 MgO含量的增加, MgO-TiO2复合物的比表面积呈下降趋势.标准状况下,测试了样品对 CO2的吸附量.结果表明,随 MgO含量的升高,吸附量先增加后减小,且 MgO-TiO2复合物的吸附量为 TiO2的1.3–1.8倍.结合样品比表面积及原位红外光谱测试结果,说明样品的 CO2吸附量受 MgO的含量与样品的比表面积双重因素的影响. CO2吸附包括物理吸附和化学吸附,而且对于同种样品,吸附量与样品比表面积正相关.当 MgO-TiO2复合物的比表面积随着 MgO含量的增加而减小时, CO2吸附量却先增加后减小,表明 MgO的加入极大地促进了 CO2的化学吸附.以 MgO-TiO2复合物作为光催化剂将 CO2和 H2O还原为 CH4. CH4的总产量随着光照时间的增加而增加,10 h后的总产量随着 MgO含量的升高先增加后减少,与样品的 CO2吸附量的变化趋势相似但不完全相同.与 TiO2(6.5μmol/g)相比, MgO-TiO2复合物样品催化作用下的 CH4的最终产量均增大,活性最好的0.2% MgO-TiO2(18.7μmol/g)的产量达到了它的2.88倍,说明 MgO对 CO2具有活化作用,且活化后的 CO2更容易生成 CH4.综合结果表明, CO2在催化剂表面的吸附量、电子的表面迁移、反应活性位点等因素共同决定了催化剂的光催化活性.     

Calibration of the complex matrix effects on the sampling of polycyclic aromatic hydrocarbons in milk samples using solid phase microextraction

Solid phase microextraction (SPME), a simple, fast and promising sampling technique, has been widely used for complex sample analysis. However, complex matrices could modify the absorption property of coatings as well as the uptake kinetics of analytes, eventually biasing the quantification results. In the current study, we demonstrated the feasibility of a developed calibration method for the analysis of polycyclic aromatic hydrocarbons (PAHs) in complex milk samples. Effects of the complex matrices on the SPME sampling process and the sampling conditions were investigated. Results showed that short exposure time (pre-equilibrium SPME, PE-SPME) could increase the lifetime of coatings, and the complex matrices in milk samples could significantly influence the sampling kinetics of SPME. In addition, the optimized sampling time, temperature and dilution factor for PAHs were 10 min, 85 °C and 20, respectively. The obtained LODs and LOQs of all the PAHs were 0.1–0.8 ng/mL and 1.4–4.7 ng/mL, respectively. Furthermore, the accuracy of the proposed PE-SPME method for milk sampling was validated by the recoveries of the studied compounds in two concentration levels, which ranged from 75% to 110% for all the compounds. Finally, the proposed method was applied to the screening of PAHs in milk samples.     

贫燃条件 In-Ag/TiO2-γ-Al2O3催化 CO选择性还原NO

汽车尾气中主要污染成分 CO和 NOx可导致酸雨、光化学烟雾和臭氧空洞效应,对生物、环境及生态系统造成重大危害。污染源中 CO是性能优良的还原剂,如能不添加还原剂实现 CO催化还原 NOx,将成为最具经济技术优势的 NOx脱除技术。在富氧、低温条件下,利用 CO选择性催化还原 NOx为 N2,是目前选择性催化还原研究中的热点和难点。催化 CO还原 NOx常用的贵金属 Ir, Rh, Pt和Pd矿藏稀少,价格昂贵,有氧条件下活性急降,而分子筛催化剂和一些金属氧化物催化剂普遍存在反应温度高,尤其对 N2选择性差等问题。为解决上述问题,需寻找新的适合我国矿产资源的催化体系。研究发现,稀散金属基催化剂对氮氧化物的净化具有一定效果,因而可将我国的稀散金属资源优势转化为技术优势和经济优势。因此,本文以 TiO2-γ-Al2O3(TA)为载体, In/Ag为活性组分,采用等体积浸渍法制备了 InAg/TA以及 In/TA, Ag/TA和InAg/Al (γ-Al2O3为载体)催化剂,考察了贫燃条件下 CO选择性还原NO的催化活性。研究表明,双金属催化剂InAg/Al和 InAg/TA的活性比单金属催化剂In/TA和 Ag/TA高, In/TA催化剂中引入 Ag物种能降低起燃温度;另外,相比于InAg/Al催化剂, InAg/TA催化剂具有较高的催化活性,550?600°C时 N2产率超过60%,说明载体中引入TiO2可以提高催化剂活性。为了深入研究 InAg/TA催化剂中 Ag物种和TiO2对 In物种的作用,通过比表面测定、X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱、紫外-可见光吸收光谱、氢气程序升温还原、傅立叶变换红外线光谱等方法分析了催化剂结构和表面形态。结果表明, Ag物种可以提高 In物种的分散性, In和 Ag物种在 TA载体表面可以很好地分散,从而有利于提高催化活性。 In和 Ag物种在 TA载体表面以氧化态形式存在,并且 Ag物种可以提高 In物种表面含量,表面 In和 Ag物种含量越高,吸附活性位越多,催化活性越高;同时, TiO2也可以促进 NO吸附,从而提高 InAg/TA催化剂活性。 InAg/TA催化剂在450°C连续反应72 h进行稳定性测试,测试前后分别在50?600°C进行活性测试,并用 XRD和 TEM对反应后的催化剂进行表征测试。结果表明, InAg/TA催化剂具有较好的稳定性,连续反应前后催化剂活性基本保持不变,推测可能由于在有 CO和O2存在的体系中, Ag物种利用自身 Ag+与 Ag0之间的氧化还原反应抑制了活性组分 In2O3的还原和聚集,稳定了 In物种乃至催化剂活性。 InAg/TA催化剂用于贫燃条件下CO还原NO具有较好的催化效果,主要归因于催化剂活性组分分散性好,稳定性高,对NO吸附能力强。 Ag物种可以稳定In物种并提高其分散性, TiO2可以改善In物种和Ag物种的分散性并促进NO吸附。     

LaF3薄片的液相合成和表征

Single-crystalline LaF3 flakes was synthesized through a facile solution-phase approach in aqueous ammonia and ethylenediamine. Applying the thermal treatment at 100 ℃ for 20 h, the LaF3 recrystallized, grew epitaxially and precipitated into flakes in aqueous ammonia or ethylenediamine. The formation of flakes could be attributed to the coordination effect of the solvent.     

New enantiomeric polylactide-block-poly(butylene succinate)-block-polylactides: syntheses, characterization and in situ self-assembly

In situ self-assemblies of new biodegradable triblock PLLA-b-PBS-b-PLLA and PDLA-b-PBS-b-PDLA have been investigated in acetonitrile solution. At first, two series of PLLA-b-PBS-b-PLLA and PDLA-b-PBS-b-PDLA, respectively denoted as the P and Q triblock copolyester series, were prepared with fixed PBS block ((overline) M(n,NMR) = 6.9 kDa) and diverse enantiomeric PLLA/PDLA blocks. Further, their chemical structures and thermal properties were characterized by means of titration, nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), polarimeter, wide-angle X-ray diffraction (WAXD) and thermal analytical instruments. When mixing the synthesized enantiomeric copolyester pairs denoted as P(1)/Q(1) - P(8)/Q(8) in acetonitrile solution at 60 degrees C, in situ self-assemblies were found to happen for the P(4)/Q(4) to P(8)/Q(8) pairs, bearing longer enantiomeric PLA block lengths. DSC and WAXD analysis of the self-assembled microparticles demonstrated that PLLA/PDLA racemic crystals were formed for the P(5)/Q(5) - P(8)/Q(8) systems, as evidenced by their melting points over 200 degrees C, and a new X-ray diffraction peak detected at 2theta = 11.8 degrees . Moreover, morphological studies by scanning electron microscopy (SEM) indicated the formation of disk- or platelet-like microparticles. It was noted that the diameters of the microparticles self-assembled in situ decreased from 1.28-1.50 mum down to 480-660 nm, through tailoring the enantiomeric PLA block length. Other factors, such as a central PBS block, the enantiomeric block length and the preparation conditions were suggested to play important roles in the in situ self-assembly of these enantiomeric triblock copolyesters. These results provide a facile way to self-assemble hydrophobic, biodegradable microparticles, through tuning the important van der Waals stereocomplexation interactions between two enantiomeric blocks in solution.     

Studies on the atom transfer radical polymerization of a maleimide AB* monomer and modification of the halogen end groups

The atom transfer radical polymerization (ATRP) of an AB* monomer, N-(4-α-bromobutyryloxy phenyl)maleimide (BBPMI), was conducted using the complex of CuBr/2,2′-bipyridine as catalyst. The study of kinetics of polymerization and the growth behavior of macromolecules show that the polymerization proceeds rapidly in first 1 h and then slows down. The decrease in the rate of polymerization is ascribed to the poor reactivity of maleimide radicals from A* to initiate the polymerization of maleimide double bonds. The molecular weight of the resulting polymer also increases with the dosage of catalyst. The coincidence of molecular weight determined by hydrogen proton nuclear magnetic resonance spectroscopy (¹H NMR) and gel permeation chromatography (GPC) proves that the resulting polymer is of linear structure, which is further verified by ¹³C NMR measurement and high performance liquid chromatography (HPLC) analysis of the hydrolysate of the resulting polymer. The stabilization modification of the halogen end groups of the resulting polymer by free-radical chain transfer reaction was attempted under ATRP condition. Isopropyl benzene was employed as the chain transfer agent. Indeed, the modified polymer with carbon-bromine bonds conversion of 40.7% shows enhanced thermal stability. The initial weight loss temperature has been increased from 193 to 243 °C. On the other hand, the atom transfer radical copolymerization of BBPMI with styrene resulted in the formation of hyperbranched polymer.     

An in silico ensemble method for lead discovery: decision forest

Recent progress in combinatorial chemistry and parallel synthesis has radically changed the approach to drug discovery in the pharmaceutical industry. At present, thousands of compounds can be made in a short period, creating a need for fast and effective in silico methods to select the most promising lead candidates. Decision forest is a novel pattern recognition method, which combines the results of multiple distinct but comparable decision tree models to reach a consensus prediction. In this article, a decision forest model was developed using a structurally diverse training data set containing 232 compounds whose estrogen receptor binding activity was tested at the U.S. Food and Drug Administration (FDA)'s National Center for Toxicological Research (NCTR). The model was subsequently validated using a test data set of 463 compounds selected from the literature, and then applied to a large data set with 57,145 compounds as a screening example. The results show that the decision forest method is a fast, reliable and effective in silico approach, which could be useful in drug discovery.     

Highly selective two-photon chemosensors for fluoride derived from organic boranes

[reaction: see text] Three organoboron compounds are shown to be two-photon fluorescent sensors for fluoride anion with high sensitivity and selectivity. The recognition mechanism is attributed to the unique steric structure of the bulky dimesitylboryl group and the Lewis acid-base interaction between trivalent boron atom and fluoride anion.