Cage Compounds as Potential Energetic Oxidizers: A Theoretical Study of a Cage Isomer of N2O3

Ab initio electronic structure calculations are employed to investigate the cage isomer of N₂O₃ (c‐N₂O₃) as a viable energetic oxidizer. c‐N₂O₃ is vibrationally stable with a large heat of formation of 7.95 kJ g⁻¹ and can produce larger enthalpies of combustion than other commonly used oxidizers such as ammonium perchlorate, O₂(l) and N₂O₄. c‐N₂O₃ is shown to have a unimolecular decomposition barrier of 24.4 kJ mol⁻¹ at the CCSD(T)/CBS(Q‐5) level of theory, and a dimer‐induced decomposition barrier of 100.8 kJ mol⁻¹. Although c‐N₂O₃ is predicted to perform well as an oxidizer, the low barrier to unimolecular decomposition is likely to render it impractical as an energetic oxidizer.     

Linking the atomistic scale and the mesoscale: molecular orbital and solid state packing calculations on poly(p-phenylene)

The energies and structures of neutral benzenoid and neutral quinonoid polyphenylenes in the gas phase were calculated at the ab initio and semi-empirical levels for oligomers containing up to 11 rings as a function of the torsion angles between consecutive aromatic rings. In the gas-phase poly(p-phenylene) (PPP) simulations, a transition to the aromatic benzenoid structure occurs in the centre of chains as short as about six to seven rings. The development of electronic properties such as ionisation potential, the carbon-carbon bond length between rings, the band gap and width of the highest occupied bands were studied. On going from a coplanar to a perpendicular conformation, qualitatively, the ionisation potential and band gap values increase and the band widths of the highest occupied bands decrease. Molecular mechanics simulations were used to model the crystal structures of PPP oligomers using Lennard-Jones and sinusoidal torsion potentials, with parameters derived initially from the gas-phase calculations. These solid state simulations reproduced known crystal structures and predictions are made for the crystal structures of PPP oligomers up to a degree of polymerisation of 11. The crystal packing forces the PPP molecules to be planar, hence increasing conductivity in the solid state. Interestingly, there is an anomaly in the packing energy results for the sexiphenylene case which is in accord with the gas phase calculations.     

Ab initio calculations of the interaction between thiophene and ionic liquids

The fundamental natures of the interaction between thiophene and ionic liquids of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]⁺[PF₆]⁻) and 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]⁺[BF₄]⁻) were investigated using ab initio calculations and correlated with previous experimental results. The optimized structures show that the anions of the ionic liquids are situated outside the ring plane of the thiophene, with the fluorine atoms interacting with the hydrogen atoms of the thiophene, and the cation of the ionic liquids approaches the thiophene with its positively charged atoms approaching the negatively charged atoms of TS. It is concluded that thiophene molecules interact with the ionic liquids mainly via Coulombian attraction. Further analysis explained the results obtained from an absorption experiment that the molar ratios of the absorbed thiophene to the ionic liquids were approximately 3.5/1 and 2.4/1 for [BMIM]⁺[PF₆]⁻ and [BMIM]⁺[BF₄]⁻, respectively. The strong electron donation of the phosphorus atom to the fluorine atoms in the PF₆⁻ cluster is believed to be the major factor resulting in the higher molar ratio of thiophene/[BMIM]⁺[PF₆]⁻. The other factor is the difference of the compactness between the cation and the anion in the two ionic liquids.     

First Principles Analysis of the Electrocatalytic Oxidation of Methanol and Carbon Monoxide

The strong drive to commercialize fuel cells for portable as well as transportation power sources has led to the tremendous growth in fundamental research aimed at elucidating the catalytic paths and kinetics that govern the electrode performance of proton exchange membrane (PEM) fuel cells. Advances in theory over the past decade coupled with the exponential increases in computational speed and memory have enabled theory to become an invaluable partner in elucidating the surface chemistry that controls different catalytic systems. Despite the significant advances in modeling vapor-phase catalytic systems, the widespread use of first principle theoretical calculations in the analysis of electrocatalytic systems has been rather limited due to the complex electrochemical environment. Herein, we describe the development and application of a first-principles-based approach termed the double reference method that can be used to simulate chemistry at an electrified interface. The simulations mimic the half-cell analysis that is currently used to evaluate electrochemical systems experimentally where the potential is set via an external potentiostat. We use this approach to simulate the potential dependence of elementary reaction energies and activation barriers for different electrocatalytic reactions important for the anode of the direct methanol fuel cell. More specifically we examine the potential-dependence for the activation of water and the oxidation of methanol and CO over model Pt and Pt alloy surfaces. The insights from these model systems are subsequently used to test alternative compositions for the development of improved catalytic materials for the anode of the direct methanol fuel cell.     

Properties of the Amide Bond Involving Proline 4,5-methanologues: an Experimental and Theoretical Study

Herein we disclose a combined experimental and theoretical study on the conformational properties of amide bonds involving diastereomeric 4,5-methano-L-proline congeners as N-acetyl ethyl esters and dimeric amide ethyl esters as substrates for cyclization to diketopiperazines. The results are discussed in light of density functional theory calculations aimed at delineating the importance of the n→π* stabilization of the trans-amide conformations. The transitions states for the cyclization of diastereomeric 4,5-methano-L-proline ethyl esters to diketopiperazines were calculated and correlated to the experimental studies.     

中小氮肥造气工艺技术对比及改进

小氮肥企业煤气炉发气量高、消耗低,与中型氮肥企业相比优势明显,前者在工艺和设备上形成了一个合理的体系,这个“造气体系”的形成有着它独特的历史和背景,中氮企业在向小氮企业学习,实施技术改造和革新的过程中,应把小氮肥企业造气经验作为一个体系加以分析。指出中氮肥企业造气技术改造、技术革新可从改善炉箅破渣和炉下排渣能力、调整时间分配,降低上部温度,提高下部温度,增加煤气炉高度,提高碳层高度以及工艺流程4个方面着手。     

降尘中氮磷含量的研究

通过对杭州西湖北山路春夏两季(3～8 月)降尘的采集和实验测定其中总氮(TN)和总磷(TP)的含量,分析出该地区降尘的粒径质量分布特点为较细颗粒的质量含量高于较粗颗粒的质量含量且较细颗粒的氮磷含量也高于较粗颗粒的氮磷含量,得出北山路降尘所携带的氮会对北里湖水体的水质造成潜在威胁,并给出建议对策.     

兼具脱氮和除磷性能菌株的优选

通过L9（34）正交试验和单因素实验优化培养条件,从七株不同菌属的异养硝化-好氧反硝化菌中优选兼具除磷性能菌株。结果表明：优选出的两株异养硝化-好氧反硝化菌分别为丛毛单胞菌WXZ-17和芽孢杆菌WXZ2-4,二者均具有厌氧除磷性能,磷化氢为重要除磷产物。优选的两株菌培养条件均为： T=32.0℃、 pH=6.50、氮源为蛋白胨＋氯化铵＋硝酸钠、总磷浓度为20.0 mg/L,相应的除磷率分别为25.6％和36.0％。在早期脱氮实验中已证实该两株菌脱氮效率分别为：89.7％和96.4％。筛选出的兼具脱氮和除磷性能的菌株使实现废水同步脱氮除磷成为可能。     

磷酸—铵产品中水份对氮磷含量影响的分析

湿法磷酸氨化生产磷酸一铵(MAP)过程中,由于原料磷酸带入杂质多且复杂,在氨、酸反应过程中生成大量沉淀,降低了磷酸一铵产品养份。在酸中杂质含量不变的情况下,如何控制磷酸一铵产品中氮、磷含量显得十分重要。经过分析得出,降低产品水份有利于提高产品中氮磷含量。     

同步生物脱氮除磷工艺的研究进展

本文分析了传统同步生物脱氮除磷工艺存在的问题,介绍了一些传统工艺的改进工艺和几种新工艺,包括A2/O工艺,改进的A2/O工艺,改进的SBR工艺及其他一些工艺,阐述了他们的特点,并探讨了同步生物脱氮除磷工艺的发展趋势。     

The Unpredictability of Research Directions and the Synergy between Theory and Experiment in Physical-Organic Chemistry

Research projects in physical-organic chemistry can go in unpredictable directions. One such project, described herein, began with the discovery of a large, imaginary, calculated vibrational frequency and soon led to the prediction that cyclobutanetetraone (CO)₄ had a triplet ground state. Molecular orbital (MO) theory provided the understanding of why (CO)₄ was calculated to have a planar triplet ground state and why, in contrast, (SiO)₄ was calculated to have a tetrahedral singlet ground state. Qualitative MO theory, as well as calculations, also predicted that (CO)₃, (CO)₅, and (CO)₆ should all be found to have singlet ground states. Testing experimentally these predictions about (CO)_n molecules, n=3–6, led to a very fruitful collaboration with Dr. Xuebin Wang, who obtained the negative ion photoelectron (NIPE) spectra of the radical anions of these four molecules and also of (CS)₄. Assignments of the signals in these five NIPE spectra required computing the vibrational progressions in them. The necessary acquisition of the ability to simulate the signals in NIPE spectra resulted in the successful analysis of the very complex spectrum of meta-benzoquinone (MBQ) radical anion, which Dr. Wang had already obtained and published. Analysis of this spectrum confirmed the prediction, made more than 20 years previously, that the ordering of the two lowest singlet states in MBQ was reversed from that in meta-benzoquinodimethane (MBQDM). The research described herein illustrates not only the unpredictability of where some research projects will eventually lead, but also the synergy between calculations and experiments in physical-organic chemistry.     

人工湿地填料对氮磷的静态吸附筛选实验

通过考察填料对水中氮磷的吸附性能,为人工湿地填料的选择提供依据。在水中投加一定量填料,在不同条件下进行磁力搅拌,测定填料对氮磷的吸附性能。结果表明填料粒径为8~12目,固液比50 mg/L,搅拌速率300 r/min,搅拌时间3 h,原水pH约为6.5,氨氮的初始质量浓度30 mg/L左右、磷的初始质量浓度3 mg/L左右时,煤灰渣对氨氮的去除率6.6%,对磷的去除率30%;沸石对氨氮的去除率40%,对磷的去除率22.8%;蛭石对氨氮的去除率28.5%,对磷的去除率9%。pH对氮磷吸附的影响较大,原水在碱性和中性的条件下,对氮磷的吸附性能要优于酸性条件。     

1-(2-羟基)乙基-3-甲基咪唑溴盐(HEMIMB)的微观结构及阴阳离子之间的相互作用

采用密度泛函理论B3PW91/6-31+G(d)方法,对1-(2-羟基)乙基-3-甲基咪唑溴盐(HEMIMB)离子液体进行了结构优化和频率分析,得到了离子对的最稳定结构。离子对的几何参数表明阴阳离子之间存在较强的氢键相互作用。自然键轨道(NBO)理论分析离子对中的原子电荷分布和电荷转移情况,结果表明离子对中阴阳离子间存在静电相互作用和氢键作用,而最稳定的离子对主要是源于Br的孤对电子与羟基之间的氢键相互作用。     

水网藻对富营养水体去氮除磷能力的研究

水体富营养化是当今世界面临的一个环境难题,笔者在工作中接触到大量的生活污水治理问题,其重要目标往往是降低污水中的氮磷浓度,从而使接受水体避免发生富营养化污染。本试验通过对水网藻除氮、除磷的能力等的研究,以探索出一条解决富营养化难题的途径,笔者测定了水网藻在不同条件下去除N、P的能力。试验结果表明:在富营养化水体中水网藻对N、P去除能力较高,达到30~80%,表明水网藻对解决富营养化问题具有现实意义。     

热质联用测试N-P-Si协同阻燃粘胶纤维性能的研究

利用纺前共混法制备了N-P-Si协同阻燃粘胶纤维,采用极限氧指数测定了阻燃粘胶纤维阻燃性能,应用同步热重―质谱联用技术研究阻燃粘胶纤维的热稳定性以及气态产物,初步探究了阻燃粘胶纤维热分解机理。结果表明:经共混法制备的N-P-Si协同阻燃粘胶纤维极限氧指数为26.8,属于难燃产物。研究表明,阻燃剂的加入促进脱水炭化作用,在高温下热分解残余量明显高于粘胶纤维,阻燃剂磷酸三(丁氧基乙基)酯(TBEP)和三聚氰胺主要在气相中起到湮灭燃烧自由基和稀释可燃气体的作用,硅酸钠兼有隔绝空气及吸烟作用。     

Valence Bond-Based Hybrid Quantum Mechanics Molecular Mechanics Approaches and Proper Inclusion of the Effect of the Surroundings

The pioneering development of multiscale models for complex chemical systems by Karplus, Levitt, and Warshel, including the hybrid quantum mechanics molecular mechanics (QM/MM) approach and its application to enzymes, established a new field in chemistry that allows the modeling of reactivity within complex chemical systems. Inspired by the potential of such methods, many groups developed different QM/MM variants. Valence bond (VB) theory, which always was and still is an important conceptual tool for chemists, is well suited to deal with problems of chemical reactivity. Hence, here we review VB-based QM/MM methods, including the early semi-empirical methods that utilize VB concepts and more recent ab initio VB-based QM/MM methods. Special emphasis is given to the different ways to include effects of the surroundings on the solute. It is shown that within the VB framework, simple mechanical embedding for each diabatic state, followed by mixing of the states, accounts for most of these effects.     

腐植酸的增氮解磷促钾作用

腐植酸对化学肥料有明显的调控和增效作用,主要表现为对氮、钾缓释,对磷活化,从而提高了化肥的利用率。作者从理论上阐述了腐植酸增氮解磷促钾的调控机理,也通过一些实例证明了化学肥料与腐植酸结合后显著的增产效果,论证了在化学肥料中添加腐植酸对减少化肥用量、提高作物品质和保护环境方面的积极意义。     

氧化钙含量测定方法的比较与选择

用三种不同方法对氧化钙含量进行测定,通过比较三种方法测定的精密度、准确度、测定速度和操作条件等,说明了各方法的优缺点,从而得出测定氧化钙含量的最佳方法。     

氮磷营养调控对微藻去除抗生素的增效作用研究

选择蛋白核小球藻和铜绿微囊藻为研究对象,头孢拉定为目标抗生素,考察了外源营养物质调控对2种微藻去除抗生素的增效作用.结果表明,通过添加氮、磷2种营养物质,使得微藻对目标抗生素的去除能力显著提升.在反应开始24h后,实验组(NaNO3、K2HPO4的质量浓度分别为250、50mg/L)2种微藻对头孢拉定的去除率即可达到7...     

氮和磷对生物滴滤塔净化煤矿乏风瓦斯的影响

研究了氮源类型和浓度以及磷元素浓度对生物滴滤塔净化极低浓度CH4的影响。利用空气和高纯CH4混合气模拟煤矿乏风瓦斯,生物滴滤塔填料为陶瓷鲍尔环,以实验室分离筛选到的甲烷氧化菌进行接种挂膜。结果表明,进气流量为2 L?min?1,喷淋液流量为0.1 L?min?1,进气CH4浓度在0.1%~1.1%,以Na NO3为氮源时,生物滴滤塔净化CH4的效果最好,优于(NH4)2SO4和NH4NO3为氮源时的表现。喷淋液中Na NO3浓度为70 mmol?L?1,进气CH4浓度为0.1%~1.1%时,生物滴滤塔的CH4去除负荷为10.67~39.72 g?m?3?h?1,去除负荷随CH4浓度增加而增加;CH4净化率为97.92%~39.70%,净化率随CH4浓度增加而下降。在最佳氮源条件下,进气CH4浓度为0.9%,P元素浓度为100 mmol?L?1时,滴滤塔CH4去除负荷最大为49.69 g?m?3?h?1,CH4净化率60.90%。