Similarities and dissimilarities in n-hexane and benzene sooting premixed flames

The flame structure of atmospheric-pressure sooting premixed flames of aliphatic and aromatic hydrocarbons with the same carbon atom number (hexane and benzene) were studied at similar temperatures and C/O ratios by sampling and chemical and spectroscopic analysis. The differences in the oxidation mechanism of hexane and benzene in fuel-rich conditions were found to produce a different chemical environment in the yield of light hydrocarbons and their relative compositions where soot inception occurs. The predominance of acetylene and simple aromatic reactants in the oxidation region of the benzene flame favoured the early appearance and steep rise of soot particles. Large formations of saturated and unsaturated hydrocarbons were observed in the main oxidation region of the hexane flame whereas a delayed formation of aromatics (mainly PAH) was observed at soot inception only after complete oxygen consumption. There are differences in soot inception mechanisms reflected by the soot structure from UV-vis spectral shapes and mass specific absorption coefficients. In the benzene flame, they appeared to be more ordered and aromatic with a narrower size of aromatic systems and/or more curved aromatic structures. By contrast, less ordering with a more complex aliphatic/aromatic structure and a larger variety of aromatic systems were found to characterize soot formed in the hexane flame.     

Positronium reactions with diamagnetic organic molecules

Rate constants for the interaction of ortho-positronium atoms with a series of diamagnetic organic compounds have been determined. Nitrated aromatic molecules interact far more readily with ortho-positronium than do nitrated aliphatic molecules. The observed rate constants for the aromatic molecules show a distinct dependency on the nature of the substituents and their relative positions in the aromatic ring. This dependency may be attributed to steric interactions which influence the relative electron charge density on the atoms in the molecule and alter the molecular energy levels.     

Surface science with aerosols

Experimental surface science with aerosol particles under atmospheric conditions is becoming a realistic possibility. The first part of this critical review focuses on nano-scopic aerosols generated in combustion of organic fuels at ambient pressures. The bizarre shape of soot agglomerates resists a simple definition of size and surface area. Yet a measure of the size known as the mobility diameter can be extracted from the mobility of the particles in their carrier gas. The total surface area must be divided into an active and a passive part. At the active surface, mass, energy, and momentum is exchanged with the molecules of the carrier gas. The active surface thus determines the dynamical properties of the particles. The passive surface is the surface enclosed in the interior as well as the surface in bays or cracks or, with larger particles, in the dead point of the laminar flow; it determines particle properties on a longer time scale. Simple automatic portable sensors measure the number density of airborne particles, their “size” and a characteristic fingerprint of the surface chemistry, making it possible to determine the source from which the particle was emitted. The response time of the sensors is ～1 s, hence one can monitor dynamical changes of the particles such as adsorption of water in the atmosphere. In the second part we examine a number of surface science techniques that have been used to characterize surfaces important to atmospheric chemistry in more detail, in particular the uptake of water and the influence of surfactants. We illustrate the application of these techniques to the investigation of alkali halide surfaces as a function of relative humidity. Finally we give first examples on how infrared spectroscopy and synchrotron-based ambient pressure X-ray photoelectron spectroscopy have been used to study more realistic aerosol particles, under conditions of ambient humidity. These examples show that in situ chemical analysis of the particles is possible with third generation synchrotron X-ray sources. In the near future, X-ray lasers might reveal the fast dynamics of chemical processes as well. Thus it is within reach to study aerosols under the conditions of the stratosphere. Stratospheric aerosols can reduce the insolation of the earth and may become one of the last resorts of humanity to counteract the effects of global warming.     

同步辐射软X射线近边吸收谱方法研究长期施肥对黑土有机碳官能团的影响

以定位20年的黑土肥料试验为平台,利用同步辐射软X射线近边吸收谱(C-1s NEXAFS)方法,研究了长期施用化肥以及化肥配施玉米秸秆对土壤有机碳官能团的影响。结果表明：与不施肥的空白处理(CK)相比,单施化肥(N,NPK)后土壤的芳香C和羧基C含量增加,脂族C和羰基C含量下降,脂族C/芳香C比值降低;与单施化肥处理相比,化肥配施玉米秸秆后芳香C含量下降而脂族C含量增加,脂族C/芳香C比值增加,并随玉米秸秆用量增加表现的更为明显;无论配施玉米秸秆与否,NPK肥混施处理的芳香C、脂族C以及脂族C/芳香C比值均高于单施N肥处理。上述结果说明,单施化肥比不施肥使土壤有机碳官能团中芳香类化合物的相对比例增加,而脂肪烃类化合物的相对比例下降;化肥配施玉米秸秆则比单施化肥增加了脂肪烃类化合物的相对比例,配施高量比低量玉米秸秆的增加趋势更为明显,同时NPK肥混施比单施N肥有利于提高脂肪烃类化合物的相对比例。C-1s NEXAFS方法能够原位表征长期定位施肥条件下土壤有机碳官能团组成的变化。     

Effect of purification on the electron structure and field emission characteristics of a carbonaceous material containing single-wall carbon nanotubes

A carbonaceous material containing single-wall carbon nanotubes (SWNTs) has been synthesized by arc-discharge evaporation of graphite with a catalytic additive of nickel and cobalt powders. The synthesized SWNTs were purified from an amorphous carbon component (soot) and the catalyst particles by boiling in nitric acid. A comparison of the X-ray fluorescence spectra measured before and after this treatment showed that acid etching significantly decreased the content of soot in the material. The material enriched with SWNTs is characterized by a reduced threshold for the appearance of the field emission current, which is explained by a decrease in the screening effect of soot. The current-voltage characteristics of SWNTs exhibit a hysteresis, which is suggested to be due to the adsorption of molecules and radicals on the surface and at the ends of carbon nanotubes.     

The Formation of Carbon in Combustion and how to Quantify the Impact on Human Health

We summarize our current research on combustion aerosols. First, sampling devices for the analyses of flame gases are described. The flame gas samples are investigated by mass spectroscopy and by standard aerosol techniques. Time-of-flight mass spectroscopy is well suited to study formation and growth of soot precursor molecules. Fullerenes can also be seen in some mass spectra of flame gases. Presumably, the fullerenes are evaporated from small soot particles in the mass spectrometer by the ionizing laser. Size spectra of soot particles from the flame are presented. The flame is optionally seeded with palladium aerosol to demonstrate that the particle size distribution is not altered during the sampling procedure. It is found that soot particles are already present low in the flame where large molecules are absent.Photoemission is applied to study surface properties of soot particles from the flame. It is shown that the surface of the particles is covered with polycyclic aromatic hydrocarbons (PAH). The PAH can be removed by heating and the properties of the carbon core are revealed. One can thereby distinguish a soot growth from a soot burnout region in the flame. Time-resolved desorption experiments of perylene (a PAH) from model aerosol particles are presented. It is shown that they follow a first order rate law. The photoelectric PAH sensor is introduced as a personal air quality monitor. The danger from inhaling combustion aerosol can be expressed in units of standard cigarettes.     

Adsorption of aromatic compounds from the biodegradation of azo dyes on activated carbon

The adsorption of three selected aromatic compounds (aniline, sulfanilic acid and benzenesulfonic acid) on activated carbons with different surface chemical properties was investigated at different solution pH. A fairly basic commercial activated carbon was modified by means of chemical treatment with HNO₃, yielding an acid activated carbon. The textural properties of this sample were not significantly changed after the oxidation treatment. Equilibrium isotherms of the selected compounds on the mentioned samples were obtained and the results were discussed in relation to their surface chemistry. The influence of electrostatic and dispersive interactions involved in the uptake of the compounds studied was evaluated. The Freundlich model was used to fit the experimental data. Higher uptakes are attained when the compounds are present in their molecular form. In general, adsorption was disfavoured by the introduction of oxygen-containing groups on the surface of the activated carbon.     

Hydrophobation of Clay Particles by Asphaltenes Adsorption

In order to throw light on the mechanism of organic compounds–clay interactions and to control the preparation of hydrophobic fillers, the effect of asphaltene adsorption from water-saturated toluene onto various clay minerals (kaolinite, illite) was studied. The modification of the clay surface charge and wettability were characterized, respectively, by microelectrophoresis and Washburn contact angle measurements. Further, the alteration of the surface area and chemical composition of the clay particles due to asphaltene adsorption were assessed using various methods such as N₂-adsorption/desorption, X-ray diffraction (XRD) measurements, FT-IR and scanning electronic microscopy. The data indicate that upon asphaltene adsorption, the clay particles become hydrophobic, their contact angle with water increases, while their surface charge and surface energy are reduced. Furthermore, according to XRD data, no swelling of the clay by asphaltenes occurs in the water-saturated toluene, indicating that asphaltenes cover the clay's external surface and lead to their aggregation, either in water or in the vacuum dried state. Finally, we elucidate the mechanisms by which asphaltenes adsorb and modify the clay surface characteristics. Such mechanisms involve mainly interactions that occur between the asphaltenes' surface groups and silanol/aluminol groups of the mineral.     

Particle formation in opposed-flow diffusion flames of ethylene: An experimental and numerical study

An experimental and numerical study on particles inception and growth is performed in opposed-flow diffusion flames of ethylene and air characterized by different sooting tendencies. Spectrally resolved UV-visible laser induced fluorescence, laser induced incandescence and laser light scattering measurements are used to characterize different classes of combustion-generated compounds. A detailed kinetic model accounting for both gas-phase and particle formation is used. Comparison between experimental results and numerical predictions gives a qualitative view of the mechanism of particle formation in opposed-flow flames.Particle inception is the result of both chemical growth and coagulation of aromatic compounds. In the region close to the flame front where the temperature is relatively high and radicals are abundant, the particle inception is due to a chemical growth mechanism by which aromatic molecules add aromatic radicals leading to the formation of biphenyl-like structures. The growth process continues as high-molecular mass aromatics are moved away from the flame zone towards the stagnation plane by the addition of acetylene and other aromatics forming particles of increasing sizes. Graphitization of these particles and thermal annealing lead to the formation of soot particles. At relatively lower temperatures, found across the stagnation plane, particles growth still occurs and it is mainly due to a process of physical coagulation of PAHs.The experimental and numerical results obtained in this work demonstrate and explain the sensibility of inception and growth of particles to radical concentration and temperature in opposed-flow flame configurations.     

Water vapor adsorption onto activated carbons prepared from cattle manure compost (CMC)

Activated carbons were prepared from cattle manure compost (CMC) using zinc chloride activation. The structural and surface chemical characteristics of CMC-based activated carbons were determined by N₂ adsorption-desorption and Boehm titration, respectively. The water vapor adsorption properties of the prepared activated carbons with various pore structure and surface nature were examined, and the mechanism of water adsorbed onto activated carbon was also discussed. The results show that the adsorption of water vapor on carbons begins at specific active sites at low relative humidity (RH), followed by micropore filling at medium RH through the formation of pentamer cluster of water molecules in the narrow micropores. The water vapor adsorption capacity of activated carbon is predominantly dependent on its pore volume and surface area. Although capillary condensation is not the mechanism for water adsorption onto activated carbon, water can adsorb on narrow mesopore to some extent.     

化学处理水稻秸秆水溶性有机物的光谱特征研究

采用紫外(UV)、傅里叶红外光谱(FTIR)和核磁共振(1H和13C NMR)分析技术对13C标记水稻秸秆化学处理过程中的水溶性有机物进行了研究。由光谱变化的分析可见,随着化学处理的进行,水稻秸秆DOM中甲基、亚甲基含量逐渐降低,脂肪性降低;含芳环的化合物逐渐分解,芳香性降低;碳水化合物分解一部分形成碳酸盐类物质,另一部分形成CO₂和H₂O;羧酸和羧酸脂类化合物形成羧酸盐类物质;有机成分中的无机元素硅释放出来,形成硅酸盐类的无机硅氧化合物;DOM中的氮素以铵盐的形式存在并逐渐积累。     

江西乐平晚二叠世煤成烃机理红外光谱研究

应用显微红外光谱技术,对江西乐平晚二叠世煤矿B₃煤层煤样在不同热模拟温度下的结构组成变化特征及规律进行了研究,结合镜下显微组分的观察和统计结果,剖析了乐平晚二叠B₃煤层煤的生烃机理,对该区煤成烃资源进行了初步评价。研究表明：煤化学结构主要由杂原子基团、脂族结构和芳香结构三部分组成,其活化能依次增加;煤成烃过程,是一种随着热演化程度的加深, 脂族侧链不断脱落,芳香结构不断缩聚,含氧基团逐渐断裂的过程;该煤层中含有的B型基质镜质体和树皮体都是很好的生烃显微组分,是该树皮煤生烃潜力巨大的主要原因。此特点对在华南地区寻找与富含“树皮体”煤系地层有关的油气资源并使“煤变油”产业化具有重要的意义。     

J酸分光光度法测定芳香族氨基化合物

综合考虑显色反应选择性、反应速度、灵敏度和偶氮化合物的水溶性等问题,通过对偶合组分分子结构的理论设计和实验筛选,研究了显色反应方法和条件,提出利用J酸(2-氨基-5-萘酚-7-磺酸)作为偶合试剂分光光度法测定水中芳香族氨基化合物。溴化钾催化,室温下,亚硝酸盐与芳香族氨基化合物在稀盐酸水溶液中发生重氮化反应,在碳酸钠水溶液中重氮盐与J酸偶合生成有色偶氮化合物,最大吸收波长480 nm。所测苯胺、4-氨基苯磺酸和1-萘胺的表观摩尔吸光系数分别为3.95×104,3.24×104和3.91×104 L·mol-1·cm-1。水中共存离子影响研究结果表明: 地表水中常见离子对测定结果不产生影响。采用J酸分光光度法测定了上海市复兴岛运河水样,同时,用标准加入法做回收实验,实验结果：苯胺回收率为98.5%～102.1%,相对标准偏差2.08%。J酸是一种常见有机试剂,易溶于水,挥发性低,其毒性大大低于盐酸萘乙二胺。J酸分光光度法测定芳香族氨基化合物具有灵敏度高、选择性好、操作简单快速、测定结果准确等优点,可用于环境水体中痕量芳香族氨基化合物的测定。     

Factors affecting the adsorption of trichloroethylene onto activated carbons

In this work, an experimental study aimed at the assessment of the factors affecting the adsorption of trichloroethylene (TCE) from water solutions onto activated carbons is presented. The influence of sorbent properties, such as B.E.T. surface area, micropore volume, chemical composition and acid/basic surface functional groups on TCE adsorption capacity is experimentally assessed by testing a set of 12 sorbents. Moreover, the effect of the presence of other species in solution, such as sodium acetate and tetrachloroethylene (PCE), is studied through parametric TCE adsorption isotherms realization. The experimental results show that the TCE adsorption capacity is promoted by a high B.E.T. surface area, micropore volume and C content and it is significantly affected by the presence of a non-ionic compound of similar structure (PCE), however it does not depend on the presence of an organic salt (sodium acetate). These results confirm that neither TCE-carbon ionic interaction nor sorbent ionization phenomena are involved in the TCE adsorption, since its mechanism is based on dispersion forces (London-Van Der Walls interaction). A thorough analysis of the experimental data set suggests that, in consideration of the TCE adsorption mechanism, the maximization of basal plane extent (as the B.E.T. surface area) and its effective fraction (as the C content) is a valid criterion to select or synthesize a new suitable sorbent for TCE adsorption from waters.     

Electrostatically mediated adsorption by nanodiamond and nanocarbon particles

Nanodiamond (ND) and other nanocarbon particles are popular platforms for the immobilization of molecular species. In the present research, factors affecting adsorption and desorption of propidium iodide (PI) dye, chosen as a charged molecule model, on ND and sp ² carbon nanoparticles were studied, with a size ranging from 75 to 4,305 nm. It was found that adsorption of PI molecules, as characterized by ultraviolet–visible spectroscopy, on ND particles is strongly influenced by sorbent-sorbate electrostatic interactions. Different types of NDs with a negative zeta potential were found to adsorb positively charged PI molecules, while no PI adsorption was observed for NDs with a positive zeta potential. The type and density of surface groups of negatively charged NDs greatly influenced the degree and capacity of the PI adsorbed. Ozone-purified NDs had the highest capacity for PI adsorption, due to its greater density of oxygen containing groups, i.e., acid anhydrides and carboxyls, as assessed by TDMS and TOF–SIMS. Single wall nanohorns and carbon onion particles were found to adsorb PI regardless of their zeta potential; this is likely due to π bonding between the aromatic rings of PI and the graphitic surface of the materials and the internal cavity of the horns.     

Neutrons for probing the ice nucleation on atmospheric soot particles

Soot resulting from combustion of kerosene in aircraft engines can act as condensation nuclei for water/ice in the atmosphere and promote the formation of contrails that turn into artificial cirrus clouds and affect the climate. The mechanisms of nucleation of water/ice particles are not well identified. Studies ??in situ?? are difficult to realize, so we try to determine by neutron diffraction the nucleation of water/ice adsorbed on soot collected at the outlet of an aircraft engine combustor within the conditions of the upper troposphere. The results are compared with those obtained on model laboratory soot. The comparison highlights the role of chemical impurities and structural defects of original aircraft engine soot on the nucleation of water/ice in atmospheric conditions.     

Surface heterogeneity effects of activated carbons on the kinetics of paracetamol removal from aqueous solution

The removal of a compound with therapeutic activity (paracetamol) from aqueous solutions using chemically modified activated carbons has been investigated. The chemical nature of the activated carbon material was modified by wet oxidation, so as to study the effect of the carbon surface chemistry and composition on the removal of paracetamol. The surface heterogeneity of the carbon created upon oxidation was found to be a determinant in the adsorption capability of the modified adsorbents, as well as in the rate of paracetamol removal. The experimental kinetic data were fitted to the pseudo-second order and intraparticle diffusion models. The parameters obtained were linked to the textural and chemical features of the activated carbons. After oxidation the wettability of the carbon is enhanced, which favors the transfer of paracetamol molecules to the carbon pores (smaller boundary layer thickness). At the same time the overall adsorption rate and removal efficiency are reduced in the oxidized carbon due to the competitive effect of water molecules.     

污水厂出水颗粒态与溶解态有机物的红外和荧光光谱特征

城市污水处理厂出水作为再生水的主要水源,其迥异的物质组成给受纳水体带来潜在环境风险。全面掌握污水厂出水水体中有机物组成及结构信息,将为污水厂提标改造及有毒有害物质排放标准的制定提供理论支撑。采用傅里叶变换红外光谱和三维荧光光谱技术,结合二阶导数光谱及区域积分分析方法,对4个典型城镇污水处理厂(W1,W2,W3,W4)出水水体中颗粒态有机物(POM)与溶解态有机物(DOM)的物质组成及结构差异特征进行了分析。结果显示： 污水处理厂出水中POM主要组分为脂肪类、芳香类、糖类及矿物盐,而DOM主要由有机酸、蛋白质、多肽、糖类及芳香类物质组成。各污水处理厂出水水体POM中,W1芳香类物质较多而矿物盐类等颗粒较少,W2较W1含有更多的糖类物质,W3含较多脂类、蛋白类及糖类,而W4含有芳香类及羧酸物质的有机物较多。水体DOM组成中,W1和W2成分较为类似,主要为芳香性较高的大分子有机酸,其含量分别占总有机物的73.9%和67.7%;W3与W4组成中蛋白、多肽及糖类含量较高,其中类蛋白物质分别占DOM总量的71.3%和53.5%。研究结果表明,采用傅里叶变换红外光谱结合二阶导数分析能很好识别不同污水处理厂出水水体中POM与DOM主要物质组成及结构差异,同时利用区域积分方法对样品三维荧光光谱进行解析,能更进一步定量分析不同来源样品物质组成特征。     

Formation of soot particles in pyrolysis and oxidation of aliphatic and aromatic hydrocarbons: Experiments and detailed kinetic modeling

Experiments on pyrolysis and oxidation of rich mixtures of various aliphatic and simple aromatic hydrocarbons in reflected shock waves have been performed. The mixtures C₂H₂/Ar, C₂H₆/Ar, C₂H₄/Ar, C₂H₄/O₂/Ar, CH₄/Ar, CH₄/O₂/Ar, C₃H₈/Ar, C₃H₆/Ar, toluene/Ar, and benzene/Ar were studied. The yield of soot and the temperature of soot particles were determined experimentally by the double-beam absorption emission method. The kinetic model of soot formation during the pyrolysis and oxidation of rich mixtures of aliphatic and aromatic hydrocarbons complemented with a set of nucleations of soot particles from both polyaromatic fragments and unsaturated aliphatic hydrocarbons was suggested. This kinetic model of soot formation was successfully tested. It describes the experimental literature data on the yield of the products of pyrolysis and oxidation of acetylene and diacetylene in a shock tube. The results of our experiments and kinetic calculations of the time, temperature, and concentration dependences are in good agreement for all hydrocarbons under study. All the kinetic parameters of the model remained strictly constant.     

The inhibition of corrosion of mild steel in 0.5 M sulfuric acid solution in the presence of benzyl triphenyl phosphonium bromide

Benzyl triphenyl phosphonium bromide (BTPPB) has been evaluated as a corrosion inhibitor for mild steel in aerated 0.5 M sulfuric acid solution by galvanostatic polarization and potentiostatic polarization methods. The effect of BTPPB on the corrosion current is measured at various temperatures and concentrations. The inhibitor efficiencies, effective activation energies and heat of adsorption have been calculated. The inhibition efficiency increases with increase in inhibitor concentration to reach 99.3% for 10⁻² M. The nature of adsorption of BTPPB on the metal surface has also been examined. Probable mode of adsorption on the metal surface has been proposed using infrared spectroscopic studies. The electrochemical results have also been supplemented by surface morphological studies and quantum chemical analysis.