Effect of Molecular Structure and Hydration on the Uptake of Gas-Phase Sulfuric Acid by Charged Clusters/Ultrafine Particles

The enhanced uptake of sulfuric acid molecules by charged clusters as a result of dipole–charge interaction is critical to the ion-mediated nucleation of particles in the atmosphere. This article illustrates the effect of the structure of the gas-phase sulfuric acid and its hydrates on the uptake of the sulfuric acid molecules by the charged clusters/ultrafine particles. It is shown that the different structures of gas-phase sulfuric acid and its hydrates lead to very big (up to ～ 230%) variations in the uptake coefficients due to the large difference in the dipole moments. On average, the hydration of gaseous sulfuric acid in the atmosphere is likely to enhance the uptake coefficients.     

一次大气颗粒物投影轮廓分维研究

构建了一次大气颗粒物投影轮廓分维模型,并以高精度数字光学显微系统为基础,测算了广州市3种一次大气颗粒物颗粒样品的投影轮廓分维,结果验证了颗粒投影轮廓分维数学模型的合理性,形成了一套简约的一次大气颗粒物投影轮廓分维分析方法。结果还表明一次大气颗粒物投影轮廓分维个数频率分布曲线呈＂S＂型,且一次大气颗粒物对数投影轮廓分维分布曲线呈对数正态分布;3种一次大气颗粒物样品中,柴油汽车排气管中沉积颗粒和餐饮过程产生的颗粒不规则程度相对低,其偏离圆的程度小,粗糙度较小;而粉煤灰颗粒的相反。     

弱酸性树脂吸附低浓度游离碱行为的研究

利用电导实验技术 ,跟踪观察弱酸性树脂吸附低浓度游离碱的行为 ,研究温度对吸附的影响 ,测定吸附活化能 ( Ea)和吸附剂 -吸附质相互作用能 ( U)。实验结果表明 ,温度升高 ,吸附剂 -吸附质相互作用能增加 ,表观吸附速率常数 ( k)增大 ,而且 U与 T存在良好的线性相关 ( r=0 .995 1 )     

The Effects of Temperature on Particle Size in the Gas-Phase Production of TiO2

Ultraflne titanium dioxide powder was synthesized by the gas-phase oxidation of titanium tetrachloride in a multistage aerosol reactor. The reactor consisted of three zones: an evaporation zone for TiCl₄, a preheating zone for oxygen and vaporized titanium tetrachloride, and a reaction zone. Preheating temperature of reactants, partial pressure of reactants, and temperature in the reaction zone were chosen as experimental variables for the control of particle size and distribution. Ultratine TiO₂ powders ranging from 30 to 70 nm in average particle sizes were produced. The preheating temperature of reactants was found to be an effective factor for particle size and distribution of ultraflne powders. As the preheating temperature was increased, average particle size became smaller and size distribution more uniform. Larger particles having narrow size distributions were produced with an increase in TiCl₄ mole fraction under the control of preheating temperature. However, variation of O₂ mole fraction did not show much difference on the average particle size. As the temperature in the reaction zone was increased, average particle size became smaller. With the decrease in the residence time of reactants in the reaction zone smaller particles were obtained.     

连续法制备单分散聚苯乙烯微球及粒径影响因素的研究

以苯乙烯为单体,偶氮二异丁腈(AIBN)为引发剂,聚乙烯吡咯烷酮(PVP)为分散剂,采用连续分段添加引发剂的方法制备微米级的聚苯乙烯微球。研究了引发剂的添加方式,各组分用量变化对聚苯乙烯微球粒径和粒径分布的影响。结果表明:在反应过程中不断地补加引发剂可以保持活性自由基的生成速率,对聚苯乙烯微球的粒径和粒径分布有着重要的影响。在此基础上,通过改变各组分的用量可以制备出表面光洁,粒径在1.3μm左右的聚苯乙烯微球,且单分散性良好,单分散系数在1.02左右。     

Measurement of Ultrafine Particles: A Comparison of Two Handheld Condensation Particle Counters

The objective of this study was to compare two real-time condensation particle counters for measurement of number concentrations of ultrafine particles (UFPs). The comparison is based on the data from side-by-side measurements conducted in several locations, both indoors and outdoors. CPC 3007 and P-Trak? 8525 manufactured by TSI (instruments A and B, respectively) were used simultaneously. They measure particles in sizes from 0.01 to greater than 1 μ m and 0.02 to greater than 1 μ m, respectively. The results reveal a good correlation between the two instruments. The ratios of measured aerosol concentrations varied from 0.81 to 1.17, which implies that in all data sets the difference between the two instruments was less than ± 20%. About 63% of the results were in the range of ± 10%, and about 44% showed differences less than ± 5%. The maximum particle concentration detected by instrument A was approximately 105,000 particles cm ^{? 3} and the minimum was about 230 particles cm ^{? 3} . Because of the lower particle size threshold for instrument A, it was expected that this instrument should never show concentrations lower than those detected by instrument B. This was the case in most of the measurement series. The results revealed that the concentration of UFPs changes rapidly, especially in the presence of a local UFP source. A sampling interval of 1 min is sufficient to provide substantial information about the change in concentration level.     

Shape and Structure of Zinc Oxide Particles Prepared by Vapor-Phase Oxidation of Zinc Vapor

The shape and structure of granular and tetrapod-like ZnO particles prepared by a vapor-phase method were analyzed by electron microscopy, and the growth mechanism is discussed. Only the wurtzite structure exists in ultrafine particles less than 50 nm, indicating that the ZnO particles have the wurtzite structure from the early stages of growth. The legs of the tetrapod-like particles are hexagonal prisms grown along the <001> direction. With regard to the geometrical orientation relationship between any two of the four legs, it was found that the (1¯0) planes of the two legs are parallel to each other.     

气溶胶细粒物对大气能见度影响的研究

文章介绍了国内外关于气溶胶细粒物对大气能见度影响的研究情况,总结出研究中存在的问题,并针对仍存在的问题提出建议与展望。     

The Influence of Relative Humidity on Nanoparticle Concentration and Particle Mass Distribution Measurements by the MOUDI

A humidity control system was operated upstream of two collocated MOUDIs (micro-orifice uniform deposit impactors) for sampling ambient aerosol particles. One MOUDI used silicone-grease-coated aluminum foils (ALs) as the impaction substrates and was considered as the reference impactor, while the other used uncoated ALs or uncoated Teflon filters (TFs) as the impaction substrates for quantifying the effect of different relative humidities (RHs) and impaction substrates on the PM_0.1 concentrations and mass distributions of ambient PMs. Test results showed that decreasing RH in general increased particle bounce from uncoated substrates with the bounce from uncoated ALs being more severe than that from uncoated TFs. Particle bounce did not influence the overall mass distribution of ambient fine particles when RH ranged between 40% and 80%, whereas it led to undersampling of particles greater than 2.5 μm in aerodynamic diameter severely. Oversampling of PM_0.1 occurred by as much as 95%–180% or 25%–55% when the MOUDI used uncoated ALs or TFs, respectively, as RH was reduced from 50% to 25%. Particle bounce was found to be negligible, and PM_0.1 and PM_2.5 could be sampled accurately with less than 5% error at the RH of 75%–80% or 65%–80% when uncoated ALs or TFs were used, respectively.     

A Differentially Pumped Particle Inlet for Sampling of Atmospheric Aerosols into a Time-of-Flight Mass Spectrometer: Optical Characterization of the Particle Beam

Two methods of characterizing the particle beam generated with a differentially pumped particle inlet are presented. Both methods are based on optical scattering of a laser beam by the particle beam. The first method images a time integrated scatter signal from the entire particle beam onto a charge coupled device (CCD), and an Abel inversion is performed on the image data to arrive at the radial particle density distribution in the beam. The second method, based on counting individual (particle) scatter pulses, yields the radial particle density directly. Initial results of the performance of the particle inlet are reported for particles with diameters between 40 and 800 nm. Under optimal working conditions, particle beams were generated with a full angle divergence on the order of 1-2 mrad. The width, measured 285 mm downstream from the exit of the particle inlet, was 250mu m, half width at half maximum (HWHM).     

Determination of Kinetics and Equilibria for Adsorption of Water Vapor on Single Zeolite Particles by a Magnetic Suspension Balance

In order to obtain kinetic and equilibrium data for the adsorption of water vapor on zeolite for use in packed bed adsorber simulations, experimental investigations have been conducted on single zeolite particles with the help of a magnetic suspension balance. The objective was, first, to present such data in a form that is accurate enough and as simple as possible for easier application of the packed bed model and, second, to investigate and discuss the potential of the magnetic suspension balance technique, comparing with more conventional methods.     

Influence of the Polyvinyl Pyrrolidone Concentration on Particle Size and Dispersion of ZnS Nanoparticles Synthesized by Microwave Irradiation

Zinc sulfide semiconductor nanoparticles were synthesized in an aqueous solution of polyvinyl pyrrolidone via a simple microwave irradiation method. The effect of the polymer concentration and the type of sulfur source on the particle size and dispersion of the final ZnS nanoparticle product was carefully examined. Microwave heating generally occurs by two main mechanisms: dipolar polarization of water and ionic conduction of precursors. The introduction of the polymer affects the heating rate by restriction of the rotational motion of dipole molecules and immobilization of ions. Consequently, our results show that the presence of the polymer strongly affects the nucleation and growth rates of the ZnS nanoparticles and therefore determines the average particle size and the dispersion. Moreover, we found that PVP adsorbed on the surface of the ZnS nanoparticles by interaction of the C–N and C=O with the nanoparticle’s surface, thereby affording protection from agglomeration by steric hindrance. Generally, with increasing PVP concentration, mono-dispersed colloidal solutions were obtained and at the optimal PVP concentration (5%), sufficiently small size and narrow size distributions were obtained from both sodium sulfide and thioacetamide sulfur sources. Finally, the sulfur source directly influences the reaction mechanism and the final particle morphology, as well as the average size.     

Studies of the Effects of Particle Size Distribution on the Packing Efficiency of Particles

In the studies of pigment volume effects in paint films, particle packing has been shown to be very important. The effects of particle size distribution on this packing has been known but has received little quantitative consideration. In this paper we consider the packing of real and model continuous distributions of particle sizes. An extension of an algorithm for the calculation of random densest packing is given which applies to continuous distributions. Using a log-normal distribution as a model, the effect of the width of a single distribution on packing is considered. Mixtures of distributions are also considered with the calculation of packing efficiency as a function of mean size ratio and distribution widths. Maxima are shown to occur in the packing efficiency of mixtures of distributions as a function of the volume fractions of the individual distributions. The implications of these packing variations in real systems are then discussed.     

The Effect of Water Vapor on the Particle Structure and Size of Silica Nanoparticles During Sintering

In this article, the influence of the water vapor concentration on structural changes of SiO₂ aerosol nanoparticle agglomerates during tempering was studied. The presence of water vapor in the carrier gas was shown to strongly accelerate the kinetics of sintering. While dry sintering at temperatures between 1100°C and 1500°C generated aggregates only, the addition of water to the process yields individual, completely coalesced nanoparticles at a temperature of 1300°C. Furthermore, depending on the water vapor concentration and temperature of the process, evaporation and condensation processes could be observed, leading to bimodal size distributions. The results prove the significant role of the water concentration in high temperature synthesis of silica and may be used to improve the control over morphology and specific surface area in these processes.     

The Acidity of Zeolites: Concepts,Measurements and Relation to Catalysis: A Review on Experimental and Theoretical Methods for the Study of Zeolite Acidity

In this article, we considered all aspects of acidity (nature of acid sites, strength, density, etc.) in solid catalysts and in zeolites in particular. After reminding the definition of acidity in liquid and solid acids, we emphasized acidity characterization by the most used physical techniques, such as Hammett's indicator titration, microcalorimetry of adsorbed probe molecules (ammonia, pyridine or other amines for acidity characterization and CO₂ or SO₂ for basicity characterization), ammonia or any amine thermodesorption, IR spectroscopy of hydroxyl groups and of several probe molecules adsorbed (ammonia, pyridine, piperidine, amines, CO, H₂, etc.), MAS-NMR of ²⁷Al, ²⁹Si, ¹H elements and of ¹H, ¹³C, ³¹P, etc. of adsorbed probe molecules, and model catalytic reactions.

Modeling the way the acid features of zeolites influence the catalytic activity of these catalysts toward acid-catalyzed reactions (relation between ammonia desorption activation energy values and catalytic activities, reaction mechanism, and kinetics) completes the general analysis of acidity and zeolite chemistry.     

浅谈重灰粒度的控制与大颗粒的消除方法

影响重灰粒度的因素很多,在实际生产过程中化合水温度的控制,粗盐中钙、镁离子的含量等对重灰粒度都有影响,如何保证一水碱的结晶显得尤为关键。通过重灰生产过程中出现一水碱结晶的粗、细情况以及在生产过程中采取的措施进行相应的探讨,对稳定重灰生产有一定的指导意义。     

浓度对超细钛白悬浮液结构及沉降性的影响

为探索浓度对超细钛白悬浮液结构及沉降性的影响,首先通过悬浮液流变实验研究固体浓度对钛白-水悬浮液流动性的影响,得到浓度与悬浮液表观粘度、剪切应力与剪切速率等的关系.然后通过悬浮液稳定性实验研究不同浓度下的悬浮液流体动力学特征.实验结果表明当浓度达到35%左右时,悬浮液开始出现网状结构,有较低的剪切屈服应力.浓度对悬浮液的结构影响很大,可分为单颗粒弥散型、单颗粒团型及网状结构等,不同结构其沉降机理也不同,分别对应的是单颗粒沉降、团聚体的干涉沉降和压缩沉降.     

Effect of Additives on the Formation of Ti02 Particles by Vapor Phase Reaction

The effect of additives on the formation of fine Ti0₂ particles by vapor phase reaction was studied. The oxygenolysis of TiC1₄ was enhanced by the addition of Fecl₃, and AlBr₃, and suppressed by SiCl₄, and ZrCl₄. Particles formed in the presence of additives were 1/2 to 1/5 the size of those formed without additives, and particle size distributions became very narrow. Particle shape was also influenced by the additives.     

Effect of High-Voltage Atmospheric Cold Plasma Treatment on Germination and Heavy Metal Uptake by Soybeans (Glycine max)

The need to feed 9.9 billion people by 2050 will require the coordination of farming practices and water utilization by nutrient-dense plants and crops. High levels of lead (Pb), a toxic element that can accumulate in plants, can lead to toxicity in humans. With the development of novel treatment technologies, such as atmospheric cold plasma (ACP) and engineered nanoparticles (NPs), the time to germination and levels of heavy metals in food and feed commodities can be reduced. This study provides insight into the impact of plasma-activated water (PAW) on the germination rates and effects of soybean seeds, and the resultant combination effects of zinc oxide uptake in the presence of lead. Soybean seedlings were watered with PAW (treated for 3, 5, and 7 min at 30, 50, and 70 kV), and the germination and growth rate were monitored for 10 days. The germinated seedlings were then grown hydroponically in a nutrient solution, and the biomass of each example was measured. The PAW treatment that resulted in the best growth of soybean seeds was then exposed to Pb and zinc-oxide nanoparticles (ZnONPs) to investigate heavy metal uptake in the presence of nanoparticles. After acid digestion, the rate of heavy metal uptake by the soybean plants was evaluated using inductively coupled plasma-mass spectrometry. The PAW seeds grew and germinated more quickly, demonstrating that the plasma therapy had an effect. The rate of heavy metal uptake by the plants was also shown to be 5x lower in the presence of ZnONP.     

Time-Dependence of the Adhesion of Micrometer-Size Particles to Substrates: Correlation with Postdeposition Particle Rotation

The time dependence of the detachment force of 7-µm ground polyester particles coated with silica nanoparticles from a ceramer-coated substrate was determined by ultracentrifugation. The detachment force of the particles from the substrate was found to increase with the time since the particle deposition. Scanning electron microscopy (SEM) results show that, following deposition, the particles rotate at approximately the same scale as the observed increase in the detachment force. This suggests that the increase in adhesion may be due to particle rotation from their initial positions obtained upon deposition to a more stable position that results from torques generated by either electrostatic or van der Waals forces acting on the particles.