Atmospheric heterogeneous reaction of acetone:Adsorption and desorption kinetics and mechanisms on SiO_2 particles

Acetone plays an important role in photooxidation processes in the atmosphere. Up to date, little is known regarding the heterogeneous fate of acetone. In this study, the adsorption and desorption processes of acetone on SiO2 particles, which are the major constituent of mineral dust in the atmos-phere, have been investigated for the first time under the simulated atmospheric conditions, using in situ transmission Fourier transform infrared spectroscopy. It is found that acetone molecules are ad-sorbed on the surfaces of SiO2 particles by van der Waals forces and hydrogen bonding forces in a nonreactive and reversible state. The rates of initial adsorption and initial desorption, initial uptake coefficients and adsorption concentrations at equilibrium have been determined at different relative humidity. The presence of water vapor cannot result in the formation of new substances, but can de-crease the adsorption ability by consuming or overlapping the isolated OH groups on the surfaces of SiO2 particles. In the desorption process, a considerable amount of acetone molecules will remain on SiO2 particles in dry air, whereas acetone molecules are almost completely desorbed at a high relative humidity. In order to evaluate the role of heterogeneous reactions of acetone and other carbonyl compounds in the atmosphere, a new model fitting the atmospheric conditions is needed.     

Heteroseneous oxidation of carbonyl sulfide on mineral oxides

Heterogeneous oxidation of carbonyl sulfide （OCS） on mineral oxides including SiO2, Fe2O3, CaO, MgO, ZnO and TiO2, which are the main components of atmospheric particles, were investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy （in situ DRIFTS）, ion chromatography （IC）, temperature-programmed desorption （TPD）, X-ray diffraction （XRD） and Brunauer-Emmett-Teller （BET） methods. The main products and intermediates of the heterogeneous oxidation of OCS on these oxides were identified with in situ DRIFTS and IC. The reaction mechanism and kinetics were also discussed. It is found that the reaction mechanism on these mineral oxides is the same as that on Al2O3 for the same final products and the intermediates at room temperature. Namely, OCS can be catalytically oxidized to produce surface SO4^2- species and gaseous CO2 through the surface hydrogen thiocarbonate （HSCO2-） and HSO; species. The activity series for heterogeneous oxidation of OCS follows： Al2O3 ≈ CaO 〉 MgO 〉 TiO2 ≈ ZnO 〉 Fe2O3 〉 SiO2. The specific area, basic hydroxyl and surface basicity of these oxides have effect on the reactivity. This study suggests that heterogeneous reactions of OCS on mineral dust may be an unneglectable sink of OCS.     

The uptake of ethyl iodide on black carbon surface

The importance of the iodine chemistry in the atmosphere has been demonstrated by recent obserations. The uptake of ethyl iodine on black carbon surface was inestigated at 298 K for the first time. Degussa FW2 （an amorphous black carbon comprising medium oxides） was used as black carbon sample. Black carbon surface was found to be deactiated in reaction with C2H51, and the uptake coefficient （r） was dependent on the time of exposure. The alue of （2.3±0.9）×10^-2 was determined for the initial uptake coefficient （No）. The result suggests that the heterogeneous loss of C2H51 on carbonaceous aerosols may be important under the atmospheric conditions.     

Influence of deposition time on the morphology and optical properties of SiO<Subscript>2</Subscript>-ZnO composite photonic crystals

SiO2 photonic crystal were successfully prepared by vertical deposition and then used as a template to fabricate SiO2-ZnO composite photonic crystals on ITO substrates by electrodeposition and subsequent calcination. A number of different deposition times were used. The morphologies of the silica opals and SiO2-ZnO composite photonic crystals were investigated by scanning electron microscopy. It was found that ZnO particles grew randomly on the surfaces of the silica spheres when the deposition time was short. As the deposition time was increased, the ZnO particles grew evenly on the surfaces of the silica spheres so that the interstitial space of the silica template was filled with ZnO particles. Reflectance spectra of the SiO2-ZnO composite crystals revealed that all of the fabricated photonic crystals exhibit a photonic band gap in the normal direction.     

SiO2/PSt纳米复合微球的制备

用Stober方法合成了SiO₂/PSt纳米微球, 并对其进行表面改性. 以SiO₂纳米微球为核, 采用乳液聚合法, 合成了SiO₂/PSt纳米复合微球. 该复合微球粒径均匀、 单分散性好. 通过控制反应条件, 可以合成不同大小的复合微球. 对两种微球的形貌、 尺寸、 所携带官能团及表面元素变化情况进行了表征, 讨论了SiO₂纳米微球用量、 乳化剂用量与反应介质配比等因素对SiO₂/PSt纳米复合微球粒径的影响.     

Theoretical study of adsorption and dissociation of NH3 on the Ir{110}（1×2） surface

The adsorption and dissociation of NH3 on Ir{110}（1×2） have been investigated using the density- functional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}（1×2） was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}（1×2） are very competitive, which is consistent with the recent experimental results.     

二氧化硅胶体聚合体吸附铀的研究

采用自制的二氧化硅胶体聚合体,进行了pH值、接触时间和铀初始浓度对二氧化硅胶体聚合体吸附铀效果影响试验,结果表明,溶液的pH对二氧化硅胶体聚合体吸附铀的效果影响较大,并且在pH为4时吸附铀的效果达到最佳;二氧化硅胶体聚合体吸附铀的速度快,30 min即可达到吸附平衡;该材料去除铀的效率高,当溶液中铀初始浓度低于10 mg/L时,该材料对铀的去除率大于98%;随着初始铀浓度增加,吸附容量增加,铀的去除率降低;扫描电镜分析结果表明,二氧化硅胶体聚合体表面形貌吸附铀前后变化不大;能谱分析结果表明,1 g吸附剂所吸附铀的质量分数为4.32%,与二氧化硅胶体聚合体从溶液中吸附铀43.0 mg相吻合.     

MAS NMR studies of modified HY zeolites

The variations in structure and acidity on the internal and external surfaces of HY zeolites modified by MgO and SiO₂ have been studied by MAS NMR, together with the selective adsorption of perfluorotributyl-amine.²⁷Al and²⁹Si MAS NMR spectra revealed that the modifications led to significant changes of the framework owing to the migration of some non-framework Si and Al into the framework in the course of the modifications.¹H MAS NMR spectra showed that the modifications decreased the acidity of the zeolite surfaces. With an increasing of the loading of the oxides, the acidity of the surface decreased further. Both of the two kinds of Brönsted acidity of the MgO-modified HY zeolites decreased, particularly those in the supercages, while those of the SiO₂-modified HY zeolites decreased less, and this result is consistent with that of NH₃-TPD. From the adsorption of perfluorotributyl-amine, it was found that the acidic sites on the external surface of the HY zeolite can be completely covered by SiO₂ after being modified by the chemical liquid deposition (CLD) method.     

MAS NMR studies of modified HY zeolites

The variations in structure and acidity on the internal and external surfaces of HY zeolites modified by MgO and SiO₂ have been studied by MAS NMR, together with the selective adsorption of perfluorotributyl-amine. ²⁷Al and ²⁹Si MAS NMR spectra revealed that the modifications led to significant changes of the framework owing to the migration of some non-framework Si and Al into the framework in the course of the modifications. ¹H MAS NMR spectra showed that the modifications decreased the acidity of the zeolite surfaces. With an increasing of the loading of the oxides, the acidity of the surface decreased further. Both of the two kinds of Brönsted acidity of the MgO-modified HY zeolites decreased, particularly those in the supercages, while those of the SiO₂-modified HY zeolites decreased less, and this result is consistent with that of NH₃-TPD. From the adsorption of perfluorotributyl-amine, it was found that the acidic sites on the external surface of the HY zeolite can be completely covered by SiO₂ after being modified by the chemical liquid deposition (CLD) method.     

Behavior and mechanism of the adsorption/desorption of tectonically deformed coals

The physical and chemical texture of tectonically deformed coals produced by various formational mechanisms are different from those of primary coals, thus resulting in major differences among the physical properties of the reservoirs of these coals. We have studied the adsorption/desorption behavior of tectonically deformed coals by the use of isothermal adsorption/desorption experiments under equilibrium moisture condition. Experiments of isothermal adsorption/desorption of methane or multi-component gases have indicated that, the adsorption curves of coals with a low degree of tectonic deformation conform to the type of isothermal adsorption curve described by the Langmuir equation; the methane adsorption curves of coals with strong tectonic deformation cannot be described by the Langmuir equation. The adsorption/desorption process of methane and multi-component gases in the deformed coals is not consistent with primary coals, which form an effect of hysteresis in different kinds of tectonically deformed coals. With the change of pore structure of tectonically deformed coals at reservoir condition, the added adsorbed CH₄ in the experiments is desorbed on the pore surface of coals during the pressure reduction process. Thus, the result shows that the adsorption volume in the process of desorbing is greater than that in adsorbing. Because of the deformation, structural change, and transformation of the adsorption potential field of coals, it is essential to form a new kind of isothermal adsorption curve and the hysteresis effect of the desorption process. Supported by National Basic Research Program of China (Grant Nos. 2006CB202201 and 2009CB219601) and National Natural Science Foundation of China (Grant Nos. 40772135, 40642013 and 40172058)     

Mechanism of the heterogeneous reaction of carbonyl sulfide with typical components of atmospheric aerosol

Carbonyl sulfide (COS) is one of the most abundantsulfur-containing species in the troposphere and lowerstratosphere. The atmospheric average concentration ofCOS is about 500 pptv with relatively little variation[1,2].In the stratosphere, where photochemical reactions occur,carbonyl sulfide can be oxidized into sulfur dioxide andfurther to sulfate aerosol[3—6]. The sulfate aerosol plays animportant role in heterogeneous chemical processes,ozone depletion and atmospheric radiation balance wh…     

Photocatalytic degradation pathways and adsorption modes of H-acid in TiO2 suspensions

Effect of adsorption mode on photodegradation of H-acid in TiO2 suspension was studied using DFT calculation,UV-Vis spec-troscopy,FTIR,and ionic chromatography.At pH 2.5,H-acid was adsorbed on TiO2 surfaces by one dissociated sulfonic group.The adsorbed sulfonic group was attacked by surface ·OH,resulting in the production of SO42-and the cleavage of the naphtha-lene ring.At pH 5.0,H-acid was adsorbed on TiO2 surfaces by two sulfonic groups.The two adsorbed sulfonic groups were sim-ultaneously attacked by surface ·OH,leading to a faster initial production of SO42-and initial degradation rate of H-acid than those under pH 2.5.Microscopic adsorption structures may be more important than adsorption amount in controlling the photo-degradation pathways of organic pollutants.     

乙酰胺/蒙脱土吸附嵌入机理的研究

通过乙酰胺在蒙脱土层面间吸附嵌入研究 ,对乙酰胺与蒙脱土的作用形态予以表征 .认为乙酰胺在蒙脱土层间的吸附嵌入机理有两种形式 ,即 :乙酰胺首先在层面上被质子化后通过离子键合作用吸附嵌入到蒙脱土层面 ,吸附嵌入量较少 (仅为 3mg g) ,对应于乙酰胺分子的单分子层吸附 (化学吸附 ) ;而乙酰胺分子以氢键缔合作用形式吸附嵌入量较大 (为 1 8mg g左右 ) ,稳定性较差 ,易在溶剂淋洗或加热过程中脱除 (物理吸附 ) .所确定的测试方法及作用机理为后续的有机单体吸附嵌入的解吸提供实验依据     

First-principles investigation on initial stage of 2H-SiC(001) surface oxidation

We present comprehensive first-principles calculations on the initial stages of SiC oxidation by atomic oxygen on the 2H-SiC(001) surface. In order to study the kinetics of oxygen incorporation at the 2H-SiC(001) surface, we investigated adsorption and diffusion of oxygen atoms and SiO₂ nucleation. The adsorption sites, corresponding to the local minima of the potential energy surface (PES) for isolated adatoms, were identified through a comparative study of the adatom binding energy at different locations. We found that the Bridge (siloxane) site is preferred over other adsorption sites. There is no energy barrier at 0K for oxygen insertion into this site. The diffusion energy barriers that the adatom has to overcome when jumping between two adsorption sites were calculated. The premises of silica nucleation were investigated by calculating the modifications of the oxygen atom binding energy due to the interaction with neighboring adatoms. Supported by Snecma Propulsion Solide (Contract FPR No. 0539298A), Natural Science Foundation of China (Grant No 50802076) and Flying Star Program of Northwestern Polytechnical University of China     

F修饰对SiO2@TiO2亲疏水性及光催化性能的影响

采用两步法制备了氟修饰疏水性F-SiO_2@TiO_2材料.以三乙氧基氟硅烷(TEFS)为硅源,采用后嫁接的方法在短孔道MCM-41小球表面引入F原子,再利用醇热法在F-MCM-41小球表面生长TiO_2纳米晶颗粒.利用透射电子显微镜(TEM)、X射线粉末散射(XRD)、X射线光电子能谱(XPS)、N_2气吸脱附等手段表征了材料的物相组成和表面结构.研究表明:所制备的氟修饰F-SiO_2@TiO_2纳米复合材料为核壳结构,具有较大的比表面积、较好的介孔结构及较佳的热稳定性.同时,TiO_2纳米颗粒在F-MCM-41小球表面分散均匀、结晶度高、颗粒尺寸小且均一、与F-SiO_2结合牢固.重量吸附实验和光催化实验进一步证实F修饰可抑制水的吸附有利于提高F-SiO_2@TiO_2材料的疏水性和对气相有机污染物的光催化性能.     

Carboxyl-modified hierarchical wrinkled mesoporous silica supported TiO2 nanocomposite particles with excellent photocatalytic performances

Titanium dioxide (TiO₂) is a common photocatalyst for organic pollutants degradation. However, in practical application, the poor adsorption capacity of pure TiO₂ seriously impeded its efficiency in the degradation of organic molecules. In this work, a series of hierarchical wrinkle mesoporous silica supported TiO₂ nano-composite particles (TiO₂ @WMS-COOH) were successfully prepared. Thanks to their high surface areas, large pore volumes and mesoporous structures, these materials showed high adsorption capacity and excellent photocatalytic performance towards dye molecules, which is comparable to or even better than commercial catalyst P25. Moreover, their photocatalytic efficiency can be further enhanced by increasing the calcination temperature during preparation process. Therefore it can be concluded that the TiO₂ @WMS-COOH particles may find promising applications in the photodegradation of organic pollutants.     

Preparation and photocatalytic activity of Cu-doped TiO2/SiO2

Cu²⁺-doped nanostructured TiO₂-coated SiO₂ (TiO₂/SiO₂) particles were prepared by the layer-by-layer assembly technique and their photocatalytic property was studied. TiO₂ colloids were synthesized by the sol-gel method using TiOSO₄ as a precursor. The experimental results showed that TiO₂ nanopowders on the surface of SiO₂ particles were well distributed and compact. The amount of TiO₂ increased with the increase in coating layers. The shell structure appeared to be composed of anatase titania nanocrystals at 550°C. The 2-layer coated TiO₂ particles on the surface showed a higher degradation rate compared with all the different-layer samples. The photocatalytic activity of Cu²⁺-doped TiO₂/SiO₂ was higher than that of undoped TiO₂/SiO₂. The optimum dopant content was about 0.10wt%.     

Petrochemical characteristics of leucogranite and a case study of Bengbu leucogranites

Leucogranites have a relatively narrow variation in SiO2 content （70.5%-75.5%）. Giving similar SiO2 content, leucogranites have relatively higher Al2O3 （〉13.5%） and lower TFeO ＋ MgO （〈2.5%） contents than those of normal granites. These petrochemical characteristics suggest that leucogranites are de- rived from partial melting at relatively low temperature and are not significantly affected by fractional crystallization. In the present study, we propose that the Al2O3 vs SiO2 and TFeO ＋ MgO vs SiO2 dia- grams can be used to distinguish leucogranites from normal granites. In addition, we report the major element compositions of the Jurassic granitic intrusions from Jingshan-Tushan-Mayishan in the Bengbu area, east-central China. Using the Al2O3 vs SiO2 and TFeO ＋ MgO vs SiO2 diagrams and the comparison with the High Himalayan leucogranites in mineralogical and petrochemical characteristics, we suggest that the Jingshan-Tushan-Mayishan intrusions belong to a leucogranite belt. Similar to those of the High Himalayan leucogranites, the Bengbu leucogranites have low Mg# values, indicating that they resulted from low temperature dehydration partial melting of the subducted continental crust of the South China Block at the crustal depth.     

硅胶的孔径结构对脱附活化能的影响

该文为研究硅胶孔结构对水蒸气吸附速率／脱附活化能的影响，在吸附水蒸气动力学实验中采用了间歇式吸附方法，用程序升温脱附技术测定了水在硅胶上的程序升温脱附（TPD）曲线并估算了水的脱附活化能。结果表明：A型、B型和C型硅胶的平均孔径分别为2nm、5．28nm和10．65nm。在10％～45％低湿范围内，硅胶的平均孔径越大，其吸附初始阶段的吸附速率越快，平衡吸湿量越小；高湿度条件下，硅胶的平均孔径和孔容越大，其吸附初始阶段的吸附速率越慢，平衡吸湿量越大。水分子在A型、B型和C型硅胶上的脱附活化能分别为35．54kJ／mol、31．41kJ／mol和26．16kJ/mol，说明水分子在硅胶上的脱附活化能随着硅胶的孔径增加而明显减小。与微孔硅胶相比．在中高湿度下中孔硅胶有较大的平衡吸附量和较低的脱附活化能。     

Li3O+超碱团簇的结构及储氢性能的理论研究

采用杂化密度泛函理论(DFT)的B3LYP方法,在6-311++G (d, p)基组水平上对Li₃O ^{0, +}超碱团簇的几何结构和稳定性进行理论计算,并研究了Li₃O⁺团簇的储氢性能。结果表明,Li₃O⁺团簇结构相比中性Li₃O团簇结构的动力学稳定性要高。氢分子在Li₃O⁺团簇表面能以介于物理吸附与化学吸附之间的形式吸附,每个Li原子最多可以有效吸附三个H₂,储氢质量分数可达33.01 wt%。H₂分子在Li₃O⁺团簇表面的平均吸附能范围为1.959~3.591 kCal/mol,该吸附能满足在近室温条件下可逆吸放氢反应的热力学要求。