Study of Heterogeneous Properties of Solids by Means of a Special Thermal Analysis Technique

Thermogravimetry (TG) was successfully applied in order to study the heterogeneous properties of solid surfaces and adsorbed liquid films. The method utilized the thermogravimetric mass-loss Q-TG and differential Q-DTG curves with respect to temperature and time for the desorption of liquidus from solid surfaces under quasi-isothermal conditions. Evaluation of the experimental data revealed the heterogeneous properties of the tested samples. It appears that this modern special TG technique is very useful for the study of liquid/solid systems and can be competitive with traditional techniques because of the speed and accuracy with which the data are obtained and the simplicity of the experimental operations. This revised version was published online in July 2006 with corrections to the Cover Date.     

苯在酸碱处理多级孔Y分子筛上的吸附及传质行为

利用H_4EDTA-NaOH共处理的方法制备了具有不同孔径分布的多级微-介孔NaY分子筛。运用XRD、N_2吸附、SEM、TEM对其结构进行了表征。采用频率响应(FR)和智能重量分析仪(IGA)技术研究了苯在改性后的多级孔NaY分子筛及微孔NaY分子筛上的吸附和传质性能。结果表明,适当的酸碱处理不会改变分子筛的晶体结构,但可调变NaY分子筛的精细结构;介孔的引入降低了分子在孔道中的扩散阻力,较大的孔径和较好的孔道贯通性有利于扩散和吸附中心的可接近性;对于微孔NaY分子筛,苯在分子筛上的吸附过程为其传质过程的速控步骤,对于酸碱处理的多级孔NaY分子筛,分子筛颗粒中微/介孔内的扩散过程及分子筛微-介孔孔道间的分子交换过程是传质过程的速控步骤。     

Application of CRTA to the study of microporosity by thermodesorption of pre-adsorbed water

Thermodesorption is here considered for its possibility of giving access to the microporosity of adsorbents. The requirements of this application (good separation of successive desorption steps, good control of the desorption pressure and temperature throughout the sample, possibility of a safe kinetic analysis of each step) are here fulfilled by carrying out the thermodesorption in the Controlled transformation Rate Thermal Analysis (CRTA) mode. The method is applied to 4 zeolites (3A, 4A, 5A and 13X) and a well characterized charcoal, from ?25 to 325°C, after pre-adsorption of water.     

The Studies of the Heterogeneous Properties of Solid Surfaces by Means of the Derivatograph Q-1500 D

A simple method has been adopted to obtain an important information on the heterogeneous properties of materials studied, adsorbed liquid films and liquid-solid interactions. The method utilizes Q-TG mass loss and the first derivative Q-DTG mass loss curves with respect to temperature and time obtained during programmed liquid thermodesorption in quasi-isothermal conditions. The values of the adsorption capacity, total porosity of material, the value of active centers, desorption energy distribution and mesopore-size distribution functions obtained by this method are in good agreement with those estimated on the basis of independent methods. The theoretical and experimental results provided novel and unique data on the heterogeneity of solid surfaces, properties of liquid adsorbed films and thermal stability of the liquid/solid interfaces. This paper presents the more important results obtained so far in the studies the liquid/solid systems by means of the Paulik's classical and quasi-isothermal techniques. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mesoporous Molecular Sieves Modified with Carbonaceous Deposits

There were investigated aluminosilicate MCM-41 samples in the as-prepared form and those modified by the deposition of carbonaceous compounds during conversion of cyclohexene for 12 h. The amount of the deposits decreased with the rising reaction temperature and increased with the Al content of the samples. The cyclohexene conversion followed mainly two mechanisms: cyclohexene skeletal isomerization and hydrogen transfer. The products with 6 carbon atoms in a molecule prevailed in all cases. The process of conversion, proceeding on the Brønsted acid sites, resulted in formation of both coke deposits and volatile products. The creation of coke caused a decrease in the effective concentration of both the Brønsted and the Lewis acid sites. Thermodesorption of pyridine showed that (i) the concentration of these sites before and after the conversion differed only slightly and (ii) the acidic strength of the Brønsted sites was practically independent of their concentration and the sample Si/Al ratio. The chemical composition of the deposits was insignificantly affected by the Al content of the materials and depended mostly on the temperature and duration of the reaction. At relatively low temperatures, both aliphatic and aromatic compounds were formed, being rather weakly bound to the surface of the material. After a longer (55 h) reaction period, some deposits appeared that were strongly bound to the surface. Isotherms of adsorption of water, benzene, and nitrogen were determined, from which a mechanism of this process was derived. It included most probably multilayer adsorption at lower relative pressures, followed by capillary condensation. The sorption capacities of the uncoked samples for benzene and nitrogen were relatively high and independent of the sample Al content. In the case of water, however, an observed reduction in the sorption capacity with the increasing Al content suggested that clusters of the adsorbed molecules formed around the Al centers and caused partial clogging of the material pores. The deposited coke strongly decreased both the surface area and the sorption capacity of the materials.     

纳米晶构筑一维多孔氧化锌的合成与表征

One-dimensional porous zinc oxide was prepared via the calcination of zinc oxalate precursor obtained by solvothermal method. The products were characterized by XRD, SEM, TEM, photoluminescence (PL) spectrum and nitrogen adsorption-desorption. The results show that the obtained zinc oxide sample is porous and constructed by nanoparticles about 30 nm in size. The specific surface area and total pore volume are 126 m²·g^-1 and 0.13 cm³·g^-1, respectively． The PL properties related with defects in ZnO nanoparticles were discussed for porous zinc oxide samples.     

医用多孔壳聚糖膜的制备及性能研究

以邻苯二甲酸二丁酯为致孔剂,制备了多孔壳聚糖膜,并用扫描电镜对其表面和断面形貌进行了分析,同时对膜的吸水性、水蒸气透过性、比表面积、力学性能及生物相容性等进行了考察。分析结果表明:以邻苯二甲酸二丁酯为致孔剂,制备的多孔壳聚糖膜孔径均匀,吸水性好,孔隙率高,比表面积大,膜的最大吸水率、孔隙率和比表面积分别为196%、71.5%和1.0472 m2.g-1;膜的力学性能好,最大抗拉强度为273.17MN/m2。     

在线固相氧化物吸附-火焰原子吸收法测定痕量银

基于硅胶表面对碱性体系中新生成的氧化银(Ag2O)的有效吸附, 建立了流动注射-固相氧化物分离富集-火焰原子吸收法测定痕量银的方法. 当银以氧化物的形式被滞留在硅胶固相表面时, 硅胶表面的硅醇基和表面电荷有利于反应体系中新生成的Ag2O胶状沉淀的吸附, 将收集的沉淀用HNO3(10%, 体积分数)洗脱后用火焰原子吸收测定. 当进样体积为5.4 mL时, 测得的富集系数为25.5, 检出限为0.6 μg/L, 采样频率为50次/h, 线性范围为2~150 μg/L, 相对标准偏差(RSD)为2.0%(40 μg/L, n=11). 将该法用于自来水、河水、井水、雪水和山泉水中银含量的测定, 加标回收率分别为93.3%, 89.5%, 96.6%, 108.4%和102.8%.     

Thermal and Mechanical Characterization of Yarn Samples from Flemish Tapestry of the Sixteenth Century

We propose a physico-chemical approach for theharacterization of the conservation condition of yarns from a Flemish tapestry of the sixteenth century. The aging effect on the yarns’ performance was evaluated by comparison with commercial materials. Water uptake experiments highlighted the aptitude of yarns toward water sorption and their increased hydrophilicity upon aging. Thermogravimetric analysis can be considered a fast approach for the fiber identification and assessment on the material life-time. The dynamic mechanical analysis provided direct evidence on the yarns, conservation state and their performance under different mechanical stresses. The proposed characterization path can be relevant for stating the condition of the tapestry and for designing a conservation protocol for the preservation of the artwork.     

Characterization of Hollow Chemical Garden Fibers from Metal Salts and Water Glass

Hollow fibers formed from water glass and metal salts of IIA(Ca), VIIB(Fe, Co, Ni) and IB(Cu) groups were characterised in this study. Fragile fibres obtained herein broke down into small pieces during isolation and drying. Quantitative information about morphology, chemical composition and surface structure of the fibres were obtained. The diameter and wall thickness of the fibers were around 50 and 3 . respectively. They had particulate inner and smooth outer surfaces. Fibers had variable composition with metal (II) oxide/SiO₂ ratio in the range 0.31 to 1.02. While group VIIB metal (II) fibres were amorphous, group IIA and IB metal (II) fibres were partially crystalline All the fibres had pores both in micro pore and meso pore region. The B.E.T surface area from N₂ adsorption data was in the range of 10–249 m³ g^–1 and 8–176 m² g^–1 from Langmuir and B.E.T models respectively.     

Thermal Characterization of Warifteine by Means of TG and a DSC Photovisual System

This work proposes thermal characterization as analytical methodology for the identification and purity assay of warifteine, an alkaloid in Cissampelos sympodialis Eichl. Thermal and kinetic parameters were determined by means of TG and DSC photovisual studies. The TG results showed that the decomposition of warifteine in air and nitrogen atmospheres proceeds in three and four steps, respectively. The TG data allowed calculation of the kinetic parameters of warifteine. The activation energy values obtained by different methods displayed a good correlation. With the DSC photovisual system applied it is possible to detect the impurity level in warifteine after its purification. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of Titania/Silica Gel by Means of Low-Pressure Nitrogen Adsorption

Adsorbents synthesized by grafting of titania onto mesoporous silica gel surfaces at different temperatures were studied by means of nitrogen adsorption–desorption and water desorption. The pore size distribution f(R_p) of titania/silica gel depends on the titania concentration (C_TiO2) and the temperature of titania synthesis. Nonuniformity of TiO₂ phase is maximal at a low C_TiO2 value (3.2 wt.% anatase deposited at 473 K), and two peaks of the fractal dimension distribution f(D) are observed at such a concentration of titania, but at larger C_TiO2 values, only one f(D) peak is seen. More ordered filling of pores and adsorption sites by nitrogen, reflecting in the shape of adsorption energy distributions f(E) at different pressures of adsorbate, is observed for adsorbent with titania (rutile+anatase) grafted on silica gel at a higher temperature (673 K).     

Analysis of Pesticides in Water Samples Using GC-ECD and GC-MS/MS Techniques

Abstract

A pesticide multiresidue method for determining dichlorvos, naled. lindane, diazinon. chlorpyri-fos-methyl, dichlofluanid, chlorpyrifos, folpet, α– and β-endosulfan, endosulfan-sulphate, fen-propathrin and acrinathrin in water samples at the levels required by the EEC Drinking Waters Directive has been developed. The pesticides were selected among the most used during die last 20 years in Almeria (Spain), where there is a high agricultural activity. Solid Phase Extraction (SPE) was selected as extraction method after being compared with Liquid-Liquid Extraction (LLE). Moreover, different gas chromatographic detectors (Electron Capture Detector, ECD; Mass Spectrometer, MS; Tandem Mass Spectrometer, MS/MS) were compared. The best results of repeatability and sensitivity were obtained for ECD and MS/MS.     

Determination of Total Nitrogen in Environmental Samples: Validation by Comparison of Techniques and Intralaboratory Studies

Abstract

A rapid, microwave-based extraction method was employed to oxidize all forms of nitrogen to nitrate in environmental samples using persulfate. The digest was then analyzed spectrophotometrically after an offline reduction of nitrate to nitrite using a cadmium reductor column was completed. The precision of the method was tested at the 0.5 mg l^?1 level and was 5.2% (N = 10). The detection limit based on S/N = 3 was calculated to be 0.15 mg l^?1. The method was thoroughly validated by comparison of analytical techniques and intralaboratory comparison studies.     

Use of Thermal Analysis in the Study of Sodium Carbonate Causticization by Means of Dolomitic Lime

Dolomitic lime samples were treated with sodium carbonate solution and the causticizing process was followed at different temperatures by recording the TG and DTA curves of the solid-phase products that separated after different time intervals. The chemical reactions occurring during causticization are discussed. From the TG curves, apparent kinetic parameters were derived. Some aspects of the kinetic compensation effect are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adsorption properties and porous structure of new carbon materials

The adsorption properties of the new carbon materials, sibunites, which are mesoporous samples with a developed surface of pores, were studied. The isotherms of the adsorption of benzene vapor were determined to estimate the porous structure of these materials. The principal methods for calculating the parameters of the porous structure of sibunites were analyzed. The application of the BET equation even in the presence of a small number of micropores can distort the results, therefore the most suitable method for estimating the surface of mesopores is one that is based on the Dubinin—Zaverina equation. The estimation of the surface of sibunites using water vapor adsorption is demonstrated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1377–1380, August, 1993.     

Thermal Characterization of Lapachol by Means of TG and DSC Coupled to a Photovisual System

Thermal characterization is proposed as analytical methodology for the purity assay of lapachol, and for determination of the quality parameters of capsules containing this molecule. The TG data revealed that lapachol is more stable in the presence of adjuvants, showing the good quality of the formulation. The kinetic parameters obtained were lower for lapachol drug than for the formulated lapachol. The DSC data demonstrated good compatibility between lapachol drug and the adjuvant in the formulated lapachol, and did not reveal impurities such as secondary products of the isolation and recrystallization processes. The data were confirmed by the DSC-photovisual findings. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of Some Cyclodextrin Derivatives by Thermal Analysis

Acetyl-cyclodextrins, maltosyl-β-cyclodextrin, methyl-β-cyclodextrin and hydroxypropyl-cyclodextrins were characterized from data obtained with hot stage microscopy, differential scanning calorimetry and thermogravimetry. Phase transformation processes were studied by thermomicroscopy. Enthalpy values of dehydration processes have been explained with the different chemical composition of the substituent groups of cyclodextrins. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characterization of Rubber Epoxy Blends by Thermal Analysis

Differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the blends ofepoxy cresol novolac (ECN) resin toughened with liquid carboxy terminated butadiene-co-acrylonitrile (CTBN) rubber have been carried out. Exothermal heat of reaction (ΔH) due to crosslinking of the resin in presence of diaminodiphenyl methane(DDM, as amine hardener) showed a decreasing trend with increasing rubber concentration. Enhancements of thermal stability as well as lower percentage mass loss of the epoxy-rubber blends with increasing rubber concentration have been observed in TG. Dynamic mechanical properties reflected a monotonic decrease in the storage modulus (E′) with increasing rubber content in the blends. The loss modulus (E″) and the loss tangent(tanδ) values, however, showed an increasing trend with rise of the temperature up to a maximum (peak) followed by a gradual fall in both cases. Addition of 10 mass% of CTBN resulted maximum E″ and tanδ. This revised version was published online in July 2006 with corrections to the Cover Date.