Application of programmed thermodesorption of the liquid under quasi-isothermal conditions to investigate physicochemical properties of liquid layers and solid surfaces

This paper presents the results of measurements of the programmed thermodesorption of polar and nonpolar liquids from the surface of different types of solids. The course of thermodesoption was found to depend on the properties of the solid and the wetting liquid. Thermodesorption occurred not exponentially but in steps, which reflects the noncontinuous changes in the properties of the surface layer with the distance from the solid surface. This effect intensified with the increase in polarity of the wetting liquid and the heterogeneity of the solid surface. The earlier investigations showed that application of the method of differential thermal analysis allowed determination of the distribution of the adsorption potential of the liquid on the solid surface.The author is indebted to Prof. M. Jaroniec for very fruitful discussions and to Prof. J. Choma for the activated carbon samples.     

Application of thermal analysis in studies of energetic heterogeneity of solid surfaces

The paper reports a study of the programmed thermodesorption of benzene, octane, methanol and propanol from the silica gel surface under quasi-isothermal conditions. The experimental data revealed the gradual desorption of the liquid, due to the heterogeneous nature of the silica gel surface. This phenomenon was used in calculations of adsorption potential distribution. It was concluded that this method can be successfully applied in studies of the heterogeneity of solid surfaces, and is more convenient than traditional adsorption methods.     

Development of master curves for discriminating the mechanism of solid state reactions from experimental data obtained by using the cyclic and controlled rate thermal analysis

The cyclic and Controlled Rate Thermal Analysis method (CRTA) has been used. The two rates automatically selected in the cyclic curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction. Thus, the activation energy can be calculated without previous knowledge of the actual reaction mechanism. Provided that the activation energy,E, is known, a procedure has been developed for determining the kinetic law obeyed by the reaction by means of master curves that represent the values of the reacted fraction, α, as a function of?E/R(1/T-1/T _0.5),T _0.5 being the temperature at which α=0.5. This procedure has been tested by studying the thermal decomposition reaction of BaCO₃.     

Application of Statistical Rate Theory of Interfacial Transport to Study Solid Surface Heterogeneity from Controlled-rate Thermal Desorption

Controlled-rate thermodesorption (CRTD) spectra are obtained by adjusting the heating rate in such a way that the rate of desorption can be constant. A quantitative analysis of the obtained spectra is presented, based on application of the statistical rate theory of interfacial transport (SRTIT) to describe both adsorption and desorption kinetics. The SRTIT approach relates the rates of adsorption and desorption to the chemical potentials of the adsorbate in the gaseous and in the adsorbed phases. This quantitative analysis of the CRTD spectra yields the condensation approximation for the actual adsorption energy distribution. For the purpose of illustration, an analysis is made of water desorption from a synthetic apatite mineral under CRTD and classical TPD conditions. The influence of the adsorption and desorption rates is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Constant rate thermal analysis for thermal stability studies of polymers

This paper explores the relationship between the shapes of temperature-time curves obtained from experimental data recorded by means of constant rate thermal analysis (CRTA) and the kinetic model followed by the thermal degradation reaction. A detailed shape analysis of CRTA curves has been performed as a function of the most common kinetic models. The analysis has been validated with simulated data, and with experimental data recorded from the thermal degradation of polytetrafluoroethylene (PTFE), poly(1,4-butylene terephthalate) (PBT), polyethylene (PE) and poly(vinyl chloride) (PVC). The resulting temperature-time profiles indicate that the studied polymers decompose through phase boundary, random scission, diffusion and nucleation mechanisms respectively. The results here presented demonstrate that the strong dependence of the temperature-time profile on the reaction mechanism would allow the real kinetic model obeyed by a reaction to be discerned from a single CRTA curve.     

Controlled rate thermal analysis of hydromagnesite

The reaction of magnesium minerals such as brucite with CO₂ is important in the sequestration of CO₂. The study of the thermal stability of hydromagnesite and diagenetically related compounds is of fundamental importance to this sequestration. The understanding of the thermal stability of magnesium carbonates and the relative metastability of hydrous carbonates including hydromagnesite, artinite, nesquehonite, barringtonite and lansfordite is extremely important to the sequestration process for the removal of atmospheric CO₂. This work makes a comparison of the dynamic and controlled rate thermal analysis of hydromagnesite and nesquehonite. The dynamic thermal analysis of synthetic hydromagnesite proves that dehydration takes place in two steps at 135 and 184°C, dehydroxylation at 412°C and decarbonation at 474°C. Controlled rate thermal analysis shows the first dehydration step is isothermal and the second quasi-isothermal at 108 and 145°C, respectively. In the CRTA experiment both water and carbon dioxide are evolved in an isothermal decomposition at 376°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of magnesium carbonates such as nesquehonite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal partial nesquehonite structure.     

Dynamic and controlled rate thermal analysis of hydrozincite and smithsonite

The understanding of the thermal stability of zinc carbonates and the relative stability of hydrous carbonates including hydrozincite and hydromagnesite is extremely important to the sequestration process for the removal of atmospheric CO₂. The hydration-carbonation or hydration-and-carbonation reaction path in the ZnO-CO₂-H₂O system at ambient temperature and atmospheric CO₂ is of environmental significance from the standpoint of carbon balance and the removal of green house gases from the atmosphere. The dynamic thermal analysis of hydrozincite shows a 22.1% mass loss at 247°C. The controlled rate thermal analysis (CRTA) pattern of hydrozincite shows dehydration at 38°C, some dehydroxylation at 170°C and dehydroxylation and decarbonation in a long isothermal step at 190°C. The CRTA pattern of smithsonite shows a long isothermal decomposition with loss of CO₂ at 226°C. CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of zinc carbonate minerals via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. The CRTA technology offers a mechanism for the study of the thermal decomposition and relative stability of minerals such as hydrozincite and smithsonite.     

Hydrazine-hydrate intercalated halloysite under controlled-rate thermal analysis conditions

Journal of Thermal Analysis and Calorimetry - The thermal behaviour of halloysite fully expanded with hydrazine-hydrate has been investigated in nitrogen atmosphere under dynamic heating and at a...     

Steam-carbon gasification catalyzed by calcium: Assessment of the porous structure of active carbons from plum stones and synthetic active carbons

A need for an elaboration of the methods for synthesis and characterization of activated carbons with a requisite porous structure has existed for a long time. One of the methods giving possibility for creating controlled mesopore and micropore structures deals with the steam gasification of various carbon materials. In this work the effects of calcium catalyst on the catalytic steam gasification of active carbons from plum stones and porous polymers are presented. Determination of micropores capacity and specific adsorption in mesopores have been performed by means of the _s method, but adsorption on the heterogeneous solids was described by the integral equation with various local isotherms. This equation has been solved by the regularization method. Based on this method the changes in structural parameters of active carbons depending on the amount of calcium catalyst were estimated.Nomenclature d width of slit-like micropore - F(x) distribution function of the half-width - p vapor pressure of sorbate - p/p _N relative pressure - PSAC Plum Stone Active Carbon - average pore radius, nm - S ₁ relative limit of the validity of experimental point on the adsorption isotherm in the computations by means of regularization method - SAC Synthetic Active Carbon - S _BET specific surface area calculated by means of BET method, m²/g - S _mes mesopore surface area, m²/g - S _mic micropore surface area, m²/g - T absolute temperature, K - V _mes sorption capacity of mesopores, cm³/g - V _mic sorption capacity of micropores, cm³/g - V _p sorption capacity of pores, cm³/g - w/w weight in weight concentration - x half-width of slit-like micropore, nm - x ₁ maximum of half-width of micropore slit, nm - average half-width of slit-like micropore, nm - X _min-X _max integration limits of thex Greek Letters Greek Letters variance of average half-width of slit-like micropore, nm² - local relative filling of micropores - total relative filling of micropores     

Detection of four different OH-groups in ground kaolinite with controlled-rate thermal analysis

The thermal behaviour of mechanochemically treated kaolinite has been investigated under dynamic and controlled rate thermal analysis (CRTA) conditions. Ten hours of grinding of kaolinite results in the loss of the d(001) spacing and the replacement of some 60% of the kaolinite hydroxyls with water. Kaolinite normally dehydroxylates in a single mass loss stage between 400 and 600°C. CRTA technology enables the dehydroxylation of the ground mineral to be observed in four overlapping stages at 385, 404, 420 and 433°C under quasi-isobaric condition in a self-generated atmosphere. It is proposed that mechanochemical treatment of the kaolinite causes the localization of the protons when the long range ordering is lost.This revised version was published online in November 2005 with corrections to the Cover Date.     

Temperature programmed desorption analysis of sol-gel-derived titania films

Sol-gel-derived titania films were analyzed by temperature programmed desorption (TPD) and X-ray diffraction (XRD) techniques. The relationship between the TPD curves measured for two types of titania gel films and their crystal structures was investigated. On the basis of the analyses, a preparation process for a titania sol solution containing anatase nanocrystals was designed and developed. Using this process, a colloidal anatase titania sol solution was prepared by heating aqueous titanium hydroxide containing HCl at 60°C for 2 h. The nanocrystal structure of the titania films obtained by coating the sol on glass substrates was confirmed by TPD and XRD measurements.     

On the interpretation of small-angle X-ray scattering during water adsorption by carbon adsorbents

Two models accounting for the changes of shape of the small-angle X-ray scattering (SAXS) curves during water adsorption by carbon adsorbents are discussed. The first model is based on the assumption of partial filling of the pore space; the second one presumes micropore swelling during water adsorption. Analysis of the results allows one to conclude that the first model is valid. This conclusion is in agreement with adsorption investigation data.Deseased 1993.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1220–1223, July, 1993.     

Suppression of Photoinduced BBO Defects Generation on TiO2(110) by Water (cited: 1)

We have investigated creation of variable concentrations of defects on TiO₂(110)-(1×1) sur-face by 266 nm laser using temperature programmed desorption technique. Oxygen-vacancy defects can be easily induced by ultraviolet light, the defects concentration has a linear dependence on power density higher than 50 mW/cm² for 90 s irradiation. No observa-tion of O₂ molecule and Ti atom desorption suggests that UV induced defects creation on TiO₂(110)-(1×1) is an effective and gentle method. With pre-dosage of thin films of water,the rate of defects creation on TiO₂(110)-(1×1) is slower at least by two orders of magnitude than bare TiO₂(110)-(1×1) surface. Further investigations show that water can be moreeasily desorbed by UV light, and thus desorption of bridging oxygen is depressed.     

Fe对胜利褐煤焦结构和气化反应性能的影响

酸洗褐煤负载不同含量的Fe催化剂在固定床反应器上进行热解,然后采用FT-IR、Raman spectra、TPD和TG研究Fe催化剂对煤焦官能团、碳微晶结构、表面活性位和气化反应性的影响。FT-IR结果表明,催化热解作用下煤焦中-OH、-CH₃、-CH₂活性官能团数量增加。Raman光谱测试结果显示,随着Fe含量的增加,I_G/I_all由0.095减少到0.087,I_D3/I_all由0.090增加至0.097,表明在Fe催化作用下部分大芳香环结构转变为小芳香环结构。TPD实验结果表明,活性位数量随着煤焦中Fe含量升高而不断增加。在3%含Fe量时煤焦活性位数量随着吸附温度的升高而增加,800 ℃后煤焦表面活性位数量开始降低。750 ℃条件下CO₂吸附量随着吸附时间的延长而增加,45 min后煤焦达到饱和吸附状态。煤焦-水蒸气等温气化实验表明,煤焦气化反应性与活性位数量有密切的关系,Fe催化剂主要通过增加煤焦表面活性位数量提高煤焦气化反应性。     

Analysis of volatiles and semivolatiles in drinking water by microextraction and thermal desorption

A new technique to analyze aqueous samples for nanograms per liter levels of volatile and semivolatile compounds using microextraction and thermal desorption into a gas chromatograph/ion trap mass spectrometer (GC/MS) is described. This method is inherently sensitive (50 mL of aqueous sample is extracted prior to each desorption), uses no solvents, and detects volatiles and semivolatiles in the same analysis. Aqueous standards and environmental samples are pumped through a length of porous-layer open-tubular capillary column, which is then thermally desorbed onto a 30 m × 0.25 mm i.d. analytical column interfaced to an ion trap mass spectrometer for subsequent separation and detection. Sharp chromatographic peaks and reproducible retention times (RT) were observed. Replicate injections of surrogates (n = 6) averaged 32.6% R.S.D. Analysis of domestic tap water detected 55 analytes, some at the low-nanograms per liter level, and detected 3 halogenated ethenes, not previously reported in drinking water. Analysis of an aqueous sample from a municipal ground water source detected the presence of numerous semivolatile compounds at trace-levels.     

Suppression of Photoinduced BBO Defects Generation on TIO2（110） by Water

We have investigated creation of variable concentrations of defects on TIO2（110）-（1×1） surface by 266 nm laser using temperature programmed desorption technique. Oxygen-vacancy defects can be easily induced by ultraviolet light, the defects concentration has a linear dependence on power density higher than 50 mW/cm2 for 90 s irradiation. No observation of O2 molecule and Ti atom desorption suggests that UV induced defects creation on TiO2（110）-（1×1） is an effective and gentle method. With pre-dosage of thin films of water, the rate of defects creation on TiO2（110）-（1×1） is slower at least by two orders of magnitude than bare TiO2（110）-（1×1） surface. Further investigations show that water can be more easily desorbed by UV light, and thus desorption of bridging oxygen is depressed.     

Distribution functions of structural heterogeneity of microporous adsorbents

The distribution functions of structural heterogeneity of microporous adsorbents have given. Influences of adsorbents and adsorbates types on this heterogeneity have been studied.

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Verteilungsfunktionen für die Struktur-Heterogenität von mikroporösen Adsorbentien

Zusammenfassung Es werden Verteilungsfunktionen für die strukturelle Heterogenität von mikroporösen Adsorbentien angegeben. Die Einflüsse der Adsorbens- und Adsorbatarten auf diese Heterogenität wurden untersucht.

     

Comments on correct determination of structural parameters for adsorbents of heterogeneous micropore systems

Summary Different forms for functions determining the micropores volume after the structural parameter are given. It is stated that the accepted range of the variability of the structural parameterk can influence considerably the values of parameters determining the structural heterogeneity of microporous adsorbents. The lack of normalization can cause great errors in the micropore volume determination.

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Über die korrekte Bestimmung von Strukturparametern für Adsorbentien auf heterogenen, mikroporösen Systemen

Zusammenfassung Es werden verschiedene Formen für Funktionen, die das Mikroporenvolumen bestimmen, gegenüber dem Strukturparameter angenommen. Man stellte fest, daß im angenommenen Bereich die Änderungen des Strukturparametersk die Werte der die Strukturheterogenität der mikroporösen Adsorbenten bestimmenden Parameter bedeutend beeinflussen. Der Mangel an Normalisierung kann große Fehler in der Bestimmung des Mikroporenvolumens verursachen.

     

迎头色谱程序升温脱附快速测定吸附热新方法

在Ｐｏｌａｎｙｉ吸附势理论基础上，结合程序升温脱附曲线的测定，建立了一个快速测定吸附热的新方法，详细讨论了该方法的原理，通过微机采样和数据处理，测定一条吸附热与覆盖度的曲线仅需１ｈ左右。