The Effect of Heat Treatment on the Structure of Zeolite A

Knowledge about the thermal properties of zeolites is extremely important due to their potential application in the chemical industry. In this work, the thermal stability and the dehydration process of zeolite A were investigated by in situ high temperature Fourier transform infrared spectroscopy. The progress of thermal decomposition that zeolite A underwent during the controlled temperature increase in the range of 25–600 °C was determined by the DRIFT spectroscopic method. Infrared spectra are presented and discussed for this compound on the basis of the crystal structure. Based on the courses of the obtained DRIFT spectra, it was found that, during heating, water was gradually removed from the structure of the material, followed by dehydration and formation of hydrogen bonds. It was established that the process of thermal degradation began as early as 550 °C. The analysis of the obtained results of structural tests can be repeated on other materials from the zeolite group and complements the research work on the thermal analysis of these materials.

EXPRESS: Application of Infrared Reflectance Spectroscopy on Plastics in Cultural Heritage Collections: A Comparative Assessment of Two Portable Mid-Fourier Transform Infrared Reflection Devices

Plastics have been increasingly used to create modern and contemporary art and design, and nowadays, museum collections hold numerous objects completely or partially made of plastics. However, the preservation of these materials is still a challenging task in heritage conservation, especially because some plastics show signs of degradation shortly after their production. In addition, different degradation mechanisms can often take place depending on the plastic composition and appropriate environmental and packaging conditions should be adopted. Therefore, methods for in situ and rapid characterization of plastic artifacts’ composition are greatly needed to outline proper conservation strategies. Infrared (IR) spectroscopy, such as attenuated total reflection Fourier transform infrared spectroscopy (ATR–FTIR), is a well-established method for polymeric material analysis. However, ATR-FTIR requires an intimate contact with the object, which makes its application less appropriate for the in situ investigation of fragile or brittle degraded plastic objects. Mid-FTIR reflectance spectroscopy may represent a valid alternative as it allows in situ measurements with minimum or even no contact, and IR data can be acquired rapidly. On the other hand, spectral interpretation of reflectance spectra is usually difficult as IR bands may appear distorted with significant changes in band maximum, shape and relative intensity, depending on the optical properties and surface texture of the material analyzed. Presently, mid-FTIR reflection devices working in external reflection (ER-FTIR) and diffuse reflection (DRIFT) modes have been used in cultural heritage research studies. As the collected vibrational information depends on the optical layout of the measuring system, differences between ER-FTIR and DRIFT spectra are thus expected when the same polymer is analyzed. So far, ER-FTIR and DRIFT spectroscopy have been individually explored for the identification of plastic objects, but comparative studies between the application of two reflectance FTIR modes have not been presented yet. In this work, the use of two portable FTIR spectrometers equipped with ER-FTIR and DRIFT modes were compared for plastics identification purposes for the first time. Both references of polymeric materials and historical plastic objects (from a Portuguese private collection) were studied and the differences between ER-FTIR and DRIFT spectra were discussed. The spectra features were examined considering the two different optical geometries and analytes’ properties. This new insight can support a better understanding of both vibrational information acquired and practical aspects in the application of the ER-FTIR and DRIFT in plastic analysis.

DEGRADATION OF PINE WOOD STRUCTURE WHEN OZONOLYTIC DELIGNIFICATION

The pine wood degradation under ozonation was studied. It was determined the contents of lignin (LG) and cellulose (CL) in cellulose-containing material (CM) obtained from the ozonized wood. The degree of polymerization (DP) of cellulose from CM was determined. Samples of CM were investigated using IR diffuse reflectance (DRIFT) spectra and XRD analysis. HPLC analysis of water-soluble LG ozonolysis products was conducted. Ozonation results in 40–42% delignification degree of wood. Aromatics destruction is confirmed by DRIFT spectra. The intensity of stretching band at 1736 cm-1 of unconjugated C=O groups in LG or hemicelluloses markedly increases. A stoichiometric ratio of absorbed ozone and an amount of destructed guaiacylpropane units as well as a composition of water-soluble products show that ozonolysis is a primary mechanism of aromatics degradation in wood. The data on XRD analysis, the amounts of removed LG and the change of cellulose DP allow conclusion that the wood ozonation is accompanied by a destruction of hemicelluloses and amorphous cellulose in the wood. It is shown that the specific ozone uptake £1.5 mmol O3/g matches the domination of the wood delignification with the lowest degradation of cellulose fibers and acceptable efficiency in terms of the ozonation process.

Differences in humic acids structure of various soil types studied by DRIFT spectroscopy

The method of diffuse reflectance infrared spectroscopy (DRIFT) proved to be useful for studying the soil organic matter structure. The aim of this study was to compare DRIFT spectra of humic acids (HAs) separated from various soils and to identify their specific nature. Samples of agricultural soils (Dystric Cambisol, Haplic Chernozem, Greyic Phaeozem, and Haplic Luvisol) were collected from humic (A) horizons. Soil samples of reclaimed dumpsites (Haplic Technosol (molic) and (calcic)) were taken from the upper part of the soil profile. Samples of forest soils were collected from surface organic (H) horizons of Cambisols in spruce (Picea abies L. Karst.) and beech (Fagus silvatica L.) forests. The selected soil types differ in pH, carbon content, texture, and humus quality. An extraction of HAs was performed using a mixture of 0.5 M NaOH and 0.1 M Na₄P₂O₇. The separated HAs were freeze-dried and analyzed using a DRIFT spectrometer (Thermo Nicolet Nexus) without KBr dilution. There were found differences in relative aromaticity among the agricultural soils HAs. The most aromatic character was observed in HAs from Chernozems and the least in Cambisols. Preservation of the natural structure of Chernozem HAs during the reclamation process was documented on the HAs spectra from Haplic Technosols (molic). By using the DRIFT spectra of HAs of forest H horizons, it is possible to identify the fragments of decomposed material (gymnosperms or angiosperms). HAs isolated from these horizons represent a certain interstage between lignin and the matured soil humic acids.

Portable diffuse reflectance infrared Fourier transform (DRIFT) technique for the non-invasive identification of canvas ground: IR spectra reference collection

Sixteen of the most important canvas grounds used since the XIV to the XX century were prepared following the ancient recipes (including grounds from Vasari, Caravaggio, and De Chirico) and a reference library of DRIFT spectra was built.