Proton NMR relaxometry as a useful tool to evaluate swelling processes in peat soils

Dramatic physical and physico-chemical changes in soil properties may arise due to temperature and moisture variations as well as swelling of soil organic matter (SOM) under constant conditions. Soil property variations may influence sorption/desorption and transport processes of environmental contaminants and nutrients in natural-organic-matterrich soils. Notwithstanding the studies reported in literature, a mechanistic model for SOM swelling is unavailable yet. The objective of the present study was the evaluation of the swelling of peat soils, considered as SOM models, by 1H NMR relaxometry and differential scanning calorimetry (DSC). Namely, information on the processes governing physical and physicochemical changes of peat during re-hydration were collected. The basic hypothesis of the present study was that the changes are slow and may affect water state as well as amounts of different water types into the peats. For this reason, such changes can be evidenced through the variations of mobility and thermal behaviour of the involved H2O molecules by using 1H NMR relaxometry and DSC. According to the experimental results, a mechanistic model, describing the fundamental processes of peat swelling, was obtained. Two different peats re-wetted at three temperatures were used. The swelling process was monitored by measuring spin-spin relaxation time (T2) over a hydration time of several months. Moreover, DSC, T1 – T2 and T2 – D correlation measurements were done at the beginning and at the end of the hydration. Supplementary investigations were also done in order to discriminate between the swelling effects and the contributions from soil solution, internal magnetic field gradients and/or soil microorganisms to proton relaxation. All the results revealed peat swelling. It was evidenced by pore size distribution changes, volumetric expansion and redistribution of water, increasing amounts of nonfreezable and loosely bound water, as well as formation of gel phases and reduction of the translational and rotational mobility of H2O molecules. All the findings implied that changes of the physical and physicochemical properties of peats were obtained. In particular, three different processes having activation energies comprised in the interval 5 – 50 kJ mol-1 were revealed. The mechanistic model which was, then, developed included water reorientation in bound water phases, water diffusion into the peat matrix and reorientation of SOM chains as fundamental processes governing SOM swelling. This study is of environmental significance in terms of re-naturation and re-watering of commercially applied peatlands and of sorption/desorption and transport processes of pollutants and nutrients in natural organic matter rich soil

Hexakis(dimethylformamide)bis(hexaphenylcyclohexasiloxanehexaolato)hexacopper(II) Dimethylformamide Solvate

The sandwich-like title complex, hexakis(dimethylformamide)-1O,2O,3O,4O,5O,6O-bis[2,4,6,8,10,12-hexaphenylsiloxane-2,4,6,8,10,12-hexaolato(6-)-1:22O1,2:32O2,3:42O3,- 4:52O4,5:62O5,1:62O6]hexacopper(II) tetrakis(dimethylformamide) solvate, [Cu6(C3H7NO)6{(C6H5)6O12Si6}2].4C3H7NO, is comprised of two regular crown-shaped macrocyclic hexadentate organosiloxanolate ligands chelating a flat Cu6 hexagon, as in the ethanol-solvated analogue investigated previously. The title complex has a more distorted shape than the trigonal ethanol-solvated analogue, being slightly side-oblated, but still contains a large empty inner channel accessible by small molecules (the diameter of the free cross-section being about 2.5 Å). Each CuII ion has square-pyramidal coordination with four basal siloxanolate O atoms and an apical dimethylformamide (DMFA) molecule (coordinated through its carbonyl group). The average bond lengths are: Cu-O(Si) 1.964 (11) Å and Cu-O(DMFA) 2.215 (10) Å. The structure contains four additional DMFA molecules per complex unit, linked by weak C-HO hydrogen bonds. Unexpectedly, the C=O bond length is longer [1.248 (10) and 1.255 (9) Å] in the uncoordinated DMFA molecules than in the coordinated [1.214-1.227 (7) Å]

Interacting effects of cation saturation and drying, freezing, or aging on the extractability of nonylphenol and phenanthrene from a sandy soil.

The structure and properties of the soil organic matter and its interactions with solutes may be altered by changes in soil chemistry and by the aging of soil. The main objective of this study was to investigate the effect of long-term aging and cation saturation of soil on the extractability and degradability of two hydrophobic xenobiotics in soil. In addition, it was tested if drying or freezing of soils can accelerate the relevant aging processes. The sandy topsoil was treated by either 0.1 M NaCl, CaCl2, AlCl3 solutions or water and samples were sterilized by gamma-radiation and spiked with C-14-labeled nonylphenol (NP) or phenanthrene (Phe) at 10 mu g g(-1) of soil. Samples were then used in four parallel experimental setups: (1) 9 months of aging under sterile conditions, (2) inoculation by native original soil with further 7 months of aging (bioaging), (3) drying and wetting or (4) freezing and thawing of soils. After different time intervals, the extractability of xenobiotics with water, cyclodextrin, and ethanol was investigated. During 9 months of aging under sterile conditions a continuous decrease of NP and Phe extractability and an increase of the non-extractable fraction occurred. During the 7 months of biologically active aging, the mineralization of NP was lower than of Phe while more NP remained extractable than Phe. In comparison to the sterile aging, the bioaging led to a less formation of non-extractable residues of NP and Phe. The long-term sterile aging effects on NP-extractability were also achieved by short-term freezing and thawing of the soils, while aging of Phe was better mimicked by drying-wetting cycles. The effects of cation saturation of soils on xenobiotics extractability were less pronounced. Sterile aging, bioaging, freezing, and thawing facilitate the formation of the non-extractable fraction of NP and Phe in the soils. Different cation treatments alter soil properties, but the effects on aging of NP and Phe in soils were negligible

Curie Temperature and Density of States at the Fermi Level for Al-Cu-Fe Phases: β-Solid State Solution-Approximants-Icosahedral Quasicrystals

A consistent reduction in the absolute value of the negative paramagnetic Curie temperature was found in a series of Al-Cu-Fe phases: β(CsCl)-solid state solution, noncanonical approximant (η-AlCu(Fe) phase), rational approximants (P1+P2-pentagonal phases) and icosahedral quasicrystal. For these Al-Cu-Fe phases, the decrease in the Curie temperature correlates with a reduction of the density of states at the Fermi level which was estimated from the low-temperature heat capacity measurements and first-principles calculations. The observed correlation was related to the antiferromagnetic indirect exchange interaction (Ruderman-Kittel-Kasuya-Yosida interaction) between the localized magnetic moments on Fe induced by the intrinsic structural defects in the Al-Cu-Fe phases. The weakening of Fe 3d-Al s, p hybridization owing to the intrinsic structural defects such as vacancies, antisite defects and distortions of coordination polyhedrons is suggested to be the main mechanism of appearance of localized magnetic moments on Fe atoms

Curie Temperature and Density of States at the Fermi Level for Al-Cu-Fe Phases: β-Solid State Solution-Approximants-Icosahedral Quasicrystals

A consistent reduction in the absolute value of the negative paramagnetic Curie temperature was found in a series of Al-Cu-Fe phases: β(CsCl)-solid state solution, noncanonical approximant (η-AlCu(Fe) phase), rational approximants (P1+P2-pentagonal phases) and icosahedral quasicrystal. For these Al-Cu-Fe phases, the decrease in the Curie temperature correlates with a reduction of the density of states at the Fermi level which was estimated from the low-temperature heat capacity measurements and first-principles calculations. The observed correlation was related to the antiferromagnetic indirect exchange interaction (Ruderman-Kittel-Kasuya-Yosida interaction) between the localized magnetic moments on Fe induced by the intrinsic structural defects in the Al-Cu-Fe phases. The weakening of Fe 3d-Al s, p hybridization owing to the intrinsic structural defects such as vacancies, antisite defects and distortions of coordination polyhedrons is suggested to be the main mechanism of appearance of localized magnetic moments on Fe atoms

Comparative study of the heat capacity of icosahedral quasicrystals in solid and liquid states

This study was supported by the Russian Foundation for Basic Research (project no. 10-02-00602-a).The heat capacity of icosahedral quasicrystals Al63Cu25Fe12 and Al62Cu25.5Fe12.5 has been studied at high temperatures up to 1700 K, which is by almost 400 K higher than the melting point of the material. It has been shown that the melt exhibits an excess heat capacity with respect to that determined by the Dulong-Petit law and that is a direct extension of the excess heat capacity of the solid state. It has been concluded that the excess heat capacity is related, as a whole, to the short-range order in the quasicrystal structure. This circumstance allows the identification of the orbital hybridization as the most probable mechanism of formation of the pseudogap in the electronic structure of the quasicrystals

Electric, magnetic, and thermal properties of quasicrystal-forming melts

This work was supported by the Russian Foundation for Basic Research, project no. 10-02-00602-a.The electric resistance, magnetic susceptibility, and specific heat of the icosahedral phases of the Al-Cu-Fe system have been examined in the melt region. It has been shown that the features of the properties of a homogeneous solid state, as well as correlations between these features, hold in melts up to temperatures above the melting point by several hundreds of degrees. The results indicate that the short-range order and orbital hybridization determine the mechanism responsible for the electronic spectrum and ultrahigh-resistance state of quasicrystals

Electric, magnetic, and thermal properties of quasicrystal-forming melts

This work was supported by the Russian Foundation for Basic Research, project no. 10-02-00602-a.The electric resistance, magnetic susceptibility, and specific heat of the icosahedral phases of the Al-Cu-Fe system have been examined in the melt region. It has been shown that the features of the properties of a homogeneous solid state, as well as correlations between these features, hold in melts up to temperatures above the melting point by several hundreds of degrees. The results indicate that the short-range order and orbital hybridization determine the mechanism responsible for the electronic spectrum and ultrahigh-resistance state of quasicrystals