357 research outputs found
Effects of ions on water structure: a low-field (1) H T1 NMR relaxometry approach
Aqueous salt solutions play an important role in nature because of their effects on environmental biogeochemical processes and on structural properties of biomolecules. Upon dissolution, salts split in ions that are solvated. Water in hydration shells is subjected to molecular motions that can be monitored by (1) H T1 NMR relaxometry. This technique allowed the evaluation of the nature of the interactions between water and ions via variable temperature experiments. Examination of relaxometry properties of aqueous solutions at variable salt concentrations allowed acknowledgement of the role played by ions in either structuring or destructuring water aggregates. A mathematical model has been applied on six environmentally relevant salts: NaCl, KCl, CaCl2 , CaCO3 , NaNO3 , and NH4 NO3 . It was linear only for the concentration dependence of KCl-R1 . This model accorded with the one reported in literature where it has been considered valid only for diluted solutions. However, in the present study, the range of linearity for KCl was extended up to the saturation point. The model was modified for NaCl, CaCl2 , and CaCO3 by using it as an exponential form in order to account for the nonlinearity of the R1 -versus-concentration curves. Nonlinearity was explained by the nonnegligible ion-ion interactions occurring as concentration was increased. Finally, further modification was needed to account for the asymmetric distribution of water around nitrate (in NaNO3 and NH4 NO3 ) and ammonium (in NH4 NO3 ). This study is preliminary to the comprehension of the diffusion mechanisms of ions in water solutions at the equilibrium condition with solid surfaces such as soils and biochar-amended soils. Copyright © 2014 John Wiley & Sons, Ltd
Environmental NMR: Fast-field-cycling Relaxometry
Fast-field-cycling (FFC) NMR relaxometry deals with the variation of the spin–lattice relaxation times (T1) in a complex system, as the strength of the applied magnetic field is changed. Information about molecular dynamics can be achieved. Until now, only model theories for FFC NMR relaxometry have been developed for polymer and material sciences. Just a few applications have been performed in the environmental sciences. These mainly deal with soil porosity, rock permeability, biomass transformations, and natural organic matter dynamics. Further, FFC NMR relaxometry can also be applied to monitor the environmental fate of contaminants, to understand the dynamics of nutrients at the soil–plant interface, and to evaluate reaction mechanisms in heterogeneous catalysis for the development of green reactions. This article summarizes the advances of the technique in environmental investigations and describes the tools used to monitor dynamics of organic and inorganic molecules in environmental compartments
conformational redistribution of honey components following different storage conditions
The present study aims at the investigation of the changes in water distribution among the organic components of selected honey samples following honey storage at different temperatures. Results, achieved by application of fast field cycling NMR relaxometry, revealed that the organic constituents were homogeneously distributed within the whole samples stored at room temperature. Conversely, after four months of refrigeration at 4°C, the organic systems were included in persistent clusters, as a consequence of the water release due to the larger stability of the intramolecular interactions over the intermolecular ones. The new conformational arrangements of the honey constituents entailed enhancement of honey moisture content. For this reason, it can be suggested that honey refrigeration prior to storage at room temperature may be detrimental for its long-term storage. In fact, higher risk of fermentation may occur once the sample is warmed after the first refrigeration step
Effect of pruning-derived biochar on heavy metals removal and water dynamics
Biomass-derived biochar is considered as a promising
heavy metal adsorbent, due to abundance of polar functional
groups, such as carboxylic, hydroxyl, and amino
groups, which are available for heavy metal removal. The
aims of this study were to evaluate the effectiveness of an
orchard pruning-derived biochar in removing some heavy
metals (through the evaluation of isotherms) and to study
water dynamics at the solid-liquid interface as affected by
heavy metal adsorption (through an innovative nuclear magnetic
resonance (NMR) relaxometry approach). Both isotherms
and NMR spectra revealed that Pb and Cr showed a
good affinity for the biochar surface (Pb > Cr), while Cu was
less affine. Accordingly, higher amounts of Pb and Cr were
adsorbed by biochar as compared to those of Cu in the single
systems. In binary systems (i.e., when two metals were applied
simultaneously), Pb showed the highest inhibition of the
adsorption of the other two metals, whereas the opposite was
evidenced when Cu was used; the competitive adsorption was
also strongly influenced by the metal residence time on biochar
surface. In ternary systems (i.e., when all metals were
applied simultaneously), even in the presence of high amounts
of Pb and Cr, considerable adsorption of Cu occurred, indicating
that some biochar adsorption sites were highly specific
for a single metal
Improvement of physical, chemical and biochemical proprieties of a salt affected Alfisol by addition of biochar and gypsum
Salinization is one of the major environmental problems threatening agricultural productivity. Soil salinization is defined as an excessive accumulation of salts within the soil profile. It negatively affects soil physical and chemical properties, as well as the biochemical ones. Reclamation of salt affected soils requires removal of soluble salts and Na+ from the soil exchange sites. Subsequently, salts are leached out the root zone by irrigation water when available.
Gypsum (CaSO4·2H2O) is the most commonly used chemical amendment for reclamation of salt affected soils since it provides Ca2+ that replaces Na+ on the exchange sites and improves soil structure. Also organic amendments have been considered, but not extensively studied, for reclamation of salt affected soils. Recent studies have reported that biochar can be rich in nutrients like Ca2+ and Mg2+ and may enhance their availability in soil when added as amendment. Therefore, addition of biochar to a salt affected soil could aid in its remediation by supplying Ca2+ and Mg2+, and replacing Na+, improving aggregate stability and hydraulic conductivity.
The objective of this study was to evaluate the effects of gypsum and biochar for the reclamation of a saline-sodic soil on some physical, chemical and biological properties.
The topsoil of an Alfisol, about fifty meters far from the foreshore in the Petrosino coast (Sicily, Italy), was used for this experiment. The soil was air-dried and sieved at 2 mm. The main physical and chemical properties of the soil were: pH 7.3, clay 23 %, total carbonates 50.9 %, electrical conductivity 0.81 dS m-1 (1:5, w/v), total organic C 11.0 g kg-1, cation exchange capacity 24.8 cmol(+) kg-1, exchangeable sodium percentage 35 %. Two doses of gypsum (2.6 and 5.1 g kg-1 of soil) and two doses of biochar (4.2 and 8.3 g kg-1) were tested. The two doses of gypsum were calculated in order to decrease ESP from 35% to 25% and to 15%, respectively, whereas biochar was added in order to achieve an amount of 10 and 20 Mg ha-1. Following addition of gypsum and biochar, either alone or in combination, 100 g of soil were incubated at room temperature in 150 mL plastic pots and maintained at 50% of soil water holding capacity during all the duration of the experiment (22 days). One week after the incubation, three horse-radish seeds were sown. Then, after 13 days, plants were removed, oven dried at 60°C for 48 hours and weighed. The soils were analyzed to determine porosity, CEC, ESP, ECe, microbial biomass C, soil respiration and microbial community structure. The experiment was carried out in octuplicate. In this work, the results are reported and discusse
Conformational Redistribution of Honey Components following Different Storage Conditions
The present study aims at the investigation of the changes in water distribution among the organic components of selected honey samples following honey storage at different temperatures. Results, achieved by application of fast field cycling NMR relaxometry, revealed that the organic constituents were homogeneously distributed within the whole samples stored at room temperature. Conversely, after four months of refrigeration at 4°C, the organic systems were included in persistent clusters, as a consequence of the water release due to the larger stability of the intramolecular interactions over the intermolecular ones. The new conformational arrangements of the honey constituents entailed enhancement of honey moisture content. For this reason, it can be suggested that honey refrigeration prior to storage at room temperature may be detrimental for its long-term storage. In fact, higher risk of fermentation may occur once the sample is warmed after the first refrigeration step
Hydration and water holding properties of cross-linked lignite humic acids
Lignite and lignite humic acids, which are used as soil amendments sometimes, are supposed to improve soil
properties such as water holding capacity. The structure of those materials is composed of various organic molecules
stabilized mostly byweak interactions. Therefore, excess ofwater causes only partial swelling, but most of
the physical structure is destabilized. This accelerates the desiccation and hampers their application as natural
hydrogel-like substances. In order to stabilize the structure of lignite humic acids and improve the water holding
capacity, we applied formaldehyde cross-linking procedure based on covalent coupling of aromatic humic acids
moieties. By combining the 1H NMR relaxometry and methods of thermal analysis, the kinetics and degree of hydration,
water distribution and moisture uptake were investigated. It was found that cross-linking induced a reduction
in moisture sorption capacity at lowrelative humidity and an increase at higher relative humidity,which
was attributed to the separation of functional groups and decreasing of structural compactness after crosslinking.
As a result, the cross-linked humic acids, exhibited faster water uptake and approximately three-fold
higher water holding capacity in comparison with the parental sample. The distribution of relaxation times of
water protons in swollen humic acids revealed the unification of pore size distribution upon cross-linking. Although
the improved hydration of cross-linked lignite humic acids already resembles the hydration of some hydrophilic
polymers, the water holding capacity is still belowthe capacity of classical hydrogels. Nevertheless, the
lowprice of lignite, sorption properties and its overall positive affect on soil quality and productivity give a promise
in application of this material both in agriculture and remediation technologies
Efficiency of biochar for reducing mobility of inorganic contaminants
Anthropogenic activities have produced numerous sites with extensive contamination close to residential areas.
Several physicochemical and biological remediation methods exist for remediation of metal contaminated soils
and lands, such as soil washing, soil flushing, phytoremediation, and electrokinetics.
Biochar (biologically derived charcoal) is produced by pyrolysis of biomasses under low oxygen conditions, and
it can be applied for recycling organic waste in soils.
The main objectives of the present study were to determine the possible use of biochar from forest ersidues (Populus nigra) in order to achieve a stabilization of inorganic contaminants by adsorption processes. Adsorption of
copper by biochar from dilute solutions showed a closer agreement with the Langmuir isotherm in a concentration
range 25-500 mM. The decontamination by biochar is very suitable because the treatment is passive and does not
require specialized equipment or extensive labor as compared to other remediation methods. Moreover, biochar
is also a possible carbon sink due to its long term storage in environment, thereby favouring mitigation of the
anthropic impact on environment
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