Luisella Celi

Interaction Of Inositol Hexaphosphate On Clays: Adsorption And Charging Phenomena

The interaction of myoinositol hexaphosphate (IHP) with goethite, and with phyllosilicates such as illite and kaolinite, was studied by assessing the adsorption mechanisms and the electrochemical modifications induced by adsorption of a molecule at such a high-charge density. In addition to quantitative studies, Fourier-Transform Infrared (FT-IR) spectroscopy was used to establish the mechanisms of interaction. Laser Doppler Velocimetry-Photon Correlation Spectroscopy (LDV-PCS) was employed to determine the electrophoretic mobility and the size of the particles. The experiments were also run with orthophosphate (Pi) for comparison. The quantity of adsorbed IHP reached 0.64 μmol m -2 on goethite, 0.38 μmol m -2 on illite, and 0.27 μmol m -2 on kaolinite. The mechanism of adsorption of IHP involved the phosphate groups, whereas the organic moiety affected the process only in terms of conformational hindrance. Thus, on goethite surfaces, because IHP occupied an area equivalent to four sites for Pi, it was supposed to be bound to the oxide by four of its six phosphate groups, whereas the other two were free. On the illite and kaolinite surfaces, the area occupied by IHP was equivalent to about two sites for Pi, suggesting that a lower number of phosphate groups are bound to phyllosilicates. The phosphate groups that did not react with the minerals caused a modification of the electrochemical properties. In particular, IHP adsorption caused dispersion of the particles and a net increase of the negative charge of the surface.

Analysis of carboxyl groups in soil humic acids by a wet chemical method, Fourier-Transform Infrared spectrophotometry, and solution-state carbon-13 nuclear magnetic resonance. A comparative study

Carboxyls are important functional groups that affect polarity and reactivity in humic acids (HAs). Carboxyls were analyzed in eight soil HAs by three methods based on widely differing principles: (i) wet chemical analysis, (ii) Fourier-Transform Infrared spectrophotometry (FT-IR), and (iii) liquid-state 13 C Nuclear Magnetic Resonance (13C NMR). The objective was to uncover the suitability of each of these methods for the analysis of COOH groups in HAs and the extent to which the three methods agreed with each other in quantitative measurements of COOH groups in HAs. In regard to reaction mechanisms, the chemical Ca-acetate method is based on ion-exchange of H of COOH for Ca of Ca-acetate. From FT-IR spectra of HAs, COOH groups were determined by totaling absorbances at 1720-1710 cm−1 (COOH) and 1620-1600 cm−1 (COO−), whereas from 13C NMR spectra of HAs, COOH groups were computed by integration of 175-185 ppm area. Good correlations were found between the three methods although the COOH values computed by 13C NMR were higher, as a result of the inclusion of small amounts of esters, amides, and lactones, than those obtained by the other two methods. Thus, depending on the equipment and facilities available, soil scientists have a choice of methods that can be used for determining COOH groups in HAs.

EFFECTS OF INTERACTION OF ORGANIC AND INORGANIC P WITH FERRIHYDRITE AND KAOLINITE-IRON OXIDE SYSTEMS ON IRON RELEASE

The solubility of iron oxides in soils is governed by crystal size, crystal order, isomorphous substitutions, and associations with other minerals. Their dissolution occurs by protonation, reduction, or complexation with ligands such as phosphate and inositol phosphates. In this work, the interaction of inositol hexaphosphate (IHP) and phosphate (Pi) with ferrihydrite (Fh) or ferrihydrite-kaolinite systems (Fh-KGa2) was studied to assess the effects on iron oxide dissolution. Adsorption of IHP and Pi on a two-line Fh and Fh-KGa2 was performed in the range 0 to 0.004 mol P L−1, and the release of P and Fe from samples of Fh or Fh-KGa2 saturated with IHP or Pi was evaluated at different pHs. The amount of P adsorbed on Fh increased, reaching a plateau at 2.12 μmol m−2 for IHP and 4.57 μmol m−2 for Pi. Sorption on KGa2 was lower. It increased to 2.24 μmol m−2 for IHP and to 2.96 μmol m−2 for Pi on Fh-KGa2. On the basis of the IHP/Pi ratios, it was hypothesised that IHP interacted with Fh through two of its six phosphate groups, whereas it interacted with Fh-KGa2 through one P group. Phosphate desorption from these complexes occurred only at pH ≥ 4.5 and was higher for Pi than for IHP and from the Fh-KGa2 system than from Fh. The desorption of IHP was followed by a consistent Fe release, higher at basic pHs. By contrast, Pi adsorption inhibited dissolution of both minerals, although the anion was desorbed in higher amounts compared with the P organic form.

Interaction of inositol phosphate with calcite.

The interaction of myo-inositol hexaphosphate with calcite was studied to evaluate the adsorption mechanisms and the electrochemical modifications induced by interaction of a molecule at such a high-charge density. In addition to quantitative information through the construction of adsorption isotherms, FT-IR and Laser Doppler Velocimetry - Photon Correlation Spectroscopy (LDV-PCS) were employed to investigate the nature of the adsorbent-adsorbate bonds and to determine the electrophoretic mobility and size of the particles before and after sorption. The experiments were also run with orthophosphate (Pi) for comparison. The amount of sorbed P increased to reach a plateau at 17.8 μmol m-2 for inositol hexaphosphate (IHP) while for Pi rose 1.4 μmol m-2 but at Ce > 6ċ10-4M it had a sharp increase reaching 155 μmol m-2. As expected, for Pi, adsorption predominated up Ce 6ċ10-4M by covering about 20% of total surface. The adsorption occurred at sites that behaved as nucleus of formation of the clustering of Ca- and PO4-ions with the ending formation of calcium phosphate precipitates at Ce higher than 6ċ10-4M. The reaction of inositol hexaphosphate with calcite involves, besides adsorption, precipitation of Ca salts and hence calcite dissolution also at the lowest added IHP concentrations, accounting for the large amount retained by calcite. Sorption of IHP on calcite caused aggregation of particles at low concentrations followed by an increase of their negative charge and hence re-dispersion at higher concentrations. These results indicate a great IHP-fixing capacity of calcite that can affect its accumulation in soils and P bioavailability, and a considerable change of calcite electrochemical properties and particle size distribution that can modify aggregate stability.

Soil Organic Matter Changes In A Spruce Chronosequence On Swedish Former Agricultural Soil: I. Carbon And Lignin Dynamics

Afforestation of former agricultural soils is an important tool to reduce atmospheric CO2 levels because of the high capacity of both biomass and soil to store carbon (C). The long-term effect of afforestation on the role of soil as C sink was investigated in a chronosequence of 18-, 29-, 64-, 73-, and 91-year-old Picea abies stands, established on former agricultural soils in southwestern Sweden. The forest floor was sampled both as a whole and in the three horizons (unaltered, semialtered, and altered organic horizons), whereas the mineral soil was sampled at 0 to 5, 5 to 15, and 15 to 30 cm depth. The physicochemical characterization of soil, C and nitrogen content, and lignin characterization by the cupric oxide oxidation method was conducted. Within the first decades of afforestation, the soil properties reflected the former soil management, and C accumulation involved mainly the organic layer (3.41-5.92 Mg C ha−1), where the new litter was accumulating, and coniferous lignin showed a low degree of degradation. Meanwhile, the mineral soil behaved as a C source (95.5-80.2 Mg C ha−1), loosening the C inherited from the previous land use probably because of the nutrient needs of the growing trees that accelerated organic matter mineralization. Vanillyl moieties were almost absent, and the syringyl units, derived from angiosperms, were considerably oxidized, indicating a low C input from the conifer litter and high degradation of the inherited organic material. With age, the C stock started to increase both in the organic and mineral layers, reaching 191.5 Mg ha−1 in 91 years. The accumulation in organic soil was accompanied by a litter nitrogen impoverishment and decrease of soil pH, which probably limited the microbial community to fungi, able to degrade lignin. In the oldest stands, the lignin material seemed to be intensively altered, mainly in the deeper organic horizons, where aromatic, mobile, acidic compounds were produced and/or translocated down in the profile. This could contribute to organic matter incorporation into mineral layers and to mineral weathering, driving the soil toward the restarting of the podzolization process. From these results, it seemed that even if the previous land use caused an initial acceleration of organic matter mineralization, soil started to accumulate C when the influence of the new vegetation dominated. The soil became a major C sink with a long forest growth of about a century. The accumulation was strongly affected by litter composition, which changed with spruce age.

Desorption And Plant Availability Of Myo-inositol Hexaphosphate Adsorbed On Goethite

The specific adsorption and high affinity of inorganic phosphate for Fe oxides limit its desorption and, hence, its availability to plants. Organic P compounds such as inositol phosphate show even greater affinity for soil oxides. This may result in low desorption and, hence, poor bioavailabilty, explaining the accumulation of these compounds in soils, although inositol phosphate desorption from Fe oxides has never been quantified. Desorption is controlled by several parameters such as soil pH, percentage of P saturation, ligand competition, and the characteristics of the P-containing compounds. In this work the desorption of myo-inositol hexaphosphate (IHP) and inorganic phosphate (Pi) from goethite (Gt) was studied while assessing the effect of pH, citrate and bicarbonate extractability and the number of desorption cycles. P availability to Lolium perenne L. was also studied in the presence of IHP or Pi added in solution or sorbed on goethite. The amount of desorbed P, as IHP, increased with pH and the number of desorption cycles, but in all cases it did not exceed one-fifth of the desorbed Pi, suggesting a limited availability of IHP when adsorbed on goethite, especially at low pH. Citrate and bicarbonate solutions extracted a small amount of IHP with respect to Pi, probably the result of the inability of their mechanisms to detach the four P groups involved in the IHP bonding with the goethite surface and of the high negative charge of the IHP-Gt complex that hampers the approach of ligands to the surface. The ryegrass that received P as IHP showed limited growth, signs of P deficiency, and a low shoot/root ratio as a consequence of the poor nutrient availability, particularly when IHP was supplied in solution and Gt was present in the pots. In contrast, significantly larger biomass productions were always obtained when P was supplied in inorganic form, and no significant differences among the tests were observed.

Paramagnetic Iron-Doped Hydroxyapatite Nanoparticles with Improved Metal Sorption Properties. A Bioorganic Substrates-Mediated Synthesis

This paper describes the synthesis of paramegnetic iron-containing hydroxyapatite nanoparticles and their increased Cu(2+) sorbent capacity when using Ca(2+) complexes of soluble bioorganic substrates from urban wastes as synthesis precursors. A thorough characterization of the particles by TEM, XRD, FTIR spectroscopy, specific surface area, TGA, XPS, and DLS indicates that loss of crystallinity, a higher specific area, an increased surface oxygen content, and formation of surface iron phases strongly enhance Cu(2+) adsorption capacity of hydroxyapatite-based materials. However, the major effect of the surface and morphologycal modifications is the size diminution of the aggregates formed in aqueous solutions leading to an increased effective surface available for Cu(2+) adsorption. Maximum sorption values of 550-850 mg Cu(2+) per gram of particles suspended in an aqueous solution at pH 7 were determined, almost 10 times the maximum values observed for hydroxyapatite nanoparticles suspensions under the same conditions.

Sorption Of Phosphate On Goethite At High Concentrations

Phosphorus (P) concentrations in soil solution are generally low, whereas those near fertilizer particles may reach much greater values. The process governing P sorption at these high concentrations is obscure. Thus, the sorption mechanisms at high P concentrations on a synthetic goethite were inves

Effects of soil organic fractions on iron oxide biodissolution under anaerobic conditions

Soil iron oxides are poorly soluble; however, their dissolution may favor not only an increase in the amount of available iron but also the release of anions and cations, adsorbed or occluded on FeIII oxides, which may have a great impact on environmental quality. In this study, the reductive biodissolution of iron oxides by microorganisms was evaluated using different soil humic fractions as electron donors. A mixed population of microorganisms extracted from an anaerobic mud was incubated for 15 days under anaerobic conditions in the presence of ferrihydrite or goethite, after adding, as electron donors, dissolved organic matter (DOM), fulvic acids (FA), humic acids (HA) or, for comparison, acetate. At regular time intervals Eh, pH, dissolved FeII and the concentration of dissolved organic compounds that remained in solution were measured. The redox potential (Eh) decreased rapidly in the first days of incubation, more with ferrihydrite than with goethite, and then returned to the initial values with some differences in specific values, depending on the organic fraction. The amounts of FeII released from ferrihydrite reached a maximum of 11.0 μg Fe mL−1 after 15 days of waterlogging compared with 7.5 μg Fe mL−1 released from goethite. Ferrihydrite released more FeII because of its higher specific surface area and its low crystallinity. DOM and FA fractions were the most effective in Fe reduction and as a C source for bacteria, suggesting that microorganisms can also use DOM for N supply as well as for C, selecting fractions rich in monosaccharides, amino acids, and carboxyl acids.

Humic acid characteristics in podzol soil chronosequence

Humic acid (HA) characteristics were studied in a natural revegetation chronosequence of 10-, 20-, 60-year-old and mature podzol soils under a pine forest, along the spoil heaps of a sand quarry. The elemental composition of HAs showed a trend towards carbon increase and hydrogen decrease with soil age. Essential differences in the atomic ratios between humic acids extracted from the different soils may be due to the intensity of the humification process as related to soil age. Compared with HAs extracted from organic horizons, those from mineral horizons showed lower C/N and H/C ratios, whereas O/C ratios were higher. Electrophoretic data showed that the proportion of the more-mobile fraction (L-MS) was higher in the mineral horizons than in the organic horizons and, among organic layers, in the Oe and Oa horizons compared with Oi. Intensive transformation of pine remains may have occurred and led to HAs with an increasing degree of humification in only 60 years. Moreover, progressive accumulation of the L-MS fraction in the E and Bs horizons with soil age might be the result of the ongoing migration of the most-polar organic compounds down through the soil profiles.