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1.
Cross-linking of humic substances with organic bridging groups is thought to contribute to the humification of soil organic matter. Model cross-linked humic substances were prepared by cross-linking Amherst soil humic acid by a diepoxide and a polycarboxylic acid, applying procedures established for cross-linking of polymers and textile fabrics. Products of the cross-linking reactions were analyzed by FTIR and 13C CPMAS NMR. Physicochemical properties of the products were determined by solubility experiments and thermal analysis. The incorporation of the cross-linker into the matrix of the humic acid by covalent linkages was confirmed by both the disappearance of bands of the reactive functional groups of the cross-linker in the FTIR spectrum and the increase of signals related to the incorporation of the cross-linker into the matrix of the humic acid in the FTIR and 13C CPMAS NMR spectra. The formation of covalent ester and ether linkages by the cross-linking reaction was indicated. Water solubilities at pH 6.2 of the cross-linked samples as determined by UV/Vis spectrometry were reduced compared to controls. Fewer water molecule bridges were formed in the cross-linked samples, which was attributed to a lower number of available functional groups and increased distances between humic acid strands caused by the cross-linking molecules. Reduced reactivities of humic acid strands in the cross-linked samples further indicated successful cross-linking. The reactions investigated in this study can be regarded as models for reactions occurring in natural soils to test the significance of cross-linking reactions in the humification process of soil organic matter and the physico-chemical properties and ecological function of organic matter in geosolids.  相似文献   

2.
To obtain information on the contribution of aromatic fragments to the chemical structure of humic substances, we carried out a study on the [1H]NMR and [13C]NMR spectra of humic and fulvic acids and their oxidative degradation products extracted from an Andosol soil.[1H]NMR spectra of all organic fractions present considerable adsorption between 7.4 and 8.8 ppm, due to the presence of aromatic protons.The percentages of aromatic protons in respect to the total amount of protons are as follows: FA 20%, HA 19%, degraded FA < 12%, degraded HA 14%. The values indicate that the contribution of aromatic structures to the humic substances is significant, also considering that they are highly substituted.The degraded fractions contain smaller amounts of aromatic protons, because degradation causes the opening of the aromatic rings. Thus results obtained from the degradation do not seem to be reliable for defining the importance of aromatic structures in humic substances.Also the [13C]NMR spectra show signals in the aromatic region which derive from unsubstituted carbon atoms, while signals originating from tertiary carbon atoms merge with the noise. We believe that, at present, [1H]NMR spectroscopy is more suited for studying the role played by aromatic compounds in organic soil fractions.  相似文献   

3.
Characterization of humic substances is challenging due to their structural complexity and heterogeneity. Solid state nuclear magnetic resonance (NMR) is regarded as one of the best tools for elucidating structures of humic substances. The primary solid state NMR technique that has been used so far is the routine 13C cross polarization-magic angle spinning (CP-MAS) technique. Although this technique has markedly advanced our understanding of humic substances, the full potential of NMR for characterizing humic substances has yet to be realized. Recent technical developments and applications of advanced solid state NMR have revealed the promise to provide deeper insights into structures of humic substances. In this paper, we summarized and demonstrated the systematic solid state NMR protocol for characterization of humic substances using a humic acid as an example. This protocol included (1) identification of specific functional groups using spectral editing techniques, occasionally assisted by 1H13C two-dimensional heteronuclear correlation (2D HETCOR) NMR, (2) quantification of specific functional groups based on direct polarization-magic angle spinning (DP-MAS) and DP-MAS with recoupled dipolar dephasing, combined with spectral editing techniques, (3) determination of connectivities and proximities of specific functional groups by 1H13C 2D HETCOR or 2D HETCOR combined with spectral editing techniques, and (4) examination of domains and heterogeneities by 1H13C 2D HETCOR with 1H spin diffusion. We used a soil humic acid as an example to demonstrate how this protocol was applied to the characterization of humic substances step by step. Afterwards, based on typical 13C NMR spectra of humic substances we described how we could combine different NMR techniques to identify specific functional groups band by band from downfield to upfield. Finally, we briefly mentioned the potential new NMR techniques that could be developed to enrich the current systematic protocol. This systematic protocol is not only applicable to humic substances but also to other natural organic matter samples.  相似文献   

4.
The phosphorus content of marine humic acids (HA) is in the range of 0.1–0.2%. The C/P ratios of the HA are 300 to 400. Marine fulvic acids (FA) contain 0.4–0.8% P and have C/P ratios of 80 to 100. High molecular weight organic matter dissolved in pore waters (DOM) contains 0.5% P and has C/P of 90. The data suggest that during the formation sequence: Plankton → DOM → FA → HA → Kerogen, phosphorus is lost, mainly in the FA → HA (and possibly also in the HA → Kerogen) step. Diagenesis of sedimentary humic acids is accompanied by loss of phosphorus (as well as of nitrogen) to form HA with C/P ratios of 1000.Soil humic substances resemble marine humates in P content (0.3%) and soil FA's are about three to fivefold enriched in P relative to HA. C/P ratios are lower in soil HA (ca. 200) as compared with marine HA. Humic acids from diagenetic products such as peat and lignite are highly depleted in P. Rough calculations indicate that humate bound P may account for 20–50% of the organic phosphorus reservoir in sediments. The chemical speciation of this P is unknown, but lack of correlation with ash, Fe, Ca or Al content (in marine humates, at least) indicates that it is organically bound.  相似文献   

5.
13C and 1H NMR spectra were obtained for humic acids isolated from marine sediments. NMR shows great promise in identifying structural components of humic acids as some new and interesting structural features are identified. Aliphatic structures were found to constitute a much larger fraction of humic acids than previously thought, and they appeared to be highly branched. Although the aromatic content of terrestrial humic acid was found to be lower than expected, the aromaticity appears to be a specific discriminator of terrestrial/aquatic source types. A humic acid isolated from an anoxic algal sapropel was found to be composed predominantly of polyuronic acids and different than other aquatic sedimentary humic substances.  相似文献   

6.
Aqueous solutions of increasing pH (7.0, 10.6 and 12.6) were used to extract exhaustively the organic matter (OM) from a pelo-stagnogley (heavy clay) soil in long term cultivation. OM yield was 1.7 times greater when the extracts were processed using an XAD-8 and XAD-4 resin-in-tandem procedure than that from the procedure of the International Humic Substances Society (IHSS). The substantial difference can be attributed to the amount retained by the XAD-4 resin, which is lost in the IHSS process. Elemental, δ13C, δ15N, cation exchange capacity, neutral sugars, amino acids and solid state CPMAS 13C NMR analyses indicated significant, but rational similarities and differences between the various fractions isolated. There was strong NMR evidence for material derived from lignin in all the humic and fulvic acid isolates. The signals were attenuated in the more transformed/oxidized fractions isolated at lower pH. Novel humic acid fractions enriched in carbohydrate/peptide functionalities were isolated from the more hydrophobic extracts at pH 10.6 and 12.6. Isolates from XAD-4, of microbial origin, were enriched in neutral sugars but not in amino acids, and had minimal aromaticity. Components isolated from the cultivated soil were broadly similar to those from a comparable soil in long term grassland. The compositions of fractions isolated from the drainage water were similar to those extracted from the soil but had higher carboxyl content. The amount and composition of the various organic fractions in grassland and the continuously cropped soil are discussed in terms of their potential to contribute to carbon sequestration by soil under similar management regimes.  相似文献   

7.
The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS 15N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by 15N NMR. Liquid state 15N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (1H–15N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.  相似文献   

8.
Carboxyl groups are abundant in natural organic molecules (NOM) and play a major role in their reactivity. The structural environments of carboxyl groups in IHSS soil and river humic samples were investigated using 2D NMR (heteronuclear and homonuclear correlation) spectroscopy. Based on the 1H-13C heteronuclear multiple-bond correlation (HMBC) spectroscopy results, the carboxyl environments in NOM were categorized as Type I (unsubstituted and alkyl-substituted aliphatic/alicyclic), Type II (functionalized carbon substituted), Type IIIa, b (heteroatom and olefin substituted), and Type IVa, b (5-membered heterocyclic aromatic and 6-membered aromatic). The most intense signal in the HMBC spectra comes from the Type I carboxyl groups, including the 2JCH and 3JCH couplings of unsubstituted aliphatic and alicyclic acids, though this spectral region also includes the 3JCH couplings of Type II and III structures. Type II and III carboxyls have small but detectable 2JCH correlations in all NOM samples except for the Suwannee River humic acid. Signals from carboxyls bonded to 5-membered aromatic heterocyclic fragments (Type IVa) are observed in the soil HA and Suwannee River FA, while correlations to 6-membered aromatics (Type IVb) are only observed in Suwannee River HA. In general, aromatic carboxylic acids may be present at concentrations lower than previously imagined in these samples. Vibrational spectroscopy results for these NOM samples, described in an accompanying paper [Hay M. B. and Myneni S. C. B. (2007) Structural environments of carboxyl groups in natural organic molecules from terrestrial systems. Part 1: Infrared spectroscopy. Geochim. Cosmochim. Acta (in press)], suggest that Type II and Type III carboxylic acids with α substituents (e.g., -OH, -OR, or -CO2H) constitute the majority of carboxyl structures in all humic substances examined. Furoic and salicylic acid structures (Type IV) are also feasible fragments, albeit as minor constituents. The vibrational spectroscopy results also suggest that much of the “Type I” signal observed in the HMBC spectrum is due to carboxylic acid esters and possibly α-substituted alicyclic acids.  相似文献   

9.
Humic acids were isolated from 5 sediments in which the origin nature of the organic matter are both typical and different. The humic acids were characterized on the basis of elemental compositions, infrared spectra and 1H and 13C NMR. This last technique, especially 13C NMR, provides qualitative and semi-quantitative information regarding aromatic structure. Combined data from the three techniques permits differentiation of marine and terrestrial organic matter as well as identification of mixtures of humic acids from the two sources.  相似文献   

10.
The molecular structural features of humic acid (HA) fractions isolated from recent sediments from the estuaries and continental platform along the Huelva littoral (SW Iberian Peninsula, Spain) were studied using complementary analytical tools. The approach included elemental analysis, solid state, 13C cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (13C CP-MAS NMR), pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) and stable C and N isotopic composition (δ13C, δ15N). The results point to the presence of vascular plant matter contributing to all the HAs, even those far from the coastal area. A contribution of lignocellulose material was detected from 13C NMR signals at 152 ppm (O-aryl C), 55 ppm (methoxyl C) and 33 ppm (alkyl chain) and confirmed by the presence of lignin derived structures (methoxy phenols) in the pyrolysis chromatograms. Nevertheless, the HAs from the westernmost part of the continental platform had the lowest aromatic and the highest C-alkyl abundance (13C NMR spectroscopy). These data, combined with low C/N and high H/C values, a relative enrichment in δ13C and the presence in the pyrolysates of conspicuous n-alkyl nitrile and amide series, together with n-alkane/ene homologues, pointed towards a relevant marine (autochthonous) contribution to this sedimentary organic matter (OM). In contrast, HAs from sediments collected from the Tinto-Odiel River mouth and Guadiana Estuary areas revealed a major input of terrestrial OM. In general, the data support the idea that the HAs still contain valuable information about the signature of aliphatic and aromatic biomacromolecules contributing to the deposited OM.  相似文献   

11.
13C NMR spectra of solid humic substances in Holocene sediments have been obtained using cross polarization with magic-angle sample spinning techniques. The results demonstrate that this technique holds great promise for structural characterizations of complex macromolecular substances such as humin and humic acids. Quantifiable distinctions can be made between structural features of aquatic and terrestrial humic substances. The aliphatic carbons of the humic substances are dominant components suggestive of input from lipid-like materials. An interesting resemblance is also noted between terrestrial humic acid and humin spectra.  相似文献   

12.
The structural, spectroscopic and phenanthrene binding characteristics were compared for humic acids (HA) extracted from two different sources: eight soils and six lake sediments. The elemental analysis revealed that HA from sediments had higher H/C, N/C, and (N + O)/C ratios compared to HA from soils, reflecting a lower degree of humification and more autochthonous organic input upon the formation of the HA for lake sediments versus soil environments. HA from soils exhibited a higher content of aromatic carbon structures than the sediment HA based on 13C NMR results. The source of HA was easily distinguished by comparing the synchronous fluorescence spectra of each HA group. The presence of a protein like fluorescence was prominent for the HA from sediment while it was minor for the HA from soil. Irrespective of the HA source, however, humification index (HIX) exhibited a common positive correlation with the aromatic content, and a negative correlation with O-alkyl carbon structures of the HA. The correlations were consistent with the general structural trends of humification processes, suggesting that HIX may serve as a source independent predictor to describe the structural information and humification degree of terrigenous HA. Aromatic carbon structures did contribute to enhancing the phenanthrene binding for both sources of HA. However, the primary structures associated with non-ideal phenanthrene binding (i.e., non-linear sorption isotherm) appear to differ by the HA source because the opposed correlations were obtained between aromaticity and the isotherm linearity for the two HA groups. Our results suggest that the HA structural function associated with specific non-linear sorption for hydrophobic organic contaminants (HOCs) may be more strongly governed by the HA source than by the apparent physico-chemical properties.  相似文献   

13.
The competitive binding of rare earth elements (REE) to purified humic acid (HA) and MnO2 was studied experimentally using various HA/MnO2 ratios over a range of pH (3 to 8). MnO2, humic acid and REE solutions were simultaneously mixed to investigate the kinetics of the competitive reactions. Aqueous REE–HA complex is the dominant species whatever the experiment time, pH and HA/MnO2 ratio. The value of the distribution coefficients between MnO2 and solution (log KdRee/Mno2) increases with the HA/MnO2 ratio, indicating that part of the REE–HA complexes are adsorbed onto MnO2. The development of a Ce anomaly appears strongly limited in comparison with inorganic experimental conditions. Throughout the experimental run time, for HA/MnO2 ratios of less than 0.4, MnO2 acts as a competitor leading to a partial dissociation of the REE–HA complex. The majority of the dissociated REE is readsorbed onto the MnO2 surface. The readsorption of REE is expressed by an increased Ce anomaly on the log KdRee/Mno2 pattern as well as a change in shape of the coefficient distribution of REE between soluble HA and solution pattern (log KdRee/HA decrease for the heavy rare earth elements — HREE). Thus, REE are not only bound to MnO2 as a REE–HA complex, but also as REE(III). Moreover, the competition between HA and MnO2 for REE binding is shown to be higher at low pH (< 6) and low DOC/Mn ratio. This study partially confirms previous work that demonstrated the control of REE adsorption by organic matter, while shedding more light on the impact of pH as well as complexation reaction competition on long-term REE partitioning between solid surface and organic solutions. The latter point is important as regards to REE speciation under conditions typical of rock and/or mineral alteration.  相似文献   

14.
Sorption of Ni2+ on Na-rectorite as a function of contact time, temperature, pH and fulvic acid (FA)/humic acid (HA) was studied under ambient conditions. A pseudo-second-order rate equation was used to simulate the kinetic sorption. The removal of Ni2+ increased with increasing pH. The presence of FA/HA enhanced the sorption of Ni2+ at low pH values, whereas no drastic effect of FA/HA on Ni2+ uptake to rectorite was found at high pH values. The diffuse layer model (DLM) fitted the experimental data of Ni2+ sorption in the absence and presence of FA/HA very well with the aid of FITEQL 3.2. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Ni2+ at different temperatures. The thermodynamic data (ΔH0, ΔS0, ΔG0) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Ni2+ on rectorite was spontaneous and endothermic. The sorption and species of Ni2+ on rectorite in the presence and absence of FA/HA was also investigated and characterized by XPS. The spectroscopic analysis indicated no drastic structural changes of Na-rectorite and the sorption of Ni2+ mainly occurred on the surface and at the edge position of Na-rectorite.  相似文献   

15.
《Applied Geochemistry》2005,20(3):537-544
Thermal analyses (TG–DTA), elemental composition and isotope analyses (13C and 15N) were performed on humic acids (HA) from peats, leonardites and lignites, in order to investigate their structure and the changes taking place during the humification process. Thermal analyses showed structural differences between HA samples in relation to their coalification rank. In particular the lignite HA were characterized by a more stable chemical composition at high temperatures.The δ13C and δ15N values can provide information on the biogeochemical processes involved in HA formation. In particular, peat HA were linked to anoxic environments that enable plant residues to persist in their structure. In contrast, leonardite and lignite HA formation seems to be governed by different biogeochemical processes from those responsible for peat diagenesis. However, the isotopic analyses did not provide any distinction between leonardite and lignite HA. On the basis of the data presented in this study, it may be concluded that TG–DTA and isotope ratio measurements are powerful tools for investigating the formation pathway of humic substances from coals.  相似文献   

16.
CPMAS 13C NMR spectra of two estuarine sedimentary humic acids were recorded on a Bruker WP-SY 200 spectrometer. Both samples were found to contain similar aromatic and aliphatic carbon fractions. The sedimentary humic acids have unusually high methoxyl contents and more than one type of methoxyl is indicated. The high methoxyl content may be related to relatively low values for estuarine sedimentary humic acid-metal complexes. Carbohydrate contents of the humic acid samples were also found to be low.  相似文献   

17.
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18.
The Humic Ion Binding Model VI (Model VI) - previously used to model the equilibrium binding of rare earth elements (REE) by humic acid (HA) - was modified to account for differences in the REE constant patterns of the HA carboxylic and phenolic groups, and introduced into PHREEQC to calculate the REE speciation on the HA binding sites. The modifications were shown to greatly improve the modeling. They allow for the first time to both satisfactorily and simultaneously model a large set of multi-REE experimental data with the same set of equations and parameters. The use of PHREEQC shows that the light rare earth elements (LREE) and heavy rare earth elements (HREE) do not bind to HA by the same functional groups. The LREE are preferentially bound to carboxylic groups, whereas the HREE are preferentially bound to carboxy-phenolic and phenolic groups. This binding differentiation might lead to a fractionation of REE-HA patterns when competition between REE and other metals occur during complexation. A survey of the available data shows that competition with Al3+ could lead to the development of HREE-depleted HA patterns. This new model should improve the hydrochemical modeling of the REE since PHREEQC takes into account chemical reactions such as mineral dissolution/precipitation equilibrium and redox reactions, but also models kinetically controlled reactions and one-dimensional transport.  相似文献   

19.
The effects of humic acid (HA) on heavy metal uptake by herbaceous plants in soil simultaneously contaminated with heavy metals and petroleum hydrocarbons were investigated. The results showed that HA reduced readily soluble and exchangeable forms of heavy metals in the contaminated soil but increased their plant-available forms. Potential bioavailability and leachability factors became larger than 1 after adding HA to the soil, except for those of Ni, suggesting that more heavy metals could be potentially phytoavailable for plant uptake. Furthermore, HA increased the accumulation of Pb, Cu, Cd, and Ni in the shoots and roots of selected plants. The greatest increase in the accumulation of heavy metals was 264.7 % in the shoot of Festuca arundinacea, with the bioconcentration factor (BCF) increasing from 0.30 to 1.10. Humic acid also increased the BCFs of the roots of Brassica campestris for Ni and Pb. These results suggest that HA amendment could enhance plant uptake of heavy metals, while concurrently reducing heavy metal leachability and preventing subsurface contamination, even in soils simultaneously contaminated with petroleum hydrocarbons.  相似文献   

20.
A sequence of alternating lacustrine marls, peat and basalts was penetrated in the Notera-3 well in the northern part of the Jordan Rift, Israel. The 2781 m thick sequence, ranges from Upper Miocene to Recent, reflects high sedimentation rate in the active continental rift associated with the Dead Sea Transform. The deep burial and the relatively high geothermal gradient (40°C km−1) compensate for the short time span so that coalification expressed by vitrinite reflectance consistently increases with depth, from about 0.32% Ro at 1040 m to 0.48% Ro at 2495 m.Analysis of the peat reveals that the O/C, S/C and δ13C of the humic acids (HA) and the heavy to light normal alkane ratios are the only parameters sensitive enough to express this slight maturation increase with depth. A sharp δ13C change from about − 18‰ prevailing in the uppermost meters to an average of − 27.5‰ at 15 m and deeper reflects a change in the higher plant source of the peat (from C4 to C3 plants) rather than an early diagenetic modification.The δ13C, O/C, S/C and N/C ratios are usually lower in the kerogens than in the corresponding HA. The decrease in the δ13C and the O/C ratios are explained by elimination of oxygen-containing functional groups during transformation and by polymerization effects. The gradual decrease in the 12C and the O/C of the HA with depth are attributed to decarboxylation coupled with kinetic effects. The N/C depletion during the transformation from HA to kerogens probably results from the breakdown of amino acids. The S/C ratio which decreases both during this transformation and also with maturation is most readily explained by the breakdown of ester sulfate-containing groups such as sulfated polysaccarids, which formed diagenetically during the humification process.  相似文献   

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