Content Of Phenolic Groups Research Articles

One-step process based on the order of hydrothermal and alkaline treatment for producing lignin with high yield and antioxidant activity

Three one-step processes based on the order of hydrothermal (170 °C, 30 min) and alkaline treatment (2% NaOH, 90 °C, 120 min) have been proposed for the production of lignin from wheat straw. The yield, purity, dissociation mechanism, structural transformation, and antioxidant activity of the lignins obtained from the various processes were systematically investigated. It was found that the order of hydrothermal and alkaline treatments had significant effects on the structural features and antioxidant activities of lignins. Hydrothermal process facilitated the subsequent alkaline delignification, releasing lignins with the highest yield (90.3%) and purity (97.4%). The β-O-4 linkages were obviously cleaved during the hydrothermal treatment, which resulted in an increase content of phenolic OH groups. The types and content of phenolic OH groups in lignins were closely related to its antioxidant properties. The lignins released during the one-step process based on successive hydrothermal and alkaline treatment had a high yield and antioxidant activity and the process would be very beneficial to the industrial production of potential antioxidant for food oils and fats, as well as food preservative that prevent the loss of food flavour.

Mechanochemically oxidized brown coal and the effect of its application in polluted water

The technology of mechanochemical oxidative modification of brown coal in solid phase was developed and scaled using flow-type equipment. With the oxidized brown coal (BCox), the yield of humic substances extracts increased from 23 to 70% and the content of phenolic and carboxylic groups increased by 55 and 103%, respectively. BCoxperforms as promising sorbent for heavy metal remediation of surface water, and its impact on the environmental fate of inorganic contaminants (heavy metals) was tested in a real fresh-water body, namely, the Novosibirsk Water Reservoir on the Ob river. Experiments were carried out with the help of meso-modeling of water pollution with a mixture of Zn(II)-Cu(II)-Cd(II). The introduction of heavy metals into water suppresses the vital activity of phytoplankton in the first few days, but the phytoplankton then adapts and begins to propagate, sorbing the pollutants. The addition of the BCox caused substantial acceleration of the withdrawal of heavy metals. The use of the BCox did not cause water blooms, distinct from sorbents based on non-oxidized humic substances with the native structure.

Physicochemical Characterization and Antioxidant Activity of Humic Acids Isolated from Peat of Various Origins

Although humic acids (HAs) from peat exhibit various therapeutic properties, there is little information available concerning their physicochemical and antioxidant properties. To address this issue, nine different types of peat, including oligotrophic, mesotrophic, and minerotrophic peat samples, were used for isolation of HA fractions by basic (HAb) and pyrophosphate (HAp) extractions. Physical parameters of the HAs were analyzed by UV-Vis, fluorescent, infrared (IR), and electron paramagnetic resonance (EPR) spectroscopy. Average Mr of the fractions ranged from 17.2 to 39.7 kDa, while their humification index (HIX) varied from 0.49 to 1.21. HAp fractions had a higher content of aromatic structures compared to HAb fractions. Moreover, HAp fractions had a significantly higher content of phenolic OH groups (3.6 ± 0.5 mmol/g) versus HAb (3.1 ± 0.5 mmol/g). All HA fractions exhibited antioxidant activity in radical scavenging and electrochemical assays, and their EPR signal had a single line with g = 2.0035, which is consistent with semiquinone type radicals. Furthermore, the HIX was found to be important in determining the number of semiquinone-type free radicals in the HA structures. Overall, these data provide a molecular basis to explain at least part of the beneficial therapeutic properties of peat-derived HAs.

Fluorescence regional integration and differential fluorescence spectroscopy for analysis of structural characteristics and proton binding properties of fulvic acid sub-fractions

Structural characteristics and proton binding properties of sub-fractions (FA3–FA13) of fulvic acid (FA), eluted stepwise by pyrophosphate buffer were examined by use of fluorescence titration combined with fluorescence regional integration (FRI) and differential fluorescence spectroscopy (DFS). Humic-like (H-L) and fulvic-like (F-L) materials, which accounted for more than 80% of fluorescence response, were dominant in five sub-fractions of FA. Based on FRI analysis, except the response of F-L materials in FA9 and FA13, maximum changes in percent fluorescence response were less than 10% as pH was increased from 2.5 to 11.5. Contents of carboxylic and phenolic groups were compared for fluorescence peaks of FA sub-fractions based on pH-dependent fluorescence derived from DFS. Static quenching was the dominant mechanism for binding of protons by FA sub-fractions. Dissociation constants (pKa) were calculated by use of results of DFS and the modified Stern-Volmer relationship. The pKa of H-L, F-L, tryptophan-like and tyrosine-like materials of FA sub-fractions exhibited ranges of 3.17–4.06, 3.12–3.97, 4.14–4.45 and 4.25–4.76, respectively, for acidic pHs. At basic pHs, values of pKa for corresponding materials were in ranges of 9.71–10.24, 9.62–10.99, 9.67–10.31 and 9.33–10.28, respectively. At acidic pH, protein-like (P-L) materials had greater affinities for protons than did either H-L or F-L materials. The di-carboxylic and phenolic groups were likely predominant sites of protonation for both H-L and F-L materials at both acidic and basic pHs. Amino acid groups were significant factors during proton binding to protein-like materials of FA sub-fractions at basic pH.

Nature differences of humic acids fractions induced by extracted sequence as explanatory factors for binding characteristics of heavy metals

The composition and structure of Humic acid (HA) is so heterogeneous that it brings significant barriers to investigate the interaction between HA and heavy metal ions. The isolation of HA with relatively homogeneity is a key to reveal the binding mechanisms between HA and heavy metals. In this work, ten HA fractions (HAs) were obtained by sequential alkali extraction procedure and nature differences of the extracted HAs were considered as explanatory factors for binding characteristics of Cu2+, Pb2+ and Cd2+. The results indicate that more large molecular weight (MW) HA subunits, less carboxyl and phenolic group contents, weaker aromaticity and polarity were measured with increasing extractions, inducing weaker binding capacity of HAs. Ligand binding and bi-Langmuir models indicated that the sorption capacity and binding affinity of earlier extracted HAs were higher than the latter ones. The peak area changes at 3427, 1599, and 619 cm−1 pre- and post-adsorption in FTIR spectra suggested carboxyl, phenolic and nitrogen-containing groups were involved in the adsorption process. At the same time, the peak area difference between HAs and HAs-metal (ΔS) of phenolic groups were 8.22–20.50, 6.81–21.11 and 10.66–19.80% for Cu2+, Pb2+ and Cd2+, respectively, ΔS of carboxyl groups 6.64–17.03, 8.96–16.82 and 9.45–17.85% for Cu2+, Pb2+ and Cd2+, respectively, ΔS of nitrogen-containing groups 0.33–0.48, 0.20–1.38 and 0.31–0.59% for Cu2+, Pb2+ and Cd2+, respectively. ΔS of phenolic and carboxyl groups were larger than those of nitrogen-containing groups, implying that these two groups were the predominant binding sites suppliers for metal ions, which were also supported by the results of correlation analysis. This work is helpful to insight the environmental impacts of natural organic matter and the fate of heavy metals in natural environment.

Coconut endocarp and mesocarp as both biosorbents of dissolved hydrocarbons in fuel spills and as a power source when exhausted

Health and environmental problems associated with the presence of toxic aromatic compounds in water from oil spills have motivated research to develop effective and economically viable strategies to remove these pollutants. In this work, coconut shell (endocarp), coconut fiber (mesocarp) and coconut shell with fiber (endocarp and mesocarp) obtained from coconut (Cocos nucifera) waste were evaluated as biosorbents of benzene, toluene and naphthalene from water, considering the effect of the solution pH (6–9) and the presence of dissolved organic matter (DOM) in natural water (14 mg/L). In addition, the heat capacity of saturated biosorbents was determined to evaluate their potential as an alternative power source to conventional fossil fuels. Tests of N2 physisorption, SEM, elemental and fiber analysis, ATR-FTIR and acid-based titrations were performed in order to understand the materials' characteristics, and to elucidate the biosorbents' hydrocarbon adsorption mechanism. Coconut fiber showed the highest adsorption capacities (222, 96 and 5.85 mg/g for benzene, toluene and naphthalene, respectively), which was attributed to its morphologic characteristics and to its high concentration of phenolic groups, associated with the lignin structure. The pH of the solution did not have a significant influence on the removal of the contaminants, and the presence of DOM improved the adsorption capacities of aromatic hydrocarbons. The adsorption studies showed biphasic isotherms, which highlighted the strong affinity between the molecules adsorbed on the biosorbents and the aromatic compounds remaining in the solution. Finally, combustion heat analysis of coconut waste saturated with soluble hydrocarbons showed that the heat capacity increased from 4407.79 cal/g to 5064.43 ± 11.6 cal/g, which is comparable with that of woody biomass (3400–4000 cal/g): this waste biomass with added value could be a promising biofuel.

STUDY OF STRUCTURAL AND FUNCTIONAL COMPOSITION OF SOIL HUMUS ACIDS OF EURO-ARCTIC REGION BY MOLECULAR ABSORPTION SPECTROSCOPY (UV / VISIBLE)

Results of the structural and functional composition of soil humus acids in the Euro-Arctic Region are presented. The molecular absorption spectroscopy (UV / visible) was used to evaluate eco-protective role of soils in relation to heavy metals, which is especially important for the sensitive soils of the Arctic, formed under the influence of cryogenic processes. Different types of soils of the Euro-Arctic region: gleyish easy loamy pelosi on loamy moraine (Kanin Peninsula, Cape Kanin Nos); humus peat oligotrophic soil (Kolguev Island, Bugrino village); typical non-calcic loamy gley soil (Vaigach Island); gray humous iron sandy lithozem (Archipelago Franz Josef Land, Heys Island) were analyzed. An alkaline solution of sodium pyrophosphate was used to extract humus acids for investigate of the structural and functional composition. Humic, fulvic and gimatomelanic acids were extracted from a humus by conforming solvents with additional fulvic acids extraction by adsorption chromatography using activated carbon as a sorbent. UV mini-1240 spectrophotometer (Shimadzu) was used to record the UV / visible spectra using 0.005% alkaline solutions (0.1 N NaOH) of humus acids. It was demonstrated that humic and gimatomelanoic acids of humus peat oligotrophic soil have more developed peripheral aliphatic component. These acids have more ability to bind heavy metals and show their eco-protective role. The humus acids of other types of soils region have a more developed aromatic component in the Euro-Arctic. Such parameters as: calculated by the Pieravuori formula aromaticity, extinction coefficient Е0.005%1cm,465, adsorption ratio D400 /D600, characterizing the degree of humification and the adsorption ratio D465 / D650, characterizing the degree of aromatic nucleus condensation and conjugate fragments were used in the quantitative assessment of the nature of humus acids. Quantitative analysis of UV/visible spectra confirmed that the maximum barrier mechanism with respect to heavy metals will be the humic and gimatomelanoic acids of humus-peat oligotrophic soil, due to the high content of phenolic and carboxyl groups in these molecules, oxidation and a more developed chain of conjugated bonds in them in comparison with other acids. However, it was found that in all types of soils studied the process of humus formation proceeds mainly by a degradation type, that is, in the direction of formation of fulvic acids. Forcitation:Prilutskaya N.S., Korel'skaya T.A., Popova L.F. Study of structural and functional composition of soil humus acids of euro-arctic region by molecular absorption spectroscopy (UV / visible). Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 97-103

Fenton Reaction-Oxidized Bamboo Lignin Surface and Structural Modification to Reduce Nonproductive Cellulase Binding and Improve Enzyme Digestion of Cellulose

Nonproductive adsorption of cellulase on lignin was a major inhibitory mechanism reducing the enzymatic saccharification efficiency of lignocellulosic material. The surface and structural properties of Fenton reaction-oxidized lignins (FRLs) and their effects on the nonproductive binding of enzymes to lignin and enzymatic saccharification of Avicel were examined. The Fenton chemistry pretreatment not only decreased the ratio of syringyl to guaiacyl units and the phenolic OH group content in lignin preparations but increased the carboxylic content and the negative zeta potential of lignin, all of which could be responsible for reducing the unproductive adsorption of cellulase on lignin. And Langmuir adsorption isotherms also proved that FRLs were provided with a lower binding ability to the cellulase enzyme when compared with untreated milled bamboo lignin (MBL). Finally, when the nonproductive binding of cellulase to FRLs was reduced significantly, the 72 h glucose yields of Avicel with 3-FRL and 5-FRL we...

Membrane filtration of kraft lignin: Structural charactristics and antioxidant activity of the low-molecular-weight fraction

Lignin, which is the second most abundant biomass component and has carbon-rich phenolic content, is a promising renewable raw material for multiple applications, such as carbon fibers, adhesives, and emulsifiers. To use lignin efficiently, it is important to ensure its purity and homogeneity. As a result, the separation of lignin into fractions with high purity and narrow molecular-weight distributions is likely a prerequisite for several applications. Ultrafiltration using ceramic membranes has many advantages, including enabling direct lignin extraction from Kraft pulp cooking liquors without pH and temperature adjustment. One challenge with membrane filtration using such a system is the potential for reduced membrane performance over time, which is associated with fouling.In this study, LignoBoost Kraft lignin was fractionated using a ceramic membrane with a molecular weight cut-off of 1kDa. The separation behavior during ultrafiltration fractionation was investigated and the antioxidant properties of the recovered low-molecular-weight (low-MW) lignin samples were evaluated.Using this model system, the permeate fluxes were unstable during the 100h of membrane operation. However, a decrease in the average MW in the permeate over time was observed. The shift in MW was most pronounced for virgin membranes, while a more stable MW distribution was evident for membranes subjected to multiple cleaning cycles. According to 2D NMR analysis, low-MW lignin that was recovered after 100h of operation, consisted of smaller lignin fragments, such as dimers and oligomers, with a high content of methoxy-groups. This was confirmed using the size exclusion chromatography method, which indicated an weigh average molecular weight in the range of 450–500Da. 31P NMR spectroscopy showed that, despite the lower total content of phenolic OH groups, the low-MW sample had a higher proportion of non-condensed phenolic OH groups. The results of the antioxidant tests demonstrated the strong potential of lignin and its low-MW fraction as a natural antioxidant, particularly for lipid-containing systems. The low-MW lignin fraction showed better antioxidant activity than the non-fractionated LignoBoost lignin in the kinetic oxygen radical absorbance capacity (ORAC) test and demonstrated three-fold stronger inhibition of the substrate (fluorescein) than the reference antioxidant Trolox (a water-soluble derivative of vitamin E).

Nature differences of fulvic acid fractions induced by extracted sequence as explanatory factors for binding characteristics of Cu2+

The isolation of fulvic acid (FA) fractions with relatively homogeneity is a key to reveal the binding mechanisms between FA and heavy metals. In this work, nine FA fractions were obtained using sequential alkali extraction procedure and nature differences of the extracted FA fractions were considered as explanatory factors for binding characteristics of Cu2+. The results indicate that the contents of carboxyl and phenolic groups decrease with increasing extractions along with an opposite trend for the content of nitrogen-containing groups. The fitted results of ligand binding and bi-Langmuir models indicate that the binding sites for Cu2+ were mainly provided by carboxyl and phenolic groups, which explained the higher sorption capacity and binding affinity of earlier extracted FAs due to its higher contents of carboxyl and phenolic groups. Furthermore, the systemic characterization of FA fractions before and after adsorption indicate the nitrogen-containing groups were gradually showing their contribution in binding Cu2+ with increasing extractions. This work is very helpful to insight the environmental effects of natural organic matter and the behavior of heavy metals in natural environment.

Revealing the structure of bamboo lignin obtained by formic acid delignification at different pressure levels

Bamboo was fractionated using formic acid based on a one-step organosolv process under high pressure (at 145°C for 45min, 0.3MPa) and at atmospheric pressure (at 101°C for 120min), respectively. High-pressure formic acid lignin, atmospheric formic acid lignin and milled wood lignin of bamboo were subjected to comprehensive structural characterization using gel permeation chromatography (GPC), Fourier transform infrared (FTIR) and solution-state NMR techniques (1H, 13C, 2D-HSQC, and 31P-NMR spectroscopies). The results indicated that the formic acid fractionation under high pressure presents a quick and efficient delignification method by enhancing the cleavage of interunitary bonds in lignin (β-O-4′, β-β and β-5′), and dissolved lignin also occurred condensation reaction. As compared to atmospheric formic acid lignin, high-pressure formic acid lignin obtained showed higher purity and yield, and had relatively higher contents of phenolic and carboxylic groups.

A Novel Gallic Acid-Grafted-Lignin Biosorbent for the Selective Removal of Lead Ions from Aqueous Solutions

The low content of phenolic groups limits the application of lignin-based materials as biosorbents for the removal of metal ions. In this work, a novel gallic acid-grafted-lignin (GAL, 4.43 mmol/g hydroxyl group) biosorbent was designed by introducing gallic acid moieties to replace the hydroxyl groups of lignin. These grafted polyphenolic groups provide additional sites for the adsorption of metal ions. The structure of GAL was characterized by FT-IR, 31P NMR, and 13C NMR spectroscopy. The adsorption properties of GAL for Pb(II) ions were investigated under batch conditions. Kinetic and isothermal adsorption processes could be well-described by the pseudo-second order kinetic model and Langmuir isothermal model, respectively. The grafting of polyphenolic groups onto lignin increased the maximum adsorption capacity of the adsorbent for Pb(II) (119.1 mg/g). The adsorption thermodynamics indicated that the adsorption process was endothermic and spontaneous. In addition, GAL could selectively adsorb Pb(II) with a selectivity coefficient (k) at 1.89 in the presence of coexisting metal ions from aqueous solution. The high adsorption capacity and selectivity for Pb(II) by GAL, together with its environmental compatibility, enable this material to act as a promising biosorbent for removing heavy metal ions from polluted water.

Enhancement of nutritional and bioactive compounds by in vitro culture of wild Fragaria vesca L. vegetative parts

In vitro culture emerges as a sustainable way to produce bioactives for further applicability in the food industry. Herein, vegetative parts of Fragaria vesca L. (wild strawberry) obtained by in vitro culture were analyzed regarding nutritional and phytochemical compounds, as well as antioxidant activity. These samples proved to have higher content of protein, polyunsaturated fatty acids, soluble sugars, organic acids (including ascorbic acid) and tocopherols (mainly α-tocopherol) than wild grown F. vesca, as well as containing additional phenolic compounds. The antioxidant activity of hydromethanolic extracts could be correlated with the content of different phenolic groups and other compounds (sugars and organic acids). It was demonstrated that in vitro culture could enhance nutritional and bioactive compounds of Fragaria vesca L. plants, providing a very interesting biotechnological tool for potential food applications.

Study of Organosolv Lignins as Adhesives in Wood Panel Production.

Organosolv lignins obtained from sugar maple bark and wood were studied as adhesives for wood particleboard production. Organosolv pulping of sugar maple wood and bark was carried out in the presence of Lewis acid FeCl3 as a catalyst. The organosolv lignins recovered from this process were investigated by determination of Klason plus acid-soluble lignin content, of sugars by HPLC analysis, and of ash content. Structural characterizations of these lignins were performed by Fourier-transform infrared (FT-IR) and by 31P NMR. The results of the latter studies indicate that the content of free phenolic groups was more important in bark than in wood lignin. The gel permeation chromatography (GPC) analyses results suggested that the weight-average molecular mass of wood lignin was higher than that of bark lignin. The studied organosolv lignins were used for the preparation of particleboards as recovered and in combination with glyoxal or isocyanate. It was found that sugar maple bark lignin, as such or modified with isocyanate, was a more efficient adhesive than its wood counterpart. On the contrary, it was the organosolv wood lignin combined with glyoxal which was a more efficient adhesive than its bark counterpart. In combination with isocyanate, it was the sugar maple bark organosolv lignin which was determined to have the best adhesive performance of all studied lignins.

Characterisation of lignin and lignin-carbohydrate complexes (LCCs) in prehydrolysed wood chips

Abstract Isolation and analysis of lignin and lignin-carbohydrate complexes (LCCs) were performed to understand the better delignification ability of prehydrolysed wood chips. Lignin analysis showed that prehydrolysis led to a slight depolymerisation and an increase in free phenolic group content. The yield measurement and composition analysis of LCCs of mixed softwoods (SWs) and mixed hardwoods (HWs) revealed essential differences. In the case of SW, the amounts of lignin and xylan involved in LCCs were significantly lowered, whereas in the case of HW, less cellulose, glucomannans, and xylans were detectable in the residual LCCs. The molecular mass distributions of glucomannan-lignin and xylan-lignin fractions were not changed significantly.

Sustainable biobutanol production using alkali-catalyzed organosolv pretreated cornstalks

Biobutanol is an important alternative fuel source, but current processing methods suffer from low yields. This study aimed to develop and optimize a pretreatment protocol for biobutanol production from cornstalks. Fractionation of cornstalks into carbohydrate (cellulose and hemicellulose) and lignin was performed by alkali-catalyzed organosolv pretreatment (ACOS). After optimization of the process parameters, more than 80% of the total lignin was removed, with minimal hemicellulose degradation, at 110°C, 4% (w/w dry cornstalk) NaOH, 90min reaction time, and 60% (v/v) ethanol. After enzymatic hydrolysis, the maximum recovery of total monosaccharide was 83.7% (85.0% cellulose, 82.0% hemicellulose). In acetone-butanol-ethanol (ABE) fermentation, a slightly higher total ABE concentration (12.8g/L vs. 11.9g/L) was produced from the enzymatic hydrolysate, compared with that from a glucose control. The physical structure and chemical properties of alkali-catalyzed organosolv lignin (ACOSL) showed higher phenolic group content and antioxidant capacity compared with alkali lignin. ACOS pretreatment is an economical method for the production of fermentable monosaccharide and high-value lignin, for use in biofuel production.

Comparison of hydrothermal, hydrotropic and organosolv pretreatment for improving the enzymatic digestibility of bamboo

Pretreatment is the crucial step to disrupt the recalcitrant structure of lignocellulosic biomass for improving the enzymatic hydrolysis efficiency. Typically, hydrothermal, organosolv and hydrotropic pretreatments are environmentally benign and effective methods. In this work, effects of hydrothermal, organosolv and hydrotropic pretreatments on improving enzymatic hydrolysis of bamboo were comprehensively compared. Hydrotropic pretreatment was more effective in removal lignin and xylose from bamboo fiber cell wall. However, the surface coverage by lignin and extractives were dramatically displaced during organosolv pretreatment as investigation by X-ray photoelectron spectroscopy. After pretreatments, the crystallinity of cellulose in pretreated substrates has a significant reduction, and pores were exposed on fiber surface. The residual content of acetyl and phenolic groups in hydrotropic pretreated substrates is lower than organosolv pretreated substrates. In order to deeply assess the delignification of pretreatments, the isolated lignins obtaining from pretreatments process were characterized by Fourier transform infrared spectroscopy also. It was revealed that hydrotropic lignin contained more phenolic hydroxyl group and syringyl units than organosolv lignin. Compared to hydrothermal and organosolv pretreatment, cellulase adsorption capacity of pretreated substrates was notably improved by hydrotropic pretreatment, which indicating the better enzyme accessibility of cellulose. Eventually, the maximum glucose yield was obtained from hydrotropic pretreated substrates.

Isolation, purification and analysis of dissolved organic carbon from Gohagoda uncontrolled open dumpsite leachate, Sri Lanka

ABSTRACTExtract and analysis of the Dissolved Organic Carbon (DOC) fractions were analyzed from the leachate of an uncontrolled dumpsite at Gohagoda, Sri Lanka. DOC fractions, humic acid (HA), fulvic acid (FA) and the hydrophilic (Hyd) fractions were isolated and purified with the resin techniques. Spectroscopic techniques and elemental analysis were performed to characterize DOCs. Maximum TOC and DOC values recorded were 56,955 and 28,493 mg/L, respectively. Based on the total amount of DOC fractionation, Hyd dominated accounting for ∼60%, and HA and FA constituted ∼22% and ∼17%, respectively, exhibiting the mature phase of the dumpsite. The elemental analysis of DOCs revealed carbon variation following HA > FA > Hyd, while hydrogen and nitrogen were similar in each fraction. The N/C ratio for HA was recorded as 0.18, following a similar trend in old dumpsite leachate elsewhere. The O/C ratios for HA and FA were recorded higher as much as 1.0 and 9.3, respectively, indicating high degree of carbon mineralization in the leachates. High content of carboxylic, phenolic and lactone groups in all DOCs was observed disclosing their potential for toxic substances transportation. The results strongly suggest the risk associated with DOCs in dumpsite leachate to the aquatic and terrestrial environment.

Binding characteristics of Cu2+ to natural humic acid fractions sequentially extracted from the lake sediments.

Humic acids (HAs) determine the distribution, toxicity, bioavailability, and ultimate fate of heavy metals in the environment. In this work, ten HA fractions (F1-F10) were used as adsorbent, which were sequentially extracted from natural sediments of Lake Wuliangsuhai, to investigate the binding characteristics of Cu2+ to HA. On the basis of the characterization results, differences were found between the ten extracted HA fractions responding to their elemental compositions and acidic functional groups. The characterization results reveal that the responses of ten extracted HA fractions to their elemental compositions and acidic functional groups were different. The O/C and (O+N)/C ratio of F1-F8 approximately ranged from 0.66 to 0.53 and from 0.72 to 0.61, respectively; the measured results showed that the contents of phenolic groups and carboxyl groups decreased from 4.46 to 2.60mmol/g and 1.60 to 0.58mmol/g, respectively. The binding characteristics of Cu2+ to the ten HA fractions were well modeled by the bi-Langmuir model; the binding behavior of Cu2+ to all the ten HA fractions were strongly impacted by pH and ionic strength. The FTIR and SEM-EDX image of HA fractions (pre- and post-adsorption) revealed that carboxyl and phenolic groups were responsible for the Cu2+ sorption on the ten sequentially extracted HA fractions process, which is the same with the analysis of the ligand binding and bi-Langmuir models Accordingly, the adsorption capacity of the former HA fractions on Cu2+ were higher than the latter ones, which may be attributed to the difference of carboxyl and phenolic group contents between the former and latter extracted HA fractions. Additionally, the functional groups with N and S should not be neglected. This work is hopeful to understand the environmental effect of humic substances, environmental geochemical behavior, and bioavailability of heavy metals in lakes.

Effects of selected chemical and physicochemical properties of humic acids from peat soils on their interaction mechanisms with copper ions at various pHs

The main aims of this study were to investigate the interactions of copper ions (Cu(II)) at pH5 and 7 with humic acids (HAs) isolated from four peat soils at different humification stages, as well as to determine the physicochemical properties of HAs that may have an influence on the above interactions. For this purpose, a number of parameters were determined for the qualitative and quantitative analysis of peat soils, HAs, and HA-Cu(II) interactions. Processes in the HA-Cu(II) systems were studied using fluorescence spectroscopy (for chemical complexation) and atomic absorption spectrometry with carbon measurements (for coagulation processes). The influence of HA properties on their interactions with Cu(II) ions was evaluated using matrices of correlation coefficients between some HA properties and parameters describing the HA-Cu(II) interactions. Results showed that the complexation capacity was higher at pH7 than at pH5. The coagulation mechanism at pH7 appeared to be based on the precipitation of Cu(II)-humates following the neutralization of HA functional groups by Cu(II) ions, while coagulation at pH5 appeared to be controlled by the ionic strength. The complexation capacity increased significantly with increasing content of carboxylic and phenolic groups, O/H atomic ratio, degree of internal oxidation and surface negative charge of HAs. The binding of Cu(II) ions was stronger for HAs characterized by a higher aromaticity and humification degree (expressed respectively as absorbance at 280nm and E4/E6 ratio). The stability constants were higher at pH7 than at pH5 and in most cases they did not correlate significantly with HA properties.