Association constants of modified humic acids with biocides of the triazole series: Cyproconazole and tebuconazole

The interaction of humic acids with biocides of triazoles in dependence on the concentration of components in solutions was investigated by spectrofluorimetry. The complex behavior of intermolecular interactions between biocides and humic acids, including donor-acceptor and hydrophobic bonds, was established. The effect of conditions of mechanochemical modification of humic acids and pH on the efficiency of interaction with biocides is shown.     

Adsorption of lignite-derived humic acids on coal-based mesoporous activated carbons

The adsorption by a coal-based mesoporous activated carbon of humic acids (HAs) isolated from two Polish lignites was studied. For comparison, a commercial Aldrich humic acid was also included into this study. The differences in chemical structure and functional groups of HAs were determined by elemental analysis and infrared spectroscopy DRIFT. Two activated carbons used differed in terms of mesopore volume, mesopore size distribution, and chemical properties of the surface. The kinetics of adsorption of HAs have been discussed using three kinetic models, i.e., the first-order Lagergren model, the pseudo-second-order model, and the intraparticle diffusion model. It was found that the adsorption of HAs from alkaline solution on mesoporous activated carbon proceeds according to the pseudo-second-order model. The correlation coefficients were close to 1. The intraparticle diffusion of HA molecules within the carbon particle was identified to be the rate-limiting step. Comparing the two activated carbons, the carbon with a higher volume of pores with widths of 10-50 nm showed a greater removal efficiency of HA. An increase in the Freundlich adsorption capacity with decreasing carbon content of HA was observed. Among the HAs studied, S-HA shows characteristics indicating the highest contribution of small-size fraction. The S-HA was removed by both activated carbons to the highest extent. The effect of pH solution on the adsorption of HA was examined over the range pH 5.4-12.2. It was found that the extent of adsorption decreased with decreasing pH of the solution.     

High-temperature carbonization of humic acids and a composite of humic acids with graphene oxide

Humic acids (HAs) isolated from high-moor peat have been studied by magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TG), and Raman spectroscopy. A composite of HAs with graphene oxide (GO) has been prepared for the first time, and the thermal carbonization (900°C) of both HAs and the HA–GO composite has been carried out. With the use of mass spectrometry, it has been found that CO₂ and H₂O molecules are mainly released from HAs into the gas phase at a low temperature (to 150°C). At higher temperatures, carbon monoxide and different low-molecular-weight hydrocarbons also begin to be released. From microscopic examinations, it follows that HA forms small agglomerates with sharply outlined edges as a result of carbonization, whereas the composite forms only large aggregates.     

The acidobasic and complexation properties of humic acids Study of complexation of Czech humic acids with metal ions

The acid-base and complexation properties of humic acids (HAs) extracted from bohemian brown coals were studied. The acid-base behavior corresponds with the model of HA as a mixture of mono- and diprotic acids. This model was also verified on commercial HA substances (Aldrich and Fluka). HA binds strongly with heavy metal ions and the highest stability constant of HA-metal ion complexes was observed for copper(II). Stability constant values were found to decrease in the order: Cu(2+)>Ba(2+)>Pb(2+)>Cd(2+)>Ca(2+). Both acidobasic models for HA alone and those for HA-metal ion interactions were proposed and the computational methodology for polyelectrolyte equilibria studies demonstrated.     

The interaction of triazine herbicides with humic acids

Summary Although the binding of pesticides to organic carbon in soil, especially to humic acid (HA), is well recognized, the mechanisms have not been completely explained. This publication deals with adsorption of atrazine and terbuthylazine by humic acid under different experimental conditions, including adsorption times longer than those used hitherto. Direct HPLC analysis of HA suspensions is assessed as an alternative to more complicated techniques for estimation of free triazines, and compared with combined solid-phase extraction and HPLC. Experimental conditions such as time of exposure, addition of neutral salt, pH of the suspension, and HA concentration have a significant impact on the extent of triazine adsorption. At alkaline pH, triazines become partitioned in the HA fraction because of its hydrophobicity, whereas at acidic pH hydrogen-bonding probably occurs between triazine molecules and humic acid polymers. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

腐植酸对砷的吸附作用研究

腐植酸中含有大量的极性基团,对金属离子有较强的吸附性能。运用氢化物-原子荧光光谱法,以泥炭腐植酸为原料,研究了腐植酸对砷(V)离子的吸附作用和腐植酸吸附剂中砷的回收,并得出了最佳的吸附和脱附条件。实验考察了酸度、时间分别对吸附和脱附的影响。结果表明,泥炭腐植酸对砷吸附的最佳模型为Freundlich吸附方程,当溶液成中性时腐植酸对砷的吸附量较大且趋于平稳。砷的浓度为1μg/mL,溶液的pH值为7,吸附时间控制在55min时,吸附效果最佳,最大吸附率为85.49%。脱附的最佳条件为:pH值14,脱附时间20min。     

Organotin biocides XV: Modelling the interactions of triorganotins with cell membranes

The interaction of triorganotins with cell membranes has been examined using synthetic phospholipid membranes (vesicles). Electron microscopy and NMR methods indicate that the organotin is in a five-coordinate environment at the membrane surface, and is associated weakly with the phosphate headgroups of the vesicle components. Both trimethyl- and tributyl-tin cause extensive modifications to the vesicles including fusion, aggregation, blebbing and total rupture, these effects being initiated at concentrations as low as 25 μmol dm^?3.     

Adsorption of humic acids onto goethite: effects of molar mass, pH and ionic strength

In this paper, the LCD (ligand charge distribution) model is applied to describe the adsorption of (Tongbersven) humic acid (HA) to goethite. The model considers both electrostatic interactions and chemical binding between HA and goethite. The large size of HA particles limits their close access to the surface. Part of the adsorbed HA particles is located in the compact part at the goethite surface (Stern layers) and the rest in the less structured diffuse double layer (DDL). The model can describe the effects of pH, ionic strength, and loading on the adsorption. Compared to fulvic acid (FA), adsorption of HA is stronger and more pH- and ionic-strength-dependent. The larger number of reactive groups on each HA particle than on a FA particle results in the stronger HA adsorption observed. The stronger pH dependency in HA adsorption is related to the larger number of protons that are coadsorbed with HA due to the higher charge carried by a HA particle than by a FA particle. The positive ionic-strength dependency of HA adsorption can be explained by the conformational change of HA particles with ionic strength. At a higher ionic strength, the decrease of the particle size favors closer contact between the particles and the surface, leading to stronger competition with electrolyte ions for surface charge neutralization and therefore leading to more HA adsorption.     

Selective extraction of metal ions associated with humic acids

The ability of a range of electrolyte solutions to release metal ions (Cu, Pb, Cd, Zn) presorbed on two samples of humic acid has been investigated. Though treatment with mineral acid or a chelating agent released a high proportion of the retained metal ion, recoveries were never total. Concentrated salt solutions displaced about 80% of the retained Cd or Zn, and about half of any Cu or Pb held by the organic matter, which indicates that most of the adsorbed metal ion is exchangeable, the extraction efficiency being controlled by competing equilibria. The effect of added clay suspensions was also examined. Analytical procedures for fractionating the total metal content of soils into subgroups have been assessed against the observed extraction behaviour.     

Catalytic ozonation of humic acids with Fe/MgO

Summary Degradation of humic acids by ozone was performed at room temperature in a stirred tank reactor with heterogeneous catalysts. Experimental results show that the ozonation with Fe/MgO induced a significant reduction in UV absorbance of humic acids, as compared to ozone alone. Fe/MgO was the most efficient catalyst in degradation humic acids in the presence of ozone. GPC (gel permeation chromatography) showed that humic acids with high molecular weight could be severely decomposed into organic compounds with low molecular weight by the Fe/MgO catalyst, indicating that humic acids could be catalytically decomposed.     

Cation interactions with polyamic acids

Polyamic acid films interact as ion-exchange substrates for dilute aqueous cation solutions. Three conditions were evaluated: basic solutions which form soluble amic acid salts and dissolve the film, weakly acidic solutions which encourage classical weak acid cation exchange, and strongly acidic solutions which discourage exchange. Thermal treatment of the generated cationamate salts generally causes degradation of the polymer backbone. Furthermore, lead and copper react directly with the polyamic acid to yield surface-bound salts, but tin and aluminum seem unreactive.     

Potentiometric and spectroscopic study of uranyl complexation with humic acids

By potentiometric study using a specific uranyl ion-selective electrode, the formation of 1:1 and 1:2 (metal:ligand) complexes of uranyl with various humic acids (HAs) was found. The conditional stability constants were calculated using the LETAGROP-ETITR program. Possible structures of the complexes are proposed. Stability constants were found to be rather high indicating that immobilized HA can be used, for example, to remove traces of uranyl from waste waters.     

Thermoanalytical investigation of lignite humic acids fractions

Differential scanning calorimetry (DSC) and thermogravimetry (TG) studies of humic acids (HA) sequentially extracted at pH 7, 8, 9 and 10 by phosphate and pyrophosphate buffers have been carried out. Supplement information were provided by elementary analysis and FTIR spectroscopy to characterize and evaluate in details the thermooxidative behavior of HA fractions. The exothermic DSC profiles of the HA samples extracted by phosphate buffers or by pyrophosphates were shifted to lower temperatures in comparison with the original sample and showed narrow distribution of humic molecules. Experimental data showed dependency of HA fraction composition on the pH used during extraction. DSC experimental data showed 1 endothermic and from 2-5 exothermic peaks associated with mass loss recorded by TG measurement. Higher degree of aliphaticity observed on samples extracted at lower pH did not remarkably affect the DSC peak temperature of the first decomposition step associated with aliphatic moieties and functional groups decomposition and recombination reactions. On the other hand, such dependency was observed in higher temperature range where destruction of aromatic structures took part. The behavior of HA samples (even after separation of specific fractions) showed high complexity of system, which resulted in complicated physical and chemical processes occurred during thermooxidation. Observed stability and released heat were affected by many factors, among them evaporation of volatile part of humic matter and a slight contribution of weak interactions among humic molecules were considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Surface-active properties of humic and sulfochlorohumic acids

The surface tension of alkaline solutions of humic acids and their sulfochloroderivatives, which are synthesized by sulfonation of chlorohumic acids isolated from coal chlorinated by the electrochemical method, is investigated. It is established that humic compounds possess weak surface activity. Basic adsorption parameters are calculated.     

Cloud-point preconcentration of fulvic and humic acids

The cloud-point extraction technique was used for preconcentration of fulvic and humic acids. The effect of the acidity of solution, the equilibration temperature and time, the amount of added surfactant (Triton X-100) and the time of centrifugation on the recovery were examined. The recoveries of fulvic and humic acids achieved under optimised conditions were 82% and 96%, respectively.     

Modification of phosphogypsum granules by humic acids

Methods for introducing humic acid into granular multicomponent phosphogypsum-based ameliorants are elaborated. The influence of modifying additives of humic acids on the physicochemical and performance characteristics of phosphogypsum granules containing crystalline solvates of calcium sulfate, and on the process of leaching different extrinsic components from the granules, were studied.     

Determination of OH groups in humic acids using methylation with dimethylsulfate

The methylation of humic acids (HA) with dimethylsulfate in acetone and methanol followed by the iodometric determination of the methoxy groups (Zeisel reaction) were applied to determine the contents of –OH groups in solid samples of HA of different origins. For the coal- and peat-derived HA samples, the contents of –OH groups determined after methylation in acetone ranged from 6.6 to 8.7 mmol/g, whereas the contents of –OH groups determined after methylation in methanol ranged from 4.0 to 5.0 mmol/g. These differences may be related to the content of carboxylic groups in the HA molecule that were not methylated in methanol, as confirmed by a comparison with results of conventional titrimetric determinations. Observed differences were interpreted as results of different polarity of both solvents and alkalinity of the reaction mixture during the methylation. The contents of alcoholic groups as well as some other minor –OH groups can be estimated using the –OH group contents obtained after methylation in both solvents together with the results of the conventional determinations of acidic functional groups. A repeatability of the –OH groups determination as estimated from a series of triplicate analyses of different HA samples (n = 7) was in range of 0.15–0.73 mmol/g and 0.08–1.06 mmol/g (standard deviations) for methylation in acetone and methanol, respectively. Thus, the average repeatability of the –OH groups determination was estimated to be 0.38 and 0.50 mmol/g for methylation in acetone and methanol, respectively.     

Interaction of humic and fulvic acids with Th(IV)

The binding of Th(IV) to three humic and two fulvic acids has been studied using a solvent extraction technique. The results are interpreted to indicate the formation of two types of thorium binding sites in the humic polymer containing one or two carboxylate groups. High complex stability is observed and thorium humate binding constants increase with increasing ionization of the humic (fulvic) acid polyelectrolyte. The results are interpreted using a modified Born equation for electrostatic interaction. Thermodynamic results indicate that the great stability of these complexes is derived from a very favorable complexation entropy.     

Evidence for strong heterodimeric interactions of phenylboronic acids with amino acids

Strong heterodimeric interactions of phenylboronic acids with l-proline or betaine are evident in the solid state. The interaction energy is over 23 kcal/mol (at MP2/6-31+G^∗).