Humic Acid In Aqueous Solution Research Articles

An investigation of the photocatalytic efficiencies of TiO 2 powders on the decolourisation of humic acids

Photocatalytic efficiencies of two commercial titania brands, Degussa P-25 and Hombikat UV-100 were discussed in relation to the degradation of humic acid in aqueous solutions. Decolourisation rate of humic acid (Colour 436, m −1) for Degussa P-25 was found to be higher than the rate achieved by using Hombikat UV-100 specimen, both in terms of pseudo-first-order and Langmuir–Hinshelwood kinetics. The adsorption isotherms exhibited different trends and the application of the Freundlich adsorption model revealed K F values 0.549 for Degussa P-25, and 0.293 for Hombikat UV-100 indicating higher adsorption capacity of Degussa P-25 for humic acid under neutral pH conditions. This observation was also consistent with the intrinsic photocatalytic activities calculated as 0.196 m −1 min −1 m −2 for Degussa P-25 and 0.0269 m −1 min −1 m −2 for Hombikat UV-100. The higher surface area of Hombikat UV-100 did not render higher adsorption capacity values leading to higher degradation rates.

Photoelectrocatalytic degradation of humic acid in aqueous solution using a Ti/TiO 2 mesh photoelectrode

Humic acid (HA) is one of natural organics existing in water supply as a precursor of trihalomethanes formation in chlorination. The photo-degradation of HA in aqueous solution by photoelectrocatalytic (PEC) oxidation using a Ti/TiO 2 mesh electrode was investigated in terms of UV absorbance at 254 nm, colour and TOC concentration. The key factors affecting the PEC oxidation efficiency were studied, including the concentration of electrolyte, electrical bias applied, pH value of HA solution, the intensity of incident light and the area of Ti/TiO 2 mesh photoelectrodes. The first-order kinetic model was applied to describe the PEC oxidation, in which the kinetic constant k was verified by the experimental data as a function of the concentration of electrolyte, light intensity, the area of Ti/TiO 2 mesh electrode and the voltage of electrical bias applied. It was found that there was an optimal bias voltage of 1.63 V and low pH value was favourable for TOC removal in HA solution. Our investigation showed that PEC oxidation was a convenient way to mineralise the organic matters with high efficiency.

X-ray photoelectron spectroscopy investigation of the interaction of U(VI) and Fe(III) with natural humic acid in aqueous solutions

X-ray photoelectron spectroscopy investigation of the interaction of U(VI) and Fe(III) with natural humic acid in aqueous solutions

X-ray photoelectron spectroscopy investigation of the interaction of U(VI) and Fe(III) with natural humic acid in aqueous solutions

Complexes of U(VI) and Fe(III) with natural humic acid (NHA) were studied by X-ray photoelectron spectroscopy (XPS). It follows from the analysis of the uranium and iron concentrations at the surface and in the bulk of the humates that the reaction in solution is heterogeneous. The NHA reacts as a particle. In solutions containing either U(VI) or Fe(III), NHA reacts similar with Fe(III) and U(VI). However, in a mixed solution of Fe(III) and U(VI), NHA reacts predominantly with iron. In comparison to Fe(III) complexes, the complexes with U(VI) are formed mostly in the inner of the NHA particle. Therefore, the concentration ratio U/Fe as measured by XPS increases by powdering of the particles. Salts of Fe(III) can be used to inhibit the uranium migration in form of its soluble humates.

Size exclusion (radio) chromatography of aqueous humic acid solutions with cesium and strontium

The high-performance size-exclusion chromatography (HPSEC) and radiochromatography (HPSERC) was used for the identification of radiocesium and radiostrontium interaction with humic acid. It was found that the behavior of humic acid on size-exclusion chromatography is sensitive to the salt concentration and pH of the mobile phase. At lower ionic strength and in acidic region of pH, the Aldrich humic acid exhibited three main fraction within the ranges >760 kDa, 25–100 kDa and <5 kDa. Radiocesium was found in the low-molecular fractions (<1 kDa) of humic acids but radiostrontium interacts preferably with the fractions of humic acid of molecular weight within the range 2–5 kDa.

Paramagnetic Relaxation of Atrazine Solubilized by Humic Micellar Solutions

This study examines a central tenet of the “membrane−micelle” model of humic substancesthat humic molecules form “micelle-like” aggregates with hydrophobic interiors into which nonpolar organic compounds partition. We solubilized atrazine, labeled by a trifluoromethyl group on the ethylamino side chain, in aqueous solutions containing 10% humic acid by weight and observed the F-19 nuclear magnetic resonance (NMR) relaxation of atrazine induced by paramagnetic probes added to the humic solution. One paramagnetic probe, Gd·EDTA anion, remains in aqueous solution while the other, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), is sorbed by humic micelles. The hydrophilic anionic paramagnetic probe induces virtually no paramagnetic relaxation in atrazine solubilized by 10% aqueous humic acid solutions while the hydrophobic neutral paramagnetic probe causes rapid paramagnetic relaxation. These results show that atrazine solubilized by concentrated humic acid solutions occupies a domain accessible only to neutral...

The role of selected cations in the formation of pseudomicelles in aqueous humic acid

The fluorescence intensity enhancement of a pyrene probe in aqueous humic acid solutions was assessed in terms of added lanthanide and thorium cations. Among the trivalent ions it was found that size played a role, with the small Lu 3+ ion producing the greatest increase in pyrene emission. This was attributed to its superior ability to cause pseudomicellization in the humic acid polymer. Slow kinetic effects were observed, leading to substantial fluorescence enhancement over a period of 7 h. This was ascribed to a continuous aggregation process in aqueous humic acid, leading to ever more viscous microenvironments for the probe molecule.

The Sequestration of Hydrophobic Micropollutants by Dissolved Humic Acids

A potential mechanism for the interactions of dissolved humic acids with nonpolar micropollutants was assessed by monitoring the fluorescence of pyrene added to aqueous humic acid solutions. The results support the concept of the cation-assisted formation of intramolecular domains in humic acids and

The microstructure of humic acid-montmorillonite composites

AbstractAn organo-clay composite was prepared by contacting Na-montmorillonite and humic acid in aqueous solution which was of variable pH. After freeze-drying the precipitate of the solution, the detailed structure of the humic acid-montmorillonite composite was observed. Transmission electron micrographs and electron diffraction patterns indicate that the composite which was formed under acidic conditions has a characteristic microstructure. Humic acid, a large organic molecule, is combined with bent or curled thin foils of montmorillonite to form a spherical aggregate. The X-ray diffraction pattern supports this observation and suggests that the montmorillonite is cleaved into thin flakes as a silicate layer. The composite formed under alkaline conditions was in the form of a thin plate or lath and had a similar morphology to that of montmorillonite. The difference in the microstructure of the composite is reasonably attributed to the chemical flexibility of humic acid, i.e., conformation changes depending on the pH of the solution.

Reactive species produced on irradiation at 365 nm of aqueous solutions of humic acids

In order to characterize the reactive species produced on irradiation at 365 nm of humic acid (HA) solutions, the photoinduced transformation of aromatic compounds was studied as a function of several parameters (concentrations of substrates, HA and oxygen, pH of the solution) and in the presence of additives such as isopropanol, ethylenediaminetetraacetic acid (EDTA), H 2O 2 and Fe 2+. No consumption of the substrates was observed in deoxygenated medium. In oxygenated solutions containing commerical HA, the rates of phenol disappearance were significant; the rate laws were dependent on the substrate and HA concentrations. In weakly oxygenated medium, the consumption rates were lower and other reactive species were involved. EDTA and citric acid led to partial inhibition of the reactions, indicating that the reactive species were related to metallic cations contained in HA. In acidic solution, hydroxyl radicals were produced by a photo-Fenton reaction. HA synthesized from phenol was incapable of photoinducing the transformation of the substrates, whereas HA synthesized from phenol-Fe 3+ produced transformation of the substrates. The formation of singlet oxygen on irradiation of commercial HA was characterized previously. Unexpectedly, no consumption of phenolic substrates through singlet oxygen reaction was observed.

Fluorescence Lifetime Measurements of Fluoranthene, 1-Naphthol, and Napropamide in the Presence of Dissolved Humic Acid

The binding of hydrophobic organic solutes and nonionic pesticides with dissolved humic substances may significantly influence their behavior and fate in natural systems. The binding of fluoranthene, 1-naphthol, and napropamide [2-(1-naphthoxy)-N,N-diethylpropionamide] by an International Humic Substances Society reference soil humic acid in aqueous solutions was studied using fluorescence quenching and lifetime measurements. The quenching of fluoranthene, 1-naphthol, and napropamide fluorescence by the humic acid was adequately described by the Stern-Volmer equation. The effects of temperature ranging from 283 to 313 K on the quenching ratios was not significant, and the fluorescence lifetimes of these compounds did not shorten as a function of increasing humic acid concentrations

Interaction between humic acids and copper(II) oxinate

The solubility of the fungicide copper(II) oxinate (Cu(OX) 2) linearly increased with the concentration of humic acid in aqueous solution. This phenomenon was attributed to the interaction between Cu(OX) 2 and hydrophobic domains in humic acid, and the Cu(OX) 2 association coefficients with humic acids K doc)_were evaluated. The evaluations of the K doc values were carried out for humic acids extracted from peat and marine sediment. For these humic acids, the K doc values increased at pH 6 with decreasing copper(II) complexing capacity and amount of acidic functional groups. This suggested that the K doc values can be correlated with the polarity of the humic acids. The interaction between Cu(OX) 2 and humic acid could be ascribed to the hydrophobic-hydrophobic interaction.

Applicability of photon correlation spectroscopy for measurement of concentration and size distribution of colloids in natural waters

The suitability of proton correlation spectrosocpy (PCS) for the determination of concentration and size distribution of colloidal matter was tested in a surface water and in a deep groundwater. Well-defined colloids (sizes predominately in the range 50–500 nm) of α-Fe2O3, γ-Al(OH)3, SiO2, kaolinite, illite and humic acid in aqueous solutions were used as references for calibration of the PCS-instrument (signal vs. concentration). The intensity of the scattered light was dependent on the composition of the colloid. The concentration ranges, where a quantitative determination of the colloid could be achieved, were 0.03–2 mg/1, 0.1–2 mg/1, 0.1–7 mg/1, 0.5–10 mg/1, 0.5–50 mg/1 and 0.5–75 mg/1 for α-Fe2O3, γ-Al(OH)3, SiO2, kaolinite, illite and humic acid, respectively (in homogeneous systems). The colloidal populations in the surface waters (inlet and outlet of a lake) had a size distribution in the range 100–500 nm. The measured count rates were around 330 kcps and 30 kcps at the inlet and outlet, respectively, which correspond to totally 2.8 mg/1 and 0.9 mg/1 of colloidal matter according to gravimetric determinations (collected on clogged 0.015 μm filters). Comparisons of concentrations estimated from measurements of reference colloids with PCS and gravimetric determinations of the colloidal showed that a combination of the two methods would be needed. The measurements of a deep groundwater were performed on-line and in situ with a PCS technique. The content of colloidal matter in the groundwater was below the detection limit for the PCS-equipment, which corresponds to a concentration not above 0.5 mg/1 and probably below 0.1 mg/1 in the present system. The feasibility and advantages of using PCS for non-disturbing size characterisation and concentration measurements of colloids in aquatic systems have been demonstrated, as well as some limitations of the method.

Mesure de la capacite complexante de solutions aqueuses d'acides humiques par titrage au cuivre et D.P.A.S.V. en tampon acetate

Abstract D.P.A.S.V. evaluation of the complexing capacity of aqueous solutions of humic acids by copper titration has been studied in non complexing solutions and in acetate buffers. Some difficulties have been evidenced due to the necessity of controlling pH and interferences from the buffers. A method using dilute buffer solutions and a semi empirical integration of the voltamperometric peaks is proposed.

A combined reversed-phase and purge and trap chromatographic method to study the interaction of volatile organic compounds with dissolved humic acid in aqueous solutions

A combined reversed-phase and purge and trap chromatographic method was used to study the interaction of dissolved Aldrich humic acid with volatile organic compounds in aqueous solution. Humic acid bound compounds were quantified by a purge and trap gas chromatographic method after separation from unbound compounds using C 18 solid-phase extraction columns. Partition coefficients (K p ) were 22.7 mL/g for dichlorotoluene, 14.9 mL/g for dichlorobenzene, and 3.6 mL/g for trichloroethene

Aggregate formation of humic acids from marine sediments

Humic acids were extracted from marine sediments and the aggregate-forming properties were studied by surface tension measurements and the solubilization of hydrocarbons. The surface tension of aqueous humic acid solutions decreases with the humic acid concentration and becomes constant; the relationship between the surface tension and the logarithm of the concentration of humic acid is represented by two straight lines. The break point is considered to be due to aggregate formation. The solubility of benzo(a)pyrene and icosane in humic acid solution increases with humic acid concentration. A marked solubility increase observed at a humic acid concentration near 0.1% indicates that the hydrocarbon is solubilized in humic acid aggregates. The concentration of aggregation can be determined from the point of intersection of two straight lines representing the relationship between solubility of hydrocarbons and log concentration of humic acid. Concentrations of aggregate formation for various humic acids determined by surface tension measurements and by the solubilization of hydrocarbons are in good agreement.

Fluorescence Quenching and Polarization Studies of Naphthalene and 1‐Naphthol Interaction with Humic Acid

AbstractAlthough it is known that the environmental behavior and fate of synthetic organic compounds are altered on association with humic materials, the nature of this interaction has been a source of controversy. Fluorescence quenching and polarization techniques were used to study the interaction between water‐soluble humic acid and naphthalene and 1‐naphthol. Stern‐Volmer plots constructed using intensity values for these fluorophores dissolved in humic acid solutions (0–25 mg L−1) were linear. The ultraviolet/visible (UV/VIS) absorption spectra of each fluorophore in the presence and absence of the humic acid quencher were identical. This, in addition to the observed increase in quenching with temperature, indicates a dynamic (collisional) mode of quenching. Fluorescent lifetimes of the probes decreased in the presence of humic acid, providing further evidence of dynamic quenching. However, the slopes of Stern‐Volmer plots constructed with lifetime values were considerably smaller than plots obtained with intensity values. Calculated bimolecular quenching constants of 5.2 × 1010 M−1 s−1 for naphthalene and 4.8 × 1011 M−1 s−1 for 1‐naphthol are above the maximum considered possible for a diffusion‐controlled interaction. Fluorescence‐polarization measurements indicate no rigid association between unquenched 1‐naphthol and humic acid. The interaction of naphthalene and 1‐naphthol with humic acid in aqueous solution occurs through a loose association in which humic acid surrounds the fluorophore in a cage‐like manner. This pseudomicelle confines the probe without rigidly binding it, promoting frequent quenching collisions and a combination of dynamic and static quenching.

Kinetic Studies of the Reactions of Benzidine with Humic Acid

AbstractThe mechanism of the reaction of benzidine (4,4′‐diaminobiphenyl), a toxic biphenyl amine, with humic acid in aqueous solutions has been studied using both commercial and soil‐extracted samples of humic acid. The reaction trend is similar for all the samples and involves a byphasic decay in the concentration of benzidine. The phase I reaction is rapid and complete within 1 h and is approximated by second‐order kinetics, while the phase II reaction (a slow process which attains a steady state in benzidine concentration after about 14 d) follows a single exponential first‐order reaction with respect to benzidine. Sorption of benzidine by humic acid was higher for the commercial samples than for the soil‐extracted sample.

Ultrasonic reflection mode tomography: Mensah S. Lefebvre, Jr., CNRS - LMA, Marseille, France

A 50 MHz high-frequency ultrasound and analysis method were developed to further improve the in situ assessment of deposition and distribution of organic fouling on the polyvinylidene fluoride (PVDF) membranes. Measurements of fouling depositions were performed from PVDF membranes filtrated with aqueous humic acid solutions (HAS) of 2 and 4 ppm concentrations in a flat-sheet module. Ultrasound signals reflected from the PVDF membranes, following filtrations at various durations including 0, 5, 15, 30, 60, and 100 min, were acquired. The thickness and distribution of fouling estimated and assessed by peak-to-peak echo voltage (Vpp) and C-mode images were found to be non-homogeneously deposited on the membranes. Following the filtrations with 2 and 4 ppm HAS for 100 min, the corresponding thickness of fouling deposition increased from 1.81±0.9 to 2.45±1.57 μm, respectively; those average Vpp decreased from 2.05±0.07 to 1.13±0.16 V and from 2.11±0.08 to 0.94±0.15 V. These results demonstrated that the deposition and distribution of organic fouling could be sensitively and rapidly evaluated by high-frequency ultrasound image incorporated with the analysis method.

Experimental studies of organic-Zn complexes and their stability

Thermal decomposition, temperatures of four organic Zn complexes were evaluated experimentally by determining the change in sphalerite solubility with temperature in aqueous solutions containing organic compounds. The results show that decomposition takes place at 180°±5°C for lactic acid-Zn complex, 200°±5°C for EDTA-Zn, 240°±5°C for quinone-Zn and 190°±5°C for fulvic acid-Zn. It is also shown that at 190°–200°C sphalerite solubility is 4 to 7 times higher in NaCl solution containing organic compounds than that in NaCl solution without organic compounds. Studies were also conducted on the contents of Pb and Zn complexed by fulvic acid and humic acid in aqueous solutions the infrared spectra of fulvic acid-Zn and humic acid-Zn complexes, the differential thermal analysis of fulvic acid, humic acid and quinone and EDTA, and the variation in fulvic acid solubility in the seawater with temperature.