Humic Acid In Aqueous Solution Research Articles

Studies of Eu(III) sorption on TiO 2: Effects of pH, humic acid and poly(acrylic acid)

The influences of pH, ionic strength, initial Eu(III) concentration, humic acid (HA) and ploy(acrylic acid) (PAA) on Eu(III) sorption onto TiO 2 were carried out using batch technique. The results indicated that the presence of HA and PAA strongly enhanced Eu(III) sorption onto TiO 2 surface in low pH range, which suggested that PAA and HA played an important role as “bridge” between Eu(III) and TiO 2 to provoke Eu(III) sorption. Furthermore, the negative effects were observed above pH 4.0 in the presence of organic matters, because the residual PAA or HA in aqueous solution could form soluble Eu–HA/PAA complexes easily. The batch analysis showed that Eu(III) sorption on TiO 2 was significantly dependent on pH and independent of ionic strength, suggesting that the sorption of Eu(III) was mainly attributed to inner-sphere complexes. Three inner-sphere complexes, namely, SOEu 2 + (log K = 3.80), SOEu(OH) + (log K = −2.55) and SOEu(OH) 2 0 (log K = −8.33), predominated for Eu(III) on TiO 2 surface.

A study on removal efficiency of phenol and humic acid using spherical activated carbon doped by TiO2

This study aimed to find a way to remove organic pollutants, phenol and humic acid in aqueous solutions using TiO2 spherical activated carbon (Ti-SPAC). The Ti-SPAC was manufactured by resin ion-exchange and a heating process. This method was very effective not only in creating TiO2 on the surface of the supports evenly, but also in making activated carbon that has highly-developed micro pores. To estimate whether Ti-SPAC has the proper features as a photocatalyst and adsorbent, it was examined in detail by X-ray patterns, SEM image, EDXS, BET, EPMA. The results proved that Ti-SPAC is a very useful material for treating wastewater by photocatalysis and absorption.

A study of dilute aqueous solutions of humic acids by scanning microcalorimetry

It has been found by reversed-phase chromatography that humic acids obtained from vermicomposts of different duration of vermicomposting consist of a hydrophilic and a hydrophobic fractions, the hydrophobic fraction having a substantially lower content of charged, probably carboxylic, groups. A change in the sign of the temperature dependence of the heat capacity of diluted aqueous solutions of humic acids at approximately 58 degrees C has been found by differential scanning microcalorimetry, which indicates an increase in the hydration of hydrophobic groups. A jumpwise increase in heat capacity in the temperature range from 86 to 90 degrees C was also found, which is due likely to the hydration of hydrophobic groups in the interior of "micelles", due to the "devitrification" of the hydrophobic nucleus of micelle-like structures. It was shown that increasing the duration of vermicomposting leads to an increase in the relative content of the hydrophobic fraction of humic acids and in the cooperativity of the thermodynamic transition, which manifests itself in a jump of heat capacity, which probably results from the increase in the "micelle" size.

Synthesis, characterisation and separation of photoreactive Hydrogen-titanate nanofibrous channel

Australia is the world's largest wool producing country, accounting for about 25–30% of world production. As a biotemplate, we explored the possibility of using wool to produce micro-channel of Hydrogen-titanate nanofibres through morphology transcription of wool microfibres. Hydrothermal method was adopted to synthesise titanate nanofibres. A facile method of impregnation followed by incineration at 600°C was utilised to prepare the nanofibrous channel. Anatase undoped nanofibrous (average nanofibre diameter=44nm) channel of around 50μm in length and an average diameter of 9.5μm were obtained. The photocatalytic activity of nanofibrous channel was monitored under UV irradiation for the decomposition of humic acid in aqueous solution using an aerobic batch reactor system. The photodegradation results showed that UV254 absorbing moeities and DOC were respectively reduced by 82% and 66% after 3h of photoreaction at 1g/L catalyst load. The novel nanofibrous channel could be easily separated from the aqueous suspension by sedimentation after the end of the photocatalytic reaction.

Removal of humic acid from aqueous solution by cetylpyridinium bromide modified zeolite

Abstract Natural zeolite was modified by loading cetylpyridinium bromide (CPB) to create more efficient sites for humic acid (HA) adsorption. The natural and CPB modified zeolites were characterized with X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and elemental analysis. The effects of various experimental parameters such as contact time, initial HA concentration, solution pH and coexistent Ca 2+, upon HA adsorption onto CPB modified zeolites were evaluated. The results showed that natural zeolite had negligible affinity for HA in aqueous solutions, but CPB modified zeolites exhibited high adsorption efficiency for HA. A higher CPB loading on natural zeolites exhibited a larger HA adsorption capacity. Acidic pH and coexistent Ca 2+ were proved to be favorable for HA adsorption onto CPB modified zeolite. The kinetic process was well described by pseudo second-order model. The experimental isotherm data fitted well to Langmuir and Sips models. The maximum monolayer adsorption capacity of CPB modified zeolite with surfactant bilayer coverage was found to be 92.0 mg/g.

TiO2-assisted photocatalytic degradation of humic acids: effect of copper ions

The present study investigated the removal efficiency of aqueous humic acid solutions by TiO(2) photocatalytic degradation in the presence of Cu(II) species. The pseudo-first-order kinetics revealed rate constants as 9.87 x 10(-3), 7.19 x 10(-3), 3.81 x 10(-3) min(-1) for Color(436), UV(254) and TOC, respectively. Comparatively, lower rate constants were attained with respect to photocatalytic degradation of humic acid. Considering the source-dependent diverse chemical and spectral characteristics of NOM, a particular interaction would be expected for humic acid with Cu(II) species (0.1 mg L(-1)). The presence of copper ions significantly altered the photocatalytic degradation kinetics of humic acids in relation to the concentration effects of humic acid as expressed by spectroscopic parameters and TOC. Batch equilibrium adsorption experiments revealed a distinct Langmuirian-type adsorptive behavior of humic acid onto TiO(2) both in terms of UV(254) and Color(436) and a C-type adsorption isotherm was attained for TOC. K(F) values displayed an inconsistent effect of Cu(II) species, while adsorption intensity factor 1/n<1 denoted a prevailing favorable type of adsorption for Color(436) and UV(254). Because of the role of intra- and intermolecular interactions between copper ions and humic molecular size fractions, spectroscopic techniques were also employed for the assessment of the adsorption as well as photocatalytic degradation efficiencies.

Investigation of the parametar influences of UV/H2O2 process on humic acid degradation

Degradation of the humic acids (HA) in aqueous solution by UV radiation in the presence of H2O2 (UV/H2O2 process) was investigated. Low-pressure mercury vapor lamps with the emission maximum at 253.7 nm were used as a UV light source. Process efficiency was monitored by the UV/VIS spectrophotometric analysis of the HA residual concentration. Without H2O2 presence, UV radiation had negligible effect on the HA in aqueous solutions. The addition of H2O2 greatly improved the efficiency of the HA degradation by UV light and the optimum H2O2 concentration was 0.01 mol dm-3. The UV light intensity, pH value, presence and concentration of the carbonate and nitrate anions were investigated. With the increase of UV light intensity the process efficiency improved. The increase of pH had negative effect on the process efficiency. The presence of carbonate and bicarbonate ions inhibited the HA degradation. The presence of nitrate ions up to the concentration of 5 mmol dm-3 had no significant effect on the process efficiency.

Photosensitized Oxidation of Tetrabromobisphenol A by Humic Acid in Aqueous Solution†

The brominated flame retardant 3,3',5,5'-tetrabromobisphenol A (TBBPA) may accumulate in the environment, including surface waters, and degrade there to potentially toxic products. We have previously shown that singlet oxygen (1O2), produced by irradiation of rose bengal with visible light, oxidizes Triton X-100-solubilized TBBPA to yield the 2,6-dibromo-p-benzosemiquinone anion radical while consuming oxygen (Environ. Sci. Technol.42, 166, 2008). Here, we report that a similar 1O2-induced oxidation can be initiated in aqueous solutions by the irradiation of TBBPA dissolved in a humic acid (HA) solution. HA is a known weak 1O2 photosensitizer and we indeed detected the infrared 1O2 phosphorescence from HA preparations in D2O. When an aqueous preparation of HA was irradiated (lambda > 400 nm) in the presence of TBBPA, oxygen was consumed, and the 2,6-dibromo-p-benzosemiquinone anion radical was generated and detected using electron paramagnetic resonance. Radical formation and oxygen consumption were inhibited by sodium azide, a singlet oxygen quencher. Our results suggest that solar radiation, in the presence of HA, may play an important role in the photodegradation of TBBPA in the aquatic environment.

A Study of the Photocatalytic Oxidation of Humic Acid on Anatase and Mixed-phase Anatase–Rutile TiO2 Nanoparticles

In this study, slurry photocatalytic oxidation process was investigated for natural organic matter removal from aqueous humic acid solutions by using different titanium dioxide (TiO2) under UV-A irradiation. Bench scale experimental studies were conducted at different humic acid concentration at the range of 10–50 mg/L and different pH. Anatase and mixed-phase anatase–rutile TiO2 nano particles used in the photocatalytic reactor. The results were evaluated in terms of the parameters that are specific to organic matter content such as dissolved organic carbon concentration, ultraviolet absorbance at 254 nm (UV254), specific ultaviolet absorbance at 254 nm, and color (VIS400). It was observed that increasing humic acid concentration decreases photocatalytic degradation efficiency. The reactivity of the mixed-phase anatase–rutile (Degussa P-25) TiO2 was greater than individual anatase particles and the highest efficiency was observed at pH 3 for anatase TiO2.

Amine–modified polyacrylamide–bentonite composite for the adsorption of humic acid in aqueous solutions

In this study a new polyacrylamide-bentonite composite with amine functionality (Am–PAA–B) was prepared by direct intercalation polymerization technique. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern, surface area analysis and potentiometric titration elucidated the characteristics of Am–PAA–B. To apply the Am–PAA–B for the removal of humic acid (HA) commonly found in wastewaters, batch tests were conducted to evaluate the adsorption capacity. The effect of process parameters such as agitation time, concentration of HA, pH, ionic strength, adsorbent dose and temperature on the extent of HA adsorption from solutions was investigated. The pH dependent sorption of HA was found maximum (>99.9%) at pH range 4.0–7.0 for an initial concentration of 25 μmol/L. The removal mechanism of HA by Am–PAA–B was mainly through the complexation of the carboxyl groups in HA with the protonated NH 2 groups in Am–PAA–B. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The equilibrium conditions were achieved within 3 h under the mixing conditions employed. The adsorption was endothermic and the rate-limiting step was found to be film diffusion process. The equilibrium data were well fitted to the Langmuir isotherm. The monolayer adsorption capacity was found to be 103.91 μmol/g at 30 °C. Regenerative efficiency of Am–PAA–B was assessed for four consecutive adsorption/desorption cycles and found to be favorable. Conclusively, we found that the Am–PAA–B was significantly effective for the removal of HA from aqueous solutions.

Behaviour of partially soluble humic acids in aqueous suspension

Solubility and dissociation of four various humic samples, including IHSS standard, in water are studied in this work. Obtained experimental data are compared with hypothesis of partial solubility of humic acids in aqueous solutions developed in our previous work. It was proved experimentally that behaviour of all used humic samples agrees with the multi-step mechanism of solid humic acids interaction with water, including partial equilibrium dissolution as well as direct equilibrium dissociation from the solid state. Experimental data further demonstrated that regardless the common mechanism, solubility and dissociation degree of various humic samples may be very different and can be estimated using parameters of model based on the proposed mechanism.

New insights into aggregation and conformational behaviour of humic substances: Application of high resolution ultrasonic spectroscopy

The potential of high resolution ultrasonic analysis (HRUS) in humic acid colloidal properties research has been demonstrated. Sodium salts of humic acids from soil and lignite showed similar behaviour, supporting the hypothesis that, at both neutral and alkaline pH, they aggregate from very low concentration. The same conclusion can be reached for solutions at high ionic strength. We tried to apply the same procedure as used for the study of micellization and determination of critical micelle concentration of common surfactants. As expected, our experiments did not show the same break as demonstrated on the HRUS records for sodium dodecyl sulfate, at least in the range of measured concentration (i.e. from 0.001 up to 10 g L −1). The colloidal state of humic acids in aqueous solution is very sensitive to the presence of other, both charged and neutral, molecules. Aggregation of humic acids can be disturbed or promoted, depending on the concentration, by electrostatic or other weak interactions with extraneous molecules. Structures of varying mechanical strength (rigidity) can be formed in solutions of the same components but at different concentration. Such behaviour reflects mechanisms which occur during the sequestration of hydrophobic organic compounds and has several implications for the protection/transportation of labile structures and contaminants which are hypothesized to be encapsulated within hydrophobic pockets of soluble humic aggregates.

Thermal stability of solid and aqueous solutions of humic acid

The effects of temperature on the stability of a soil humic acid were studied in the present work. Solid samples of Gohy-573 humic acid (HA) and dissolved ones in aqueous solution (pH 6.0, 0.1 mol L −1 NaClO 4) were investigated in order to understand the impact of temperature on the chemical properties of the material. The methods applied to solid samples in the present investigation were thermogravimetric analysis (TGA), temperature-programmed desorption coupled with mass spectrometry (TPD–MS), and in situ diffuse reflectance infrared Fourier transformed spectroscopy (in situ DRIFTS). Humic acid samples were studied in the 25–800 °C range, with focus on thermal/chemical processes up to 250 °C. The reversibility of the changes observed was investigated by cyclic changes to specified temperature ranges (40–110 °C). All measurements were conducted under inert-gas atmosphere in order to avoid samples combustion at increased temperatures. Aqueous solutions were analyzed by UV–vis absorption spectroscopy after storage at temperatures up to 95 °C, and storage times up to 1 week. For temperatures below 100 °C experiments on solid and aqueous samples have shown results which were consistent to each other. The amount of water desorbed is temperature dependent and up to 70 °C this process was totally reversible. Above 70 °C an irreversible loss of water was also observed, which according to UV–vis spectroscopy corresponds to water produced by condensation leading to more condensed polyaromatic structures. The water released up to 110 °C was about 7 wt% of the total mass of the dried humic acid, where less than 50% corresponded to reversibly adsorbed water. At higher temperatures (>110 °C), gradual decomposition resulting in the formation of carbon dioxide (110–240 °C), and carbon monoxide (140–240 °C) takes place. Hence, thermal treatment of Gohy-573 humic acid above 70 °C results in irreversible structural changes, that could affect chemical properties (e.g., complex formation) of the material.

Radiation-chemical transformations of humic acid in aqueous solutions

The transformations of kinetically stable aqueous humic acid solutions saturated with Ar, N2O, or air by the action of fast electrons at absorbed doses to 20 kGy were studied. In radiolytic and postradiation processes, humic acid was converted into insoluble compounds, whose precipitation accelerated with dose. The formation of insoluble compounds was enhanced in neutral and acidified solutions saturated with air and/or N2O. As low-molecular-mass carboxylic acids that resulted from the radiolytic fragmentation of humic acid were accumulated in solution, the phase transformation weakened. The irradiated solutions were easy to purify by chemical coagulation.

Evaluation of solubilizing ability of humic aggregate basing on the phase-separation model

Solubilizing abilities of aggregates of humic acid (HA) to chlorinated benzenes (CBs) were investigated by means of the apparent water solubility enhancement. Both the water solubilities of 1,4-dichlorobenzene (DCB) and 1,2,4,5-tetrachlorobenzene (TeCB) linearly increased with increasing concentration of HA above the critical micelle concentration (CMC). Such solubilization behavior of CBs for HA was compatible with those for sodium dodecyl sulfate (SDS). These results indicate that the solubilization of CBs in the aqueous solution of HA above the CMC can be interpreted on the basis of the phase-separation model. Thus, the partition coefficients ( K mic) of CBs between water and HA aggregate phases were calculated by assuming this model. The fact that the K mic value increased with increasing K ow of CBs supported the partition into the HA aggregate phase by hydrophobic interaction. The estimated K mic values of DCB were not dependent on the solution pH. Both K mic values of DCB and TeCB for the HA aggregate were found to be 4–5-fold lower than those of SDS.

Formation of haloacetic acids during monochloramination

Factors that affect the formation of haloacetic acids (HAAs) during monochloramination, such as monochloramine application techniques, the initial chlorine (Cl) to ammonia-N (N) ratios, the bromide concentrations, and the wastewater quality, were studied. Aqueous humic acid solutions and undisinfected wastewater effluent samples obtained from two Hong Kong Sewage Treatment Works (STWs) were monochloraminated under various conditions. HAA formation was strongly affected by the monochloramine application techniques. The formation of trichloroacetic acid (TCAA) and total HAAs was reduced by adding preformed monochloramine. A higher initial Cl:N ratio indicated a higher chlorine demand and consequently led to higher HAA yields. Increasing the bromide concentration shifted HAAs from chlorinated species to brominated species and increased the yields of total HAAs, concurrent with decreases in the yields of dichloroacetic acid (DCAA) and TCAA but with increases in those of the other HAAs measured. Variations in the patterns of HAA formation were observed in monochloraminated wastewater effluent samples. The variations cannot be simply explained by the chlorine chemistry involving ammonia and/or bromide but are likely attributable to the combining effects of the water quality and the characteristics of the organics in the wastewater.

Preliminary study on photoproduction of hydroxyl radicals in aqueous solution with Aldrich humic acid, algae and Fe(III) under high‐pressure mercury lamp irradiation

AbstractUnder a high‐pressure mercury lamp (HPML) and using an exposure time of 4 h, the photoproduction of hydroxyl radicals (*OH) could be induced in an aqueous solution containing humic acid (HA). Hydroxyl radicals were determined by high performance liquid chromatography using benzene as a probe. The results showed that *OH photoproduction increased from 1.80 to 2.74 μM by increasing the HA concentration from 10 to 40 mg L−1 at an exposure time of 4 h (pH 6.5). Hydroxyl radical photoproduction in aqueous solutions of HA containing algae was greater than that in the aqueous solutions of HA without algae. The photoproduction of *OH in the HA solution with Fe(III) was greater than that of the solution without Fe(III) at pH ranging from 4.0 to 8.0. The photoproduction of *OH in HA solution with algae with or without Fe(III) under a 250 W HPML was greater than that under a 125 W HPML. The photoproduction of *OH in irradiated samples was influenced by the pH. The results showed that HPML exposure for 4 h in the 4‐8 pH range led to the highest *OH photoproduction at pH 4.0.

PROTON CORRELATION TIMES AND SEGMENTAL MOBILITY OF HUMIC ACIDS IN TWO SOLVENTS

Molecular dynamics of humic acid in solution are rarely investigated. Thus, the objective of this study is to determine proton correlation time and segmental mobility of humic acids in solution. Proton spin-lattice relaxation time (T1) was determined for humic acids in DMSO-d6 and 0.5 M NaOD at NMR frequencies of 300 MHz and 600 MHz; the correlation times were then estimated for aliphatic protons, protons associated with oxygen-containing functionalities, and aromatic protons. Results suggest that proton correlation times of humic acids in solvents were in the order of 10−10 seconds, which were near the T1 minimum at 600 MHz. Carbohydrate was identified as the largest and the most immobile component in humic acids, whereras aliphatic and aromatic fragments were relatively smaller and more mobile. The relaxation measurement is a useful approach for investigating the segmental mobility of humic acids in aqueous solution.

Preliminary study on the photoproduction of hydroxyl radicals in aqueous solution with Aldrich humic acid, algae and Fe(III) under high-pressure mercury lamp irradiation.

Under a high-pressure mercury lamp (HPML) and using an exposure time of 4 h, the photoproduction of hydroxyl radicals (*OH) could be induced in an aqueous solution containing humic acid (HA). Hydroxyl radicals were determined by high-performance liquid chromatography using benzene as a probe. The results showed that *OH photoproduction increased from 1.80 to 2.74 microM by increasing the HA concentration from 10 to 40 mg L(-1) at an exposure time of 4 h (pH 6.5). Hydroxyl radical photoproduction in aqueous solutions of HA containing algae was greater than that in the aqueous solutions of HA without algae. The photoproduction of *OH in the HA solution with Fe(III) was greater than that of the solution without Fe(III) at pH ranging from 4.0 to 8.0. The photoproduction of *OH in HA solution with algae with or without Fe(III) under a 250 W HPML was greater than that under a 125 W HPML. The photoproduction of *OH in irradiated samples was influenced by the pH. The results showed that HPML exposure for 4 h in the 4-8 pH range led to the highest *OH photoproduction at pH 4.0.

Wettability of Montmorillonite Clays in Humic Acid Solutions

AbstractThe effect of humic acid (HA) adsorption on the hydrophilicity of two different montmorillonite samples (Na-montmorillonite, NaMt, and a Na-fluorinated Na-montmorillonite, FNaMt, or ‘Rassoul’) was investigated. The changes in the wettability of clays were discussed in terms of the non-electrostatic free energy of interaction between the clay particles immersed in aqueous humic acid solutions (ΔG121), using the van Oss-Chaudhury-Good (vOCG) model. The surface free energy components (both non-polar or Lifshitz-van der Waals, and polar or acid-base) of clays were obtained from contact angle measurements, after adsorption of humic acid, at acid or basic pH, in 10−2 M NaCl solutions. It was found that: (1) at acid pH, a progressive decrease in the hydrophilic character of both clays was observed when the humic acid concentration was increased; (2) at basic pH, the hydrophilic character of both samples studied increased with HA concentration; (3) the effect of humic acid adsorption on the wettability of model edge surfaces of the laminar montmorillonite particles was estimated from a parallel study on silica and alumina surfaces, and only a slight decrease in the hydrophilicity was observed, whatever the pH of the liquid media. The ζ potentials of both clays in the absence and presence of humic acid were determined and the linkage between ζ potential and the electron-donor character of the materials is discussed.