石墨炉原子吸收光谱法测定土壤中铅量的测量不确定度评定

通过石墨炉原子吸收光谱法对土壤中的铅量进行了测定,对影响测量结果的不确定度分量进行了量化的计算.从而得出影响铅量测量不确定度的主要因素是测量样品消解液中的铅的质量浓度引起的不确定度.     

Study on the influence of humic acid of different molecular weight on basic ion exchange resin''s adsorption capacity

In this paper, humic acid (HA) was ultra-filtered into different molecular weight sections and was characterized by multi-element analysis, UV₂₅₄/TOC, FT-IR and three-dimensional fluorescence spectrometric. Since humic acids of different molecular weights have different hydrophilic and molecular size, the maximum adsorption capacity of basic ion exchange resins appears on the humic acid whose molecular weight ranges from 6000 to 10,000 Da.     

Preparation of silicon-doped ferrihydrite for adsorption of lead and cadmium: Property and mechanism

In this study, Si-doped ferrihydrite (Si-Fh) was successfully synthesized by a simple coprecipitation method for removal of heavy metals in water. Subsequently, the physicochemical properties of Si-Fh before and after adsorption were further studied using several techniques. The Si-Fh exhibited good adsorption capacity for heavy metal ions such as Pb(II) and Cd(II). The maximum adsorption capacities of lead and cadmium are respectively 105.807, 37.986 mg/g. The distribution coefficients of the materials for Pb(II) and Cd(II) also showed a great affinity (under optimal conditions). Moreover, it was found that the adsorption fit well with the Freundlich isotherm and pseudo-second-order kinetic model which means this was a chemical adsorption process. It can be conducted from both characterization and model results that adsorption of Pb(II) and Cd(II) was mainly through the complexation interaction of abundance oxygen functional groups on the surface of Si-Fh. Overall, the Si-Fh adsorbents with many superiorities have potential for future applications in the removal of Pb(II) and Cd(II) from wastewater.     

Enhancing the organic dye adsorption on porous xerogels

We investigate the adsorption of four different organic dyes (i.e., methyl orange, alizarin red S, brilliant blue FCF, and phenol red) on porous xerogels. To understand the factors affecting the adsorption capacity of the xerogels, we vary the hydrophobicity and the textural properties of the xerogels as well as the solution pH. We control the hydrophobicity by mixing two different precursors (i.e., vinyltriethoxysilane (VTES) and tetraethoxysilane (TEOS)) and the textural properties by using cetyltrimethylammonium bromide (CTAB) as a templating agent. We find that the adsorption capacity is enhanced as the organic/inorganic hybrid xerogel or the templated xerogel is used instead of the purely inorganic or the untemplated xerogel. In all the cases studied, adsorption decreases as the pH is increased due to the electrostatic repulsion between the dyes and the xerogel surface. We find that both the hydrophobic surface and larger pore size/volume are required to enhance the adsorption capacity significantly.     

Properties of different natural organic matter influence the adsorption and aggregation behavior of TiO2 nanoparticles

Natural organic matter (NOM) has considerable influence on the aggregation and stability of titanium dioxide nanoparticles (TiO₂ NPs). However, the effect of chemical properties of NOM on the interface interaction and the aggregation process is still not clear. In this study, we investigated the effects of two typical types of NOM (fulvic acid (FA) and humic acid (HA)) on its adsorption onto TiO₂ nanoparticles and their aggregation behavior in aqueous phase. Nuclear Magnetic Resonance (NMR) was used to study their functional groups, indicating that HA has a stronger hydrophobicity than FA. The presence of HA or FA lowered the critical coagulation concentration (CCC) of TiO₂ NPs, while FA showed a more significant effect. HA promotes the aggregation of TiO₂ NPs when ionic strength (IS) > CCC, which was likely due to the bridging effect. Contact angle measurements indicate that HA has higher hydrophobic properties than FA, and it is easier to transfer from water to the surface of TiO₂ NPs. Transmission Electron Microscopy (TEM) was applied to investigate the aggregate formation and colloid interface morphology of NOM-coated-TiO₂ NPs and NOM entanglement. Different structures of HA and FA result in various behavior and their interface interaction mechanisms including IS-induced entanglement and NOM/IS bridging.     

Effects of low-molecular-weight organic ligands and phosphate on DNA adsorption by soil colloids and minerals

Adsorption of DNA on montmorillonite, kaolinite, goethite and soil clays from an Alfisol in the presence of citrate, tartrate and phosphate was studied. A marked decrease in DNA adsorption was observed on montmorillonite and kaolinite with increasing anion concentrations from 0 to 5 mM. However, the amount of DNA adsorbed by montmorillonite and kaolinite was enhanced when ligand concentration was higher than 5 mM. In the system of soil colloids and goethite, with the increase of anion concentrations, a steady decrease was found and the ability of ligands in depressing DNA adsorption followed the sequence: phosphate > citrate > tartrate. Compared to H2O2-treated clays (inorganic clays), a sharp decrease in DNA adsorption was observed on goethite and organo-mineral complexes (organic clays) with increasing ligand concentrations. The results suggest that the influence of anions on DNA adsorption varies with the type and concentration of anion as well as the surface properties of soil components. Introduction of DNA into the system before the addition of ligands had the greatest amount of DNA adsorption on soil colloids and goethite. Organic and inorganic ligands promoted DNA adsorption on montmorillonite and kaolinite when ligands were introduced into the system before the addition of DNA. The results obtained in this study have important implications for the understanding of the persistence and fate of DNA in soil environments especially rhizosphere soil where various organic and inorganic ligands are active.     

Extractability of dioxins from soil: I. Extractability of dioxins from airborne particulates and humic acid fraction in soil

The extractability of dioxins (polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar polychlorinated biphenyls) from airborne particulates (APs) and humic acid (HA) in soil was evaluated. APs collected from ambient atmosphere and dioxins-associated precipitated HA fraction (PHA) were extracted by pressurized liquid extraction with either toluene or acetone. Native dioxins were equivalently extracted from APs with both solvents, whereas only acetone could satisfactorily recover the ¹³C-labelled compounds from metal-free PHA. The recovery rates of dioxins by toluene extraction from metal-free PHA varied with the organic carbon content of the PHA. However, even with acetone, the recovery of dioxins from metal-bound HA was poor (11–40%). These results suggest that PHA prevented the solvents from accessing sequestered dioxins. This characteristic of solid HA may influence the extractability of dioxins from humus-rich soil.     

Influence of the adsorption on the oxidation of oxalic acid on a gold electrode in acid media

Summary The influence of an adsorption process on the oxidation of oxalic acid on a gold electrode has been analysed. To disclose this influence, different supporting electrolytes have been used with different adsorption of the anion (SO ₄ ^2– , NO ₃ ^– and ClO ₄ ^– ). Moreover, it has been studied the modifications produced in the oxidation process by the presence of some species in solution with a strong adsorption (halides), but at low concentration levels.

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Der Einfluß der Adsorption auf die Oxidation von Oxalsäure an der Goldelektrode in saurem Medium

Zusammenfassung Um den Einfluß der Adsorption auf die Oxidation von Oxalsäure an der Goldelektrode in saurem Medium zu untersuchen, wurden Support-Elektrolyten mit verschiedener Anionenadsorption verwendet (SO ₄ ^2– , NO ₃ ^– und ClO ₄ ^– ). Außerdem wurden Modifikationen des Oxidationsprozesses in der Gegenwart von stark adsorbierten Spezies, diese allerdings in geringen Konzentrationen, untersucht (Halogenide).

     

Simultaneous analysis of small organic acids and humic acids using high performance size exclusion chromatography

An accurate and fast method for simultaneous determination of small organic acids and much larger humic acids was developed using high performance size exclusion chromatography. Two small organic acids, i.e. salicylic acid and 2,3‐dihydroxybenzoic acid, and one purified humic acid material were used in this study. Under the experimental conditions, the UV peaks of salicylic acid and 2,3‐dihydroxybenzoic acid were well separated from the peaks of humic acid in the chromatogram. Concentrations of the two small organic acids could be accurately determined from their peak areas. The concentration of humic acid in the mixture could then be derived from mass balance calculations. The measured results agreed well with the nominal concentrations. The detection limits are 0.05 mg/L and 0.01 mg/L for salicylic acid and 2,3‐dihydroxybenzoic acid, respectively. Applicability of the method to natural samples was tested using groundwater, glacier, and river water samples (both original and spiked with salicylic acid and 2,3‐dihydroxybenzoic acid) with a total organic carbon concentration ranging from 2.1 to 179.5 mg C/L. The results obtained are promising, especially for groundwater samples and river water samples with a total organic carbon concentration below 9 mg C/L.     

Multivariate curve resolution applied to Fourier transform infrared spectra of macromolecules: structural characterisation of the acid form and the salt form of humic acids in interaction with lead

The significance of evolving mixtures structural spectroscopic studies might appear limited when the experimental spectra do not present a sufficient quality for a precise interpretation. It is the case when the chemical behaviour of macromolecules is studied on the basis of infrared spectra. If the effective resolution is low, the spectral profiles appear similar despite the applied chemical conditions change. This makes impossible the interpretation of the raw spectra and mathematical treatments are required to separate the different contributions that overlap.To determine the behaviour of the reactive sites of humic acids in the binding with heavy metals, infrared spectra are recorded under various chemical conditions. The cation to be considered is Pb²⁺ and the two chemical variables to be studied are pH and initial lead concentration. Four series of FTIR spectra are recorded, but no visible difference can be directly assigned to the different chemical states of the macromolecules. Multivariate self-modelling curve resolution is thus proposed as a tool for resolving these complex and strong overlapping datasets. First, initial estimates are obtained from pure variable detection methods: it comes out that two spectra are enough to reconstruct the experimental matrices. In a further step, the application of the multivariate curve resolution-alternating least squares (MCR-ALS) algorithm with additional constraints on each individual dataset, as well as on column-wise augmented matrices, allows to optimise the profiles and spectra that appear to be highly characterising the acid and the salt form of the molecule. Moreover, the concentrations profiles associated to these two limit spectral forms allow interpreting the analytical measurements made during the reactions between humic acids and H⁺ or Pb²⁺. Consequently, depending on the initial state of the humic acid, two distinct reactional mechanisms are proposed.     

Accuracy and precision of adsorption isotherm parameters measured by dynamic HPLC methods

The fluctuations of the column temperature, the composition and the flow rate of the mobile phase affect the accuracy and precision of the adsorption isotherm parameters measured by dynamic HPLC methods. Experimental data were acquired by frontal analysis (FA) for phenol in equilibrium between C18-bonded Symmetry and a methanol:water mixture (20:80, v/v), at 303 K and a flow rate of 1 mL/min. The fluctuations of the experimental parameters were 0.1 K for the temperature, 0.1% for the mobile phase composition and 0.001 mL/min for the flow rate. The best isotherm model was shown to be the tri-Langmuir isotherm. Random errors were calculated and shown to agree with experimental results. Overloaded band profiles of phenol were acquired at low (sample size, 100 microL, concentration 3 g/L) and high (same sample size, concentration 60 g/L) loadings, at seven temperatures (298, 300, 302, 303, 304, 306, and 308 K), for seven mobile phase compositions (methanol 16, 18, 19, 20, 21, 22, and 24%), and with seven mobile phase flow rates (0.95, 0.97, 0.99, 1.00, 1.01, 1.03, and 1.05 mL/min), always keeping two experimental parameters at the values selected for the FA runs. Assuming that the isotherm model stays the same, the inverse method (IM) was used to derive the isotherm parameters in each case. Temperature affects the equilibrium constants according to Van't Hoff law. A temperature change of 1 K around 303 K causes a relative variation of 1.5% of the high-energy adsorption constant b3 and of 0.6% of the saturation capacity q3. The isotherm parameters are very sensitive to the mobile phase composition, especially the highest energy mode. Both adsorption constants b2 and b3 follow the linear strength solvent model (LSSM). A methanol volume fraction change of 1% causes a relative decrease of 3.2 and 5.0% of b2 and b3, respectively and a 2% decrease of the saturation capacity q3. Finally, flow rate changes affect only the saturation capacities. A flow rate change of 1 % causes a 2% change in the saturation capacity parameters.     

氨基修饰超高交联树脂对没食子酸的吸附性能

以亲水性小分子有机酸没食子酸作为研究对象,研究了氨基修饰超高交联树脂对没食子酸的吸附行为和机理.结果表明,氨基修饰超高交联树脂WJN-10对没食子酸有较高的吸附容量和吸附作用力;π-π共轭作用是树脂WJN-10吸附没食子酸主要作用力;WJN-10吸附没食子酸是物理吸附主导;吸附速率主要受控于颗粒内扩散过程;WJN-10对没食子酸有较好的吸附-脱附性能.     

Molecular evaluation of soil organic matter characteristics in three agricultural soils by improved off-line thermochemolysis: The effect of hydrofluoric acid demineralisation treatment

The molecular composition of soil organic matter (SOM) in three agricultural fields under different managements, was evaluated by off-line thermochemolysis followed by gas chromatography mass spectrometry analysis (THM-GC-MS). While this technique enabled the characterization of SOM components in coarse textured soil, its efficiency in heavy textured soils was seriously affected by the interference of clay minerals, which catalyzed the formation of secondary artifacts in pyrolysates. Soil demineralization with hydrofluoric acid (HF) solutions effectively improved the reliable characterization of organic compounds in clayey soils by thermochemolysis, while did not alter significantly the results of coarse textured soil. A wide range of lignin monomers and lipids molecules, of plant and microbial origin, were identified in the pyrograms of HF treated soils, thereby revealing interesting molecular differences between SOM management practices. Our results indicated that clay removal provided by HF pretreatment enhanced the capacity of thermochemolysis to be a valuable and accurate technique to study the SOM dynamics also in heavy-textured and OC-depleted cultivated soils.     

弱碱性大孔吸附树脂对腐殖酸的吸附

研究了腐殖酸分子量对弱碱性大孔树脂吸附腐殖酸的影响, 阐明了溶液中小分子芳环化合物(苯酚)及盐含量对树脂吸附腐殖酸的影响机制. 结果表明, 树脂对低分子量腐殖酸的吸附效果要优于高分子量腐殖酸; 低浓度苯酚在溶液中可以促进树脂吸附腐殖酸, 但溶液中苯酚浓度过高会对树脂吸附腐殖酸产生抑制作用; 溶液中的盐对树脂吸附腐殖酸的影响取决于溶液的pH值.     

含氰基聚合物微球对铜离子吸附性能的研究

以火焰原子吸收光谱法(FAAS)为检测手段,研究了聚丙烯腈微球(PANMS)对溶液中Cu2+的吸附及其影响因素,并建立了PANMS分离富集-FAAS法。实验结果表明,溶液pH为5、静态吸附时间为1.5 h、温度为20℃时,其对Cu2+的吸附达到饱和而稳定,吸附容量为30.2 mg/g,吸附率可达到87.5%。随着吸附时间的延长吸附率有所提高,但幅度不是很大。以0.1 mol/LHC l溶液作为解吸剂,解吸率可达到96.5%。经富集50倍后,测Cu2+工作曲线的回归方程为A=0.0025C(μg/L)-0.0026(r=0.9993),方法的检出限为1.68μg/L,相对标准偏差(RSD)小于2.9%。加标回收率为91.4%~97.0%。     

Amides as a model system of low molar mass algal organic matter. Influence on the adsorption of p-nitrophenol on activated carbon

In this study, the adsorption equilibrium and diffusivity parameters of p-nitrophenol were estimated for water containing different concentrations of secondary amides. Commercial powdered activated carbon was used as an adsorbent. The external mass transfer coefficient (k_f), the surface diffusion coefficient (D_s) and the standard free Gibbs energy were calculated for p-nitrophenol in the presence of different secondary amide concentrations. The analysis established that there are correlations between structural parameters of amides, on the one hand, and diffusion and thermodynamic parameters for p-nitrophenol adsorption process, on the other. It was noticed that voluminous hydrophobic amides decreased the adsorption capacity of p-nitrophenol on activated carbon. On the basis of the results obtained for external mass transfer coefficients, it is assumed that amides cause the reduction of adsorption capacity of p-nitrophenol onto activated carbon by concentrating at the solid/liquid interface.     

Optimization of lead adsorption from lead-acid battery recycling unit wastewater using H2SO4 modified activated carbon

During the recycling of exhausted lead-acid battery, large amount of wastewater is discharged, which contains the toxic Pb(II) ions in high concentration. In this study, the granular activated carbon after modification with sulfuric acid has been used to remove the Pb(II) ions from this wastewater. Adsorbents were characterized using Fourier Transform Infrared, Scanning Electron Microscope, and X-Ray Diffraction analyzer. Taguchi orthogonal L16 array (4^3) was used for batch adsorption study with four levels of three factors initial pH, adsorbent dose, and contact time. Optimum level of parameters was fourty + nd pH 4.5, time 240 min, and dose 0.05 g/50 mL using signal-to-noise ratio (larger-the-better response). Analysis of variance technique was used to signify the adsorption experiment model. The effect of parameters on uptake capacity of adsorbent has been evaluated. Maximum adsorbent capacity for Pb(II) uptake from wastewater of battery recycling unit was found 8.19 mg/g after modification with sulfuric acid. To further understand the mechanism of adsorption, isotherm and kinetic studies were carried out. Experimental data were well fitted with Langmuir isotherm model and pseudo-second-order kinetic model. The study suggested that H₂SO₄ modified granular activated carbon can be potentially used to remove Pb(II) from lead-acid battery recycle wastewater.     

Arylations mediated by lead(IV) in the presence of formazan and imine ligands

The use of formazan and imine ligands in arylations of β-dicarbonyl systems by phenyl boronic acid/lead(IV) carboxylates is examined.     

Application of sequential injection-square wave voltammetry (SI-SWV) to study the adsorption of atrazine onto a tropical soil sample

Square wave voltammetry automated by sequential injection analysis was applied to determine the Freundlich adsorption coefficients for the adsorption of atrazine onto a clay rich soil. The detection limit in soil extracts was between 0.18 and 0.48 μmol L⁻¹, depending on the medium used to prepare the extracts (0.010 mol L⁻¹ KCl, CaCl₂ or HNO₃ and 0.0050 mol L⁻¹ H₂SO₄), all of them conditioned in 40 mmol L⁻¹ Britton-Robinson buffer at pH 2.0 in presence of 0.25 mol L⁻¹ NaNO₃. Also in soil extracts the linear dynamic range was between 1.16 and 18.5 μmol L⁻¹ (0.25-4.0 μg mL⁻¹), with a sampling frequency of 190 h⁻¹. The K_f Freundlich adsorption coefficient was 3.8 ± 0.2 μmol^1−1/n Lⁿ kg⁻¹ in medium of 0.010 mol L⁻¹ KCl or CaCl₂, but increased to 7.7 ± 0.1 and 9.0 ± 0.3 μmol^1−1/n Lⁿ kg⁻¹ in 0.010 mol L⁻¹ HNO₃ and 0.0050 mol L⁻¹ H₂SO₄, respectively. The increase of K_f was related to the decrease of pH from 6.4-6.7 in KCl and CaCl₂ to 3.7-4.0 in presence of HNO₃ or H₂SO₄, which favors protonation of atrazine, facilitating electrostatic attractions with negative charges of the clay components of the soil. The 1/n parameters were between 0.76 and 0.86, indicating that the isotherms are not linear, suggesting the occurrence of chemisorption at specific adsorption sites. No statistically significant differences were observed in comparison to the adsorption coefficients obtained by HPLC. The advantage of the proposed SI-SWV method is the great saving of reagent because it does not use organic solvent as in the case of HPLC (50% (v/v) acetonitrile in the mobile phase). Additionally the start up of SI-SWV is immediate (no column conditioning necessary) and the analysis time is only 19 s.     

Effects of soil pH and organic matter on distribution of thorium fractions in soil contaminated by rare-earth industries

The labilities of thorium fractions including mobility and bioavailability vary significantly with soil properties. The effects of soil pH and soil organic matter on the distribution and transfer of thorium fractions defined by a sequential extraction procedure were investigated. Decrease of soil pH could enhance the phytoavailability and the potential availability of thorium in soil. Increase of organic matter reduced the phytoavailability of thorium, but enhanced the potential availability of it. The reasons why soil pH and soil organic matter affect thorium fractions were discussed, and the behavior of the effects of soil properties on thorium fractions was elucidated. Fourier-transform infrared (FTIR) spectra were employed to reveal the positive relationship between the amounts adsorbed in humic material and/or amorphous oxides and the content of soil organic matter.