Spectroscopic study of dinitrophenol herbicide sorption on smectite

Sorption of two dinitrophenolic herbicides, 4,6-dinitro-o-cresol (DNOC) and 4,6-dinitro-2-sec-butylphenol (DINOSEB) to smectite was studied using FTIR, HPLC, and quantum chemical methods. The high affinity of DNOC and DINOSEB for smectite surfaces was attributed to site-specific interactions with exchangeable cations and nonspecific van der Waals interactions with the siloxane surface. The positions of the nu(asym)(NO) and nu(sym)(NO) vibrational modes were perturbed by the exchangeable cations with similar changes occurring for both alkali and alkaline earth cations as a function of ionic potential. The cation-induced changes to the vibrational bands of the NO2 groups indicate that exchangeable metal cations are coordinated to -NO2 groups. Quantum chemical methods predicted a red-shift of the nu(asym)(NO) band and a corresponding blue-shift of the nu(sym)(NO) modes, as was observed experimentally. The nature of the smectite surface itself did not strongly influence the vibrational modes of sorbed DNOC or DINOSEB on the basis of a comparison of DNOC sorbed to three different smectites (K-SWy-2, K-SAz-1, and K-SHCa-1). FTIR spectra of DNOC and DINOSEB sorbed to a K-SWy-2 smectite were studied quantitatively using a modified form of Beers law. The FTIR-derived sorption isotherm of DNOC sorbed to K-SWy-2 was in good agreement with the isotherm derived from HPLC measurements. The molar absorptivity value of DNOC sorbed to K-SWy-2 smectite was 1.43 x 10(7) cm2/mol in good agreement with literature values for nitroaromatics (average value of 1.72 x 10(7) +/- 0.3 cm2/mol). On the basis of this value, the limit of detection using the FTIR method of approximately 5 microgDNOC g(clay) was determined. These two observations (sorption isotherms and molar absorptivity) provide a direct link between the macroscopic sorption results and the FTIR spectra.     

Geochemical modulation of pesticide sorption on smectite clay

Pesticide adsorption by soil clays can be dramatically influenced by the exchangeable cations present. Among the common exchangeable base cations in soils (Ca2+, Mg2+, K+, and Na+), K+-saturated clays frequently demonstrate the strongest affinity for pesticides. In the presence of multiple exchangeable cations in the system, we hypothesize that the magnitude of pesticide sorption to soil minerals is proportional to the fraction of clay interlayers saturated with K+ ions. To test this hypothesis, we measured sorption of three pesticides with different polarities (dichlobenil, monuron, and biphenyl) by homoionic K- and Ca-smectite (SWy-2) in KCl/CaCl2 aqueous solutions. The presence of different amounts of KCl and CaCl2 resulted in varying populations of K+ and Ca2+ on the clay exchange sites. The sorption of dichlobenil and, to a lesser extent monuron, increased with the fraction of K+ on clay mineral exchange sites. Ca- and K-SWy-2 displayed the same sorption capacities for nonpolar biphenyl. X-ray diffraction patterns indicated that at lower fractions of K+-saturation, exchangeable K+ ions were randomly distributed in clay interlayers and did not enhance pesticide sorption. At higher populations of K+ (vs Ca2+), demixing occurred causing some clay interlayers, regions, or tactoids to become fully saturated by K+, manifesting greatly enhanced pesticide sorption. The forward and reverse cation exchange reactions influenced not only K+ and Ca2+ populations on clays but also the nanostructures of clay quasicrystals in aqueous solution which plays an important, if not dominant, role in controlling the extent of pesticide sorption. Modulating the cation type and composition on clay mineral surfaces through cation exchange processes provides an environmental-safe protocol to manipulate the mobility and availability of polar pesticides, which could have applications for pesticide formulation and in environmental remediation.     

Influence of smectite hydration and swelling on atrazine sorption behavior

Smectites, clay minerals commonly found in soils and sediments, vary widely in their ability to adsorb organic chemicals. Recent research has demonstrated the importance of surface charge density and properties of exchangeable cations in controlling the affinity of smectites for organic molecules. In this study, we induced hysteresis in the crystalline swelling of smectites to test the hypothesis that the extent of crystalline swelling (or interlayer hydration status) has a large influence on the ability of smectites to adsorb atrazine from aqueous systems. Air-dried K-saturated Panther Creek (PC) smectite swelled less (d(001) = 1.38 nm) than never-dried K-PC (d(001) = 1.7 nm) when rehydrated in 20 mM KCl. Correspondingly, the air-dried-rehydrated K-PC had an order of magnitude greater affinity for atrazine relative to the never-dried K-PC. Both air-dried-rehydrated and never-dried Ca-PC expanded to approximately 2.0 nm in 10 mM CaCl2 and both samples had similar affinities for atrazine that were slightly lower than that of never-dried K-PC. The importance of interlayer hydration status in controlling sorption affinity was confirmed by molecular modeling, which revealed much greater interaction between interlayer water molecules and atrazine in a three-layer hydrate relative to a one-layer hydrate. The entropy change on moving atrazine from a fully hydrated state in the bulk solution to a partially hydrated state in the smectite interlayers is believed to be a major factor influencing sorption affinity. In an application test, choice of background solution (20 mM KCl versus 10 mM CaCl2) and air-drying treatments significantly affected atrazine sorption affinities for three-smectitic soils; however, the trends were not consistent with those observed for the reference smectite. Further, extending the initial rehydration time from 24 to 240 h (prior to adding atrazine) significantly decreased the soil's sorption affinity for atrazine. We conclude that interlayer hydration status has a large influence on the affinity of smectites for atrazine and that air-drying treatments have the potential to modify the sorption affinity of smectitic soils for organic molecules such as atrazine.     

Ionic strength-induced formation of smectite quasicrystals enhances nitroaromatic compound sorption

Sorption of organic contaminants by soils is a determinant controlling their transport and fate in the environment. The influence of ionic strength on nitroaromatic compound sorption by K+- and Ca2+ -saturated smectite was examined. Sorption of 1,3-dinitrobenzene by K-smectite increased as KCl ionic strength increased from 0.01 to 0.30 M. In contrast, sorption by Ca-smectite at CaCl2 ionic strengths of 0.015 and 0.15 M remained essentially the same. The "salting-out" effect on the decrease of 1,3-dinitrobenzene aqueous solubility within this ionic strength range was <1.5% relative to the solubility in pure water. This decrease of solubility is insufficient to account for the observed increase of sorption by K-smectite with increasing KCl ionic strength. X-ray diffraction patterns and light absorbance of K-clay suspensions indicated the aggregation of clay particles and the formation of quasicrystal structures as KCI ionic strength increased. Sorption enhancement is attributed to the formation of better-ordered K-clay quasicrystals with reduced interlayer distances rather than to the salting-out effect. Dehydration of 1,3-dinitrobenzene is apparently a significant driving force for sorption, and we show for the first time that sorption of small, planar, neutral organic molecules, namely, 1,3-dinitrobenzene, causes previously expanded clay interlayers to dehydrate and collapse in aqueous suspension.     

Enhanced sorption of trichloroethene by smectite clay exchanged with Cs+

Trichloroethene (TCE) is one of the most common pollutants in groundwater, and Cs+ can be a cocontaminant at nuclear facilities. Smectite clays have large surface areas, are common in soils, have high affinities for some organic contaminants, and hence can potentially influence the transport of organic pollutants entering soils and sediments. The exchangeable cations present near smectite clay surfaces can radically influence the sorption of organic pollutants by soil clays. This research was undertaken to determine the effect of Cs+, and other common interlayer cations, such as K+ and Ca2+, on the sorption of TCE by a reference smectite clay saponite. Cs-saturated clay sorbed the most TCE, up to 3500 mg/kg, while Ca-saturated smectite sorbed the least. We hypothesize that the stronger sorption of TCE by the Cs-smectite can be attributed to the lower hydration energy and hence smaller hydrated radius of Cs+, which expands the lateral clay surface domains available for sorption. Also, Cs-smectite interlayers are only one or two water layers thick, which may drive capillary condensation of TCE. Our results implicate enhanced retention of TCE in aquifer materials containing smectites accompanied by Cs+ cocontamination.     

Fermentation of tea in aqueous suspension

The fermentation of macerated tea leaf in aqueous suspension has been studied both manometrically and in a suitably controlled fermentation vessel. Oxygen consumption proceeded rapidly at a steady rate for an initial period, termed the primary fermentation, then decreased sharply as the availability of simple polyphenol substrates became rate limiting. Maximum reaction rates were observed at 20-35 mg ml^?1 total solids, as a result of substrate inhibition. At higher concentrations of solids reaction rates were also affected by diffusion effects within the leaf particles. At 50 mg ml^?1 total solids and 25°C the system approximated to Michaelis-Menton kinetics with K_m⁰² = 5 × 10^?5M and V_max corresponding to a primary fermentation time (PFT) of 10-15 min. The PFT corresponded with the attainment of maximum total colour and maximum level of theaflavins (TF) (often >30% of total colour). Beyond the PFT total colour remained constant, TFs decreased and non-dialysable pigments increased with time. At fixed levels of dissolved oxygen and solids concentration > 60 mg ml^?1 the proportion of TFs was inversely related to solids concentration. At 50 mg ml^?1 total solids TFs increased to ca 60% of total colour as the dissolved oxygen level was increased to 0.175 mM. As temperature was increased from 15-35°C the reaction rate increased, the proportion of TFs decreased slightly and thearubigins of intermediate molecular weight increased markedly.     

干酪素悬浮液的制备

研究了干酪素悬浮液的配制方法和工艺参数对其浓度的影响。研究表明，在反应温度为60℃，搅拌时间为50min，pH值为9-10时可以制备浓度较高、品质较好的干酪素悬浮液。     

Effect of aqueous Fe(II) on arsenate sorption on goethite and hematite

Biogeochemical iron cycling often generates systems where aqueous Fe(II) and solid Fe(III) oxides coexist. Reactions between these species result in iron oxide surface and phase transformations, iron isotope fractionation, and redox transformations of many contaminant species. Fe(II)-induced recrystallization of goethite and hematite has recently been shown to cause the repartitioning of Ni(II) at the mineral-water interface, with adsorbed Ni incorporating into the iron oxide structure and preincorporated Ni released back into aqueous solution. However, the effect of Fe(II) on the fate and speciation of redox inactive species incompatible with iron oxide structures is unclear. Arsenate sorption to hematite and goethite in the presence of aqueous Fe(II) was studied to determine whether Fe(II) causes substantial changes in the sorption mechanisms of such incompatible species. Sorption isotherms reveal that Fe(II) minimally alters macroscopic arsenate sorption behavior except at circumneutral pH in the presence of elevated concentrations (10?3 M) of Fe(II) and at high arsenate loadings, where a clear signature of precipitation is observed. Powder X-ray diffraction demonstrates that the ferrous arsenate mineral symplesite precipitates under such conditions. Extended X-ray absorption fine structure spectroscopy shows that outside this precipitation regime arsenate surface complexation mechanisms are unaffected by Fe(II). In addition, arsenate was found to suppress Fe(II) sorption through competitive adsorption processes before the onset of symplesite precipitation. This study demonstrates that the sorption of species incompatible with iron oxide structure is not substantially affected by Fe(II) but that such species may potentially interfere with Fe(II)-iron oxide reactions via competitive adsorption.     

Effect of fluorotelomer alcohol chain length on aqueous solubility and sorption by soils

Fluorotelomer alcohols (FTOHs) are a group of polyfluorinated alkyl chemicals that have been widely studied as precursorsto perfluorocarboxylates such as perfluorooctanoic acid and for which knowledge on their fate in soils is sparse. The solubility and sorption by soil of the homologous 4:2 to 10:2 FTOHs were measured in water or cosolvent/ water solutions. For the smaller 4:2 and 6:2 FTOHs, solubility and sorption could be measured adequately in aqueous systems although transformation was apparent even in gamma-irradiated and autoclaved systems. Sorption coefficients estimated by measuring both sorbed and solution-phase concentrations were not significantly affected by the biotransformation process. The use of cosolvents was employed for probing the behavior of the longer-chain FTOHs with limited aqueous solubility. A single log-linear correlation between aqueous solubility and modified McGowan molar volumes resulted for the n-alkanols and FTOHs. Soil organic carbon (OC) consistently appeared to be the key soil property influencing sorption of the FTOHs while the perfluorocarbon chain length was the dominant structural feature influencing solubility and sorption. Each CF2 moiety decreased the aqueous solubility by -0.78 log units (compared to 0.60 log units for each CH2 addition in hydrogenated primary alcohols), and increased OC-normalized sorption coefficients (Koc) by -0.87 log units. Good log-log linear correlations between Koc and both octanol-water partition coefficients and solubility were observed for the FTOHs.     

Thermodynamics of nitroaromatic compound adsorption from water by smectite clay

Nitroaromatic compounds enter the environment through their use as explosives, pesticides, solvents, and synthetic intermediates in the manufacturing of dyes, perfumes, and drugs. Recent studies have found that many nitroaromatic compounds are strongly retained by smectites, especially K+-saturated smectites. Sorption occurs when nitroaromatic compounds replace water associated with the clay and form complexes between K+ and -NO2 groups. This study seeks to further understand nitroaromatic-clay interactions from the viewpoint of energetics. Adsorption isotherms of 1,3-dinitrobenzene, 1,4-dinitrobenzene, and 1,3,5-trinitrobenzene from aqueous solution by K+- and Ca2+-saturated smectite (SWy-2) were measured at several temperatures between 4 degrees C and 37 degrees C to determine the molar differential adsorption enthalpies. Adsorption was found to be an exothermic process on both homoionic K+- and Ca2+-smectite. The smaller adsorption enthalpy on Ca-SWy-2 was consistent with its much smaller adsorption capacity for nitroaromatics compared to K-SWy-2. Our best estimate forthe enthalpy of 1,3,5-trinitrobenzene interactions with K-SWy-2 is -124 kJ/mol, which is referenced to gas-phase 1,3,5-trinitrobenzene, corrected forthe displacement of interlayer water, and can be directly compared with quantum chemical enthalpies from the literature. Our comparable estimates for 1,3- and 1,4-dinitrobenzene interaction enthalpies are near -90 kJ/mol. We conclude that our adsorption enthalpy results are consistent with the hypothesis that nitroaromatic compounds are sorbed strongly by K-smectites because they form inner- and/or outer-sphere complexes with K+ cations in clay interlayers. Indeed, the basal spacings of rewetted clay films in the presence of nitroaromatic compounds imply that water molecules cannot effectively compete with the adsorbed nitrobenzenes for reactive sites on K-SWy-2.     

EXAFS study of Zn sorption mechanisms on montmorillonite

Extended X-ray absorption fine structure (EXAFS) analysis of zinc sorption on montmorillonite showed that different types of surface complexes or surface precipitates were formed depending on the reaction time. With an initial zinc concentration of 10(-3) M at neutral pH, zinc remained octahedrally coordinated with about six oxygen atoms at Zn-O bond distances of 2.02-2.07 A for up to six months. For samples aged up to 11 days, the Zn-Zn contribution in the second shell suggested formation of multinuclear surface complexes or surface precipitates. For samples aged 20 days and more, Zn-Zn and Zn-Si contributions in the second shell suggested formation of mixed metal coprecipitates such as a Zn phyllosilicate-like phase. Formation of these mixed metal solids probably accounts for the slow continuous sorption reaction at aging times exceeding 20 days. Sequestration of Zn in mixed metal precipitates and the stability of these phases can reduce the concentration, mobility, and toxicity of Zn in soils or sediments.     

Spectroscopic studies of the effects of selenate and selenite on cobalt sorption to gamma-Al2O3

The fate and transport of toxic metal ions and radionuclides in the environment is often controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including the presence of cosorbing or complexing ligands. To study the impact of anion cosorption on metal cation sorption behavior, Co(II) sorption to gamma-Al2O3 in the presence of selenium oxyanions was investigated. To aid in the interpretation of macroscopic sorption results, X-ray absorption spectroscopy (XAS) experiments were conducted on single and bisorbate samples where the Co(II) surface coverage of the bisorbate sample was greater than or equal to the single sorbate sample. XAS data for single sorbate Co(II) samples were consistent with reported spectra of Co(II)-Al(III) layered double hydroxides (LDHs), indicating coprecipitates are forming in these samples. Comparison of data from single and bisorbate samples showed a decrease in the number of nearest neighbor cobalt atoms in the presence of Se(IV), irrespective of the order of Se(IV) addition and no change in Co coordination in the presence of Se(VI). The extent of the decrease in cobalt second shell features between single and bisorbate samples with equal Co(II) coverage increased with an increase in the Se:Co surface coverage ratio. This trend suggests that the effect of Se(IV) on Co(II) sorption is a function of the Se(IV) surface coverage. At low ratio values, Co(II)-Al(III) LDH precipitates dominate. Increasing the Se:Co surface coverage ratio results in a progressive conversion of coprecipitate to an unknown, disordered Co(ll)/Se(IV) phase. Based on macroscopic data, this new phase could be an LDH with Se(IV) in the interlayer, an alternative precipitate such as a mixed metal Se(IV) hydrate, or a ternary complex.     

Fermentation of tea in aqueous suspension. Influence of tea peroxidase

The natural peroxidase and catalase of tea leaf were shown to be active under the conditions employed for the fermentation of minced tea leaf in aqueous suspension. Fermentations carried out under nitrogen with ethyl hydrogen peroxide, which is not decomposed by catalase, yielded predominantly thearubigins, a high proportion of which were polymeric in nature. Fermentations using an excess of hydrogen peroxide gave similar results. Fermentations under conditions of controlled dissolved oxygen using both air and hydrogen peroxide resulted in a pigment distribution intermediate between those observed using air alone and using ethyl hydroperoxide under nitrogen. Adjustment of the amount of hydrogen peroxide used to around 120 μmol g^?1 leaf resulted in a pigment distribution closely similar to that of a good quality black tea. A mixture of theaflavins was stable in the presence of air and tea polyphenoloxidase but decomposed rapidly to yield polymeric materials under the action of hydrogen peroxide and peroxidase derived from tea or horseradish. Kinetic measurements suggest that tea flavanols are generally poorer substrates for peroxidase than for catechol oxidase. However, the level of peroxidase is high and, furthermore, in view of the respective pH optima of the two enzymes, its action would be favoured as the pH falls during fermentation. It is postulated that the nature and distribution of the pigments formed during the fermentation of tea is governed in part by the relative actions of catechol oxidase and peroxidase. These actions are, in turn, influenced by the availability of oxygen and the action of catalase.     

Photocatalytic degradation and mineralization of commercial methamidophos in aqueous titania suspension

The photocatalytic degradation of a commercial methamidophos (MAP) emulsion in aqueous suspension containing mesoporous titania (m-TiO2) nanoparticles under UV irradiation was investigated. The mineralization rate of MAP went up steadily as prolonging the irradiation time and reached ca. 95% after 4 h irradiation based on determination of the end-products (NO3-, PO4(3-), and SO4(2-)) of MAP through IC analysis. Moreover, the degradation kinetics of MAP followed the first-order reaction and has been monitored through GC-PFPD analysis, which also showed that MAP and the organic solvent as well as additive in the pesticide emulsion can be degraded readily and simultaneously. Photodegradation intermediates derived from two different concentrations of MAP were detected by GC-MS technique. The experimental facts indicated that the photodegradation mechanism of MAP mainly involves electron transfer process and hydroxylation process, and the dominant mechanism for MAP degradation in the initial steps can be attributed to the electron transfer process, which resulted in the formation of all intermediates containing P species detected in the initial photodegradation stage.     

Implications of aqueous silica sorption to iron hydroxide: mobilization of iron colloids and interference with sorption of arsenate and humic substances

This work highlighted practical implications of aqueous silica sorption to iron hydroxide in natural and engineered systems. Two types of surfaces were prepared by exposing 10 mg/L preformed Fe(OH)3 to aqueous silica (0-200 mg/L as SiO2) for periods of 1.5 h or 50 days. After 1.5 h, the concentration of iron passing through a 0.45 microm pore size filter at pH 6.0-9.5 was always negligible, but if zeta potential < or =-15 mV as much as 35% of the iron passed through filters after 50 days of aging. When arsenate was added to 10 mg/L iron hydroxide particles equilibrated with aqueous silica for 1.5 h, percentage arsenate removals were high. In contrast, if silica was preequilibrated with iron for 50 days, arsenate removals decreased markedly at higher pH and aqueous silica concentrations. Similar trends were observed for humic substances, although their removal was nearly completely prevented at pH 8.5 at SiO2 concentrations above 50 and 10 mg/L at 1.5 h and 50 days exposure, respectively. The mechanism of interference was hindered sorption to the iron hydroxide surface.     

Moisture sorption study on Nigerian foods: Kuka

Kuka is an important vegetable in the Nigerian food chain. The moisture sorption characteristics of the vegetable studied at 34, 37 and 45°C between a_w 0.10–0.96, revealed a BET type II behaviour. The Kuka exhibited hysteresis and an increase in EMC with increase in a_w and decrease in temperature. Four sorption models (Oswin, Halsey, Kuhn, and GAB) were studied and the Oswin model was the most suitable. The constants in the Oswin model and GAB monolayer moisture contents were obtained and found to be temperature-dependent. Heats of sorption were greater for desorption than adsorption and in either mode, they reduced with an increase in moisture content. An exponential equation was obtained to relate heat of sorption with moisture content.     

The use of chlorine dioxide to control Alicyclobacillus acidoterrestris spores in aqueous suspension and on apples

Alicyclobacillus acidoterrestris, a thermoacidophilic, spore-forming bacterium, has been identified as a spoilage organism in commercial, pasteurized fruit juices. This study was undertaken to evaluate chlorine dioxide for reducing numbers of A. acidoterrestris spores on laboratory media and on apples. A. acidoterrestris spores in aqueous suspension and on apple surfaces of four different cultivars were treated with several concentrations of chlorine dioxide. Spores in aqueous suspension treated with 40 ppm for 5 min were reduced by more than 4 log. Treatment with 80 ppm for 1 min and 120 ppm for 30 s resulted in about 1.8 log and 4.8 log reductions of spore viability, respectively, and treatment at 80 and 120 ppm for 5 min reduced spore viability to undetectable levels (<0.7 log CFU/ml). When applied to the surfaces of four different apple cultivars ('Red Delicious', 'Golden Delicious', 'Gala', and 'Fuji'), 40 ppm free chlorine dioxide reduced A. acidoterrestris spore numbers by 1.5, 3.2, 4.5, >4.8 log after 1-, 2-, 3-, and 4-min treatments, respectively. Spore numbers were reduced by >4.8 log with 120 ppm free chlorine dioxide after only 1-min treatment. However, there was no significant difference between apple cultivars (P>0.05) on spore reduction. These results show the great effectiveness of chlorine dioxide in controlling A. acidoterrestris spores both in aqueous suspension and on apple surfaces. There was no synergistic effect on spore reduction when chlorine dioxide treatment of aqueous suspension was followed by heat.