Electron Microscopy of Rhamnolipid (Biosurfactant) Morphology: Effects of pH, Cadmium, and Octadecane

A rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 is reported to increase the aqueous dispersion and biodegradation of petroleum hydrocarbons and to complex heavy metals. These reports indicate the potential for application of rhamnolipids in remediation of contaminated sites. Effective use of rhamnolipids will require understanding of rhamnolipid morphology and the effects of pH and organic and inorganic contaminants on that morphology. We used cryo-transmission electron microscopy to investigate the morphology of vitrified, frozen hydrated suspensions of rhamnolipid over a pH range of 5.5 to 8.0, and to determine the effect of a model alkane, octadecane, and a model heavy metal, cadmium, on rhamnolipid morphology. Micrographs clearly showed that rhamnolipid morphology was a function of pH, changing from lamellar, to vesicular, to micellar as pH increased. The effect of cadmium and octadecane on rhamnolipid morphology was determined at pH 6.8 and 7.0, where maximum cadmium complexation and maximum octadecane dispersion occurs. Cadmium seemed to stabilize rhamnolipid vesicle structures as shown by an increase in vesicle number and a decrease in vesicle diameter. In contrast, octadecane favored the micellar structure as shown by the complete absence of vesicles.     

燃煤电厂异相凝并飞灰重金属淋滤特性

采集了燃煤电厂的异相凝并后飞灰，分析了其物理化学特性。并通过淋滤实验研究了飞灰中重金属As、Se、Pb的环境稳定性。结果表明，凝并飞灰的粒径峰值为138.04 μm，而粉煤灰为60.26 μm；凝并后细颗粒凝聚成了较大的颗粒；凝并飞灰中重金属As、Se、Pb含量均高于同工况下粉煤灰中的含量，且后序脱硫环节所产生石膏中重金属的含量有所下降；批淋滤实验研究结果表明，凝并飞灰中的重金属浸出能力受淋滤液的pH值影响较大，温和环境和碱性条件抑制了As的浸出，酸性和碱性条件抑制了Se的浸出，而碱性条件抑制了Pb的浸出。柱淋滤实验研究结果表明，在酸性溶液和水溶液中，凝并飞灰的重金属浸出能力均受到了抑制。     

An unusual morphological transformation of rhamnolipid aggregates induced by concentration and addition of styrene: A small angle neutron scattering (SANS) study

The aggregation behaviour of rhamnolipid as mixed with styrene (as a representative of hydrophobic molecules commonly found in contaminated soils) was investigated by small angle neutron scattering (SANS) as a function of both rhamnolipid and styrene concentrations. Contrast variation was applied (i.e., deuterated and hydrogenated styrene) to resolve the morphologies of aggregates. A structural transformation from cylindrical micelles to a binary mixture of cylindrical micelles and vesicles induced by both elevated rhamnolipid and styrene concentration is proposed based on the analysis of the SANS data. The resultant structure of the aggregates, vesicle, is different from the “oil droplets” commonly reported in the microemulsions of water-oil-surfactant mixtures. It is also found that this transformation is far from being complete even at the highest styrene solubility, implying that further dissolution of styrene may be constrained by other factors.     

贵阳污灌区菜地土壤团聚体中有机碳和重金属的含量特征及相关性分析

以贵阳某污灌区菜地土壤为研究对象,分别采用微波消解-电感耦合等离子体质谱(ICP-MS)法和水合热重铬酸钾氧化分光光度法分析不同粒径土壤团聚体中重金属和有机碳的含量特征,并对有机碳和重金属的相关性进行分析。结果表明,以2mm粒径团聚体的含量为最高,约占75%。Cu、Zn、Cd和Pb在0.25～0.5mm粒径团聚体中含量最高,Cr在5～8mm粒径团聚体中含量最高,As在不同粒径团聚体中的含量变化不大,重金属含量随土层深度增大而减小。土壤重金属富集因子表现为CuPbCdZnCrAs,Cu、Zn、Cd和Pb在0.25～0.5mm粒径团聚体中分布因子最高,而在5～8mm粒径团聚体中重金属的质量负载因子最大。土壤有机碳含量随团聚体粒径的增大表现为先增大后减小,不同粒径团聚体中Cu、Cd、Pb和As含量与有机碳含量均呈显著正相关(p0.05)。污灌区菜地土壤Cr、As在5～8mm粒径团聚体中富集现象显著,Cu、Zn、Cd、Pb在0.25～0.5mm粒径团聚体中均表现出显著的富集特征。6种重金属在5～8mm粒径团聚体中的质量负载因子均为最高,表明6种重金属在5～8mm粒径团聚体中的贡献最大。     

Novel method for preparation of photocrosslinkable poly(vinyl alcohol)

A convenient procedure to prepare photosensitive poly(vinyl alcohol) by acetalization with 1-methyl-4-(p-formylstyryl)pyridinium methosulfate in heterogeneous condition is described. The reaction of fully saponified poly(vinyl alcohol) was carried out in suspension in acidic aqueous solution, while partially saponified poly(vinyl alcohol) was acetalized in acidic aqueous organic solvent. The photosensitive poly(vinyl alcohol) thus prepared was purified by filtration and successive washing out with methanol. The effect of the preparative condition on the electronic absorption spectra of the styrylpyridinium group attached to poly(vinyl alcohol) is discussed.     

Self-aggregates of hydrophobically modified poly(2-hydroxyethyl aspartamide) in aqueous solution

Dehydrocholic acid (DHA) grafted poly(2-hydroxyethyl aspartamide) (PHEA)s were successfully synthesized and their self-aggregates in aqueous solution were characterized by fluorescence spectra and light scattering. PHEA was obtained by a simple reaction of ethanolamine with synthesized poly(succinimide) (PSI), and then PHEA-g-DHA was synthesized through an ester linkage between DHA and PHEA. The degree of substitution (DS) of DHA groups, defined by grafted mole%, was determined from both ¹H-NMR and elemental analysis. The grafting reaction of DHA was retarded up to almost 10 mole% feed ratio of DHA/PHEA, but increased linearly above the threshold ratio. Nano-size self-aggregates in aqueous solution were examined with four DSs less than 10. As DS increased, the critical aggregation concentrations (CAC) of polymers were continuously reduced and the size of primary aggregates reduced to as small as 40 nm in diameter. When stored, the sonicated aggregates of high DS were destabilized, apparently forming large aggregates with small curvatures. The formation of irreversible interfused secondary structures would be induced by the curvature change or aggregation of primary particles. A simple calculation indicates that a small change of separation between grafted DHA groups may induce the large curvature shift, in fact, sphere-to-planar surface transition.     

Insight on Structural Change in Sol–Gel-Derived Silica Gel with Aging under Basic Conditions for Mesopore Control

Structural rearrangement of sol–gel-derived silica gel by aging under basic conditions was investigated using small angle X-ray scattering (SAXS) and ²⁹Si nuclear magnetic resonance (NMR). A wet silica gel prepared under acidic conditions had a fractal nature, and many unreacted silanols remained on the surface. During aging of the gel in ammonia solution, additional Si—O—Si bonds rapidly formed, whereas the change in mesoscale structure gradually proceeded. This result was compared with that of simulation modeling the Ostwald ripening, i.e. dissolution from positive curvature and reprecipitation on negative curvature. In the simulation, structural change in a cluster from fractal nature to particle aggregates was well visualized in 2-dimmensional square lattice. Both scattering profiles calculated from the model clusters and the change in average coordination number of monomers in the cluster well agreed with the experimental SAXS and NMR results, respectively. This agreement strongly ensures us that structural change by aging under basic conditions proceeds through the Ostwald ripening. The mesopore size as well as mesopore volume in calcined silica gel is determined by the shrinkage degree during drying and calcination. The sample aged in basic solution restrains the shrinkage because of the growth of particulate structure, and retains large size and volume of pores.     

pH‐Responsive Aggregation of Amphiphilic Glyco‐Homopolymer

The first example of amphiphilic glyco‐homopolymers is reported and their aggregation properties as a function of solution pH are studied. Two structurally similar polymers with different hydrophobicity (C8 and C6 alkyl chains) are examined. Both polymers form micelle‐type aggregates in aqueous solution. The size and micro‐environment of the aggregates are found to be strongly dependent on solution pH because of the state of protonation of the tertiary amine group. At acidic pH, swollen multi‐micellar aggregates are formed, presumably because of the electrostatic repulsion among the ammonium ions. At basic pH more compact particles are found, which further co‐assemble to generate either garland type (C8) or fractal‐aggregates (C6).     

The removal of Cu,Ni, and Zn in industrial soil by washing with EDTA-organic acids

In order to improve the heavy metal removal ability of traditional single washing agents and explore the removal mechanism of heavy metals. Then, the washing reagents that mixed by low-molecular weight organic acids (citric acid, oxalic acid, and tartaric acid) and artificial chelating compound ethylenediaminetetraacetic acid disodium (EDTA) were selected. Furthermore, the effect of soil washing parameters, the variation of leaching toxicity, mobility, stability and speciation of heavy metals were also considered. The results of soil washing experiments showed that mixing an equal volume of 0.05 M EDTA and 0.2 M organic acids (citric acid, oxalic acid, and tartaric acid) could remove more than about 80% heavy metals from soil under the optimal conditions. In addition, the soil leaching toxicity was decreased and the stability of remaining heavy metals was increased, indicating that EDTA-organic acid washing reagents could effectively reduce the ecological risk of contaminated soil. EDTA had a stronger chelating ability with heavy metals than the organic acids, and the organic acids could not only chelate heavy metals but also decrease the pH of the mixture for promoting the desorption of heavy metals. Thus, mixing EDTA and organic acids was advisable method to improve soil washing technology.     

Electrolyte-induced mesoscopic aggregation of thiacarbocyanine dye in aqueous solution: counterion size specificity

Countercation size specificity is presented for the electrolyte-induced aggregation of 3,3'-disulfopropyl-5,5'-dichloro-9-methyl thiacarbocyanine (TCC) dye in aqueous solution. Addition of electrolytes having a small monovalent cation (Na+, NH4+, or Cs+) induced pure H aggregates of TCC, whereas J aggregates were preferentially promoted by electrolytes with a large monovalent cation ([N(CH3)4]+ or [N(C2H5)4]+). The electrolyte-induced H aggregate (HS aggregate) differed spectroscopically from that spontaneously self-assembled in aqueous solution. Mesoscopic structure of the HS aggregates was revealed via polarized-light microscopy and atomic force microscopy; a rodlike morphology of 50-70 nm wide and tens to hundreds of micrometers long with very strong negative birefringence. A simple structural model based on semiempirical molecular orbital calculations can explain the aggregation behaviors: The anionic TCC monomer shows a considerable planar geometry between two benzothiazole end groups when it involves a sodium cation, which favors the H-type molecular arrangements in a face-to-face orientation. On the other hand, the TCC dye has a twisted conformation when it implicates a large tetramethylammonium cation, resulting in the formation of the J aggregates.     

Controlled crystallization of titanium dioxide particles in the presence of poly(vinyl alcohol) from peroxytitanic acid

Crystallization of TiO₂ particles from peroxytatanic acid in the presence of poly(vinyl alcohol) (PVA) via a hydrothermal process was investigated. The crystal structure and morphology of TiO₂ were significantly affected by pH and PVA dosage. High acidic condition without PVA led to the formation of rutile TiO₂, while addition of PVA resulted in the formation of anatase TiO₂. Much amount of PVA addition, and neutral or high pH circumstance were favorable for formation of anatase TiO₂ particles. The pH of solution also affected morphology of TiO₂ particles produced. From TEM images, it was observed that in pH 5.5 solution rod-shaped clusters and in pH 8.5 solution nanoparticles aggregates composed of 20–30 nm TiO₂ particles were formed.     

改性羽毛对锌离子的吸附

使用单宁酸对禽类羽毛进行化学改性.研究了改性前后羽毛对金属锌离子的吸附及解吸性能,探讨了羽毛上单宁酸负载量,锌盐溶液的pH值等因素对羽毛金属离子吸附性能的影响.结果表明,经单宁酸化学改性的羽毛在碱性环境下能明显增加对金属锌离子的吸附,此时对应Zn2 的最大吸附量为O.97mmol/g,而未改性羽毛在相同条件下的最大吸附量为0.64mmol/g.在酸性环境中,改性羽毛中金属锌离子的解吸附率为16.8%,未改性羽毛的锌离子解吸附率为64.0%,表明改性羽毛的金属复合物具有较高的稳定性.羽毛作为一种廉价的重金属吸附材料,对整治环境污染具有应用前景.     

Treated Rice Bran for Scavenging Cr(III) and Hg(II) from Acidic Solution

The purpose of this study was to examine the efficiency with which rice bran (treated or untreated) removes heavy metals, especially Cr(III) and Hg(II), from acidic solution. Sorption assays were done in shaken flasks in the presence of rice bran. Different experimental conditions such as pH, volume of solution, bran weight, particle size, exchange time and stirring time were improved. The efficiency of bran was studied before and after treatments. For treatment, solutions of acid, alkali and salt were used. The results show that after treating with 4 M sodium chloride solution, its efficiency in removal of Cr(III) and Hg(II) was improved. Kinetic measurements of chromium and mercury removal by bran have revealed that sorption equilibrium was obtained after 10 min of contact. Sorption experiments done with various granulometric fractions of rice bran have shown that this sorbent has the same efficiencies in meshes higher than 20. Further research is necessary in order to determine a mechanism for cations removal by the bran. It is mentioned that the process of making polished rice from brown rice discharges rice bran; therefore, it is very inexpensive, with a cost of 1/50 ? 1/40 of that of synthetic sorbent, and thus its use would significantly lower the cost of wastewater treatment.     

Core-corona structure of cubic silsesquioxane-poly(ethylene oxide) in aqueous solution: fluorescence, light scattering, and TEM studies

Well-defined amphiphilic cubic silsesquioxane-poly(ethylene oxide) (CSSQ-PEO) was prepared from octakis (dimethylsiloxy)octasilsesquioxane (Q8M8(H)) and allyl-PEO through a hydrosilylation reaction. The structure of CSSQ-PEO was characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). The amphiphilic properties and aggregation process of CSSQ-PEO in aqueous solution were investigated by fluorescence, dynamic and static light scattering (DLS and SLS), and transmission electron microscopy (TEM). The critical aggregation concentration (CAC) determined by fluorescence measurements was found to be 0.28 mg/mL. Combinations of DLS, SLS, and TEM studies showed the existence of core-corona micelle with hydrophobic CSSQ as the core and hydrophilic PEO as the corona in aqueous solution. The observation of two size distribution peaks from DLS measurements revealed the coexistence of small amounts of unassociated unimolecular micelles (approximately 10% of the scattered intensity) together with micellar aggregates when the CSSQ-PEO concentration was < or = 2 mg/mL. The hydrodynamic radii (R(h)) of unassociated unimolecular micelle and micellar aggregates were found to be 26 and 79 nm, respectively. A large R(g)/R(h) ratio (1.46) and the extremely small value of average chain density (4 x 10(-4) g/cm3) indicate the small hydrophobic CSSQ core was surrounded by the extended PEO coronae. The aggregation number (N(agg)) of CSSQ-PEO in aqueous solution was found to be 38 +/- 2 from SLS and 31-40 from TEM, respectively. The long PEO segments act as a spacer between the spherical aggregates, which facilitate the formation of a network-like structure at high concentration.     

Effect of amorphous precipitated silica on the properties and structure of poly(p-phenylene sulfide)

Using a precipitation technique, silicas were obtained from sodium metasilicate solution employing an acidic agent. Alcohol solutions were used in the process of production of highly dispersed silicas, which resulted in partial blocking of the silica surface silanol groups. Moreover, studies on morphology and microstructure using transmission electron microscopy and scanning electron microscopy were performed. The size distributions of primary particles and aggregate and agglomerate structures were determined using a ZetaPlus instrument using the dynamic light scattering method. The structure and molecular dynamics of the nanocomposite, consisting of poly (p-phenylene sulfide) (PPS) and of the precipitated silica, were studied using atomic force microscopy and nuclear magnetic resonance. It was proved that during annealing the fragmentation of PPS agglomerates takes place. This phenomena probably resulted from repulsion forces existing between agglomerates and aggregates. Fragmentation in the polymer network probably resulted from repulsion forces between agglomerates and smaller aggregates. Received: 7 November 2000 Accepted: 5 April 2001     

A facile method for dye and heavy metal elimination by pH sensitive acid activated montmorillonite/polyethersulfone nanocomposite membrane

Modified clay/polyethersulfone (PES) mixed matrix membranes (MMMs) were prepared by acid activated montmorillonite (AA-MMT) with different concentrations and used to eliminate dyes and remove heavy metals from aqueous solution.The morphology and physiochemical properties of prepared clay nanoparticles and MMMs were characterized using X-ray diffraction (XRD),Fourier transform infrared (FTIR) spectroscopy,scanning electron microscopy (SEM),enegy dispersive X-ray (EDX) spectroscopy,Brunauer-Emmett-Teller (BET) analysis,atomic force microscopy (AFM),contact angle measurement and fouling studies.The filtration study showed that removal of dyes and heavy metals was strongly dependent on pH so that dyes with positive and negative charges showed different separation efficiency in acidic and alkaline conditions.The modified membranes possessed better heavy metal removal in acidic and alkaline pHs.When the rejection of heavy metals was measured in an alkaline environment,it was observed that the rejection had a great increase compared to the neutral values for Zn2+ and Ni2+ ions,while rejection of Cu2+ and Cd2+ did not undergo significant changes.So it can be concluded that modified membranes show good selectivity for elimination of Zn2+ and Ni2+ ions with respect to other cations.     

Counterion dependent dye aggregates: nanorods and nanorings of tetra(p-carboxyphenyl)porphyrin

Atomic force microscopy (AFM) of porphyrin aggregates formed on silica from acidic aqueous solution is used to investigate the basis for the previously reported counterion dependence of the optical spectra of aggregates of H(2)TCPP(2+), the diacid form of tetra(p-carboxyphenyl)porphyrin (TCPP). Resonance light scattering confirms the presence of excitonically coupled porphyrin aggregates in solutions of H(2)TCPP(2+) in both aqueous HCl and HNO(3). Aggregates formed in aqueous HNO(3) solutions show resonance light scattering (RLS) at wavelengths within both the H and J aggregate absorption bands and are imaged on the surface of silica as nanorods about 3 to 4 nm in height. H(2)TCPP(2+) aggregates in aqueous HCl solution exhibit RLS when excited within the blue-shifted Soret band (H band) and produce AFM images on silica of ring-shaped structures ranging from about 200 to 2000 nm in diameter. Fluorescence excitation and emission spectra reveal quenching of the Q-band emission in the aggregates at a pH less than 1 and confirm the existence of a single species, assigned to a dimer, at a pH just above 1. The morphology of the nanostructures as revealed by AFM provides insight into the structural basis for the counterion-dependent optical properties of H(2)TCPP(2+) aggregates.     

Vesicle-to-spherical micelle-to-tubular nanostructure transition of monomethoxy-poly(ethylene glycol)-poly(trimethylene carbonate) diblock copolymer

Recently, we reported a temperature-sensitive biodegradable diblock copolymer of monomethoxy-poly(ethylene glycol)-b-poly(trimethylene carbonate) (mPEG-PTMC; Macromolecules 2007, 40, 5519-5525). In this paper, we report the detailed morphological transition of the polymer in water as a function of polymer concentration and temperature, using cryo-transmission electron microscopy (cryo-TEM). At a low polymer concentration (0.05 wt %), the mPEG-PTMC diblock copolymers formed vesicles in water. On the other hand, vesicle-to-micelle transition was observed as the polymer concentration increased. The polymer predominantly formed micelles above 2.0 wt %. In the 2.0 wt % polymer solution, the mPEG-PTMC underwent spherical micelle-to-tubular nanostructure transition as the temperature increased from 10 to 40 degrees C, and the transition accompanied an increase in turbidity of the polymer aqueous solution due to the increase in the apparent size of the polymer aggregates. Here, we report that the morphology of vesicles, spherical micelles, and tubular nanostructures is reversibly controlled by a thermosensitive polymer of mPEG-PTMC and the variation of the morphology can be carefully traced by using cryo-TEM. This paper will not only provide an important method for morphological control of an amphiphilic polymer but also improve our understanding of a temperature-sensitive transition mechanism of the polymer.     

Extractions with long-chain amines-I Extraction of some metal-xylenol orange complexes into methyltrioctylammonium chloride (aliquat 336-S)

The extraction of traces of metals forming intensely coloured complexes with Xylenol Orange in acidic medium (pH 0-3) has been studied. For such extractions in the presence of sulphates, chlorides and nitrates, a solution of methyltrioctylammonium chloride (Aliquat 336-S) in chloroform has been used. It is shown that it is possible to detect small amounts of gallium in indium and vice versa, and titanium or zirconium in thorium. These reactions should be capable of adaption to spectrophotometric determinations. The principle of the extraction of metals as their complexes with various metallochrornic indicators is briefly discussed.     

Use of an o-aminobenzoic acid-functionalized XAD-4 copolymer resin for the separation and preconcentration of heavy metal(II) ions

XAD copolymer resins may be functionalized with heavy metal ion-selective ligands either by covalent linkage to the polymer backbone or by impregnation. These resins may be tailored to be specific for certain heavy metals by adjusting the adsorption and elution parameters, thereby enabling simple and cost-effective spectrophotometric and flame atomic absorption spectrometry (FAAS) determinations of these metals without requiring the more sophisticated coupled instrumental techniques. For the synthesis of o-aminobenzoic acid (ABA)-immobilized XAD-4 copolymer resin that is expected to preconcentrate a number of transition and heavy metals, the azo-linkage method was chosen. For this purpose the copolymer was nitrated, reduced to the corresponding amine, converted to the diazonium salt with nitrite, and reacted with o-aminobenzoic acid to produce the XAD-ABA sorbent. This sorbent was capable of preconcentrating Pb(II), Cd(II), Ni(II), Co(II) and Zn(II) from weakly acidic or neutral aqueous solution. The retained metals were eluted with 1.0 M HNO₃ from the resin column, and were subsequently determinated with by flame atomic absorption spectrometry. The developed resin preconcentration and determination method was successfully applied to the analysis of a synthetic metal mixture solution, a certified reference material (CRM) of coal sample, and brackish lake water.