Characterization of zero-valent iron nanoparticles

The iron nanoparticle technology has received considerable attention for its potential applications in groundwater treatment and site remediation. Recent studies have demonstrated the efficacy of zero-valent iron nanoparticles for the transformation of halogenated organic contaminants and heavy metals. In this work, we present a systematic characterization of the iron nanoparticles prepared with the method of ferric iron reduction by sodium borohydride. Particle size, size distribution and surface composition were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (HR-XPS), X-ray absorption near edge structure (XANES) and acoustic/electroacoustic spectrometry. BET surface area, zeta (ζ) potential, iso-electric point (IEP), solution Eh and pH were also measured. Methods and results presented may foster better understanding, facilitate information exchange, and contribute to further research and development of iron nanoparticles for environmental and other applications.     

Stability of manganese dioxide by guar gum in the absence or presence of surfactants

Stability of the manganese dioxide (MnO₂) suspensions by non-ionic guar gum (GG) in the absence or presence of the surfactants: anionic sodium dodecyl sulphate (SDS), cationic hexadecyltrimethylammonium bromide (CTAB) and non-ionic Triton X-100 (t-octylphenoxypolyethoxyethanol) and their equimolar mixtures (SDS/TX-100; CTAB/TX-100) was measured using turbidity. The obtained results of the manganese dioxide suspensions stability were discussed together with the adsorption data and with the data concerning the thicknesses of the adsorption layers. In order to gain more information about the structure of the electric double layer surface charge density and the zeta potential measurements were performed. The obtained results show that the addition of guar gum to the MnO₂ suspensions increases MnO₂ stability. The larger this increase is, the higher is the concentration of the polymer (concentration range 10–200 ppm). Moreover, the addition of single surfactants also causes the increase in the effectiveness of stabilizing the manganese dioxide suspensions. The reason for that is formation of multilayer complexes between the polymer and the surfactants. In such a system both the adsorption of polymer and the thickness of polymer adsorption layer increase. The greatest increase in the stability of MnO₂/GG suspensions was provided by the mixture of anionic and non-ionic surfactants due to a strong synergistic effect. Also, mixing the polymer and two surfactants reduces the stability of the suspension.     

羟丙基瓜尔胶的制备及表征

瓜尔胶(guar gum)是一种天然半乳甘露聚糖,其水溶性和增稠性很好,广泛用做增稠剂、破乳剂等。原粉胶溶解较慢、水不溶物含量高、粘度不易控制,人们常利用化学手段改变其理化特性以满足实际工业生产需要,羟丙基化是有效的手段之一,但对羟丙基化的表征较为困难。S．     

Dynamo-mechanical and rheological characterization of guar gum hydrogels

Polymeric systems gained great interest in the last decades as specialties in the field of drug delivery, being very attractive for their peculiar physico-chemical characteristics. In this paper we report the characterization of a chemical network based on guar gum (GG) cross-linked with glutaraldehyde (Ga). The system was studied at three different temperatures, 7, 25 and 37 °C and at different ageing times in order to evaluate the influence of these two parameters on its stability. The experiments were carried out with a Texture Analyzer thus hardness, cohesion and Young modulus of the hydrogel were evaluated in the different conditions. Furthermore, relaxation experiments were performed and their interpretation, according to the Maxwell generalized model, allowed to describe the mechanical behaviour in terms of materials viscoelasticity theory. The kinetics of the chemical cross-linking was followed at 37 °C by means of rheological measurements, i.e. recording the mechanical spectra of the gelling system. The storage and loss moduli followed a power law, expression of the mechanical and structural self-similarity which evolves during the cross-linking reaction. The critical exponent at the gel point was evaluated, together with the critical time corresponding to the infinity connectivity of the system and the phase angle between stress and strain. Furthermore, also the fractal dimension was evaluated assuming a complete screening of the excluded volume of the chains at the critical point. Information about the release behaviour of the hydrogel, used as a matrix for modified drug delivery of model molecules with different steric hindrance, is also given.     

葡萄糖接枝瓜尔胶的合成及表征

本文在研究1,6-脱水葡萄糖均聚的基础上,提出了一种用1,6-脱水葡萄糖对瓜尔胶进行绿色化改性的新方法,并通过核磁对瓜尔胶的葡萄糖接枝产物进行表征,发现随着1,6-脱水葡萄糖与瓜尔胶质量比的增加,产物的葡萄糖摩尔取代度逐渐增大,当1,6-脱水葡萄糖与瓜尔胶质量比为3:1时,共聚产物的摩尔取代度可达0.6.1,6-脱水葡...     

羟丙基瓜尔胶在离子液体中的制备

本文以离子液体1-烯丙基-3-甲基咪唑氯盐(AmimCl)为反应介质,以氢氧化钠为催化剂合成了羟丙基瓜尔胶(HPG),并通过1H NMR确定了产品的摩尔取代度。探讨了水的用量、环氧丙烷的用量、反应温度和反应时间对摩尔取代度的影响。在水与瓜尔胶的质量比为1.7、氢氧化钠与瓜尔胶的质量比为5%、环氧丙烷与瓜尔胶的质量比为3.5、反应温度为60℃和反应时间为12h的条件下,摩尔取代度(MS)可以达到0.76。同时发现在不加催化剂NaOH的情况下,瓜尔胶在AmimCl中的羟丙基化反应同样可以发生,只是得到的HPG的MS相对较小。     

Enhanced aggregation of alginate-coated iron oxide (hematite) nanoparticles in the presence of calcium, strontium, and barium cations

Early-stage aggregation kinetics studies of alginate-coated hematite nanoparticles in solutions containing alkaline-earth metal cations revealed enhanced aggregation rates in the presence of Ca2+, Sr2+, and Ba2+, but not with Mg2+. Transmission electron microscopy (TEM) imaging of the aggregates provided evidence that alginate gel formation was essential for enhanced aggregation to occur. Dynamic light scattering (DLS) aggregation results clearly indicated that a much lower concentration of Ba2+ compared to Ca2+ and Sr2+ was required to achieve a similar degree of enhanced aggregation in each system. To elucidate the relationship between the alginate's affinities for divalent cations and the enhanced aggregation of the alginate-coated hematite nanoparticles, atomic force microscopy (AFM) was employed to probe the interaction forces between alginate-coated hematite surfaces under the solution chemistries used for the aggregation study. Maximum adhesion forces, maximum pull-off distances, and the work of adhesion were used as indicators to gauge the alginate's affinity for the divalent cations and the resulting attractive interactions between alginate-coated hematite nanoparticles. The results showed that alginate had higher affinity for Ba2+ than either Sr2+ or Ca2+. This same trend was consistent with the cation concentrations required for comparable enhanced aggregation kinetics, suggesting that the rate of alginate gel formation controls the enhanced aggregation kinetics. An aggregation mechanism incorporating the gelation of alginate is proposed to explain the accelerated aggregate growth in the presence of Ca2+, Sr2+, and Ba2+.     

N,N-二乙基胺乙基取代瓜尔胶的合成及结构表征

在碱催化条件下,利用N,N-二乙基氯乙胺盐酸盐与瓜尔胶和羟丙基瓜尔胶一步法合成得到N,N-二乙基胺乙基瓜尔胶和N,N-二乙基胺乙基羟丙基瓜尔胶。结果显示合成过程中温度、反应时间、羟丙基取代度及溶剂等因素对产品分子量和N,N-二乙基胺乙基取代度有影响。通过红外光谱和核磁法对N,N-二乙基胺乙基瓜尔胶和羟丙基N,N-二乙基胺乙基瓜尔胶的分子结构进行了分析,并通过碳谱对N,N-二乙基胺乙基在瓜尔胶分子链中糖环上的取代分布进行了分析。     

羧甲基羟丙基瓜尔胶的流变特性

考查了羧甲基羟丙基瓜尔胶溶液的流变特性,发现其水溶液呈典型的假塑性,不同浓度下溶液表观粘度随剪切速率的变化可以用Ostwald-Dewaele方程描述;零切粘度与温度的关系符合Andrade方程;溶液的粘度在酸性条件下随溶液pH的减小迅速降低,在碱性条件下则变化不大;溶液对NaCl很敏感,表现出典型的聚电解质的特征。     

Cellulose acetate composite films fabricated with zero-valent iron nanoparticles and its use in the degradation of persistent organic pollutants

Cellulose acetate (CA), and CA blended with Nicotiana tabacum ash (ACA) membranes have synthesized and fabricated with zero-valent Fe NPs (ZVI) and named as CA@Fe⁰ and ACA@Fe⁰. The as-synthesized membranes were inspected for the removal and detoxification of toxic organic pollutants. Comparative studies of CA@Fe⁰ and ACA@Fe⁰ NPs were investigated for five model pollutants, such as 4-nitrophenol (4NP), methyl orange (MO), Congo red (CR), methylene blue (MB), and bromocresol green (BCG). The kinetic model indicated that the apparent rate constant K_app value of ACA@Fe⁰ was highest for all model pollutants compared to CA@Fe⁰ NPs. The K_app value is derived from pseudo-first-order kinetics. The K_app value of MO discoloration was 8.17 × 10⁻¹ min⁻¹ with ACA@Fe⁰ which is highest than CA@Fe⁰ (3.08 × 10⁻¹ min⁻¹). The turnover frequency (TOF) was highest for ACA@Fe⁰ for all the pollutants compared to CA@Fe⁰ and the highest TOF value was found for CR dye with ACA@Fe⁰ which is 0.523 h⁻¹. Both the membranes also showed promising antibacterial activity against Salmonella typhi. Furthermore, CA, ACA membrane and CA@Fe⁰ and ACA@Fe⁰ NPs were characterized through FESEM, EDS, XRD, FTIR and TGA analysis.     

Dynamic Monte Carlo simulation of aggregation of nanoparticles in the presence of diblock copolymer

The aggregation of hydrophobic nanoparticles in the presence of diblock copolymers is investigated using dynamic Monte Carlo simulation on a simple cubic lattice. One nanoparticle occupies one lattice site, one block copolymer (A(m)B(m)) occupies 2m sequentially linked sites with m segments of A and m segments of B, and solvents are represented by any unoccupied sites. All of them are self-avoiding and nearest-neighbor interactions are considered. A compact big aggregate, dispersed aggregates wrapped by polymer chains, and an ordered lamellar structure are obtained by varying the concentration of copolymer. The structures are seen to be controlled by competing forces between the interaction of copolymer with nanoparticles and the self-assembly of copolymer in solution. The critical concentration of copolymer needed to form the lamellar structure, C(p,L), decreases with the chain length. It is also found that C(p,L) decreases roughly linearly with the concentration of nanoparticles C(n), which can be approximately expressed as C(p,L)=0.764-0.857C(n) when m=2. The simulation demonstrates that addition of diblock copolymer can effectively control the aggregation of nanoparticles and lead to the formation of a variety of nanostructures.     

瓜尔胶及其衍生物的过硫酸铵氧化降解研究

通过考察90℃,0.5‰过硫酸铵对瓜尔胶、羟丙基瓜尔胶及其羧甲基羟丙基瓜尔胶不同时间的氧化降解反应,发现开始时瓜尔胶主链主要是以糖苷键断裂的降解为主,当降解到一定程度后,才出现糖链上糖环的氧化。瓜尔胶的结构对降解反应有着很大的影响,而且降解速度:羧甲基羟丙基瓜尔胶羟丙基瓜尔胶瓜尔胶。形态观测结果表明氧化降解对微观结构有一定的影响。     

离子液体的合成及其对瓜尔胶的溶解性能

本文合成了氯化1-烯丙基-2-丙烯基-4,5-二氢化咪唑(AihimCl),氯化1-丁基-2-丙烯基-4,5-二氢化咪唑(BihimCl),氯化1-己基-2-丙烯基-4,5-二氢化咪唑(HihimCl),氯化1-辛基-2-丙烯基-4,5-二氢化咪唑(OihimCl)四种离子液体;并用傅立叶转换红外光谱(FT-IR),核磁共振氢谱(1H NMR)和碳谱(13C NMR)表征了其结构;研究了这四种离子液体对瓜尔胶(GG)的溶解性,并用偏光显微镜观察了其溶解过程,瓜尔胶在BihimCl中的溶解度可达5.5%;比较了瓜尔胶在四种离子液体中的溶解速度,在BihimCl和OihimCl中的溶解速度比在AihimCl和HihimCl中快,6小时后都能够完全溶解。     

羟乙基瓜尔胶中羟乙基摩尔取代度以及取代位置的表征

本文探索了表征羟乙基瓜尔胶(HEG)中羟乙基摩尔取代度(MS)以及取代位置的化学方法。当反应温度为110℃,时间为14hr,HEG中羟基与混酐比例为1:2.5时,用混酐化学法可准确测定HEG的羟乙基MS,测定结果与计算值的相对误差小于10%。在pH=10.30和0℃的条件下,瓜尔胶的伯羟基被2,2,6,6-四甲基哌啶氮氧化物(TEMPO)-NaClO-NaBr体系选择性氧化成羧基,由此可表征羟乙基链段的取代位置。在瓜尔胶醚化生成羟乙基瓜尔胶的过程中,醚化反应并不是完全发生在伯羟基上。伯羟基的反应活性是仲羟基的6-10倍。随着MS的增大,连接在仲羟基上羟乙基链段占所有羟乙基链段的比例逐渐增大,当MS=0.4时该比例基本不再变化,为40%左右。     

羟丙基瓜尔胶中羟丙基摩尔取代度以及取代位置的表征

本文探索了表征羟丙基瓜尔胶(HPG)中羟丙基摩尔取代度(MS)以及取代位置的化学方法.当反应温度为110℃、反应时间为14h以及HPG中羟基与对甲苯磺酸-乙酸酐摩尔比为1:3.5时,用对甲苯磺酸-乙酸酐化学法和气相色谱法可准确测定HPG的羟丙基MS,与1H-NMR测定结果相对误差小于10%.在pH=10.30和0℃的条件下,瓜尔胶的伯羟基被2,2,6,6-四甲基哌啶氮--氧化物(TEMPO)-NaClO-NaBr体系选择性氧化成羧基,由此可表征羟丙基链段的取代位置.     

Effects of material properties on sedimentation and aggregation of titanium dioxide nanoparticles of anatase and rutile in the aqueous phase

This study investigated the sedimentation and aggregation kinetics of titanium dioxide (TiO(2)) nanoparticles with varying material properties (i.e., crystallinity, morphology, and chemical composition). Used in the study were various types of commercially available TiO(2) nanoparticles: three spherical anatase (nominal diameters of 5, 10, and 50 nm) and two rutile nanoparticles (10×40 and 30×40 nm). The 50 nm anatase and 10×40 nm rutile showed higher stability in deionized water and 5 mM NaCl solutions at pH 7 than the 5, and 10 nm anatase nanoparticles in sedimentation experiments. In aggregation experiments, critical coagulation concentration values for the 50 nm anatase were the highest, followed by the 10×40 nm rutile and the 5 nm anatase nanoparticles in NaCl and CaCl(2) solutions. The aggregation kinetics was fitted reasonably well with the Derjaguin-Landau-Verwey-Overbeek (DLVO) equations for the TiO(2) nanoparticles tested. Results showed that crystallinity and morphology are not influential factors in determining the stability of TiO(2) nanoparticle suspensions; however, the differences in their chemical compositions, notably, the varying concentrations of impurities (i.e., silicon and phosphorus) in the pristine materials, determined the surface charge and therefore the sedimentation and aggregation of TiO(2) nanoparticles in the aqueous phase.     

Determination of locust bean gum and guar gum by polymerase chain reaction and restriction fragment length polymorphism analysis

A polymerase chain reaction (PCR) was developed to differentiate the thickening agents locust bean gum (LBG) and the cheaper guar gum in finished food products. Universal primers for amplification of the intergenic spacer region between trnL 3' (UAA) exon and trnF (GAA) gene in the chloroplast (cp) genome and subsequent restriction analysis were applied to differentiate guar gum and LBG. The presence of <5% (w/w) guar gum powder added to LBG powder was detectable. Based on data obtained from sequencing this intergenic spacer region, a second PCR method for the specific detection of guar gum DNA was also developed. This assay detected guar gum powder in LBG in amounts as low as 1% (w/w). Both methods successfully detected guar gum and/or LBG in ice cream stabilizers and in foodstuffs, such as dairy products, ice cream, dry seasoning mixes, a finished roasting sauce, and a fruit jelly product, but not in products with highly degraded DNA, such as tomato ketchup and sterilized chocolate cream. Both methods detected guar gum and LBG in ice cream and fresh cheese at levels <0.1%.     

Acylhydrazone-modified guar gum material for the highly effective removal of oily sewage

Oily sewage poses a serious environmental risk normally; thus, herein, the modified guar gum (GG-SH) was prepared through rapid condensation reaction between polysaccharide and stearic hydrazide. GG-SH exhibited high removal efficiency of crude oil, the maximum adsorption capacity was calculated to be 2157.3 mg?g-1. The kinetics and isotherm statistical theories showed that the sorption of crude oil onto GG-SH was governed by pseudo-second-order, and Langmuir models, respectively. The removal rate was still high after six cycles of regeneration, indicating an outstanding technique to prepare polysaccharide-based material for the oily sewage treatment with high efficiency and recyclability.     

Adsorption of guar gum onto quartz from dilute mixed electrolyte solutions

The effect of potassium, sodium, calcium, magnesium, and hydrogen cations on adsorption of guar gum onto quartz was investigated at natural pH. The role of the background ions was analyzed in terms of their water-structure making or breaking capabilities. In dilute solutions (0.01 mol/L) of structure-makers (NaCl, HCl, CaCl2, and MgCl2), the guar gum adsorption density did not change compared to the adsorption densities obtained in distilled water. Potassium, the only structure-breaking ion (chaotrope) among the tested cations, significantly enhanced guar gum adsorption. The results obtained in mixed electrolytes demonstrate that the strong structure-breaking properties of K+ overcome any contributions from weak structure making ions (kosmotropes), and guar gum adsorption remains at the levels observed in KCl alone. Only when strongly hydrated Mg2+ ions are mixed with KCl, the overall effect becomes additive and the influence of potassium is proportionally reduced by increasing concentrations of magnesium cations. In this approach, guar gum adsorption on quartz is viewed as a competition between polysaccharide and water molecules for silanol surface sites. The hydration of the quartz surface inhibits the adsorption process but the competition equilibrium, and hence polysaccharide adsorption, can be affected by the presence of chaotropes or kosmotropes.     

Syntheses and properties of superabsorbent composites based on natural guar gum and attapulgite

Utilization of raw materials available in nature and their application to derive other useful products without any adverse impact on the environment has long been a desired goal. In this work, guar gum (GG) and attapulgite (APT) clay were used as raw materials for preparing guar gum‐g‐poly(acrylic acid)/attapulgite (GG‐g‐PAA/APT) superabsorbent composites through the graft copolymerization of GG, partially neutralized acrylic acid (AA) and APT in aqueous solution. The effects of reaction conditions such as concentrations of the initiator and crosslinker, APT content, etc. on water absorbency were investigated. The composite prepared under optimal conditions gave the best absorption of 529 g/g sample in distilled water and 61 g/g sample in 0.9 wt% NaCl solution. Swelling behaviors revealed that the superabsorbent composites retained a high water absorbency over a wide pH range of 4–11, and the developed composites also exhibited improved reswelling and water‐retention capabilities. The superabsorbent composites can be utilized as eco‐friendly water‐manageable materials for agricultural and horticultural applications. Copyright © 2008 John Wiley & Sons, Ltd.