Actinide sequestration using self-assembled monolayers on mesoporous supports

Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometalate anions, and radionuclides. Details addressing the design, synthesis, and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental cleanup necessary after 40 years of weapons-grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented.     

Incorporation of hydroxypyridinone ligands into self-assembled monolayers on mesoporous supports for selective actinide sequestration

In this study, three isomers of hydroxypyridinones (1,2-HOPO, 3,2-HOPO, and 3,4-HOPO) were attached to self-assembled monolayers on mesoporous silica (SAMMS). The HOPO-SAMMS materials have superior solid adsorbents properties: they do not suffer from solvent swelling; their rigid, open pore structure allows rapid sorption kinetics; their extremely high surface area enables the installation of high functional density; and being silica-based, they are compatible with vitrification into a final vitreous waste form. Kinetics, equilibrium, and selectivity of the adsorptions of actinide on the HOPO-SAMMS at various pH values and in the presence of other metal cations, anions, and competing ligands are reported. Rapid sequestration of U(VI), Np(V), and Pu(IV) was observed. Very little competition from transition metal cations and common species was observed.     

Neurite outgrowths of neurons on patterned self-assembled monolayers

The effects of specific chemical functionalities on the neurite outgrowths of embryonic chick dorsal root ganglia (DRG) neurons and PC12h cells were investigated using a set of chemically functionalized surfaces prepared by self-assembled monolayers (SAMs) of alkanethiolates with R = NH2, COOH, and CH3 on patterned gold surfaces. The numbers of neurons with neurite outgrowths were compared in the course of a two-week cultivation period. Neurons with neurite outgrowths were observed predominantly on a patterned SAM of long-chain alkanethiolates with amino groups. After about two weeks, the neurons detached from the patterned SAM. However, the activity of beta-galactosidase immobilized via a patterned SAM did not decrease over a 13-d period, reflecting the long-term stability of the SAM. Therefore, the neurons became detached upon cell death. These results demonstrate that the patterned SAM of 11-amino-1-undecanethiolate is a scaffold suitable for making cell chips.     

High-temperature sorption of cesium and strontium on dispersed kaolinite powders

Sorption of cesium and strontium on kaolinite powders was investigated as a means to minimize the emissions of these metals during certain high-temperature processes currently being developed to isolate and dispose of radiological and mixed wastes. In this work, nonradioactive aqueous cesium acetate or strontium acetate was atomized down the center of a natural gas flame supported on a variable-swirl burner in a refractory-lined laboratory-scale combustion facility. Kaolinite powder was injected at a postflame location in the combustor. Cesium readily vaporized in the high-temperature regions of the combustor, but was reactively scavenged onto dispersed kaolinite. Global sorption mechanisms of cesium vapor on kaolinite were quantified, and are related to those available in the literature for sodium and lead. Both metal adsorption and substrate deactivation steps are important, so there is an optimum temperature, between 1400 and 1500 K, at which maximum sorption occurs. The presence of chlorine inhibits cesium sorption. In contrast to cesium, and in the absence of chlorine, strontium was only partially vaporized and was, therefore, only partially scavengeable. The strontium data did not allow quantification of global kinetic mechanisms of interaction, although equilibrium arguments provided insight into the effects of chlorine on strontium sorption. These results have implications for the use of sorbents to control cesium and strontium emissions during high-temperature waste processing including incineration and vitrification.     

Experimental and theoretical examination of surface energy and adhesion of nitrifying and heterotrophic bacteria using self-assembled monolayers

Biofilm-based systems, including integrated fixed-film activated sludge and moving bed bioreactors, are becoming increasingly popular for wastewater treatment, often with the goal of improving nitrification through the enrichment of ammonia and nitrite oxidizing bacteria. We have previously demonstrated the utility of self-assembled monolayers (SAMs) as tools for studying the initial attachment of bacteria to substrata systematically varying in physicochemical properties. In this work, we expanded these studies to bacteria of importance in wastewater treatment systems and we demonstrated attachment rates were better correlated with surface energy than with wettability (water contact angle). Toward the long-term goal of improving wastewater treatment performance through the strategic design of attachment substrata, the attachment rates of two autotrophic ammonia-oxidizing bacteria (Nitrosomonas europaea and Nitrosospira multiformis) and a heterotroph (Escherichia coli) were evaluated using SAMs with a range of wettabilities, surface energies, and functional properties (methyl, hydroxyl, carboxyl, trimethylamine, and amine terminated). Cell attachment rates were somewhat correlated with the water contact angles of the SAMs with polar terminal groups (hydroxyl, carboxyl, trimethylamine, and amine). Including all SAM surfaces, a better correlation was found for all bacteria between attachment rates and surface free energy, as determined using the Lewis Acid-Base approach. The ammonia-oxidizers had higher adhesion rates on the SAMs with higher surface energies than did the heterotroph. This work demonstrated the successful application of SAMs to determine the attachment surface preferences of bacteria important to wastewater treatment, and it provides guidance for a new area of research aimed at improving treatment performance through rational attachment surface design.     

Probing the specific sorption sites on montmorillonite using nitroaromatic compounds and hexafluorobenzene

The objective of this work was to test two possible sorption mechanisms of organic chemicals to montmorillonite: n-π electron-donor-acceptor (EDA) interaction with lone electron pairs of siloxane oxygens (n-donors) and complexation with exchangeable cations. Batch sorption experiments were performed for 1,3-dinitrobenzene, 1,4-dinitrobenzene (π-electron acceptors and cation binders), and hexafluorobenzene (π-electron acceptor only) to homoionic montmorillonites in water or hexane. For all three sorbates, the aqueous sorption affinity showed large cation dependency (Cs(+) > K(+) > Na(+)), wherein sorption of hexafluorobenzene to Cs(+)-montmorillonite was the strongest (K(d) in the order of 10(4) L/kg). Change of the solvent media from water to hexane generally favored sorption, indicating suppressive effect by cation hydration. Cosorption of 1,4-dinitrobenzene prominently decreased sorption of 1,3-dinitrobenzene to all cation-exchanged montmorillonites; however, hexafluorobenzene caused strong competition only to Cs(+)-montmorillonite. Furthermore, complexation of exchangeable cations by 18-crown-6 ether dramatically suppressed sorption of 1,3-dinitrobenzene to K(+)-montmorillonite in water and all cation-exchanged montmorillonites in hexane, but not to the rest. The contrast patterns of binary competitive sorption between nitroaromatics and hexafluorobenzene indicated they sorbed to different sites on montmorillonite. It was proposed that sorption of hexafluorobenzene was dominated by n-π EDA interaction, while sorption of nitroaromatics was dominated by cation-polar interaction.     

类Fenton试剂MCM-41负载Fe催化降解甲基橙的研究

通过浸渍法制备了MCM-41负载铁催化剂Fe-MCM-41,采用XRD、UV-vis光谱、N2吸附-脱附分析和SEM等对Fe-MCM-41进行表征,结果表明,Fe-MCM-41具有载体MCM-41的介孔结构,孔道分布均匀,平均孔径1.88 nm.研究了以Fe-MCM-41为催化剂的类Fenton体系对甲基橙染料快速降解的方法,考察了分子筛中Fe含量、H2O2及甲基橙初始浓度、溶液p H和催化剂用量等条件对染料降解率的影响.当p H=3、H2O2及甲基橙初始浓度分别为30 mmol/L和20 mmol/L、催化剂用量为2 g/L、反应60 min时,甲基橙的降解率可达96.82%.动力学研究表明,采用Fe-MCM-41催化降解甲基橙遵循一级反应动力学模型(R=0.992),对应的速率常数为8.51×10-2min-1.     

Characterization of sorption mechanisms of VOCs with organobentonites using a LSER approach

To fully utilize the sorption traits of organobentonites to control volatile organic compounds (VOCs) pollution, the sorption mechanisms of VOCs with organobentonites need to be understood adequately. The sorption of VOCs as vapors to a typical organobentonite, modified with cetyltrimethylammonium bromide (CTMAB-bentonite), was characterized using a linear solvation energy relationship (LSER) of the type log Kc = c + rR2 + s pi2H + a sigma(alpha2)H + b sigma(beta2)H + l log L16. The fitted LSER equation, log Kc = 0.434 + 0.968R2 - 0.0886pi2H + 2.170sigma(alpha2)H + 1.611sigma(beta2)H + 0.417 log L16, was obtained by a multiple regression of the partition coefficients of 22 probe solutes against the solvation parameters of the solutes. The coefficients of the LSER equation show that CTMAB-bentonite is a sorbent with nonsignificant dipolarity/polarizability, interacts with solutes partly through pi-/n-electron pairs, behaves both as hydrogen-bond donor and hydrogen-bond acceptor, and can interact with solutes by cavity/dispersion interactions. The related terms in LSER suggest that the potential factors governing the sorption of VOCs onto CTMAB-bentonite are dispersion interactions, hydrogen-bond acidity interactions, hydrogen-bond basicity interactions, and pi-/n-electron interactions. The dispersion interaction is recognized to be the predominant parameter for most solutes, whereas the contributions of the other parameters depend on specific solutes. The derived LSER equation successfully predicted the VOC partition coefficients and the selectivity of CTMAB-bentonite for the VOCs. The relationship between LSER and adsorption/partition model was compared. The classification of sorption mechanisms by LSER goes on the molecular interaction types between sorbate and sorbent, and classification by adsorption/partition model goes on the property difference among various components of sorbent. The LSER approach coupled with inverse gas chromatography (IGC) is a comparatively simple and reliable tool to rapidly characterize the sorption mechanism of VOCs with solid sorbents such as CTMAB-bentonite, and may potentially be applied to the design of an organoclay sorbent for control of VOCs.     

Selective removal of cobalt species using nanofiltration membranes

Selective removal of cobalt species from simulated nuclear liquid waste was investigated with different nanofiltration (NF) membranes at various solution pH levels, initial cobalt concentrations, and background ion concentrations. This study provides insight into the understanding of the relationships between rejections of a target compound (cobalt) and chemical equilibria of various species in the feed solution during NF. Particularly, the ratio of electrostatic rejection to steric rejection for different membranes used was quantitatively evaluated to find outthe relative significance in NF. Substantial cobalt rejection by NF was achieved along with partial separation of monovalent ionic species, although it depended on the level of liquid pH and the presence of background species. Greater cobalt rejection at increased pH was attributed to the precipitation of CoCO3(s) associated with natural carbonates originating from atmospheric CO2 gas rather than that of Co(OH)2(s). A loose NF membrane (e.g., NTR7410) gave as high a rejection as other tighter ones due to the stronger influence of electrostatic rejection, particularly at low pH where no cobalt precipitation was occurring. The decrease of cobalt rejection with the addition of boric acid was found to occur due to the formation of complexes between cobalt and boric acid, which was verified by the analyses of solution turbidity and near-infrared spectroscopy.     

动态水分吸附法研究发酵饼干水分吸附特性

以发酵饼干为研究对象,采用动态水分吸附法研究发酵饼干在25℃的水分吸附等温线与水分吸附动力学特性,同时与饱和盐溶液法得到的水分吸附等温线进行对比,并基于常用的等温吸湿模型对实验数据进行拟合。结果表明:动态水分吸附仪能在更短的时间里采集更多的数据,高频率的实时数据采集能够更准确地获得食品的水分吸附动力学特性;其从水分活度适用范围和拟合精度方面来看,GAB模型拟合饼干的等温吸湿的效果最佳。与饱和盐溶液法结果相比,动态水分吸附法得到的饼干平衡含水率略低。      

Modeling water sorption dynamics of cellular solid food systems using free volume theory

Water sorption and dynamical properties of bread crust were studied using gravimetric sorption experiments. Water uptake and loss were measured while relative humidity (RH) was step-wise in- or decreased. Experimental results were compared with Fickian diffusion models and empirical models like the exponential and power-law model. From comparison of experimental sorption curves and the power-law model for short times it followed for all bread crust that the diffusional coefficient n is close to one. It turned out that this is not due to so-called case II diffusion and water transport that is limited by relaxation of the solid material but due to the fact that RH did not instantaneously but gradually increased to the set value.Sorption curves of isotherm experiments could be best described by the Fickian diffusion model for low RH and by the exponential model for large RH. Transport rates depend on moisture content and show a maximum around RH = 0.7, corresponding to a water mass fraction ω₁ = 0.12. Diffusion rates could be well described by free volume theory up to the maximum, but this theory could not explain the strong decrease at higher ω₁. Indications for a local glass-rubber transition at room temperature were found near a water mass fraction ω₁ ≈ 0.09. This corresponds very well to the start of the crisp–non-crisp transition as measured by a sensory panel, but not to the glass-rubber transition at ω₁ ≈ 0.12 as measured by other techniques like Differential Scanning Calorimetry. So it seems that more than one glass-rubber like transitions may be important to describe the properties of heterogeneous cellular food systems.     

Competitive sorption of pyrene on wood chars

Sorption isotherms of pyrene on original and heat-treated wood chars were examined to understand its sorption behavior. Pyrene in single-solute systems had nonlinear isotherms. Polanyi-based dual-domain model fit sorption data well, and the model results showed that the adsorption component dominated pyrene sorption by original char at all aqueous concentrations. In contrast, this adsorption component contributed a much lower fraction to the total sorption by the heat-treated char, and dominated only at low solute concentrations; with increasing concentration, partitioning became a predominant contributor to the total sorption. Competitive effect of four cosolutes, phenanthrene (Phen), benzo[a]anthracene (BaA), 2,2-methylene-bis (4-methyl-6-tert-butylphenol) (MMBP), and phenol on pyrene sorption by original and treated chars was examined to understand the underlying mechanism of competition. Hydrophobicity (adsorbability) and molecular size of competitors played an important role in competition with pyrene by both chars, suggesting the direct competition for sorption sites and pore blockage mechanism. Competitive sorption results indicated that the fate and transport of hydrophobic organic chemicals (e.g., pyrene) could be strongly affected in the presence of coexisting organic contaminants with high hydrophobicity and large molecularsize,thereby, enhancing the mobility and leachability of these chemicals.     

介孔二氧化硅制备固定化菠萝蛋白酶的研究

采用经扫描电镜和透射电镜表征的介孔二氧化硅制备固定化菠萝蛋白酶,具有工艺简便、条件温和及操作方便的特点。考察了给酶量、pH和时间对固定化菠萝蛋白酶活力的影响,在酶量25mg/mL、pH5.0、固定化时间22h时,固定化酶的酶活为603U/g。介孔二氧化硅固定的菠萝蛋白酶在50℃水浴60min后,固定化酶的活力保持在92%以上,说明固定化酶的热稳定性较高。该固定酶持续操作三次后,使用活性逐渐衰减,但第3次相对酶活仍然达38.5%,反映了菠萝蛋白酶分子与载体有较强的物理吸附作用而且固定的菠萝蛋白酶有一定的可重复使用性。      

Study of water sorption behaviour of pectins using a computerised elution gas chromatographic technique

The moisture sorption isotherms of apple and citrus pectins using a computerised inverse gas chromatographic (IGC) method were constructed at 25, 30, 40 and 50°C. Sorption isotherm data are calculated from a single injection of water with the aid of a personal computer and a program developed to perform data handling. Thus sorption isotherms are constructed in < 3 h. Good agreement was observed between moisture sorption isotherms of apple and citrus pectins obtained with the computerised IGC method and the gravimetric static method.     

Investigating the moisture sorption behavior of amorphous sucrose using a dynamic humidity generating instrument

ABSTRACT:  The moisture sorption behavior of freeze-dried amorphous sucrose was investigated using a dynamic humidity generating instrument, the Dynamic Vapor Sorption (DVS) instrument. The kinetic moisture sorption profiles of freeze-dried amorphous sucrose samples with 29% crystalline content were obtained using the DVS instrument at 9 relative humidity (RH) values, ranging from 10% to 90%, at 25 °C. Moisture-induced crystallization was observed for %RH values between 40% and 80%, where the crystallization onset time decreased as %RH increased. The moisture sorption behavior of freeze-dried amorphous sucrose with 3 crystalline contents, 23%, 29%, and 80%, was also compared, revealing that the crystalline content had a significant impact on the pseudo-sorption isotherm of freeze-dried amorphous sucrose. In general, for %RH values below 90%, samples that had a lower percent crystalline content had a higher pseudo-equilibrium moisture content, with the difference becoming most pronounced for the 60% to 80% RH values. The moisture-induced crystallization results as a function of %RH obtained in this study were compared to those previously reported in the literature, leading to an extensive discussion of both the experimental protocols used and the hypothesized mechanisms governing the long-term stability of amorphous materials. The hypothesized mechanisms discussed included the glass transition temperature boundary, the zero mobility temperature, and the hydration limit. Based on the dissimilarity in these hypothesized mechanisms, additional theoretical and experimental exploration is still merited in order to adequately predict the conditions (for example, moisture content, %RH, and temperature) required to ensure long-term stability of amorphous solids.