Aggregation and sedimentation of aqueous nanoscale zerovalent iron dispersions

Nanoscale zerovalent iron (NZVI) rapidly transforms many environmental contaminants to benign products and is a promising in-situ remediation agent. To be effective, NZVI should form stable dispersions in water such that it can be delivered in water-saturated porous media to the contaminated area. Limited mobility of NZVI has been reported, however, attributed to its rapid aggregation. This study uses dynamic light scattering to investigate the rapid aggregation of NZVI from single nanoparticles to micrometer size aggregates, and optical microscopy and sedimentation measurements to estimate the size of interconnected fractal aggregates formed. The rate of aggregation increased with increasing particle concentration and increasing saturation magnetization (i.e., the maximum intrinsic magnet moment) of the particles. During diffusion limited aggregation the primary particles (average radius = 20 nm) aggregate to micrometer-size aggregates in only 10 min, with average hydrodynamic radii ranging from 125 nm to 1.2 microm at a particle concentration of 2 mg/L (volume fraction(phi= 3.2 x 10(-7)) and 60 mg/L (phi = 9.5 x 10(-6)), respectively. Subsequently, these aggregates assemble themselves into fractal, chain-like clusters. At an initial concentration of just 60 mg/L, cluster sizes reach 20-70 microm in 30 min and rapidly sedimented from solution. Parallel experiments conducted with magnetite and hematite, coupled with extended DLVO theory and multiple regression analysis confirm that magnetic attractive forces between particles increase the rate of NZVI aggregation as compared to nonmagnetic particles.     

Growth and structure of aggregates of heat-denatured β-Lactoglobulin

Summary The aggregation of the globular protein β-lactoglobulin after heat-denaturation was studied in aqueous solution at pH 7 using static and dynamic light scattering. The structure of the aggregates is self-similar with fractal dimension 2.0. Size exclusion chromatography and dynamic light scattering measurements show that the aggregates have a broad size distribution. Initially clusters of about 85 proteins and 15 nm radius are formed which are the elementary units of the larger fractal aggregates. At low ionic strength the formation of the larger aggregates is impeded by electrostatic interactions.
The structure of the aggregates is independent of the concentration and the temperature. The rate of aggregation has an Arrhenius temperature dependence with an activation energy of about 350 kJ/mol weakly dependent on the concentration. The apparent reaction order of the aggregation is 1.5. In the mixture both variants A and B have the same aggregation rate. The gel time increases with decreasing concentration and diverges at about 0.7g L⁻¹. At lower concentration the aggregate growth stagnates when all protein has aggregated.     

Sequestration of zinc from zinc oxide nanoparticles and life cycle effects in the sediment dweller amphipod Corophium volutator

We studied the effects of ZnO nanoparticles [ZnO NPs, primary particle size 35 ± 10 nm (circular diameter, TEM)], bulk [160 ± 81 nm (circular diameter, TEM)], and Zn ions (from ZnCl(2)) on mortality, growth, and reproductive endpoints in the sediment dwelling marine amphipod Corophium volutator over a complete lifecycle (100 days). ZnO NPs were characterized by size, aggregation, morphology, dissolution, and surface properties. ZnO NPs underwent aggregation and partial dissolution in the seawater exposure medium, resulting in a size distribution that ranged in size from discrete nanoparticles to the largest aggregate of several micrometers. Exposure via water to all forms of zinc in the range of 0.2-1.0 mg L(-1) delayed growth and affected the reproductive outcome of the exposed populations. STEM-EDX analysis was used to characterize insoluble zinc precipitates (sphaerites) of high sulfur content, which accumulated in the hepatopancreas following exposures. The elemental composition of the sphaerites did not differ for ZnO NP, Zn(2+), and bulk ZnO exposed organisms. These results provide an illustration of the comparable toxicity of Zn in bulk, soluble, and nanoscale forms on critical lifecycle parameters in a sediment dwelling organism.     

碳纳米管-二氧化钛光催化降解普萘洛尔

水环境中普萘洛尔残留会对水产食品安全造成危害,并通过食物链威胁人体健康,因此需采取有效的方法去除普萘洛尔。本实验以碳纳米管- 二氧化钛纳米复合材料(MWCNTs-TiO2)为光催化剂,对普萘洛尔溶液进行光催化降解研究,在最佳实验条件：普萘洛尔质量浓度20mg/L、溶液初始pH 值为7、10% MWCNTs-TiO2 光催化剂加入量2.0g/L 时,紫外光照射180min 普萘洛尔的降解率达到95%。并对普萘洛尔的降解机理进行初步探讨,结果表明MWCNT-TiO2 降解普萘洛尔主要发生·OH 氧化反应,从而达到有效降解普萘洛尔的效果。     

Integrating plasmonic nanoparticles with TiO₂ photonic crystal for enhancement of visible-light-driven photocatalysis

Aimed at enhancing photocatalysis through intensifying light harvesting, a new photocatalyst was fabricated by infiltrating Au nanoparticles into TiO(2) photonic crystals (TiO(2) PC/Au NPs). Scanning electron microscopy (SEM) and transmission electron microscope (TEM) images showed that the Au NPs with average diameter around 15 nm were dispersed uniformly into the porous TiO(2) material. The results of the transmittance spectra demonstrated that the light absorption by Au NPs was amplified after they were infiltrated into TiO(2) 240, which was fabricated from 240 nm polystyrene spheres. In the photocatalytic experiments of 2,4-dichlorophenol degradation under visible light (λ > 420 nm) irradiation, the kinetic constant using TiO(2) 240/Au NPs was 2.3 fold larger than that using TiO(2) nanocrystalline/Au NPs (TiO(2) NC/Au NPs). The excellent photocatalysis benefited from the cooperatively enhanced light harvesting owing to the localized surface plasmon resonance of Au NPs, which extended the light response spectra and the photonic effect of the TiO(2) 240 which intensified the plasmonic absorption by Au NPs. The hydroxyl radicals originated from the electroreduction of dissolved oxygen with photogenerated electrons via chain reactions were the main reactive oxygen species responsible for the pollutant degradation.     

A new route for degradation of volatile organic compounds under visible light: using the bifunctional photocatalyst Pt/TiO2-xNx in H2-O2 atmosphere

The bifunctional photocatalyst Pt/TiO2-xNx has been successfully prepared by wet impregnation. The properties of Pt/ TiO2-xNx have been investigated by diffuse reflectance spectra, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, a photoluminescence technique with terephthalic acid, and electric field induced surface photovoltage spectra. The photocatalytic activity of the sample was evaluated by the decomposition of volatile organic pollutants (VOCs) in a H2-O2 atmosphere under visible light irradiation. The results demonstrated that nitrogen-doped and platinum-modified TiO2 in a H2-O2 atmosphere could enormously increase the quantum efficiency of the photocatalytic system with excellent photocatalytic activity and high catalytic stability. The increased quantum efficiency can be explained by enhanced separation efficiency of photogenerated electron-hole pairs, higher interface electron transfer rate, and an increased number of surface hydroxyl radicals in the photocatalytic process. A mechanism was proposed to elucidate the degradation of VOCs over PtTiO(2-x)Nx in a H2-O2 atmosphere under visible light irradiation.     

多孔TiO2薄膜在PET纤维上的负载及其光催化性能

采用浸渍法将低温制备的TiO2溶胶在普通和碱减量PET纤维上负载成膜,并以聚苯乙烯（PS）微球为模板剂使TiO2膜多孔化,制备了一系列TiO2/PET光催化纤维。采用XRD、SEM对TiO2和纤维进行了表征,并通过对甲基橙的降解来考察其光催化性能。结果表明：溶胶经室温陈化后可得到具有较高光催化活性的纳米锐钛矿型TiO2。PET纤维上TiO2的负载率随着溶胶在浸渍液中的含量增加而增大。PET纤维的碱减量有利于TiO2的负载和光催化活性的提高,且随着TiO2负载率的增加,甲基橙降解率具有先增加后缓慢减小的趋势。当碱减量纤维的TiO2负载率为4.2%时,光催化活性最好。利用PS为模板剂使TiO2薄膜多孔化可以进一步提高光催化纤维的比表面积和吸附能力,从而提高光催化活性。     

Granulomorphometry: a suitable tool for identifying hydrophobic and disulfide bonds in β-lactoglobulin aggregates. Application to the study of β-lactoglobulin aggregation mechanism between 70 and 95°C

This work deals with the investigation of β-lactoglobulin (β-LG) aggregation by granulomorphometry. In the first part of this study, we showed that the binding interactions involved in aggregate structure could be identified by their appearance in granulomorphometric pictures. The reliability of this analytical approach was demonstrated by comparing the appearance of β-LG aggregates in the presence and absence of a thiol-blocking agent (N-ethylmaleimide). The translucency of the aggregates was associated with hydrophobic interactions and their opacity was associated with disulfide bonds. We state, based on the morphology of the aggregates, along with the color of protein aggregates and insoluble materials, that hydrophobic interactions had a better water-holding capacity than disulfide bonds. Additionally, our results suggest that disulfide and hydrophobic bonds compete for β-LG aggregate shaping. In the second part of this work, interesting features of granulomorphometry useful for identifying aggregate binding interactions were highlighted to clarify the effect of temperature on the aggregation mechanisms occurring in a β-LG concentrate with a moderate calcium content (6.6mmol·L(-1)). Heat treatment experiments were performed between 70 and 95°C, and granulomorphometric measurements (aggregate size, aggregate number, and gray level of the picture) were conducted at different sampling times up to 4h. Results, which were interpreted in light of calculated β-LG denaturation levels, revealed that the aggregation mechanism could be split into 2 steps. Initially, β-LG denatured quickly, leading to fast β-LG aggregation by disulfide bonds. The denaturation rate then declined, which drastically slowed the disulfide aggregation mechanism. From that point on, a second aggregation path became preponderant. It consisted of the agglomeration of small aggregates by hydrophobic interactions and resulted in the formation of large aggregates containing both interaction types. This second aggregation mechanism was clearly favored at high temperatures because it was not detected in our experiments at temperatures below 85°C.     

二氧化钛纳米管的制备及其光催化性能

为提高TiO_2的光催化性能,通过电化学阳极氧化法在金属钛箔基体上制备了结构有序的TiO_2纳米管(TiO_2NTs),并以此为基础通过连续离子层吸附反应技术(SILAR)制备了Ag、CdS共修饰的TiO_2纳米管(AgCdS/TiO_2NTs)。采用X射线衍射仪、扫描电子显微镜、透射电子显微镜、元素分析仪和紫外可见漫反射光谱等表征手段,对Ag-CdS/TiO_2NTs形貌结构、元素组成和光吸收特性等进行了表征,并研究了Ag、CdS修饰后的TiO_2纳米管的光催化性能。结果表明:Ag和CdS纳米粒子被成功沉积在TiO_2纳米管上;与纯TiO_2纳米管的吸收光谱相比,Ag-CdS/TiO_2NTs对光的吸收范围延伸到整个可见光区域;与纯TiO_2纳米管或CdS修饰的TiO_2纳米管相比,Ag(3)-CdS/TiO_2NTs对甲基橙脱色率最高,70 min后脱色率达100%。     

Plasma surface modified TiO2 nanoparticles: improved photocatalytic oxidation of gaseous m-xylene

Titanium dioxide (TiO(2)) is a preferred catalyst for photocatalytic oxidation of many air pollutants. In an effort to enhance its photocatalytic activity, TiO(2) was modified by pulsed plasma treatment. In this work, TiO(2) nanoparticles, coated on a glass plate, were treated with a plasma discharge of hexafluoropropylene oxide (HFPO) gas. By appropriate adjustment of discharge conditions, it was discovered that the TiO(2) particles can be either directly fluorinated (Ti-F) or coated with thin perfluorocarbon films (C-F). Specifically, under relatively high power input, the plasma deposition process favored direct surface fluorination. The extent of Ti-F formation increased with increasing power input. In contrast, at lower average power inputs, perfluorocarbon films are deposited on the surface of the TiO(2) particles. The plasma surface modified TiO(2) nanoparticles were subsequently employed as catalysts in the photocatalytic oxidation of m-xylene in air, as carried out inside a batch reactor with closed loop constant gas circulation. Both types of modified TiO(2) were significantly more catalytically active than that of the unmodified particles. For example, the rate constant of m-xylene degradation was increased from 0.012 min(-1) with untreated TiO(2) to 0.074 min(-1) with fluorinated TiO(2). Although it is not possible to provide unequivocal reasons for this increased photocatalytic activity, it is noted that the plasma surface treatment converted the TiO(2) from hydrophilic to highly hydrophobic, which would provide more facile catalyst adsorption of the xylene from the flowing air. Also, based on literature reports, the use of fluorinated TiO(2) reduces electron-hole recombination rates, thus increasing the photocatalytic activity.     

Whey protein aggregation under shear conditions – effects of lactose and heating temperature on aggregate size and structure

Summary Whey protein concentrates with different lactose contents were heat- and shear-treated in a scraped surface heat exchanger at various temperatures. The properties of the resulting protein aggregates are closely correlated with the denaturation kinetics of β-lactoglobulin and the different mechanisms – unfolding and aggregation – which determine the overall reaction rate. At temperatures below 85 °C, unfolding is slowed down especially if there is a high content of lactose. A loose, porous aggregate structure is formed and the particle size and the serum binding capacity increase. The smallest aggregates are produced when heating takes place between 85 and 95 °C. In the temperature range above 100 °C aggregation is the rate-limiting step and the aggregate structure is very dense and compact. The particle size increases and is no longer dependent on the concentration of lactose.     

光催化除甲醛苎麻织物的低温复合制备

为解决在无黏结剂条件下纳米光催化材料在纺织品上复合牢度低的问题,采用低温复合处理技术,将TiO2纳米颗粒均匀负载于苎麻织物上,并通过扫描电子显微镜、傅里叶红外光谱仪、透气性测试仪、万能拉伸仪和甲醛测试系统等测试方法对织物性能进行表征。结果表明：TiO2纳米颗粒可通过低温复合处理技术均匀固定于苎麻织物上,织物在-10 ℃低温浴配合400 N/cm 的压力下每次浸渍10 min,浸扎处理３ 道后除甲醛效果最佳;处理后织物表面羟基量增多,织物保持了原有透气性且断裂强力和断裂伸长未受到处理影响;处理后织物在120 min内实现了87.14%甲醛去除率。     

秸秆还田对植烟土壤有机质及团聚体特征的影响

通过2010—2012年的秸秆还田定位试验,利用干、湿筛法研究了不同用量小麦以及玉米秸秆还田后对植烟土壤有机质和团聚体特征的影响。结果表明,随着秸秆还田量的增加,土壤有机质含量、团聚体平均重量直径（MWD）及几何平均直径（GMD）有所增加,但不同秸秆还田对土壤有机质及团聚体特征的效果不同。干筛法测得土壤团聚体的分形维数随两种秸秆还田量增加而减少,湿筛法测得高量玉米秸秆还田（7500 kg/hm²）较低量秸秆还田（1500 kg/hm²）处理的团聚体分形维数显著降低,同时分形维数随着小麦秸秆还田量的增加而降低。等量玉米秸秆较小麦秸秆在提高土壤有机质含量及团聚体特征方面效果较好。土壤有机质与干筛测得MWD及GMD呈极显著正相关,与干筛测得分形维数呈极显著负相关,与湿筛测得GMD及>0.25 mm团聚体含量呈显著性的正相关。总之,通过秸秆还田可增加土壤有机质含量,影响团聚体分布并提高团聚体稳定性。     

Impact of virus aggregation on inactivation by peracetic acid and implications for other disinfectants

Viruses in wastewater and natural environments are often present as aggregates. The disinfectant dose required for their inactivation, however, is typically determined with dispersed viruses. This study investigates how aggregation affects virus inactivation by chemical disinfectants. Bacteriophage MS2 was aggregated by lowering the solution pH, and aggregates were inactivated by peracetic acid (PAA). Aggregates were redispersed before enumeration to obtain the residual number of individual infectious viruses. In contrast to enumerating whole aggregates, this approach allowed an assessment of disinfection efficiency which remains applicable even if the aggregates disperse in post-treatment environments. Inactivation kinetics were determined as a function of aggregate size (dispersed, 0.55 and 0.90 μm radius) and PAA concentration (5-103 mg/L). Aggregation reduced the apparent inactivation rate constants 2-6 fold. The larger the aggregate and the higher the PAA concentration, the more pronounced the inhibitory effect of aggregation on disinfection. A reaction-diffusion based model was developed to interpret the experimental results, and to predict inactivation rates for additional aggregate sizes and disinfectants. The model showed that the inhibitory effect of aggregation arises from consumption of the disinfectant within the aggregate, but that diffusion of the disinfectant into the aggregates is not a rate-limiting factor. Aggregation therefore has a large inhibitory effect if highly reactive disinfectants are used, whereas inactivation by mild disinfectants is less affected. Our results suggest that mild disinfectants should be used for the treatment of water containing viral aggregates.     

TiO₂-photocatalytic reduction of pentavalent and trivalent arsenic: production of elemental arsenic and arsine

Heterogeneous photocatalytic reduction of As(V) and As(III) at different concentrations over TiO(2) under UV light in deoxygenated aqueous suspensions is described. For the first time, As(0) was unambiguously identified together with arsine (AsH(3)) as reaction products. As(V) reduction requires the presence of an electron donor (methanol in the present case) and takes place through the hydroxymethyl radical formed from methanol oxidation by holes or hydroxyl radicals. On the contrary, As(III) reduction takes place through direct reduction by the TiO(2)-conduction band electrons. Detailed mechanisms for the photocatalytic processes are proposed. Although reduction to solid As(0) is convenient for purposes of As removal from water as a deposit on TiO(2), attention must be paid to formation of AsH(3), one of the most toxic forms of As, and strategies for AsH(3) treatment should be considered.     

Kinetics and mechanisms of photocatalytic degradation of (CH3)nNH(4-n)+ (0 < or = n < or = 4) in TiO2 suspension: the role of OH radicals

The photocatalytic degradation of a series of (CH3)nNH(4-n)+ (0 < or = n < or = 4) was systematically studied in the UV-illuminated TiO2 aqueous suspensions at pH ranges of 3-11. By investigating the pH-dependent kinetics and analyzing intermediates and products, we elucidated the mechanistic pathways and the role of OH radicals in the photocatalytic oxidation. The deprotonated neutral species more rapidly degraded than their protonated counterparts for these homologous compounds because the OH radicals favorably reacted with the lone-pair electron on the nitrogen atom. Therefore, the photocatalytic degradation was highly enhanced at alkaline solutions for all substances except (CH3)4N+. The H-atom abstraction (from (CH3)4N+) by OH radicals initiated successive demethylation processes to generate tri-, di-, and monomethylammonium/amine as an intermediate and NH3/NH4+ as a final product. On the other hand, the OH-addition to the N-atom with the lone-pair electron led to NO2-/NO3- whose production was highly favored at alkaline conditions. The photocatalytic degradation rates of (CH3)4N+ were comparable at both acidic and alkaline conditions, which could not be explained by a simple electrostatic surface charge model. By using OH-scavenging tert-butyl alcohol as a diagnostic probe into the mechanism, it is suggested that the photocatalytic oxidation of (CH3)4N+ at acidic conditions proceeds through free OH radicals in the solution bulk, not on the surface of TiO2.     

Aggregation kinetics of alginate-coated hematite nanoparticles in monovalent and divalent electrolytes

The early stage aggregation kinetics of bare and alginate-coated hematite nanoparticles are acquired through time-resolved dynamic light scattering (DLS). Varying concentrations of monovalent (NaCl) and divalent (MgCl2 and CaCl2) electrolytes are employed to induce aggregation. In the presence of NaCl and MgCl2, the alginate-coated hematite nanoparticles undergo aggregation through electrostatic destabilization as described by the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This is ascertained through examination of the favorable and unfavorable regimes of the stability curves depicting the attachment efficiency as a function of salt concentration. Additional evidence may be found in the aggregation kinetics of alginate-coated particles, which, under favorable aggregation conditions, are reasonably close to that of bare hematite nanoparticles. However, in the presence of CaCl2, the aggregate growth rate of alginate-coated hematite nanoparticles is much higher than that which conventional diffusive aggregation predicts. Dispersed hematite primary particles and lower-order aggregates enmeshed within extended alginate gel networks were observed under transmission electron microscope (TEM). The proposed mechanism for enhanced aggregation suggests an apparent increase in the collision radii of alginate-coated hematite nanoparticles through alginate gel network formation from the particle surface. Additionally, cross-linking between unadsorbed (suspended) alginate macromolecules may form bridges between hematite-alginate gel clusters. It is further established that the presence of background electrolyte NaCl in solution is detrimental to the calcium-induced enhanced aggregation.     

反相微乳液水热法合成锐钛矿TiO2微球及其光催化性能

以钛酸丁酯（TBT）为钛源、辛烷基苯酚聚氧乙烯醚(Triton X-100)为表面活性剂,采用反相微乳液水热法制备锐钛矿TiO2微球,并研究了反应体系中水含量对生成的锐钛矿TiO2微球性能的影响。采用粉末X射线粉末衍射（XRD）、傅里叶变换红外光谱（FTIR）、场发射扫描电子显微镜（FE-SEM）、透射电子显微镜（TEM）、荧光光谱（PL）对锐钛矿TiO2微球的结构、形貌和物相等进行表征。结果表明：在一定范围内增加钛酸丁酯/水（TBT/H2O）摩尔比,锐钛矿TiO2微球形貌由无规则形态向规则形貌转变,颗粒尺寸也随之变均匀。同时,以亚甲基蓝为目标降解物,对其光催化活性进行评价,结果表明颗粒尺寸和形貌的变化对其催化活性有较大影响,当TBT/H2O摩尔比为1:25时,微球尺寸均匀,催化活性最好,优于商业化P25。     

A new role for Fe3+ in TiO2 hydrosol: accelerated photodegradation of dyes under visible light

The effect of Fe3+ on the photocatalytic activity of TiO2 hydrosol prepared through a low-temperature route has been investigated under visible light irradiation. The total reactive oxygen species (ROS) level and the accumulation of Fe2+ during the photodegradation process were detected to examine the role of Fe3+. In contrastto an aqueous TiO2 dispersion where Fe3+ strongly inhibited the photoactivity of TiO2 via suppressing the reduction of O2 and decreasing the production of ROS, Fe3+ accelerated the photodegradation of all dyes examined in the hydrosol through increasing the yield of oxidative ROS. The influence of the prebound hydroxyl groups on the surface of TiO2 was compared to that of free alcohols in aqueous solution, which revealed the cooperative function of the surface hydroxyl groups. The thoroughly contrary effect of Fe3+ on the photocatalysis of TiO2 hydrosol and TiO2 powder, which are all anatase nanocrystallites but are synthesized with different procedures, was ascribed to the complexation of the hydroxyl groups bound to TiO2 surface with Fe3+. The formation of such complexes has resulted in an altered electron-transfer pathway of the dye-sensitized photocatalysis under visible light irradiation.     

蛋白质氧化对核桃蛋白质结构的影响

为了深入明晰氧化对核桃蛋白质结构性的影响,本文以核桃分离蛋白为研究对象,采用不同浓度的2,2'-盐酸脒基丙烷(AAPH)热降解形成烷过氧自由基(ROO·)代表脂质过氧化反应过程中产生的脂质自由基,对核桃分离蛋白进行氧化修饰得到不同氧化程度的核桃氧化蛋白。对不同氧化程度蛋白的羰基、巯基和总巯基,表面疏水性(H₀)、内源荧光、粒径分布、相对分子质量和二级结构进行研究和分析。结果表明,随着AAPH浓度的增加,核桃氧化蛋白羰基含量显著增加(p<0.05),巯基和H₀显著降低(p<0.05);圆二色谱结果表明,随着AAPH浓度的增加,核桃蛋白α-螺旋结构和β-折叠含量下降,而无规卷曲结构含量增加,说明氧化破坏了蛋白质的二级结构,使有序结构变为无序结构。最大内源荧光值降低,且出现蓝移现象,说明烷过氧自由基氧化导致分子聚集,使得色氨酸残基包埋;粒径分布结果表明,核桃氧化蛋白可溶性聚集体可被共价交联和非共价聚集转变成不可溶性部分;体积排阻色谱结果表明,核桃氧化蛋白相对分子质量随着氧化浓度的增大聚集程度逐渐增大。研究结果表明,核桃蛋白在烷过氧自由基(ROO·)氧化体系中产生了显著氧化作用并导致其结构发生一定的改变,为进一步阐明核桃蛋白氧化机理提供理论依据。