Advances in Colloid and Interface Science (v.245, #C)

Lanthanide-doped upconversion nanoparticles (UCNPs) have recently attracted great attention in theranostics due to their exceptional optical and physicochemical properties, which enable the design of a novel UCNP-based nanoplatform for luminescent imaging, temperature mapping, sensing, and therapy. In addition, UCNPs are considered to be ideal building blocks for development of multimodal probes for cells and whole body imaging, exploiting simple variation of host matrix, dopant ions, and surface chemistry. Modalities responsible for magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET)/single-photon emission computed tomography (SPECT) are embedded in a single UC nanocrystal, providing integrating effect over any modality alone in terms of the efficiency and sensitivity for clinical innovative diagnosis through multimodal bioimaging. In particular, we demonstrate applications of UCNPs as a new nanoplatform for optical and multimodal cancer imaging in vitro and in vivo and extend discussions to delivery of UCNP-based therapeutic agents for photodynamic and photothermal cancer treatments.Display Omitted
Keywords: Upconversion nanoparticles; Photoluminescent imaging; Magnetic resonance imaging; Computed tomography; Positron emission tomography; Single-photon emission computed tomography;

Artificial neural networks (ANNs) have been widely applied for the prediction of dye adsorption during the last decade. In this paper, the applications of ANN methods, namely multilayer feedforward neural networks (MLFNN), support vector machine (SVM), and adaptive neuro fuzzy inference system (ANFIS) for adsorption of dyes are reviewed. The reported researches on adsorption of dyes are classified into four major categories, such as (i) MLFNN, (ii) ANFIS, (iii) SVM and (iv) hybrid with genetic algorithm (GA) and particle swarm optimization (PSO). Most of these papers are discussed. The further research needs in this field are suggested. These ANNs models are obtaining popularity as approaches, which can be successfully employed for the adsorption of dyes with acceptable accuracy.Display Omitted
Keywords: Adsorption; Removal; Dye; ANN; ANFIS; SVM;

Colloidal 2D nanosheets of MoS2 and other transition metal dichalcogenides through liquid-phase exfoliation by Ekaterina D. Grayfer; Mariia N. Kozlova; Vladimir E. Fedorov (40-61).
This review focuses on the exfoliation of transition metal dichalcogenides MQ2 (TMD, M = Mo, W, etc., Q = S, Se, Te) in liquid media, leading to the formation of 2D nanosheets dispersed in colloids. Nowadays, colloidal dispersions of MoS2, MoSe2, WS2 and other related materials are considered for a wide range of applications, including electronic and optoelectronic devices, energy storage and conversion, sensors for gases, catalysts and catalyst supports, biomedicine, etc. We address various methods developed so far for transferring these materials from bulk to nanoscale thickness, and discuss their stabilization and factors influencing it. Long-time known exfoliation through Li intercalation has received renewed attention in recent years, and is recognized as a method yielding highest dispersed concentrations of single-layer MoS2 and related materials. Latest trends in the intercalation/exfoliation approach include electrochemical lithium intercalation, experimenting with various intercalating agents, multi-step intercalation, etc. On the other hand, direct sonication in solvents is a much simpler technique that allows one to avoid dangerous reagents, long reaction times and purifying steps. The influence of the solvent characteristics on the colloid formation was closely investigated in numerous recent studies. Moreover, it is being recognized that, besides solvent properties, sonication parameters and solvent transformations may affect the process in a crucial way. The latest data on the interaction of MoS2 with solvents evidence that not only solution thermodynamics should be employed to understand the formation and stabilization of such colloids, but also general and organic chemistry. It appears that due to the sonolysis of the solvents and cutting of the MoS2 layers in various directions, the reactive edges of the colloidal nanosheets may bear various functionalities, which participate in their stabilization in the colloidal state. In most cases, direct exfoliation of MQ2 into colloidal nanosheets is conducted in organic solvents, while a small amount of works report low-concentrated colloids in pure water. To improve the dispersion abilities of transition metal dichalcogenides in water, various stabilizers are often introduced into the reaction media, and their interactions with nanosheets play an important role in the stabilization of the dispersions. Surfactants, polymers and biomolecules usually interact with transition metal dichalcogenide nanosheets through non-covalent mechanisms, similarly to the cases of graphene and carbon nanotubes. Finally, we survey covalent chemical modification of colloidal MQ2 nanosheets, a special and different approach, consisting in the functionalization of MQ2 surfaces with help of thiol chemistry, interaction with electrophiles, or formation of inorganic coordination complexes. The intentional design of surface chemistry of the nanosheets is a very promising way to control their solubility, compatibility with other moieties and incorporation into hybrid structures. Although the scope of the present review is limited to transition metal dichalcogenides, the dispersion in colloids of other chalcogenides (such as NbS3, VS4, Mo2S3, etc.) in many ways follows similar trends. We conclude the review by discussing current challenges in the area of exfoliation of MoS2 and its related materials.Display Omitted
Keywords: Molybdenum disulfide; Transition metal dichalcogenide; Colloidal dispersion; Exfoliation; Nanosheet; Functionalization;

Layered double hydroxides as the next generation inorganic anion exchangers: Synthetic methods versus applicability by Natalia Chubar; Robert Gilmour; Vasyl Gerda; Matej Mičušík; Maria Omastova; Katja Heister; Pascal Man; Jacques Fraissard; Vladimir Zaitsev (62-80).
This work is the first report that critically reviews the properties of layered double hydroxides (LDHs) on the level of speciation in the context of water treatment application and dynamic adsorption conditions, as well as the first report to associate these properties with the synthetic methods used for LDH preparation. Increasingly stronger maximum allowable concentrations (MAC) of various contaminants in drinking water and liquid foodstuffs require regular upgrades of purification technologies, which might also be useful in the extraction of valuable substances for reuse in accordance with modern sustainability strategies. Adsorption is the main separation technology that allows the selective extraction of target substances from multicomponent solutions. Inorganic anion exchangers arrived in the water business relatively recently to achieve the newly approved standards for arsenic levels in drinking water. LDHs (or hydrotalcites, HTs) are theoretically the best anion exchangers due to their potential to host anions in their interlayer space, which increases their anion removal capacity considerably. This potential of the interlayer space to host additional amounts of target aqueous anions makes the LDHs superior to bulk anion exchanger. The other unique advantage of these layered materials is the flexibility of the chemical composition of the metal oxide-based layers and the interlayer anions. However, until now, this group of “classical” anion exchangers has not found its industrial application in adsorption and catalysis at the industrial scale. To accelerate application of LDHs in water treatment on the industrial scale, the authors critically reviewed recent scientific and technological knowledge on the properties and adsorptive removal of LDHs from water on the fundamental science level. This also includes review of the research tools useful to reveal the adsorption mechanism and the material properties beyond the nanoscale. Further, these properties are considered in association with the synthetic methods by which the LDHs were produced. Special attention is paid to the LDH properties that are particularly relevant to water treatment, such as exchangeability ease of the interlayer anions and the LDH stability at the solid-water interface. Notably, the LDH properties (e.g., rich speciation, hydration, and the exchangeability ease of the interlayer anions with aqueous anions) are considered in the synthetic strategy context applied to the material preparation. One such promising synthetic method has been developed by the authors who supported their opinions by the unpublished data in addition to reviewing the literature. The reviewing approach allowed for establishing regularities between the parameters: the LDH synthetic method―structure/surface/interlayer―removal―suitability for water treatment. Specifically, this approach allowed for a conclusion about either the unsuitability or promising potential of some synthetic methods (or the removal approaches) used for the preparation of LDHs for water purification at larger scales. The overall reviewing approach undertaken by the authors in this work mainly complements the other reviews on LDHs (published over the past seven to eight years) and for the first time compares the properties of these materials beyond the nanoscale.Display Omitted
Keywords: Layered double hydroxides; Adsorption; Synthesis; Inorganic anion exchangers; Water treatment;

Probing the threshold of membrane damage and cytotoxicity effects induced by silica nanoparticles in Escherichia coli bacteria by Marion Mathelié-Guinlet; Laure Béven; Fabien Moroté; Daniel Moynet; Christine Grauby-Heywang; Ibtissem Gammoudi; Marie-Hélène Delville; Touria Cohen-Bouhacina (81-91).
The engineering of nanomaterials, because of their specific properties, is increasingly being developed for commercial purposes over the past decades, to enhance diagnosis, cosmetics properties as well as sensing efficiency. However, the understanding of their fate and thus their interactions at the cellular level with bio-organisms remains elusive. Here, we investigate the size- and charge-dependence of the damages induced by silica nanoparticles (SiO2-NPs) on Gram-negative Escherichia coli bacteria. We show and quantify the existence of a NPs size threshold discriminating toxic and inert SiO2-NPs with a critical particle diameter (Φc) in the range 50nm–80nm. This particular threshold is identified at both the micrometer scale via viability tests through Colony Forming Units (CFU) counting, and the nanometer scale via atomic force microscopy (AFM). At this nanometer scale, AFM emphasizes the interaction between the cell membrane and SiO2-NPs from both topographic and mechanical points of view. For SiO2-NPs with Φ > Φc no change in E. coli morphology nor its outer membrane (OM) organization is observed unless the NPs are positively charged in which case reorganization and disruption of the OM are detected. Conversely, when Φ < Φc, E. coli exhibit unusual spherical shapes, partial collapse, even lysis, and OM reorganization.Display Omitted
Keywords: E. coli; Silica nanoparticles; Membrane; Toxicity; AFM;

The composition and physical-chemical properties of the milk fat globule membrane (MFGM) is a subject that has gained increased interest in the field of food colloids, mainly because the nutritional and technological value of the MFGM. In fact, related changes in integrity and structure during milk processing pose a huge challenge as far as efforts directed to isolate the components of the fat globule membrane. MFGM characteristics and potential utilization are subjects of dissension. Thus, the effects of processing and the colloidal interactions that exist with other milk constituents need to be better understood in order to exploit milk fat and MFGM, their functionality as colloids as well as those of their components. These are the main subjects of this review, which also reports on the results of recent inquiries into MFGM structure and colloidal behavior.Display Omitted
Keywords: Milk fat globule membrane (MFGM); Fat colloids; Protein-stabilized colloids; Adsorption; Glycoproteins; Colloidal stability;

On the cohesion of fluids and their adhesion to solids: Young's equation at the atomic scale by J.-C. Fernandez-Toledano; T.D. Blake; P. Lambert; J. De Coninck (102-107).
Using large-scale molecular dynamics simulations, we model a 9.2 nm liquid bridge between two solid plates having a regular hexagonal lattice and analyse the forces acting at the various interfaces for a range of liquid-solid interactions. Our objective is to study the mechanical equilibrium of the system, especially that at the three-phase contact line. We confirm previous MD studies that have shown that the internal pressure inside the liquid is given precisely by the Laplace contribution and that the solid exerts a global force at the contact line in agreement with Young's equation, validating it down to the nanometre scale, which we quantify. In addition, we confirm that the force exerted by the liquid on the solid has the expected normal component equal to γ lv  sin  θ 0, where γ lv is the surface tension of the liquid and θ 0 is the equilibrium contact angle measured on the scale of the meniscus. Recent thermodynamic arguments predict that the tangential force exerted by the liquid on the solid should be equal to the work of adhesion expressed as Wa 0  =  γ lv (1 + cos  θ 0). However, we find that this is true only when any layering of the liquid molecules close to liquid-solid interface is negligible. The force significantly exceeds this value when strong layering is present.Display Omitted
Keywords: Wetting; Adhesion; Three-phase contact zone; Liquid-solid interface; Molecular-dynamics;

Deposits and scales formed on heat transfer surfaces in power plant water/steam circuits have a significant negative impact on plant reliability, availability and performance, causing tremendous economic consequences and subsequent increases in electricity cost. Consequently, the improvement of the understanding of deposition mechanisms on power generating surfaces is defined as a high priority in the power industry. The deposits consist principally of iron oxides, which are steel corrosion products and usually present in colloidal form. Magnetite (Fe3O4) is the predominant and most abundant compound found in water/steam cycles of all types of power plants. The crucial factor that governs the deposition process and influences the deposition rate of magnetite is the electrostatic interaction between the metal wall surfaces and the suspended colloidal particles. However, there is scarcity of data on magnetite surface properties at elevated temperatures due to difficulties in their experimental measurement. In this paper a generalized overview of existing experimental data on surface characteristics of magnetite at high temperatures is presented with particular emphasis on possible application in the power industry. A thorough analysis of experimental techniques, mathematical models and results has been performed and directions for future investigations have been considered. The state-of-the-art assessment showed that for the characterization of magnetite/aqueous electrolyte solution interface at high temperatures acid-base potentiometric titrations and electrophoresis were the most beneficial and dependable techniques which yielded results up to 290 and 200 °C, respectively. Mass titrations provided data on magnetite surface charge up to 320 °C, however, this technique is highly sensitive to the minor concentrations of impurities present on the surface of particle. Generally, fairly good correlation between the isoelectric point (pHiep) and point of zero charge (pHpzc) values has been obtained. All obtained results showed that the surface of magnetite particles is negatively charged in typical high temperature thermal power plant water, which indicates the low probability of aggregation and deposition on plant metal surfaces. The results also gave strong evidence on decline of pHiep and pHpzc with temperature in the same manner as neutral pH of water. The thermodynamic parameters of magnetite surface protonation reactions were in good agreement with each other and obtained using one site/two pK and mainly one site/one pK model. All collected data provided evidences for interaction between particles, probability of deposition and eventual attachment to the steel surface at various pH and temperatures and can serve as a foundation for future surface studies aimed at optimizing plant performances and reducing of magnetite deposition. In future works it would be indispensable to provide the surface experimental data for extended temperature ranges, typical solution chemistries and metal surfaces of power plant structural components and thus obtain entire set of results useful in modeling the surface behavior and control of deposition process in power reactors and thermal plant circuits. Moreover, the acquired results will be applicable and greatly valuable to all other types of power plants, industrial facilities and technological processes using the high temperature water medium.Display Omitted
Keywords: Magnetite; Surface properties; High temperature; Deposits;