Particles In Aqueous Suspension Research Articles

Removal of Mn2+ from water by bentonite coated with immobilized thin layers of natural organic matter

A bentonite-based composite was synthesized by applying thin coatings of natural organic matter onto bentonite particles in aqueous suspension. Natural organic matter, mostly comprised of humic acids, was isolated from peat by alkaline extraction. It was insolubilized and immobilized on bentonite by heating at 350 °C in an inert nitrogen atmosphere. The composite obtained was then used to remove manganese from aqueous solutions. The results showed that manganese was removed significantly; the degree of removal was above 94% for initial concentrations of manganese from 0.250 to 10 mg/l. The effect of initial pH on manganese removal, dissolution of immobilized organic matter as well as the changes of pH and conductivity of water after treatment with composite were examined and explained.

Facile Access to Highly Fluorescent Nanofibers and Microcrystals via Reprecipitation of 2-Phenyl-benzoxazole Derivatives

2-Phenyl-benzoxazole and five derivatives bearing an alkyl or alkoxy substituent on the phenyl ring were used to prepare aqueous suspensions of particles via a solvent-exchange method. In these conditions, the methyl and methoxy derivatives spontaneously gave nanofibers, while the other compounds led to microcrystals. This shows that minor chemical changes are enough to direct the formation of a given type of particle. From a spectroscopic viewpoint, all compounds strongly emit blue light in the solid state, with spectra much broader than those registered in n-heptane and ethanol solutions. The photoluminescence quantum yields reached 38% and were slightly affected in aqueous suspension by the polarity of the environment. The molecular arrangement, deduced from X-ray analysis for the methyl and methoxy derivatives, was used to explain the fluorescence properties in the solid state. This work shows that 2-phenyl-benzoxazole derivatives are interesting candidates for applications as fluorescent nanomaterials, including in aqueous and biological media.

Synthesis of composite by application of mixed Fe, Mg (hydr)oxides coatings onto bentonite – A use for the removal of Pb(II) from water

The procedure for obtaining a bentonite based composite involves the application of mixed Fe and Mg hydroxides coatings onto bentonite particles in aqueous suspension and subsequent thermal treatment of the solid phase at 498 K. Structural and textural modifications of montmorillonite which occurred during the synthesis of composite were confirmed by XRD technique and N 2 adsorption at 77 K. The composite structure was found to be less ordered, while its specific surface area was about two times higher than the specific surface area of the starting/native bentonite. The effectiveness of the composite in Pb(II) removal from aqueous solutions at different initial concentrations, pH and ionic strengths of the solutions was examined. The equilibrium adsorption data were analyzed using three widely applied isotherms: Langmuir, Freundlich and Dubinin–Radushkevich. The composite effectively removes both ionic and colloidal forms of Pb(II) from water and the maximum adsorption capacity obtained from the Langmuir equation was 95.88 mg/g. The main mechanisms of Pb(II) removal at low pH values were ion-exchange and outer-sphere surface complexation.

Photocatalytic degradation of phenol on different phases of TiO2 particles in aqueous suspensions under UV irradiation

Photocatalytic degradation of phenol on different phases of TiO(2) particles was examined under 400-W UV irradiation. The effects of various operating parameters including TiO(2) dosage, solution pH (4-10), and initial phenol concentration (0.13-1.05mM) on phenol degradation were investigated. Three forms of TiO(2) photocatalysts such as pure anatase phase, pure rutile phase, and the mixed phase were prepared by sol-gel method and followed annealing at different temperatures. The annealing temperature used were 500°C, 700°C and 900°C for pure anatase phase, the mixed phase, and pure rutile phase, respectively. It was shown that pure anatase TiO(2) exhibited higher photocatalytic activity than the physical mixture of pure anatase and rutile TiO(2). Moreover, the TiO(2) particle with a specific fraction of mixed anatase and rutile phases exhibited better performance than pure anatase TiO(2). Finally, the degradation rate could be satisfactorily fitted by a pseudo-first-order kinetic model.

Role of the Polar Properties of Water in Separation Methods

The role of the polar properties of water in separation methods are presented in two parts: Part I: Properties of Water General principles are given of the three non-covalent energy types acting upon non-polar as well as polar entities when these are immersed in water: Lifshitz-van der Waals (LW), Lewis Acid-Base (AB) and Electrostatic (EL) energies. The dominant one of these three is the Lewis acid-base (AB) interaction, which in biochemical and other organic interactions are about an order of magnitude stronger than the van der Waals and electrostatic energies combined. Included are the most important equations, describing these interactions when occurring in water. Part II: Forces Originating in Water and their Significance in Separation Methods • Hydrophobic attraction between particles. • Hydrophobic interaction between solute molecules immersed in liquid water is caused by the hydrogen-bonding free energy of cohesion between the water molecules which surround these particles or solute molecules. • The solubility equation is given, which links the free energy of interaction, ΔGiwi, between the solute molecules (i) immersed in water (w), and the natural logarithm of the aqueous solubility (s) of i, expressed in mol fractions. Insolubility and partial solubility in water are due to strong mutual attraction and moderate attraction among molecules, respectively. Total solubility in water is due to mutual repulsion between solute molecules. • Discusses conditions of stability versus instability (flocculation) of aqueous particle suspensions. • Discusses the hyper-hydrophobicity of the water-air interface and its interactions with: A) small water-soluble molecules (it repels them) and: (B) amphiphilic molecules such as surfactants, alcohols, proteins, etc. (it strongly attracts them). • Treats adhesion and adsorption energies between two different entities, immersed in water, such as antigens and antibodies. These energies are commonly expressed as affinity constants (Kaff), the value of which is strongly influenced by the time spent during the initial adhesion or adsorption step, where the Kaff value steadily increases the longer that initial adsorption step lasts. This phenomenon is called hysteresis, or binding hysteresis. However the hysteresis effect can be avoided by reducing the initial exposure episode to time (t) approaching t = 0, to obtain Kaff t→0. • Two different aqueous phases can be formed by dissolving two different water-soluble polymers, e.g., poly-(ethylene oxide) and dextran, which repel one another in aqueous solution. Such aqueous two-phase systems can be used cause the preferential migration of two different solutes to two different phases and thus to effect their separation and purification. Results of a study of multiple sub-phases forming within the middle phase of micro-emulsions are also discussed. • Advancing freezing fronts are discussed in this Section, i.e., the rejection or engulfment of certain solutes or cells by a vertical ice column which is made to advance further vertically by continuing to cool it from below. • The size, or rather the radius of curvature (R) of blood cells, blood proteins, bacteria and viruses, can play an important role in, e.g., the in vivo phagocytic engulfment of bacteria by leucocytes, the transformation of platelets to become “sticky”, the attachment of viruses to cells and of bacteriophages to bacteria.

Densification, Phases, Microstructures and Mechanical Properties of Liquid Phase-Sintered SiC

This paper reports the influence of sintering additives (RE2O3, Al2O3RE2O3, RE = Yb, Y and Gd, 13 vol%) and mixing effect of 30 nm SiC powder with 800 nm SiC powder on phases of grain boundaries, grain size of SiC, fracture toughness and strength of SiC hot-pressed at 1950°C under 39 MPa of applied pressure. Rare earth ions were uniformly adsorbed on negatively charged SiC particles with 150 nm Al2O3 particles in aqueous suspensions at pH 5. A rapid densification of SiC with one component RE2O3 occurred above 1700°C when a liquid of SiO2 (formed on SiC particles)RE2O3 system was formed. The Al2O3RE2O3 additives lowered a liquid formation temperature to 14001500°C and enhanced the densification rate of SiC. An increased solubility of 30 nm SiC in a liquid during dissolution-precipitation process provided an amorphous phase of SiCSiO2Al2O3RE2O3 system at grain boundaries and suppressed the grain growth of SiC. The fracture toughness of dense SiC was dominated by the grain boundary thickness controlled by grain size of SiC and amount of oxide additives. Mixing of 30 nm SiC with 800 nm SiC improved greatly the strength of SiC with two component oxides and the mean flexural strengths reached 740810 MPa.

Physicochemical Characterization and In Vitro Hemolysis Evaluation of Silver Nanoparticles

Silver nanomaterials are increasingly being used as antimicrobial agents in medical devices. This study assessed the in vitro hemolytic potential of unbound silver particles in human blood to determine which physical and chemical particle properties contribute to mechanisms of red blood cell (RBC) damage. Four silver particle powders (two nano-sized and two micron-sized) were dispersed in water and characterized using transmission electron microscopy, dynamic light scattering, surface-enhanced Raman spectroscopy, and zeta potential measurement. Particle size and agglomeration were dependent on the suspension media. Under similar conditions to the hemolysis assay, with the particles added to phosphate buffered saline (PBS) and plasma, the size of the nanoparticles increased compared with particles suspended in water alone due to interaction with chloride ions and plasma proteins. To determine hemolysis response, aqueous particle suspensions were mixed with heparinized human blood diluted in PBS for 3.5 h at 37°C. Both nanoparticle preparations were significantly more hemolytic than micron-sized particles at equivalent mass concentrations > 220 μg/ml and at estimated surface area concentrations > 10 cm(2)/ml. The presence or absence of surface citrate on nanoparticles showed no significant difference in hemolysis. However, the aqueous nanoparticle preparations released significantly more silver ions than micron-sized particles, which correlated with increased hemolysis. Although significant size changes occurred to the silver particles due to interaction with media components, the higher level of in vitro hemolysis observed with nanoparticles compared with micron-sized particles may be related to their greater surface area, increased silver ion release, and direct interaction with RBCs.

Paramagnetic Properties of Size-Controlled Squid Ink Particles Dispersed in Water

The paramagnetic properties of size-controlled ink particles isolated from the ink sacs of squid were studied by electron spin resonance (ESR). ESR spectra of the large and small ink particles dispersed in water were successfully observed at room temperature. Both the ink particles in aqueous suspensions seemingly indicated similar ESR spectra consisting of a singlet with a slightly asymmetrical signal. The linewidth below saturation was almost the same in both the ink particles, but the linewidth of the small ink particle was obviously broadened with an increase in microwave power. On the other hand, the progressive microwave power saturation revealed a clear difference between the paramagnetic behaviors of the ink particles in aqueous suspensions and in solid states. In comparison with dehydrated samples, the ESR signals of the ink particles dispersed in water showed the inhomogeneous broadening and faster spin–lattice relaxation processes. The fundamental characteristics of size-controlled ink particles would serve as basic information for various applications.

Preservation of catechin antioxidant properties loaded in carbohydrate nanoparticles

Epigallocatechin gallate (EGCG), an antioxidant with several pharmacological and biological activities, was encapsulated in carbohydrate particles to preserve its antioxidant properties and improve its bioavailability. Gum arabic–maltodextrin particles loaded with EGCG (EGCG/P) were successfully produced by homogenization and spray-drying, with an EGCG loading efficiency of 96±3%. Spray-dried particles are spherical or corrugated and polydisperse with diameters less than 20μm. The particles in aqueous suspension revealed two main populations, with mean average diameters of 40nm and 400nm. Attenuated total reflection-infrared spectroscopy (ATR-IR) confirmed that EGCG was incorporated in the carbohydrate matrix by intermolecular interactions, maintaining its chemical integrity. Atomic force microscopy imaging proved the particle spherical shape and size. The present study demonstrates that the carbohydrate matrix is able to preserve EGCG antioxidant properties, as proof of concept to be used as polymeric drug carrier.

Aqueous Suspensions of Natural Swelling Clay Minerals. 1. Structure and Electrostatic Interactions

In this article, we present a general overview of the organization of colloidal charged clay particles in aqueous suspension by studying different natural samples with different structural charges and charge locations. Small-angle X-ray scattering experiments (SAXS) are first used to derive swelling laws that demonstrate the almost perfect exfoliation of clay sheets in suspension. Using a simple approach based on geometrical constraints, we show that these swelling laws can be fully modeled on the basis of morphological parameters only. The validity of this approach was further extended to other clay data from the literature, in particular, synthetic Laponite. For all of the investigated samples, experimental osmotic pressures can be properly described by a Poisson-Boltzmann approach for ionic strength up to 10(-3) M, which reveals that these systems are dominated by repulsive electrostatic interactions. However, a detailed analysis of the Poisson-Boltzmann treatment shows differences in the repulsive potential strength that are not directly linked to the structural charge of the minerals but rather to the charge location in the structure for tetrahedrally charged clays (beidellite and nontronites) undergoing stronger electrostatic repulsions than octahedrally charged samples (montmorillonites, laponite). Only minerals subjected to the strongest electrostatic repulsions present a true isotropic to nematic phase transition in their phase diagrams. The influence of ionic repulsions on the local order of clay platelets was then analyzed through a detailed investigation of the structure factors of the various clay samples. It appears that stronger electrostatic repulsions improve the liquidlike positional local order.

Spontaneous Formation of Fluorescent Nanofibers and Reticulated Solid from Berberine Palmitate: A New Example of Aggregation-Induced Emission Enhancement in Organic Ion Pairs

The salt formed between the large aromatic berberine cation and the long-chain palmitate anion was synthesized and used to prepare aqueous suspensions of particles owing to a solvent-exchange method. Under these conditions, elongated particles were readily obtained. They were studied by transmission microscopy with polarized light, as well as by fluorescence and electron microscopy. They were shown to be probably crystallized nanofibers, which were stable in suspension. Unexpectedly, upon filtration and drying, these fibers evolved to give a reticulated solid. The fluorescence properties of the compound were analyzed in solution, in aqueous suspension and in the powder crystalline state. Interestingly, berberine palmitate is virtually not fluorescent in aqueous solution because of the quenching effect of water, but transition to the solid state was accompanied by a strong increase in fluorescence intensity. This phenomenon was explained by the original molecular arrangement in the solid state. Actually, in the crystal, the anions form a distinct layer, which limits parallel-stacking of the fluorescent cations. Moreover, the berberine cations are protected from the access of water molecules, and so no quenching effect can take place. This example confirms that the newly introduced concept of ion-pair aggregation-induced fluorescence enhancement can be extended to a variety of structures. It also shows the interest of ion pairs for preparing fluorescent nanofibers and reticulated solids using a solvent-exchange method that is particularly easy to implement.

Adsorção do corante azul de metileno em partículas de argilominerais: análise dos tamanhos das partículas

Interactions of cationic dye methylene blue (MB) with clay particles in aqueous suspension have been extensively studied. As already known, the number of natural negative charges on the clay modifies significantly the particle sizes dispersed in water and therefore the nature of the interaction with the dye. This work evaluated with UV-Vis spectroscopy method how the clay particle sizes weighted on the adsorption and rearrangement of the dye molecules in aqueous system. The results obtained from light-scattering measurements confirmed that larger particles are found in suspensions containing the high-charged clays as the visible absorption band related to the MB aggregates (570 nm) on these suspensions prevailed.

Use of tunable nanopore blockade rates to investigate colloidal dispersions

Tunable nanopores fabricated in elastomeric membranes have been used to study thedependence of ionic current blockade rate on the concentration and electrophoretic mobilityof particles in aqueous suspensions. A range of nanoparticle sizes, materials and surfacefunctionalities has been tested. Using pressure-driven flow through a pore, the blockaderate for 100 nm carboxylated polystyrene particles was found to be linearly proportional toboth transmembrane pressure (between 0 and 1.8 kPa) and particle concentration (between7 × 108 and4.5 × 1010 ml − 1). This result can be accurately modelled using Nernst–Planck transport theory, enablingmeasurement of particle concentrations. Using only an applied potential across a pore, theblockade rates for carboxylic acid and amine coated 500 and 200 nm silica particles werefound to correspond to changes in their mobility as a function of the solutionpH. Scanning electron microscopy and confocal microscopy have been used tovisualize changes in the tunable nanopore geometry in three dimensions as a functionof applied mechanical strain. The pores were conical in shape, and changes inpore size were consistent with ionic current measurements. A zone of inelasticdeformation adjacent to the pore has been identified as important in the tuning process.

Contact angle and adsorption behavior of carboxylic acids on α-Al2O3 surfaces

The hydrophilic character of aluminum oxide surfaces may be altered through coating such surfaces with carboxylic acids. The initially hydrophilic nature of the solid substrate changes towards a less hydrophilic character as the bulk concentration and the chain length of the acids increases. The acids employed in this work (propionic, valeric and enanthic) show a certain affinity to the liquid-gas, solid-liquid and solid-gas interfaces, being the relative adsorption on them competitive. The adsorption behavior of these carboxylic acids is experimentally investigated combining pendant drop tensiometry, contact angle measurements on α-Al(2)O(3) polycrystalline ceramics and adsorption on particles in aqueous suspensions, as a function of the hydrocarbon chain length of the acids and their bulk concentration, at pH equal to the acids' pKa. The hydrophilic character of the coated alumina decreases with the acids concentration upon a certain concentration beyond that, it increases. The minimum of hydrophilicity is reached right before bi-layer arrangements on the adsorption pattern of the acids on the solid substrates take place.

The hybrid process TiO2/PAC: performance of membrane filtration

In investigations concerning the photocatalytic degradation by TiO(2) usually filter discs with a pore size of 0.22 mum and 0.45 mum are used for the removal of photocatalyst particles in aqueous suspensions. In this study the effective rejection of suspended particles by microfiltration in different types of membrane modules and with different membrane materials was investigated. Furthermore, Powdered Activated Carbon (PAC), which can be used to gain an increase in photocatalytic degradation rates, was investigated concerning its influence on the membrane performance. It is shown that by membrane filtration with a pore size above 0.1 mum, irrespective of the experimental conditions, no complete removal can be achieved. However, UV irradiation was found to improve the removal efficiency for all types of tested membrane materials. The addition of PAC also led to a higher performance of membrane filtration with regard to particle rejection. In long-term experiments with a hollow fibre membrane module in the presence of PAC a five-fold decrease of TiO(2) particles in the permeate could be proven. Besides, it was shown that added PAC can shield the membrane regarding the abrasivity of TiO(2), which could otherwise lead to the destruction of the membrane. Therewith PAC exhibits another crucial advantage besides its synergetic effect in photodegradation.

Spectroscopic Analysis of Poly (Methacrylic Acid-co-Ethylene Glycol Dimethacrylate) Submicron Particles by Fluorescence Emission and Light Scattering upon Binding with 17β-Estradiol in Water Treatment

An investigation of light scattering of non-imprinted poly methacrylic acid-co-ethylene glycol dimethacrylate (PMAA-co-EGDMA) submicron particles (300±5 nm) in aqueous suspension before and after 17β-estradiol (E2) binding was conducted by using a spectrofluorimeter. An optimal excitation wavelength to determine Mie scattering from these submicron particles was 725±1 nm for the highest intensity. This light scattering from non-imprinted polymer (NIP) sub- micron particles in aqueous suspension was increased by spiking E2 at various concentrations (from 0.1 to 1.0 ppm). Thus, a new alternative method was found to determine E2 in a water sample by measurement of light scattering from NIP particles using spectrofluorimetry. Furthermore, the light scattering at 725 nm from E2 solution was increased by spiking NIP particles at various concentrations (from 0.02 to 0.12 ppm) but the fluorescence emission essentially stayed constant. The fluorescence emission from E2, however, increased more significantly in the presence of NIP particles than E2 spiking into water alone.

Oriented Aggregation: Formation and Transformation of Mesocrystal Intermediates Revealed

Oriented aggregation is a special case of aggregation in which nanocrystals self-assemble and form new secondary single crystals. This process has been suggested to proceed via an intermediate state known as the mesocrystal, in which the nanocrystals have parallel crystallographic alignment but are spatially separated. We present the first direct observations of mesocrystals with size and shape similar to product oriented aggregates by employing cryo-TEM to directly image the particles in aqueous suspension. The cryo-TEM images reveal that mesocrystals not only form but also transform to the final single crystal product while in the dispersed state. Further, high-resolution cryo-TEM images demonstrate that the mesocrystals are composed of spatially separated and crystallographically aligned nanocrystals.

Role of Sodium Hexametaphosphate in the Flotation of Acanthite Fines from Finely Disseminated Ores

The improvement of the flotation of acanthite fines from a finely disseminated ore through the addition of sodium hexametaphosphate (SHMP) as the dispersant has been studied in this work. This study was carried out on the silver scavenger concentrate from the Fresnillo concentration plant in Mexico. The experimental results have shown that the dispersion processing by adding SHMP as the dispersant greatly increased the separation efficiency and the flotation rate of acanthite fines from the ore. This increase was much more remarkable for smaller mineral particles. It has been found that the improvement might be attributed to the fact that SHMP increased simultaneously the electric double layer repulsion and steric repulsion between minerals (valuable and gangue) particles in aqueous suspensions upon the adsorption of polymetaphosphate anions on the mineral surfaces, and thus eliminated the hetero-coagulation of the fine mineral particles in the aqueous ore suspension.

Molecular Structures of Citrate and Tricarballylate Adsorbed on α-FeOOH Particles in Aqueous Suspensions

In this work, the adsorption of citric (2-hydroxypropane-1,2,3-tricarboxylic acid) and tricarballylic (propane-1,2,3-tricarboxylic acid) acids onto alpha-FeOOH (goethite) in aqueous suspensions was studied as a function of pH and total ligand concentration in 0.1 M NaCl at 25.0 degrees C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The adsorption experiments were carried out as a series of batch experiments, and a newly developed simultaneous infrared and potentiometric titration technique was used to collect in situ infrared spectra with high signal-to-noise ratios. The high quality of the infrared spectra allowed analysis by means of two-dimensional correlation spectroscopy formalism that aided the resolution of pH-dependent spectral features. This has enabled the detection of two previously unidentified citrate-goethite surface complexes: one protonated species at low pH, and one inner sphere complex prevailing at high pH and coordinated via a combination of hydroxyl and carboxylate groups. In addition, an inner sphere complex involving only carboxylate coordination predominating at low pH and an outer sphere complex existing in the circumneutral pH region were identified. The behavior of tricarballylate parallels that of citrate, except no inner sphere surface complex is formed at high pH values, which is in accordance with the lack of an alpha-hydroxyl group. The comparison between citrate and tricarballylate reinforces previous observations showing that inner sphere surface complexes of pure carboxylates at water-iron oxide interfaces are suppressed at high pH values, where outer sphere species are relatively more predominant. It also shows that significant amounts of inner sphere surface complexes of carboxylates only seem to form in the basic pH region when the ligands contain complementary functional groups, such as the hydroxyl or amine groups.

Deflocculation and Classification of Electric Arc Furnace Dust in Aqueous Solution

Electric arc furnace (EAF) flue dust is generated during EAF steelmaking from iron-containing scrap such as recycled automobile bodies. The relatively high level of Zn (20–30 wt%) in EAF dusts provides a potentially valuable resource, even though the zinc is present as oxide phases such as zincite (ZnO) and zinc ferrite (ZnFe2O4). In this work, a method to deflocculate and disperse ZnO and ZnFe2O4 particles in aqueous suspension of EAF dust is developed and the efficiency of Zn recovery by the classification method was evaluated. Major findings of this study indicate that citric acid, a tetradendate chelating agent, demonstrates the best liberation and dispersion efficiency for EAF dust. Elutriating at 0.01 cm/min fluid velocity we recover 10 wt% of EAF dust (mostly ZnO particles) at a grad of 70 wt% Zn from a well-liberated and dispersed suspension of EAF dust. About 30 wt% of Zn recovery may be achieved using only simple classification.