Formation Of Colloidal Particles Research Articles

Experimental Research on the Photodegradation of the Organic Compounds of Natural Waters

The photodegradation of organo-mineral complexes in natural conditions was studied using samples of soil and swamp waters to study the effect of sunlight on the composition and properties of organic matter and metal forms dissolved in natural waters. The total contents of certain aliphatic and aromatic carboxylic acids increased in the samples after irradiation. Photodegradation of organic matter of the natural waters with the high Fe content is accompanied by the formation of colloidal particles (Fe hydroxides). The number of negatively-charged complexes of Ni, Cu, Zn, and Cd increased under insolation in swamp waters and decreased in soil waters.

Experimental research of photodegradation processes of organic compounds of natural waters

In order to study the effect of sunlight on the composition and properties of dissolved organic matter and metal forms in natural waters, the process of photodegradation of organo-mineral complexes in field conditions with samples of soil and swamp waters was studied. Total content of certain aliphatic and aromatic carboxylic acids increased in the studied samples after irradiation. Photodegradation of organic matter of the natural waters that are rich in iron is accompanied by formation of colloidal particles (Fe hydroxides). The amount of negatively-charged complexes of Ni, Cu, Zn and Cd increases during the insolation in swamp waters and decreases in soil waters.

Flash nanoprecipitation of poly(styrene-co-acrylonitrile) colloids in the presence of hydrophobic organoplatinum and their derived Pt-carbon nanocomposites for oxygen reduction reaction

Herein, we present a flash nanoprecipitation process for one-step formation of soft colloidal particles, in which platinum (II) acetylacetonate is entrapped within poly(styrene-co-acrylonitrile) nanospheres. The protection of the polymer matrix in the flash nanoprecipitated composites would ensure that the monodisperse platinum nanoparticles are uniformly dispersed in the carbon matrix after carbonization. Electrochemical characterization shows that the obtained Pt-carbon nanocomposites (denoted as Pt@NC) exhibit a high catalytic performance and low polarization loss toward oxygen reduction reaction (ORR) in an alkaline electrolyte via a favorable four-electron pathway.

Constrained-volume assembly of organometal confined in polymer to fabricate multi-heteroatom doped carbon for oxygen reduction reaction

The design and preparation of non-precious metal and carbon-based nanocomposites are critical to the development of efficient catalysts for technologies ranging from water splitting to fuel cell. Here, we present a constrained-volume self-assembly process for the one-step continuous precipitation-induced formation of soft colloidal particles, in which hydrophobic organoferrous compound, (Ph3P)2Fe(CO)3, is encapsulated within poly(styrene-co-acrylonitrile) nanoparticles (NPs). The protective and confining polymer matrix ensures uniform carbonization and dispersion of (Ph3P)2Fe(CO)3 within a carbon matrix after a pyrolysis process. The obtained carbon NPs are successfully co-doped with Fe, P and N with a relatively high surface area of ~380 m2 g−1. The Fe-P-N-doped carbon catalyst exhibits high catalytic performance and stability toward oxygen reduction reaction in both alkaline and acidic electrolytes via a favorable four-electron pathway. Meanwhile, the catalytic capability of Fe-P-N-doped carbon can be tailored by the tunable nanostructures.

Preparation and Properties of Coir-Based Substrate Bonded by Modified Urea Formaldehyde Resins for Seedlings

In order to form a firm root plug for the mechanical transplantation, modified urea formaldehyde (UF) resins were applied to bond coir based substrate and form substrate blocks. The physical and chemical structure, thermal stability, and crystallinity of the substrate blocks before and after nursery seedlings were characterized. The results showed that the -NH2 and -OH in the substrate reacted with the modified UF resins to form macromolecular structures. There was almost no difference between the XRD spectra of substrate blocks before and after the growth of seedlings. The modified resins in the substrate block were cured in the form of colloidal particles. The substrate block contained 53.8 At% carbon, 15.0 At% nitrogen, and 23.5 At% oxygen. When compared with the original substrate, the height, stem diameter, root length, and leaf area of tomato seedlings grown in substrate block were improved by 56.1%, 43.3%, 1.3%, and 63.3%, respectively. The qualification percentage of the substrate block was 94.3%, which was well above that of the original substrate (83.4%) according to JB/T 10291 (2013) standards. The substrate block bonded by the modified UF resins was suitable for tomato seedlings growth.

Evaluation of Pazopanib Phase Behavior Following pH-Induced Supersaturation.

Salts of weakly basic active pharmaceutical ingredients are widely used to improve aqueous solubility and/or dissolution rate. However, these compounds are prone to precipitation due to the lower solubility of the un-ionized species at the higher pH in the intestinal region, and this can result in poor and/or variable absorption. The goal of this study was to investigate the degree of supersaturation achieved following dissolution of different amounts of pazopanib hydrochloride at low pH, followed by rapid pH increase. Using pH solubility profiles, phase boundaries were defined for crystalline and amorphous free base forms. The resultant phase diagram was used to rationalize the observed supersaturation and phase behavior of pazopanib following pH adjustment. In the presence of a crystallization inhibitor, hydroxypropylmethyl cellulose (HPMC), the degree of supersaturation was found to be very high, approximately 600-fold, at pH 6.5. At a dose equivalent to the clinical dose, the maximum free drug concentration observed at pH 6.5 was dictated by the amorphous solubility. Solutions that exceeded the amorphous solubility upon pH increase were found to undergo glass-liquid phase separations (GLPS) with the formation of amorphous colloidal drug-rich particles. Microscopic observations confirmed that HPMC delayed the appearance of pazopanib free base crystals. The phase behavior upon pH change is thus well predicted by the phase diagram, after taking into consideration the initial dose, the extent of supersaturation generated upon pH change, and the presence or absence of a crystallization inhibitor.

Techno-economic assessment for the large-scale production of colloidal lignin particles

Economical large-scale production of colloidal lignin particles.

Removal of macro-pollutants in oily wastewater obtained from soil remediation plant using electro-oxidation process.

Electro-oxidation process by niobium boron-doped diamond (Nb/BDD) electrode was used to treat non-biodegradable oily wastewater provided from soil leachate contaminated by hydrocarbons. Firstly, the diffusion current limit and mass transfer coefficient was experimentally measured (7.1mAcm-2 and 14.7μms-1, respectively), in order to understand minimum applied current density. Later on, the oxidation kinetic model of each pollutant was investigated in different current densities ranged between 3.8 and 61.5mAcm-2. It was observed that direct oxidation was the main removal mechanism of organic and inorganic carbon, while the indirect oxidation in higher current density was responsible for nitrogen oxidation. Hydrocarbon in the form of colloidal particles could be removed by electro-flotation. On the other hand, electro-decomposition on the surface of cathode and precipitation by hydroxyl ions were the utmost removal pathway of metals. According to the initial experiments, operating condition was further optimized by central composite design model in different current density, treatment time, and electrolyte addition, based on the best responses on the specific energy consumption (SEC), chemical oxygen demand (COD), and total organic carbon (TOC) removal efficiency. Unde r optimum operating condition (current density = 23.1mAcm-2, time = 120min, Ti/Pt as a cathode, and Nb/BDD as the anode), electro-oxidation showed the following removal efficiencies: COD (84.6%), TOC (68.2%), oil and grease (99%), color (87.9%), total alkalinity (92%), Ntot (18%), NH4+ (31%), Ca (66.4%), Fe (71.1%), Mg (41.4%), Mn (78.1%), Ptot (75%), S (67.1%), and Si (19.1%). Graphical abstract Environmental significance statement Soil treatment facilities are rapidly grown throughout the world, especially in North America due to its intense industrialization. High water content soil in humid area like Canada produces significant amount of leachate which is difficult to remove by physical and biological processes. Current treatment facility was modified by applying the electro-chemical oxidation process. The kinetic models of each macro-pollutant included carbon, nitrogen, phosphorous, and metals were developed to investigate their oxidation mechanism (graphical abstract). The efficiency of treatment was monitored in order to optimize the decisive operating parameters of electro-oxidation process. The result of this article could pave the way of future investigation on efficient treatment of variety of oily wastewater.

Effect of citrate on the species and levels of Al impurities in ferrihydrite

Ferrihydrite in natural environment is commonly produced in the presence of significant amounts of Al and low molar mass organic impurities, which affect the surface reactivity of ferrihydrite depending on the impurity levels. Here, we investigated the effect of citrate on the species and levels of Al impurities in ferrihydrite. Al-bearing ferrihydrite was synthesized at different citrate/(Fe+Al) and Al/(Fe+Al) molar ratios. The samples were then characterized by chemical analysis, TEM, XRD, XPS and FTIR. The results showed that citrate promoted the formation of stable colloidal ferrihydrite particles, and induced Al accumulation in colloidal fraction at the citrate/(Fe+Al) ratio of 25% as well as in the surface layer of ferrihydrite at the citrate/(Fe+Al) ratios of 25 and 50mol%. DFT analysis showed that Al-for-Fe substitution was closely related to the particular sites in ferrihydrite structure. We also estimated the mass of citrate (or aluminum citrate complexes) required to occupy the reactive sites on ferrihydrite nanoparticles. The results revealed that with increasing citrate content, the surface reactive sites favorable for Al-substitution of ferrihydrite became occupied by adsorbed citrate, which partially inhibited the substitution of Fe by Al but increased the adsorption of Al through Al-citrate surface complexation.

Formation of Polyelectrolyte Complex Colloid Particles between Chitosan and Pectin with Different Degree of Esterification

The effects of degree of esterification, pectin/chitosan ratio and pH on the formation of polyelectrolyte complex colloid particles between chitosan (CS) and pectin (PE) were investigated. Low methoxyl pectin (LPE) was achieved by de-esterifying high methoxyl pectin (HPE) with pectin methyl esterase. Turbidity titration and colorimetric method was used to determine the stability of complex colloid particles. The structure and morphology of complex particles were characterized by FTIR and TEM. When pectin solution was dropped into chitosan solution, complex colloidal dispersion was stable as PE/CS mass ratio was no more than 3:2. Colloidal particles of HPE-CS complex coagulated at larger ratio of PE/CS than LPE-CS. The maximum complex occurred at pH 6.1 for HPE-CS and pH 5.7 for LPE-CS, and decreasing pH leaded to the dissociation of complex particles. Electrostatic interactions between carboxyl groups on pectin and amino groups on chitosan were confirmed by FTIR. Colloidal particle sizes ranged from about 100 nm to 400 nm with spherical shape.

Silicification process in diatom algae using different silicon chemical sources: Colloidal silicic acid interactions at cell surface

The silicon transport and use inside cells are key processes for understanding how diatoms metabolize this element in the silica biogenic cycle in the ocean. A spin-probe electron paramagnetic resonance (EPR) study over time helped to investigate the interacting properties and the internalization mechanisms of silicic acid from different silicon sources into the cells. Diatom cells were grown in media containing biogenic amorphous substrates, such as diatomaceous earth and sponge spicules, and crystalline sodium metasilicate. It was found that the amorphous biogenic silicon slowed down the internalization process probably due to formation of colloidal particles at the cell surface after silicic acid condensation. Weaker interactions occurred with sponge spicules silicon source if compared to the other sources. The EPR results were explained by analyzing transcript level changes of silicon transporters (SITs) and silaffins (SILs) in synchronized Thalassiosira pseudonana cultures over time. The results indicated that the transport role of SITs is minor for silicic acid from both biogenic and crystalline substrates, and the role of SIT3 is linked to the transport of silicon inside the cells, mainly in the presence of sponge spicules. SIL3 transcripts were expressed in the presence of all silicon sources, while SIL1 transcripts only with sponge spicules. The data suggest that the transport of silicic acid from various silicon sources in diatoms is based on different physico-chemical interactions with the cell surface.

Mathematical modeling of concentration dependences of electric conductivity and diffusion permeability of anion-exchange membranes soaked in wine

The formation of organic colloidal particles in the pores and on the surface (fouling) of membranes used in the food industry is a significant constraint on the further development of membrane technology. A model to describe the effect of these particles on electric conductivity and diffusion permeability has been proposed. It is based on a microheterogeneous two-phase model constructed in terms of the concepts of nonequilibrium thermodynamics and effective medium theory. The model takes into account the presence of two phases: (i) the gel phase comprising a polymer matrix and fixed ions whose charge is compensated for by mobile ions and (ii) the electrically neutral solution filling the intergel spaces. Each of the phases is characterized by intrinsic thermodynamic and kinetic parameters. The model takes into account changes in the values of these parameters caused by the formation of organic nanoparticles in meso- and macropores (fouling). It is assumed that the formation of colloidal particles in the intergel solution leads to a decrease in the ion mobility. In addition, these particles are capable of deprotonating a portion of the fixed ions and thereby decreasing the exchange capacity of the membrane. A high degree of hydration of these particles is responsible for an increase in the volume fraction of intergel spaces. Selection of relevant model parameters provides good agreement between calculation and experimental results.

Relationships of formation and characteristics of colloidal particles in tin-containing organosols intended for activation of the surface of fibrous polyester materials

Formation of colloidal particles in tin-containing alcoholic solutions was studied in relation to the SnCl2 concentration, storage time, and kind of the solvent and stabilizing additive. The highest category of flame resistance and the highest resistance of the fireproofing coating to repeated launderings are reached when the poly(ethylene terephthalate) fabric is activated with alcoholic SnCl2 solutions with high concentration of 10–15-nm colloidal particles prior to application of an inorganic fireproofing compound.

Non-covalent assembly of poly(allylamine hydrochloride)/triethylamine microcapsules with ionic strength-responsiveness and auto-fluorescence

Ionic strength-responsive microcapsules with auto-fluorescence were fabricated by incubation of poly(allylamine hydrochloride) (PAH)-doped CaCO3 particles in triethylamine (Et3N), followed by core removal using HCl. Based on the combination of hydrophobic interaction and hydrogen bonding, PAH and Et3N formed a complex with a molar ratio of 3:1 (repeating unit of PAH: Et3N). The as-prepared capsules showed extraordinary stability against 1M HCl, 1M NaOH and 6M urea solutions, and could swell or shrink reversibly in response to the ionic strength. Furthermore, the capsules possessed auto-fluorescence, allowing easily tracking of capsules during applications. Such interaction may be expanded to formation of stimuli-responsive multilayer films and other colloidal particles.

Specific Ion Effects of Salt Solutions on Colloidal Properties of Octadecylamine Hydrochloride

AbstractFlotation continues to be a major technique for the production of potash from low grade, complex systems containing a variety of ores and ions. The specific ion effects on the behavior of the flotation collector in the KCl flotation system becomes important to the interpretation of the flotation mechanism. In this work, specific ion effects on the turbidity, surface tension and aggregation behavior of the common collector in KCl flotation, octadecylamine hydrochloride (ODA), have been investigated. The results from turbidity and surface tension studies of ODA solutions show that both cations and anions can affect the colloidal properties of ODA. Molecular dynamics simulations show that the binding that energy barrier between ODA headgroups and anions is principally responsible for the specific anion effect of γCAC of ODA solutions. In addition, the ion effect on the ODA aggregation particle size was also studied by using transmission electron micrographs (TEM) and dynamic light scattering. The data reveal that the presence of salt ions can induce the formation of larger ODA colloidal particles, on which the cation effect is more significant. This work provides detailed information of specific ion effect on colloidal properties of ODA, which may promote a further understanding of the flotation mechanism and help to improve the flotation of KCl from brine sources.

Destruction of humic substances by pulsed electrical discharge

Currently, the water recourses in the territory of Tomsk region are groundwater which is limited to the high concentration of iron and manganese ions and organic substances. These impurities present in water in different forms such as soluble salts ant the colloid forms. Therefore, the present work is a part of a continuations researcher of the processes in natural waters containing humic substances at the influence of pulsed electrical discharges in a layer of iron pellets. It is shown that the main stage of water purification process of humic substances during treatment by pulsed electric discharge in the layer of iron granules is a difficult process including several stages such as formation of iron oxyhydroxide colloid particles, sorption and coagulation with humic macromolecules substances, growth of particle dispersed phase and precipitation. The reason for the formation and coagulation of the dispersed phase is a different state of charge of the colloid particles (zeta potentials of (Fe (OH)3) is +8 mV, zeta potentials of (Humic substances) is -70 mV. The most intense permanganate oxidation reduction to the maximum permissible concentration occurs at the processing time equal to 10 seconds. The contact time of active erosion products with sodium humate is established and it equals to 1 hour. The value of permanganate oxidation achieves maximum permissible concentration during this time and iron concentration in solution achieves maximum permissible concentration after filtration.

Swelling-Induced Deformation of Spherical Latex Particles

Experimental evidence is presented showing that the direct formation of anisotropic colloidal polymer particles via aqueous heterophase polymerization is essentially controlled by the entropy gain of the linear fraction in the semi-interpenetrating network of the seed particles during swelling. Anisotropic particles are produced via photoinitiated polymerization, allowing swelling and polymerization to take place at the same temperature. These experiments prove that the temperature effect on rubber elasticity is, if at all, only of minor importance for the formation of anisotropic polymer particles. The major significance of swelling of the seed particles for the whole process is underlined by additional studies with optical microscopy and model simulations.

Experimental study on the kinetics of silica polymerization during cooling of the Bouillante geothermal fluid (Guadeloupe, French West Indies)

Despite many studies, our understanding of silica precipitation from natural waters remains limited, in particular for geothermal waters. Here we present a detailed study on the kinetics of silica polymerization as a function of fluid temperature and pH using high-temperature (250-260°C) seawater-derived geothermal fluids as those discharged from the Bouillante geothermal site. We monitored the on-site decrease in monomeric silica concentration (initial SiO2 concentration of about 600mgl−1) with time using the molybdenum blue spectrophotometric method on samples of separated water collected from the high-pressure separator at 167°C and cooled to 25, 50, 75, and 90°C and for pH values ranging from 5 to 8. During all these experiments, only silica polymerization was observed, with the formation of colloidal particles in suspension in the solutions. No scaling of amorphous silica was formed. The collected data were after modeled in order to determine the useful kinetic parameters for predicting and preventing amorphous silica precipitation in the production wells during fluid exploitation in the specific context of Bouillante. Results under the investigated experimental conditions show that the kinetics of silica precipitation is affected more strongly by pH than by temperature change. The reaction in the acidic Bouillante solution begins with a transition period that significantly decreases the kinetics of silica polymerization. Modeling the experimental data indicates that the silica polymerization up to the state of equilibrium is characterized by a 2nd-order kinetic law relative to dissolved silica; this could indicate that the polymerization is controlled mainly by the formation of dimers. However, the first hour of the experiments is better characterized by a 4th-order kinetic law, suggesting more complex polymerization reactions in the initial stage with the formation of nanocolloidal particles containing 3 to 4 monomers. In both cases, the corresponding kinetics rate constant k is linearly dependent on pH for pH between 5 and 7. The activation energy Ea for the overall reaction, calculated using the Arrhenius equation under the considered pH and temperature conditions, ranges between 41±9.8 and 54±9.6kJmol−1. To complete this work, the colloid particles formed at the end of the kinetics experiments were extracted and analyzed by SEM and TEM microscopy, X-ray Diffraction and the BET method. Results show that the size of the colloids increase and their specific surface decrease with increasing pH and are thus dependent on pH. Globally, our work provides a reliable database for understanding silica polymerization kinetics in natural geothermal brines or geologic waters characterized by a near neutral pH and moderate dissolved silica concentrations.

Photoinduced Formation of Colloidal Silver in Nitrocellulose Solutions Containing Titanium Alkoxides

The study shows the possibility of photo-induced reduction of silver nitrate and formation of stable colloidal silver particles in an isopropanol-N,N-dimethylacetamide solution of titanium alkoxide (polybutyl titanate) stabilized by nitrocellulose. It is established that titanium alkoxide and the products of its partial hydrolysis in the liquid composition play the role of a photocatalyst for the reduction of silver ions; the introduction of nitric or acetic acid additives to the composition significantly increases its photosensitivity. The films deposited from the liquid composition, previously irradiated with visible or UV light, consist of hydrated titanium dioxide and nitrocellulose with incorporated colloidal silver. Thermal treatment of the films at 150–245°C leads to the decomposition of nitrocellulose and an increase in the absorption by silver particles.

Soft Multifaced and Patchy Colloids by Constrained Volume Self-Assembly

Soft colloidal particles with multiple surface patches of differing composition are critical to the development of complex macroscopic structures that can serve as interfacial catalysts, macroscale surfactants, electronically responsive materials, and drug delivery vehicles. Here, we present a continuous process for the scalable formation of soft colloidal particles with multiple surface domains that employs well-established principles of polymer precipitation and phase separation to controllably shape particle architectures. Our results illustrate the broad range of particle morphologies, including Janus and Cerberus structures, and surface compositions accessible to our versatile solution-based assembly system. We also identify polymer diffusion, precipitation, and vitrification as the primary determinants of particle structure for the first time.