Analysis of colloids released from bentonite and crushed rock

Factors influencing polycation/siRNA colloidal stability toward aerosol lung delivery

Microbial reduction of ferric iron is partly dependent on Fe hydroxide particle size: nanosized Fe hydroxides greatly exceed the bioavailability of their counterparts larger than 1μm. Citrate as a low molecular weight organic acid can likewise stabilize colloidal suspensions against aggregation by electrostatic repulsion but also increase Fe bioavailability by enhancing Fe hydroxide solubility. The aim of this study was to see whether adsorption of citrate onto surfaces of large ferrihydrite aggregates results in the formation of a stable colloidal suspension by electrostatic repulsion and how this effect influences microbial Fe reduction. Furthermore, we wanted to discriminate between citrate-mediated colloid stabilization out of larger aggregates and ferrihydrite dissolution and their influence on microbial Fe hydroxide reduction. Dissolution kinetics of ferrihydrite aggregates induced by different concentrations of citrate and humic acids were compared to microbial reduction kinetics with Geobacter sulfurreducens. Dynamic light scattering results showed the formation of a stable colloidal suspension and colloids with hydrodynamic diameters of 69 (±37) to 165 (± 65) nm for molar citrate:Fe ratios of 0.1 to 0.5 and partial dissolution of ferrihydrite at citrate:Fe ratios⩾0.1. No dissolution or colloid stabilization was detected in the presence of humic acids. Adsorption of citrate, necessary for dissolution, reversed the surface charge and led to electrostatic repulsion between sub-aggregates of ferrihydrite and colloid stabilization when the citrate:Fe ratio was above a critical value (⩽ 0.1). Lower ratios resulted in stronger ferrihydrite aggregation instead of formation of a stable colloidal suspension, owing to neutralization of the positive surface charge. At the same time, microbial ferrihydrite reduction increased from 0.029 to 0.184mMh−1 indicating that colloids stabilized by citrate addition enhanced microbial Fe reduction.Modelling of abiotic dissolution kinetics revealed that colloid stabilization was most pronounced at citrate:Fe ratios of 0.1 – 0.5, whereas higher ratios led to enhanced dissolution of both colloidal and larger aggregated fractions. Mathematical simulation of the microbial reduction kinetics under consideration of partial dissolution and colloid stabilization showed that the bioaccessibility increases in the order large aggregates<stable colloids<Fe-citrate.These findings indicate that much of the organic acid driven mobilization of Fe oxy(hydr)oxides is most likely due to colloid formation and stabilization rather than solubilisation.

The colloidal stability and photocatalysis of nano-TiO2 particles were investigated in the presence of fulvic acids (FA) and electrolytes (NaNO3, Na2SO4, Na3PO4) at different pH. Results showed that increasing FA concentration, the absolute value of zeta potential of nano-TiO2 increased and particle size decreased at all pH which promoted the colloidal stability of nano-TiO2. Particle size of nano-TiO2 was larger with the coexistence of FA and electrolytes than with FA only as the concentration of electrolytes was greater than or equal to 0.01 mol/L. The largest particle size occurred in the presence of Na3PO4, followed by Na2SO4 and NaNO3. Particle size of nano-TiO2 decreased with higher pH and stability further increased in the presence of FA and/or electrolytes. Nano-TiO2 stabilization was enhanced by increasing FA concentration when the solution pH was 7.0. However, the removal efficiency of atrazine by nano-TiO2 decreased with the increase in FA concentration. Adding electrolytes (0.01 mol/L), atrazine removal by nano-TiO2 further decreased, albeit slightly. The inhibitory effect of electrolytes on nano-TiO2 removal of atrazine was highest for Na3PO4, followed by Na2SO4, and NaNO3, which were consistent with the results of colloidal stability of nano-TiO2. These findings help to better understand the mechanisms and correlation between colloidal stability and photocatalysis of nano-TiO2 in the presence of FA and electrolytes.

Stability of GMZ bentonite colloids: Aggregation kinetic and reversibility study

Steric stabilisers govern the colloidal and chemical stability but not in vitro cellular toxicity of linoleoylethanolamide cubosomes

Different forces play key roles in the stability of food colloid dispersions. The focus here is on those controlling attraction and/or repulsion, which concur to stabilization, phase separation, coagulation and are quite evident in water-based systems. The combination of attractive and repulsive forces favors or hinders the association of colloid entities; such processes are often met in food technology. The above processes depend on the forces at work and colloid concentration in the medium (i.e., on interparticle distance). Worked examples deal with milk manipulation procedures, ending in cheese formation. The whole milk sequence is controlled by the combination of forces leading to aggregation and phase separation of casein and other milk components. Thereafter, one gets either fresh, for prompt consumption, or aged cheeses. The combination of attractive (van der Waals, vdW, and depletion) with repulsive (double layer, DL, but also steric) forces results in the dominance of aggregation versus dispersion modes in the milk transformation chain, which depends on the distance among colloid particles, on the amplitude of the mentioned forces, and on their decay. The combined role of double layer and van der Waals (vdW) forces is at the basis of the DLVO theory on colloid stability, which is properly modified when these forces overlap with steric stabilization and, eventually, with depletion. Steric effects are dispersive, and depletion ones favor colloid nucleation in a single phase. The milk manipulation chain is a worked example of the intriguing association features controlled by the mentioned forces (and of ancillary ones, as well), and indicates which forces favor the formation of products such as parmesan or mozzarella cheese but are not alien to the preparation of many other dairy products.

Release and sedimentation behaviors of biochar colloids in soil solutions

Improved magnetic induction heating of nanoferrites for hyperthermia applications: Correlation with colloidal stability and magneto-structural properties

Recent experimental work on well-defined colloids has shown that in certain systems, colloid stability increases, reaches a maximum and then decreases as the particle size increases. This finding, in apparent violation of D.L.V.O. theory predictions, is shown to be understood in terms of an energetic rather than a kinetic criterion of colloid stability. By incorporating both primary and secondary minima coagulation, and by the construction of coagulation domain diagrams, these "anomalous" particle size effects are shown to be in agreement with D.L.V.O. theory. The theory is applied to recent studies on monodisperse latex colloids of varying particle size.

Hematite (α-Fe2O3) nanomaterials, a stable phase of iron oxide, hold significant potential for diverse materials science and technology applications. In this study, red mud was employed as a low-cost precursor for synthesizing hematite nanomaterials, with ethylenediaminetetraacetic acid (EDTA) used as a capping agent to prevent particle agglomeration. The effect of EDTA on particle size and colloidal stability was investigated by comparing three synthesis variations: (a) without EDTA (NPH-1), (b) with EDTA via the precipitation method (NPH-2), and (c) with EDTA via the hydrothermal method (NPH-3). XRD analysis confirmed the formation of crystalline hematite (α-Fe2O3) in all samples. FT-IR spectroscopy revealed absorption bands at 1624 cm−1 and 1382 cm−1, corresponding to the symmetric and asymmetric stretching vibrations of the carboxylate (COO−) group, respectively. The difference in these wavenumbers suggests monodentate coordination between the carboxyl groups of EDTA and the hematite nanoparticle surfaces. Particle size analysis indicated that the EDTA-assisted synthesis via precipitation (NPH-2) produced the smallest average particle size (149.6 nm) with a narrow size distribution, as reflected by a polydispersity index (PDI) of 0.43. Furthermore, this sample demonstrated enhanced colloidal stability with a zeta potential of −34.0 mV. These findings suggest that the synthesized α-Fe2O3 nanomaterials produced with narrow particle size distribution and high colloidal stability, are promising for visible-light photocatalysis.

Applying iron (Fe) amendments to arsenic (As)-contaminated groundwater to form As-laden Fe precipitates represents a promising in situ remediation approach. However, less is known about the secondary risk of As mobilization due to formation of Fe-As colloids released from these precipitates. Here, we systematically explored the nanoscale formation, composition, and stability of Fe-As colloids in high-As contaminated groundwater following the addition of Fe salts under oxic conditions. Batch experiments show that total aqueous As is incorporated into settled particles upon adding Fe(II) and Fe(III). However, we also observe substantial release of Fe-As colloids (168-719 nm), which can remain stably suspended in water for more than 9 days. Higher colloid concentrations and stability occurred at lower molar Fe/As ratios (Fe/As < 5.8), suggesting that colloid-facilitated transport may dominate secondary As mobilization. Colloid characterization confirmed that low Fe/As ratios promote the formation of stable colloids enriched with surface-bound As, with electrostatic interactions stabilizing the colloids. Using advanced analytical and computational techniques, we elucidate the nanoscale structural properties of colloids, showing that As(V) inhibits Fe octahedral polymerization and favors the formation of smaller particles. These mechanistic insights are crucial for evaluating the long-term fate and transport of sequestered As and designing effective groundwater remediation strategies.

It is necessary to understand the cellular uptake and cytotoxicity of food-grade delivery systems, such as β-lactoglobulin (β-lg) nanoparticles, for the application of bioactive compounds to functional foods. The objectives of this study were to investigate the relationships between the physicochemical properties of β-lg nanoparticles, such as particle size and zeta-potential value, and their cellular uptakes and cytotoxicity in Caco-2 cells. Physicochemical properties of β-lg nanoparticles were evaluated using particle size analyzer. Flow cytometry and confocal laser scanning microscopy were used to investigate cellular uptake and cytotoxicity of β-lg nanoparticles. The β-lg nanoparticles with various particle sizes (98 to 192 nm) and zeta-potential values (−14.8 to −17.6 mV) were successfully formed. A decrease in heating temperature from 70°C to 60°C resulted in a decrease in the particle size and an increase in the zeta-potential value of β-lg nanoparticles. Non-cytotoxicity was observed in Caco-2 cells treated with β-lg nanoparticles. There was an increase in cellular uptake of β-lg nanoparticles with a decrease in particle size and an increase in zeta-potential value. Cellular uptake β-lg nanoparticles was negatively correlated with particle size and positively correlated with zeta-potential value. Therefore, these results suggest that the particle size and zeta-potential value of β-lg nanoparticles play an important role in the cellular uptake. The β-lg nanoparticles can be used as a delivery system in foods due to its high cellular uptake and non-cytotoxicity.

Surface chemical effects on colloid stability and transport through natural porous media

Multilayer assembled MFGM mimetics improve digestive fate of human milk structural lipids.

Microstructure and mechanical behavior of cemented gold/tungsten mine tailings-crushed rock backfill: Effects of rock gradation and content