Colloid Concentration Research Articles

A new way to prepare gold nanoparticles by sputtering - Sterilization, stability and other properties.

We have developed a novel simple method for effective preparing gold nanoparticles (AuNPs) intended for utilization in biomedicine. The method is based on gold sputtering into liquid poly(ethylene glycol) (PEG). The PEG was used as a basic biocompatible stabilizer of the AuNP colloid. In addition, two naturally occurring polysaccharides - Chitosan (Ch) and Methylcellulose (MC) - were separately diluted into the PEG base with the aims to enhance the yield of the sputtering without changing the sputtering parameters, and to further improve the stability and the biocompatibility of the colloid. The colloids were sterilized by steam, and their stability was measured before and after the sterilization process by dynamic light scattering and UV-Vis spectrophotometry. The results indicated a higher sputtering yield in the colloids containing the polysaccharides. The colloids were also characterized by atomic absorption spectroscopy (AAS) to reveal the composition of the prepared nanoparticles by transmission electron microscopy (TEM) to visualize the nanoparticles and to evaluate their size and clustering, and by rheometry to estimate the viscosity of the colloids. The zeta-potential of the AuNPs was also determined as an important parameter indicating the stability and the biocompatibility of the colloid. In addition, in vitro tests of antimicrobial activity and cytotoxicity were carried out to estimate the biological activity and the biocompatibility of the colloids. Antimicrobial tests were performed by a drip test on two bacterial strains - Gram-positive Staphylococcus epidermidis and Gram-negative Escherichia coli. AuNP with chitosan proved to possess the highest antibacterial activity, especially towards the Gram-positive S. epidermidis. In vitro tests on eukaryotic cells, i.e. human osteoblastic cell line SAOS-2 and primary normal human dermal fibroblasts (NHDF), were performed after a 7-day cultivation to determine the effect and the toxic dose of the colloids on human cells. The studied colloid concentrations were in the range from 0.6 μg/ml to 6 μg/ml. Toxicity of the colloids started to reappear at a concentration of 4.5 μg/ml, especially with chitosan in the colloid, where the colloid with a concentration of 6 μg/ml proved to be the most toxic, especially towards the SAOS-2 cell line. However, the PEG and PEG-MC containing colloids proved to be relatively non-toxic, even at the highest concentration, but with a slowly decreasing tendency of the cell metabolic activity.

Micro-scale 2D quasi-nanosheets formed by 0D nanocrystals: from single to multicomponent building blocks

Self-assembly of colloidal nanocrystals (NCs) into large-scale superlattices with complex and controllable structures has attracted extensive attention due to their collective properties and promising device applications. Plasmonic NCs are very popular for long-range ordered superstructures by virtue of their collective nanogaps for electromagnetic field enhancement, in particular bulk-scale single-layer assembly. Large-area two-dimensional (2D) quasinanosheets (QNSs) composed of mono-component Au NCs or multi-component Au@ZnS core-shell hetero-nanocrystals (HNCs) were successfully prepared, via careful solvent evaporation-induced interfacial self-assembly. The entire self-assembly process was carried out on the liquid-air surface and mediated simply by tuning the operating temperatures and concentrations of the NCs. Specifically, monolayer and double-layer 2D QNSs in tens of micrometers scale with different stacking models were fabricated by precisely controlling the solvent evaporation rate and colloidal concentration.

SILVER NANOPARTICLES AND RESISTANCE INDUCERS IN THE CONTROL OF BANANA ANTHRACNOSIS

The search for techniques to control anthracnose (Colletotrichum musae) of lower toxicity to human health and environmental impact is essential for the development of a sustainable system in the banana production chain. Among these strategies, with great potential for use in agriculture and still lacking efficiency studies, silver nanoparticles (AgNPs) and resistance inducers stand out. Thus, the aim of this work was to evaluate the in vitro antifungal activity of AgNPs and resistance inducers in the control of post-harvest banana anthracnose. In in vitro experiment, the fungus was cultured in PDA culture medium added of different AgNP concentrations (0, 25, 50, 100 and 200 ppm) and resistance inducers (Bacillus subtilis, acibenzolar-S-methyl and Saccharomyces cerevisiae). The variable analyzed was mycelial growth inhibition (%), while in the post-harvest experiment, banana fruits were immersed for three minutes using the same treatments as the in vitro study. In this case, incidence (% of fruits with lesions) and severity (% of epidermis covered by lesions) were evaluated. Colloidal silver concentration at 100 ppm, as well as the resistance of Bacillus subtilis and acibenzolar-S-methyl inducers were the most efficient treatments in the control of post-harvest banana anthracnose caused by Colletotrichum musae.

Effect of bentonite particles’ presence on two-dimensional chromium transmission

The co-transport of pollutants with colloidal particles to lower depths of groundwater and porous environments has been demonstrated in many studies in recent three decades. Despite the numerous researches, all experimental and numerical studies of pollutant transfer in the presence of colloidal particles have been carried out in one dimension, which causes significant errors in this phenomenon. In this study, the two-dimensional transfer experiment of chromium in the presence of bentonite colloidal particles is done in saturated porous media. In order to conduct the experiment in two-dimensional conditions, the sampling was done in central and lateral of the last experiment column section. The results have been demonstrated that the transmission along the longitudinal direction is higher than lateral in the three tests of the transfer of chromium, bentonite, and chromium in the presence of bentonite colloidal particles at the beginning of the experiment, and due to completed mixing in the section, it reached to a constant value as lateral samples. While the presence of bentonite colloidal particles facilitates the transfer of chromium in both longitudinal and lateral directions, increasing the bentonite colloidal particle concentration causes more getting stuck of colloid particles between the sand grains and reduction of the chromium transfer in both longitudinal and lateral directions. So, it can be concluded that transfer in the lateral direction is lower in bentonite colloidal particles compared with chromium, and the reason is the bentonite colloidal particles getting stuck between sand grains, which is exacerbated by increasing the concentration of the bentonite. Also, due to the chromium co-transport with colloid particles in the fraction of chromium total transport, increasing the bentonite concentration causes decreasing the chromium lateral transfer.

New Generation of Antibacterial Products Based on Colloidal Silver.

The main objective of the present paper is the green synthesis of colloidal silver by ultrasonication starting from silver nitrate and using soluble starch as the reducing agent. Soluble starch has been used during synthesis because it is a cheap and environmentally friendly reactive. Silver colloid has been characterized by physicochemical methods: UV–VIS spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-Ray spectroscopy. This colloidal material was prepared in order to prove and establish its toxicity on heterotrophic bacteria. Toxicity tests were carried out using test cultures with and without silver colloid with different concentrations. This way was possible to establish the minimum silver concentration that presents a toxic effect against used bacteria. Quantitative evaluation of bacterial growth was performed by using the Most Probable Number method. By counting the bacterial colony number, the antibacterial effect was determined for colloidal silver deposited onto the cotton gauze by adsorption. During the present study, we optimized the adsorption specific parameters: solid:liquid ratio, temperature, contact time, colloidal silver concentration. By thermodynamic, equilibrium and kinetic studies, the adsorptive process mechanism was established.

Stable nano-silver colloid production via Laser Ablation Synthesis in Solution (LASiS) under laminar recirculatory flow

ABSTRACT As nanomaterials find applications in an increasingly diverse range of fields such as wastewater treatment, biotechnology and flexible electronics, the demand for nanomaterials with specific properties has increased. This increase is coupled with an increasing emphasis on nanomaterials with highly specific properties for specialised applications. Industrially, nanomaterials are produced via wet-chemical techniques which employ the use of solvents and reagents which are environmentally harmful. As we move forward with the use of nanomaterials, the ability to produce nanomaterials in a sustainable manner has become a topic of great significance. Towards this end, Laser Ablation Synthesis in Solution (LASiS) is a physical production technique capable of producing tailored nanomaterial colloids in a sustainable manner. These colloids are produced by ablating a solid target immersed in a solvent using a laser. Typically, LASiS is conducted in a batch process and in small volumes limiting commercial viability. To overcome this, there has been a move towards the use of continuous production via LASiS using flow systems. This allows an increase in nanomaterial yield, resulting in colloid concentrations approaching those of commercial colloids. This work investigates a new production technique incorporating a laminar recirculatory flow system to produce stable high concentration nano-silver colloids.

The role of particle size and molar ratio of Ca2+/Na+ in the retention and remobilization of colloids in saturated porous media

The paper examined the effects of colloid size and molar ratio of Ca2+/Na+ on the retention and release of colloids under transients in ionic strength (IS). Column experiments were conducted to elucidate the transport behavior of three-sized polystyrene latex microspheres (300 nm, 500 nm, and 1000 nm) by varied molar ratios of Ca2+/Na+. Colloid concentration breakthrough curves showed the retention of colloids enhanced with the increase of molar ratio and the decrease of colloid size, which can be explained by Derjaguin–Landau–Verwey–Overbeek theory and the existence of nanoscale surface roughness. When the IS of the eluting solution was reduced from 10 to 1 mM, and when the eluting solution changed to ultrapure water, peak concentrations of colloid release were observed. Colloid recovery rates during the injection of ultrapure water were low, and substantial proportion of colloid still retained in the column even after the injection of ultrapure water, which suggested a stronger influence caused by the primary minimum compared with the secondary minimum on the retention of colloid. A modified numerical model considering the processes of Langmuirian dynamics blocking associated with a conservative tracer equation was successfully developed to simulate the transport process of all the experiments.

Co-transport behavior of ammonium and colloids in saturated porous media under different hydrochemical conditions.

To investigate co-transport behavior of ammonium and colloids in saturated porous media under different hydrochemical conditions, NH4+ was selected as the target contaminant, and silicon and humic acid (HA) were selected as typical organic and inorganic colloids in groundwater. Column experiments were then conducted to investigate the transport of NH4+ colloids under various hydrochemical conditions. The results showed that because of the different properties of colloidal silicon and HA after combining with NH4+, the co-transport mechanism became significantly different. During transport by the NH4+-colloid system, colloidal silicon occupied the adsorption sites on the medium surface to promote the transport of NH4+, while humic acid (HA) increased the number of adsorption sites of the medium to hinder the transport of NH4+. The co-transport of NH4+ and colloids is closely related to hydrochemical conditions. In the presence of HA, competitive adsorption and morphological changes of HA caused NH4+ to be more likely to be transported at a higher ionic strength (IS = 0.05m, CaCl2) and alkalinity (pH = 9.3). In the presence of colloidal silicon, blocking action caused the facilitated transport to be dependent on higher ionic strength and acidity (pH = 4.5), causing the recovery of NH4+ to improve by 7.99%, 222.25% (stage 1), and 8.63%, respectively. Moreover, transport increases with the colloidal silicon concentrations of 20mg/L then declines at 40mg/L, demonstrating that increased concentrations will lead to blocking and particle aggregation, resulting in delayed release in the leaching stage. Graphical abstract.

Simultaneous measurement of refractive index, diameter and colloid concentration of a droplet using rainbow refractometry

In the present study, droplets of colloidal suspensions or emulsions are characterized using rainbow refractometry according to diameter, relative refractive index and concentration of the dispersed phase. The position and angular spacing of the rainbow are used to retrieve the relative refractive index and droplet size. For the measurement of colloid concentration, a novel method using the intensity ratio of the p = 2 (second-order refraction) and p = 0 (reflection) scattering components present in the rainbow signal is introduced. The experimental system, comprising a monodisperse droplet generation system and standard rainbow refractometry, has been used for validation of the technique. Distilled water mixed with monodisperse polystyrene nanoparticles at different volume concentrations (CV = 0 − 0.3%) were tested, providing ground truth values of concentration. The measured relative refractive index and droplet diameter agree well with results obtained using the extended effective medium approximation for turbid media and with the known experimental values. The measured highly sensitive relation found to exist between intensity ratio attenuation and colloid concentration is numerically verified using a Monte Carlo ray tracing method.

Optimization of Colloidal Chitin and Inoculum Concentration in Chitinase Production byStreptomycessp. PB2 Using Response Surface Methodology

Chitinase is an enzyme capable of catalyzing the hydrolysis of chitin. Bacteria is one of the sources for chitinase and the modification process of production are continously developed.Streptomycessp. is one of Actinomycetes group that shows high activity in hydrolyzing chitin. This study aimed to find the optimal conditions ofStreptomycessp. PB2 for producing chitinase at various colloidal chitin (0.5%, 1%, 1.5%) and inoculum (0.5%, 1%, 1.5%) concentration in the chitin broth medium using Respons Surface Methodology (RSM). The examined parameters included Total Plate Count (CFU/ml) and chitinase activity (U/ml). Chitinase activity was statistically analyzed by MiniTab 17 to obtain a mathematical model, then were validated. The mathematical model of chitinase activity was Y = -0.000075 + 0.00056 K + 0.00067 I, with the optimum colloidal chitin concentration (K) of 1.5% and inoculum concentration (I) of 1.5%. The highest chitinase activity of 0.0019 U/ml in day-2 fermentation. The validation test showed that the mathematical model had a low accuracy with the SSE value of 0.5306. This study shows that colloidal chitin and inoculum concentration are important factors to be optimized. However, further model is needed to be developed for a better estimation of process.

Photothermal structural modification of porous gold nanoshells via pulsed-laser irradiation: effects of laser wavelengths and surface conditions.

Pulsed lasers are promising candidates for fabricating plasmonic nanoparticles having unique structures, and there is a strong need for studies on the detailed effects of various experimental conditions on laser-induced fabrications. In this work, we demonstrate the effects of laser wavelengths and nanoparticle surface conditions, as well as laser fluences, in the structural modification of porous gold nanoshells induced by picosecond pulse irradiation. Laser wavelengths play a critical role in the modification because irradiating laser pulses excite not only porous gold nanoshells but also gold nanospheres, which have been produced via the melting of irradiated porous gold nanoshells. Significantly different localized surface plasmon resonances of gold nanospheres and porous gold nanoshells make the effect of laser wavelengths noticeable. The polyvinylpyrrolidone (PVP) concentration of colloid containing porous gold nanoshells also modifies the deformation of the structures. Gold nanostructures become positively charged by the irradiation, strengthening gold-PVP attraction. The stronger binding affinity of PVP is considered to reduce the deformation of irradiated porous gold nanoshells.

The effect of particle size and concentration on the ballistic resistance of different shear thickening fluids

Shear thickening fluids (STF) have the unique property of increased energy dissipation combined with increased elastic modulus making it ideal for shock absorption applications. The study investigates the effect of particle size and concentration of colloidal silica on the rheological parameters of STF. The particle size of colloidal silica ranged from 100 to 750 nm. Intended for the ballistic performance of STF, the present work also studies the ballistic performance of STF which is a suspension made up of silica of different colloidal particle concentrations in polyethylene glycol (PEG).

Effect of dispersion degree and colloidal suspension concentration on the coagulation process – a computer simulation

Effect of dispersion degree and colloidal suspension concentration on the coagulation process – a computer simulation

Transport behaviors of humic acid, kaolin and kaolin\u2013humic acid compound colloids on naphthalene in floating islands with biofilmed fillers

As one of the persistent organic pollutants, the investigations of naphthalene transports with humic acid, kaolin and kaolin–humic acid compound colloids by passing through the floating islands with biofilmed filler matrix pores were checked out. Naphthalene was easily captured onto the biofilmed fillers while it was passing through the floating islands with the filling percentages of 0.0 to 60.0 by absorbing bigger contaminated colloids, reflecting that the naphthalene concentrations in influents were, respectively, decreased from 200 to 57 μg L−1 for the humic acid colloids, to 32 μg L−1 for the kaolin colloids and to 13 μg L−1 for the kaolin–humic acid compound colloids. With the filling percentages of 60.0 to 80.0, the naphthalene concentrations in effluents were maintained at 57 ± 2 μg L−1 for the humic acid colloids, at 32 ± 3 μg L−1 for the kaolin colloids and at 13 ± 3 μg L−1 for the kaolin–humic acid compound colloids, respectively. The naphthalene distribution amounts on the biofilmed fillers were, respectively, from 213 to 96 ng m−1 for the humic acid colloids, from 274 to 96 ng m−1 for the kaolin colloids and from 340 to 83 ng m−1 for the kaolin–humic acid compound colloids. Thus, the biofilmed fillers in the floating islands could decrease the naphthalene concentrations by the captures of the humic acid, kaolin and kaolin–humic acid compound colloids to make the contaminated colloid concentrations reduced and promote the water qualities.

Quantification and molecular characterization of organo-mineral associations as influenced by redox oscillations

Organo-mineral association is one of the most important stabilization mechanisms of soil organic matter. However, few studies have been conducted to assess the retention, transformation, and transportation of colloids (1–1000 nm) and associated organic carbon (OC) in soil. Given the particularly significant role that wetland soils play in carbon storage and cycling, we quantified the dynamics of organo-mineral association within colloidal size range by conducting three consecutive 35-day redox (reduction-oxidation) oscillation experiments using a wetland soil. Molecular compositions of natural nanoparticle (NNP, 2.3–100 nm), fine colloid (100–450 nm), and particulate (450–1000 nm) fractions were measured using isotope ratio mass spectrometry (IRMS) and x-ray photoelectron spectroscopy (XPS). Results showed that NNP and fine colloids constituted up to 8.94 ± 0.50% and 22.19 ± 7.52% of bulk C concentration (2.3–1000 nm), respectively; indicating substantial contributions of these two fractions to the operationally defined “dissolved” (<450 nm) fraction. There was significant enrichment in heavier δ13C isotopes (p < 0.001) with size: NNP (−29.64 ± 0.32‰) < fine colloid (−28.81 ± 0.31‰) < particulate (−28.34 ± 0.25‰) fractions. NNP had the highest percentages of carbonyl/carboxyl C (C=O); while fine colloid and particulate fractions contained more reduced aromatic or aliphatic C (C–C, C=C, C–H). OC became more enriched (‰) in microbial-derived C (higher δ13C) with increasing particle size as well as with repeated redox oscillations. Our findings clearly demonstrate limitations of using the operationally defined “dissolved” fraction (<450 nm) to assess C cycling in ecosystems such as wetlands. Increase in colloid and OC concentrations and presence of more microbial-derived C in larger size fractions additionally imply that redox oscillations promote the formation of molecularly diverse sub-colloid sized organo-mineral associations. Being a composite unit of soil microaggregates, organic-mineral associations can thus influence the overall stability of OC in wetland soils that undergo frequent redox oscillations.

Parameter control and concentration analysis of graphene colloids prepared by electric spark discharge method

AbstractIn this study, graphene colloids were prepared using the electric spark discharge method (ESDM) with graphite rods (99.9% purity) in deionized water (DW) at a normal temperature and pressure. Five different types of graphene colloids were prepared using an electrical discharge machine (EDM) with five different pulse cycle switching times (Ton:Toff) = 10:10, 30:30, 50:50, 70:70, and 90:90 μs. According to the Ultraviolet-visible spectra (UV-Vis) and Zetasizer analysis, the results showed that the 10:10 μs parameter was the most suitable for the preparation of graphene colloids. UV-Vis was also used to detect the concentration of the graphene colloids; a comparison with a graphene oxide (GO) confirmed that this method could be used to calculate the discharge time needed to produce graphene colloids with different concentrations in the ESDM process.

Silica extraction from hydrothermal heat carrier by coagulation

We have carried out the experiments on coagulation and precipitation of silica from the separate of Verkhne-Mutnovsky geothermal electric power plant (Mutnovskoe hydrothermal field). Silica precipitation from the water solution was conducted in two ways: by adding slaked lime CaO and by electrocoagulation treatment on aluminium electrodes. Silica precipitation with addition of slaked lime was carried out under laboratory conditions at the temperature of 20 and 96 °C. Colloid and monomeric silica concentrations, solution pH, flakes sizes and physical-chemical properties of material precipitated with different quantities of added lime were determined. We also carried out series of experiments on solution treatment of mixed type: addition lime with freshly precipitated flakes, and addition lime with sea water. In the experiments on electric coagulation, current intensity and distance between electrodes were changed. Dependence of silica concentration on treatment duration was studied. Quantities of electric energy and anode aluminium consumed for reducing of silica concentration to a certain level were obtained. The results of our experiments can be used for developing of technological scheme of silica precipitation and utilization optimal for Verkhne-Mutnovsky geothermal electric power plant.

A statistical field theory of salt solutions of ‘hairy’ dielectric particles

In this paper, we formulate a field-theoretical model of dilute salt solutions of electrically neutral spherical colloid particles. Each colloid particle consists of a ‘central’ charge that is situated at the center and compensating peripheral charges (grafted to it) that are fixed or fluctuating relative to the central charge. In the framework of the random phase approximation, we obtain a general expression for electrostatic free energy of solution and analyze it for different limiting cases. In the limit of infinite number of peripheral charges, when they can be modelled as a continual charged cloud, we obtain an asymptotic behavior of the electrostatic potential of a point-like test charge in a salt colloid solution at long distances, demonstrating the crossover from its monotonic decrease to damped oscillations with a certain wavelength. We show that the obtained crossover is determined by certain Fisher–Widom line. For the same limiting case, we obtain an analytical expression for the electrostatic free energy of a salt-free solution. In the case of nonzero salt concentration, we obtain analytical relations for the electrostatic free energy in two limiting regimes. Namely, when the ionic concentration is much higher than the colloid concentration and the effective size of charge cloud is much bigger than the screening lengths that are attributed to the salt ions and the central charges of colloid particles. The proposed theory could be useful for theoretical description of the phase behavior of salt solutions of metal-organic complexes and polymeric stars.

Adsorption of bacteriophage MS2 to colloids: Kinetics and particle interactions

Virus adsorption to colloidal particles is an important issue in the water quality community. Namely, if viruses can quickly and strongly associate to colloids, this can potentially lead to significant implications for the management of biohazardous wastes at water reclamation facilities. This research evaluated the adsorption of bacteriophage MS2 to colloidal suspensions of kaolinite (KAO) and fiberglass (FG). Observed pseudo first-order MS2 removal rate constants were between 0.53 and 5.1 min−1 and between 2.4 and 3.5 min−1 for KAO and FG, respectively. These kinetics were at least an order of magnitude faster than previously reported values when compared to data retrieved at similar colloid concentrations. Fluorescent and bright field microscopic images showed clusters of MS2 on and around the edges of the colloids, and the majority of the bound MS2 was not readily removed during a vigorous wash step, suggesting comparatively strong, operationally relevant adsorption. MS2 aggregation was observed experimentally and predicted on the basis of interaction energies calculated with XDLVO models. When virus-containing biohazardous wastes are introduced into wastewater treatment plants, removing colloids is essential.

The electrochemical decoration of multi-walled carbon nanotubes with nickel oxide coating

In this paper, nickel coatings have been deposited on the multi-walled carbon nanotubes (MWCNT). In the first stage, MWCNT powder was ultra-wave mixed in the acid bath (H2SO4 and HNO3). The acid treating activates inert carbon surface introducing functional –OH and –COOH groups on the MWCNT surface. The mixture was diluted with distilled water and filtered for several times. The filtered sediment was dried in a plasma cleaner. The powder of such cleaned functionalized MWCNTs (fMWCNTs) was ultrasonicated with deionized water to produce stable colloid. Nickel atoms were injected into the colloid from a positive nickel electrode (with a negative graphite one). The Ni containing tubular nanostructures decorated the fMWCNTs at the specified regulated conditions (temperature, colloid concentration, electric current density). The electrochemically treated colloid was filtered and dried to a powder state (Ni-containing-fMWCNT powder). Hollow NiO nanotubes were produced by the annealing of the powder at 600°C (tubular nanostructured NiO powder). Both powders were examined by the Raman spectroscopy (RS), high-temperature X-ray diffraction (HTXRD), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The estimated high specific surface area of the nanostructured NiO powder is up to 97 m2/g at least and may be varied by time and the electric current of the electrochemical process.