Aqueous Nanoparticle Suspensions Research Articles

Quantum-Chemical and Experimental Study on the Interactions between the Magnetic Core and the Molecular Shell of Cobalt Ferrite Nanoparticles in Aqueous Suspensions

This article is focused on the theoretical and experimental study of the interactions between the perchlorate anions and the cations of cobalt ferrite magnetic nanoparticles prepared by a co-precipitation method. The magnetic nanoparticles with surface modified using perchloric acid were stabilized in aqueous dispersion based upon the predominant electric repulsive forces between the coated nanoparticles, balancing the magnetic dipole-dipole attraction. Quantum chemical modeling has revealed the physical-chemical properties of perchlorate anion (electric charges, dipole moment, and energies of frontier orbitals) that suggests the ability to interact with both nanoparticle metal cations and surrounding water molecules. Microstructural investigations by scanning electron microscopy, X-ray diffractometry, and vibrating sample magnetometry revealed crystallinity and granulation of the suspended ferrophase, thus confirming the adequate surface coating with perchlorate anions. The nanotoxicity study, carried out on agricultural plantlets in early ontogenetic stages has revealed differences in the photosynthesis pigment concentrations induced by the magnetic nanoparticle supply.

Incorporation of permethrin into chitosan polymeric nanoparticles using nanoprecipitation method for rubberwood preservation against termite attack

ABSTRACT Permethrin-loaded chitosan nanoparticle was successfully synthesised through the nanoprecipitation method. The hydrodynamic particle size and permethrin loading efficiency of the synthesised permethrin-chitosan nanoparticles were 199.7 ± 6.4 mm and 84.6 ± 2.20%, respectively. Hevea brasiliensis samples were then treated with 0.0025% w/v aqueous suspension of nanoparticles by vacuum pressure treatment. The optimisation studies proved that the pressure and duration of wood treatment with the permethrin-chitosan nanoparticles could be halved (100 psi and 60 min) as compared to the previously used standard condition (200 psi and 120 min). Results depict that the treatability and chemical retention achieved by the H. brasiliensis treated with permethrin-chitosan nanoparticles was 355.12 ± 9.50 L m−3 and 8.23 ± 1.23 kg m−3, respectively. Meanwhile, the weight loss of treated H. brasiliensis with permethrin-chitosan nanoparticles against subterranean termites; Coptotermes curvignathus reduced from 7.35 ± 0.080% to 1.20 ± 0.340%, whereas the visual rating increased from very severe attack to trace only (surface nibbles permitted). Findings from this study indicated that polymeric nanoparticles of chitosan could act as a carrier to deliver the permethrin into H. brasiliensis through water-based vacuum pressure treatment and also provide good protection against termites.

Лабораторный стенд на основе СКВИД-магнитометров для исследования магнитных свойств наноматериалов

The laboratory stand with the squid-based gradiometer was developed and tested in experimental studies of magnetic nanoparticles used in medicine. Two versions of the cryogenic probe were tested in investigations, the first of which included an additional XYZ squid-based magnetometer for "electronic" balancing of the input signal gradiometer in a uniform magnetic field. The second probe contained in its design movable trimmers with superconducting plates located in the area of the input loops of the gradiometer for its mechanical balancing. Both cryogenic probes demonstrated stable operation of the squid-based gradiometer at usual laboratory conditions without additional magnetic shielding. The stand was used to study the magnetization of aqueous suspensions of magnetite nanoparticles in various concentrations, which was induced using an uniform magnetic field with an amplitude of up to 15 milliTesla, created by a special system of Helmholtz coils at a frequency range of 4-12 Hz in the vertical and horizontal directions. The magnetic signals of nanoparticles were recorded using a second-order axial gradiometer in a «2:4:2» configuration with an input loop diameter of 8 mm and a base length of 29 mm. The experimental studies of the magnetization of aqueous suspensions of magnetite nanoparticles were aimed at estimating the limiting resolution of the SQUID gradiometer by the number of detected magnetic nanoparticles. The possibility of registering a magnetic signal from about 6 × 109 MNPs of magnetite 6 nm in size in a volume of 1 ml from a distance of about 20 mm from the receiving coils of the gradiometer was demonstrated. Dry liver extracts of small animals containing MNPs were also used as objects of study. Directions of further improvement the used instrumental elements and methods of magnetic measurements for increasing the sensitivity of squid-based gradiometers in experiments with MNPs are determined.

The Cavitation Activity of Aqueous Suspensions of Porous Silicon Nanoparticles with Different Degrees of Surface Hydrophobicity

The Cavitation Activity of Aqueous Suspensions of Porous Silicon Nanoparticles with Different Degrees of Surface Hydrophobicity

Oxidative Precipitation Synthesis of Calcium-Doped Manganese Ferrite Nanoparticles for Magnetic Hyperthermia.

Superparamagnetic nanoparticles are of high interest for therapeutic applications. In this work, nanoparticles of calcium-doped manganese ferrites (CaxMn1-xFe2O4) functionalized with citrate were synthesized through thermally assisted oxidative precipitation in aqueous media. The method provided well dispersed aqueous suspensions of nanoparticles through a one-pot synthesis, in which the temperature and Ca/Mn ratio were found to influence the particles microstructure and morphology. Consequently, changes were obtained in the optical and magnetic properties that were studied through UV-Vis absorption and SQUID, respectively. XRD and Raman spectroscopy studies were carried out to assess the microstructural changes associated with stoichiometry of the particles, and the stability in physiological pH was studied through DLS. The nanoparticles displayed high values of magnetization and heating efficiency for several alternating magnetic field conditions, compatible with biological applications. Hereby, the employed method provides a promising strategy for the development of particles with adequate properties for magnetic hyperthermia applications, such as drug delivery and cancer therapy.

Experimental study of a nanofluid-based photovoltaic/thermal collector equipped with a grooved helical microchannel heat sink

• Energetic and exergetic performances of a nanofluid-based PVT unit are assessed. • The unit is equipped with a grooved helical microchannel heat sink. • Aqueous suspension of magnetite nanoparticles is considered as coolant. • The Staggered PVT unit performs better that the parallel and plain PVT units. • Energetic and exergetic performance of units intensify with boosting Φ nf and M nf . Helical geometry is widely used in heat transfer systems due to the high heat transfer surface and the creation of swirling flow. Grooving the spiral channel can lead to the strengthening of these effects and improve the channel performance. In the present study, the energy and exergy performance of a nanofluid-based photovoltaic thermal unit equipped with a grooved helical microchannel heat sink is investigated experimentally. For this purpose, a plain helical microchannel heat sink, a parallel grooved helical microchannel heat sink and a staggered grooved helical microchannel heat sink are designed and fabricated. The employed nanofluid is the aqueous suspension of Fe 3 O 4 nanoadditives. The experiments were performed at different values of flow rates (20–80 kg/h) and nanoadditive concentrations (0.0–2.0 %). The highest thermal energy/exergy, electrical energy, and their corresponding efficiencies have been recorded at the mass flow rate of 80 kg/h and nanoadditive concentration of 2.0 %. It is seen that the overall energy efficiency of the staggered unit is 17.05 % and it is 6.96 % higher than the plain and parallel unit. Further, the staggered unit demonstrated the highest exergy efficiency (14.67 %) compared to other studied photovoltaic/thermal units.

Degradable Vinyl Copolymer Nanoparticles/Latexes by Aqueous Nitroxide-Mediated Polymerization-Induced Self-Assembly

The synthesis of degradable vinyl polymer nanoparticles/latexes in aqueous dispersed media is receiving much attention, particularly for biomedical applications and plastic pollution control, as it can circumvent the severe limitations associated with the emulsification of preformed degradable polymers. Polymerization-induced self-assembly (PISA), which enables the in situ formation of aqueous suspensions of diblock copolymer nano-objects of high solids content, has become a very popular polymerization process due to its many advantages in terms of simplicity, robustness, scalability, and versatility. However, the preparation of degradable vinyl polymer nanoparticles by direct aqueous PISA has never been reported. This severely limits the use of PISA in biomedical and environmental applications. Herein, we report the first aqueous emulsion PISA able to generate degradable vinyl polymer nanoparticles. It relies on radical ring-opening polymerization-induced self-assembly (rROPISA) of traditional vinyl monomers (n-butyl acrylate or styrene) with dibenzo[c,e]oxepane-5-thione (DOT), a thionolactone that features high stability in protic solvents and favorable reactivity with many vinyl monomers and is a precursor of labile thioester groups in the main chain. Stable aqueous suspensions of thioester-containing diblock copolymer nanoparticles were obtained with both vinyl monomers. Extensive degradation of the copolymers and the nanoparticles was successfully demonstrated under aminolytic or basic conditions. Given the success of the PISA process within the polymer community, this work has the potential to greatly expand its use in many areas, from nanomedicine (providing applicability to biocompatible vinyl polymers) to degradable coatings and sustained materials.

Effect of Magnetic Heating on Stability of Magnetic Colloids.

Stable aqueous suspension of magnetic nanoparticles is essential for effective magnetic hyperthermia and other applications of magnetic heating in an alternating magnetic field. However, the alternating magnetic field causes strong agglomeration of magnetic nanoparticles, and this can lead to undesirable phenomena that deteriorate the bulk magnetic properties of the material. It has been shown how this magnetic field influences the distribution of magnetic agglomerates in the suspension. When investigating the influence of the sonication treatment on magnetic colloids, it turned out that the hydrodynamic diameter as a function of sonication time appeared to have a power-law character. The effect of magnetic colloid ageing on magnetic heating was discussed as well. It was shown how properly applied ultrasonic treatment could significantly improve the stability of the colloid of magnetic nanoparticles, ultimately leading to an increase in heating efficiency. The optimal sonication time for the preparation of the magnetic suspension turned out to be time-limited, and increasing it did not improve the stability of the colloid. The obtained results are important for the development of new materials where magnetic colloids are used and in biomedical applications.

Synthesis and characterization of goethite (α-FeOOH) magnetic nanofluids

Magnetic nanofluids consisting of goethite nanoparticles in aqueous suspensions have been successfully synthesized using two sodium-free routes. Nanoparticle morphology, nanofluid stability and optical properties have been studied and compared with a goethite nanofluid whose nanoparticles are synthesized with a different protocol using NaOH. The synthesis procedure determines the nanoparticle size and morphology, which, in turn, is connected to optical properties and their sensitivity to external magnetic fields. The highest sensitivity is shown by the sample synthesized with NaOH, which is characterized by the largest nanoparticles (261±5 nm hydrodynamic size) and whose absolute transmittance values increase or decrease by about 11% and 20%, respectively, depending on to the mutual directions of magnetic field and electromagnetic wave polarization/wave vector, for an applied magnetic field of 5.60 mT. Nanoparticles in the fluid are therefore able to discriminate both the absolute value and the direction of the magnetic field and, moreover, being their response non-spectrally flat, specific spectral ranges exist where their response is maximized.

Thickening of aqueous nanoparticle suspension using DC electric field

It is challenging to thicken a well-dispersed nanoparticle suspension without changing the particle dispersion state. In our previous report, we demonstrated that several kinds of particles can be quickly settled from solutions by applying a DC electric field. Thus, we attempted to gravitationally thicken a well-dispersed aqueous nanoparticle suspension using a DC electric field instead of a flocculant. To increase the recovery ratio of nanoparticles, it is necessary to prevent particle deposition on the electrodes. Therefore, in this study, we investigated the effect of switching the direction of the DC electric field after certain intervals, and clarified the effect of the switching time on the concentration and particle size of the concentrated suspension. The concentration of an alumina nanoparticle suspension quickly increased by a factor of at least three by applying the DC electric field. In addition, the particle size measured by dynamic light scattering after the application of the DC electric field was almost the same as the nominal average particle size, suggesting that the particles in the aggregates did not overcome the potential barrier and redisperse when the field was removed. Therefore, the use of the DC electric field successfully thickened the aqueous nanoparticle suspension and the particles in the thickened suspension were well dispersed. The findings show that the proposed method has the potential to change material fabrication processes, enabling a dilute nanoparticle suspension prepared by synthesis to be easily and rapidly concentrated.

H2 production from the radiolysis of aqueous suspensions of ZnO nanoparticles by 5.5 MeV He2+ ions

The effects of ion beam irradiation on aqueous suspensions of metal oxides has received relatively little attention compared to γ-ray irradiation despite being a highly prevalent process in spent nuclear fuel storage and reprocessing. This is partly due to the difficulties associated with homogeneously irradiating condensed-phase matter using α-particles. Here, we report experimental yields of H2 from the 5.5 MeV He2+ ion irradiation of aqueous suspensions of ZnO nanoparticles. The obtained results are compared to our previously measured results for the γ-radiolysis of the same system. The amount of H2 increases linearly with adsorbed dose for all studied concentrations. The measured yields are of the same order of magnitude as those observed for pure water, but decrease with increasing water content. Overall, the yields follow a similar trend to those observed for γ-ray radiolysis.

Microwave-Assisted Synthesis of N/TiO2 Nanoparticles for Photocatalysis under Different Irradiation Spectra.

Nitrogen-doped TiO2 (N/TiO2) photocatalyst nanoparticles were derived by the environmentally friendly and cost-effective microwave-assisted synthesis method. The samples were prepared at different reaction parameters (temperature and time) and precursor ratio (amount of nitrogen source; urea). The obtained materials were characterized by X-ray diffraction (XRD), photoelectron spectroscopy (XPS), Raman spectroscopy (RS), infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Two cycles of optimizations were conducted to determine the best reaction temperature and time, as well as N content. The phase composition for all N/TiO2 nanomaterials was identified as photoactive anatase. The reaction temperature was found to be the most relevant parameter for the course of the structural evolution of the samples. The nitrogen content was the least relevant for the development of the particle morphology, but it was important for photocatalytic performance. The photocatalytic activity of N/TiO2 nanoparticle aqueous suspensions was evaluated by the degradation of antibiotic ciprofloxacin (CIP) under different irradiation spectra: ultraviolet A light (UVA), simulated solar light, and visible light. As expected, all prepared samples demonstrated efficient CIP degradation. For all irradiation sources, increasing synthesis temperature and increasing nitrogen content further improved the degradation efficiencies.

ZnS quantum dots as fluorescence sensor for quantitative detection of tetracycline

X–ZnS quantum dots (QDs) are synthesized in aqueous solution by a simple aqueous chemical route where X represents 3-mercaptopropionic acid (MPA) or 3-mercapto-1-propanesulfonic acid (MPS) which are two well-known low cost and stable ligands. The synthesized X–ZnS QDs yielded aqueous suspensions of nanoparticles with excellent monodispersity, water solubility and fluorescence stability with a relatively high fluorescence quantum yield of 11% and 10% for MPA-ZnS QDs and MPS-ZnS QDs respectively. Under optimal conditions, the prepared X–ZnS QDs are used to detect tetracycline (TC) based on their fluorescence quenching induced by the target analyte via electrostatic interaction. The Stern–Volmer-type equation has been fitted to the quenching curve of each QDs, from which MPA-ZnS QDs has shown a larger linear range and a lower limit of detection than MPS-ZnS QDs. The fluorescence response of MPA-ZnS QDs is linearly with respect to TC concentration over a wide range from 200 nM to 6000 nM with a detection limit of 30 pM. The combination of non-toxicity, simplicity and low cost together with high analytical performance of the proposed MPA-ZnS QDs make it promising for the determination of trace TC in food products of animal origin.

A Simple Route to Aqueous Suspensions of Degradable Copolymer Nanoparticles Based on Radical Ring-Opening Polymerization-Induced Self-Assembly (rROPISA)

A Simple Route to Aqueous Suspensions of Degradable Copolymer Nanoparticles Based on Radical Ring-Opening Polymerization-Induced Self-Assembly (rROPISA)

Synthesis of antibacterial polymer metal hybrids in irradiated poly‐1‐vinyl‐1,2,4‐triazole complexes with silver ions: pH tuning of nanoparticle sizes

AbstractPoly‐1‐vinyl‐1,2,4‐triazole (PVT)‐based materials with silver nanoparticles are promising antibacterial products. The metal nanoparticles with controllable sizes were obtained by radiation‐induced reduction of the dispersions of complexes of PVT with silver ions. Formation of the silver nanoparticles in aqueous suspensions irradiated at pH 6.0, 2.5, and 2.0 was studied using methods of UV–VIS spectroscopy and transmission electron microscopy. UV–VIS spectroscopy has detected a change in the efficiency of interaction between protonated or non‐protonated PVT units and the surface of silver nanoparticles. The interaction of macromolecules with the metal surface under different degrees of protonation of PVT functional groups afforded the nanoparticles with a narrow size distribution and an average size from 3 to 10 nm. An increase in the acidity also leads to a decrease in the ratio of the generation/growth of nanoparticles. The radiation approaches both provide the synthesis of the nanoparticles of controlled sizes and permits to obtain the nanocomposites containing no impurities of chemical reducing agents. The nanocomposites obtained exhibit high antibacterial activity against various bacterial strains, which depends on the size of silver nanoparticles.

Microliter-stirred sample setup for X-ray spectroscopy analysis of nanomaterials in suspension

Analysis of samples in the liquid environment using X-ray spectroscopy techniques is a very attractive approach as it provides specimen characterization in its native conditions thanks to the penetrating properties of X-rays. However, very often due to challenging synthesis procedures and the high cost of specimens it is difficult to obtain a sample in quantities for optimal measurement. Additionally, nanoparticles (NPs) aqueous suspensions are often not stable and undergo agglomeration and sedimentation processes that can be avoided either by sonication or sample stirring. Relatively small sample volumes and intrinsic agglomeration processes make X-ray spectroscopy measurements challenging especially when long periods are needed for the collection of high-quality data. To address both issues, we developed dedicated sample system that allows measurements down to few tens of μL of the liquid sample with capability of continuous stirring of the suspension. The X-ray spectroscopy measurements of ZnO nanoparticles suspension in water showed a stable signal for hours of acquisition time. On the other hand, in the absence of stirring, agglomeration and subsequent sedimentation processes were visible already within few minutes with maximum sedimentation rate of 2.5% of concentration loss in the beam field per minute.

Kinetic and thermodynamic control of tetraphenylethene aggregation‐induced emission behaviors

AbstractMany aggregation‐induced emission (AIE) systems exhibit broad and structureless luminescence emission spectra resembling the Gaussian distribution, which is likely due to kinetically locked molecular conformers in the condensed phase. To verify the hypothesis, a series of tetraphenylethene (TPE) derivatives are synthesized and characterized as aqueous nanoparticle suspensions. It is found that the unsubstituted TPE exhibits reduced fluorescence intensity accompanied by a blueshift of the emission maximum, after the temperature of the aqueous suspension is elevated and cooled to room temperature again. For a naphthalimide‐substituted TPE compound, thermal treatment of the AIE aqueous suspension results in complete, irreversible aggregation‐caused quenching (ACQ) of fluorescence, which can be restored by a redissolving‐precipitation process of thermally treated aggregates. The phenomenon is ascribed as a relative population shift of a kinetic AIE (k‐AIE) state to a thermodynamic AIE (t‐AIE) or ACQ state, evidenced by differential scanning calorimetry, dynamic light scattering, and scanning electron microscopy. The phenomenon may be universal for many other AIE systems and could be explored as stimuli‐responsive materials.

Porous Silicon Nanoparticles with Rare Earth as Potential Contrast Agents for MRI and Luminescent Probes for Bioimaging

Nanoparticles of porous silicon with incorporated europium and gadolinium ions were prepared by using mechanical grinding of electrochemically grown mesoporous silicon films followed with impregnation with rare earth ions from aqueous solutions. The photoluminescence spectroscopy of europium doped porous silicon nanoparticles allowed us to reveal narrow lines associated with the 5D0→7F4 transitions in Eu3+ ions. Measurements of the proton relaxation in aqueous suspensions of nanoparticles with embedded Gd3+ ions showed an effect of the shortening of both the longitudinal and transverse relaxation times. Potential applications of rare earth doped porous silicon nanoparticles as contrast agents in MRI and fluorescent labels in bioimaging are discussed.

Применение ультразвуковой обработки для повышения фотохимической активности электровзрывных бикомпонентных наночастиц TiO2-Ag

TiO2-Ag nanoparticles with thermal and chemical stability, wide band gap and low toxic are more used photocatalysts for decomposition of organic substances. However, high rate of recombination of electron-hole pairs and high energy of photoactivation significantly limit their usage. Modification of TiO2 with silver promotes surface separation of charges and increases their photochemical activity. In the present study for obtain TiO2-Ag bicomponent nanoparticles was use electric explosion of metal wires in atmosphere 85 vol.% Ar - 15 vol.% O2. This method has a high productivity (170-200 g/h) which is enough for industrial application of nanoparticles. However, electroexplosive nanoparticles are mostly agglomerates with a size of 200-500 nm, which significantly reduces their photochemical activity in the test reaction of decomposition of the model dye methylene blue under the visible light radiation. Ultrasonic treatment of nanoparticles in aqueous suspension for 15 min. contributed to an increase in the photoactivity of TiO2-Ag nanoparticles by 10%

Reaction of H2 with polyoxometalate supported Rhodium(0) and Iridium(0) nanoparticles in aqueous suspensions: a kinetic study

The mechanism of the reaction between Rh0 and Ir0 NPs with H2 was measured in the absence of an electrical bias via monitoring the catalytic reduction of PW12O403− and it was compared to the previous results of Pt0 NPs.