Stable Aqueous Suspensions Research Articles

Production of Cellulose Nanocrystals Suspension with High Yields from Water Hyacinth

ABSTRACT Acid hydrolysis is commonly used to extract cellulose nanocrystals (CNC) from natural fibers. This research thus investigates the effect of hydrolysis temperatures and time on the yields of CNC from water hyacinth. The aim is to determine the optimal acid hydrolysis condition for water hyacinth fiber that effectively enhances the CNC yield. The acid hydrolysis temperatures were varied between 50 and 60°C and the hydrolysis time between 15, 30, 60, and 120 min. Prior to the hydrolysis, raw water hyacinth fiber was treated with alkaline and bleached by hydrogen peroxide. The results showed that the optimal hydrolysis condition was 60°C and 30 min, with the crystallinity index of 80%, the crystalline size of 3.91 nm, and the CNC yield of 71.5%. The transmission electron microscopy morphology of CNC from water hyacinth was of whisker shape, with the diameter and length of 10 nm and 200–500 nm. The results also indicated that, unlike the hydrolysis time, the hydrolysis temperature had a negligible effect on the crystallinity index. Besides, under the optimal hydrolysis condition, CNC was of stable aqueous suspension with a zeta potential of −43.21 mV, indicating high physical colloidal stability.

Optimization of Betulin Colloidal Aqueous Suspension Pretreatment for Determination of Particle Characteristics

Dynamic light scattering (DLS) is a well-established technique to analyze particle size in a liquid medium and sample preparation is an essential step of the analysis to obtain reliable data. In this study, the pretreatment of an aqueous suspension containing betulin particles was studied to characterize the colloidal betulin particles in supramolecular hydrogels obtained by the liquid antisolvent precipitation from purified and unpurified betulin samples. Parameters of two-step homogenization process using rotor and ultrasonic homogenizer, particle concentration, and pH were systematically varied to obtain stable aqueous suspensions that meet the requirements of DLS technique for good particle size analysis. It was found that the purified betulin particles have a higher tendency to agglomerate and their suspension is stable in a narrower concentration and pH range than unpurified. Particle size analysis in suspensions prepared independently shows good reproducibility of sample preparation.

Effect of hydrolysis time, pH and surfactant type on stability of hydrochloric acid hydrolyzed nanocellulose

Nanocelluloses are the subject of much interest on the account of their mechanical properties, high surface area, porosity, etc. Typically, sulfuric acid is used to produce cellulose nanocrystals with high aspect ratio and dispersibility in water suspensions. However, hydrolysis in sulfuric acid leads to cellulose esterification, which has some drawbacks such as lower thermal stability of nanocellulose. Hydrochloric acid does not cause functionalization of the nanocellulose surface, yet yields in poor colloidal stability in aqueous solutions due to the lack of ionic interactions between CNC/CNF and water molecules. Therefore, it should be possible to tune the colloidal stability of nanocellulose aqueous suspensions by modifying the properties of the solution (such as pH and/or the presence of surfactants). In this work, we attempted to obtain stable aqueous CNF suspensions via hydrochloric acid hydrolysis. Hydrolysis was performed at three time intervals, at 60 °C temperature and 6 mol/dm3 of hydrochloric acid. To find the optimum stabilizing conditions, the effect of different pH values and various surfactants on CNF stability was explored. The best stabilizing effect was observed at pH range 5–9 and in nonionic surfactant. The obtained products were characterized by using spectroscopic (FTIR), microscopic (AFM), thermogravimetric and X-ray diffraction techniques.

Comparison of physicochemical and functional properties of elemental sulfur, sulfur nanoparticles, and sulfur quantum dots for sustainable biological applications

Elemental sulfur (ES) and sulfur nanoparticles (SNPs) have been widely used as antibacterial ingredients, especially in dermatological formulations. However, their use in biological systems is greatly limited because of their inability to form hydrophilic and stable aqueous suspensions. On the other hand, sulfur quantum dots (SQDs) are surface-passivated nano-sulfur particles with less than 10 nm, are hydrophilic, and exhibit superior biological activity to ES or SNPs. It is also a sustainable material produced from sublimated sulfur, obtained as a by-product in huge quantities from petroleum refineries. However, systematic comparisons of these sulfur particles' physicochemical and functional properties have not yet been performed, resulting in knowledge gaps. The present work has characterized and compared the physicochemical and functional properties of ES, SNPs, and SQDs. SQDs had the highest zeta potential (−11.9 mV) of these three sulfur forms and were most stable in aqueous suspension. Surface-passivated SQDs with polyethylene glycol were more biologically compatible without cytotoxicity to L929 mouse fibroblasts. Unlike ES or SNPs, SQDs showed high antioxidant activity, showing 100% oxidative free radical scavenging activity in an aqueous medium. In addition, SQDs showed potent antibacterial activity against pathogenic bacteria such as Listeria monocytogenes and Escherichia coli and the fungal strains such as Penicillium chrysogenum and Aspergillus niger. With its aqueous stability and diverse biological activities, SQDs are expected to have tremendous potential as multifunctional components in various biological and related applications such as biomedical engineering and food packaging.

PREPARATION OF NANOCRYSTALS AND CHITIN MICROFIBRILS

Chitin nanocrystals and microfibrils were prepared based on the strong acid hydrolysis method. The change in the molecular structure was studied by Fourier-transform infrared and Raman spectroscopy. The surface morphology of chitin materials was observed using scanning electron and optical microscopy. The separation of nano-crystals and microfibril crystalline regions from native chitin may increase the scope of its application for the creation of bioactive composites and scaffolds for tissue culture. As a result of the conducted experimental work, it was possible to loosen the amorphous areas and partially separate nano-crystals and chitin microfibrils. Stable aqueous suspensions of chitin nano-crystals and microfibrils were obtained, which can be used for further experimental work.

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.

Null-thermal expansion coefficient LAS-nSiC composite by slip-casting

In the present work, lithium aluminosilicate (LAS) reinforced with SiC nanoparticles (nSiC) is successfully prepared by slip-casting for the first time. The stability of aqueous suspension is investigated in terms of its rheological properties. The isoelectic point (IEP) of β-Eucryptite particulate system was found to be at pH 6.1. To obtain the best processing conditions, LAS-nSiC suspension with 55 wt% of solids and 0.06 wt% of Tetramethyl ammonium hydroxide (TMAH) as dispersant is recommended. The slurry is slip-casted in plaster of Paris molds and sintered at 1430ºC for different holding times in controlled atmosphere. Microstructure, mechanical and coefficient of thermal expansion (CTE) properties of the sintered samples have been evaluated. LAS-nSiC composite sintered at 1430ºC shows dense and free-cracked microstructure with a CTE close to zero.

Substituted Poly(Vinylphosphonate) Coatings of Magnetite Nanoparticles and Clusters

Magnetite nanoparticles and clusters of nanoparticles have been of Increasing scientific interest in the past decades. In order to prepare nanoparticles and clusters that are stable in suspension, different coatings have been used. Phosphates and phosphonates are a preferred anchoring group for the coating of magnetite nanomaterials. However, poly(vinylphosphonates) have rarely been used as a coating agent for any nanoparticles. Here, poly(methylvinylphosphonate) and other substituted polyvinylphosphonates are described as new coatings for magnetite nanoparticles and clusters. They show great stability in aqueous suspension. This is also the first time phosphonate-coated magnetite clusters have been synthesized in a one-pot polyol reaction. The coated magnetite nanoparticles and clusters have been characterized by TEM, EDX, FTIR, magnetization measurement, XRD as well as XPS. It has been shown that substituted vinylphosphonates can be easily synthesized in one-step procedures and as a polymeric coating can imbue important properties such as stability in suspension, tight binding to the particle surface, the ability to be further functionalized or to tightly adsorb metal ions. For the synthesis of magnetite clusters the cluster formation, polymerization and coating are done in a one-pot reaction and the resulting magnetite clusters show a higher amount of phosphonate coating than with a three-step procedure including a ligand exchange.

Biosynthesized zinc oxide nanoparticles using seed and bark extract of Azadirachta indica for antibacterial, photocatalytic and supercapacitor applications

We have reported biosynthesis of zinc oxide (ZnO) nanoparticles (NPs: S3/B3) using an aqueous extract of seeds and barks of Azadirachta indica for antibacterial, photocatalytic, and supercapacitor applications. XRD pattern demonstrates a hexagonal wurtzite structure while FTIR spectra confirm the phytochemicals coating. Morphology is revealed from the FE-SEM images: (a) block-shaped S3 with ∼ 50–100 nm width and 90–125 nm length; (b) bar-shaped B3 with ∼ 40–50 nm thickness and 200 nm length. DLS study showed a zeta potential value of −28.93/-28.00 mV for S3/B3 indicating their good colloidal stability in aqueous suspension. Besides, antimicrobial activity of S3 is performed on various gram-negative/-positive bacteria and minimum inhibitory concentrations (MIC) are determined as 125–150 μg/mL. Moreover, methyl orange dye has been degraded with B3 NPs with a degradation efficiency of 84.62% in 180 min. Furthermore, the specific capacitance (Cs) and energy density (E) values of the S3/B3 confirmed their potentiality for supercapacitor applications.

Dual-Functional Antioxidant and Antiamyloid Cerium Oxide Nanoparticles Fabricated by Controlled Synthesis in Water-Alcohol Solutions.

Oxidative stress is known to be associated with a number of degenerative diseases. A better knowledge of the interplay between oxidative stress and amyloidogenesis is crucial for the understanding of both, aging and age-related neurodegenerative diseases. Cerium dioxide nanoparticles (CeO2 NPs, nanoceria) due to their remarkable properties are perspective nanomaterials in the study of the processes accompanying oxidative-stress-related diseases, including amyloid-related pathologies. In the present work, we analyze the effects of CeO2 NPs of different sizes and Ce4+/Ce3+ ratios on the fibrillogenesis of insulin, SOD-like enzymatic activity, oxidative stress, biocompatibility, and cell metabolic activity. CeO2 NPs (marked as Ce1–Ce5) with controlled physical–chemical parameters, such as different sizes and various Ce4+/Ce3+ ratios, are synthesized by precipitation in water–alcohol solutions. All synthesized NPs are monodispersed and exhibit good stability in aqueous suspensions. ThT and ANS fluorescence assays and AFM are applied to monitor the insulin amyloid aggregation and antiamyloid aggregation activity of CeO2 NPs. The analyzed Ce1–Ce5 nanoparticles strongly inhibit the formation of insulin amyloid aggregates in vitro. The bioactivity is analyzed using SOD and MTT assays, Western blot, fluorescence microscopy, and flow cytometry. The antioxidative effects and bioactivity of nanoparticles are size- or valence-dependent. CeO2 NPs show great potential benefits for studying the interplay between oxidative stress and amyloid-related diseases, and can be used for verification of the role of oxidative stress in amyloid-related diseases.

Antiseptic Materials on the Base of Polymer Interpenetrating Networks Microgels and Benzalkonium Chloride.

Polymer microgels, including those based on interpenetrating networks (IPNs), are currently vastly studied, and their practical applications are a matter of thriving research. In this work, we show the perspective for the use of polyelectrolyte IPN microgels either as scavengers or carriers of antiseptic substances. Here, we report that poly-N-isopropylacrylamide/polyacrylic acid IPN microgels can efficiently absorb the common bactericidal and virucidal compound benzalkonium chloride. The particles can form a stable aqueous colloidal suspension or be used as building blocks for soft free-standing films. Both materials showed antiseptic efficacy on the examples of Bacillus subtilis and S. aureus, which was approximately equal to the commercial antibiotic. Such polymer biocides can be used as liquid disinfectants, stable surface coatings, or parts of biomedical devices and can enhance the versatility of the possible practical applications of polymer microgels.

Biocompatible acid-degradable micro-mesoporous CaCO3:Si:Fe nanoparticles potential for drug delivery

Calcium carbonate nanoparticles of 50 nm in diameter are synthesized within the mesoporous silica particles with a subsequent etching out of the template material. Due to interaction of the filler with a template the as-prepared CaCO 3 nanoparticles are doped with Si which allows preserving their small size and porous structure. To make an aggregatively stable aqueous suspension of the nanoparticles they are additionally doped with Fe. The obtained CaCO 3 :Si:Fe nanoparticles possess a micro-mesoporous structure with specific surface area of 205 m 2 g −1 and pore volume of 0.59 cm 3 g −1 . It is shown that the particles are fully dissolved in dilute HCl in several minutes. It is demonstrated that nanoparticles are nontoxic and are able to penetrate across the cell membrane and accumulate in HeLa and K-562 cells. Owing to high adsorption capacity a loading of 25 wt% doxorubicin (DOX) into CaCO 3 :Si:Fe nanopaticles is performed. Being internalized by cells DOX-loaded CaCO 3 :Si:Fe nanoparticles provide greater amount (up to three times) of DOX within the intracellular space compared to free doxorubicin. Encapsulation of the drug into the nanoparticles reduces its toxicity, IC 50 value increases by 2.5 and 5 times for HeLa and K-562 cells, respectively. - Micro-mesoporous CaCO 3 nanoparticles with high porosity were synthesized by hard template method - The CaCO 3 nanoparticles are aggregatively stable in water, not subjected to recrystallization and can be easily dissolved in acidic media - Porous CaCO 3 nanoparticles are non-toxic and easily penetrate across the cell membrane - Encapsulation of Doxorubicin (DOX) into the CaCO 3 nanoparticles substantially reduces toxicity of the drug and provide greater amount of DOX within the intracellular space

Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition

Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition

Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition.

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse applications. Here we describe how to form these materials in a hydrothermal process that permits the independent control of product cluster size (from 30 to 120 nm) and manganese content of the resulting material. Parameters such as the total amount of water added to the alcoholic reaction media and the ratio of manganese to iron precursor are important factors in achieving multiple types of MFC nanoscale products. A fast purification method uses magnetic separation to recover the materials making production of grams of magnetic nanomaterials quite efficient. We overcome the challenge of magnetic nanomaterial aggregation by applying highly charged sulfonate polymers to the surface of these nanomaterials yielding colloidally stable MFCs that remain non-aggregating even in highly saline environments. These non-aggregating, uniform, and tunable materials are excellent prospective materials for biomedical and environmental applications.

Novel pathway for the sonochemical synthesis of silver nanoparticles with near-spherical shape and high stability in aqueous media

The present study shows the development of a novel sonochemical synthesis pathway of sub-15 nm silver nanoparticles (AgNPs) with quasi-spherical shape and high stability in aqueous suspension. Different analytical techniques such as on-line UV–Vis spectroscopy, Atomic Force Microscopy (AFM), and Transmission Electron Microscopy (TEM) were complementarily used to characterize the evolution of the properties of AgNPs synthesized with this new route. Furthermore, different centrifugation conditions were studied to establish a practical, simple and straightforward purification method. Particle size was determined by TEM employing two different deposition methods, showing that purified AgNPs have a size of 8.1 nm ± 2.4 nm with a narrow dispersion of the size distribution (95% coverage interval from 3.4 to 13 nm). Critical information of the shape and crystalline structure of these sub-15 nm AgNPs, provided by shape descriptors (circularity and roundness) using TEM and high resolution (HR)-TEM measurements, confirmed the generation of AgNPs with quasi-spherical shapes with certain twin-fault particles promoted by the high energy of the ultrasonic treatment. Elemental analysis by TEM-EDS confirmed the high purity of the sub-15 nm AgNPs, consisting solely of Ag. At the optical level, these AgNPs showed a bandgap energy of (2.795 ± 0.002) eV. Finally, the evaluation of the effects of ultraviolet radiation (UVC: 254 nm and UVA: 365 nm) and storage temperature on the spectral stability revealed high stability of the optical properties and subsequently dimensional properties of sub-15 nm AgNPs in the short-term (600 min) and long-term (24 weeks).

Cr(VI) adsorption on binary and ternary composites of raw cocoa shell with magnetic nanoparticle and Prussian blue

Binary and ternary composites of raw cocoa shell (CS) were investigated as novel adsorbents for chromate (Cr(VI)) ions adsorption. CS incorporated with magnetite nanoparticle (MNP) and MNP-Prussian blue (MNP-PB) composites of CS were fabricated for the first time in this study. The characterization of the adsorbents was performed by using Fourier-transform infrared (FTIR), BET/N2 surface area analysis, particle size and zeta potential measurements, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) analysis. The measured zeta potential values are high enough to point out stable aqueous suspensions. The efficiency of Cr(VI) adsorption were examined by evaluating the effects of contact time and initial chromate concentration. The kinetic behaviors of all adsorbents fitted Pseudo Second Order Model. The adsorption capacities were calculated as 23.36, 10.73 and 11.76 mg CrO42−/g adsorbent on CS, MNP-CS and MNP-PB-CS, respectively. Additionally, the pH dependency of the adsorption was investigated by considering surface acidity properties of CS and species distribution of Cr(VI) ions at different pHs. As a result, it was observed that the HCrO4− species was responsible for adsorption at pHs between 2 and 8.

Fabrication and properties of highly transparent Li0.07Al2.76O3.64N0.36 ceramics by aqueous gelcasting and two-step preparation

Highly transparent Li0.07Al2.76O3.64N0.36 discs (φ 22 × 2.0 mm) and blocks (45 × 40 × 12 mm) were successfully prepared by aqueous gelcasting and two-step preparation. After introducing a small amount of lithium, the lower N1s binding energy and higher intensity of Al–N bonds on the surface of Li0.07Al2.76O3.64N0.36 powder cause Al–N breakage to be effectively avoided, which inhibits the hydrolysis of powder. Using MAM and MABM as monomers and gelling agents, a stable aqueous suspension with solid loading up to 55 vol% and low viscosity of 83 mPa s was prepared, and the rheological properties and gelating behaviour of the slurries were evaluated. Due to its composition and novel crystalline structure, the Li0.07Al2.76O3.64N0.36 component presented significantly different performances from γ-AlON. The Vickers hardness reached 15.44 ± 0.34 GPa at a load of 9.8 N, and the in-line transmittance reached ∼84.7% at 3.7 μm.

A Magnetocatalytic Propelled Cobalt–Platinum@Graphene Navigator for Enhanced Tumor Penetration and Theranostics

A Magnetocatalytic Propelled Cobalt–Platinum@Graphene Navigator for Enhanced Tumor Penetration and Theranostics

Filtration of Nanoparticle Agglomerates in Aqueous Colloidal Suspensions Exposed to an External Radio-Frequency Magnetic Field.

The study investigated the phenomenon of the fast aggregation of single-domain magnetic iron oxide nanoparticles in stable aqueous colloidal suspensions due to the presence of a radio-frequency (RF) magnetic field. Single-domain nanoparticles have specific magnetic properties, especially the unique property of absorbing the energy of such a field and releasing it in the form of heat. The localized heating causes the colloid to become unstable, leading to faster agglomeration of nanoparticles and, consequently, to rapid sedimentation. It has been shown that the destabilization of a stable magnetic nanoparticle colloid by the RF magnetic field can be used for the controlled filtration of larger agglomerates of the colloid solution. Two particular cases of stable colloidal suspensions were considered: a suspension of the bare nanoparticles in an alkaline solution and the silica-stabilized nanoparticles in a neutral solution. The obtained results are important primarily for biomedical applications and wastewater treatment.

Optimization of Sintering Process of Alumina Ceramics Using Response Surface Methodology

In this work, alumina (Al2O3) ceramics were prepared using an environmentally friendly slip casting method. To this end, highly concentrated (70 wt.%) aqueous suspensions of alumina (Al2O3) were prepared with different amounts of the ammonium salt of a polycarboxylic acid, Dolapix CE 64, as an electrosteric dispersant. The stability of highly concentrated Al2O3 aqueous suspensions was monitored by viscosity measurements. Green bodies (ceramics before sintering) were obtained by pouring the stable Al2O3 aqueous suspensions into dry porous plaster molds. The obtained Al2O3 ceramic green bodies were sintered in the electric furnace. Analysis of the effect of three sintering parameters (sintering temperature, heating rate and holding time) on the density of alumina ceramics was performed using the response surface methodology (RSM), based on experimental data obtained according to Box–Behnken experimental design, using the software Design-Expert. From the statistical analysis, linear and nonlinear models with added first-order interaction were developed for prediction and optimization of density-dependent variables: sintering temperature, heating rate and holding time.