Prismatic Particles Research Articles

Sol-gel synthesis, structure and adsorption properties of LiMgxMn(2-x)O4 (0 ≤ x ≤ 0.7) Oxides

Lithium manganese оxides with a spinel structure LiMgxMn(2–x)O4, doped with Mg2+ ions in the range 0 ≤ x ≤ 0.7, were obtained by sol-gel synthesis. Phase composition and morphology of obtained оxides were studied by using X-ray phase analysis and scanning electron microscopy. It is shown, that in the studied range 0 ≤ x ≤ 0.7 Mg-doped lithium manganese оxides saved the structure of the original cubic spinel LiMn2O4, while an increase in parameter a was observed from 8.175 to 8.309 Å and average crystallite size practically unchanged (30–36 nm). Samples of the initial LiMn2O4 and Mg-doped spinels were represented by prismatic particles of submicron (0.1–0.2 µm) and micron (1.0–3.0 µm) sizes, respectively. The effect of the adsorbent dose (0.05–0.3 g/l) and pH (3.0–13.0) of the solution on the adsorption efficiency was studied. The adsorption isotherms of the LiMg0.3Mn1.7O4 samples were described by the Langmuir monomolecular adsorption equation. An increase in the temperature of the model solution from 25 to 45°C was accompanied by an increase in the maximum adsorption of the LiMg0.3Mn1.7O4 samples from 10.50 to 10.98 mmol/g, which indicates the endothermic nature of the adsorption process. The kinetics of adsorption was well described by a pseudo-second order equation, which indicates the occurrence of chemical interaction during the adsorption process.

The Origin of Magnetofossil Coercivity Components: Constraints From Coupled Experimental Observations and Micromagnetic Calculations

AbstractBiogenic magnetite crystals produced by magnetotactic bacteria (MTB) and associated magnetofossils in sediments are characterized by variable morphologies, grain sizes, and chain structures. Magnetofossils are widely used in paleomagnetic and paleoenvironmental studies, but the complex magnetofossil shapes and particle arrangements significantly affect magnetic properties, hampering their magnetic detection and proxy interpretation. Here we perform coupled experimental and micromagnetic modeling analyses of typical magnetofossil‐rich sediments, where the effects of magnetofossil crystal forms and microstructures on magnetic properties can be quantitatively separated. Since the in situ magnetofossil chain structures in sediments remain poorly known, we compare results from magnetic measurements and micromagnetic simulations based on realistic magnetofossil shapes and grain size distributions. Our results suggest that bullet‐shaped magnetofossils certainly contribute to the biogenic hard (BH) coercivity component with a minor contribution from elongated prismatic particles, and collapsed equidimensional grains to the biogenic soft (BS) component. Micromagnetic simulations with different collapse models of bullet‐shaped magnetofossils produce variable FORC (first‐order reversal curve) central‐ridge contributions with similar coercivity distributions. Sensitivity test suggests that samples containing different forms of magnetofossils can produce the BH coercivity component if the proportion of the bullet‐shaped particles is more than ∼2%. Magnetofossil assemblages with a higher proportion of bullet‐shaped particles have higher coercivities, squareness ratios, and larger BH contents. Our data shed new light on understanding the origin of magnetofossil coercivity components and the in situ magnetofossil microstructures in sediments, which is widely useful for interpreting magnetofossil proxy signals in geological records.

Synthesis of nano-zinc oxide by conventional chemical precipitation vs microwaves and its effect on the germination of cucumber (Cucumis sativus) seeds

Nanostructured ZnO (ZnO-NE) were successfully synthesized and seed germination and growth of cucumber seedlings in the laboratory were evaluated. The synthesis of ZnO-NE was done by direct precipitation (DP) and microwave-assisted heating with a domestic microwave (Domestic MW) vs a professional microwave (Professional MW). The crystalline phases, morphology, and absorption properties of the samples were characterized by XRD, FTIR, HR-SEM, and UV–Vis DRS respectively. The germination of cucumber seeds was evaluated through an experimental design completely randomized with five treatments and six repetitions. The number of roots, length and diameter of the main root, length and diameter of the hypocotyl were quantified. The germination percentage, germination indices and seedling vigor were calculated. All ZnO-NE synthesis methods presented wurtzite structure; smaller size (34 nm) of crystal with DP and larger (60 nm) with professional microwave. The synthesis with a Professional MW produced hexagonal prismatic particles while with a Domestic MW and DP there was no defined morphology, but with a tendency to form bars. All syntheses had a high percentage of Zn, O and a higher percentage of C in the ZnO-NE by Domestic MW, and in the ZnO-NE by DP and Professional MW Na was detected, both with a similar stoichiometric ratio, although the closest to one was with Domestic MW. The Eg values were 3.12, 3.14 and 3.16 eV for ZnO-NE synthesized by Professional MW, Domestic MW and DP, respectively. The different sources of ZnO-NE modified the length of the root and hypocotyl, the number of secondary roots, the vigor index and percentage of survival of seedlings in containers. Therefore, the preparation of ZnO-NE and its application in the germination of cucumber seeds contributes to improving the morphological characteristics of post-emergence seedlings.

Correlation between phase composition and physicochemical properties in Cu-, Mo-, and W- doped bismuth vanadate

We report a detailed study about the correlation between the physicochemical properties of solvothermally synthesized pristine and 1 %, 2.5 %, and 5 % Cu, Mo, and W-doped bismuth vanadate (BiVO4, BVO) with its phase composition. The effect of the dopant and the duration of synthesis (8 h and 20 h) on the physicochemical properties of BVO allowed us to tune the ratio of monoclinic scheelite to tetragonal zircon phase in BVO powders. This approach helped us to establish the relationship between the presence of monoclinic scheelite or tetragonal zircon phase with structural, morphological and optical properties of BVO powders, obtained by different physicochemical methods (e.g. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Spectroscopy (DRS) and Photoluminescence spectroscopy (PL)). The results indicated that, in addition to XRD, Raman, and DRS, several other methods could distinguish between the two phases. For example, SEM analysis revealed that monoclinic scheelite BVO exhibits either elongated assemblies of cube-like particles or prismatic particles with sizes ∼500 nm. In contrast, tetragonal zircon BVO exclusively exhibited porous spherical particles with diameter ∼2 μm. DRS and Raman spectroscopy indicated that there is a possibility of distinguishing between the two phases if their shares are large enough. For instance, monoclinic BVO showed band gap values in the range of 2.35–2.52 eV, while tetragonal zircon BVO exhibited values in the range of 2.80–3.00 eV. XPS showed a correlation between phase composition and surface chemistry of BVO only for Cu-doped samples, revealing the presence of Cu+ in monoclinic BVO and the presence of both Cu+ and Cu2+ in tetragonal zircon BVO. PL showed that monoclinic scheelite BVO displayed decreased charge recombination compared to tetragonal zircon BVO. Deeper insight into the correlation between the physicochemical properties and phase composition of Cu, Mo, and W-doped bismuth vanadate (BiVO4, BVO) was based on water/pentanol medium (2:1 vol%) as a novel synthesis pathway. This may open new avenues for the broader methodological exploration of surface chemistry, particle size, and morphology of BVO particles through the use of diverse functionalization agents. Finally, the established links between phase composition and structural, morphological, and other physicochemical properties provide new and more predictable opportunities for further improvement of BVO properties for various applications.

Evaluation potential hazard of molybdenum (VI) oxide nanoparticles for human health

BACKGROUND: The expanding scope of molybdenum (VI) oxide (MoO3 NPs) nanoparticle application has increased the risk of developing pathological disorders in the exposed population due to the negative effects of this nanomaterial. As such, there is a need to assess the potential hazard of MoO3 NPs to human health.
 AIM: To determine the degree of potential danger of MoO3 nanoparticles for human health.
 MATERIAL AND METHODS: The potential hazard of MoO3 NPs was assessed in accordance with MR 1.2.2522-09. A comparative assessment of the physical parameters of nano- and micropowder MoO3 particles (Sigma-Aldrich, USA) in terms of size, specific surface area, total pore volume, and shape was conducted based on the results of our own experimental studies. Generalization of information on physicochemical, molecular biological, cytological, physiological and ecological properties was performed according to the data presented in the scientific literature. Based on the predictive-analytical modeling of the properties of MoO3 NPs, the potential hazard coefficient (D) and the coefficient of incompleteness of data assessment (U) was calculated.
 RESULTS: Our findings showed that 84.17% of the nanopowders consists of spherical particles 100 nm in size with an average diameter of 58.80 nm, a specific surface area of 3.66 m2/g, and a total pore volume of 0.0133 cm3/g. Micropowders consist of prismatic particles that are 57.99 times larger in size and but 1.17 and 1.18 times smaller in specific surface area and total pore volume compared to the MoO3 NPs, respectively. MoO3 NPs enhance the generation of intracellular free radicals, accumulate in cells, damage organelle membranes, cause DNA strand breaks, affect gene expression and proteomic profile, which leads to cell death. The toxic effects of MoO3 NPs in vivo are showed in pathomorphological changes in the tissues of the liver, organs of the reproductive system, changes in blood parameters, death of exposed animals, and long-term effects. It has been established that MoO3 NPs have an average degree of potential hazard to human health (D=1.750), the assessment is statistically significant (U=0.147).
 CONCLUSION: The obtained results should be taken into account to improve the methodology for the sanitary regulation of nanomaterials in environmental objects and develop preventive measures for workers and populations exposed to MoO3 NPs.

Investigation on formation mechanisms of ash and deposit from cotton stalk vibrating grate boiler combustion based on their characteristics

The formation mechanisms of ash and deposit from cotton stalk (CS) water-cooled vibrating grate boiler combustion were explored according to their characteristics. Measurements of the ash fusion characteristics indicate the sintering temperatures under an oxidizing atmosphere (O2/CO2, 3:7, volume ratio) decrease in the order fly ash (Fcs) > bottom ash (Bcs) > deposit on the super-heater (Dcs) > CS ash; while four characteristic fusion temperature all increase in the order Bcs < Fcs < Dcs < CS ash. This results from the basic/acid ratio differences in their ash-compositions. Potassium feldspar and anorthite were found in Fcs; the sulfates (from chlorination and vulcanization of K or Ca during combustion) presented in Dcs was closely related to deposit formation; and calcium silicate and gehlenite were found in Bcs. The Fcs was composed of small prismatic particles with molten surface. In the Dcs, only the small spherical particles attached to aggregates were molten, whereas the Bcs contained mostly molten particles. Formation mechanisms of ash and deposit were deduced from the perspective of ash-formed elemental migration and transformation transform during CS combustion. And the layer-structure forming process of Dcs was also deduced.

Crystallization of meloxicam in the presence of hydrophilic additives to tailor its physicochemical and pharmaceutical properties

It is known that the presence of impurities can affect the morphology and properties of crystals. In this study, the effects of various hydrophilic additives including polyvinylpyrrolidone, polyethylene glycol 4000, Pluronics F68 and F127 were investigated to modify crystal properties of meloxicam microcrystals (a poorly-soluble anti-inflammatory drug) aimed to enhance its dissolution. Two different methods (cooling and anti-solvent precipitation) were employed to prepare meloxicam microcrystals in the presence of different additives. Scanning electron microscope, X-ray diffraction, infrared spectrophotometry and differential scanning calorimetry were used to study morphology and crystalline characteristics of the particles. Physicochemical properties of the engineered meloxicam namely particle size, solubility, wettability and dissolution behavior were also evaluated. Different additives used in both crystallization methods resulted in prismatic particles without any polymorphic transition. Although the employed crystallization techniques decreased the particle size, the most crystal growth inhibition was observed for the particles prepared by the anti-solvent precipitation method in the presence of Pluronics F127 and F68. The dissolution rate of all samples was improved compared to the untreated MLX. Relative dissolution and dissolution efficiency (DE120) of those crystals were increased up to 2.5 and 3.3-fold compared to the intact meloxicam, respectively. These improvements in the dissolution of meloxicam could be attributed to the smaller particle size, higher wettability, and modified crystal habit of meloxicam.

Clays in Cosmetics and Personal-Care Products

AbstractClays are used in various cosmetic formulations, such as sunscreens, toothpastes, deodorants, creams, hair cosmetics, makeups, nail polish, facial masks, and shampoos, among others, to improve the organoleptic and physicochemical characteristics, to increase the stability, or to facilitate elaboration. Together with their technological functionalities, clays are cosmetologically active ingredients with cleaning, anti-aging, anti-wrinkling, and sun-care functionalities. Talc, kaolinite, mica, and some smectites are the clay minerals used most frequently in cosmetic products, but several other phyllosilicates as well as modified and synthetic clays are also used. Sometimes, clays are useful in the design of cosmetics just because they are made of rigid, small, and anisometric particles. Kaolinite and mica are made of hard prismatic particles which are lightly abrasive over the skin, teeth, or hair. Electric charges in smectites result in ion-exchange capacities useful in the loading of active cosmetics but also adsorbing and cleaning waste substances. Intermediate net negative charges of smectites result in layer expansion in polar media and specific rheological properties that are very useful in cosmetic formulations. The absence of charged particles in talc and kaolin make them flow easily resulting in lubricant effects. Protection against radiation from the sun by clay particles and decorative effects complete the possibilities of clays in cosmetics. The nomenclature for clays used as ingredients in cosmetics follows historical use and the names of commercial products, rather than following strict compositional principles. In this sense, an effort was made here to correlate the names of the minerals that make up each of the clay-based cosmetic ingredients.

The Wentzel-Kramers-Brillouin approximation for light scattering by horizontally oriented prismatic particles

In this research, we propose a simple approximation technique based on the decomposition of particles and on the Wentzel-Kramers-Brillouin approximation (WKB). The latter allows us to express analytically the expression of the form factor of a particle of a regular prismatic ice crystal shape. Our focus will be on studying the light scattering by horizontally oriented prismatic particles which rotate about their principal axes. To illustrate our formalism, a few numerical examples will be analyzed.

How do specific surface area and particle size distribution change when granular media dissolve?

The measured dissolution rate of a granular medium depends on its surface area and how the surface area changes during the course of the measurement. Moreover, the assumption that the specific surface area either remains constant or initially increases during dissolution is not always valid. This paper demonstrates that when the particle size distribution has sufficient variance, the instantaneous change in surface area during dissolution can be negative, even before the smallest particles dissolve away. The concept is explained using spherical particles, extended for use with prismatic particles, and demonstrated experimentally with gypsum powder. For the commercial gypsum powder used, the specific surface area decreases by about 50% during the first 10% of mass loss in water, so this effect may have practical importance and have a significant impact on the uncertainty in reported dissolution rates measured with batch reactors.

Chemical Transformations as a Tool for Controlling the Properties of Calcium Carbonate Powder

Calcium carbonate CaCO3 (calcite) powder with 100 – 200 nm size particles with nearly isometric shape was obtained by heat-treating at 600°C a product synthesized from a 2 M solution of citric acid H3C6H5O7∙ H2O and commercial calcium carbonate CaCO3 (calcite) powder with 1 – 4 μm size prismatic particles. The sequence of chemical transformations CaCO3→ CaC6H6O7∙3H2O/Ca3(C6H5O7)2→ 4H2O → CaCO3 makes it possible to change the properties (size and shape) of the particles of calcium carbonate CaCO3. Thanks to these properties the obtained highly dispersed calcite CaCO3 powder can be recommended as a filler for obtaining unique composites with inorganic (glass, ceramic, cement) or polymer matrices.

Carbothermal Reduction Nitridation of Fly Ash, Diatomite and Raw Illite: Formation of Nitride Powders with Different Morphology and Photoluminescence Properties

Rare-earth-doped SiAlON and Si3N4 materials from aluminosilicate starting materials have been reported to show superior photoluminescence (PL) properties. Three different starting materials, including pulverized coal furnace fly ash, diatomite and raw illite, were used for synthesis of nitride materials. The phase and morphology evolution of these products were carefully monitored at the low temperature range of 1350 °C to 1450 °C by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR). The PL properties of Eu-doped nitride products were also comparatively characterized. The results show that the type of starting material affects the phase composition and the photoluminescence properties of products. The existence of aluminum and alkali metals could effectively promote nitridation reactions. Aluminum in the starting materials led to the formation of different aluminum-rich nitride phases. Thus, β-SiAlON could be achieved at a much lower temperature (1350 °C) using raw illite or fly ash containing the proper amount of aluminum. Additionally, excess aluminum led to the formation of corundum and 15R-SiAlON. The products from pulverized coal furnace fly ash had more prismatic particles, and the products from diatomite had more fibrous particles. With the progress of the nitridation process, the fibers were increased, becoming longer and straighter, and the prismatic particles were more obvious. The presence of aluminum in the starting materials led to a blue shift in the photoluminescence spectrum.

Discrete and Continuous Approaches for the Failure Analysis of Masonry Structures Subjected to Settlements

Numerical modelling of masonry structures is nowadays still an active research field, given a number of open issues related to preservation and restoration of historical constructions and the availability of computational tools that have become more and more refined. This work focuses on the analysis of settlement-induced failure patterns characterizing the in plane response of two-dimensional dry-joints masonry panels, which differ in terms of texture, geometry and settlement configuration. Brick-block masonry, interpreted as a jointed assembly of prismatic particles in dry contact, can be modelled as a discrete system of rigid blocks interacting through contact surfaces with no tensile strength and finite friction, modelled as zero thickness elasto-plastic Mohr-Coulomb interfaces. Different approaches and numerical models are adopted herein: Limit Analysis (LA), a discrete model DEM and a continuous Finite Element Model (FEM). Limit Analysis is able to provide fast and reliable results in terms of collapse multiplier and relative kinematics. In this work, a standard LA procedure is coded through Linearised Mathematical Programming to take into account sliding mechanisms through dilatant joints. Discrete models are particularly suitable to study historical masonry materials, where rigid bodies interacts between contact and friction. Here, a combined Finite/Discrete Element approach (FEM/DEM) is adopted. Finally, analyses are conducted through the Finite Element approach, resorting to a continuum anisotropic elastic-perfectly plastic constitutive model. Some selected case-studies have been investigated adopting the above mentioned models and numerical results have been interpreted to highlight the capability of the approaches to predict failure patterns for various geometrical features of the structure and settlement configurations.

The use of cooling and anti-solvent precipitation technique to tailor dissolution and physicochemical properties of meloxicam for better performance

Low dissolution rate of pharmaceutical agents with poor water-solubility limits their bioavailability after oral administration. These two parameters are pivotal when a fast onset of action required which could be the case for meloxicam (MLX), an anti-inflammatory and pain reliever compound. In the present study, the effects of various solvents and method of crystallization were investigated to modify the physicochemical properties and dissolution of MLX crystals. X-ray diffractometry, infrared spectrophotometry and differential scanning calorimetry were used to investigate the crystalline characteristics of the particles. Dissolution, particle size, solubility, contact angle and morphology of crystals were also evaluated. It was found that the type of solvent and crystallization methods modified the shape of crystals from polyhedral irregular to prismatic particles. The results ruled out any polymorphic changes occurred during the processes for most samples. The dissolution rate of MLX was improved by recrystallization and the best dissolution performance was observed for crystals prepared by anti-solvent precipitation in the presence of acetone, ethanol, and propanol with a 2-3-fold increase in dissolution efficiency than that of the parent drug. This could be related to the decreased particle size, lower contact angle, improved wettability and crystalline modifications.

Preparation of AlN-Cu composite powders by electroless plating of controlled oxidized nitride particles to prevent degradation by hydrolysis

The present work describes the preparation of AlN-Cu composite powders by electroless plating. Initially, the hydrolysis reaction of the ceramic particles in the electroless solution was studied as a reference element for the design of a protective surface barrier that enabled the coating process, with no ceramic phase degradation. The metal source of the electrolytic bath was copper sulfate, with formaldehyde as the reducing agent, under alkaline conditions of pH 12. The microstructural characterization indicated the formation and growth of aluminum hydroxides from AlN particles, inhibiting the coating of Cu by increasing the OH− ions in the solution. As the exposure time increased, the ellipsoidal bayerite grew from AlN and transformed into prismatic particles of the thermodynamically more stable gibbsite phase. To prevent the degradation of AlN, a controlled oxidation stage was implemented to form a protective barrier of non-reactive alumina on the surface through thermal treatment in oxidizing atmospheres. An atmosphere of dry air was found to be more appropriate than pure oxygen for the formation of a continuous and dense layer of crack-free alumina on nitride surfaces, and a temperature of 1000 °C for 1 h enabled the formation of 3.9 by weight of α-Al2O3, capable of reducing the hydrolysis reaction of AlN. The process of autocatalytic deposition on the passivated particles, applied in three consecutive steps of metallization, led to AlN-Cu composite powders with 29 wt% Cu. Finally, the coated powders were treated in a hydrogen-reducing atmosphere at 400 °C to remove traces of the Al(OH)3 phase encountered, as well as to improve the adhesion of the nanostructured deposit of the cauliflower-like structure to the AlN surfaces, obtaining AlN-Cu composite powders suitable for the preparation of metal/ceramic composites.

Mathematical model of sapphire micromachining by CVD diamond coating tool

A CVD diamond coating tool with prismatic crystal structure was prepared by hot filament chemical vapor deposition (HFCVD) method to improve sapphire’s lapping efficiency. The full plastic removal model of Sapphire (0001) plane is established based on the extended domain removal theory of hard and brittle materials such as sapphires. This model is used to analyze the effect of parameters such as prismatic particle’s size of the CVD diamond coating, lapping rate, lapping pressure, and material properties on the removal rate during the lapping process, and to predict the material removal rate, which lays the foundation for the high-efficiency micromachining of sapphire.

The Contact Angle Variation of Floating Particles Makes It Difficult to Use the Neumann Condition To Quantify the Air-Water Interface Deformation in Three-Dimensional Space.

Capillary force is critical to the floatability of particles at the air-water interface. Quantification of the capillary force requires solving the Young-Laplace equation using suitable boundary conditions (BCs) at the triple contact line. For axisymmetric (two-dimensional, 2D) systems, such as single spheres floating at an initially flat air-water surface, both the Dirichlet (constant contact depth) and Neumann (constant contact angle) BCs can be applied. For three-dimensional (3D) systems, Neumann BCs (NBCs) have been successfully used. In this paper, we have challenged the use of NBCs for the 3D deformation of the air-water surface induced by floating particles, which always exhibit intrinsic contact angle (CA) hysteresis that is significantly amplified in 3D systems. Specifically, we designed and conducted the experiments using single prismatic particles, which allowed for the determination of two characteristic CAs at the two diagonal axes with a high degree of certainty. We calibrated the numerical solution to the 3D Young-Laplace equation using the deformed air-water interface profiles at the two diagonal axes and then validated the numerical solution for the capillary force on the floating particles with the measured force. We obtained reliable data for the CA along the three-phase contact line (TPCL), which displayed a significant distribution. We also discussed the findings that were significant to floating spheres in asymmetric systems, such as pairs of floating spheres. This paper provides experimental and theoretical evidence that the CA is not constant along the contact line in a 3D geometry, which invalidates the use of NBCs for 3D systems of floating particles. This study highlights the significance of the CA variation known as CA hysteresis, which should be considered when predicting the floatability of particles at the air-water interface.

Identifying Trends in Gold Nanoparticle Toxicity and Uptake: Size, Shape, Capping Ligand, and Biological Corona

The drive behind the growing interest in understanding gold nanoparticle (AuNP) cytotoxicity originates from the promise of AuNPs for diverse biological applications across the fields of drug delivery, biosensing, biological imaging, gene therapy, and photothermal therapy. Although we continue to investigate the novel biomedical applications of AuNPs, progress is currently stalled at the periphery of understanding the forces that govern critical nano–bio interactions. In this work, we systematically probe the size, shape, and surface capping effects of nanogold by designing a set of eight unique AuNPs. This allowed us to undertake a systematic study involving each of these parameters in the context of their influence on the cytotoxicity and cellular uptake by human prostate cancer cells (PC3) as a model biological system. While studying the influence of these parameters, our study also investigated the influence of serum proteins in forming different levels of biological corona on AuNPs, thereby further influencing the nano–bio interface. As such, increased cellular uptake (by nanoparticle number) was observed with decreasing the AuNP size and increased uptake levels were observed for gold nanospheres (of the same size) stabilized with amino acids compared to citrate or cetyltrimethylammonium bromide (CTAB). Spherical particles were found to be taken up in greater numbers compared to the shapes with broad flat faces. When measuring cytotoxicity, CTAB-stabilized rod- and cube-shaped particles were well tolerated by the cells, whereas toxicity was observed in the case of CTAB-stabilized spherical and prismatic particles. These effects, however, are underpinned by different mechanisms. Further, it is demonstrated that it is possible for different chemical stabilizers to elicit varied cytotoxic effects. Although we find the limited role of serum proteins in mediating toxicity, they do play a critical role in influencing the cellular uptake of AuNPs, with lower levels of uptake generally observed in the presence of serum. Our findings offer a useful step in the direction of predicting the biological interactions of AuNPs based on specific parameters of the AuNP design.

Phase and structural features of tubular halloysite (7 Å)

ABSTRACTDespite many reviews and original articles, the actual crystal structure of tubular halloysites remains unclear. Analysis of the structural features of defect-free kaolinite, refined by Bish &amp; von Dreele (1989), shows that the ordered 1Tc kaolinite structure can be described equally well by the orthogonal layer cell {a0, b0, γ0} (γ0 = 90°) or by two enantiomorphic oblique layer cells {a1, b1, γ1} and {a2, b2, γ2}, related to each other by a mirror plane. To simulate diffraction effects for tubular halloysite, the parameters and atomic coordinates of the orthogonal layer unit cell and the layer-displacement vectors t1 and t2 responsible for formation of the kaolinite enantiomorphs were deduced by transformation of the parameters of the defect-free kaolinite refined by Bish &amp; von Dreele (1989). Modelling X-ray diffraction patterns show that the samples consist of either single, two or three phases, with the number and their structural features depending on the morphology of the particles. Samples formed of prismatic particles consist of halloysite-like structure (HLS), kaolinite-like structure (KLS) and halloysite cylindrical structure (HCS) phases occurring in various proportions. Samples of proper cylindrical tubes consist of a single HCS phase, whilst samples formed by particles having morphologies intermediate between proper cylindrical and well-developed prismatic forms consist of the KLS and HCS phases. The KLS phase is comparable to low-ordered platy kaolinite with identical unit-cell parameters, layer-displacement vectors and arbitrary stacking faults, except that the layer displacements are not random as in kaolinite, but are distributed at R = 1 such that t1 and t2 displacements have a strong tendency to be segregated. Structural parameters describing the HLS and KLS phases are identical, but in the HLS phase there is a strong tendency to the regular alternation of the t1 and t2 displacements, and the HLS phases do not contain arbitrary stacking faults. A characteristic feature of the three-phase prismatic samples is that the stacking of the layers along the c* axis is periodic and the layer thicknesses are similar to those of platy kaolinite. In contrast, in the KLS phase formed in samples with particles of intermediate morphologies, the hydrated 10 and 7.25 Å layers are interstratified. The relationship between the structural and morphological features of the coexisting phases suggests a sequence of phase formation from the centre to the surface of halloysite tubes that progresses from the HCS to the HLS via the KLS phase. The results of this study demonstrate that all kaolinite and halloysite (7 Å) varieties are built by the same fundamental structural units.

Pulsed plasma chemical synthesis of carbon-containing titanium oxide-based composite

ABSTRACTThe carbon-containing titanium oxide-based composite was first obtained using a pulsed plasma chemical method. The composite was obtained from the following reagents: TiCl4, CH4, and O2. The physical and chemical properties of the TixCyOz composite powders were studied (morphology, chemical, elemental and phase composition). The presence of spherical particles and the cubic and prismatic particles were typical for the synthesised carbon-containing titanium oxide-based composites. The large particles are observed (the average size exceeds 150 nm) and smaller particles (the average size is 15–30 nm). The presence of the dense layer of amorphous carbon (10–15 nm thick) around particles is typical for the composites. The peak with a maximum of 1080 cm−1 is registered in IR absorption spectrum of the TixCyOz synthesised composite. The presence of IR radiation in this region of the spectrum is typical for the deformation of atomic oscillations in the Ti-O-C bond, which indicates that carbon and titanium in the composite are bound through oxygen. The content of the defined amount of titanium carbide has not been detected.