The Effect of Boundary Conditions on Gas-phase Synthesised Silver Nanoparticles

We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size.     

Aerosol flow in a tube furnace reactor of gas-phase synthesised silver nanoparticles

In a previous work, gas-phase synthesis of silver nanoparticles through evaporation of silver powder and subsequent particle nucleation by cooling was shown to be a viable method for achieving high purity silver nanoparticles (Backman et al. J Nanopart Res 4:325–335, 2002). In order to control the size of the produced nanoparticles, careful design of the reactor is required with respect to thermal and flow characteristics. In the present work, the silver nanoparticle reactor is rigorously simulated by means of multidimensional computational fluid and particle dynamics. The CFD-computed flow is input for a combined simulation of the vapour field and particle homogeneous nucleation, growth and coagulation. The results are compared with the experimental data and with the predictions from the usually employed simple model of an idealized plug flow reactor. The multidimensional CFD-based analysis is shown to explain and help understand different aspects of the reactor operation and size distribution of the particles produced. Yet the simple plug flow method is found to provide reasonable accuracy when an appropriate correction factor is used for the nucleation rate. Considering its robustness and computational simplicity, the plug flow method can be qualified as adequate from the engineering practical point of view for the case of silver nanoparticle reactors.     

Controlled oxidation of iron nanoparticles in chemical vapour synthesis

Enteric-coated formulations can delay the release of drugs until they have passed through the stomach. However, high concentration of drugs caused by rapidly released in the small intestine leads to the intestinal damage, and frequent administration would increase the probability of missing medication and reduce the patient compliance. To solve the above-mentioned problems, aspirin-loaded enteric-coated sustained-release nanoparticles with core–shell structure were prepared via one-step method using coaxial electrospray in this study. Eudragit L100-55 as pH-sensitive polymer and Eudragit RS as sustained-release polymer were used for the outer coating and inner core of the nanoparticles, respectively. The maximum loading capacity of nanoparticles was 23.66 % by changing the flow rate ratio of outer/inner solutions, and the entrapment efficiency was nearly 100 %. Nanoparticles with core–shell structure were observed via fluorescence microscope and transmission electron microscope. And pH-sensitive and sustained drug release profiles were observed in the media with different pH values (1.2 and 6.8). In addition, mild cytotoxicity in vitro was detected, and the nanoparticles could be taken up by Caco-2 cells within 1.0 h in cellular uptake study. These results indicate that prepared enteric-coated sustained-release nanoparticles would be a more safety and effective carrier for oral drug delivery.     

Production of cobalt and nickel particles by hydrogen reduction

Cobalt and nickel nanoparticles were produced by hydrogen reduction reaction from cobalt or nickel chloride precursor vapour in nitrogen carrier gas. This aerosol phase method to produce nanoparticles is a scalable one-step process. Two different setups were introduced in particle production: a batch type reactor and a continuously operated reactor. Common feature in these setups was hydrogen mixing in a vertical flow reactor. The process was monitored on-line for particle mass concentration and for gas phase chemical reactions. Tapered element oscillating microbalance measured the particle mass concentration and Fourier transform infrared spectroscopy was used to monitor relevant gas phase species. The produced cobalt and nickel particles were characterised using transmission electron microscopy and x-ray diffraction. The produced cobalt and nickel particles were crystalline with cubic fcc structure. Twinning was often observed in cobalt particles while nickel particles were mostly single crystals. The cobalt particles formed typically long agglomerates. No significant neck growth between the primary particles was observed. The primary particle size for cobalt and nickel was below 100 nm.     

Atmospheric pressure chemical vapour synthesis of silicon–carbon nanoceramics from hexamethyldisilane in high temperature aerosol reactor

Silicon–carbon nanoceramics have been synthesised from hexamethyldisilane (HMDS) by the atmospheric pressure chemical vapour synthesis (APCVS). Direct aerosol phase synthesis enables continuous production of high purity materials in one-stage process. The particle formation is based on the decomposition of the precursor in a high temperature reactor. Reaction of the gas phase species leads to homogeneous nucleation and formation of the nanoparticles with a narrow size distribution (geometric mean diameter range of particle number size distribution 160–200 nm with 1.5–1.6 geometric standard deviation at reaction temperatures 800–1200 °C). A systematic investigation of the influence of the process temperature on the powder characteristics, including the particle size, crystallinity, chemical structure, surface and bulk composition and surface morphology, was carried out. At the reactor temperature of 800 °C, the synthesised nanoparticles were amorphous preceramics containing mostly SiC₄, Si–CH₂–Si and Si–H units. The composition of the powder turned towards nanocrystalline 3C–SiC (crystal size under 2 nm) when the reaction temperature was increased to 1200 °C. The reaction temperature appeared to be a key parameter controlling the structure and properties of the synthesised powders.     

Aerosol characterization and lung deposition of synthesized TiO2 nanoparticles for murine inhalation studies

This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO₂) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m^?3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm^?3. Particle concentration varied from 4 × 10⁵ cm^?3 at mass concentrations of 0.8 mg m^?3 to 12 × 10⁶ cm^?3 at 28.5 mg m^?3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO₂ particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO₂ powder was 61 m² g^?1. We defined mice respiratory minute volume (RMV) value during exposure to TiO₂ aerosol. Both TiO₂ particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO₂ matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs.     

Poly[(acetone)tetraaqua[μ6‐ethyl (dichloromethylene)diphosphonato][μ5‐ethyl (dichloromethylene)diphosphonato]tribarium(II)]

The novel title compound, [Ba₃(C₃H₅Cl₂O₆P₂)₂(C₃H₆O)(H₂O)₄]_n, has a polymeric two‐dimensional network structure which lies parallel to the (10) plane. The asymmetric unit consists of three independent Ba²⁺ ions, two of them eight‐coordinated and the third nine‐coordinated, and two independent ethyl (dichloromethylene)diphosphonate(3−) ligands, one acetone ligand and four aqua ligands. The coordination environments around the BaO₈ polyhedra are best described as bicapped trigonal prismatic, while the BaO₉ polyhedron is in a distorted tricapped trigonal prismatic geometry. The two diphosphonate ligands adopt different coordination modes. Both ligands chelate three metal cations, but one is coordinated to six metal cations in total and forms two six‐membered and one four‐membered chelate ring, while the other is coordinated to five metal cations in total and forms one six‐membered and two four‐membered chelate rings, the fifth unsubstituted O atom remaining uncoordinated.     

Gas-phase Crystallization of Titanium Dioxide Nanoparticles

We have investigated the development of crystal morphology and phase in ultrafine titanium dioxide particles. The particles were produced by a droplet-to-particle method starting from propanolic titanium tetraisopropoxide solution, and calcined in a vertical aerosol reactor in air. Mobility size classified 40-nm diameter particles were conveyed to the aerosol reactor to investigate particle size changes at 20–1200°C with 5–1-s residence time. In addition, polydisperse particles were used to study morphology and phase formation by electron microscopy. According to differential mobility analysis, the particle diameter was reduced to 21–23-nm at 600°C and above. Precursor decomposition occurred between 20°C and 500°C. The increased mobility particle size at 700°C and above was observed to coincide with irregular particles at 700°C and 800°C and faceted particles between 900°C and 1200°C, according to transmission electron microscopy. The faceted anatase particles were observed to approach a minimized surface energy by forming {101} and {001} crystallographic surfaces. Anatase phase was observed at 500–1200°C and above 600°C the particles were single crystals. Indications of minor rutile formation were observed at 1200°C. The relatively stable anatase phase vs. temperature is attributed to the defect free structure of the observed particles and a lack of crystal–crystal attachment points.     

Comparison of nanoparticle measurement instruments for occupational health applications

Nanoparticles are used in many applications because of their novel properties compared to bulk material. A growing number of employees are working with nanomaterials and their exposure to nanoparticles trough inhalation must be evaluated and monitored continuously. However, there is an ongoing debate in the scientific literature about what are the relevant parameters to measure to evaluate exposure to level. In this study, three types of nanoparticles (ammonium sulphate, synthesised TiO₂ agglomerates and aerosolised TiO₂ powder, modes in a range of 30–140 nm mobility size) were measured with commonly used aerosol measurement instruments: scanning and fast mobility particle sizers (SMPS, FMPS), electrical low pressure impactor (ELPI), condensation particle counter (CPC) together with nanoparticle surface area monitor (NSAM) to achieve information about the interrelations of the outputs of the instruments. In addition, the ease of use of these instruments was evaluated. Differences between the results of different instruments can mainly be attributed to the nature of test particles. For spherical ammonium sulphate nanoparticles, the data from the instruments were in good agreement while larger differences were observed for particles with more complex morphology, the TiO₂ agglomerates and powder. For instance, the FMPS showed a smaller particle size, a higher number concentration and a narrower size distribution compared with the SMPS for TiO₂ particles. Thus, the type of the nanoparticle was observed to influence the data obtained from these different instruments. Therefore, care and expertise are essential when interpreting results from aerosol measurement instruments to estimate nanoparticle concentrations and properties.