In situ determination of Si, N, and P utilization by the demosponge Tethya citrina: A benthic-chamber approach.

Sponges consume dissolved silicon (DSi) to build their skeletons. Few studies have attempted to quantify DSi utilization by these organisms and all available determinations come from laboratory measurements. Here we measured DSi consumption rates of the sponge Tethya citrina in its natural habitat, conducting 24h incubations in benthic chambers. Sponges consumed DSi at an average rate of 0.046 ± 0.018 µmol h-1 mL-1 when DSi availability in its habitat was 8.3 ± 1.8 µM. Such DSi consumption rates significantly matched the values predicted by a kinetic model elsewhere developed previously for this species through laboratory incubations. These results support the use of laboratory incubations as a suitable approach to learn about DSi consumption. During the field incubations, utilization of other dissolved inorganic nutrients by this low-microbial-abundance (LMA) sponge was also measured. The sponges were net sources of ammonium (-0.043 ± 0.031 µmol h-1 mL-1), nitrate (-0.063 ± 0.031 µmol h-1 mL-1), nitrite (-0.007 ± 0.003 µmol h-1 mL-1), and phosphate (-0.004 ± 0.005 µmol h-1 mL-1), in agreement with the general pattern in other LMA species. The detected effluxes were among the lowest reported for sponges, which agreed with the low respiration rates characterizing this species (0.35 ± 0.11 µmol-O2 h-1 mL-1). Despite relatively low flux, the dense population of T. citrina modifies the availability of dissolved inorganic nutrients in the demersal water of its habitat, contributing up to 14% of nitrate and nitrite stocks. Through these effects, the bottom layer contacting the benthic communities where siliceous LMA sponges abound can be partially depleted in DSi, but can benefit from inputs of N and P dissolved inorganic nutrients that are critical to primary producers.

Biological Actions, Electrical Conductance and Silicon-Containing Microparticles of Arsenicum Album Prepared in Plastic and Glass Vials.

INTRODUCTION: According to the "silica hypothesis" formulated to explain homeopathy, the information of starting materials would be transferred to cells by silica nanoparticles detached from the glassware walls by serial dilution and agitation through epitaxy. We compared the biological activity, electrical current and silicon microparticle content (by means of scanning electron microscopy/energy-dispersive X-ray spectroscopy) of high dilutions (HDs) of arsenic prepared in plastic and glass vials to investigate the role of silica in their biological effects in vitro. MATERIALS AND METHODS: Co-cultures of macrophages and yeast (Saccharomyces cerevisiae) were treated with different HDs of arsenic prepared in plastic and glass vials. Macrophage morphology, phagocytosis index, nitric oxide (NO), and cytokine production were evaluated. RESULTS: Measurable amounts of silicon microparticles were detected only in the HDs prepared in glass vials, but ultra-centrifugation eliminated them. Specific and non-specific results were observed. Non-specific pro-inflammatory effects were seen in all dilutions prepared in plastic vials, including elevation of pro-inflammatory cytokines, NO and macrophage phagocytic index. Only the 200th centesimal dilution of arsenic produced specific decrease in interleukin-6 production in macrophages, and it was independent of the vial type or the presence of microparticles of silica in the medicine samples. The nature of the vials had an impact on the electric flow in the respective fluids. CONCLUSION: The non-specific, pro-inflammatory effects might be attributed to organic residuals detached from the vials' plastic walls during manipulation. Instead, specific silica-independent effects of the homeopathic medicine can be attributed to the decrease of interleukin-6 after treatment with the 200th centesimal dilution of arsenic.

Effect of pH and added slag on the extractability of Si in two Si-deficient sugarcane soils.

The effects of increasing pH on the adsorption and extractability of Si in two Si-deficient Australian sugarcane soils was investigated and the effects of increasing rates of fertilizer Si (as blast furnace slag) on pH and extractable Si were also examined. Equilibrium studies showed that maximum adsorption of Si by the two soils occurred in the pH range 9-10. When soil pH was increased from 5.0 to 6.5, subsequent adsorption of Si by the two soils, as measured by adsorption isotherms, increased. After incubation with progressive lime additions there was a decline in CaCl2- extractable Si due to its increased adsorption and an increase in acid (H2SO4- and acetic acid)-extractable (mainly adsorbed) Si. The increase in acid extractable Si was greater than the decrease in CaCl2- extractable Si suggesting a supply from an additional source. Alkali (Na2CO3 and Tiron)-extractable Si decreased greatly with increasing pH suggesting dissolution of the amorphous (mainly biogenic) pool of silica was occurring with increasing pH. When increasing rates of slag were incubated with the soils, pH, CaCl2- and acid- extractable Si were all increased because upon dissolution slags release both silicic acid and OH- ions. There was, therefore, a positive relationship between extractable Si and soil pH. However, Na2CO3-and Tiron-extractable Si decreased with increasing slag rates (and increasing soil pH) suggesting dissolution of the biogenic pool of soil Si. It was concluded that future research needs to examine the desorption potential of adsorbed Si and the effects of liming on dissolution of the biogenic pool of soil silica under field conditions.

Spatially Separated Photosystem II and a Silicon Photoelectrochemical Cell for Overall Water Splitting: A Natural-Artificial Photosynthetic Hybrid.

Integrating natural and artificial photosynthetic platforms is an important approach to developing solar-driven hybrid systems with exceptional function over the individual components. A natural-artificial photosynthetic hybrid platform is formed by wiring photosystem II (PSII) and a platinum-decorated silicon photoelectrochemical (PEC) cell in a tandem manner based on a photocatalytic-PEC Z-scheme design. Although the individual components cannot achieve overall water splitting, the hybrid platform demonstrated the capability of unassisted solar-driven overall water splitting. Moreover, H2 and O2 evolution can be separated in this system, which is ascribed to the functionality afforded by the unconventional Z-scheme design. Furthermore, the tandem configuration and the spatial separation between PSII and artificial components provide more opportunities to develop efficient natural-artificial hybrid photosynthesis systems.

Continuing Assessment of the 5-Day Sodium Carbonate-Ammonium Nitrate Extraction Assay as an Indicator Test for Silicon Fertilizers.

The 5-day sodium carbonate-ammonium nitrate extraction assay (5-day method) has been recognized by the American Association of Plant Food Control Officials as a validated test method to identify fertilizers or beneficial substances that provide plant-available silicon (Si). The test method used the molybdenum blue colorimetric assay to quantify percentage Si; however, laboratories may use inductively coupled plasma optical emission spectroscopy (ICP-OES) for elemental analysis. To examine the use of either colorimetric or ICP-OES methods for Si determination, the 5-day method was performed on the following Si-containing compounds; wollastonite, sand, biochar, and a basic oven furnace (BOF) slag. Grow-out studies using Zinnia elegans were also performed using varying rates of the wollastonite, biochar, and BOF slag. Our results show using the 5-day method, wollastonite had the highest extracted amounts of silicic acid (H4SiO4) at 4% followed by biochar (2%), BOF slag (1%), and sand (0%). Extraction values calculated using either the molybdenum blue colorimetric assay or ICP-OES for detection of the H4SiO4 had a significant correlation, supporting the application of either detection method for this type of analysis. However, when extracted values were compared to amounts of Si taken up by the plants, the 5-day method overestimated both wollastonite and biochar. While this method is a valid indicator test for determining a soluble Si source, other plant species and methods should be perused to potentially provide more quantitative analyses for plant-available Si content of all materials.

Stepwise extraction of valuable components from red mud based on reductive roasting with sodium salts.

The feasibility of an integrated technological route for comprehensive utilization of red mud was verified in this study. Valuable components in the mud, including Fe2O3, Al2O3 and SiO2 were stepwise extracted by magnetic separation and sulfuric acid leaching from reduced red mud, and meanwhile TiO2 was enriched in the leaching residue. Sodium salts were proved to be favorable for the magnetic separation of metallic iron and the subsequent acid leaching of Al and Si, through facilitating the reduction of iron oxides and the growth of metallic iron grains, together with enhancing the activation of Al and Si components during the roasting process. After reductive roasting in the presence of 6% Na2CO3 and 6% Na2SO4, a magnetic concentrate containing 90.2% iron with iron recovery of 95.0% was achieved from the red mud by magnetic separation. Subsequently, 94.7% Fe, 98.6% Al and 95.9% Si were extracted by dilute sulfuric acid leaching from the upper-stream non-magnetic material, yielding a TiO2-rich material with 37.8% TiO2. Furthermore, value-added products of silica gel and Al(OH)3 were prepared from the leachate by ripening and neutralizing.

Recycling silicon wire-saw slurries: separation of silicon and silicon carbide in a ramp settling tank under an applied electrical field.

UNLABELLED: The growing demand for silicon solar cells in the global market has greatly increased the amount of silicon sawing waste produced each year. Recycling kerf Si and SiC from sawing waste is an economical method to reduce this waste. This study reports the separation of Si and SiC using a ramp settling tank. As they settle in an electrical field, small Si particles with higher negative charges have a longer horizontal displacement than SiC particles in a solution of pH 7, resulting in the separation of Si and SiC. The agreement between experimental results and predicted results shows that the particles traveled a short distance to reach the collection port in the ramp tank. Consequently, the time required for tiny particles to hit the tank bottom decreased, and the interference caused by the dispersion between particles and the fluid motion during settling decreased. In the ramp tank, the highest purities of the collected SiC and Si powders were 95.2 and 7.01 wt%, respectively. Using a ramp tank, the recycling fraction of Si-rich powders (SiC < 15 wt%) reached 22.67% (based on the whole waste). This fraction is greater than that achieved using rectangular tanks. IMPLICATIONS: Recycling Si and SiC abrasives from the silicon sawing waste is regarded as an economical solution to reduce the sawing waste. However, the separation of Si and SiC is difficult. This study reports the separation of Si and SiC using a ramp settling tank under an applied electrical field. As they settle in an electrical field, small Si particles with higher negative charges have a longer horizontal displacement than SiC particles in a solution of pH 7, resulting in the separation of Si and SiC. Compared with the rectangular tanks, the recycling fraction of Si-rich powders using a ramp tank is greater, and the proposed ramp settling tank is more suitable for industrial applications.

Ensemble brightening and enhanced quantum yield in size-purified silicon nanocrystals.

We report on the quantum yield, photoluminescence (PL) lifetime, and ensemble photoluminescent stability of highly monodisperse plasma-synthesized silicon nanocrystals (SiNCs) prepared though density-gradient ultracentrifugation in mixed organic solvents. Improved size uniformity leads to a reduction in PL line width and the emergence of entropic order in dry nanocrystal films. We find excellent agreement with the anticipated trends of quantum confinement in nanocrystalline silicon, with a solution quantum yield that is independent of nanocrystal size for the larger fractions but decreases dramatically with size for the smaller fractions. We also find a significant PL enhancement in films assembled from the fractions, and we use a combination of measurement, simulation, and modeling to link this "brightening" to a temporally enhanced quantum yield arising from SiNC interactions in ordered ensembles of monodisperse nanocrystals. Using an appropriate excitation scheme, we exploit this enhancement to achieve photostable emission.

Silicon sawing waste treatment by electrophoresis and gravitational settling.

In silicon wafer manufacturing for solar cells, a great amount of hazardous sawing waste with tiny Si particles is produced, resulting in serious environmental problems. Recycling Si and abrasives from the waste is regarded as an effective solution. Based on the view of recycling, Al(2)O(3) might be good abrasives for cutting Si ingot due to its larger density and higher isoelectric point than SiC. This study reports the separation of Si/SiC and Si/Al(2)O(3) mixtures by electrophoresis and gravitational settling. At pH 9, nearly uncharged Al(2)O(3) settled quickly and the negatively charged Si moved toward the anode, leading to an obvious Si distribution on the cell bottom. The experimental results show the separation performance of Si and Al(2)O(3) at pH 9 was better than at pH 2.5, and the performance was higher than that between Si and SiC. The minimum and maximum Al(2)O(3) contents remaining in Si/Al(2)O(3) mixture were 9 wt% and 90 wt% after applying 1 V/cm for 24h at pH 9. The recovered material with high Si content can be considered as a new Si source for solar cell, and the abrasives can be reused in the sawing process.

Silicon-hydroxyapatite bioactive coatings (Si-HA) from diatomaceous earth and silica. Study of adhesion and proliferation of osteoblast-like cells.

The aim of this study consisted on investigating the influence of silicon substituted hydroxyapatite (Si-HA) coatings over the human osteoblast-like cell line (SaOS-2) behaviour. Diatomaceous earth and silica, together with commercial hydroxyapatite were respectively the silicon and HA sources used to produce the Si-HA coatings. HA coatings with 0 wt% of silicon were used as control of the experiment. Pulsed laser deposition (PLD) was the selected technique to deposit the coatings. The Si-HA thin films were characterized by Fourier Transformed Infrared Spectroscopy (FTIR) demonstrating the efficient transfer of Si to the HA structure. The in vitro cell culture was established to assess the cell attachment, proliferation and osteoblastic activity respectively by, Scanning Electron Microscopy (SEM), DNA and alkaline phosphatase (ALP) quantification. The SEM analysis demonstrated a similar adhesion behaviour of the cells on the tested materials and the maintenance of the typical osteoblastic morphology along the time of culture. The Si-HA coatings did not evidence any type of cytotoxic behaviour when compared with HA coatings. Moreover, both the proliferation rate and osteoblastic activity results showed a slightly better performance on the Si-HA coatings from diatoms than on the Si-HA from silica.

Isolation and structure of a silicocationic species with 1,3-aryl bridging between silicon atoms: a bis-silylated benzenium ion or a bridging Ph group?

Hydride abstraction from (Me3Si)3CSiMePhH by Ph3C+ affords the cation [(Me3Si)2CSiMe2-Ph-SiMe2]+, which is shown by X-ray crystallography to contain the first structurally characterised example of a Ph group bridging between two silicon atoms.

A new quantitative method to evaluate the in vitro bioactivity of melt and sol-gel-derived silicate glasses.

Two melt-derived glasses (45S5 and 60S) and four sol-gel glasses (58S, 68S, 77S, and 91S) have been synthesized. The activation energy for the silicon release was determined, and a very close correlation was observed between this value and published results of the bioactive behavior of the glasses. This relationship can be explained in terms of the influence of chemical composition, textural properties, and structural density on the silanol group formation and silicon dissolution. These measurements provide a quantitative method to evaluate the in vitro bioactivity of SiO(2)-based glasses. Preliminary studies suggest an activation energy gap (Ea) of 0.35-0.5 eV as a boundary between bioactive and nonbioactive glasses.

Observation of assembly of fluorescent Si nanoparticles under the influence of electric current.

A silicon substrate patterned by an oxide is immersed in an alcohol solution of low-doped 1-nm Si nanoparticles. Reverse biasing draws particles to the substrate, mostly along the conducting current paths. Scanning electron and fluorescence microscopy show a tree-like network on the substrate. Avoidance of closed loops and preference for an angle of branching of 90 degrees-120 degrees are observed. The building block of the tree network is not individual particles but spherical particle aggregates approximately 150 nm in diameter.

Molecular dynamics study of hypothetical silicon nanotubes using the Tersoff potential.

We have performed classical molecular dynamics simulations for hypothetical silicon nanotubes using the Tersoff potential. Our investigation presented a systematic study about the thermal behavior of hypothetical silicon nanotubes and showed the difficulty in producing silicon nanotubes or graphitelike sheets. However, since the elastic energy per atom to curve the sheet into cylinders for silicon atoms is as low as that for carbon atoms, if graphitelike sheets of silicon are formed, the extra cost to produce the tubes is of a similar order to that in carbon. Through the investigations on the structure and properties of a double-wall silicon nanotube, we concluded that quasi-one-dimensional structures consisting of silicon atoms become nanowires rather than nanotubes in order to minimize the number of sp2 bonds.

Structural and optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition.

Silicon nanocrystals (Si-nc) embedded in SiO2 matrix have been prepared by high temperature thermal annealing (1000-1250 degrees C) of substoichiometric SiOx films deposited by plasma-enhanced chemical vapor deposition (PECVD). Different techniques have been used to examine the optical and structural properties of Si-nc. Transmission electron microscopy analysis shows the formation of nanocrystals whose sizes are dependent on annealing conditions and deposition parameters. The spectral positions of room temperature photoluminescence are systematically blue shifted with reduction in the size of Si-nc obtained by decreasing the annealing temperature or the Si content during the PECVD deposition. A similar trend has been found in optical absorption measurements. X-ray absorption fine structure measurements indicate the presence of an intermediate region between the Si-nc and the SiO2 matrix that participates in the light emission process. Theoretical observations reported here support these findings. All these efforts allow us to study the link between dimensionality, optical properties, and the local environment of Si-nc and the surrounding SiO2 matrix.

A first step in prediction of the nanoscale structure of porous silicon from processing parameters.

The present work addresses the formation of porous silicon layers by means of anodic dissolution of p- and p(+)-type boron-doped (100) silicon wafers in 15, 25, and 35 vol% HF-ethanol solutions. The study concerned the dependence of the porous silicon layer growth rate dh/dt on electric current density i as well as on HF concentration. The formation of a porous silicon layer was found to follow a generic linear relationship, in(dh/dt)--in(i), which holds irrespective of the processing conditions. The combination of two equations, experimental and theoretical, derived from Faraday's equation, allowed us to reach conclusions on the relationship between the growth rate dh/dt and the degree of porosity, constituting a first step in prediction of the nanoporous structure of silicon based on processing parameters. This electrochemical approach complements physical models of silicon pore formation.

Morphological control of laser-synthesized silicon nanoparticles.

Size and crystallinity controlled silicon nanoparticles were prepared by a laser ablation, in situ annealing and mobility size-selection with a differential mobility analyzer (DMA). The shape and crystal structure of generated particles were observed by a transmission electron microscopy (TEM). Both densification of agglomerates and crystal growth of the particles were observed. The size of silicon primary particle was increased by the annealing, and the uniformity of the particle classified at 10 nm was improved as a result.

Overstoichiometric low-energy nitrogen implantations into silicon--formation of gas nanobubbles vs. silicon nanowhiskers.

Accelerator-based ion implantation can be used to produce stoichiometric ratios beyond thermodynamic equilibrium. In the studies reported here, single crystalline silicon wafer material was implanted with high fluences of nitrogen. The implantations, performed with 15N at 5 keV/ion, resulted in the formation of highly swollen nitrogen rich surfaces that incorporated up to 63 at.% nitrogen. The implanted specimens were subsequently annealed with electron beams at high temperature, typically 1150 degrees C for moderately short periods of time (15 s) to investigate the formation of silicon nanowhiskers. However, it was observed that nanowhiskers, the formation of which can be expected by comparable understoichiometric implantations, did not appear. Although the shallow implantations created ultrathin silicon nitride films with typical thickness of 25 nm, laterally swollen areas of 400 +/- 50 nm were observed with atomic force microscopy operated in supersonic mode.

Element selective detection for supercritical-fluid chromatography.

This manuscript describes the use of Supercritical-Fluid Chromatography (SFC) with plasma spectrometric detection for the analysis of organometallics. An introduction on the principles and characteristics of Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is included, along with a discussion about requirements for coupling SFC to plasma detection and the different approaches for interfacing SFC to ICP. The last part of this review paper provides a comprehensive description of SFC-ICP applications for the analysis of organometallics containing iron, silicon, tin, chromium, arsenic, lead, mercury and antimony.

Particle migration from haemodialysis circuit: electron microscopy and microprobe analysis.

It has been recognized that storage inflammation in organs of uraemic patients is due to silicone particle migration from tubing segments of the haemodialysis circuit to blood. Nevertheless, iatrogenic storage of foreign material containing Si has been also observed in long-term dialysis patients which, in our Unit, used only PVC or PU-PVC tubings. The origin and the nature of the particulate has been investigated in vivo and in vitro on bioptical samples as well as on cuprophan dialyser and PVC tubing eluates. This study carried out by means of TEM, SEM and microprobe EDS revealed the presence of variously shaped material and particles containing Si in bioptical samples and in eluates. Si containing contaminants were not demonstrated in eluates filtered in absence of the dialyser. This result suggests that leachable products can result from the dialyser and that such release can be an additional risk for uraemic patients.