Silicate sensor

Ionic conduction in silicate sensors and biosensors is important in order to decrease ohmic drops in amperometric applications. The conductivity of silicate networks is dependent on the imbedded salts and it is amply discussed in references within the context of ionic membranes (Wakamatsu, 1992 Gautierlimeau, 1992). Conductivity of silicates can be improved by surface modification so as to increase the concentration of the surface charges within the porous network or by incorporation of cationic or anionic polymers such... 

The mesoporous ordered silicas of different type represent the new generation of materials with unique properties. The discovery of these materials became basis for creation of new catalysts, adsorbents, sensors and supporter for other molecules. The most important way of the modifying physical and chemical properties of mesopurous silicas consist in organic components incorporation on the silica surface as part of the silicate walls or their insertion within channels of the mesopores. This ensured that interest in synthesis and study of functionalized mesoporous materials shai ply grew. In spite of it, these materials are studied insufficiently. 

Makote R., Collinson M.M., Organically modified silicate films for stable pH sensors, Analytica Chimica Acta 1999 394 195-200. 

Figure 6.3 Leaching of sensor layers M4, M1, M2 and M3 (from top) on exposure to a flow of buffer solution (left) and titration plots of AF in poly-TMOS (Ml), an organically modified silicate (M4), and covalently immobilized on ICPS (M2) and GOPS (M3) (right). (Reproduced from ref. 4, with permission.)...

Figure 6.5 A fluorinated organically modified silicate doped with [Ru(dpp)3]2+ is a highly sensitive 02 sensor. Fluorine here ensures unprecedented sensitivity and a remarkable stability (2% drift over 6 months). The material has been implemented in sol-gel handheld oxygen sensors that are already commercialized. (Reproduced from ref. 6, with permission.)...

Amperometric cells, sensors using, 22 271 Amperometric measurements, 14 612 Amphetamine, 3 89-90 Amphibole asbestos, 1 803 3 288 crystal structure, 3 297-298 exposure limits, 3 316 fiber morphology, 3 294-295 silicate backbone, 3 296 Amphibole potassium fluorrichterite, glass- ceramics based on, 12 637 Amphiphile-oil-water-electrolyte phase diagram, 16 427-428 Amphiphile-oil-water phase diagrams,... 

Sampling sites are also referred to as station locations. For water column work, depth profiles are constructed from seawater samples collected at representative depths. Temperature and salinity are measured in situ with sensors. Remote-closing sampling bottles deployed from a hydrowire are used to collect water for later chemical analysis, either on the ship or in a land-based laboratory. The standard chemical measurements made on the water samples include nutrients (nitrate, phosphate, and silicate), dissolved O2, and total dissolved inorganic carbon (TDIC) concentrations. 

Wall V. I and England R. N. (1979). Zn-Ee spinel-silicate-sulphide reactions as sensors of metamorphic intensive variables and process. Geol Soc. Amer. Abstr. Progr, 11 534. 

Figure 5.13 — Irreversible-reusable flow-through sensor for the kinetic multidetermination of phosphate and silicate based on integrated sorption of a reaction product, reaction (/ situ reduction) and photometric detection. (A) Microsensor block (1) and components (2). (B) Continuous-flow configuration coupled on-line to the sensor. P peristaltic pumps SV switching valve W waste. For details, see text. (Reproduced from [39] with permission of the American Chemical Society).

Analytical Methods. Temperature, pH, and oxygen were measured in situ by using a combined sensor (Ztillig). Ammonium was determined by flow injection analysis (27), and nitrate and silicate by spectrophotometric methods (Auto-Analyzer) (28). Sulfide was determined by using a H2S-specific electrode (29). 

By preparing polycyclic aromatic hydrocarbon nanocrystals grown in porous silicate films, Botzung-Appert et al. [57] have prepared potential fluorescent sensors based on electronic energy transfer quenching to an acceptor... 

Many of the UV-VIS spectrophotometric methods (shown in Tables 12.3 and 12.6) have been automated by using flow analyzers. Thus, nitrite and nitrate,50,82 ammonium,50,83 orthophosphate,50,84,85 silicates,50,86 chloride,50,87 cyanide,50,88 and sulfate50,89 are measured by CFA and FIA. Oxygen is measured by iodometric titration51,90 and electrochemical methods91 (Table 12.7). Other dissolved gasses (Table 12.2) are measured by ISE-based gas sensors. 

PEBBLEs are water-soluble nanoparticles based on biologically inert matrices of cross-linked polymers, typically poly(acrylamide), poly(decylmethacrylate), silica, or organically modified silicates (ORMOSILs), which encapsulate a fluorescent chemo-sensor and, often, a reference dye. These matrices have been used to make sensors for pH, metal ions, as well as for some nonionic species. The small size of the PEBBLE sensors (from 20 to 600 nm) enables their noninvasive insertion into a living cell, minimizing physical interference. The semipermeable and transparent nature of the matrix allows the analyte to interact with the indicator dye that reports the interaction via a change in the emitted fluorescence. Moreover, when compared to naked chemosensors, nanoparticles can protect the indicator from chemical interferences and minimize its toxicity. Another important feature of PEBBLEs, particularly valuable in intracellular sensing applications, is that the polymer matrix creates a separate... 

Because of their biocompatibility, chemical stability, high thermal and electrical conductivity, sorption ability, tuneable surfaces area, pore-size distribution and straightforward functionalization chemistry, porous carbons have found application in diverse topical areas such as sensors, fuel cells, hydrogen storage, and sorption.39 11 One particular property that distinguishes porous carbon from porous silica materials is the electrical conductivity of the former that has no counterpart in siliceous-based scaffoldings. This feature opens the route for certain applications... 

Since mesoporous materials contain pores from 2 nm upwards, these materials are not restricted to the catalysis of small molecules only, as is the case for zeolites. Therefore, mesoporous materials have great potential in catalytic/separation technology applications in the fine chemical and pharmaceutical industries. The first mesoporous materials were pure silicates and aluminosilicates. More recently, the addition of key metallic or molecular species into or onto the siliceous mesoporous framework, and the synthesis of various other mesoporous transition metal oxide materials, has extended their applications to very diverse areas of technology. Potential uses for mesoporous smart materials in sensors, solar cells, nanoelectrodes, optical devices, batteries, fuel cells and electrochromic devices, amongst other applications, have been suggested in the literature.11 51... 

Segmented gas-liquid (Taylor) flow was used for particle synthesis within the liquid slugs. Tetraethylorthosilicate in ethanol was hydrolyzed by a solution of ammonia, water and ethanol (Stober synthesis) [329]. The resulting silicic acid monomer Si (OH)4 is then converted by polycondensation to colloidal monodisperse silica nanoparticles. These particles have industrial application, for example, in pigments, catalysts, sensors, health care, antireflective coatings and chromatography. 

The book explores various examples of these important materials, including perovskites, zeolites, mesoporous molecular sieves, silica, alumina, active carbons, carbon nanotubes, titanium dioxide, magnesium oxide, clays, pillared clays, hydrotalcites, alkali metal titanates, titanium silicates, polymers, and coordination polymers. It shows how the materials are used in adsorption, ion conduction, ion exchange, gas separation, membrane reactors, catalysts, catalysts supports, sensors, pollution abatement, detergency, animal nourishment, agriculture, and sustainable energy applications. 

Fig. 7 Vertical distribution versus density (agy kg m 3) of temperature (T), salinity (S), transmission (Xmiss), dissolved oxygen measured with YSI oxygen sensor (02SB), dissolved oxygen measured by Winkler titration (02), hydrogen sulfide (H2S), phosphate (PO4), silicate (Si), nitrite (N02), ammonia (NH4), dissolved manganese (Mn diss), bivalent iron (Fe(II)), and trivalent iron (Fe(III)) at a station near the Bosporus (Cast 16, RV Knorr 172-05 cruise, April 04,2003). Concentrations of chemical parameters are in xM...

Instead of the system silica/silicate also other systems such as titania/titanate, zirconia/zirconate can be used as a reference system [xiv]. The response time of freshly fabricated thick-film sensors based on thin-film /3-alumina is very short (about 15 ms at 650 °C). After several weeks of operating this time increases 10 times (150 ms) [xv]. Solid electrolyte C02 sensors using Ni/carbonate composite as measuring electrode are suited for measuring of C02 in equilibrated water gases [xiv]. Using semiconducting oxides and carbonates like ITO (indium tin oxide) Nasicon-based C02 sensors are able to measure at room temperature [xvi]. 

Another state-of-the-art detection system contains a surface acoustic wave (SAW) device, which is based on a piezoelectric crystal whose resonant frequency is sensitive to tiny changes in its mass—it can sense a change of 10-1° g/cm2. In one use of this device as a detector it was coated with a thin film of zeolite, a silicate mineral. Zeolite has intricate passages of a very uniform size. Thus it can act as a molecular sieve, allowing only molecules of a certain size to pass through onto the detector, where their accumulation changes the mass and therefore alters the detector frequency. This sensor has been used to detect amounts of methyl alcohol (CH3OH) as low as 10 9 g. 

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