Gilbert M. Brown

Mesoporous TiO2–B Microspheres with Superior Rate Performance for Lithium Ion Batteries

Advanced energy storage systems such as lithium ion batteries are important approaches to mitigate energy shortage and global climate warming issues that the world is currently facing. High power and high energy density are essential to batteries for applications in electric vehicles, stationary energy storage systems for solar and wind energy as well as smart grids. Because conventional lithium ion batteries are inadequate to meet these needs, advanced materials with high capacity and fast chargedischarge capability are critical for next generation lithium ion batteries. [ 1 ] Titanium dioxide (TiO 2 ) with various polymorphs (anatase, rutile, and TiO 2 –B (bronze)) have been widely investigated as lithium ion battery anode materials, due to their advantages in terms of cost, safety and rate capability. [ 2 ] In particular, the polymorph of TiO 2 –B shows a favorable channel structure for lithium mobility, which results in fast chargedischarge capability of a lithium cell. [ 3 ] It has been identifi ed that the lithium intercalation in TiO 2 –B features a pseudocapacitive process, rather than the solid-state diffusion process observed for anatase and rutile. [ 4 ] Theoretical studies have uncovered that this pseudocapacitive behavior originates from the unique sites and energetics of lithium absorption and diffusion in TiO 2 –B structure. [ 5 ] As a result, TiO 2 –B nanoparticles, [ 6 ] nanotubes, [ 7 ]

A novel self-assembled monolayer (SAM) coated microcantilever for low level caesium detection

We report a new sensor concept based on an ion-selective SAM modified microcantilever which can detect caesium ion concentrations in situ in the range 10−11–10−7 M and shows potential for use in developing a new family of real time in situ metal ion sensors with high sensitivity/selectivity and low cost, for chemical and biological applications.

A pH Sensor Based on a Microcantilever Coated with Intelligent Hydrogel

Abstract Hydrogels that contain different amounts of amino groups were used to modify microcantilevers for the pH measurements. These microcantilevers deflected upon exposure to various pH solutions due to the swelling and shrinking of the hydrogels. The microcantilever deflection, as a function of pH, is nearly linear in a wide pH range. A significant 1000 nm/pH bending response was observed from a Gel‐4 coated microcantilever, which could be used for precise pH measurements. Such hydrogel coated microcantilevers could potentially be used to prepare microcantilever chemical and biological sensors when molecular recognition agents are immobilized into the polymer.

Electrochemically induced adsorption of radio-labeled DNA on gold and HOPG substrates for STM investigations

In a scanning tunneling microscope (STM) electrochemical cell we have studied the effects of electrode potential on both the surface topography and the adsorption of deoxyribonucleic acid (DNA) to graphite and gold surfaces. Images of the surface of highly oriented pyrolytic graphite (HOPG), of the same area, in response to a positive increase in surface potential show degradation of the step edges with little change in the crystal plane. Images of the same area of a gold surface demonstrate the formation of and the progressive increase in nodular structures on the crystal planes, in response to increased potential, with little effect on the step edges. Using radio-labeled DNA we monitored electrochemical absorption onto HOPG and gold surfaces. Although at no applied potential and at negative surface potentials some DNA was bound, at positive potentials 3 to 5 times more DNA was incorporated onto both surfaces. DNA adsorbed to a surface at a positive potential was not removed by reversing the potential.

The Chemistry of Perchlorate in the Environment

The persistence of perchlorate in groundwater can be understood from its chemical and physical properties and its chemical reactivity. Although perchlorate is a powerful oxidizing agent, its notorious lack of reactivity can be understood from the requirement that reduction involves oxygen atom transfer. Because perchlorate is relatively unreactive, remediation schemes involving direct chemical or electrochemical reduction are not effective. The low hydration energy of perchlorate anions favors sorption on organic anion exchange resins. Remediation methods involving collection on such resins prior to reduction or some other means of disposal are feasible. Biological systems that naturally reduce and degrade perchlorate are also a potentially practical means of remediating perchlorate-contaminated groundwater in a cost-effective manner.

Efficient Treatment of Perchlorate (ClO4 −)-Contaminated Groundwater with Bifunctional Anion Exchange Resins

The perchlorate (ClO4 −) anion originates as a contaminant in the environment primarily from the disposal of solid salts of ammonium or sodium perchlorate, which are very soluble in water.1,2 Although thermodynamically a strong oxidizing agent, the perchlorate anion is known to be kinetically inert in many redox reactions and noncomplexing in its interactions with typical metal ions found in the environment. These properties make the perchlorate ion exceedingly mobile in the subsurface soil environment. It can persist for many decades under typical groundwater and surface-water conditions because of kinetic barriers in its reactivity with other organic or inorganic constituents. Large volumes of perchlorate-containing compounds have been disposed of in the environment since the 1950s.1 However, the extent of the problem was not folly realized until 1997, shortly after the development of a sensitive ion Chromatographic method for detecting ClO4 − in water.3 A national survey indicates that 44 states have former perchlorate manufacturers or users; ClO4 − has now been detected in groundwater or surface water in 14 states.2 For example, water suppliers in California have detected ClO4 − in 144 public water-supply wells; 3 8 of these are above California’s advisory action level of 18 μg L−1 ClO4 −.

The reduction of chlorate and perchlorate ions at an active titanium electrode

Perchlorate ion is electrochemically reduced to chloride ion at an active titanium electrode in aqueous 1.0 M HClO4. The reduction occurs by direct reaction at the surface rather than a pathway involving catalysis by soluble titanium corrosion products. The reaction occurs by oxygen atom transfer to the titanium surface, and the implications of this mechanism for the surface composition of active titanium electrodes are discussed. Chlorate ion is also reduced at titanium, and the rate constant for chlorate reduction is at least 105 times greater than that for perchlorate reduction.

Quantitative Electrochemical Measurements Using In Situ ec-S/TEM Devices

Insight into dynamic electrochemical processes can be obtained with in situ electrochemical-scanning/transmission electron microscopy (ec-S/TEM), a technique that utilizes microfluidic electrochemical cells to characterize electrochemical processes with S/TEM imaging, diffraction, or spectroscopy. The microfluidic electrochemical cell is composed of microfabricated devices with glassy carbon and platinum microband electrodes in a three-electrode cell configuration. To establish the validity of this method for quantitative in situ electrochemistry research, cyclic voltammetry (CV), choronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were performed using a standard one electron transfer redox couple [Fe(CN)6]3-/4--based electrolyte. Established relationships of the electrode geometry and microfluidic conditions were fitted with CV and chronoamperometic measurements of analyte diffusion coefficients and were found to agree with well-accepted values that are on the order of 10-5 cm2/s. Influence of the electron beam on electrochemical measurements was found to be negligible during CV scans where the current profile varied only within a few nA with the electron beam on and off, which is well within the hysteresis between multiple CV scans. The combination of experimental results provides a validation that quantitative electrochemistry experiments can be performed with these small-scale microfluidic electrochemical cells provided that accurate geometrical electrode configurations, diffusion boundary layers, and microfluidic conditions are accounted for.

Survey of bottled waters for perchlorate by electrospray ionization mass spectrometry (ESI-MS) and ion chromatography (IC)†

Perchlorate has been identified in ground and surface waters around the USA including some that serve as supplies for drinking water. Because perchlorate salts are used as solid oxidants in rockets and ordnance, water contamination may occur near military or aerospace installations or defense industry manufacturing facilities. This ion has been added to the Environmental Protection Agencys Contaminant Candidate List and the Unregulated Contaminant Monitoring Rule. Concern over perchlorate has prompted many residents in affected areas to switch to bottled water; however, bottled waters have not previously been examined for perchlorate contamination. Should the EPA promulgate a regulation for municipal water systems, US law requires the Food and Drug Administration to take action on bottled water. Methods will therefore be required to determine perchlorate concentrations not only in tap water, but also in bottled waters. Ion chromatography (IC) is the primary technique used for its analysis in drinking water, but it does not provide a unique identification. Confirmation by electrospray ionization mass spectrometry (ESI-MS) can serve in this capacity. The ESI-MS method can be applied to these products, but it requires an understanding of matrix effects, especially of high ionic strength that can suppress electrospray. When using methyl isobutyl ketone (MIBK) as the extraction solvent, the ESI-MS method can reach lower limits of detection of 6 ng ml −1 for some bottled waters. However, dilution required to negate ionic strength effects in mineral waters can raise this by a factor of 10 or more, depending on the sample. Decyltrimethylammonium cation (added as the bromide salt) is used to produce an ion pair that is extracted into MIBK. After extraction, the sum of the peak areas of the ions C10H21NMe3(Br)(ClO4)− (m/z = 380) and C10H21NMe3(ClO4)2− (m/z = 400) is used to quantitate perchlorate. Standard additions are used to account for most of the matrix effects. In this work, eight domestic brands and eight imported brands of bottled water were comparatively analyzed by the two techniques. For comparison, a finished potable water known to contain perchlorate was also tested. None of the bottled waters were found to contain any perchlorate within the lower limit of detection for the IC method. Recoveries on spiked samples subjected to the IC method were ≥98%. Published in 2000 for SCI by John Wiley & Sons, Ltd

Organic scintillators for neutron detection

The goal of the present work has been to develop a method for the efficient and reliable production of gadolinium- and boron-containing solid scintillator. Polyvinyl toluene, silicone rubber, and other materials were investigated. Gadolinium in a solid overcomes the limitations of the physical form of a liquid, and silicone rubber as a carrier for either gadolinium or boron overcomes the thermal limitations of plastics. Silicone rubbers also introduce some interesting and useful properties (such as flexibility) of their own. We report here the fabrication of solid organic scintillators loaded with as much as 2% gadolinium, and more than 5% boron. A gadolinium-containing compound, soluble in vinyl toluene monomer and not inhibiting polymerization, was found. The same compound was also found to be soluble in phenyl-substituted silicone fluids that subsequently could be polymerized. In addition, a class of boron compounds also soluble in silicone fluids and not inhibiting polymerization was found. In the absence of phosphors, the resulting boron- and gadolinium-loaded disks were clear and colorless, or only slightly yellow. The disks were compatible with UV-, blue-, blue-green, and green-emitting phosphors and a variety of colors were realized. In addition, it was found in the case of gadolinium loading, the discrete spectrum due to atomic x-rays and conversion was observable if the scintillator sample was small.