Short-Pathlength, High-Pressure Flow Cell for Static and Time-Resolved Infrared Spectroscopy Suitable for Supercritical Fluid Solutions Including Hydrothermal Systems

An optical flow cell for high pressures and temperatures is described. The use of a novel window design allows for a precise, fixed optical pathlength that can be varied by use of spacers that range from a few micrometers to several millimeters. The cell pathlength is not affected by changes in pressure or temperature. The novel window design may be applicable to other high-pressure spectroscopic cells. The flow-cell design has a minimal sample dead volume, which is important for kinetic studies. The design eliminates the need for brazing or for a soft-sealing material for the optical windows, thereby minimizing the number of materials in contact with the sample. Using only diamond and platinum or platinum alloys as the corrosion resistant materials, the design is optimized for the study of aqueous solutions at high temperatures. Infrared spectra of an aqueous sodium tungstate solution up to 400 °C and 380 bar pressure are presented. Time-resolved infrared data are also presented for the ultraviolet photolysis reaction of β-naphthoyl azide in supercritical carbon dioxide

Detection of Cd, Pb, and Cu in non-pretreated natural waters and urine with thiol functionalized mesoporous silica and Nafion composite electrodes

Electrochemical sensors have great potential for environmental monitoring of toxic metal ions in waters due to their portability, field-deployability and excellent detection limits. However, electrochemical sensors employing mercury-free approaches typically suffer from binding competition for metal ions and fouling by organic substances and surfactants in natural waters, making sample pretreatments such as wet ashing necessary. In this work, we have developed mercury-free sensors by coating a composite of thiol self-assembled monolayers on mesoporous supports (SH-SAMMS(™)) and Nafion on glassy carbon electrodes. With the combined benefit of SH-SAMMS(™) as an outstanding metal preconcentrator and Nafion as an antifouling binder, the sensors could detect 0.5 ppb of Pb and 2.5 ppb of Cd in river water, Hanford groundwater, and seawater with a minimal amount of preconcentration time (few minutes) and without any sample pretreatment. The sensor could also detect 2.5 ppb of Cd, Pb, and Cu simultaneously. The electrodes have long service times and excellent single and inter-electrode reproducibility (5% RSD after 8 consecutive measurements). Unlike SAMMS(™)-carbon paste electrodes, the SAMMS(™)-Nafion electrodes were not fouled in samples containing albumin and successfully detected Cd in human urine. Other potentially confounding factors affecting metal detection at SAMMS(™)-Nafion electrodes were studied, including pH effect, transport resistance of metal ions, and detection interference. With the ability to reliably detect low metal concentration ranges without sample pretreatment and fouling, SAMMS(™)-Nafion composite sensors have the potential to become the next generation metal analyzers for environmental and bio-monitoring of toxic metals

Nanostructured Metal Oxide Sorbents for the Collection and Recovery of Uranium from Seawater

The ability to collect uranium from seawater offers the potential for a long-term green fuel supply for nuclear energy. However, extraction of uranium, and other trace minerals, is challenging because of the high ionic strength and low mineral concentrations in seawater. Herein we evaluate the use of nanostructured metal oxide sorbents for the collection and recovery of uranium from seawater. Chemical affinity, chemical adsorption capacity, and uptake kinetics of sorbent materials were evaluated. Materials with higher surface area clearly produced better sorbent performance. Uptake kinetics showed that the materials could rapidly equilibrate in a few hours with effective solution contact. Manganese, iron oxide, and especially Mn–Fe nanostructured composites provided the best performance for uranium collection from seawater. The preferred materials were demonstrated to extract uranium from natural seawater with up to 3 mg U/g-sorbent in 4 h of contact time. Inexpensive nontoxic carbonate solutions were demonstrated to be an effective and environmentally benign method of stripping the uranium from the metal oxide sorbents. Various formats for the utilization of the nanostructured metals oxide sorbent materials are discussed, including traditional methods and nontraditional methods such as magnetic separation

Manganese Doping of Magnetic Iron Oxide Nanoparticles: Tailoring Surface Reactivity for a Regenerable Heavy Metal Sorbent

A method for tuning the analyte affinity of magnetic, inorganic nanostructured sorbents for heavy metal contaminants is described. The manganese-doped iron oxide nanoparticle sorbents have a remarkably high affinity compared to the precursor material. Sorbent affinity can be tuned toward an analyte of interest simply by adjustment of the dopant quantity. The results show that following the Mn doping process there is a large increase in affinity and capacity for heavy metals (i.e., Co, Ni, Zn, As, Ag, Cd, Hg, and Tl). Capacity measurements were carried out for the removal of cadmium from river water and showed significantly higher loading than the relevant commercial sorbents tested for comparison. The reduction in Cd concentration from 100 ppb spiked river water to 1 ppb (less than the EPA drinking water limit of 5 ppb for Cd) was achieved following treatment with the Mn-doped iron oxide nanoparticles. The Mn-doped iron oxide nanoparticles were able to load ∼1 ppm of Cd followed by complete stripping and recovery of the Cd with a mild acid wash. The Cd loading and stripping is shown to be consistent through multiple cycles with no loss of sorbent performance