Nanostructured Materials for Selective Collection of Trace‐Level Metals from Aqueous Systems

Abstract

Several separations and fi ltration techniques are available for the collection of trace -level species and each method must be matched to a specifi c application. For trace -level metals in solution arguably the best and most widely used methods involve solid phase sorbent materials that provide effective capture of desired metal species. Effectiveness of the solid phase sorbent for any given application is determined by availability, cost, and performance. Activated carbon and ion exchangers are widely available and relatively cheap but lack, in most cases, the performance necessary for many analytical applications. Activated carbon and ion exchangers generally fail to have the selectivity and affi nity needed for trace analyte collection from actual environmental matrices.To understand and respond to situations involving toxic materials it is critical to quickly identify the toxic material(s) involved and the extent of contamination. This is a key issue for circumstances ranging from responding to terrorist attacks to monitoring the effects of environmental remediation. Unfortunately, analytical technology does not presently exist to meet these needs. Instruments powerful enough to meet the required speed, sensitivity, and selectivity requirements often do not function well outside of rigorously controlled laboratory conditions and are usually very complex and expensive. Simple screening methods that provide immediate results in the fi eld enable on -site, near real -time decisions. These fi eld screening methods are typically less costly and more rapid than formal laboratory analysis; this is signifi cant since site testing and monitoring typically involves extensive sampling. To meet this need, a wide range of fi eld screening methods for identifying chemical, biological, and nuclear materials is presently being marketed and used. Unfortunately, existing fi eld assay methods are typically inadequate because they lack the selectivity and sensitivity needed to provide reliable information. The degree and type of improvement needed vary with the application but sensitivity improvements of greater than 1000 × are typically required, and much larger enhancements would usually be preferred. This large 192 8 Nanostructured Materials for Selective Collection of Trace-Level Metals from Aqueous Systems leap in analytical performance is very unlikely to be achieved with incremental improvements in measurement procedure, instrument design, or improved electronics. A new analytical approach is required.In many circumstances the defi ciencies in selectivity and sensitivity could be addressed with high -performance sorbent materials that selectively concentrate target analytes. In addition to concentrating target analytes the sorbent can exclude interfering species and provide a uniform, well -defi ned sample matrix for analysis. Sorbents coupled with instrumentation could be used for either real -time analysis of the signature species or as a rapid screening method to fl ag those samples that require more detailed analysi...

Functionalized Nanoporous Silica for the Removal of Heavy Metals from Biological Systems: Adsorption and Application

“…This binding consistency indicates that the thiol surface remains active throughout the pH range encountered in the gastrointestinal tract. While speciation in the biological solution can be complex, the observed pH-dependent adsorption of Cd and Pb ions can likely be attributed to the hydrolysis behavior of these ions over the pH range because a similar behavior has been observed in aquatic matrices (83)(84)(85). The K d value of As was high at pH 1.1 (K d ∼ 17 000), decreased to by a factor of 10 as the pH increased from 1.1 to 4.0, and rose again as the pH became more neutral (5.6-8.3).…”

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

“…Nanomaterials have seen increased attention for heavy metal remediation applications since the nanostructured surfaces offer large surface areas that provide enhanced capacity as well as the ability to enhance contaminant affinity with chemical modification of the surface. − Sorbents comprised of bare magnetite and maghemite − as well as examples of each of these iron oxide phases coated with affinity ligands or polymers − have been used increasingly for the targeting of contaminants from wastewater. They are attractive candidates due to the oxides’ inherent affinity for many toxic chemicals but have the added advantage that they are also easily removed through magnetic manipulation .…”