Colloidal environmental applications

Environmental applications of FIFFF have been carefully collected in a review by Gimbert et al. [35]. Separations of nanoparticles belong to the FIFFF tradition and this sector has recently found new, fully deserved impulse for microparticle separations. The FIFFF technique has been applied to analyze humic material and submicron Fe colloids. Coupled with ICP-MS, FIFFF has been applied to detect the major and trace element chemistry of aquatic colloids in groundwaters and to determine the trace element distribution in soil and compost-derived humic and colloidal fractions in municipal wastewater. Recently, the ICP-AES has also been proposed as a specific detector for FIFFF to analyze inorganic nanoparticles (Figure 12.12). 

A number of environmental applications [3] have been performed in order to size characterize colloids collected in rivers (riverbome particles, SPM, and sediments), clay samples and ground limestone (from soils), coal particles, diesel soot particles (from combustion processes), or airborne particles in urban areas (from waste incinerators, vehicles, household-heating systems, and manufacturing). In many of these cases, not only the size but also the particle size distribution was important and thus, in conjunction with the traditional UV detector, specific detectors such as ETAAS, ICP-MS, ICP-AES were used [40] in order to obtain more detailed, more specific compositional information. 

By coupling flow field-flow fractionation (flow FFF) to ICP-MS it is possible to investigate trace metals bound to various size fractions of colloidal and particulate materials.55 This technique is employed for environmental applications,55-57 for example to study trace metals associated with sediments. FFF-ICP-MS is an ideal technique for obtaining information on particle size distribution and depth profiles in sediment cores in addition to the metal concentrations (e.g., of Cu, Fe, Mn, Pb, Sr, Ti and Zn with core depths ranging from 0-40 cm).55 Contaminated river sediments at various depths have been investigated by a combination of selective extraction and FFF-ICP-MS as described by Siripinyanond et al,55... 

FT SER spectra have been obtained of many different types of compounds including some environmental contaminants. Initially, for environmental applications, very simple monosubstituted aromatic compounds are being studied. One of the simplest of these is 3-chloropyridine (CP). This compound gives very intense NIR-SER spectra on Cu colloids and on Cu electrodes (see Figure 7). Plot A of Figure 7 shows the SER spectrum of 1 mM CP on a Cu electrode and Plot B... 

Mackenzie, K., Hildebrand, H., and Kopinke, F. D. 2007. Nano-catalysts and colloidal suspensions of carbo-iron for environmental application. NSTI-Nanotech, 2, 639-642. 

Almost all urethane materials are synthesized without the use of solvents or water as diluents or earners and are referred to as being 100% solids. This is true of all foams and elastomers. There are many products, however, which do utilize solvents or water, and these are known as solvent-borne and waterborne systems, respectively. In the past, many coatings, adhesives, and binders were formulated using a solvent to reduce viscosity and/or ease application. However, the use of volatile solvents has been dramatically curtailed in favor of more environmentally friendly water (see Section 4.1.3), and now there are many aqueous coatings, adhesives, and associated raw materials. Hydrophilic raw materials capable of being dispersed in water are called water reducible (or water dispersible), meaning they are sufficiently hydrophilic so as to be readily emulsified in water to form stable colloidal dispersions. 

What we have covered in this chapter barely scratches the surface of a vast area of applications of colloidal phenomena in chemical and materials processing industries and in environmental and other operations. There are many fundamental, as well as practical, problems in the above topics (especially ones involving polymers, polyelectrolytes, and polymer-colloid and polymer-surfactant mixtures) that are currently areas of active research in engineering, chemistry, physics, and biology. Some of the references cited at the end of this chapter contain good reviews of topics that are extensions of what we have covered in this chapter (see, e.g., Elimelech et al. 1995, Hirtzel and Rajagopalan 1985, Israelachvili 1991, Gregory 1989, and O Melia 1990). 

Colloid and surface chemistry occupy a paradoxical position among the topics of physical chemistry. These are areas which have traditionally been considered part of physical chemistry and are currently enjoying more widespread application than ever due to their relevance to environmental and biological problems. At the same time, however, colloid and surface chemistry have virtually disappeared from physical chemistry courses. These topics are largely absent from the contemporary general chemistry course as well. It is possible, therefore, that a student could complete a degree in chemistry without even being able to identify what colloid and surface chemistry are about. 

Development of new in situ analytical methods for species determination - There is a disparity between the amount of speciation information obtained from laboratory studies on well-defined systems, and that which is applicable to the real environmental situation (Buffle, 1990). Development of in situ methods will facilitate more relevant measurements which minimise perturbation of the system. Systems particularly prone to measurement-induced artefacts include anoxic waters, the sediment-water interface and colloidal materials. Methods for accurate measurement of free metal ion concentration over a much broader concentration range than that currently available are particularly required. 

Maurice, P. (1996) Applications of atomic-force microscopy in environmental colloid and surface chemistry. Coll. Surf. A., 107, 57-75. 

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