Organic colloidal materials, particle size

Sorption coefficients quantitatively describe the extent to which an organic chemical is distributed at equilibrium between an environmental solid (i.e., soil, sediment, suspended sediment, wastewater solids) and the aqueous phase it is in contact with. Sorption coefficients depend on (1) the variety of interactions occurring between the solute and the solid and aqueous phases and (2) the effects of environmental and/or experimental variables such as organic matter quantity and type, clay mineral content and type, clay to organic matter ratio, particle size distribution and surface area of the sorbent, pH, ionic strength, suspended particulates or colloidal material, temperature, dissolved organic matter (DOM) concentration, solute and solid concentrations, and phase separation technique. 

It may be deduced from KP = Koc x foc that partition coefficients of hydro-phobic organic compounds in general are dependent upon the chemical of interest (compound-specific properties affect the value of Koc) and the matrix properties of the medium in which it resides. In addition to the fraction of organic carbon present in the sorption phase, additional environmental factors affect partitioning. These factors include temperature, particle size distribution, the surface area of the sorbent, pH, ionic strength, the presence of suspended material or colloidal material, and the presence of surfactants. In addition, clay minerals may act as additional sorption phases for organic compounds. Nevertheless, organic carbon-normalized partition... 

Stable colloids of nanometer-sized lamellar manganese oxides have been prepared by intercalation and self-assembly direct reduction methods. The structures, particle sizes, and optical properties of the materials have been described. Organic amine/ammonium species (TAA and DA) were used to intercalate birnessite H-OL-1 to prepare TAA-OL-1. Many kinds of structures and their formation processes were also described. The effects of organic ammonium cations and organic amines on the preparation of the manganese oxides were studied systematically. 

Another interesting aspect of particle size effect is related to the density of photons absorbed by semiconductor particles, in comparison with the density of particles in a solution. Considering two solutions containing colloids of different sizes, in one case for instance 3-nm and in the other 4-pm particles, then many more particles are present in the solution of 3-nm colloid than in that of 4-pm colloid, provided that the total concentration of the semiconductor material is identical in both solutions. The two solutions differ only insofar as the same material is distributed over a small density of large particles (4 pm) or over a high density of small particles (3 nm). As can be easily calculated, a time interval of 5.4 ms exists between the absorption events of two photons in one individual 3-nm particle for a photon flux of 4 x lO cm s , assuming that all photons are absorbed in the colloidal solution [62], In the case of the 4-pm particles, the time interval between two absorption events is only about 20 ps for the same photon flux, i.e. it is shorter by a factor of 10, compared with the time interval estimated for the 3 nm particle. This difference can be important for reactions where two or more electrons are involved, typically in many oxidation and reduction reactions with organic molecules. 

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