Sorption sites range

Results of adsorption experiments for butylate, alachlor, and metolachlor in Keeton soil at 10, 19, and 30°C were plotted using the Freundlich equation. A summary of the coefficients obtained from the Freundlich equation for these experiments is presented in TABLE IV. Excellent correlation using the Freundlich equation over the concentration ranges studied (four orders of magnitude) is indicated by the r values of 0.99. The n exponent from the Freundlich equation indicates the extent of linearity of the adsorption isotherm in the concentration range studied. If n = 1 then adsorption is constant at all concentrations studied (the adsorption isotherm is linear) and K is equivalent to the distribution coefficient between the soil and water (Kd), which is the ratio of the soil concentration (mole/kg) to the solution concentration (mole/L). A value of n > 1 indicates that as the solution concentration increases the sorption sites become saturated, resulting in a disproportionate amount of chemical being dissolved. Since n is nearly equal to 1 in these studies, the adsorption isotherms are nearly linear and the values for Kd (shown in TABLE IV) correspond closely to K. These Kd values were used to calculate heats of adsorption (AH). 

Developed inner surfaces are represented to give clever illustrations of sorption sites geometry. Depending on the temperature range and the molecular size of sorbed... 

NaY relative to NaX, particularly in sites within socialite units (2g). Proton magnetic relaxation studies show that in hoth types NaX and NaY zeolites, up to about 5% of the total sorption sites for water, or ca. 1.3 g/100 g zeolite, the range covered in the present study, are distinguished by the fact that the residence time of individual water molecules retained on them is one-hundred times larger than that of molecules occupying all other sites (26) this observation was interpreted, however, as being due to sorption at crystal imperfections. 

These assumptions are justifiable as the heat of adsorption of the small inert sorbate (e.g., N2 or Ar) is rather low and, hence, differences between sorption sites at the surface will be very small. Similarly, the interaction between the first and the following layers will be close to the heat of condensation, as the effect of polarization by the surface will be small beyond the first layer (screening of the long-range van der Waals forces). From its conception, the BET theory extends the Langmuir model to multilayer adsorption. It postulates that under dynamic equilibrium conditions the rate of adsorption in each layer is equal to the rate of desorption from that layer. Molecules in the first layer are located on sites of constant interaction strength and the molecules in that layer serve as sorption sites for the second layer and so forth. The surface is, therefore, composed of stacks of sorbed molecules. Lateral interactions are assumed to be absent. With these simplifications one arrives at the BET equation... 

With both ethane and propane the heats of sorption in NaY increased gradually with loading due to sofbate-sorbate interactions over the range 0-5 molecules per supercage. This increase was 2 and 9 kJ moH respectively for these two soibates. The smaller ethane molecule was able to pick up some h erogeneity in the sorption sites of the NaY supercages at... 

Standard swption entropy values, AS°, that refer te a gas-phase pressure, => 760 torr, as standard state, show wave-like concentration dependences for the two gases on NaLSX, (f.. Fig. 4. Compared to their standard gas phases, a remarkable entropy loss takes place ovct the entire ranges of n. Particular, CO2 experiences less lieedom than N2O, due to its stronger interaction with sorption sites and, probabfy, denser sorption-phase paddng. 

The response dynamic range of the typical SAW sensor is very broad and could be up to six orders of magnitude. The sensor reaches its saturation point only when the target chemical in the sample is sufficiently concentrated to occupy most or all active sorption sites available on the polymer-coated surface. 

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