Influence of the Primary Structural Parameters of a Precipitated SiO on the Specific Parameters of the Adsorption Isotherms of Cholesterol Dissolved in Toluene

The influence of the primary structural parameters of the precipitated SiO 2 [globular diameter (d g ), coordination number (CN) and coalescence coefficient (CC)] on the specific parameters associated with the shapes of the adsorption isotherms [range of linearity (P), adsorption sensitivity (IS) and equilibrium adsorption capacity (a max )], the constants of the Freundlich isotherm (k and z) and the energy density distribution function parameters of the adsorption centres (β, m) was investigated. It was found that increasing the coordination number and coalescence coefficient values led to a decrease in the a max and z values, as well as in the fraction of dominant adsorption centres, while the β value and the specific amount of cholesterol adsorbed on the remained centres (a 2 ) increased. The changes in the range of linearity (P) of the adsorption isotherms were in agreement with the parameter values of the density distribution function, while the changes in adsorption sensitivity and the Freundlich constant k correlated with the changes in the specific amount of cholesterol adsorbed at the dominant adsorption centres. The optimal values for cholesterol adsorption and of the primary structural parameters of the adsorbents based on the precipitated SiO 2 were defined

Kinetics of the Release of Nicotinamide Absorbed on Partially Neutralized Poly(acrylic-co-methacrylic acid) Xerogel under the Conditions of Simultaneous Microwave Heating and Cooling

The kinetics of release of nicotinamide (NIAM) that was absorbed on partially neutralized poly(acrylic-co-methacrylic) (PAM) xerogel/hydrogel, under the conditions of simultaneous microwave heating and cooling (SMHC) were examined. The kinetics curves of NIAM release into an aqueous solution at temperatures of 308–323 K were recorded. By applying the model-fitting method (MFM), it was found that the kinetics of NIAM release can be modeled by a kinetic model of a first-order chemical reaction. The values of the release rate constants (kM) at different temperatures were calculated, and their values were found to be within the range 8.4 10−3 s −1−15.7 10−3 s−1. It has been established that the Arrhenius equation was valid even in the conditions of SMHC. The values of the kinetic parameters (activation energy (Ea) and pre-exponential factor (A) of the NIAM release process adsorbed on PAM xerogel/hydrogel were calculated as follows: Ea = 25.6 kJ/mol and ln (A/s−1) = 5.21. It has been proven that the higher value of the rate constant at SMHC in relation to CH is not a consequence of the overheating of the reaction system or the appearance of “hot-points”. The values of change of the enthalpy of activation (ΔH*) and the change of entropy of activation (ΔS*) were calculated as follows: ΔH* = +23.82 kJ/mol and ΔS* = −201.4 J/mol K. The calculated higher values of the kinetic parameters and thermodynamic parameters of activation are explained by the formation of a specific activated complex under SMHC, whose structure and degree of order are different than in the one formed under CH