Fluorapatite nanopowders with different amounts of fluoride ions were
prepared using the surfactant-assisted microwave method under isothermal
conditions. Microwave irradiation was applied for the rapid formation of
crystals. A micellar solution of polyoxyethylene (23) lauryl ether was used
as a regulator of nucleation and crystal growth. Characterization studies
from X-ray diffraction, field-emission scaning electron microscopy and
Fourier-transform infrared spectra showed that crystals have an apatite
structure and particles of all samples are nano size, with an average length
of 50 nm and about 15-25 nm in diameter. Antimicrobial studies have
demonstrated that synthesized fluorapatite nanopowders exhibit activity
against tested pathogens: Escherichia coli, Staphylococcus aureus and
Candida albicans. Activity increased with the amount of fluoride
ions. The synthesized fluorapatite nanomaterials are promising as
materials in environmental protection and medicine for orthopedics and
dental restorations. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 43009]
Phenol is a major pollutant in the waste waters coming from coal processing. Hydrodynamic cavitation presents a novel technology for phenol removal from waste waters. Hydrodynamic cavitation device with a cavitator of Ventury type for waste water purification was constructed. The hydraulic characteristic of the device were determined: the dependences of flow and cavitation number on inlet pressure. The effects of cavitation number, phenol concentration, pH, temperature, time, and quantity of added H 0 on the degree of phenol reduction in the waste water was investigated. The optimal 2 2 technological parameters of the investigated cavitation purification process of waste waters from phenol were determined.
Article Highlights • The exchange of adsorbed water with ethanol is an elementary kinetic process • The kinetics can be best mathematically described with the kinetic model of the first order • The values of activation energy and the pre-exponential factor of exchange are calculated • The entropy term has a dominant influence on the kinetics of exchange • The exchange of the absorbed water with ethanol results in shrinking of the hydrogel
Isothermal kinetics of the exchange of absorbed water in a silica hydrogel
(SH) with ethanol was examined. The isothermal kinetic curves of absorbed
water exchange with ethanol were measured at the temperatures: T = = 297,
306 and 316 K. The rate of the exchange was analysed as a function of time.
The possibility of mathematical description of the kinetics of exchange by
the Brouers and Sotolongo-Costa?s (BS) fractal?s kinetics model was
examined. Parameter values (n, ?, ?) of the model and their changes with
temperature were calculated. By applying the method of Ozao, it was
determined that the rate limiting step of the process of exchange was the
rate of exchange of the absorbed water with ethanol. Values of the fractal
dimension of the SH-ethanol interphase were calculated. The dependences of
the effective time-dependent rate coefficient, activation energy and
pre-exponential factor on time and degree of exchange were calculated and
discussed. The proposed model of the mechanism of the exchange of absorbed
water with ethanol was discussed.
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