ZnO/ZnWO
4
composite rod-like nanoparticles were synthesized by low-temperature soft solution method at 95 °C with different reaction times (1–120 h), in the presence of non-ionic copolymer ...surfactant Pluronic F68. Obtained nanoparticles had diameters in the range around 10 nm and length of 30 nm. Optical properties such as reflection and room temperature photoluminescence of obtained samples showed strong dependence on their crystallinity and composition. Photocatalytic activity of ZnO/ZnWO
4
nanopowders was checked using photodegradation of selected dyes as model system. Obtained results were correlated with specific surface area, particle sizes, crystallinity and ZnO/ZnWO
4
ratio of the samples. As crystallinity of ZnWO
4
component in the ZnO/ZnWO
4
increase, photocatalytic activity also increases. The main findings can be explained by charge transfer reactions that follow light absorption by ZnO and ZnWO
4
in nanocomposite.
A statistical design was used to investigate the effect of various processing
conditions on the structure of sol-gel derived Mg(II) doped alumina. Six
processing variables were selected based on the ...Plackett-Burman design:
concentration of magnesium nitrate, time and temperature of alcohol
evaporation, temperature and time of annealing and heating rate were changed
at two levels. For every set of conditions, samples with different specific
surface area and degree of crystallinity were obtained. Analysis of the
results showed that annealing temperature , heating rate and concentration of
magnesium nitrate were the main factors affecting average crystallite size of
the predominant phase of alumina. In the case of the specific surface area,
two of selected six variables had pronounced effect; however the temperature
of annealing was more effective than others. The present results show that
the proposed model that uses crystallite size as a response variables is
preferable to further research.
Experimental adsorption isotherms were used to evaluate the specific surface area and the surface fractal dimensions of acid-activated bentonite samples modified with a heteropoly acid (HPW). The aim ...of the investigations was to search for correlations between the specific surface area and the geometric heterogeneity, as characterized by the surface fractal dimension and the content of added acid. In addition, mercury intrusion was employed to evaluate the porous microstructures of these materials. The results from the Frankel-Halsey-Hill method showed that, in the p/p sub(0) region from 0.75 to 0.96, surface fractal dimension increased with increasing content of heteropoly acid. The results from mercury intrusion porosimetry (MIP) data showed the generation of mesoporous structures with important topographical modifications, indicating an increase in the roughness (fractal geometry) of the surface of the solids as a consequence of the modification with the heteropoly acid. By comparison, MIP is preferable for the characterization because of its wide effective probing range.
Active porous alumina was prepared via a sol-gel method and subjected to thermal treatment in the temperature range 500-1200 ?C. The addition of lanthanum effectively inhibited the surface area loss ...of the aluminas. Fractal analysis from nitrogen adsorption isotherm was used to study the pore surface roughness of alumina samples with different chemical compositions (PEG, PEG and lanthanum) and calcinations conditions in terms of the surface fractal dimension, d. The Mahnke and M?gel (MM) model was used to determine the value of d of La(III)-doped alumina. Following the MM model, the d value of the activated aluminas increased as the calcination temperature increased from 500 to 700 ?C but decreased after calcination at 1000, 1100 and 1200 ?C. The addition of polyethylene glycol (PEG 5600) to the boehmite sol reduced the surface fractal of the activated alumina due to the heterogeneous distribution of the pores. With increasing La(III) concentration from 0.015 to 0.045 mol La(III)/mol Al(III), the d value of La-modified alumina samples decreased, indicating a smoother surface. The obtained PEG+La-doped boehmite sol can be used as a precursor dispersion for the deposition of mesoporous alumina coatings on stainless steel foil, by the spray pyrrolysis method.
Sintering and crystallization of low-density polyethylene glycol (PEG) and
lanthanum, La(III)-doped Al2O3 aerogels prepared from aluminum isopropoxide
were investigated. The sintering behavior of ...non-doped and doped aerogels was
examined by following the change of specific surface area with isothermal
heat-treatment. The specific surface area and crystalline phases of non-doped
and PEG+La(III)-doped aerogels were determined, and the effects of dopants on
the sintering and crystallization of Al2O3 aerogels are discussed. Isothermal
sintering experiments showed that the sintering mechanism of non-doped and
PEG+La(III)-doped Al2O3 aerogels is surface diffusion. The specific surface
areas of alumina samples decrease rapidly during the initial period of
sintering, and more slowly with prolonged sintering time. The change of the
porous structure is correlated with the phase transformation of ?-Al2O3
during calcinations of Al2O3 aerogels. The surface area of non-doped Al2O3
aerogels came to about 20 m2g-1 with heat-treatment at 1100?C because of
crystallization of ?-Al2O3 after densification. In the case of heattreatment
at 1200?C, the largest surface area was observed for PEG+La(III) doped Al2O3
aerogels and the XRD pattern showed only low ordered ?-Al2O3. These indicate
that the addition of PEG+La(III) to boehmite sol prevents Al2O3 aerogels from
sintering and crystallizing to the ?-Al2O3 phase. Even after 20 h at 1000?C,
PEG+La (III)-doped alumina samples maintain a rather good specific surface
area (108 m2 g-1) in comparison to the non-doped, containing mainly ?-Al2O3
and minor amounts of ?-Al2O3. Aluminum-oxides with these structural and
textural properties are widely used as a coatings and catalyst supports in
the field of various catalysis.
nema
In this study, the statistical design of the experimental method was applied
on the acid activation process of bentonite with microwave irradiation. The
influence of activation parameters (time, acid ...normality and microwave
heating power) on the selected process response of the activated bentonite
samples was studied. The specific surface area was chosen for the process
response, because the chemical, surface and structural properties of the
activated clay determine and limit its potential applications. The
relationship of various process parameters with the specific surface area of
bentonite was examined. A mathematical model was developed using a
second-order response surface model (RSM) with a central composite design
incorporating the above mentioned process parameters. The mathematical model
developed helped in predicting the variation in specific surface area of
activated bentonite with time (5-21 min), acid normality (2-7 N) and
microwave heating power (63-172 W). The calculated regression models were
found to be statistically significant at the required range and presented
little variability. Furthermore, high values of R2 (0.957) and R2 (adjusted)
(0.914) indicate a high dependence and correlation between the observed and
the predicted values of the response. These high values also indicate that
about 96% of the result of the total variation can be explained by this
model. In addition, the model shows that increasing the time and acid
normality improves the textural properties of bentonites, resulting in
increased specific surface area. This model also can be useful for setting an
optimum value of the activation parameters for achieving the maximum specific
surface area. An optimum specific surface area of 142 m2g-1 was achieved with
an acid normality of 5.2 N, activation time of 7.38 min and microwave power
of 117 W. Acid activation of bentonite was found to occur faster with
microwave irradiation than with conventional heating. Microwave-assisted
processes have the potential to develop into a cost efficient route for acid
activation of bentonite.
nema
ZnO/ZnWO(4) composite rod-like nanoparticles were synthesized by low-temperature soft solution method at 95 degree C with different reaction times (1-120 h), in the presence of non-ionic copolymer ...surfactant Pluronic F68. Obtained nanoparticles had diameters in the range around 10 nm and length of 30 nm. Optical properties such as reflection and room temperature photoluminescence of obtained samples showed strong dependence on their crystallinity and composition. Photo-catalytic activity of ZnO/ZnWO(4) nanopowders was checked using photodegradation of selected dyes as model system. Obtained results were correlated with specific surface area, particle sizes, crystallinity and ZnO/ZnWO(4) ratio of the samples. As crystallinity of ZnWO(4) component in the ZnO/ZnWO(4) increase, photocatalytic activity also increases. The main findings can be explained by charge transfer reactions that follow light absorption by ZnO and ZnWO(4) in nanocomposite.
The experimental results obtained at the pilot plant and industrial reactor level, have led to the following conclusions: the technology of activating diatomite with characteristics feasible for ...application in the synthesis of a nickel hydrogenation catalyst and the technology of the nickel hydrogenation catalyst synthesis, have been mastered. The performed synthesis of a "scale-up" catalyst has confirmed the high reproducibility of the synthesis methodology, as well as the good catalytic performances of the laboratory-level synthesized catalyst. The results obtained in the edible vegetable oils (soybean and sunflower oil) hydrogenation process, in a pilot plant and in an industrial 5-ton reactor, do indisputably demonstrate that the synthesized catalyst NICAT-2000 possesses all the properties of other modern catalysts of the same type. The parameters tested such as: the hydrogenation duration-related change of the fatty acids concentration; good selectivity of the catalyst; change in the refractive index and the hydrogenated mass melting point relative to the iodine value change; the change and content of total trans-fatty acids; dilatation changes; good filterability of the catalyst and a negative reaction to the residual nickel that may be present in the product after primary filtration, all indicate that the NICAT-2000 catalyst may be successfully applied in the food industry's vegetable oils hydrogenation processes.
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