Search

Diante dos desafios com o armazenamento e secagem de sementes no Brasil, é fundamental desenvolver alternativas para aprimorar esses processos. Este trabalho avalia a eficácia da sílica-gel na secagem de sementes de aveia. O estudo, realizado na Universidade Federal de Pelotas, analisou a secagem de sementes de aveia branca com umidade inicial de 15% e 17%. Foram distribuídas 15 g de sementes em estações experimentais com diferentes quantidades de sílica-gel (6 g, 12 g, 18 g) e um controle, em esquema fatorial 2 x 3. As sementes foram colocadas sobre uma tela de alumínio adaptada em gerbox com sílica, e amostras foram coletadas durante 24 h, com leituras a cada 6 h. Com 15% de umidade, recipientes com 6 e 18 g de sílica apresentaram uma perda de água de 0,4581 e 0,8012 g. Com 17% de umidade, as sementes perderam 0,8339 e 1,2016 g. O estudo indica que a sílica-gel é eficaz na secagem de sementes de aveia, sendo uma alternativa viável para minimizar perdas e manter a qualidade.

The hydratable magnesium carboxylate (HMC) bonded castables have a high-level gas permeability while the mechanical strength decreased sharply during drying process. Silica-gel with high activity is a porous structure after drying and can potentially increase the intermediate-temperature strength without reducing the gas permeability of the castables. In this study, the mechanism of silica-gel modified the HMC, and the effects on the properties of the castables were investigated. The surface of the hydration products of HMC is covered with a thin protective layer of siloxane network. The proportion of fine permeable pores (0.1 μm ∼1 μm) increased, optimizing the connected network channels in the castables. Compared to the pure HMC bonded castables, with the HMC/silica-gel mass ratio of 2, the cold modulus of rupture of the castables increased by 2 times after heat treatment in the range of 400 °C ∼600 °C. Especially, the permeability constants Darcian k 1 and non-Darcian k 2 increased by 37 times and 38 times after heat treatment at 600 °C, respectively. [ABSTRACT FROM AUTHOR]

The main energy input of a desiccant air conditioning system is the low-quality thermal energy required for regeneration, which can be obtained from waste heat, geothermal resources or solar energy. Regeneration thermal energy can be produced as well as energizing components such as fans, pumps, auxiliary air heaters, and control elements of the system by using photovoltaic-thermal solar collectors (PV/T). In this study, parametric analyzes were performed to investigate the effect of regeneration temperature and air frontal velocity on the temperature and dehumidification performance of a solid silica-gel desiccant wheel and on the water-cooled PV/T collectors used to provide the regeneration thermal energy. The regeneration temperature was varied between 50 and 70°C, and air frontal velocity between 1.3 and 4.1 m/s. The analyzes show that the dehumidification efficiency increases from 13.94% to 33.04% as regeneration temperature increased from 50°C to 70°C at 1.3 m/s air frontal velocity at which dehumidification efficiency is maximum. At 4.1 m/s air frontal velocity, the required regeneration thermal energy is maximum and increases from 49.64 kW to 132.48 kW at the same regeneration temperature change. The low regeneration temperature resulted in desirable latent performance and undesirable sensible heat transfer performance in DEW. Finally, considering the whole system, it was concluded that the optimum regeneration air temperature for the performance parameters is 60°C. [ABSTRACT FROM AUTHOR]

A simple solvothermal reaction was used to prepare a 3-aminopropyl-functionalized silica-gel-based adsorbent for adsorbing Pd(II) from the nitric acid solution. Scanning electron microscopy, fourier transform infrared spectroscopy, and thermogravimetry analysis were performed on the as-synthesized adsorbent to demonstrate the successful introduction of Schiff base groups. Batch experiments were used to investigate the effects of contact time, nitric acid concentration, solution temperature, and adsorption capacity. It is worth noting that the prepared adsorbent exhibited a higher affinity toward Pd(II) with the uptake approximately 100% even in a 2 M HNO3 solution. At an equilibrium time of 5 h, the maximum adsorption capacity of Pd(II) was estimated to be 0.452 mmol/g. The adsorbed Pd(II) could be completely eluted by dissolving 0.2 M thiourea solution in 0.1 M HNO3. Using a combination of particle-induced X-ray emission analysis and an X-ray photoelectron spectrometer, the adsorbed Pd was found to be uniformly distributed on the surface of the prepared adsorbent and the existing species were Pd(II) and zero-valent Pd(0). Due to the desirable performances, facile preparation method, and abundant raw material source, the prepared adsorbent demonstrated a high application potential in the recovery of Pd(II) from simulated high-level liquid waste treatment.

In this study, silica-gel (SG)-supported deep eutectic solvent (DES) with a different loading dosage as the novel nanocomposite materials has been synthesized by sol–gel method. And the supported nanocomposite materials were used as the catalyst for the synthesis of 1,10-phenanthroline from the 8-aminoquinoline and acrolein. The properties and structure of catalysts were characterized by Fourier transform infrared, N2 adsorption–desorption, scanning electron microscopy, thermogravimetric analysis and elemental analysis techniques. It was found that the 12%DES/SG catalyst with the best catalytic activity possessed the suitable specific surface area 132 m2/g and 12% loading amount of DES, which combines the excellent properties of mesoporous materials and DES. The result of thermogravimetric analysis was exhibited that the nanocomposite materials could not be decomposed below 240 °C, which can be used as a stable catalytic material under reaction conditions. Furthermore, the effect of reaction parameters such as reaction temperature and catalyst amount, molar ratio of 8-aminoquinoline and acrolein and reaction time was also studied. Under the optimal process parameters, within the optimum parameters: 130 °C, acrolein: 8-AQ = 2:1, catalyst amount 20 wt%, and time 4 h, the conversion of 8-aminoquinoline and selectivity of 1,10-phenanthroline were 83.8% and 84.3%, respectively. Otherwise, the catalyst can be separated from the reaction system and reused. Therefore, the silica-gel-supported deep eutectic solvent nanocomposite materials can be considered as a potential catalytic material for the synthesis of 1,10-phenanthroline and other nitrogen-containing heterocyclic organic chemical intermediates. Replacing traditional sulfuric acid and hydrochloric acid with silica-gel-supported deep eutectic solvents as new nanocomposite catalysts provides a more efficient, greener and more economical strategy for the synthesis of 1,10-phenanthroline. [ABSTRACT FROM AUTHOR]

TiO2 is supported on silica gel surface (TiO2(0.5)/SiO2(0.5) composite) by physical mixing technique of TiO2 and silica gel with mole ratio 1:1.329 TiO2(0.5)/SiO2(0.5) composite characterized by physico-chemical techniques; (SEM), (FT-IR), (DTA-TG), porosity measurements, and X-ray diffraction and used as a sorbent for 134Cs and 60Co radionuclides from aqueous solutions. Optimization of the parameters affecting sorption process is studied. The saturation sorption capacity of TiO2(0.5)/SiO2(0.5) composite towards 134Cs at pH 9.5 and 60Co at pH 5.5 are 33.1 and 17.7 m g g-1, respectively. The adsorption reaction mechanism is applicable with Freundlich isotherm and the process is spontaneous and favorable. [ABSTRACT FROM AUTHOR]

To long-term immobilization of secondary iodine-waste, iodine loaded silver-coated silica-gel (AgIs), glass-powder was used to directly solidify AgIs at low temperature. B2O3-Bi2O3-ZnO-SiO2 was used as raw materials to manufacture the glass-matrix under different temperature. The samples with the richest glass phase were obtained at 1000 °C, and were used to solidify AgIs with different content of I−. The sample with 30 wt% I− possessed the highest amorphous index (0.62) at 600 °C. Element I was uniformly distributed, and the density reached to 3.06 g/cm3. This work highlights a simple way to solidify secondary iodine-waste at low temperature. [ABSTRACT FROM AUTHOR]

High-level bio-decontamination, which involves reducing microorganisms by 99.9999%, is essential in preventing Hospital Acquired Infections and controlling pandemics. This study demonstrates that nanoporous materials, which can retain molecules within their pores, and subsequently release them, can be used in high level bio-decontamination. H 2 O 2 vapour is a golden-standard in high level bio-decontamination. This work demonstrates that various nanoporous materials, particularly mesoporous silicas, can be utilized to store and release H 2 O 2 in the vapour phase. H 2 O 2 concentrations of over 2500 ppm were achieved by desorbing it from the carrier material at low temperatures of 60–80 °C. Generation of H 2 O 2 -vapour by desorption from nanoporous materials is technically much simpler than vaporization of aqueous H 2 O 2 solutions, which use flash vaporization processes occurring at 130–150 °C. This has important technical implications, highlighting the potential of nanoporous materials as carriers for H 2 O 2 for high-level bio-decontamination. [Display omitted] • High-level bio-decontamination involves reducing microorganisms by 99.9999%. • H 2 O 2 vapour is a golden-standard in high level bio-decontamination. • Generation of H 2 O 2 vapour can be made by desorption from nanoporous materials. • Amongts several nanoporous materials, a mesoporous silica showed the best performance. • A new application of nonporous, materials as carriers of H 2 O 2 , was demonstrated. [ABSTRACT FROM AUTHOR]

To further increase the quantity and density of functional groups on adsorbent, terminal triethylenetetramine hyperbranched dendrimer-like polymer modified silica-gel (SG-TETA and SG-TETA2) was synthesized. The hyperbranched dendrimer-like polymer was successfully introduced onto silica gel and new cavities were formed, which was demonstrated by FTIR, SEM, and BET. The highest adsorption capacities of SG-TETA and SG-TETA2 obtained from Langmuir model toward Au(III) were 2.11, and 2.27 mmol g−1, respectively, indicating that SG-TETA2 possessing more functional groups had a better adsorption ability. Moreover, the adsorbents combined with Au(III) ion through chelation and electrostatic attraction mechanism, after which reduction reactions for Au(III) ion loaded on adsorbents proceeded. SG-TETA2 had better adsorption selectivity than SG-TETA in removing Au(III) in Au-existed ion solution systems. SG-TETA2 had higher overall adsorption capacities compared to silica-gel-based hyperbranched polymers functionalized by diethylenetriamine. Therefore, the effective recovery makes SG-TETA2 a practical adsorbent in removing Au(III) ion from e-wastes and industrial effluents with much prospect.

Silica-gel supported ester-terminated polyamidoamine (PAMAM) dendrimers (SG-G0.5, SG-G1.5, and SG-G2.5) were utilized as adsorbents for the removal of Fe(III) from fuel ethanol. The adsorption property was systematically investigated by determining the effects of dendrimer generation, contact time, temperature, initial Fe(III) concentration, and adsorbent dosage on the adsorption. Static saturated adsorption indicates the adsorption capacity increases with the increasing of dendrimer generation by following the sequence of SG-G2.5 > SG-G1.5 > SG-G0.5. Adsorption kinetic shows that the adsorption equilibrium can reach within 200 min for all the adsorbents. The adsorption kinetic can be well fitted by pseudo-second-order model and is controlled by film diffusion process. Adsorption isotherm demonstrates the adsorption favors high temperature and initial Fe(III) concentration. The adsorption isotherm follows Langmuir model and carries out by monolayer chemical ion-exchange mechanism. Thermodynamic parameters imply the adsorption process of Fe(III) by SG-G0.5, SG-G1.5 and SG-G2.5 is a spontaneous, endothermic and entropy increased process. The regeneration property shows the adsorbents exhibit good reusability and maintain excellent adsorption capacity after three adsorption-desorption cycles. Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculation indicate the interaction of carbonyl oxygen and amine nitrogen groups with Fe(III) mainly dominate the adsorption process. [ABSTRACT FROM AUTHOR]

• Measurement of isothermal water vapor adsorption rate to silica-gel by a quartz crystal microbalance. • A thin layer of consolidated adsorbent was used in moist air. • Overall mass transfer resistance in the air flow was revealed by the time constants. • It was separated into resistance inside adsorbent and in concentration boundary layer. • Resistance in the boundary layer was negligible at condition above 0.1 m s−1. A quartz crystal microbalance (QCM) technique was used to measure amounts of adsorbed and desorbed water vapor in a moist air to a thin layer of adsorbent consolidated with silica-gel micro particles on the quartz crystal coated with thin gold electrodes. First, measured relative isothermal equilibrium adsorption was confirmed to reproduce the catalogue data of the silica gel. Then, the adsorption and desorption rates to the layer were measured under a condition of a step change of the surrounding relative humidity. Overall mass transfer resistance which related to both the mass diffusion in the particle and the mass transfer in the boundary layer was revealed by the obtained time constants of these reactions. The resistance decreased with the increase of the velocity, and it became a negligible quantity in the boundary layer when the flow rate was above 0.1 m s−1. Finally, correlations were proposed to predict these resistances. [ABSTRACT FROM AUTHOR]

Water pollution caused by Cr(III) is a serious environmental problem which bring adverse effect to environmental protection and public safety. Efficient removal of Cr(III) from aqueous solution is important for the remediation of Cr(III) pollution. Herein, a series of silica-gel/polyamidoamine (PAMAM) dendrimer hybrid materials (SG-G0~SG-G4.0) were used for the removal of Cr(III) from aqueous solution. The factors that affect the adsorption were extensively studied and the adsorption mechanism was demonstrated based on the experimental results and density functional theory (DFT) calculation. Result demonstrates the adsorption capacity of ester-terminated silica-gel/PAMAM dendrimers follow the order of SG-G2.5 > SG-G3.5 > SG-G1.5 > SG-G0.5, while that of amino-terminated ones decrease in the order of SG-G2.0 > SG-G4.0 > SG-G3.0 > SG-G1.0 > SG-G0. The highest adsorption is achieved at pH 4.0 for both ester- and amino-terminated materials. Adsorption kinetic indicates the adsorption equilibrium can be reached at about 240 and 180 min for amino- and ester-terminated hybrids, respectively. Adsorption kinetic can be well fitted by pseudo-second-order kinetic model with film diffusion process as the rate-limiting step. Adsorption isotherm follows Langmuir model with monolayer adsorption behavior. Fourier transform infrared spectra (FTIR) indicate the adsorption of Cr(III) by PAMAM dendrimer mainly involve the participation of N–H and C=O groups. DFT calculation demonstrates the uptake of Cr(III) by ester-terminated adsorbents mainly involves carbonyl oxygen and secondary amine nitrogen atoms to form tetra-coordinated chelate, while that of amino-terminated one tends to form hexa-coordinated chelates by carbonyl oxygen, primary and secondary amine nitrogen atoms. [ABSTRACT FROM AUTHOR]

A series of silica gel supported amino-terminated PAMAM dendrimers (SG-G1.0 - SG-G3.0) were used for the removal of Cd(II) and Fe(III) from dimethylsulfoxide (DMSO). Various parameters that influence adsorption behaviors including temperature, contact time, and initial metal ion concentration were studied. The adsorption mechanism was revealed by combining the results of experiment and density functional theory (DFT) calculation. It indicates that the adsorption capacities for Cd(II) and Fe(III) are largest among the metal ions tested. The adsorption capacity of SG-G1.0 - SG-3.0 for Cd(II) and Fe(III) follows the order of SG-G2.0 > SG-3.0 > SG-G1.0. The adsorption isotherm shows the adsorption capacities for both metal ions increases with raising the temperature and initial metal ion concentration. The adsorption isotherm is consistent with Langmuir model and the adsorption process is dominated by chemical adsorption mechanism. Thermodynamic parameters indicates that the adsorption for both Cd(II) and Fe(III) is spontaneous and endothermic. Kinetic adsorption indicates that the adsorption equilibrium times for Cd(II) and Fe(III) is about 200 and 350 min, respectively, which can be described by a pseudo-second-order model and controlled by film diffusion process. FTIR analysis and theoretical calculation revealed that the carbonyl O atoms, secondary amine N atoms, and primary amine N atoms are the primary factor responsible for PAMAM adsorption by forming tetra- and penta-coordinated chelates with metal ions. [ABSTRACT FROM AUTHOR]

In this study the enhancement effect of adsorption mass transfer by acoustic wave is investigated to understand how the acoustic wave influences the adsorption performance. The experimental data were obtained to show the behavior of silica-gel adsorption with/without acoustic field. The experimental results showed the adsorption speed with acoustic wave became higher than that without acoustic wave although the equilibrium adsorption amount was kept to be the same. From the viewpoint of acoustic wave conditions, the adsorption speed was increased with increasing the velocity amplitude, while the pressure amplitude had no effect on the enhancement. The maximum adsorption speed attained five times as high as the case without acoustic wave when the velocity amplitude was 1.35 m/s. Background air flow velocity is also an influential factor. The experimental results support that the non-dimensional ratio of the velocity amplitude to the background flow velocity is essential to describe the enhancement effect. Based on the observed data, an empirical formula was estimated to express the relationship between the enhancement effect and the non-dimensional velocity amplitude. The liner regression showed the good agreement and gave the critical non-dimensional velocity amplitude of 1.9 over which acoustic wave is effective to amplify the mass transfer rate of adsorption. [ABSTRACT FROM AUTHOR]

This paper addresses the discrepancies among the common adsorption isotherms of silica-gel/water provided in the literature. It is reported that the Freundlich model and Tòth equation cannot be used to estimate the uptake at relative pressure less than 0.15. In addition, inconsistencies are found among the various models and equations used to describe the uptake of water vapor onto silica-gel. New coefficients for the Dubinin–Astakhov (D–A) model are proposed to eliminate these disagreements. Due to the limited experimental measurements, an experimental setup is designed and built to measure the sorption kinetics and equilibrium uptake of any working pairs. Experimental measurements show that the maximum uptakes of silica gel RD-2060 and Type-RD are 0.38 kg kg −1 and 0.48 kg kg −1 , respectively. Apparent capillary condensation is observed at a relative pressure of 0.4 and 0.35 for silica-gel RD and RD-2060, respectively. Also, it is found that the D–A model can fit the adsorption isotherms of silica-gels appropriately for the entire range of relative pressure when the characteristic energy is set as a function of relative pressure instead of assuming constant values. [ABSTRACT FROM AUTHOR]

An experimental study has been carried out to clarify the effect of quantity of absorbed water on behaviour of single silica-gel particles in oil with dc electric field, as a basic research to augment adsorption. The progress of adsorption changes mass and physical properties of a silica-gel particle, and the change might influence the behaviour of the particle. The experiment is conducted under condition that the adsorbed material is only water, and the quantity of water is adjusted beforehand to prescribed value. Two electrode plates are horizontally set up 40 mm apart in silicone oil. Particle diameter is adopted of 2.7, 4.0 and 5.0 mm, and the range of applied voltage is 0 - 28 kV. The applied voltage is increased at approximately 2kV/min. Observation of behaviour of a silica-gel particle starts from resting condition on a lower electrode. As a result, a dried silica-gel particle does not begin moving even at the maximum voltage. For a silica-gel particle of water adsorbed, following four stages have been observed, excluding a very few exceptions; rise from the upper side of lower electrode to the upper electrode, bound and rest on the lower side of the upper electrode, descent to the lower electrode, and bound and rest on the lower electrode. The rest time on the electrode is not seen to a completely water-absorbed silica-gel particle. It is thought that the particle exchange the electric charge at the rest time. The applied voltage for the leave of a silica-gel particle from the lower electrode, rest time on each electrode, and bound height from each electrode are also shown.

In this study, different multi-bed water adsorption systems have been used to generate cooling and electricity at the same time using 9 different cases including 7 bed configurations and 7 time ratios (R = total switching and adsorption time /the total switching and desorption time) utilizing advanced adsorption materials such as AQSOA-Z02 and MOF Aluminium-Fumarate additionally to traditional Silica-gel. A MATLAB Simulink program of multi-bed adsorption system for cooling and power generation has been developed to investigate the effect of using different cases on the overall system performance. Results showed that using three-bed configuration with time ratio of (R = 1/2) produced the highest specific cooling power (SCP) and specific power (SP) for Silica-gel (for all heat source temperature range), Aluminium-Fumarate (for heat source temperature higher than 120 °C) and AQSOA-Z02 (at heat source temperature of 160 °C). Moreover, using two-bed configuration with time ratio of (R = 1) generates the highest coefficient of performance (COP) for all adsorption materials within the range of heat source temperature used in this study. Results also, showed that maximum COP of 0.64 can be achieved using Silica-gel, while maximum SCP, SP and adsorption power efficiency of 650 W/kg ads , 64 W/kg ads , 4.6% can be achieved using AQSOA-Z02. [ABSTRACT FROM AUTHOR]

Silica-gel supported PAMAM dendrimers (SiO 2 -G0.5 ∼ SiO 2 -G3.0) were used for the removal of Co(II) from fuel ethanol by batch method. The adsorption mechanism was revealed by combining the results of experiment and density functional theory (DFT) calculation. Results indicated the adsorption capacity was closely related with the generation number of PAMAM dendrimer, contact time, Co(II) concentration, and temperature. Amino-terminated PAMAM dendrimers exhibited better adsorption performance than the corresponding ester-terminated ones. Kinetic adsorption followed pseudo-second-order model and dominated by film diffusion. Isotherm adsorption can be well depicted by Langmuir isotherm model and proceeded by chemical mechanism. Thermodynamic parameters implied the adsorption was spontaneous, endothermic, and randomness incremental process. DFT calculation demonstrated that ester-terminated PAMAM tended to chelate with Co(II) by secondary amine nitrogen atoms and carbonyl oxygen atoms in a quadri-coordinated manner, while amino-terminated PAMAM preferred to act as tetradentate and pentadentate ligand to bind Co(II) with secondary amine nitrogen atom, carbonyl oxygen atom, and primary amine nitrogen atom. Charge transfer of the adsorption process mainly occurred from PAMAM dendrimer to Co(II). [ABSTRACT FROM AUTHOR]

A mathematical model for estimating the moisture content in silica‐gel inside a breather of a power transformer has been developed. The model equations are derived considering the possible real‐time operating conditions of the transformer. These operating conditions are the fast rise or decrease of oil temperature due to a step change in the electrical loads and the cyclic heating and cooling of the oil due to the natural loading of the transformer. An experimental setup has been developed for monitoring the variations in moisture concentration in silica‐gel inside an artificially constructed breather. Finally, the validation of the model has been done with the experimentally obtained data and the standard input signals. The model has been analysed using the equilibrium relations of the moisture concentration between the silica‐gel and the environment of the breather. The response of the model indicates the dynamic behaviour of a moisture sensor placed in the breather. The model has been used in predicting the moisture level in the silica‐gel, the moisture concentration inside the breather and the degradation in the performance of the silica‐gel. [ABSTRACT FROM AUTHOR]

O objetivo deste trabalho foi estudar a impregnação do corante fotocromático Reversacol Graphit® em filmes do compósito de policarbonato (PC) e sílica-gel (Si), com a finalidade de obter aplicações em lentes fotocrômicas. Filmes de PC puros também foramimpregnados nas mesmas condições, para verificar o efeito da adição de sílica-gel. Os filmes do compósito foram produzidos em proporções de Si:PC de 1:40 e 1:80 (m m-1), pelo método casting. Para a impregnação do corante Reversacol Graphit nos filmes obtidos foiutilizado o processo supercrítico, pela sua eficiência e benefícios. A impregnação foi feita nos tempos de 15, 30, 45, 60, 90, 120, 150 e 180 min. A temperatura e a pressão adotadas foram de 60ºC e 120 bar. A quantidade de pigmento impregnado nos filmes de Si:PC – 1:40e 1:80 (m m-1) foi de 29 e 23% de massa de corante por massa de compósito, respectivamente, e para o filme de PC puro foi de apenas 2,2% massa de corante por massa de compósito. Pelas análises térmicas, verificou-se que os filmes do compósito apresentarammaior estabilidade térmica. Pela técnica de microscopia eletrônica, observou-se que os filmes de PC puro e dos compósitos Si:PC – 1:40 e 1:80 (m m-1) apresentaram uma superfície lisa e homogênea.The aim of this work was to study the impregnation of the photochromic dye Reversacol Graphit® in composite films ofpolycarbonate (PC) and silica gel, with the purpose of finding applications in photochromic lenses. Pure PC films were also impregnated in the same conditions, to verify the effect of the silica-gel addition. The composites films were produced in Si:PC ratios of 1:40 and 1:80 (m m-1), using the casting method . For the impregnation of the dye Reversacol Graphit in the obtained films, the supercritical process was used due to its efficiency and benefits. The impregnation was made in the times of 15, 30, 45, 60, 90, 120, 150 and 180 minutes. The adopted temperature and pressure were 60ºC and 120 bar, respectively. The amount of pigment impregnated in Si:PC films – 1:40 and 1:80 (m m-1) was 29 and 23% of dye mass per composite mass, respectively, and for pure PC film it was only 2.2% dye mass per composite mass. From the thermal analyses, it was verified that the composite films presented greater thermal stability. From the technique of electronic microscopy, it wasobserved that pure PC films and the composites Si:PC – 1:40 and 1:80 (m m-1) presented a smooth and homogeneous surface.

O objetivo deste trabalho foi estudar a impregnação do corante fotocromático Reversacol Graphit® em filmes do compósito de policarbonato (PC) e sílica-gel (Si), com a finalidade de obter aplicações em lentes fotocrômicas. Filmes de PC puros também foram impregnados nas mesmas condições, para verificar o efeito da adição de sílica-gel. Os filmes do compósito foram produzidos em proporções de Si:PC de 1:40 e 1:80 (m m-1), pelo método casting. Para a impregnação do corante Reversacol Graphit® nos filmes obtidos foi utilizado o processo supercrítico, pela sua eficiência e benefícios. A impregnação foi feita nos tempos de 15, 30, 45, 60, 90, 120, 150 e 180 min. A temperatura e a pressão adotadas foram de 60ºC e 120 bar. A quantidade de pigmento impregnado nos filmes de Si:PC – 1:40 e 1:80 (m m-1) foi de 29 e 23% de massa de corante por massa de compósito, respectivamente, e para o filme de PC puro foi de apenas 2,2% massa de corante por massa de compósito. Pelas análises térmicas, verificou-se que os filmes do compósito apresentaram maior estabilidade térmica. Pela técnica de microscopia eletrônica, observou-se que os filmes de PC puro e dos compósitos Si:PC – 1:40 e 1:80 (m m-1) apresentaram uma superfície lisa e homogênea.

An environmental acidic ionic liquid was prepared with 1-allyl-1H-imidazole, 1,3-propyl sulfonic acid lactone and H 2 SO 4 and was immobilized on silica-gel to synthesize the catalyst used to prepare biodiesel from waste cooking oil by a one-step method. The structure of the catalyst was characterized by BET, FTIR, DSC/TGA and SEM. The effect of methanol oil mole ratio, catalyst dosage, reaction temperature, and reaction time on the conversion of waste cooking oil to biodiesel was investigated, and the optimum reaction conditions were determined by an orthogonal test. The optimum reaction conditions were shown as follows: methanol oil mole ratio of 25:1, catalyst dosage of 5 wt% of oil, reaction temperature of 60 °C, reaction time of 20 h, and the yield of 87.58%. The yield could reach 70.02% after reusing the catalyst 5 times. [ABSTRACT FROM AUTHOR]

The paper deals with the structure, morphology and magnetic properties of two different iron concentrations (20 and 33 mol.%) of Fe 2 O 3 −SiO 2 nanocomposites, prepared by sol–gel technique and exposed to different gamma-irradiation doses (0, 30 and 60 kGy). The nanocomposites were investigated through XRD, TEM, SEM, FTIR and EPR measurements. Superparamagnetic iron (III) oxide nanoparticles with a narrow size distribution, dispersed over the amorphous silica matrix, are assumed to be present in all the samples before and after irradiation. Before irradiation, a lot of γ-Fe 2 O 3 crystalline ferromagnetic nanoparticles are assumed to be formed particularly for sample containing 33 mol.% Fe 2 O 3 , while exposing the samples to irradiation results in the transformation of γ- to α-Fe 2 O 3 . Iron concentrations and/or irradiation of the samples are assumed to cause changes in the bond angles and/or bond lengths of the structural silicate units within network, as well, the increase of more defect centers induced by irradiation as evident through the variations of the IR bands intensity. The EPR results show both intensity and line width increase with increasing Fe 2 O 3 concentration. The EPR signals for the samples consist of a well defined symmetrical broad signal at g ≈ 2.0 ascribed to antiferromagnetic interactions between the Fe 2+ and Fe 3+ clusters. Condensed clusters of Fe 3+ ions are observed to give rise to a resonance line at g ∼ 2 whose position and width do not depend on the Fe 2 O 3 concentrations. The EPR signal intensity is observed to be significantly decreased in the sample 33 mol.% or stabilized in the sample 20 mol.% by γ-irradiation. This reflects simultaneous spin transformation from the high-spin state of Fe III to the low-spin state of Fe II. As a final point, an effort has been given to found the possibility to use one of these studied nanocomposite materials as candidate for radiation shielding purposes. [ABSTRACT FROM AUTHOR]

Synthesis procedure of disordered mesoporous carbon, using commercial silica gel as template, was optimized. The replica method by sucrose/silica gel composite carbonization, followed by silica removal, was used to prepare the mesoporous carbon. Plackett-Burman experimental design allowed the comparison of the individual influence of five parameters on the textural properties and the adsorption capacity of Methylene Blue. All parameters were investigated at two widely spaced levels. Statistical analysis revealed that the sucrose/silica weight ratio and the number of impregnation steps were the variables with major influence in the properties of the as-synthesized carbon. Deeper study, with more levels for the optimization of these variables, was carried out. Mesoporous carbon with large BET surface area (>900 m/g with ≈10 % of microporous area), narrow pore size distribution and adsorption capacity above 230 mg/g was obtained carrying out the impregnation in only one step and with a sucrose/silica weight ratio of 0.8. The effect of time and temperature carbonization in the properties of the final mesoporous carbon was negligible. However, these variables are important in the reduction of the process cost by saving energy. The lowest values of these variables, which provide a mesoporous carbon with suitable properties and acceptable adsorption capacity, were 600 °C and 15 min. [ABSTRACT FROM AUTHOR]

Silica-gel-based adsorbents (SG-DETA and SG-DETA2) grafting of dendrimer-like highly branched polymer were prepared by an improved methods of a combination of homogeneous and heterogeneous. FTIR analysis, SEM analysis, pore structure analysis and thermodynamic analysis manifested that dendrimer-like highly branched polymer was successfully grafted onto the silica surface. The results of the adsorption thermodynamics and kinetics of the as-synthesized SG-DETA and SG-DETA2 showed the adsorbents had good adsorption capacity for Au(III), and the best interpretation for the experimental data was given by the Langmuir isotherm equation. The maximum adsorption capacity for Au(III) were 2.09 and 2.12 mmol g −1 of SG-DETA and SG-DETA2 at 35 °C, respectively. Moreover, the study indicated the adsorption kinetics of SG-DETA and SG-DETA2 could be modeled by the pseudo-second-order rate equation wonderfully. The SG-DETA and SG-DETA2 adsorbents had excellent adsorption selectivity for Au(III) in binary metal solution systems. Therefore, the high adsorption capacity make these adsorbents have significant potential for Au(III) uptake from aqueous solutions using adsorption method. [ABSTRACT FROM AUTHOR]

A transient two dimensional local thermal non-equilibrium model is developed to investigate the influences of heat transfer and operating parameters on the dynamic behavior of a cylindrical adsorbent bed during the adsorption process. Local volume averaging method is used to drive the macro scale governing conservation equations from the micro scale ones. In the model, linear driving force model and Darcy’s equation are considered to account for the resistances to internal and external mass transfer, respectively. Silica gel–water pair widely used in the adsorption cooling systems is chosen to be an adsorbent–adsorbate working pair. The parameters of interest are convective heat transfer coefficient, solid phase thermal conductivity, bed thickness, evaporator pressure, condenser pressure, driving heat source temperature and cooling source temperature. It is found that amount of refrigerant circulated through the system increases with increasing evaporator pressure-driving heat source temperature and decreasing condenser pressure-cooling source temperature. The duration of adsorption process is more sensitive to heat transfer resistances than to mass transfer resistances. The conductive and convective resistances need to be reduced to reach the equilibrium conditions in a short period of time and hence to have a better specific cooling power. [ABSTRACT FROM AUTHOR]

A robust and rapid method for the determination of natural levels of beryllium (Be) in seawater was developed to facilitate mapping Be concentrations in the ocean. A solid-phase extraction method using a silica gel column was applied for preconcentration and purification of Be in seawater prior to determination of Be concentrations with inductively coupled plasma mass spectrometry (ICP-MS). Be was quantitatively adsorbed onto silica gel from solutions with pH values ranging from 6.3 to 9, including natural seawater. The chelating agent ethylenediamine tetraacetic acid was used to remove other ions in the seawater matrix (Na, Mg, and Ca) that interfere with the ICP-MS analysis. The reproducibility of the method was 3% based on triplicate analyses of natural seawater samples, and the detection limit was 0.4 pmol kg −1 for 250 mL of seawater, which is sufficient for the analysis of seawater in the open ocean. The method was then used to determine the vertical profile of Be in the eastern North Pacific Ocean, which was found to be a recycled-type profile in which the Be concentration increased with depth from the surface (7.2 pmol kg −1 at <200 m) to deep water (29.2 pmol kg −1 from 3500 m to the bottom). [ABSTRACT FROM AUTHOR]

Biological control of gastrointestinal nematodiasis in ruminants is an alternative to reduce the number of infective larvae. The fungal isolates predatory activity preservation is a basic requirement for the success of this control type. The aim of this work is to evaluate the predatory capacity of the fungus Arthrobotrys robusta (isolate I-31), preserved on silica gel on infective larvae of Haemonchus contortus under laboratory conditions on 2 % water agar (2 % WA). In this essay, A. robusta storage on silica gel showed successful predatory activity on H. contortus L larvae ( p < 0.01) compared to the control group. Nematophagous fungi were not observed in the control group during the experiment. There was a significant reduction ( p < 0.01) of 73.84 % in the means of H. contortus (L) recovered from treatment with isolate I-31 compared to the control without fungi. Results indicate that A. robusta (I-31) could survive stored on silica gel for at least 7 years and keep its predatory activity on H. contortus (L). [ABSTRACT FROM AUTHOR]

Trace amounts of Fe3+, Pb2+, Cu2+, Ni2+, Co2+and Zn2+ions were efficiently enriched following complexation with silica-gel chemically functionalized with 2-((3-silylpropylimino)methyl)-5-bromophenol. The enriched metal ions efficiently eluted with 6 mL of 4.0 mol L−1nitric acid and their metal contents were determined by flame atomic absorption spectrometry (FAAS). The influences of the analytical parameters and experimental variables on the recoveries of the metal ions under study were investigated and optimized. The method has high sorption preconcentration efficiency even in the presence of various interfering ions. At optimum values of all variables the method is applicable for analysis of real samples with recoveries in the range of 95 to 105% with RSD lower than 4.2% and detection limits between 1.4 and 2.8 µg L−1. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption properties of silica-gel supported hyperbranched polyamidoamine dendrimers (SiO2-G0–SiO2-G4.0) have been investigated by batch method. The effect of pH of the solution, contact time, initial Pb(II) ion concentration, temperature and coexisting metal ions have been demonstrated. The results indicated that the optimum pH value was 5. Adsorption kinetics was found to follow the pseudo-second-order model and controlled by film diffusion. The adsorption isotherms were fitted by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Langmuir isotherm model was found to be more suitable to describe the equilibrium data, suggesting the uptake of Pb(II) ions by monolayer adsorption. From D–R isotherm model, the calculated mean free energy E demonstrated the adsorption processes occurred by chemical ion-exchange mechanism. FTIR analysis revealed that amine groups were mainly responsible for the adsorption of Pb(II) by amino-terminated adsorbents, while Cr groups also participated in the adsorption process of ester-terminated ones. The adsorbents can selectively adsorb Pb(II) from binary ion systems in the presence of Mn(II), Cu(II), Co(II), and Ni(II). Based on the results, it is concluded that SiO2-G0–SiO2-G4.0 had great potential for the removal of Pb(II) from aqueous solution. [Copyright &y& Elsevier]

Abstract: Composite adsorbents were synthesized from activated carbon, silica-gel and CaCl2. The optimized condition for adsorption cooling systems was obtained when raw activated carbon was impregnated by soaking in 10 wt.% sodium silicate solution for 48 h and then in 30 wt.% CaCl2 solution for 48 h. A 0.805 kg kg−1 of difference in equilibrium water uptake between 25 °C and 115 °C was recorded at atmospheric pressure. Besides, an adsorption rate test unit was built to study the adsorption isotherms and adsorption rates in which 0.23 kg kg−1 of adsorption capacity was recorded at 27 °C and a water vapor pressure of 900 Pa. The ideal coefficient of performance (COP) and the average specific cooling power (SCP) for an adsorption cooling system using the composite adsorbent were estimated to be 0.70 and 378 W kg−1 respectively. The results demonstrated that the composite adsorbents can be a good candidate for low temperature heat-driven adsorption cooling and dehumidification systems. [Copyright &y& Elsevier]

Abstract: This paper shows the numerical investigation of the developed solar-desiccant cooling system applied in the East Asian climatic conditions with two different desiccant wheel coating materials – the Silica-Gel (SiO2) and the Titanium Dioxide (TiO2). The developed and validated numerical model of the system is currently used in the present study incorporating the two new materials in the desiccant wheel. The system was applied in temperate climate (Beijing and Tokyo), subtropical climate (Taipei and Hong Kong) and tropical climate (Manila and Singapore). The study showed that the specification of the solar-desiccant cooling system varies depending on the climatic conditions. It showed that the required flat plate collector area was getting larger from the temperate climate to the tropical climate. The storage tank requirement was getting bigger in the tropical climate compared to the subtropical and temperate climate. The volumetric flow rate of air was getting higher from temperate climate to tropical climate. In the comparison of the two materials, it was found that the Titanium Dioxide (TiO2) can support lower indoor temperature and humidity ratio than the Silica-Gel (SiO2) with the same specification of the solar thermal system and desiccant cooling system. In general, the solar-desiccant cooling system can provide the required indoor temperature and humidity ratio. However, for the hot and humid climate such as in tropical, large size of the solar thermal system is needed. In addition, higher volumetric flow of air to support the high cooling load is required. With regard to the new material, Titanium Dioxide, it is proven to be a good alternative material since it can provide lower indoor temperature and humidity ratio with higher cooling performance than the Silica-Gel. [Copyright &y& Elsevier]

In this study, trypsin was immobilized onto commercial silica gel and the transesterification of N-acetyl-L-tyrosine ethyl ester (ATEE) and 1-propanol in an organic solvent was used as a model reaction. The amount of trypsin adsorbed onto the support affected the time required to achieve full conversion. The concentration of immobilized trypsin that provided a maximum yield of product in a minimal amount of time was 43 (imol of trypsin/g silica gel. At the end of transesterification reactions, the turnover frequency (9.3 · 10-5 to 6.8 · 10-1 s-1) and turnover number (8 to 520) of transesterification markedly increased when the initial concentration of the substrate had increased from 0.8 to 100 mmol L-1. The kinetic parameters Km (64.8 mmol L-1 ATEEinitial) and Kmax (0.364 mmol L-1 ethanol min-1) were determined. The immobilized trypsin maintained enzymatic activity and reusability after one month of storage at 4 °C. [ABSTRACT FROM AUTHOR]

Multisubstituted pyrroles with a 2-sulfonamido-group were synthesized through a CuI-catalyzed three-component coupling and a 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) / silica-gel promoted cyclization under mild conditions in moderate yields. [ABSTRACT FROM AUTHOR]

Abstract: Imidazolium-silica heterogeneous catalyst (SG-[(CH2)3SO3H-HIM]HSO4) was prepared by immobilization of acidic ionic liquid 1-(propyl-3-sulfonate) imidazolium hydrosulfate ([(CH2)3SO3H-HIM]HSO4) on silica–gel using tetraethoxysilane (TEOS) as silica source in this study. The properties of the samples were characterized by FT-IR, SEM and TG/DSC. The results suggested that [(CH2)3SO3H-HIM]HSO4 had been successfully immobilized on the surface of silica–gel and the immobilized ionic liquid catalyst SG-[(CH2)3SO3H-HIM]HSO4 had good thermal stability. The original smooth surface of silica–gel was covered with [(CH2)3SO3H-HIM]HSO4 and a rough surface of SG-[(CH2)3SO3H-HIM]HSO4 was formed, but the size of particles had no obvious change. Moreover, SG-[(CH2)3SO3H-HIM]HSO4 exhibited high catalytic activity for a series of acetalization and could be recovered easily. After reused for 10 times in the synthesis of benzaldehyde ethanediol acetal, the catalyst could still give satisfactory catalytic activity. [Copyright &y& Elsevier]

Abstract: The continued maintenance of nematophagous fungi predatory activity under laboratory conditions is one of the basic requirements for a successful biological control. The purpose of this study was to evaluate the influence of time on the preservation of the fungus Duddingtonia flagrans (AC001 and CG722) stored in silica-gel for 7years and their subsequent predatory activity on cyathostomin L3 larvae in 2% water-agar medium (2% WA). Samples of the isolates AC001 and CG722, originating from vials containing grains of silica-gel sterilized and stored for 7years, were used. After obtaining fungal conidia, the predation test was conducted over 7days on the surface of 9.0cm Petri dishes filled with 2% WA. In the treated groups each Petri dish contained 500 cyathostomin L3 and conidia of fungal isolates in 2% WA. In the control group (without fungi) the plates contained 500 L3 in 2% WA. The experimental results showed that isolated AC001 and CG722 were efficient in preying on cyathostomin L3 (p <0.01) compared to control (without fungus). However, no difference was observed (p >0.01) in the predatory activity of the fungal isolates tested. Comparing the groups, there was a significant reductions of cyathostomin L3 (p <0.01) of 88.6% and 78.4% on average recovered from the groups treated with the isolates AC001 and CG722, respectively, after 7days. The results of this test showed that the fungus D. flagrans (AC001 and CG722) stored in silica-gel for at least 7years maintained its predatory activity on cyathostomin L3. [Copyright &y& Elsevier]

Abstract: New optical sensors for trace amounts of oxygen are based on platinum(II) and palladium(II) complexes of 5,10,15,20-meso-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin covalently attached to the surface of amino-modified silica-gel particles. The dye-doped silica-gel particles are dispersed in silicone rubber. The Stern–Volmer plots show linear response and are virtually identical for either luminescence intensity and decay time. Other features include high photostability and rapid response times (∼150ms in gas phase). The sensors based on the palladium(II) complex show significantly higher sensitivity (K SV about 67kPa−1 at 25°C) with the dynamic range from 0.02 to 100Pa. The sensitivity of the platinum(II) complexes is significantly lower (K SV =3.7–4.2kPa−1, dynamic range 0.3–1000Pa). The sensors can be suitable for application in breweries, water boilers and for marine research (monitoring of oxygen minimum zones). [Copyright &y& Elsevier]

Abstract: Cerrena unicolor laccase was immobilized by adsorption and covalent bonds formation on silica-gel carriers, functionalized with different organosilanes and surface densities. The effects of protein concentration, pH value of the coupling mixture and the enzyme purity on immobilization efficiency of the best carrier, moderately modified (0.75mmol/g carrier) with 3-aminopropyltriethoxysilane were investigated. Activity of the best biocatalysts, expressed in ABTS oxidation, was 4028U/mL of the carrier or 3530U/mg of bound protein. Properties of immobilized laccase were determined to find excellent thermal stability improvement; t 1/2 for freely suspended enzyme was 2–3min at 80°C, whereas after immobilization over 100min. Kinetic experiments in both batch and packed-bed reactors gave only four times lower k cat/K m value than for the native enzyme. A packed-bed reactor with silica-gel-bound laccase beads appeared to be very efficient in ABTS oxidation and its exceptional potentials were shown in the continuous decolorization of indigo carmine for 18days without loss in activity. This system offers perfect ability to degrade recalcitrant dyes, but we can also envisage its use, with ABTS acting as a mediator, in regeneration of nicotinamide cofactors. [Copyright &y& Elsevier]

Abstract: Self-disproportionation of enantiomers of heterocycles having a tertiary trifluoromethyl alcohol center on an achiral silica-gel stationary phase is discussed. During the chromatographic separation of an enantiomerically enriched mixture of 1-(3,4-dimethoxyphenethyl)-3-hydroxy-3-(trifluoromethyl)-6,7-dihydro-1H-indole-2,4(3H,5H)-dione (1) by eluting with ether on a non-chiral regular silica-gel significant enantiomeric enrichment was observed. Separation of non-racemic samples of 1 with enantiomeric excess values of 10–54% was carefully investigated: enantiomerically pure 1 with 99.9% ee was obtained by the use of 1 with at least 40% ee. A remarkable enantiomeric enrichment in the faster eluting fractions was also observed for compound 1 with only 30% ee to transform into 80% ee. Other enantiomeric mixtures of heterocyclic molecules containing a trifluoromethyl alcohol moiety at their quaternary carbon center were also examined from an SDE view point. [Copyright &y& Elsevier]