ДЕСОРПЦИЈА НА β-КАРОТЕН ОД БЕНТОНИТСКИ АТСОРБЕНТ ВО УСЛОВИ НА МИКРОБРАНОВА ИРАДИЈАЦИЈА

The desorption behavior of β-carotene from a bentonite adsorbent under microwave irradiation in isopropanol was studied as a function of temperature and different initial loading concentrations. A first-order, two-component, three-parameter model described the desorption kinetics with a coefficient of de-termination R2 > 0.9932, and the β-carotene desorption process under microwave irradiation was con-trolled by both rapid and slow desorption. The activation energies of β-carotene desorption for the rapid and slow desorption processes were 19.61 and 53.04 kJ mol-1, respectively. It was observed that the de-sorption equilibrium data fitted well to both the Freundlich and Langmuir isotherms. The data obtained from the desorption-isotherm model were used to determine the thermodynamic parameters. The positive value of free energy indicates the non-spontaneity of β-carotene desorption. The change in entropy rela-tive to the enthalpy of desorption reveals that the reaction is physical in nature.Десорпциското однесување на β-каротенот од бентонитски атсорбент беше истражувано во услови на микробранова ирадијација како функција на температурата и различни концентрации на полнењето. Кинтетички двокомпонентен модел од прв ред со три параметри ја опишува десорпциската кинетика со коефицинет на корелација R 2 > 0.9932. Десорпцискиот процес на βкаротенот во услови на микробранова ирадијација е контролиран и со брза и со бавна десорпција. Активациските енергии на десорпцијата на β-каротенот за брзата и за бавната десорпција соодветно изнесуваат 19,61 kJ mol–1 и 53,04 kJ mol–1 . Забележано е дека десорпциската рамнотежа добро се вклопува во изотермите на Freundlich и на Langmuir. Добиените податоци на моделот на десорпциската изотерма се употребени за определување на термодинамички параметри. Позитивната вредност на слободната енергија укажува на неспонтаност на десорпцијата на βкаротенот. Промената на ентропијата во однос на енталпијата укажува дека десопцијата по природа е физичка

The role of ruthenium in perovskite-type mixed oxide in the electrochemical degradation of 4-nitrophenol

U ovom radu su okarakterisani novi elektrodni materijali na bazi perovskita za detekciju 4-nitrofenola. Mešoviti oksidi perovskitnog tipa hemijske formule La0.7Sr0.3Cr1-XRuXO3 (X= 0; 0.05) su sintetisani konvencionalnim keramičkim postupkom. Rezultati rendgenske difrakcione analize su pokazali da je sintetizovani sistem dvofazan, i da pored dominantne perovskitne faze sadrži udeo stroncijum hromata. Ugljenična pasta elektroda je modifikovana sintetisanim perovskitima kako bi se ispitala njihova elektroaktivnost. Tako dobijene elektrode su primenjene za oksido-redukciju 4-nitrofenola u kiseloj sredini. Prisustvo rutenijuma u perovskitnoj strukturi dovodi do povećane elektrohemijske aktivnosti elektrode za redukciju 4-nitrofenola.In this paper new perovskite-based electrode materialsfor 4-nitrophenol detection were characterized. Mixed oxides of pereovskite type with general molecular formula La0.7Sr0.3Cr1-XRuX03 (X= 0; 0.05) were synthesized by ceramic procedure. The results of X-ray diffraction analysis showed that synthesized system has two-phase structure, including strontium chromate phase beside dominant perovskite phase. Carbon paste electrode was modified with synthsized perovskites in order to study their electrochemical activity. Electrode prepared innn such manner were used for oxido-reduction of 4-nitrophenol in acidic media. The addition of ruthenium to perovskite structure lead to increased electrochemical activity of this electrode for reduction of 4-nitrophenol

Faktorijalni i ortogonalno centralno kompozitni plan eksperimenta kiselinske aktivacije smektita

The purpose of this study was to determine the effective operating parameters and the optimum operating conditions of an acid activation process within the framework of improvement of the process. Full two-level factorial and orthogonal central composite design methods were used successively. The examined parameters were the main and interaction effects of temperature, leaching time, acid normality, solid-to-liquid ratio and stirring rate. The selected process response was the leaching yield of the MgO content because Mg is the element most readily removed from the octahedral sheet, which affects the tendency for activation. Statistical regression analysis and analysis of variance were applied to the experimental data to develop a predictive model, which revealed that temperature, leaching time and acid normality exert the strongest influence on the specific surface area of smectite, whilst the solid-to-liquid ratio and the stirring rate have a secondary effect. Furthermore, the highest leaching yield of MgO was found to be 41.86 %, which is responsible for the increase in the specific surface area of up to 221 m2 g-1.Svrha ovog rada bila je određivanje efektivnih procesnih parametara i optimalnih procesnih uslova kiselinske aktivacije smektita iz Srbije. Uspešno su korišćene dve metode matematičkog modelovanja: pun faktorijalni i ortogonalni centralni kompozitni plan eksperimenta. Pri optimalnom planiranju eksperimenta istovremeno se menjaju svi parametri koji utiču na proces, što nam omogućava određivanje njihovog međusobnog uticaja i smanjenje ukupnog broja eksperimenata. Tokom planiranja eksperimenata razmatran je uticaj sledećih relevantnih parametara: temperature, vremena aktivacije, koncentracije kiseline, odnosa tečno/čvrsto i broja obrtaja mešalice, na stepen izdvajanja magnezijum-oksida. Rezultati optimizacije parametara kiselinske aktivacije smektita, na bazi statističkih planova eksperimenta, pokazali su da koncentracija kiseline, temperatura i vreme aktivacije imaju najjači uticaj na promenu specifične površine smektita, dok odnos tečno/čvrsto i broj obrtaja mešalice imaju sekundarni efekat. Maksimalni stepen izdvajanja magnezijum-oksida od 41,86 % uzrokuje i najveći porast specifične površine do 221 m2 g-1

Uticaj termičkog tretmana na mikro-strukturu alumine sa dodatkom PEG-a i La3+ dobijene sol-gel postupkom

Active porous alumina was prepared via a sol-gel method and subjected to thermal treatment in the temperature range 500 - 1200°C. The effect of calcinations temperature, polyethylen glycol combined with La3+, added to the boehmite sol, on activated alumina surface area, pore size, pore distribution and surface fractal dimension was studied. The N2 adsorption/desorption analyses of samples was performed to determine the adsorption isotherms, hysteresis and the textural properties. The adding of La3+ to boehmite sol inhibits the surface area loss of produced aluminas during its calcinations at high temperatures. Thermal treatment of La3+-doped alumina samples at temperature from 500 to 1200°C causes a considerable decrease of its specific surface area from 280 to 65 m2g-1, pore volume from 0,44 to 0,27 cm3g-1, increase of its pore size data from 3 to 6 nm and increase of its surface fractal dimension form 2,068 to 2,192. From behavior of surface fractal dimension of doped alumina samples can be concluded that there is no phase transformation to α-Al2O3 in all temperature range, i.e. addition of lanthanum to boehmite sol in atomic ratio of 0,03 La3+/Al3+ can raise phase transformation temperature to α-Al2O3 above 1200°C. .Aktivni porozni aluminijumoksid, dobijen sol - gel metodom, je termički obrađen na povišenim temperaturama u intervalu od 500 do 1200°C. Ispitivan je uticaj temperature termičke obrade i dodatka polietilen glikola (PEG) i La3+-jona na specifičnu površinu, zapreminu pora i prečnik pora, kao i fraktalnu dimenziju površine aktiviranog aluminijum-oksida. Na osnovu podataka iz adsorpciono-desorpcionih izotermi azota određen je tip pora i izračunate su vrednosti osnovnih parametara teksturalnih svojstava uzoraka. Porast temperature termičke obrade prouzrokovao je smanjenje specifične površine sa 280 na 65 m2g-1, zapremine pora sa 0,45 na 0,27 cm3g-1, porast preovlađujućeg prečnika pora od 3 do 6 nm i porast fraktalne dimenzije površine od 2,068 do 2,192. Na osnovu dobijenih rezultata rendgenostrukturne analize može se zaključiti da u ispitivanom temperaturnom intervalu ne dolazi do fazne transformacije u α-Al2O3 i da dodatak lantana u odnosu 0,03 molLa3+/ molAl3+ pomera faznu transformaciju aktiviranog aluminijum-oksida u α-Al2O3 iznad 1200°C.

Uticaj termičkog tretmana na mikro-strukturu alumine sa dodatkom PEG-a i La3+ dobijene sol-gel postupkom

Active porous alumina was prepared via a sol-gel method and subjected to thermal treatment in the temperature range 500 - 1200°C. The effect of calcinations temperature, polyethylen glycol combined with La3+, added to the boehmite sol, on activated alumina surface area, pore size, pore distribution and surface fractal dimension was studied. The N2 adsorption/desorption analyses of samples was performed to determine the adsorption isotherms, hysteresis and the textural properties. The adding of La3+ to boehmite sol inhibits the surface area loss of produced aluminas during its calcinations at high temperatures. Thermal treatment of La3+-doped alumina samples at temperature from 500 to 1200°C causes a considerable decrease of its specific surface area from 280 to 65 m2g-1, pore volume from 0,44 to 0,27 cm3g-1, increase of its pore size data from 3 to 6 nm and increase of its surface fractal dimension form 2,068 to 2,192. From behavior of surface fractal dimension of doped alumina samples can be concluded that there is no phase transformation to α-Al2O3 in all temperature range, i.e. addition of lanthanum to boehmite sol in atomic ratio of 0,03 La3+/Al3+ can raise phase transformation temperature to α-Al2O3 above 1200°C. .Aktivni porozni aluminijumoksid, dobijen sol - gel metodom, je termički obrađen na povišenim temperaturama u intervalu od 500 do 1200°C. Ispitivan je uticaj temperature termičke obrade i dodatka polietilen glikola (PEG) i La3+-jona na specifičnu površinu, zapreminu pora i prečnik pora, kao i fraktalnu dimenziju površine aktiviranog aluminijum-oksida. Na osnovu podataka iz adsorpciono-desorpcionih izotermi azota određen je tip pora i izračunate su vrednosti osnovnih parametara teksturalnih svojstava uzoraka. Porast temperature termičke obrade prouzrokovao je smanjenje specifične površine sa 280 na 65 m2g-1, zapremine pora sa 0,45 na 0,27 cm3g-1, porast preovlađujućeg prečnika pora od 3 do 6 nm i porast fraktalne dimenzije površine od 2,068 do 2,192. Na osnovu dobijenih rezultata rendgenostrukturne analize može se zaključiti da u ispitivanom temperaturnom intervalu ne dolazi do fazne transformacije u α-Al2O3 i da dodatak lantana u odnosu 0,03 molLa3+/ molAl3+ pomera faznu transformaciju aktiviranog aluminijum-oksida u α-Al2O3 iznad 1200°C.

ДЕСОРПЦИЈА НА β-КАРОТЕН ОД БЕНТОНИТСКИ АТСОРБЕНТ ВО УСЛОВИ НА МИКРОБРАНОВА ИРАДИЈАЦИЈА

The desorption behavior of β-carotene from a bentonite adsorbent under microwave irradiation in isopropanol was studied as a function of temperature and different initial loading concentrations. A first-order, two-component, three-parameter model described the desorption kinetics with a coefficient of de-termination R2 > 0.9932, and the β-carotene desorption process under microwave irradiation was con-trolled by both rapid and slow desorption. The activation energies of β-carotene desorption for the rapid and slow desorption processes were 19.61 and 53.04 kJ mol-1, respectively. It was observed that the de-sorption equilibrium data fitted well to both the Freundlich and Langmuir isotherms. The data obtained from the desorption-isotherm model were used to determine the thermodynamic parameters. The positive value of free energy indicates the non-spontaneity of β-carotene desorption. The change in entropy rela-tive to the enthalpy of desorption reveals that the reaction is physical in nature.Десорпциското однесување на β-каротенот од бентонитски атсорбент беше истражувано во услови на микробранова ирадијација како функција на температурата и различни концентрации на полнењето. Кинтетички двокомпонентен модел од прв ред со три параметри ја опишува десорпциската кинетика со коефицинет на корелација R 2 > 0.9932. Десорпцискиот процес на βкаротенот во услови на микробранова ирадијација е контролиран и со брза и со бавна десорпција. Активациските енергии на десорпцијата на β-каротенот за брзата и за бавната десорпција соодветно изнесуваат 19,61 kJ mol–1 и 53,04 kJ mol–1 . Забележано е дека десорпциската рамнотежа добро се вклопува во изотермите на Freundlich и на Langmuir. Добиените податоци на моделот на десорпциската изотерма се употребени за определување на термодинамички параметри. Позитивната вредност на слободната енергија укажува на неспонтаност на десорпцијата на βкаротенот. Промената на ентропијата во однос на енталпијата укажува дека десопцијата по природа е физичка

Morphology and fractal dimension of tio2 thin films

The influence of annealing temperature on the morphology and surface fractal dimension of titanium dioxide (TiO2) films prepared via the spray deposition process was investigated. Thin films with various morphologies were obtained at different temperatures and characterized by X-ray diffraction and atomic force microscopy (AFM). It was found that the crystalline structure of TiO2 films depends strongly on annealing temperature. At higher temperatures, the partial phase transformation of anatase-to-rutile was observed. The morphology and surface fractal dimensions were evaluated by image analysis methods based on AFM micrographs. The results indicate that the value of surface roughness (the standard deviation of the height values within the given area of AFM image) of TiO(2)films increases with increasing annealing temperature. Fractal analysis revealed that the value of the fractal dimension of the samples decreases slowly from 2.23 to 2.15 following the annealing process

Study of the effect of Mg(II) addition and the annealing conditions on the structure of mesoporous aluminum oxide using Plackett-Burman design

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 process 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 the annealing temperature, heating rate and concentration of magnesium nitrate were the main factors affecting the average crystallite size of the predominant alumina phase. In the case of the specific surface area, two of selected six variables had pronounced effects; however, the temperature of annealing was more effective than others. The present results showed that the proposed model that uses crystallite size as a response variable is preferable to other research

Optimalno faktorno planiranje procesa kiselinske aktivacije bentonita u mikrotalasnom polju

In this study, the statistical design of the experimental method was applied on the process of acid activation 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 developed mathematical model helped to predict 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.Radi dobijanja efikasnog adsorbensa štetnih i opasnih materija izvršena je optimizacija parametara procesa sinteze kiselinski aktiviranog bentonita u mikrotalasnom polju na bazi statističkih planova eksperimenta. Tokom planiranja eksperimenata razmatran je uticaj snage mikrotalasnog polja, vremena aktivacije i koncentracije kiseline na poroznu strukturu aktiviranog materijala. Utvrđeno je da specifična površina zavisno od uslova procesa, ima minimalnu vrednost od 114,0 m2 g-1 za adsorbens sintetisan pri uslovima definisanim u eksperimentu 11 (4,5 N HCl, 21 min i 117 W), a maksimalnu vrednost od 153,5 m2 g-1 za adsorbens dobijen u eksperimentu 8 (3 N HCl, 17 min i 85 W). Ustanovljeno je da tokom procesa kiselinske aktivacije bentonita u mikrotalasnom polju najveći uticaj na formiranje specifične površine ima faktor vreme. Rezultati optimizacije procesa zasnovane na funkciji poželjnosti uz uslov minimalnog vremena aktivacije, vrednosti koncentracije kiseline i snage mikrotalasnog zračenja u zadatom opsegu, pokazali su da je optimalno vreme aktivacije bentonita u mikrotalasnom polju 7,38 min dok kod hidrotermalne aktivacije sa kiselinom iste koncentracije potrebno vreme iznosi 2,8 h

Svojstva adsorbensa dobijenog aktivacijom bentonita na konvencionalan način i u mikrotalasnom polju

In this paper the effect of acid activation by conventional and under microwave irradiation on the textural and structural properties of bentonite was studied. The adsorbents were characterized by powder X-ray diffraction and the BET method using the nitrogen adsorption technique. The XRD patterns of raw clay demonstrated maximum intensities within the ranges typical for smectite group minerals. From X-ray powder diffraction patterns of both activated samples absent of calcite characteristic reflection was confirmed. Higher degree of dealumination and decationization was achieved for sample activated by conventional, as can be determined from XRD patterns. Sorption analysis results showed that activated bentonite samples contain slit shaped pores, and meso- and microporosity better than natural bentonite. Sample activated under microwave irradiation has developed microporosity and high specific surface area, with no leaching of the structural cautions.U ovom radu je ispitivan uticaj hemijske aktivacije, na konvencionalan način i aktivacije u mikrotalasnom polju, na strukturna i teksturalna svojstva dobijenog adsorbensa. Kao polazni materijal korišćen je bentonit. Kao metode karakterizacije korišćene su rendgenska difrakcija i BET-metoda analize niskotemperaturnih adsorpciono-desorpcionih izotermi azota. Rendgenskom difrakcijom na prahu je utvrđeno da je smektitna faza dominantna. Nakon aktivacije kod oba aktivirana uzorka uočen je gubitak karakteristične refleksije kalcita usled rastvaranja u kiseloj sredini. Hemijska analiza je pokazala da je veći stepen dealuminacije i dekatjonizacije postignut kod uzorka aktiviranog na konvencionalan način, što je potvrđeno i difraktogramima praha uzoraka. Rezultati sorpcione analize su pokazali da aktivirani uzorci sadrže pore tipa prskotina i da imaju bolje razvijenu poroznost u oblasti mikro i mezopora od prirodnog bentonita. Kod uzorka aktiviranog u mikrotalasnom polju došlo je do razvoja mezoporozne strukture i rasta specifične površine, a da je pri tome očuvana smektitna struktura u većoj meri nego kod uzorka sintetisanog na konvencionalan način