SYNTHESIS, CHARACTERIZATION AND PHOTOLUMINESCENCE STUDIES OF SR2CEO4: EU NANO PHOSPHOR
Paleena Thulimilli1, Dr.K.V.R.Murthy2
1Department of Physics, St.Pious X Degree & PG College for Women, Hyderabad, Telengana
2DisplayMaterials Laboratory, Applied Physics Department, Faculty of Technology
Engineering, M.S University of Baroda, Baroda–390001, India
Abstract: Nanotechnology is a common word these days, but many of us don’t realize the amazing impact it has on our daily lives. It is also a rapidly expanding field. Scientists and engineers are having great success making materials at the Nano scale to take advantage of enhanced properties in display applications.For the last one and half decade the nanotechnology, with size limitation of less than 100nm, has been moving at a pace and gaining momentum, research in this field is becoming more and more active. In this regard the phosphor research has also awakened to the challenge and new and better materials with the size limitations are being pursued rigorously. The current world market place for phosphors is about $450m annually with an expectation to grow in the 8-10% range. And, they have to compete with and against several display technologies and applications such as liquid crystal, plasma, LEDs, OLEDs, automotive and field emission, which in turn require a growing range of phosphor types to satisfy new and existing uses. Up till now the commercial Nano phosphors are synthesized using solid state reaction which requires the raw materials to be ground using an high speed grinders/ball mills and fired at 1200-1600°C or more depending on the synthesis temperature for many hours with two or more intermediate grindings. By considering all the applications into account in this paper the detailed description of synthesis of the Sr2CeO4 Nano phosphor by various techniques and their luminescent properties are discussed
Keywords: Sr2CeO4, solid state reaction technique, sol-gel technique, Photoluminescence, XRD; SEM
Nano crystals and the size dependent properties of the Phosphors
The optical properties of the solids have been an area of interest for the past few centuries, but for the past few decades they have been an area of high interest for those working with Nano crystals. The optical properties can give an insight to the mechanism and the nature of the material formed. These properties have led to the discovery of various inorganic hosts having different technological applications. The concentration of these have mainly been on the metallic Nano crystals 1 and semiconductors (mainly the Doped Nano crystals (DNC)), which shows the quantum confined effect.
In the last two decades considerable interest has been directed towards the synthesis and characterization of economical and efficient rare earth doped phosphors using different hosts has been developed for various applications. The red 5D0 7F2 and orange emission 5D07F1 of Eu3+ and green emission of Tb3+ 55D45D4 7F5, is usually used in these phosphors. These phosphors find applications in fluorescent lamps, color TV screen, cathode ray tubes, Plasma Display Panels, discharge lamps etc. These phosphors are not commercially synthesized in India, and are imported 2, 3. Also no systematic efforts were made towards studying the use of indigenous chemicals for the synthesis of these phosphors. 4,5.6.
Solid State Reaction: The starting materials taken for solid state reactions were SrCO3, CeO2 purchased from S.D. fine chemicals (Boisar). The stoichiometric ratio of Sr:Ce was taken as 2:1. The samples were first grinded using agate mortar and pestle and then kept in a furnace. The temperature of the furnace was set at 1200°C from the room temperature. The heating rate of the furnace was fixed at 6.67°C/minute. The samples were kept in the furnace at 1200°C for 10 to 30 hours with two or three intermediate grindings. After the heating was done, the sample was allowed to cool by switching it off. The samples were again grinded using agate mortar and pestle. The resulting powder was white in colour.
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Sol-gel technique: The starting materials taken were Sr(NO3)3, Ce(NO3)3.6H2O, Citric Acid, Ethylene Glycol and Liquid ammonia (NH3) purchased from S.D. fine chemicals (Boisar, Mumbai, India). The stoichiometric ratio of Sr: Ce were taken in 2:1. The nitrates were first dissolved in around 20ml of double distilled water and kept for stirring on a magnetic plate at room temperature until it becomes transparent in color and all the salt have mixed. Gradually the temperature of the plate was increased to 40-50°C. After a certain time of continuous stirring, citric acid was added to the transparent solution. The pH of the resulting solution was maintained 6-7 by adding droplets of ammonia. The temperature of the solution was raised to 60-80°C. The solution at this stage becomes milky in colour due to the precipitation taking place in the solution due to citric acid acting as a chilating agent. After few hours of stirring Ethylene glycol was added to the solution and stirring was maintained. The solution now changes its colour and becomes yellow, becoming more viscous and the formation of gel takes place. The starting materials used are nitrates in aqueous media, which form stable gels through gelation with citric acid, followed by cross-linking after polycondensation of ethylene glycol at increased temperature. The synthesis of Sr2CeO4 by sol-gel has been shown in figure-3. This mechanism ensures that the gel formation takes place. The gel is then kept in an oven at 110°C for 4 hours to remove water content if any and for drying. The dried gel was then made into 4 parts. Each part was given a different heat treatment.
Part- 1 A – Kept for heating at 400 C for 2 hrs.
Part- 2 B – Kept for heating at 800 C for 4 hrs.
Part- 3 C – Kept for heating at 1000 C for 4 hrs.
Part- 4 D – Kept for heating at 1200 C for 2 hrs.
X-ray Diffraction studies: by using X-ray powder diffraction using RIGAKU D’MAX III Diffractometer having Cu K? radiation (?=1.54nm) Phase identification of the powders was carried out. The scan range was kept from 50 to 800 was the scan range at the scan speed of 0.050 per second.
Scanning Electron microscope (SEM): The SEM images of the samples were taken using JEOL make JSM-5610 LV for studying the morphology of the compound.
Photoluminescence measurements: The photoluminescence (Emission and Excitation spectra) were recorded at room temperature using spectrofluorophotometer RF-5301 PC of SHIMADZU. Xenon lamp is used as source. For the emission and excitation the slit width was kept at 1.5nm for all the measurements. To remove the second order peak of the excitation light in the PL measurements a filter was used. The sensitivity of the instrument was set as high unless stated otherwise.
Results & discussion:
1. X-ray diffraction studies: The crystallinity of the compound as revealed by the XRD pattern, increased on raising the calcining temperature. From the analysis of the XRD pattern, it was understood that the introduction of activator Eu3+ did not influence the crystal structure of the phosphor matrix. The calculated average crystal size of the sample calculated by measuring the full width half maxima was found to be of about 40 nm for europium 1 mole percentage doped sample.
2. Scanning Electron microscope (SEM) studies The Scanning Electron Microscopy studies have been done on the particles prepared by both the solid state reaction as well as Sol-gel technique. All the SEM micrographs have been presented in the Figure-1From the SEM micrographs we can see that the morphology of the samples prepared by the sol-gel is better. The shape and the size of the sol-gel prepared are round and they appear to be less agglomerated when compared with the solid state one. The solid state synthesized sample has been sintered and appear heavily agglomerated, the morphology is not uniform and they are tightly aggregated to one another to form large secondary particles. They also do not have narrow size distribution and appear very hard. The sol-gel synthesized samples are spheroidal in shape and even at high temperature of annealing they appear less agglomerated. The size of the sol-gel synthesized is very small compared to solid state and they appear very soft with respect to solid state ones. The micrographs of the sample prepared from the europium doped Sr2CeO4 and one plain are shown in figure-1 for comparison.
Figure 1: All Europium doped Sr2CeO4 micrographs and one plain shown for comparison
Photoluminescence Emission Spectra of Europium doped Sr2CeO4:
The emission spectra of the europium (0.5mol %) doped in Sr by sol-gel has been shown in figure-2. The peak at 595nm is highest in intensity for the 5D07F1 transitions and even higher than that at 467nm (5D27F0) but as the percentage of europium doping is increased the intensity of this decreases. The stark splitting for the 5D07F1 would be three (2J+1) theoretically and experimentally all the three are observed with the intensity of the 595nm being highest, increasing the concentration decreases it with subsequent increase of the 586nm intensity. This is unique observation for the 0.5mol% doped and not for all. The stark splitting for 5D07F2 would be five theoretically and four lines are found experimentally.
Figure-2 The Photoluminescence emission spectra of the sol-gel synthesized Sr2CeO4 with europium (0.5mol%) doping excited with 254nm wavelength.
The emission spectra measured for different excitation wavelengths, 254nm, 280nm and 467nm respectively is shown in the figure-3. It is observed that the emission is highest for the 280nm wavelength and the emission pattern is same for excitation wavelengths except for 467nm. The emission observed from 467nm excitation wavelength shows minor changes than the other two. As the emission coming from 467nm is not governed by charge transfer band hence we can see the small shift of the 585nm peak towards higher wavelength region, the stark splitting of the 5D07F1 transitions is also not clear. These results prove that the different excitation wavelength can change the composition of different sites spectrum components.
Figure-3 The Photoluminescence emission spectra of the sol-gel synthesized Sr2CeO4 with europium (0.5 mol%) doping excited with 254nm wavelength.
Conclusions: The main conclusions that can be drawn by studying the effect of europium doping on the luminescence properties of the Sr2CeO4 are as follows:
Europium doped Sr2CeO4 phosphor was synthesized successfully using sol-gel technique.
Comparison with solid state reaction revealed a marked difference in the emission characteristics from 580nm-630nm for the 0.5mol% doped europium sample. This may be due to the Nano crystal size (~55nm) of the phosphor formed with sol-gel.
Greater splitting of the 5D07F1, 5D07F2 when compared with solid state reaction and few additional lines were seen at 595nm and 611nm for the sol-gel prepared sample.
Excellent tunablity of phosphor observed when doped with various concentrations of Europium.
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Synthesis, characterization, and application of olive/oleic bio-alkyd resin for determination of molybdenum in pharmaceutical samples
Elhossein A. Moawed*, Maha A. El-Hagrasy, Alaa E.A. Senan
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
*Corresponding author: E-mail [email protected]; Phone: 00201028921272; Fax: 0020572403868; P.O. Box: 34517- Damietta; Egypt
The study of (olive/oleic bio-alkyd resin, OOBAR) as a new biosorbent was prepared in open esterification system from an olive tree, glycerol, oleic acid and phthalic anhydride. OOBAR characterization was performed by using ultraviolet/visible, infrared spectra, Boehm titration, zero-point charge, iodine number, methylene blue index and bulk DC electrical conductivity. The obtained data of acidic and basic sites show that the OOBAR surface was contained 2.6 and 1.3 mmol/g. The pHZCP was 3.6, ?pH at pH 9.27 was -4.33, the I2 number was 2.3 mmol/g (291.9 mg/g), methylene blue was 0.69 mmol/g (220.7 mg/g) and DC conductivity was 1.0 ×10-9 ?-1 cm-1. The effects of acidity, reducing agent, NH4SCN concentration, contact shaking time, Mo concentration, temperature, OOBAR dose, batch factor and ionic strength for Mo(V) were determined. The maximum OOBAR capacity for Mo(V) sorption was 1.3 mmol/g. The molar ratio of Mo(SCN)6-, OOBAR+ was 1:1 in acidic medium. The equilibrium isotherms, kinetics, diffusion and thermodynamic models for Mo(V) sorption onto OOBAR were studied. Thermodynamic parameters such as enthalpy (?H), entropy (?S) and Gibbs free energy (?G) were -46.2 kJ/mol, -0.082 kJ/Kmol and -21.8 kJ/mol was shown that the sorption process was spontaneous, exothermic nature with decrease disorder and randomness at the solid-liquid interface of Mo with OOBAR. Dynamic experiments using glass column was indicated a good affinity chromatographic separation for its applications in many pharmaceutical and biological samples including liver mice tissue and pharmaceutical vitamin drugs. The lower relative standard deviation (RSD%) value for pharmaceutical applications samples (n=5) was found from 1.1%.
Keywords: Olive; Oleic acid; Alkyd resin; Molybdenum; Pharmaceutical; Sorption
Molybdenum (Mo) has applications in many pharmaceutical and biological samples 1. Mo is an economically silvery-white transition metal and has five main oxidation states ranging from (II) to (VI). It has an atomic number of 42 and an atomic mass of 96 2, 3. Mo is a bio-essential metal for humans, animals, and plants. It has relatively low toxicity because of a component or co-factor of enzymes which are important for life, so without Mo, organisms cannot work and will show signs of deficiency 2-5. Metallic Mo offers many advantages like good corrosion resistance, excellent mechanical, thermal, electrical properties, high temperature and its melting point (2883 K) because of the low coefficient of its thermal expansion and a high thermal conductivity. These excellent properties make it be widely used in electronics, metallurgy, aerospace and electrical industries 6-9.
Biosorbent is a biological origin solid system from bacterial, fungal, plant or animal origin 10. It has several functional groups such as carboxyl, ether, carbonyl, hydroxyl, and ester groups and more effective alternatives for metal ions sorption (e.g Mo) from aqueous solution 11-16. Adsorption using a cheap, abundant and environmental-friendly adsorbent originated from a plant such as an olive tree (Olea Europea) is currently being researched as effective substitutes as is the simplest and most useful method 17, 18. The olive tree was one of the first small fruit domesticated trees in the family Oleaceae cultivated by man for more than 5500 years ago. Its common name was for about 35 species of evergreen shrubs and trees in the olive family of the genus Olea. It has varieties of parts such as fruit, leaves, and oil. Olive trees native to the Medial East, Egypt, Palestine, Jordon, Syria, Africa and Asia. They have many varieties that exhibit major or minor phenotypical and genetic differences 19-23.
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Oleic acid (OA, cis-9 C18:1) is a monounsaturated fatty acid (MUFA). It is abundant in most of the fatty acids by (48%) or in olive oil by (70%-80%). It can be extracted from peanut and its products. Researches indicate that the MUFA-rich diet has protective effects on cardiovascular risk and diabetes 24-27.
Alkyd resins are highly branched polymer with a polyester backbone which significant for synthetic polymers 28, 29. They are thermoplastic polyester resins can be synthesized by polycondensation 30, 31 of three types of monomers of polyhydric alcohols (e.g; glycerol), fatty acids (e.g; oleic acid) and dibasic acids or their anhydrides (e.g; phthalic anhydride) 32-37. They can be dissolved in organic solvents and have good interactions with polar substrates such as wood and steel 38. They have excellent properties such as acceptable, inexpensive to produce, high gloss, retention color, dissolved in organic solvents, excellent thermal stability, eco-friendly, excellent wetting properties, good adhesion and good interactions with polar substrates such as wood and steel 26, 34, 35. These properties make them suitable to apply in industrial coating, adhesives, the binder for composites and anticorrosion paint 39. Bio-alkyd resin contains reactive sites such as carbon-carbon double bond, a polar ester group, methylene group attached to the carbonyl site, allylic methylene attached to double bond 40.
The present paper approaches the study of OOBAR as a new biosorbent which used for Mo(V) sorption was synthesis. Properties of OOBAR are were characterized by UV-Vis, FTIR, and bulk DC electrical conductivity. The sorption of Mo(V) onto OOBAR was studied to optimize the best conditions for the sorption process. The obtained data have been examined for kinetic, thermodynamic, and equilibrium situations. Mo was applied in many pharmaceutical and biological areas including tissue of lever mice, tap water, and vitamin drugs.
2. 1. Apparatus
The JASCO FTIR-4100 spectrometer in the 4000–400 cm-1 regions by using KBr disc (KBr pellet) was performed the characterization of olive bio-alkyd resin. Ammonium molybdate tetrahydrate ((NH4)6Mo7O24.4H2O) absorbance measurements were demonstrated by using JASCO (V-630 UV-VIS Spectrophotometer, Japan) at ?max 485. Bulk DC conductivity was established using Keithley, 6517B electrometer-high resistance meter after pressing OOBAR disk by a Hydraulic press at 12 tons. Dynamic technique for chromatographic separation experiments was carried out by using a glass column with a bed height of 15 cm approximately that contained 9.5 g of OOBAR was 35 cm long and 1.5 cm in diameter.
2. 2. Reagents, materials and real samples
Olive biosorbent (OB): Olive tree legs and green leaves were cut to small particle size followed by washing with water, drying at 250 ?C and blending using food blender. Carboxy olive biosorbent (COB) preparation: 100 g of OB with 80 mL of concentrated HNO3 were heating in a beaker until brown foams finished, then washing with distilled water and methanol then drier at 80 ?C.
Olive/oleic bio-alkyd resin (OOBAR) Preparation: A 85 g of oleic acid with 28 g of glycerol were heated for 6 h. Then the product was heated with 15 g biosorbent 6 h, followed by adding 15 g of phthalic anhydride then heated 6 h. The final product was washed with distilled water then methanol and left to dry at room temperature then blending and sifting at 355 µm (0.0355 cm).
Molybdenum stock solution (1 g/L): was prepared by dissolving 0.185 g of (NH4)6Mo7O24.4H2O in distilled water to 100 mL.
Vitamins drugs stock solutions: 1.217 g Vitayami for the deficiency of iron and vitamins tablets which contain (Cu: 1000 mcg; Fe: 30 mg: Mn: 2.5 mg: Mo: 15 mcg) and other content (Multi-Apex for Pharmaceutical Industries, Badr City – Cairo – Egypt), 1.067 g V2 plus multivitamins and minerals capsules which contain (Mo: 0.2 mg; Cu: 1 mg: Mn: 1 mg: Fe: 10 mg) and other content (Pharco pharmaceuticals, Alexandria – Egypt), 1.299 g Vitamax plus dietary supplements capsules which contain (Cu: 2 mg: Fe: 9 mg; Mn: 5 mg; Mo: 30 mcg) and other content (El Salam City – Cairo – Egypt) and 1.67 g Vitona plus energized and biotonic capsules which contain (Fe: 14 mg; Cu: 2 mg; Mn: 2.5 mg; Mo: 0.186 mg) and other contents (Egyptian Int. Pharmaceutical Industries CO, E. I. P. CO, 10th of Ramadan City – Egypt) were prepared by dissolving of each one in aqua regia and gently evaporated several times till dryness and removing any excess of them. The residual was dissolved in distilled water to 100 mL in a measuring flask containing 1mL of concentrated HNO3.
The tissue of lever mice stock solution: A 0.5 g of liver tissue spiked with Mo nanoparticle (0.25 mg) was prepared by dissolving in aqua regia and gently evaporated several times till dryness and removing any excess of them. The residual was dissolved in distilled water to 10 mL in a measuring flask containing 1mL of concentrated HNO3.
2.3. Recommended procedures
A 0.1 g of OOBAR was mixed with adjust concentration of molybdenum solution, H2SO4, L-ascorbic acid, and NH4SCN then diluted to 25 mL and shaken 60 min at room temperature. The remaining concentrations of Mo(V) were determined using spectrophotometrically (?max 485 nm) 41. The sorption percentage of Mo(V) and sorption capacity of OOBAR (Q, mmol/g) were calculated.
By using a dynamic technique, 10 g of OOBAR was packed through glass column which has 35 cm long and 1.5 cm in diameter with a bed height at L= 15 cm. A series of 25 mL of tap water, liver mice tissue or vitamins solutions (n = 5) were passed through the OOBAR columns at different flow rate 0.2-1.7 mL/min. The effluent solutions were collected and analyzed spectrophotometrically. Mo(V) was eluted from OOBAR columns with NH4OH (0.05 mol/L) as eluent at a flow rate of 3 mL/min then determined spectrophotometrically.
3. Result and discussion
3. 1. Characterization of olive bio-alkyd resin (OOBAR)
FTIR spectroscopy was used for identification of specific functional groups of OB, COB, OOBAR, and Mo:OOBAR in range 4000–400 cm-1. OB spectrum have broadband at 2996-3660 cm-1 (?OH), sharp peaks at 2933 cm-1 (?CH), 1612 cm-1 (?C?C) and 1084 cm-1 (?C-O-C). The bands of COB spectrum were shifted to 2343-3664, 1606 and 1097 cm-1. In addition, the new band has appeared at 37001 cm-1 while the band at 2933 was absent due to an oxidation process. Also, the bands of OOBAR spectrum were shifted to 3027-3741, 2925, 1631.5 and 1166 cm-1. The new bands have appeared at 2979, 2854 and 1739 and 1459 cm-1 due to C-H (aromatic), C-H (aliphatic), C=O and COOR. There are many sharp peaks for Mo:OOBAR was appeared at 780, 693, 519 and 507 cm-1 due to Mo(V) complexion and other bands for O-H, C-H (aromatic), C-H (aliphatic), C=O and COOR was disappeared due to the cleating agent.
UV-VIS electronic spectra of OB, COB, OOBAR, and Mo:OOBAR were estimated in solid state using Nujol mulls procedure. The higher energy of UV spectra bands of OB was performed at 241-265 nm which were attributed to the ?-?* transitions, and 293-340 nm which was attributed to the n-?* transitions localized on the conjugated system. Higher energy adsorption band in COB was assigned to 241-265 nm which was attributed to the ?-?* transitions, the second band was shifted to 293-355 nm and after oxidation process, there was a new band at 368-370 nm which were assigned to the n-?* transitions localized on the conjugated system. UV spectrum of OOBAR was shown that many absorption bands between 200 and 250 nm at (201, 205, 216, 224, 227-229, 232, 237, 241 and 245) nm which were assigned to ?-?* transitions and due to the several functional groups of OOBAR. Also, many lower energy bands have appeared between 300 and 320 nm due to n-?* transitions that localized on the conjugated system. Mo:OOBAR has higher energy adsorption bands at 233-245, 250 and 261 nm which were attributed to the ?-?* transitions, and 264-296 nm which was attributed to the ?-?* and n-?* transitions, and also at 299 and 307 nm which were attributed to the n-?* transitions localized on the conjugated system. There are many lower energy bands were appeared at 247, 255 and 259 nm which were assigned to ?-?* transitions, and also between 300 and 340 nm due to n-?* transitions that localized on the conjugated system.
Boehm titration offers an identification of the active surface sites such as carboxylic, carbonyl and phenolic 42. Total acidic and basic sites were detected by back titration using 0.1 mol/L HCl and NaOH solutions. Carboxylic, lactonic and phenolic groups were evaluated by using titration with 0.1 mol/L NaHCO3, Na2CO3, and NaOH solutions. The acidic and basic sites of OB were (1.8 and 0.9 mmol/g), COB was (1.6 and 0.9 mmol/g), and OOBAR was (2.6 and 1.3 mmol/g). It is clear that the amount surface of total acidic sites was greater than basic sites in OB, COB, and OOBAR which have mainly acidic character. OB has 0.7 mmol/g carboxylic sites, 0.6 mmol/g lactonic sites and 0.5 mmol/g phenolic sites. The quantity of lactonic and phenolic sites was decreased from 1.1 mmol/g in OB to 0.6 mmol/g of COB while the number of carboxylic sites of COB was increased to 1.0 mmol/g due to an oxidation process. The amount of carboxylic and carbonyl groups of OOBAR is higher than COB due to the addition of phthalic acid.
The values of iodine number (I2 No) of OB, COB, and OOBAR were evaluated using back titration with 0.05 mol/L I2 and Na2S2O3 solutions. The I2 No of OB, COB, and OOBAR were 406.1, 320.1 and 291.9 mg/g (3.2, 2.5 and 2.3 mmol/g). The I2 No of OOBAR were decreased than OB and COB due to the coupling the biosorbent with phthalic acid. Methylene blue value (MB) of OB, COB and OOBAR were 176.97, 216.32 and 220.7 mg/g (0.59, 0.68 and 0.69 mmol/g). The increasing of MB value of OOBAR due to additional of functional groups. The results obtained indicated that the I2 No depends on the adsorption process while the MB value depends on the cation exchange process (the amount surface of total acidic sites is greater than basic sites in OB and COB). The I2 No of OOBAR was 291.9 mg/g (2.3 mmol/g) and methylene blue was 220.7 mg/g (0.69 mmol/L), these values are greater than those reported for other biosorbents 43-55.
The zero-point charge is the pH value that the charge of a biosorbent surface is equal to zero 56. The pHPZC values of OB, COB and OOBAR were7.0, 3.2 and 3.6. Maximum values of ?pH was 1.5, -1.9 at pH= 5.2, 9.1 for OB, -6.7 at pH= 11 for COB and -4.4 at pH= 9.4 for OOBAR. The surface would be negatively charged due to the deprotonation of the surface functional groups for OB, COB and OOBAR at pH values above 7.0, 3.2 and 3.6 while the surface became positively charged below pH 7.0, 3.2 and 3.6. The shifted of pHPZC value OB from pH 7 to pHs 3.2 and 3.6 for COB and OOBAR due to the increasing of functional groups in the matrix of COB and OOBAR. The OB, COB, and OOBAR sorbents have surface buffering (non-effect with acidic and basic medium) at pHs (5.4-9), (4.2-10.8), and (6.9-9.3).
The higher percentages (98%) for the sorption of molybdenum (V) from aqueous solution were in strongly acidic medium H2SO4 (0.6 – 3.6 mol/L). This was happened because of ion association complex between cationic OOBAR+ in acidic medium (pH < 3.6) and anionic ammonium thiocyanate Mo(SCN)6– complex.
Electrical conductivity measurements were obtained by the method of Ahmenda using an EDT instrument BA380 57. Bulk electrical DC conductivity (?) was recorded at room temperature in the solid state, pressing the samples at 10 tons in the form of a circular disk and potential equal to 2 volts. The values of electrical conductivity were 0.12×10-7 and 4.1×10-6 ?-1 cm-1 for OB and COB. The value of COB was greater than OB due to increasing of active sites (functional groups) with the oxidation process. While the lower value of OOBAR than COB (0.001 ?-1 cm-1) indicates that due to converting from matrix of COB to polymer chain in OOBAR.
3. 2. Batch sorption behavior of the sorption of Mo(SCN)6– using OOBAR
The obtained data was shown that higher values of sorption percentages were in strongly acidic medium H2SO4 (3.6 mol/L) at low concentrations of both ascorbic acid (0.08 mol/L) as reducing agent and NH4SCN (0.12 mol/L) which form orange-red color for Mo(V) complex (Fig. 4). In the effect of dose batch factor (0.05-0.5 g OOBAR in 25mL sample volume), the higher sorption percentages slightly increased (92-100%) and its capacity decreased by decreasing batch factor (v/m) and increasing amount of OOBAR dose so the sorption process can’t depend on it (Fig. 5). While in the effect of volume batch factor, the sorption percentages (98-22%) and its capacity were decreased by increasing batch factor (V/M) and sample volume (25-100 mL) (Fig. 6). By studying the effect of ionic strength of salts, the results indicate that the sorption behavior of both NaCl and KCl are similar with maximum sorption percentages (86-92%), unlike the sorption behavior percentages (80-21%) of NH4Cl indicate that the ammonium salts can be used in the stripping of Mo ion from OOBAR biosorbent (Fig. 7).
3. 3. Equilibrium studied
A 3.6 mol/L H2SO4, 0.08 mol/L ascorbic acid, 0.12 mol/L NH4SCN and shaking 1 h at room temperature, the OOBAR capacity for sorption Mo(V) was increased by increasing initial concentrations until be reached to maximum capacity (Qmax). The Qmax value of OOBAR for Mo(V) was 0.17 mmol/g (16.3 mg/g) with intercept and the correlation coefficients (R2) were 0.001 and 0.991.
There are many isotherm models which employed to analyze the sorption mechanism and determined the parameters equilibrium. These models are Langmuir, Freundlich, Dubinin–Radushkevich, Temkin and Harkins Jura models which selected to predict the adsorption capacities and suitable for the experimental equilibrium data. Adsorption isotherm of the Langmuir model is an empirical model was obtained from an assumption of the uniform energy of adsorption sites onto the absorbent surface and the adsorbate along the plane hasn’t existed on the surface. It hypothesis that there is a fixed number of active sites is homogeneous in which adsorption occurs inside the surface of the adsorbent. These active sites have the identical affinity for a monolayer adsorption molecule and there is no interaction between molecules adsorbed. For sorption of Mo(V) complexion, the values of b, KL, and R2 were 50.5 L/mmol, 0.18 mmol/g and 0.997. Freundlich adsorption isotherm model is an empirical equation assigned to characterize adsorption on heterogeneous systems with an interaction between the adsorbed molecules, and formation of a monolayer unrestricted. It assumes due to adsorbate concentration increases; its concentration also increases on the adsorbent surface. The resulted values for sorption of Mo(V) complexion of 1/n, KF and R2 were 0.35, 0.28 L/g and 0.933. The observed results of correlation coefficients (R2) of sorption Mo(V) complexion in Langmuir and Freundlich isotherms indicated that the Langmuir model is a good fit to the adsorption experimental data and suggests monomolecular layer as well as a homogeneous distribution of active sites on OOBAR surface.
Dubinin-Radushkevich model of adsorption isotherm is an empirical equation employed to indicate the difference between physical and chemical adsorption, describes adsorption for both heterogeneous and adsorption mechanism. R2 value was 0.975 which approximately agreement with Freundlich isotherm model, ? was -0.008 mmol2/kJ2 and KD-R was 0.19 mmol/g. The sorption free energy (?E = (-2 ?)-½) can be obtained from the value of ? as 7.91 kJ/mol.
Temkin isotherm model was obtained as the effect of some indirect sorbate/adsorbate interactions and suggested that because of these interactions the adsorption heat of all molecules in the layer would decrease linearly. The results obtained of sorption Mo(V) complexion were R2: 0.984, A: 1.7×103 mmol/g and B: 0.03. By applied Harkins Jura adsorption isotherm model, A, B constant parameters and R2 were -1.2×10-3, 0.8 and 0.6 for sorption Mo(V) complexion.
3. 3. Kinetic studies
Rate sorption percentage (74-91%) of Mo(V) complexion was very rapid at the initial stage of the contact period time (0.5-3 min) then rate sorption became slower until reached to the equilibrium time. This phenomenon was occurred due to the fact during the initial stage of the adsorption process, a large number of vacant surface sites were available for adsorption. Near the equilibrium, vacant surface sites remaining were difficult to occupy due to the slow Mo(V) ion pores diffusion on OOBAR and the repulsive forces between bulk phases and solid molecules.
Kinetic studies were estimated to investigate the effects of contact shaking time at a definite quantity adsorbed of initial Mo ion concentration at room temperature. It was illustrated by using five simplified kinetic models namely (pseudo-first-order and pseudo-second-order) and diffusion models (Weber and Morris intraparticle, Reichenberg, Boyd, and Bangham) to identify the rate and kinetics of sorption of Mo(V) complexion on OOBAR.
In contact shaking time batch experiments, the sorption rate of Mo(V) ion onto a given adsorbent is proportional to the adsorbed amount of Mo(V) ion from the solution phase. Adsorption kinetics can be characterized by a pseudo-first-order equation, its k1, t1/2 and R2 factors were 0.072 min-1, 9.65 min and 0.951 while resulted factors of k2, t1/2, and R2 in the pseudo-second-order kinetic model were 0.02 g/mmol min, 0.98×103 min and 1 for sorption of Mo(V) ion complex. By comparing values of correlation coefficients in both pseudo-first-order and pseudo-second-order, it clears that the pseudo-second-order is a good fit for the experiment.
Weber-Morris or intraparticle-diffusion is a single-resistance model used to analyze the nature of the ‘rate?controlling step’. It has a basic attention due to in most liquid systems the internal diffusion determines its adsorption rate. The results obtained for R2 and ki were 0.518 and 9×10-4 mmol/g min0.5. In Reichenberg diffusion model, its linear relation Bt and t was plotted, it clears that R2 value was 0.951 for Mo(V) sorption. The better suggestion known as Boyd’s film-diffusion model is an intraparticle diffusion in a spherical particle which its Di and R2 parameters were obtained as 7.3×10-9 cm2/s and 0.518. By plotting a linear relation for Bangham’s pore diffusion model between log log Co/ (Co-Qt m) vs. log t, it does not pass through the origin and values of ko, ? and R2 were 6.3×10-5 mL/g L, 0.042 and 0.761.
3. 4. Thermodynamic studies
Temperature solution (22-57 ?C) that effect on sorption Mo(V) complexion was studied. Sorption percentages of Mo(V) complexion were slightly decreased from 98% to 84% with increasing of temperature. Parameters value of thermodynamic obtained from batch adsorption studies were recorded by using the Van’t Hoff equation. The negative parameter values for ?G value: -21.8 kJ/mol indicated that the sorption process has a spontaneous process, ?H: -46.2 kJ/mol has exothermic nature and ?S: -0.082 kJ/K.mol at the solid-liquid interface of Mo with OOBAR has the decrease disorder and randomness.
3. 3. Application
Application of real samples such as liver tissue mice, tap water, and vitamins drug for recovery of Mo(V) using OOBAR was estimated. A series of 25 mL from each sample were studied at optimum strong acidic medium, suitable reducing agent, NH4SCN, constant concentration and shaking for 1 hour with 0.1 g of OOBAR at room temperature.
The average recovery percentage of remaining concentration of Mo(V) was from 82-97%. The higher limit of quantitation (LOQ = 10 ?, where ? is the standard deviation) was 6-11.6 ?g/L and lower limit of detection (LOD = 3 ?) was 1.8-3.5 ?g/L which both indicates the higher sensitivity of Mo(V) determination. The addition values in liver mice tissue (0.95-0.551 mg/L) (950 – 551 ?g/L), in tap water (184-2760 ?g/L), in vitayami (50.8-33.5 ?g/L), in V2 plus (800-458.6 ?g/L) (0.8-0.46 mg/L), in vitamax plus (95.8-58.2 ?g/L) and in vitona plus (636-401 ?g/L) (0.64-0.4 mg/L) plus have recovery percentage of Mo(V) in the range 95-55% for liver mice tissue, 89-42% for tap water, 86-55% for vitayami, 100-57% for V2 plus, 80-48% for vitamax plus, 86-53% for vitona plus. Average lower values of relative standard deviation (RSD%) for real samples (n=5) were found at 1.1 % (less than 10%), which reflect the accuracy and precision of the proposed method. The result obtained was shown that OOBAR was suitable for recovery Mo(V) ions in pharmaceutical and biological samples.
The sample flow rate effect depends on the recovery percentage of Mo(V) in real samples through OOBAR columns was studied. So, recovery of Mo(V) from OOBAR column were determined at different flow rates. Maximum recovery percentages (93.7-97.3%) was shown at a flow rate in the range of 0.3-1.04 mL/min in vitamins drugs. It clears that the recovery of Mo(V) from vitamins drugs was very fast and this indicated that it doesn’t depend on the change in flow rate effects. Also, at the flow rate (0.25-1.6 mL/min) and (0.2-1.2 mL/min) with recovery percentages (95-55%) and (89-42%) which decreased by increasing Mo-liver mice tissue and Mo-Tap water concentrations.
The elution of Mo(V) from OOBAR columns was carried out at a flow rate of 3 mL/min by using NH4OH (0.05 mol/L) as eluent due to form ammonium molybdate complexes, then the eluent concentration was determined spectrophotometrically. The chromatogram separation of Mo(V) was completely eluted at a flow rate in the range of 0.95 to 6 mL/min with recovery percentages (32.3-0%) at first 3-15 mL in Mo-Vitamins drug.
Olive Bio-alkyd resin was successfully prepared as a new biosorbent in open esterification system. OOBAR surface was characterized by UV-VIS, FTIR, Boehm titration, zero-point charge, iodine number, methylene blue index and bulk DC electrical conductivity. From obtained thermodynamic parameters for sorption of Mo(V) which indicates a spontaneous nature for them. They indicate also chemisorption and exothermic with decreased disorder and randomness. Due to the observed correlation coefficients for Mo(V) sorption, it clears that the Pseudo-second-order is a good fit to the experimental adsorption data and also the Langmuir model is the best isotherm model which suggests monomolecular layer as well as a homogeneously. The result obtained was shown that OOBAR was suitable for recovery Mo(V) ions in pharmaceutical and biological samples including liver mice tissue and pharmaceutical vitamin drugs. The efficiency of chromatographic column decreases due to smaller plate height and larger plates number, so OOBAR column has a good effect for Mo(V) separation.
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