Preparation and Characterization of Nano Titanium Molybdate Gel as a Base Material for 99 Mo/ 99m Tc Chromatographic Column Generator

Transcription

1 The Egyptian Arab Journal of Nuclear Sciences and Applications Society of Nuclear Sciences and Vol 5, 3, )-34( 17 Applications ISSN Web site: esnsa-eg.com (ESNSA) Preparation and Characterization of Nano Titanium Molybdate Gel as a Base Material for Mo/ m Tc Chromatographic Column Generator M. Mostafa, M. Atef, M.A. El-Amir Radioactive Isotopes and Generators Department, Hot Labs Center, Atomic Energy Authority, Cairo, Egypt Received: 26/9/16 Accepted: 28/1/16 ABSTRACT Nano crystalline porous titanium molybdate- Mo (Ti Mo) gel was prepared by dropwise addition of molybdate (VI)- The Egyptian Society of Nuclear Sciences and Applications Mo solution to a vigorously stirred mixture of TiCl3 and (NH4)2 Ce(NO3)6 solution at ph 5. The precipitated gel was dried at 5 C. The performance of the prepared Mo/ m Tc column generator based on the optimumti Mo gel was investigated. It was found that the specifications of the m Tc elutates met the requirements of use in nuclear medicine applications ( m Tc elution yield = 88 %, Mo breakthrough = %, eluate ph = 6-6.5, radiochemical purity = 98.2 % and accepted chemical purity). TiMo gel was characterized by BET surface area and pore size analyzer, DLS, XRD, SEM, IR spectroscopy and thermal analysis (TGA and DTA). The optimum TiMo gel was found to be crystalline in the form of brownish yellow fine granules with a particle size average of 58.1 nm and a total pore volume of 4.1 x 1-2 cm 3 /g. Keywords: nano titanium molybdate gel, column generator, m Tc elution, hydrothermal route. INTRODUCTION Due to its unique nuclear properties, m Tc radioisotope is used in nearly 8% of all diagnostic imaging procedures of nuclear medicine. It is used for imaging of brain, lung, salivary glands, gastric mucosa, cardiac blood pool, liver, spleen, kidneys, inflammations, etc (1-4). m Tc (t 1/2 = 6 h) is commercially available usually as eluate from fission- Mo/ m Tc column generators based on alumina. However, (n, ) Mo/ m Tc gel generators based on gel materials (e.g., zirconium molybdate, tin molybdate, zirconium molybdosilicate, titanium molybdate, etc) can represent a viable option to meet the increasing requirement of m Tc (5-8). Pre-irradiation titanium molybdate (TiMo) gels were prepared by different methods and tested as a base material for Mo/ m Tc column generator. Vanaja et al. (9) used TiCl 4 and MoO 4 2- solutions to prepare TiMo gel. The irradiated TiMo gel was packed into a column containing hydrous zirconium oxide/ alumina, and washed with K 2 CrO 4 before elution. Elution yield from such column could reach > 9 %. However, when the gel material was irradiated at a neutron flux > n cm -2 s -1, it decomposed causing the release of high Mo content in the eluate. Shafiq and Yousif (1) used TiCl 4 to prepare TiMo gel, which was then irradiated. The highest m Tc elution yield was 45.5 % using K 2 CrO % NaCl. So (11) reported that the extraction yield of m Tc from neutron-irradiated TiMo gel was 7-8 % using acetone, while it did not exceed 4 % with other solvents (MEK, ethyl ether, chloroform, etc). Nieto and Osso (12) prepared the pre-irradiation TiMo gels trying both TiCl 3 and TiO 2. They reported that best results were obtained with TiCl 3. Elution yield of m Tc was ~ 75 %. 2

2 Monroy-Guzman et al. (13) prepared pre-irradiation TiMo using TiCl 3 and TiCl 4 with molybdate solution and reported that the best results were obtained with TiCl 3 ( m Tc elution yield reached >95%. Preparation of the pre-irradiation gel materials is advantageous because it omits the unavoidable Mo partial decay during preparation time (such as these in the case of the post-irradiation gels). On the other hand, the changes in the gel structure are very sensitive to irradiation conditions. Such structural changes can cause the release of unacceptable levels of Mo in m Tc eluates (9). The present work work aims at the preparation and characterization of post-irradiation nano titanium molybdate gel of macroporosity (as a bed for Mo/ m Tc column generator) with a new method, and studying the effect of different preparation parameters on m Tc elution yield and Mo breakthrough in the m Tc eluate. Chemical Reagents and Instruments EXPERIMENTAL All chemicals used in this work were of AR grade. Distilled water was used for preparation of all solutions. A γ-ray spectrometer of a high-purity germanium (HPGe) coaxial detector of GX2518 model was used for γ-radiometric assays. A ph-meter (Hanna Instruments ph 211 model, Portugal) was used for ph-measurements. An analytical balance (A&D Engineering Inc., ANDHR-2 model, USA) having dual range (42 g/.1 mg, 21g/.1 mg) was used for weighing. A centrifuge (REMI Laboratory, R32A model, India) was used for centrifugation of the mixtures to collect the formed gels. Gas-tight autoclaves (hydrothermal reactors), made of S316 SS with -ml PTFE (Teflon) inner chambers, were used for hydrothermal preparations. A UV-VIS spectrophotometer (Shimadzu, UV- 16 A model, Japan) was used for the detection of Ti, Ce and Mo in m Tc eluted from the nano Ti Mo gel column. The pore size was determined by BET surface area and pore size analyzer (Quantachrome Nova 1 E, USA). Particle size was determined via dynamic light scattering (DLS) using Malvern Zeta sizer, Nano Series (HT), Nano ZS, UK. X-ray diffraction (XRD) was performed with an 18 kv diffractometer (Bruker, model D8 Advance, USA) with monochromated CuKα radiation (λ = Å). FESEM images were taken using field emission scanning electron microscope (FESEM) (JEOL JSM-65F, USA). Elemental analysis was carried out using an X-ray fluorescence spectrometer (Philips XRF, BW-1 sequential spectrometer, Netherlands). The IR spectra, in the range from 4 to 4 cm 1 at room temperature, were recorded using an FT-IR spectrometer (Bomem, model MB157S, Canada). Thermal analysis, including simultaneous TGA and DTA, was performed using a thermal analyzer (Shimadzu, modeldtg-6h, Japan). Molybdenum- Radiotracers The first Mo radiotracer solution was fission Na 2 MoO 4 solution (.1 M NaOH solution) obtained from the Radioisotope Production Facility (RPF), ETRR-II, Egyptian Atomic Energy Authority. The second radiotracer Mo solution was (NH 4 ) 2 MoO 4 solution obtained by eluting the commercial alumina Mo/ m Tc generator (Mon-Tek Generator, Monrol Nuclear Products Industry and Trade Inc., Turkey) with ml of 2 M NH 4 OH solution. Suitable activity dilutions of Na 2 MoO 4 and (NH 4 ) 2 MoO 4 solutions were made. Then, 1-ml samples of diluted Na 2 MoO 4 (.1 M NaOH) or diluted (NH 4 ) 2 MoO 4 (2 M NH 3 ) containing ~ 3 mci Mo were used during preparation studies of titanium molybdate- Mo (Ti Mo) gels. Preparation of titanium molybdate gel materials The Mo precipitation yield (into the prepared Ti Mo gel) and/or m Tc elution yield and Mo breakthrough in m Tc eluate were studied as a function of the parameters mentioned below ( ). Table 1 compiles preparation data of Ti Mo gels in different experiments. 1) Effect of urea (series A) The molybdate(vi)- Mo solution was prepared by dissolving.719 g of MoO 3 in 1 ml 2 M NaOH containing 1 ml of diluted Na 2 MoO 4 solution. TiCl 3 solution was prepared by dissolving

3 ml of 15 % TiCl 3 (in 1 % HCl, 1.21 g/ml) and different urea content (1, 3 and 5 g) in 4 ml H 2 O solution (Table 1, exps. A1-A4). Molybdate(VI)- Mo solution was added dropwise to the vigorously stirred Ti(III) solution in a Pyrex glass beaker. After mixing, the beaker containing the mixture was covered with a watch glass and heated in a water bath at 8 C for different times with different urea content (9-1 min) to obtain a final ph-value of 5. Thereafter, the mixture was cooled in a tap-water bath (to control further hydrolysis of the dissolved urea) and centrifuged to collect the precipitated gels. Finally, the gels were dried in an electric furnace for h at 1 C. Table (1): Preparation conditions of Ti Mo gels Series A B C D E F GA GB GC Exp. Reagents for ph adjustment H2O2, ml Urea amount, g Concentration in solution mixture, M Ce Ti Mo (VI) Ti:Mo molar ratio ph-value of the gel precipitation Autoclaving temp., C Drying Temp., C Color A1 1 A2 HCl, NaOH :1 5 1 Greenish blue A3 5 B1 15 B2 1 B3 6 B4 HCl, NaOH 4 1 Yellow.1.1 1:1 5 B5 2.5 B6 1 B7.5 B8 - Greenish blue C1.25 Light greenish blue C2.5 C3 HCl, NH4OH :1 6 5 Brownish yellow C4.2 D :1.3 D2.99 1:1.1 D3.1 1:1 HCl, NH4OH.2.1 D :1 D :1 D6.2 2:1 E1 E Brownish yellow E3 HCl, NH4OH :1 6 5 Brownish yellow E4 7.5 E5 8 F1 5 Brownish yellow F2 1 HCl, NH4OH :1 5 F3 15 Dark brownish yellow F4 GA1 5 Dark brownish yellow HCl, NH4OH :1 5 1 GA2 1 GB1 3 Dark brownish yellow HCl, NH 4OH :1 1 5 GB2 5 GC1 5 Dark brownish yellow GC2 HCl, NH4OH : GC3 15 Brown

4 2) Effect of H2O2 (Series B) Both of molybdate(vi)- Mo and TiCl 3 solutions were prepared as mentioned above for series A but without urea. Molybdate(VI)- Mo solution was added to the vigorously stirred TiCl 3 solution. For exps. B1-B7, after mixing, different volumes of 3 % H 2 O 2 (15, 1, 6, 4, 2.5, 1 and.5 ml) were added. For exp. B7, no H 2 O 2 was added. Then the mixtures were heated as mentioned above in a water bath at 8 C for 6 min, cooled and centrifuged to collect the precipitated gels. Finally, the gels were dried in an electric furnace for h at 1 C. 3) Effect of Cerium Ammonium Nitrate (Series C) The molybdate(vi)- Mo solution was prepared by dissolving.719 g of MoO 3 in 1 ml 2 M NH 4 OH containing 1 ml of (NH 4 ) 2 MoO 4 radiotracer solution. ph of molybdate (VI)- Mo solution was then adjusted to 4.5 with 4 M HCl. TiCl 3 -Ce(IV) solution was prepared by mixing different amounts of Ce(NH 4 ) 2 (NO 3 ) 6 (.685,.137,.274 and.548 g) and ml of 15 % TiCl 3 (in 1 % HCl, 1.21 g/ml) in 3 ml H 2 O. After complete dissolution, the molybdate(vi)- Mo solution was added to the vigorously stirred TiCl 3 -Ce(IV) solution. ph-value of the mixtures was adjusted to 5-6 with 4 M NH 4 OH solution. Then H 2 O was added to complete the mixture volume to 5 ml. Thereafter the mixture was centrifuged to collect the precipitated gels. Finally, the gels were dried in an electric furnace for h at 5 C. 4) Effect of Ti:Mo Molar Ratio (Series D) The molybdate(vi)- Mo solution was prepared as described in series C. TiCl 3 -Ce(IV) solutions were prepared by mixing.548 g of Ce(NH 4 ) 2 (NO 3 ) 6 with different volumes (8.546, 5.555, 4.7, 4.273, and ml) of 15 % TiCl 3 (in 1 % HCl, 1.21 g/ml) in 3 ml H 2 O. The molybdate(vi)- Mo solution was added to the vigorously stirred TiCl 3 -Ce(IV) solutions to obtain Ti:Mo molar ratios of 2:1, 1.3:1, 1.1:1, 1:1, 1:1.1 and 1:1.3, respectively. ph adjustment, completing the mixtures to 5 ml and centrifugation and final drying were carried out as described in series C. 5) Effect of ph of gel Precipitation (Series E) Ti Mo gels were prepared as described in exp. D5, but precipitated at different final phvalues; 3, 5, 6, 7.5 and 8. 6) Effect of Drying Temperature (Series F) The Ti Mo gels prepared as described in exp. E2 were dried at different temperatures; 5, 1, 15 and C. 7) Preparation by the Hydrothermal Process (Series G) In this process, the Ti-Ce-molybdate(VI)- Mo mixtures (with Ti:Ce:Mo molar ratio of 1.3:.2:1) were placed in Teflon chambers which were subsequently put into the gas tight hydrothermal reactors (autoclaves) and heated for h, centrifuged to collect the precipitated gels. The precipitated gels were then dried in an electric furnace for h. The effect of drying temperature (series GA), ph-value of gel precipitation (series GB) and autoclaving temperature (GC) was studied (Table 1). Precipitation Yield of Mo Where, Precipitation yield of Mo, Y Mo-, during Ti Mo gel preparation was calculated from: Y Mo Mo Mo Co C f 1 Mo C o Mo C o and Mo C s are count rates of 74-keV peak of Mo in Na 2 MoO 4 or (NH 4 ) 2 MoO 4 radiotracer solution and supernatant (corrected for decay time) obtained after precipitation and centrifugation of Ti Mo gel, respectively. (A) 2

5 Mo/ m Tc Column Generator Performance Glass columns (each of.6 ID), with stopcocks at their bottoms and cotton wool pieces as support, were packed with 1. g of Ti Mo gel materials prepared in different exps. Elution of m Tc from these columns was performed by passing 1 ml of.9 % NaCl solution at a flow rate of 1. ml/min. Time periods between each successive elution processes were 23 h. Elution yield, Y Tc-m, was calculated from: Where, Tc C o and Tc C f are count rates of 14-keV peak of m Tc present on the column before and after elution, respectively, taking into consideration the contribution of Mo to this peak (14). The corresponding elution profiles of m Tc (percent activity of the eluted m Tc against eluate volume at different flow rates) were plotted for the optimum Ti Mo gel. To determine the Mo breakthrough in the m Tc eluate, the eluate was radiometrically analyzed immediately and 72 h after elution by the -ray spectrometer. The radiochemical purity of m Tc eluate (as m TcO 4- ) was determined via the ascending paper chromatography using Whatman No. 1 chromatographic paper (3 cm long and 5 cm wide) and a developing solvent of 85 % methanol. For this process, R f -value is for m TcO 4 - (15). The possible impurities of molybdenum, cerium and titanium originated from the matrix, were spectrophotometrically determined in m Tc eluate by using thiocyanate method (maximum absorption at 47 nm), persulfate method (maximum absorption at 3 nm), and hydrogen peroxide method (maximum absorption at 41 nm), respectively (16, 17). ph-value of m Tc eluates was measured using the ph-meter. TiMo Gel Characterization The TiMo gels, prepared without Mo radiotracer, were characterized with BET surface area and pore size analyzer, DLS, XRD, FESEM, XRF, IR spectroscopy and thermal analysis. Chemical Speciation Y Tc Tc Tc Co C f m 1 Tc C o Chemical speciation of Mo(VI) and Ti(III) in aqueous solutions as a function of ph was investigated by using Visual Minteq v 3.1 software. (B) Pore-Forming and Nanoparticle Stabilization RESULTS AND DISCUSSION Urea (series A) can be used as a pore forming agent and a nanoparticle stabilizer (18, 19). Urea hydrolyzes in the aqueous phase according to () : NH 2 CONH 2 + H 2 O 2NH 3 + CO 2 (1) 2

6 Ammonium salts (series C-GC), e.g., ammonium chloride, ammonium nitrate and ammonium oxalate, can also be used as a pore forming agent and a nanoparticle stabilizer (as foaming or gas blowing agent) (21-23). Ammonium salts decomposes in aqueous solutions according to (24) : Hydrolysis and Redox Chemistry NH4 H2O NH3 H3O At low ph-values, Ti(ΙΙΙ) experiences a primary hydrolysis in dilute chloride solutions according to (25) : Ti(H 2 O) OH - Ti(OH)(H 2 O) H 2 O (3) (2) At higher ph-values (ph ), a secondary hydrolysis occurs giving the brown Ti(OH) 3 precipitate according to (25) : or: Ti(OH)(H 2 O) OH - Ti(OH) 3(s) + 5H 2 O (4) The dissolved oxygen in aqueous solution can oxidize Ti(III) to Ti(IV) (26, 27) : 2H + + 2Ti 3+ +1/2O 2 2Ti 4+ + H 2 O (5) Ti 3+ + H 2 O TiOH 2+ + H + (6) TiOH 2+ + O 2 + H + TiO 2 + H 2 O (7) Where, Ti(IV) oxo species is an intermediate between TiOH 2+ and TiO 2, partially consisting of dehydrated polymeric Ti(IV) hydroxide. Ti(III) is oxidized by H 2 O 2 (series B; exps. B1-B7) according to (28) : Ti 3+ + H 2 O 2 Ti 4+ + OH - +. OH (8) Ti(IV) forms peroxospecies with H 2 O 2 as follows: - In strongly acidic solutions (29) : Ti H O Ti(O )(OH) nh 4 (4-n) n 2 (9) For example, at ph 3, n = 4, i.e., the existing species is Ti(O 2 )(OH) 2. At ph 7, n = 5, i.e., the existing species is Ti(O 2 )(OH) 3-. At ph 5, species like [Mo 2 O 3 (O 2 ) 4 (H 2 O) 2 ] 2- and [MoO(OH)(O 2 ) 2 ] - may exist in excess hydrogen peroxide (series B) (3). Ti(III) can also be oxidized with nitrate (series C-GC) (31, 32). The redox reactions for Ti(III)- nitrate can be represented as: Reduction-half reactions: - NO 3 + 3H + + 2e - HNO 2 + H 2 O E =.94 v (1) 2HNO 2 +4H + + 4e - N 2 O + 3H 2 O E = 1.29 v (11) N 2 O + H 2 O + 6H + + 4e - 2NH 3 OH + E = -.5 v (12) NH 3 OH + + 2H + + 2e - + NH 4 + H 2 O E = 1.35 v (13) 2

7 Oxidation-half reactions: Ti 3+ Ti 4+ + e - E = -.4 v (14) Ti 3+ + H 2 O TiO H + + e - E =.1 v (15) E for Reaction 14 is independent of ph while that of Reaction 15 is dependent on ph. By comparing E -values of Reactions 1-14, The Redox reaction can be stopped in moderate and strong acid solutions (Reaction 12). It is also known that Ti(III) is oxidized to Ti(IV) with Ce(IV) (series C-GC) (31-35) : Reduction-half reactions: Ce 4+ + e - Ce 3+ E = 1.72 v (16) CeOH 3+ + H + + e - Ce 3+ + H 2 O E = v (17) Oxidation-half reaction: Reactions 14 and 15. In addition, in acidic mixture of nitrate-chloride mixtures (series C-GC), Cl 2 is generated according to (36) : 3HCl + HNO 3 2H 2 O + NOCl + Cl 2 (18) Cl 2 is then forms OCl - according to (37) : Ti(III) is oxidized by Cl 2 according to (38) : Cl 2 + H 2 O HOCl + Cl - + H + (19) HOCl OCl - + H + () 2Ti H 2 O + Cl 2 2TiO Cl - + 4H + (21) Cerium(III) obtained in Reactions 16 and 17 (series C-GC) can be re-oxidized by OCl - ion obtained in Reaction according to (39) : 2Ce 3+ + OCl - + 2H + 2Ce 4+ + Cl - + H 2 O (22) As indicated in Table 1, in absence of H 2 O 2 and cerium ammonium nitrate (series A and exp. B8) or even in the presence of insufficient cerium ammonium nitrate (exp. C1), the gel color (greenish blue or light greenish blue) was an indication for the reduction of molybdate(vi) to other molybdenum species of lower oxidation states. It is thought that, the formation mechanism of titanium molybdate from aqueous mixtures containing Ti-Mo, includes the hydrolysis of titanium forming hydrous titanium oxide, TiO 2.nH 2 O and then replacement of water molecules in TiO 2.nH 2 O with molybdate anions (4). In the same way, Ce(IV) hydrolyzes in aqueous solutions forming CeO 2.nH 2 O with subsequent replacement of water with molybdate. The presence of Ce(IV) within the structure of the formed gel may help in increasing the elution yield of m Tc via oxidation of any reduced m Tc species to m TcO 4 - (41, 42). Chemical Speciation Against ph According to Figure 1(a), Mo 8 O is the predominant species (~ 85 %) at ph 3 with a considerable coexistence of H 3 Mo 8 O (~ 12 %) and HMo 7 O (~ 2 %). At ph 5, the predominant species is Mo 7 O (~ 64 %) with a significant contribution of HMo 7 O (~ 24 %) and H 3 Mo 8 O

8 (~ 12 %). At ph 6, the predominant species is MoO 4 2- (~ 68 %) along with Mo 7 O (~ 26 %) and HMo 7 O (~ 4 %). At ph > 6, the contribution of MoO 4 2- is more than %. According to Figure 1(b), at ph 3, the existing species are Ti(OH) 4 (~ 93 %) and Ti(OH) 3 + (~ 7 %), while at ph 4 the contribution of Ti(OH) 4 is more than %. 1 1 (a) (b) Contribution, % Mo 8 O H 3 Mo 8 O H 2 Mo 6 O HMo 7 O Mo 7 O 24 MoO 4 2- Contribution, % Ti(OH) 4 Ti(OH) 3 + Ti(OH) 5 - HMoO ph ph Fig.(1): Contribution of (a) molybdenum species in.1 M Mo(VI) solution and (b) Ti(IV) hydrolytic species in.13 M Ti(III) solution, after oxidation of Ti(III) to Ti(IV), as a function of ph using Visual Minteq v 3.1 software Mo precipitation Yield Table (2) compiles the precipitation yield of Mo into nano Ti Mo gels and the performance of the subsequent prepared Mo/ m Tc column generators. It was observed that the Mo precipitation yield was generally high ( %), except for exp. C1, exp. E4 and exp. E5 (where at ph7.5 and 8, the predominant Mo species are the non-polymerized MoO 4 2- according to Figure 1). Mo/ m Tc Generator Performance It was found that the m Tc elution yield was very low (< 1 %) in the absence of cerium (exps. A2, A3 and B8). When cerium ammonium nitrate was added, the elution yield was > 85 % (series A-F), except for exp. C1 where it was 14 % due to the insufficient low concentration of cerium ammonium nitrate ( M). Another exception was observed when the formed gel precipitated at ph 3 (exp. E1), where the elution yield (76 %) was obviously lower than the higher precipitation phvalues (exps. E2-E5). In the hydrothermal process (series GA-GC), increasing the autoclaving temperature adversely affected the elution yield. In the absence of cerium ammonium nitrate, Mo breakthrough was very high (exps. A2, A3 and B8). It is obvious that the presence of cerium ammonium nitrate greatly decreases Mo breakthrough, which was further decreased as the concentration of cerium ammonium nitrate increased (series C). As Ti:Mo molar ratio increased, Mo breakthrough decreased (series D). Series A showed a very low m Tc elution yield which may be due to the reduction of m TcO 4 - by Ti(III) included in the gel material. H 2 O 2 was used as oxidizing agent during the precipitation of the gel to increase the elution yield (series B; exps. B1-B7). it was found that, no precipitate was formed when excess volume of H 2 O 2 was used for the preparation of Ti Mo gel, which may be due to the formation 2

9 of soluble peroxospecies. The gel started to form and precipitate as the H 2 O 2 decomposed with continuing the heating process. The precipitation yield of Mo was found to be 5.1, 6.5, 79.3, 82.1, 83, 84 and 85 % with 15, 1, 6, 4, 2.5, 1, and.5 ml H 2 O 2, respectively. Elution of m Tc from all the gels prepared using H 2 O 2 could not be proceeded because a jelly-like material was obtained after passing the eluent in the column resulting in a column blockage and, consequently, no solution could pass through the columns. However, the best performance at all was achieved by the generator based on F1 TiMo gel ( m Tc elution yield = 88±1 %, Mo breakthrough = %, radiochemical purity as m - TcO 4 = 98.2 % along with.5, 1 and.2 ppm of Ti, Mo and Ce, respectively). According to Figure( 2), F1 TiMo generator showed sharp elution profiles at which 97 % of eluted m Tc were concentrated at the 1 st three milliliters of the 1 ml eluent solution, 1 st ml of eluate contained 68, 66 and 55 % of the m Tc for elution flow rate of.5, 1. and 2. ml/min, respectively. Whereas among the hydrothermal runs (series GA-GC), the best performance was achieved by the generator based on GC1 TiMo gel ( m Tc elution yield = 87±2 %, Mo breakthrough =.7 %, radiochemical purity as m - TcO 4 = 96 % along with.4, 1.2 and.2 ppm of Ti, Mo and Ce, respectively). 7 m Tc eluted activity, % Flow rate:.5 ml/min 1. ml/min 2. ml/min Eluate volume, ml Fig.(2): Elution profiles of m Tc with 1 ml of.9 % NaCl from.6 ID glass column based on 1. g of nano Ti Mo gel (prepared according to exp. F1) at 25 C 2

10 Table (2): Precipitation yield of Mo into nano Ti Mo gels and performance of the subsequent prepared Mo/ m Tc column generators Series A B C D E F GA GB GC Exp. Mo precipitation yield, % ph-value of the eluate Average m Tc elution yield (± ), % Average Mo breakthrough, % Radiochemical purity (as TcO4 - ), % Ti, Ce and Mo content, ppm Ti Mo Ce A Column blockage Column blockage A ±4 3 A ± B Column blockage Column blockage B Column blockage Column blockage B Column blockage Column blockage B Column blockage Column blockage B Column blockage Column blockage B Column blockage Column blockage B Column blockage Column blockage B8 6 3± C ±4 8.5 C ±2 1.9 C ±3.9 C ±1.15 D ±2 1.3 D ±1.6 D ±1.15 D4.7 86±2.93 D5.5 88±2.92 D6.9 87±3.9 E1.9 76±3.5 E2.9 88±1.5 E ±2.92 E ±2.39 E ±2.4 F1.9 88± F ±3.11 F3.9 71±4.19 F4.9 56±6.2 GA ±3.1 GA2.9 73±2.1 GB1.9 - Column blockage Column blockage GB ±3.1 GC1.9 87± GC ±3.1 GC ±2 1.1 Characterization F1 and GC1 TiMo gels are, respectively, brownish yellow and dark brownish yellow fine granules. According to Table 3, F1 and GC1 TiMo gels have total pore volumes of and cm 3 /g, pore sizes of 687 and 79 Å, average particle sizes of 58.1 and 39.5 nm (Figure 3, a and b) and average crystallite sizes of 36.1 and 3.2 nm, respectively (Figure 4). Thus, crystallinity index (I cry ) for F1 TiMo gel was 1.6, while that of GC1 gel was 1.3, where I cry can be defined as: I cry Average particle size determined from DLS(nm) Average cystallitesize determined from XRD (nm) 2 (C)

11 Table (3): Some physical properties of nanotimo gels prepared according to exps. F1 and GC1 Property Nano TiMo gel Exp. F1 Exp. GC1 Appearance Fine granules Color Brownish yellow Dark brownish yellow Total pore volume* cm 3 /g cm 3 /g pore size* 687Å 79 Å Average particle size** 58.1 nm 39.5 nm Crystallite size*** 36.1 nm 3.2 nm Crystallinity index (Icry) * Determined from BET method. ** Determined from DLS. *** Determined from XRD. 3 (a) 25 (b) 25 TiMo gel (GC1) TiMo gel (F1) Number, % 15 Number, % Size (r, nm) Size (r, nm) Fig. (3): Particle size distribution of (a) F1 and (b) GC1 TiMo gels obtained from dynamic light scattering (DLS) According to Figure 4, XRD patterns of F1 and GC1 TiMo gels (a and b, respectively) indicate crystalline structures, with somewhat higher crystallinity of GC1 gel (b). The crystalline structure (which may be not preferred in gel generators, since the rigid crystal structure hinders the diffusion of m Tc during elution) was compensated by macroporosity of F1 and GC1 gels, which resulted in high m Tc elution yields (Table 2). As shown in FESEM images (Figure 5), GC1 gel (b) had clearly smaller particles with more definite shapes (spherical to quasi-spherical particles) than in the case of F1 gel (a). XRF studies revealed that Ti:Mo:Ce molar ratio in F1 and GC1 gels were ~ 1.2:1:.12 and 1.2:1:.15, respectively, which were close to that in preparation mixture (Table 1). Figure 6 shows IR spectra of F1 and GC1 gels (a and b, respectively). The bands at 893 cm -1 (a) and 885 cm -1 (b) may be assigned to O-Mo-O and Ti-O bonds, respectively. The band at 141 cm -1 22

12 may be assigned to interaction between vibrations of O-H and Mo-O. The bands in the ranges of and may be attributed to lattice water (8). However, two weak bands appeared at 471 and 526 cm -1 in the IR spectrum of GC1 gel (Figure 6, b) which can be assigned to Ce-O-Ce vibrations (43). The latter two bands did not not clearly appear in the spectrum of F1 gel (Figure 6, a) may be because it contained a slightly less Ce molar ratio, as revealed by XRF results mentioned above. 3 (a) 35 (b) Intensity, a.u (a) TiMo gel (F1) Intensity, a.u (b) TiMo gel (GC1) , degree 2, degree Fig. (4): XRD patterns of (a) F1 and (b) GC1 TiMo (a) (b) Fig. (5): FESEM images of (a) F1 and (b) GC1 TiMo gels Figure 7 shows the TGA and DTA thermograms of F1 and GC1 gels (a and b, respectively). Due to the removal of surface adsorbed water, F1 gel lost 7.3 % of its weight at 122 C, while GC1 gel lost 7.2 % at 126 C. A second loss (3.8 %) was observed due to release of lattice water in the temperature ranges of 122- C and C. A third loss was obtained which was attributed to the elimination of structural hydroxyl groups and structural ammonia groups (25.7 % for F1 gel in the range of -347 C and 25.3 % for GC1 gel in the range of C) (8). Two distinct endothermic 22

13 DTA peaks accompanied the loss of water (at 17 and 111 C for F1 and GC1 gels, respectively). Loss of lattice water was accompanied by endothermic peaks at 198 for F1 and 197 C for GC1 and the loss of structural OH groups and structural ammonia groups (at 32 and 37 C for F1 and GC1 gels, respectively). A fourth loss was observed due to partial release of oxygen and formation of metal oxides (7.9 % for F1 gel in the range of C and 7 % for GC1 gel in the range of C) (44). A fifth loss resulted may be because of sublimation of MoO 3 (14.7 % for F1 gel in the range of and 18.1 % for GC1 gel in the range of C) (45). 1 (a) TiMo gel (F1) 1 (b) TiMo gel (GC1) 8 8 Transmittance, % 6 4 Transmittance, % Wavenumber, cm Wavenumber, cm -1 Fig. (6): IR spectra of (a) F1 and (b) GC1 TiMo gels Weight, mg TGA (a) TiMo gel (F1) DTA - DTA signal, microvolts Weight, mg TGA (b) DTA - DTA signal, microvolts Temperature, C Temperature, C Fig. (7): TGA and DTA thermograms of (a) F1 and (b) GC1 TiMo gels

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