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Azhar Alowasheeir, Miharu Eguchi, [Yoshitaka Fujita](https://orcid.org/0000-0001-9585-4145), Kunihiko Tsuchiya, Ryutaro Wakabayashi, Tatsuo Kimura, [Katsuhiko Ariga](https://orcid.org/0000-0002-2445-2955), Kentaro Hatano, Nobuyoshi Fukumitsu, Yusuke Yamauchi

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This is a pre-copyedited, author-produced version of an article accepted for publication in [Bulletin of the Chemical Society of Japan] following peer review. The version of record [Azhar Alowasheeir, Miharu Eguchi, Yoshitaka Fujita, Kunihiko Tsuchiya, Ryutaro Wakabayashi, Tatsuo Kimura, Katsuhiko Ariga, Kentaro Hatano, Nobuyoshi Fukumitsu, Yusuke Yamauchi, Extraordinary 99Mo adsorption: utilizing spray-dried mesoporous alumina for clinical-grade generator development, Bulletin of the Chemical Society of Japan, Volume 97, Issue 10, October 2024, uoae099] is available online at: https://doi.org/10.1093/bulcsj/uoae099[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Extraordinary 99Mo adsorption: utilizing spray-dried mesoporous alumina for clinical-grade generator development](https://mdr.nims.go.jp/datasets/a6052124-4d09-4fd7-a70e-638bd4eebfe7)

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1  Azhar Alowasheeir,1 Miharu Eguchi,2,3 Yoshitaka Fujita,*4 Kunihiko Tsuchiya,4 Ryutaro Wakabayashi,5 Tatsuo Kimura,5 Katsuhiko Ariga,6,7 Kentaro Hatano,8 Nobuyoshi Fukumitsu,9 and Yusuke Yamauchi1,3,6  1Department of Materials Process Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8601, Japan 2School of Advanced Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan 3Australian Institute for Bioengineering and Nanotechnology (AIBN), The University of Queensland, Brisbane, Queensland 4072, Japan 4Department of JMTR, Japan Atomic Energy Agency, 4002 Narita, Oarai, Ibaraki 311-1393, Japan 5National Institute of Advanced Industrial Science and Technology (AIST), Sakurazaka, Moriyama-ku, Nagoya 463-8560, Japan 6Research Center for Materials Nanoarchitectonics (MANA), National Institute for Material Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan 7Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-0827, Japan 8Department of Applied Molecular Imaging, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan 9Department of Radiation Oncology, Kobe Proton Center, 1-6-8 Minatojima-Minamimachi, Chuo-ku, Kobe, Hyogo 605-0047, Japan *Corresponding author: Department of JMTR, Japan Atomic Energy Agency, 4002 Narita, Oarai, Ibaraki, 311-1393. Email: fujita.yoshitaka@jaea.go.jp   1   2 Extraordinary 99Mo Adsorption: Utilizing Spray-Dried Mesoporous Alumina for Clinical-Grade Generator Development Abstract Mesoporous alumina spherical particles, synthesized via spray-drying with the self-assembly of EOnPOmEOn, have been utilized for the development of clinical-grade molybdenum-99/technetium-99m (99Mo/99mTc) generators. When evaluated as molybdenum (Mo) adsorbents, the mesoporous alumina spherical particles are useful for effective adsorption of molybdenum ions rather than commercially available particulate alumina. The effects of surfactant removal methods on the Mo adsorption property are also systematically investigated using the batch method. Batch adsorption studies reveal practical adsorption capacities ranging from 45.9 to 91.2 mg Mo/g in a Mo solution (1000 mg-Mo/L) at pH 3. The experimental results indicate the following trend in Mo adsorption capacity: solvent extraction > calcination (400 °C and 800 °C) > commercially available alumina (Medical Al2O3 used as is). To explore the feasibility of developing a clinical-scale generator, a novel tandem column generator concept is employed. Using the spray-dried and extracted mesoporous alumina, 99mTc eluted from the generator exhibits high radionuclidic, radiochemical, and chemical purity, making it suitable for the preparation of 99mTc-labeled radiopharmaceuticals.  Keywords: Alumina, 99Mo/99mTc generators, Mo adsorbent Graphical abstract  Yoshitaka Fujita Yoshitaka Fujita was assigned to department of JMTR, Japan Atomic Energy Agency (JAEA) in 2015. His research focuses on development of Mo adsorbents used for medical 99Mo/99mTc generators. He received his Ph.D. from Nagaoka University of Technology in 2022. Currently, He is involved in Ac-225 production development at the experimental fast reactor Joyo.  PreparationMesoporous alumina spherical particlesMo adsorptionPumpQuartz woolGlass tubeGlass tubeSEM image & Elemental mappingMesoporous alumina spherical particles, synthesized via spray-drying with the self-assembly of EOnPOmEOn, have been utilized for the development of clinical-grade 99Mo/99mTc generators. 99mTc eluted from the generator exhibits high radionuclidic, radiochemical, and chemical purity, making it suitable for the preparation of 99mTc-labeled radiopharmaceuticals. mailto:fujita.yoshitaka@jaea.go.jp2   1. Introduction 1 The use of radiopharmaceuticals in nuclear medicine is an 2 indispensable tool in modern medical diagnostics.1-3 3 According to the latest survey published in 2023,4 in our 4 country, technetium-99m (99mTc) is used in an average of 5 682,430 examinations annually. This is the highest figure 6 among all radioactive isotopes. Fluorine-18 (18F) used in 7 positron emission tomography (PET) (with 612, 909 8 examinations annually) closely follows 99mTc, but the number 9 of PET facilities is still limited. Therefore, 99mTc is 10 overwhelmingly the most frequently used single-photon 11 emitting isotope available in many medical facilities. 99mTc is 12 used for the diagnosis of conditions such as dementia, 13 cerebral infarction, pulmonary embolism, myocardial 14 infarction, bone metastasis, lymph node metastasis, and renal 15 dysfunction, accounting for over 60% of all examinations 16 using single-photon emission isotopes. 17 99mTc is characterized as a radiopharmaceutical suitable for 18 nuclear medicine examinations due to its emission of a γ-ray 19 with an energy of 140 keV and a short half-life of 6 hours.5,6 20 99mTc is generated from its parent nuclide, 99Mo (half-life: 66 21 hours). The production of 99Mo is mainly obtained by 22 irradiating 235U with thermal or fast neutrons. All 99Mo is 23 imported from other countries, Therefore, supply shortages 24 occur every few years due to various situations overseas, 25 significantly impacting medical systems. 99Mo can also be 26 obtained by irradiating natural Mo, but because of the large 27 amount of other Mo isotopes present, this method requires the 28 adsorption of more Mo to obtain a sufficient amount of 29 99mTc.7 Current commercial 99Mo/99mTc generators typically 30 have an adsorption capacity of 2 to 20 mg Mo g-1 alumina8, 31 but our calculations suggest that an adsorption capacity of 32 around 200 mg Mo g-1 is needed to obtain 99mTc from the 33 irradiation of natural Mo. Therefore, the development of 34 alumina absorbents with improved 99Mo adsorption capacity 35 is extremely important. Extensive research has been 36 conducted in recent years to address this need, including the 37 exploration of advanced materials.9-12 Cecilia C. Guedes-38 Silva et al. achieved the adsorption of Mo at 92.45 mg Mo 39 per g alumina by calcinating alumina at 900 °C for 5 hours, 40 resulting in the presence of θ and γ-Al2O3 with a high specific 41 surface area (153.7 m2 g-1).13 42 Our objective is to advance the field of nuclear medicine 43 by exploring various alumina-based sorbents. In the previous 44 reports, mesoporous/nanoporous alumina materials with 45 various structural and compositional decorations have been 46 synthesized to achieve high Mo adsorption performance.14-16 47 Building on previous knowledge, which demonstrated that 48 Mo ions interact with surface hydroxyl (Al-OH) groups,17 our 49 goal in this study is to retain a large number of Al-OH groups 50 for maximizing the amount of adsorbed Mo ions. As a model 51 study, we investigate the effect of adsorbed Mo amount using 52 mesoporous alumina prepared through different surfactant 53 removal methods (i.e., solvent extraction method, and 54 calcination methods at different temperatures). The extracted 55 mesoporous alumina with a sufficient amount of Al-OH 56 groups exhibits 82.6 mg g-1 of Mo adsorption. To investigate 57 the feasibility of developing a clinical-scale generator, we 58 employ a novel tandem column generator concept. By 59 utilizing the spray-dried and extracted mesoporous alumina, 60 we achieve a high radionuclidic, radiochemical, and chemical 61 purity in the eluted 99mTc from the generator. This makes it 62 suitable for the preparation of 99mTc-labeled 63 radiopharmaceuticals. 64  65 2. Experimental 66 Materials 67 Aluminum tri-sec-butoxide (Al(OsBu)3) was obtained from 68 Kanto Chemical Co., Inc. Concentrated aqueous hydrochloric 69 acid (conc. HCl, 35-37 wt%), ethanol (EtOH) and 70 triethylamine (Et3N), 6 M NaOH solution, 2 M HCl solution 71 and camphor was obtained from Fujifilm Wako Pure 72 Chemical Corporation. Pluronic P123 (EO20PO70EO20) was 73 purchased from Sigma-Aldrich. MoO3 powder was 74 purchased from Taiyo Koko Co., Ltd., 99.99 %. 5 M sodium 75 chloride solution was purchased from Nacalai Tesque Inc. 76 Commercially available medical alumina powders (hereafter 77 abbreviated as Medical Al2O3) (MP Alumina R for isotope, 78 acid pH, 63-200 μm) were also purchased as comparison 79 samples. 80  81 Spray-dried mesoporous alumina: 82 Spherical particles of high-surface-area mesoporous alumina 83 can be prepared by spray-drying precursor solutions 84 containing aluminum alkoxides with a rational approach to 85 improve the connectivity of EOnPOmEOn templated 86 mesopores.18,19 Referring to our previous paper utilizing 87 Al(OsBu) a clear ethanolic precursor solution was prepared 88 as follows and spray-dried at an inlet temperature of 170 ºC.19 89 Al(OsBu)3 (10 mmol, 24.6 g) was dispersed in EtOH,  (60 90 mL) followed by a dropwise addition of conc. HCl solution. 91 After stirring for 3 hr at room temperature, the resultant 92 solution containing pre-hydrolyzed aluminum species was 93 combined with another ethanolic solution of Pluronic P123 94 (EO20PO70EO20, 15 g in 120 mL of EtOH). The resultant 95 powder sample was calcined at 400 ºC and 850 ºC (named as 96 Al2O3_400” and “Al2O3_850”, respectively). Our 97 neutralization-mediated extraction process was also applied 98 for removing Pluronic P123, which was assisted by organic 99 bases such as Et3N as a scavenger of residual HCl and 100 stabilizer of alumina framework.20 The advantage of solvent 101 extraction is the retention of abundant Al-OH groups, 102 preventing thermal condensation between Al-OH groups. 103 The resultant powder sample (0.5 g) was added to an 104 ethanolic solution containing 0.1 M Et3N (10 mL), mixed for 105 1 h at room temperature, and recovered by vacuum filtration 106 (named as “Extracted Al2O3”).  107 Characterization: 108 The phase purity of the samples was confirmed by powder X-109 ray diffraction (PXRD) using a Rigaku RINT Ultima III 110 diffractometer (Cu Kα radiation, 40 kV and 40 mA) at a 111 scanning rate of 10 ° min-1. The XRD data were collected in 112 the 2θ range of 10–90° under ambient conditions. A small-113 angle X-ray scattering (SAXS) Rigaku MicroMax-007H was 114 employed to obtain the mesostructural periodicity of the 115 samples. The morphological characterization of the samples 116 was conducted using a Hitachi SU8000 scanning electron 117 microscope (SEM) operating at an accelerating voltage of 5 118 3   kV. N₂ adsorption-desorption isotherms of the samples were 1 measured on a Quantachrome Autosorb gas sorption system 2 (Anton Paar) at 77 K. Before the measurement, the samples 3 were treated at 100°C for 24 hours. Fourier Transform 4 Infrared Spectroscopy (FT-IR) was carried out on a JASCO 5 FTIR-4100 using the potassium bromide (KBr) pellet method, 6 where the alumina sample (0.5 mg) was mixed with KBr (100 7 mg) for qualitative evaluation. The sample was stored in dry 8 atmospheres without heating before measurement. 9 Preparation of 99Mo solution.  10 The typical preparation of the sodium molybdenum solution 11 involved dissolving 75 mg of MoO3 powder in 1.74 mL of 6 12 M NaOH solution. The solution’s pH was then carefully 13 adjusted to 3 by slowly adding 2 M HCl solution. After pH 14 adjustment, deionized water was added gradually until the 15 molybdenum concentration reached the desired endpoint of 16 1000 mg Mo L-1, thus creating the solution for further 17 analytical procedures. 18 Evaluation of molybdenum adsorption capacity.  19 0.07 g of each Al2O3 sample was mixed with 7 mL of the 20 above-prepared Mo solution. The mixture was then gently 21 agitated for 2 hours at room temperature. Afterward, the 22 mixture was filtered through a 0.2 μm filter. The remaining 23 Al2O3 was washed with deionized water. Meanwhile, the 24 filtrate containing the Mo solution was combined with the 25 rinse fluid from the Al2O3 and used for Mo concentration 26 analysis. The Mo adsorption capacity was calculated by 27 subtracting the measured Mo concentration from the initially 28 added concentration. 29 Mo adsorption/99mTc elution.  30 The MoO3 pellets were fabricated by blending MoO3 powder 31 with 2 wt% camphor and ethanol, then the mixture was 32 shaped into pellets using a uniaxial press. These moldings 33 underwent sintering at 650 °C. Once adequately dried, the 34 MoO3 pellets were roughly crushed, with approximately 1.5 35 g utilized for neutron irradiation. Neutron irradiation of the 36 MoO3 pieces occurred at 5 MW for 20 min, utilizing the 37 irradiation orifice of pneumatic tube Pn-2 from the Kyoto 38 University Research Reactor (KUR). After irradiation, the 39 MoO3 pieces were allowed to decay for 4 days before being 40 utilized in experiments. Subsequently, the irradiated MoO3 41 pieces were dissolved in a 6 M NaOH aqueous solution. The 42 pH of the solution was adjusted to 3 by titrating with 2 M HCl 43 solution, and the Mo concentration was adjusted to 20 g Mo 44 L-1 by diluting with deionized water. This resulting solution, 45 termed the Mo solution, was then employed for Mo 46 adsorption and 99mTc elution property evaluations. In the 47 experiment, a glass tube with an inner diameter of 4.2 mm 48 was filled with 0.07 g of alumina specimen for further testing. 49 The setup involved fixing the alumina specimen within the 50 tube using upper and lower quartz wool. The alumina bed 51 heights were approximately 8 mm. This alumina column was 52 then connected to a peristaltic pump, through which 1 ml of 53 Mo solution was passed. The flow rates were 4.29 mL min–1 54 and 2.31 mL min–1 for Extracted Al2O3 and Medical Al2O3, 55 respectively. Subsequently, 10 mL of saline solution was 56 passed through the column to remove any remaining 99mTc 57 and 99Tc. The saline solution was prepared as a 0.90 % w/v 58 solution of NaCl using 5 M sodium chloride solution. The 59 activities of 99Mo in both the Mo solution and the saline 60 solution after passing through the column were measured. 61 Following a 24 h interval, the column underwent a milking 62 procedure. In this step, 1 mL of saline was passed through the 63 column five times, totaling 5 mL, to assess the elution 64 properties of 99mTc. The flow rates were 1.08 mL min–1 and 65 2.90 mL min–1 for Extracted Al2O3 and Medical Al2O3, 66 respectively. 67 The activities of both 99Mo and 99mTc in the resulting 99mTc 68 solution were determined. These activities were measured 69 using a γ-ray spectrometer manufactured by Mirion 70 Technologies (Canberra) KK. To calculate the Mo adsorption 71 capacity of the alumina specimen, the Mo content in the 72 solution after adsorption was subtracted from the Mo content 73 in the solution before adsorption. The Mo adsorption capacity, 74 expressed in milligrams of Mo per gram of alumina (mg Mo 75 g-1), was calculated based on the specific activity of 99Mo at 76 the beginning of the adsorption process. 77  78 3. Results and discussion 79 The SEM images (Fig. S1a) confirm the formation of 80 spherical particles of as-synthesized Al2O3, which is typical 81 for samples recovered by the spray-drying process of a 82 precursor solution. The extracted sample and those calcined 83 at two different temperatures (400 °C and 850 °C) retain the 84 original spherical morphology (Fig. 1a-c). Notably, the 85 morphology is maintained even after undergoing the high-86 temperature calcination (850 ºC). For reference, the SEM 87 image and wide-angle XRD pattern of Medical Al2O3 show 88 irregular shapes consisting of aggregated particles. (Fig. S1b 89 and S2). 90  91  92 Fig. 1.  (a-c) SEM images of (a) Extracted Al2O3 (b) Calcined 93 Al2O3_400 and (c) Calcined Al2O3_850 before Mo adsorption. 94 (d-f) SEM images of (d) Extracted Al2O3 (e) Calcined 95 Al2O3_400 and (f) Calcined Al2O3_850 after Mo adsorption. 96  97 To validate the periodicity of the EOnPOmEOn templated 98 mesopores and investigate the crystal structure, both low-99 angle and wide-angle XRD measurements were carried out. 100 The low-angle XRD patterns of the samples (Fig. 2a) exhibit 101 an obvious single peak, indicating the periodic arrangement 102 of the mesopores. The d-spacings of Extracted Al2O3, 103 Calcined Al2O3_400, and Calcined Al2O3_850 were 104 measured to be 7.4 nm, 6.1 nm, and 5.3 nm, respectively. 105 After calcination, the framework is solidified by 106 condensation of Al-OH groups, resulting in a reduction of the 107 mesostructural periodicity. Further increasing the calcination 108 4   temperature up to 850 °C reduces the d-spacing to support the 1 condensation between the Al-OH groups to proceed with 2 alumina framework shrinkage. 3   4  5 Fig. 2.  (a) Low-angle XRD patterns and (b) wide-angle XRD 6 patterns of (i) Extracted Al2O3, (ii) Calcined Al2O3_400, and 7 (iii) Calcined Al2O3_850. 8  9 Meanwhile, the wide-angle XRD patterns (Fig. 2b) 10 suggest a transition to the γ- phase of Al2O3 as the calcination 11 temperature increases. In the wide-angle XRD patterns, both 12 the extracted and calcined (at 400 °C) samples display broad 13 peaks, indicating the presence of amorphous Al2O3.21 14 Following calcination at 850 °C, small diffraction peaks 15 emerge at 2θ = 45.74 and 66.96º, corresponding to the (400) 16 and (440) planes of γ-Al2O3, respectively.22 Although the 17 crystallinity is modest, a polycrystalline alumina framework 18 is formed. The average crystallite size, calculated from the 19 full width at half-maximum of the (400) peak at 2θ = 45.74º, 20 is approximately 0.87 nm. Thus, the heat treatment at 850 °C 21 initiates the transformation from amorphous to γ-Al2O3.  22 The N2 adsorption-desorption isotherms of the samples 23 are shown in Fig. 3. The specific surface areas and pore 24 volumes are summarized in Table 1. Extracted Al2O3 shows 25 a lower surface area of 180.4 m² g-1 due to a small amount of 26 remaining carbon content after the extraction process (The 27 remaining carbon content is around 3.7 wt.% by CHN 28 analysis.20). Therefore, the pore size distribution curve does 29 not show a clear peak. Although the carbon content is 30 significantly reduced by the extraction process compared to 31 the as-prepared sample, we expect that some fragments of 32 EOnPOmEOn remain in the extracted mesoporous alumina. 33 Since the Japanese Minimum Requirements for 34 Radiopharmaceuticals (MRRP) specify only Al, the influence 35 of the remaining P123 was not evaluated in this study. 36 However, due to medical applications, confirming its effect 37 remains a future challenge. 38 It is noteworthy that the specific surface area increases 39 following heat treatment. However, Calcine d Al2O3_850 40 exhibits a lower surface area (341 m2 g-1) compared to 41 Calcined Al2O3_400 (449 m2 g-1). The reduction of specific 42 surface area by calcination at 850 °C is attributable to the 43 collapse of the mesoporous structure with thermal 44 condensation of Al-OH groups and following alumina grain 45 growth. This is supported by a significant reduction of the 46 primary peaks (Fig. 2a). 47  48  49 Fig. 3.  (a) N2 adsorption-desorption isotherms, and (b) BJH 50 pore size distribution curves of Extracted Al2O3, Calcined 51 Al2O3_400, and Calcined Al2O3_850. 52  53 The pH of the solution influences on adsorption of 99Mo, 54 as it affects the difference molybdenum species present23 and 55 the surface charge of the adsorbents.24 Where Mo7O243- is 56 dominant at < pH 2, while both Mo7O246- and Mo8O284- exist 57 at pH 2-5, and MoO42- predominates at > pH 6.25 Previous 58 reports demonstrated a study on the distribution ratios (Kd) to 59 assess the potential use of the synthesized sorbent for the 60 radiochemical separation of 99mTc from 99Mo at various 61 pHs.26 It was observed that at pH 3, the Kd value of molybdate 62 ions was the highest. This phenomenon was attributed to the 63 presence of hydroxyl groups on the surface of Al2O3, which 64 became protonated, resulting in a positively charged surface 65 that attracts Mo7O246− ions.14 Based on these findings, Mo 66 solutions with a pH of 3 were prepared in the experimental 67 section of this study. The adsorption capacities of different 68 Al2O3 samples were determined using batch equilibration 69 methods (static) in 4 different batches. When the alumina 70 samples were mixed with Mo solution, the solution became 71 cloudy except for Medical Al2O3. Therefore, it is estimated 72 that the alumina samples prepared in this study have finer 73 grain size than Medical Al2O3. The Mo adsorption capacities 74 obtained from all samples are shown in Table 1. The 75 extracted Al2O3 exhibits the highest adsorption capacity of 76 91.2 mg Mo/g, surpassing other Al2O3 samples. The 77 experimental results indicate the following trend in Mo 78 adsorption capacity: solvent extraction method > calcination 79 method (at 400 °C and 800 °C) > Medical Al2O3. SEM 80 images in Fig. 1d-f show that the morphology of all the Al2O3 81 samples remains unaltered even after Mo adsorption, 82 although the surface of the particles becomes slightly bumpy 83 with some flakes appearing. Energy-dispersive X-ray 84 spectroscopy (EDX) confirms a uniform distribution of 85 aluminum (Al) and adsorbed molybdenum (Mo) throughout 86 Table 1.   Summary of surface areas, pore volumes, and Mo adsorption capacity of alumina samples (Extracted as-prepared sample, two calcinated samples at different temperatures (400 and 850 °C), and commercially available Medical Al2O3 sample.). Sample names Surface area (m2 g-1) Pore Volume (cm g-1) Mo adsorption capacity (mg Mo g-1) Extracted Al2O3 180.4 0.21 91.2 Calcined Al2O3_400 499.4 0.85 45.9 Calcined Al2O3_850 340.8 0.47 48.8 Medical Al2O3 115.0 0.23 35.5  5   the entire area, as revealed by corresponding elemental 1 mapping images in Fig. 4. 2  3  4 Fig. 4.  SEM images and EDX mapping of (a) Extracted 5 Al2O3 (b) Calcined Al2O3_400 and (c) Calcined Al2O3_850 6 after Mo adsorption. 7  8 As discussed above, the presence of hydroxyl groups 9 plays a significant role in the adsorption of 99Mo, as 10 demonstrated in previous reports.17 To investigate this point, 11 the existence of hydroxyl groups on the Extracted Al2O3 and 12 Medical Al2O3 before the adsorption process was confirmed 13 using FTIR. In order to compare the amount of OH groups, 14 the alumina samples were thoroughly dried in a dry 15 atmosphere without heating. In Fig. 5, a broad peak is 16 observed at 3600-3200 cm-1 and around 1635-1622 cm-1, 17 corresponding to OH stretching groups.27 The intensity of 18 these peaks indicates the quantity of OH groups present, with 19 the intensity of OH groups being higher in the Extracted 20 Al2O3 than in Medical Al2O3. A large number of OH groups 21 enhance Mo adsorption due to the strong interaction between 22 protonated OH groups on the surface of Al2O3 and negatively 23 charged Mo species at pH=3.17 In our previous study,20 from 24 thermogravimetry differential thermal (TG-DTA) analysis, it 25 was revealed that many –OH groups were present in the 26 extracted sample, significantly more than in the mesoporous 27 (still amorphous) alumina obtained by direct calcination at 28 400°C. This result is related to the room-temperature 29 extraction process being very mild, thus avoiding the 30 condensation of surface –OH groups. 31  32  33 Fig. 5. FTIR of Extracted Al2O3 and Medical Al2O3. The same 34 amount of samples was measured by FTIR to compare the 35 relative abundance of hydroxyl groups (-OH) on the surfaces 36 of Extracted Al2O3 and Medical Al2O3. 37  38 Extracted Al2O3 was chosen for Mo adsorption and 39 elution of 99mTc due to its demonstrated high Mo adsorption 40 capacity. For comparison, commercial Medical Al2O3 was 41 also utilized in this study. The radioactivity of 99Mo was 42 calculated using the Covell method from the energy of 0.739 43 MeV, as specified in MRRP (Scheme 1). The specific 44 radioactivity of 99Mo upon adsorption is determined to be 45 22.9 MBq/g Mo. The 99Mo adsorption capacity of Extracted 46 Al2O3 is calculated to be 1.90 MBq 99Mo g–1 Al2O3. 47 Converting the Mo adsorption capacity using the specific 48  Table 2.  Summary of analyzing milking metrics with Extracted Al2O3 and Medical Al2O3.  *Based on the literature (Nuclear Instruments and Methods, 82 (1970) 273-277), detection limits were calculated and 99Mo was non-detectable. 6   activity of 99Mo upon adsorption yielded 82.6 mg Mo g–1 1 Al2O3. This value is noteworthy when compared to the 2 current limit of use in 99Mo/99mTc generators which is 3 typically from 2 to 20 mg Mo g–1 Al2O3.8 On the other hand, 4 the 99Mo adsorption capacity by Medical Al2O3 is 22.6 MBq 5 g–1 Mo. When the Mo adsorption capacity is recalculated 6 using the specific activity of 99Mo upon adsorption, it results 7 in 41.3 mg Mo g–1 Al2O3. The Extracted Al2O3 thus exhibits 8 approximately twice the Mo adsorption capacity of Medical 9 Al2O3. The radioactivity of 99Tc is determined to be 0.141 10 MeV by using the Covell method, as specified in MRRP for 11 the radioactivity of 99mTc from the energy peak. Fig. 6a and 12 Table 2 show the total 99mTc elution ratio by Extracted Al2O3 13 and Medical Al2O3. The vertical axis represents the ratio of 14 the activity of 99mTc present on the alumina column at the start 15 of milking to the activity of eluted 99mTc. The ratios for 16 Extracted Al2O3 and Medical Al2O3 are saturated (57.8% and 17 61.7%, respectively) with 5 mL of milking. Since the elution 18 ratios for both are about 60%, these results are probably due 19 to the effects of column size. In this experiment, the column 20 is too small to control the flow rate. The ratios can be 21 improved by increasing the column size and setting the 22 appropriate flow rate. Both eluted 99mTc solutions are clear 23 and colorless. Because 99mTc solution is injected into the body 24 as a radiopharmaceutical, MRRP defined the standard pH 25 value of 99mTc solutions to be pH 4.5 to 7.0. The pH of the 26 99mTc solution obtained from Extracted Al2O3 is pH 4.4, 27 which is a lower limit of the pH standard value, but an 28 improvement can be expected by increasing the liquid 29 volume. The pH of the 99mTc solution obtained from Medical 30 Al2O3 (4.5) is within the standard range of values. In MRRP, 31 the amount of 99Mo desorbed in a 99mTc solution is defined 32 using the 99Mo/99mTc ratio as an index and the standard value 33 for 99Mo/99mTc is less than 0.015 %. 34  35 Scheme 1.  Procedure of milking test. 36  37 Fig. 6b and Table 2 show the 99Mo/99mTc ratio in the 38 99mTc solution after the milking test. The 99Mo concentration 39 obtained from Extracted Al2O3 is below the detection limit 40 (i.e., 0 % in Table 2) and meets the standard value for the 41 99Mo/99mTc ratio. On the other hand, the 99Mo/99mTc ratio 42 obtained from Medical Al2O3 is 13.3-16.5 %, which exceeds 43 the standard value specified in MRRP. These results suggest 44 that the amount of -OH group significantly influences both 45 Mo adsorption and 99mTc elution. The pH of the final solution 46 after the milking test is almost within the standard pH range 47 defined by MRRP. 48  49  50 Fig. 6.  (a) The 99mTc elution properties and (b) 99Mo/99mTc 51 ratio in the 99mTc solution, obtained by extracted and Medical 52 Al2O3. 53  54 4. Conclusion 55 The high specific surface area as well as the presence of 56 abundant surface -OH group on Extracted Al2O3 are helpful 57 for exceptional Mo adsorption and 99mTc elution at low pH 58 value, highlighting its potential for developing more efficient 59 and scalable 99Mo/99mTc generators compared to commercial 60 Medical Al2O3. Further optimization and scale-up of the 61 synthesis process can enhance its applicability in nuclear 62 medicine diagnostics, addressing the growing clinical 63 demand for 99mTc. 64  65 Acknowledgement 66 The authors acknowledge Mr. Y. Fujihara, Mr. H. Yoshinaga, 67 and Prof. J. Hori for supporting the irradiation experiments at 68 the KUR. 69  70 Supplementary data 71 Supplementary material is available at Bulletin of the 72 Chemical Society of Japan. 73  74 Funding 75 This work was supported by JSPS KAKENHI Grant Number 76 JP22H03974. 77  78 Conflict of interest statement. None declared. 79  80 References 81 1 A. Boschi, L. Uccelli, L. Marvelli, C. Cittanti, M. Giganti, P. 82 Martini, Molecules 2022, 27, 1188. 83 2 M. Riondato, D. Rigamonti, P. Martini, C. Cittanti, A. Boschi, L. 84 Urso, L. Uccelli, J. Med. Chem. 2023, 66, 4532. 85 3 I. G. T. Baeten, J. P. Hoogendam, B. Jeremiasse, A. J. A. T. Braat, 86 W. B. Veldhuis, G. N. Jonges, I. M. Jürgenliemk‐Schulz, C. H. 87 van Gils, R. P. Zweemer, C. G. Gerestein, Cancer Rep. 2022, 5, 88 e1401. 89 4 Y. Nishiyama, A. Okizaki, Y. Inui, H. Otsuka, K. Takanami, M. 90 Nakajo, K. Nakatani, M. Nogami, K. Hirata, Y. Maeda, M. 91 Yoshimura, H. Wakabayashi, Radioisotopes 2023, 72, 49. 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