Preparation and Evaluation of Epoxy-based Polymeric Sorbents with Potential Applications in Nuclear Wastewater Decontamination and Management

Philippine e-Journal for Applied Research and Development 15(2025), 62-70 ISSN 2449-3694 (Online) URL: https://pejard.slu.edu.ph/vol.15/2025.11.28.pdf DOI: https://doi.org/10.5281/zenodo.17744709 Preparation and Evaluation of Epoxy-based Polymeric Sorbents with Potential Applications in Nuclear Wastewater Decontamination and Management Erwin C. Escobar1,2,*, Grace M. Nisola2,3, Wook-Jin Chung2,3, Maria Morissa D. Lu1, Resmond L. Reaño4, Joel M. Sareno5, and Adeliza A. Dorado6 1Smart Materials for Energy, Environment, and Technology (Smart MEET) Laboratory, Department of Engineering Science, College of Engineering and Agro-industrial Technology, University of the Philippines Los Baños, College Laguna (4031) 2Environmental Waste Recycle Institute (EWRI), Department of Energy Science and Technology (DEST), Myongji University, Myongji-ro 116, Cheoin-gu, Yongin-si, Gyeonggi-do (17058), South Korea 3Sustainable Energy Materials (SEM, Co. Ltd.), 109, Beomjigi-ro, Danwon-gu, Ansan-si, Gyeonggi-do (15429), South Korea 4Biomedical Technology and Devices Laboratory, Department of Engineering Science, College of Engineering and Agro-industrial Technology, University of the Philippines Los Baños, College Laguna (4031), Philippines 5Laguna Science Integrated High School, Bay Laguna (4033) 6Institute of Food Science, College of Agriculture and Food Science, University of the Philippines Los Baños, College Laguna (4031) *[email protected] Received, 19 August 2025; Accepted, 20 November 2025; Published, 28 November 2025 Copyright @ 2025 E.C. Escobar, G.M. Nisola, W.J. Chung, M.M.D. Lu, R.L. Reaño, J.M. Sareno, and A.A. Dorado. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract With the Philippines set to include nuclear power in its energy mix, effective nuclear waste decontamination strategies must be developed. Spent nuclear fuel water waste contains very high concentrations of HNO3 and a variety of metal ions which makes sorbent development for radionuclide sequestration extremely difficult. In this study, we report two polymeric resin sorbents prepared by curing bis-epoxides with diaminopropane in dimethyl sulfoxide. The sorbents Ep-NGDE and Ep-BOMB are able to resist physical deterioration in 3 M HNO3 while exhibiting unique sorption characteristics that may prove useful in nuclear water waste decontamination. Ep-NGDE exhibits high capacity and selectivity for Na+ while Ep-BOMB exhibits high capacity for radionuclides Cs+ and Sr2+. The reasons underlying their sorption behaviors are navigated and a procedure for their deployment is proposed. Keywords: Spent nuclear fuel, highly acidic and oxidizing wastewater, radionuclide decontamination, epoxy polymer Philippine e-Journal for Applied Research and Development Website: pejard.slu.edu.ph ISSN 2449-3694 (Online) Introduction Just recently, the Philippine government took another step forward in its long-standing plan to introduce nuclear power in the country’s energy mix with the crafting of a policy framework by its Department of Energy that defines the policies and procedures in financing and setting up nuclear energy infrastructures (Salting, 2025). Based on its Nuclear Energy Roadmap 2024, the Philippines is set to introduce 1200 MW of nuclear power in its energy mix by 2032 and gradually increase production to 4800 MW by 2050 (Department of Energy, 2024). A major concern in nuclear energy production is the management of nuclear water wastes which Preparation and Evaluation of Epoxy-based Polymeric Sorbents with Potential Applications in Nuclear Wastewater Decontamination and Management 63 Philippine e-Journal for Applied Research and Development Website: pejard.slu.edu.ph ISSN 2449-3694 (Online) Philippine e-Journal for Applied Research and Development 15(2025), 62-70 contain high amounts of radioactivity that can be treated only by waiting for the radioactivity to decay naturally over hundreds of years (Escobar et al., 2021b). For this reason, radioactive wastes must be kept in sealed containers for long-term storage on-site or in remote facilities. Prior to storage, it is recommended that radioactive components are collected in concentrated form (Xu et al., 2012). A convenient method to pre-concentrate radioactivity in nuclear water waste is via adsorption (Escobar et al., 2021a; Escobar et al., 2022a; Escobar et al., 2022b; Sio et al., 2024). However, because nuclear water waste contains high concentrations of oxidizing acid (~ 3 M HNO3), the development of effective adsorbents that do not easily deteriorate in highly acidic and oxidizing media is a major challenge. Very few adsorbents have been found effective at decontaminating nuclear water waste of its longlived and most abundant radioactive components (Cs-137 and Sr-90 with half-lives of approximately 30.17 and 28.8 years, respectively) due to its highly acidic and highly oxidizing nature, and these sorbents usually employ calixarenes which are expensive and yet deliver very low adsorption capacities (Zhang & Chai, 2012; Zhang et al., 2018; Escobar et al., 2021b; Escobar et al., 2022a). Previously, we reported polymeric adsorbents prepared from different bis-epoxide monomers for the sequestration of different metal ions in highly acidic media (Torrejos et al., 2021; Escobar et al., 2021b). In this paper, we report two new epoxybased sorbents with interesting and potentially useful sorption characteristics under the highly acidic and highly oxidizing aqueous conditions of nuclear water waste. Bis-epoxide monomers with an abundance of electronegative oxygen atoms, namely, neopentyl glycol diglycidyl ether (NGDE) and 1,3-bis(oxiran-2-ylmethoxy) benzene (BOMB), that can interact with cations were crosslinked with diaminopropane to form tough, solid, resin sorbents. New strategies at improving the selectivity and capacity of epoxy-based adsorbents for specific metal ions in highly acidic and highly oxidizing nuclear water waste are elucidated, and a procedure for their implementation in the preconcentration of radionuclides Cs+ and Sr2+ is proposed. Experimental Materials Technical grade bis-epoxides neopentyl glycol diglycidyl ether and 1,3-bis(oxiran-2ylmethoxy)benzene were purchased from SigmaAldrich (MO, USA). Dimethyl sulfoxide (99.9% DMSO) was manufactured by Fisher Scientific (U.K.) while 1,3-diaminopropane (98% DAP) was produced by Alfa Aesar (Germany). Hydrochloric acid (>36% RHM grade HCl) and methanol (99.5% MeOH) were supplied by Samchun Chemicals Co., Ltd. (Korea). Nitric acid (70% RHM grade HNO3) was purchased from DaeJung Chemicals and Metals (Korea). High purity metal chloride salts (CsCl, SrCl2, NaCl, BaCl2∙2H2O) were supplied by Alfa Aesar (Korea). Ni(NO3)2.6H2O was obtained from DaeJung Chemicals and Metals (Korea), while RbCl and Cr(NO3)3.9H2O were purchased from Sigma-Aldrich (MO, USA). Deionized (DI) water (18.2 mΩ· cm-1 at 25 oC) was prepared via a Millipore Milli-Q system. Synthesis of epoxy-based adsorbents The epoxy polymer sorbents were prepared via an epoxy-amine addition reaction which was carried out by mixing bis-epoxide (BE), diaminopropane (DAP), and dimethyl sulfoxide (DMSO) in specific proportions and curing the mixture in an oil bath to come up with solid resins. Approximately 50% molar excess of BE relative to DAP was maintained in all reactions. Since the amount of solvent determines the solidity of the resin, initial tuning of reagents and solvent was performed. The combination of materials for preparing epoxy polymers from neopentyl glycol diglycidyl ether (Ep-NGDE) and 1,3-bis(oxiran2-ylmethoxy)benzene (Ep-BOMB) is summarized in Table 1 while the overall synthesis scheme is depicted in Figure 1. Epoxy polymer synthesis was initiated by vortex-mixing measured amounts of BE, DAP and DMSO in a sealed glass tube. The mixture was allowed to polymerize by heating in an oil bath at 80 oC for 1 h, and then at 150 oC for 4 h. Crude epoxy polymer was crushed, washed repeatedly with methanol, and then dried under vacuum at 60 oC for 12 h. Polymer particles that passed through a 500 µm sieve were washed vigorously 64 E.C. Escobar, G.M. Nisola, W.J. Chung, M.M.D. Lu, R.L. Reaño, J.M. Sareno, and A.A. Dorado Table 1 Schedule of materials for the preparation of epoxy polymers using bis-epoxides (BE) neopentyl glycol diglycidyl ether (Ep-NGDE) and 1,3-bis(oxiran-2-ylmethoxy)benzene (Ep-BOMB) by curing with DAP at different BE to DMSO (wt/wt) ratios. Entry BE, mmol DAP, mmol BE / DMSO (wt/wt) Product after curing Ep-NGDE-125 2.33 1.56 1.25 Solid (golden brown) Ep-NGDE-83 2.35 1.58 0.83 Solid, soft Ep-NGDE-63 2.34 1.56 0.63 Solid, soft gel Ep-BOMB-83 2.26 1.47 0.83 Solid, very tough Ep-BOMB-63 2.26 1.46 0.63 Solid, tough Ep-BOMB-50 2.26 1.47 0.50 Solid (off-white) Figure 1 Scheme for the preparation of epoxy polymers using bis-epoxides (BE) neopentyl glycol diglycidyl ether (NGDE) and 1,3-bis(oxiran-2-ylmethoxy)benzene (BOMB) by curing with DAP in DMSO to produce resins Ep-NGDE and Ep-BOMB, respectively. 65 Philippine e-Journal for Applied Research and Development Website: pejard.slu.edu.ph ISSN 2449-3694 (Online) Philippine e-Journal for Applied Research and Development 15(2025), 62-70 (300 rpm for 24 h) in 2 M HCl to leach out preadsorbed metal ions. The polymer particles were then washed repeatedly with deionized water until a neutral filtrate was achieved. Lastly, the polymer particles were washed with acetone and then dried under vacuum at 60 oC for 12 h. Degradation studies in different concentrations (0.5 M, 1.0 M, 2.0 M and 3.0 M) of HNO3 was conducted to determine whether the resins retain their solidity under highly acidic and oxidizing conditions. The degradation study was conducted over four days. Epoxy polymer characterization and evaluation of sorption characteristics The functional groups of the epoxy polymers were determined via FTIR analysis (Thermo Scientific, Nicolet 4 iS5). Their density was measured after equilibrating in water for 24 h at 25 oC using a pycnometer (25 mL) with thermometer (Witeg, Germany). The swelling behavior of the resins was evaluated by measuring their water uptake after 1 h using Eq. (1) where m1 and m2 refer to their dry mass and mass after soaking, respectively. Surface morphology imaging was conducted via scanning electron microscopy (SEM-EDX, Hitachi S-3500N, Japan). 3 85 Figure 1. Scheme for the preparation of epoxy polymers using bis-epoxides (BE) neopentyl 86 glycol diglycidyl ether (NGDE) and 1,3-bis(oxiran-2-ylmethoxy)benzene (BOMB) by curing 87 with DAP in DMSO to produce resins Ep-NGDE and Ep-BOMB, respectively. 88 89 Epoxy polymer synthesis was initiated by vortex-mixing measured amounts of BE, 90 DAP and DMSO in a sealed glass tube. The mixture was allowed to polymerize by heating in 91 an oil bath at 80 oC for 1 h, and then at 150 oC for 4 h. Crude epoxy polymer was crushed, 92 washed repeatedly with methanol, and then dried under vacuum at 60 oC for 12 h. Polymer 93 particles that passed through a 500 µm sieve were washed vigorously (300 rpm for 24 h) in 2 94 M HCl to leach out pre-adsorbed metal ions. The polymer particles were then washed 95 repeatedly with deionized water until a neutral filtrate was achieved. Lastly, the polymer 96 particles were washed with acetone and then dried under vacuum at 60 oC for 12 h. 97 98 Degradation studies in different concentrations (0.5 M, 1.0 M, 2.0 M and 3.0 M) of 99 HNO3 was conducted to determine whether the resins retain their solidity under highly acidic 100 and oxidizing conditions. The degradation study was conducted over four days. 101 102 Epoxy polymer characterization and evaluation of sorption characteristics 103 The functional groups of the epoxy polymers were determined via FTIR analysis 104 (Thermo Scientific, Nicolet 4 iS5). Their density was measured after equilibrating in water for 105 24 h at 25 oC using a pycnometer (25 mL) with thermometer (Witeg, Germany). The swelling 106 behavior of the resins was evaluated by measuring their water uptake after 1 h using Eq. (1) 107 where m1 and m2 refer to their dry mass and mass after soaking, respectively. Surface 108 morphology imaging was conducted via scanning electron microscopy (SEM-EDX, Hitachi S-109 3500N, Japan). 110 111 % 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑢𝑢𝑢𝑢𝑊𝑊𝑊𝑊 = (𝑚𝑚𝑚𝑚 2 − 𝑚𝑚𝑚𝑚 1 ) 𝑚𝑚𝑚𝑚1 ×100 (1) (1) To evaluate the ability of Ep-NGDE and Ep-BOMB to adsorb metal ions in highly acidic and oxidizing aqueous media, their adsorption capacity for Cs+--- the most abundant radionuclide in nuclear water waste--- was determined in 0.5 M, 1.0 M, 2.0 M and 3.0 M HNO3 containing 10 mM Cs+. To evaluate how temperature affects the adsorption capacity of Ep-BOMB for Cs+, adsorption runs using 3 M HNO3 containing 10 mM Cs+ were performed at 30 oC, 40 oC, 50 oC, and 60 oC. The adsorption of Ep-NGDE and Ep-BOMB for different metal ions was also evaluated using simulated spent nuclear fuel water waste (also called high-level liquid waste or HLLW) containing Na+ (66.04 mM), Cr3+ (4.96 mM), Ni2+ (4.52 mM), Rb+ (5.01 mM), Sr2+ (8.50 mM), Cs+ (19.50 mM) and Ba2+ (11.89 mM) in 3 M HNO3. This composition was based on a previous study by other researchers (Parajuli & Hirota, 2009). A dose of 0.5 mg epoxy polymer per mL of the simulated waste was maintained in all adsorption experiments. The adsorption process was performed for 12 h under mixing (300 rpm) in a temperature-controlled rotary mixer set at 30 oC. Treated filtrates were collected and passed through 0.2 µm polytetrafluoroethylene (PTFE) syringe filters prior to acid digestion in metal-free HNO3 using a microwave oven (MARS-5 CEM, USA). Metal ion concentrations were measured via inductively coupled plasma mass spectroscopy (ICP-MS Agilent 7500 series, USA) while the amount of metal ion adsorbed per gram of epoxy polymer was quantified as Q in Eq. (2) where m is the mass of sorbent, V is the volume of liquid, and Co and Ce are the initial and equilibrium metal ion concentrations, respectively. 4 112 To evaluate the ability of Ep-NGDE and Ep-BOMB to adsorb metal ions in highly 113 acidic and oxidizing aqueous media, their adsorption capacity for Cs+--- the most abundant 114 radionuclide in nuclear water waste--- was determined in 0.5 M, 1.0 M, 2.0 M and 3.0 M HNO3 115 containing 10 mM Cs+. To evaluate how temperature affects the adsorption capacity of Ep-116 BOMB for Cs+, adsorption runs using 3 M HNO3 containing 10 mM Cs+ were performed at 30 117 oC, 40 oC, 50 oC, and 60 oC. 118 119 The adsorption of Ep-NGDE and Ep-BOMB for different metal ions was also evaluated 120 using simulated spent nuclear fuel water waste (also called high-level liquid waste or HLLW) 121 containing Na+ (66.04 mM), Cr3+ (4.96 mM), Ni2+ (4.52 mM), Rb+ (5.01 mM), Sr2+ (8.50 mM), 122 Cs+ (19.50 mM) and Ba2+ (11.89 mM) in 3 M HNO3. This composition was based on a previous 123 study by other researchers (Parajuli & Hirota, 2009). A dose of 0.5 mg epoxy polymer per mL 124 of the simulated waste was maintained in all adsorption experiments. The adsorption process 125 was performed for 12 h under mixing (300 rpm) in a temperature-controlled rotary mixer set 126 at 30 oC. Treated filtrates were collected and passed through 0.2 µm polytetrafluoroethylene 127 (PTFE) syringe filters prior to acid digestion in metal-free HNO3 using a microwave oven 128 (MARS-5 CEM, USA). Metal ion concentrations were measured via inductively coupled 129 plasma mass spectroscopy (ICP-MS Agilent 7500 series, USA) while the amount of metal ion 130 adsorbed per gram of epoxy polymer was quantified as Q in Eq. (2) where m is the mass of 131 sorbent, V is the volume of liquid, and Co and Ce are the initial and equilibrium metal ion 132 concentrations, respectively. 133 134 𝑄𝑄𝑄𝑄= (𝐶𝐶𝐶𝐶 𝑜𝑜𝑜𝑜 − 𝐶𝐶𝐶𝐶 𝑒𝑒𝑒𝑒 )𝑉𝑉𝑉𝑉 𝑚𝑚𝑚𝑚 (2) 135 Results 136 Epoxy resin synthesis: Effect of amount of solvent 137 With molar amounts of reacting species (BE and DAP) kept essentially constant, the 138 amount of solvent (DMSO) was varied to determine the mixture composition that will yield 139 polymers with the desired solidity and processability (ease of grinding). It was found that the 140 optimal amount of solvent differs for each reaction system (Table 1), with Ep-NGDE and Ep-141 BOMB requiring BE/DMSO mass ratios of 1.25 and 0.50, respectively. This means that for the 142 same mass of BE, the NGDE-DA system requires less DMSO than the BOMB-DA pair to 143 produce solid polymer resins that are easily pulverized. In both cases, a lack of solvent during 144 the curing process gives rise to very tough solids that are difficult to grind while an excess of 145 it yields soft gels that easily deteriorate in acid, highlighting the importance of solvent 146 optimization in resin synthesis. 147 148 Effect of oxidizing acid concentration and period of exposure to resin solidity 149 Both Ep-NGDE and Ep-BOMB exhibit resistance to degradation in oxidizing acid but 150 with different degrees. Ep-NGDE remains solid in all HNO3 concentrations even after four 151 days of soaking (Figure S1). On the other hand, Ep-BOMB exhibits gradual darkening, and 152 more profoundly so at higher concentrations of HNO3 (Figure S1). Complete degradation of 153 Ep-BOMB was observed after 2 days of exposure in 3M HNO3. 154 155 Epoxy resin characterization 156 Golden brown Ep-NGDE and off-white Ep-BOMB appear as glass-like particles 157 (Figure 1) and have apparent densities of 1.403 g cm-3 and 1.382 g cm-3, respectively. Their 158 densities allow the resins to settle quickly after agitation. Both polymers swell in water which 159 (2) Results Epoxy resin synthesis: Effect of amount of solvent With molar amounts of reacting species (BE and DAP) kept essentially constant, the amount of solvent (DMSO) was varied to determine the mixture composition that will yield polymers with the desired solidity and processability (ease of grinding). It was found that the optimal amount of solvent differs for each reaction system (Table 1), with Ep-NGDE and Ep-BOMB requiring BE/ DMSO mass ratios of 1.25 and 0.50, respectively. This means that for the same mass of BE, the NGDE-DA system requires less DMSO than the BOMB-DA pair to produce solid polymer resins that are easily pulverized. In both cases, a lack of solvent during the curing process gives rise to very tough solids that are difficult to grind while an excess of it yields soft gels that easily deteriorate in acid, highlighting the importance of solvent optimization in resin synthesis. 66 E.C. Escobar, G.M. Nisola, W.J. Chung, M.M.D. Lu, R.L. Reaño, J.M. Sareno, and A.A. Dorado Effect of oxidizing acid concentration and period of exposure to resin solidity Both Ep-NGDE and Ep-BOMB exhibit resistance to degradation in oxidizing acid but with different degrees. Ep-NGDE remains solid in all HNO3 concentrations even after four days of soaking (Figure S1). On the other hand, EpBOMB exhibits gradual darkening, and more profoundly so at higher concentrations of HNO3 (Figure S1). Complete degradation of Ep-BOMB was observed after 2 days of exposure in 3M HNO3. Epoxy resin characterization Golden brown Ep-NGDE and off-white EpBOMB appear as glass-like particles (Figure 1) and have apparent densities of 1.403 g cm-3 and 1.382 g cm-3, respectively. Their densities allow the resins to settle quickly after agitation. Both polymers swell in water which means that both are hydrophilic. Their water uptake was found to be about 38.45% for Ep-NGDE and 33.73% for Ep-BOMB. The predicted chemical structures of EpBOMB and Ep-NGDE (Figures 2a & 2b) coincide well with functional groups revealed in their FTIR spectra (Figure 2c). Both possess an abundance of -OH/-NH (3277 to 3312 cm-1), -CH- (2864 to 2929 cm-1 and 1359 to 1489 cm-1), and -C-O-C- (1042 to 1154 cm-1) groups. Moreover, Ep-BOMB contains aryl groups as revealed by stretching vibrations at 1590 and 763 cm-1. Ep-BOMB features rugged but essentially pore-less surfaces as revealed by SEM images at different magnifications (Figures 2d, 2e, & 2f) similar to previous reports on epoxybased sorbents (Torrejos et al., 2021; Escobar et al., 2021b). Adsorption performance The uptake of Cs+ by Ep-NGDE and Ep-BOMB in 0.5 M, 1.0 M, 2.0 M and 3.0 M HNO3 initially containing 10 mM Cs+ was measured to evaluate the ability of the resins to sequester metal ions despite potentially strong competition with hydronium (H3O+) ions and possible deterioration of the resin structure due to prolonged oxidation. It was found that although it remains intact after the 12-hour adsorption process, the uptake of Cs+ by Ep-NGDE was very low. On the other hand, Ep-BOMB registers a high capacity for Cs+ (>1 mmol g-1) which is essentially maintained across the different concentrations of HNO3 (Figure 3a). This means that Ep-BOMB contains sorption sites for Cs+ and that these sorption sites remain structurally potent despite possible degradation under prolonged exposure to strong oxidizing acid and even with potentially strong competition for these sorption sites by hydronium ions. Also, Ep-BOMB retains its solidity after the 12-hour adsorption process (Figure S2), which means that it’s separation from the liquid phase may still be accomplished via simple techniques such as filtration or decantation. Results also show that Ep-BOMB retains its ability to sequester Cs+ over a range of temperatures (Figure S3) which means that it can be expected to work as intended under the temperature conditions (< 50 oC) of nuclear water waste (Xu et al., 2023). Despite its minimal uptake (< 0.1 mmol g-1) of priority radionuclides Cs+ and Sr2+ and other metal ions in HLLW (Cr3+, Ni2+, Rb+, and Ba2+), EpNGDE nevertheless exhibits very high capacity (~11 to 15 mmol g-1) for Na+ (Figure 3b). On the other hand, Ep-BOMB exhibits high capacity for Cs+ (1.5-1.8 mmol g-1) and substantial capacity for Sr2+ (~0.6 mmol g-1) (Figure 3c). Discussion Ep-NGDE exhibits low uptake capacity for the relatively larger metal ions Cs+ (r = 1.70 Å), Rb+ (r = 1.49 Å), Ba2+ (r = 1.36 Å), and Sr2+ (r = 1.13 Å). It also exhibits low capacity for the relatively smaller multivalent metal ions Ni2+ (r = 0.69 Å) and Cr3+ (r = 0.62 Å). Meanwhile, its uptake capacity for Na+ (r = 1.02 Å) is very high. These results suggest that the high selectivity of Ep-NGDE for Na+ could be due to appropriately-sized channel spaces in the resin matrix that preferentially permit the permeation of bare or hydrated Na+. Although smaller than Na+ in their bare ion form, multivalent ions Ni2+ and Cr3+ could have remained in their enlarged hydrated form due to their high dehydration energy requirement (Table 2) which prevented their transport into the narrow channels of EpNGDE. 67 Philippine e-Journal for Applied Research and Development Website: pejard.slu.edu.ph ISSN 2449-3694 (Online) Philippine e-Journal for Applied Research and Development 15(2025), 62-70 Table 2 Ionic radii and Gibb’s free energy of hydration of selected metal ions in HLLW (Marcus, 1991). Metal ion Na+Cr3+ Ni2+ Rb+Sr2+ Cs+Ba2+ r, Å 1.02 0.62 0.69 1.49 1.13 1.70 1.36 ∆Ghyd, kJ mol-1 365 4010 1980 275 1380 250 1250 Figure 2 Proposed chemical structure of (a) Ep-BOMB and (b) Ep-NGDE and (c) their corresponding FTIR spectra; SEM images of Ep-BOMB at (d) 1,000x, (e) 10,000x, and (f) 25,000x magnification; and (g) proposed adsorption mechanism of Sr2+ and Cs+ by Ep-BOMB. 68 E.C. Escobar, G.M. Nisola, W.J. Chung, M.M.D. Lu, R.L. Reaño, J.M. Sareno, and A.A. Dorado On the other hand, Ep-BOMB is able to sequester the relatively larger metal ions, most importantly Cs+ and Sr2+, and it appears that the abundance of aromatic groups in Ep-BOMB is responsible for this outcome. Because of its rigidity, the benzene moiety may have induced the formation of larger channel spaces in the resin matrix that allow the permeation of large metal ions and their complexation via electrostatic interactions with oxygen and nitrogen atoms in the polymer matrix (Figure 2g). Second, the benzene moiety could have interacted preferentially with Cs+ since Cs+ has the lowest dehydration energy among the metal ions in the medium (Table 2). Cation-π interactions in the aqueous phase had been known to be strongly correlated with the dehydration energy of metal ions, with low dehydration energy being associated with more stable cationπ complexes (Kumpf & Dougherty, 1993; Pichierri, 2018). As such, the adsorption capacity of Ep-BOMB for Cs+ under highly acidic and oxidizing conditions is much higher than those reported in other studies (Table S1). Ep-NGDE having a very high capacity for Figure 3 (a) Uptake of Cs+ by Ep-BOMB at different HNO3 concentrations (Co = 10 mM Cs+, 12 h, 300 rpm, 30 oC). Uptake of different metal ions in simulated HLLW by (b) Ep-NGDE and (c) Ep-BOMB [Simulated HLLW contains Na+ (66.04 mM), Cr3+ (4.96 mM), Ni2+ (4.52 mM), Rb+ (5.01 mM), Sr2+ (8.50 mM), Cs+ (19.50 mM) and Ba2+ (11.89 mM) in 3 M HNO3 ; Adsorption conditions: S/L=0.5, 300 rpm, 12 h, 30 oC]. (d) Proposed process flow for the utilization of Ep-NGDE and Ep-BOMB in radionuclide decontamination of HLLW. 69 Philippine e-Journal for Applied Research and Development Website: pejard.slu.edu.ph ISSN 2449-3694 (Online) Philippine e-Journal for Applied Research and Development 15(2025), 62-70 Na+ may be used in a stage-wise decontamination process of HLLW wherein Na+--- a major competing ion in various aqueous media such as HLLW--- is initially removed to enhance the subsequent removal of Cs+, Sr2+, and target metal ions by other sorbents like Ep-BOMB (Figure 3d). On the other hand, Ep-BOMB, with its high capacity for Cs+ and Sr2+, can serve to collect these radionuclides for subsequent vitrification and long-term storage. However, in view of the strong oxidizing effect of 3 M HNO3, Ep-BOMB must be separated from the liquid phase before it completely deteriorates. Conclusion Two polymeric sorbents capable of resisting physical deterioration in highly acidic and highly oxidizing conditions of spent nuclear fuel water waste or HLLW were synthesized and evaluated. The two sorbents possess unique metal ion sorption characteristics that make them useful in radionuclide decontamination of nuclear water wastes containing high concentrations of oxidizing acid (3 M HNO3). Ep-NGDE shows preference for the uptake of Na+ while Ep-BOMB exhibits high capacity for both Cs+ and Sr2+. It is anticipated that Ep-NGDE and Ep-BOMB can be implemented in a sequential treatment process for spent nuclear fuel water waste where Na+ is first removed using Ep-NGDE. Thereafter, the water waste may be treated with Ep-BOMB to sequester and preconcentrate the target radionuclides Cs+ and Sr2+ prior to long-term storage. 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