A Carbazole-Functionalized Porous Aromatic Framework for Enhancing Volatile Iodine Capture via Lewis Electron Pairing

molecules Article A Carbazole-Functionalized Porous Aromatic Framework for Enhancing Volatile Iodine Capture via Lewis Electron Pairing Zhuojun Yan 1, Bo Cui 1, Ting Zhao 2, Yifu Luo 2, Hongcui Zhang 1, Jialin Xie 1, Na Li 1, Naishun Bu 2, *, Ye Yuan 3, * and Lixin Xia 1,4, * 1 College of Chemistry, Liaoning University, Shenyang 110036, China; zjyan@lnu.edu.cn (Z.Y.); cuibo2019@163.com (B.C.); zhanghongcui2021@126.com (H.Z.); xjl810888632@163.com (J.X.); linaa627@163.com (N.L.) 2 School of Environmental Science, Liaoning University, Shenyang 110036, China; zhaot17865818271@163.com (T.Z.); royjacklyf@126.com (Y.L.) 3 Key Laboratory of Polyoxometalate and Reticular Material Chemistry of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024, China 4 Yingkou Institute of Technology, Yingkou 115014, China * Correspondence: bunaishun@lnu.edu.cn (N.B.); Yuany101@nenu.edu.cn (Y.Y.); lixinxia@lnu.edu.cn (L.X.) Citation: Yan, Z.; Cui, B.; Zhao, T.; Luo, Y.; Zhang, H.; Xie, J.; Li, N.; Bu, N.; Yuan, Y.; Xia, L. A Carbazole- Functionalized Porous Aromatic Framework for Enhancing Volatile Iodine Capture via Lewis Electron Pairing. Molecules 2021, 26, 5263. https://doi.org/10.3390/ molecules26175263 Abstract: Nitrogen-rich porous networks with additional polarity and basicity may serve as effective adsorbents for the Lewis electron pairing of iodine molecules. Herein a carbazole-functionalized porous aromatic framework (PAF) was synthesized through a Sonogashira Hagihara cross-coupling polymerization of 1,3,5-triethynylbenzene and 2,7-dibromocarbazole building monomers. The resulting solid with a high nitrogen content incorporated the Lewis electron pairing effect into a π-conjugated nano-cavity, leading to an ultrahigh binding capability for iodine molecules. The iodine uptake per specific surface area was ~8 mg m 2 which achieved the highest level among all reported I 2 adsorbents, surpassing that of the pure biphenyl-based PAF sample by ca. 30 times. Our study illustrated a new possibility for introducing electron-rich building units into the design and synthesis of porous adsorbents for effective capture and removal of volatile iodine from nuclear waste and leakage. Keywords: iodine capture; porous aromatic framework; Lewis electron; pairing effect; Sonogashira- Hagihara cross-coupling Academic Editor: Constantina Papatriantafyllopoulou Received: 9 August 2021 Accepted: 27 August 2021 Published: 30 August 2021 Publisher s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1. Introduction To overcome the energy shortages and environmental concerns originated from fossil fuels, nuclear power, the only mature technology, is considered a possible approach for providing electricity on a large scale with little greenhouse gases emission [1]. However, the treatment of nuclear waste and the emergency response for nuclear leakage, cause consternation in the increasing development of the nuclear industry [2]. The 129 I and 131 I atoms originated from the uranium fission are the two main ingredients of nuclear waste, especially 129 I, which has an ultra-long radioactive half-life (t 1/2 = 15.7 10 6 years) [3,4]. Because the enrichment and toxic effects in organisms, effective methods for the capture and removal of radiological iodine aroused strong concerns. To date, several strategies have been proposed, including dry dedusting [5,6], chemical precipitation [7], and physical adsorption [8 10]. Among them, the physical adsorption method has specific advantages of high adsorption efficiency, low cost, simple operation, and high recyclability [11,12]. Porous aromatic frameworks (PAFs) composed of covalently bonded light atoms (H, B, C, N, and O), have superb thermal and chemical stability, high surface area, and tunable pore size, which make them ideal candidates for iodine capture from the nuclear waste stream containing volatile iodine radionuclides [13 16]. In the past few decades, PAF solids with tunable pore properties including surface area, volume, and size distribution were demonstrated to play important roles for the physical adsorption for guest Molecules 2021, 26, 5263. https://doi.org/10.3390/molecules26175263 https://www.mdpi.com/journal/molecules

Molecules 2021, 26, x FOR PEER REVIEW 2 of 10 waste stream containing volatile iodine radionuclides [13 16]. In the past few decades, Molecules 2021, 26, 5263 2 of 10 PAF solids with tunable pore properties including surface area, volume, and size distribution were demonstrated to play important roles for the physical adsorption for guest molecules [17 20]. However, pure carbon-based PAFs with a micropore cavity do not show molecules an excellent [17 20]. capacity However, and pure fast carbon-based kinetics for I2 PAFs matter with adsorption. a micropore For cavity instance, do not PAF-1 show with an excellent an exceptionally capacityhigh and fast surface kinetics area for (5600 I 2 matter m 2 g 1 ) adsorption. and micropore Forvolume instance, (0.89 PAF-1 cm 3 with g 1 ) exhibits an exceptionally a low iodine high vapor surface capture area capability (5600 m 2 gwith 1 ) and 186 micropore wt% at 298 volume K per 40 (0.89 Pa [21]. cm 3 It g 1 is ) obvious exhibitsthat a low the iodine adsorption vaporcapacity capture of capability the adsorbent 186 for wt% iodine atis 298 not Konly per 40 related Pa [21]. to the It is surface obvious area that and thepore adsorption size, but the effective of theadsorption adsorbentsites for iodine on the isaccessible not related surface to may the possess surfacea area more andimportant size, role but to theinteract effective with volatile sites iodine ongases. the A detailed surface investigation may possess should a more be important conducted role to to reveal interact the with relationship volatile iodine between gases. the A chemical detailed investigation features of PAFs should and be iodine conducted molecules, to reveal which the relationship provides significant between advantages the chemical and features opportunities of PAFs and of PAFs iodine for molecules, the development which provides of next-generation significant advantages porous adsorptions. and opportunities of PAFs for the development Based on the of next-generation polarization effect, porous active adsorptions. sites transform the speciation of iodine molecules into multiple oxidation states ( 1, 0, +1, +3, +5, and +7), primarily as molecular io- Based on the polarization effect, active sites transform the speciation of iodine molecules into multiple oxidation states ( 1, 0, +1, +3, +5, and +7), primarily as molecular iodine (I 2 ), dine (I2), iodide (I iodide (I ), iodate, ), iodate, or organic iodine (org-i) [22 25]. A nitrogenous fragment or organic iodine (org-i) [22 25]. A nitrogenous fragment possesses possesses lone pair electrons, thereby revealing highly negative charge to enhance the lone pair electrons, thereby revealing highly negative charge to enhance the binding affinity for the polarizable electron cloud of I 2 molecules [26]. Herein, 2,7-dibromocarbazole binding affinity for the polarizable electron cloud of I2 molecules [26]. Herein, 2,7-dibromocarbazole was adopted as the functional building monomer to prepare a was adopted as the functional building monomer to prepare a carbazole-containing PAF carbazole-containing PAF network through a one-step Sonogashira-Hagihara coupling network through a one-step Sonogashira-Hagihara coupling reaction. Consequently, the reaction. Consequently, the resulting PAF sample with the electron-rich system exhibits resulting PAF sample with the electron-rich system exhibits an outstanding performance an outstanding performance for the capture of a volatile iodine for the capture of a volatile iodine with an uptake of 2.10 g g 1 with an uptake of 2.10 g. The results of this study g provide 1. The results of this study provide useful guidance for the development of new porous useful guidance for the development of new porous adsorbents for the removal of adsorbents for the removal of radioactive iodine. radioactive iodine. 2. 2. Results and anddiscussion LNU-13 was synthesized synthesized through through the Sonogashira-Hagihara the Sonogashira-Hagihara coupling of coupling 2,7-dibromo- of 2,7-dibromocarbazole and 1,3,5-triethynylbenzene and 1,3,5-triethynylbenzene (Figure 1a). As (Figure determined 1a). As by the determined Fourier transform by the Fourier infraredtransform spectroscopy infrared (FTIR, spectroscopy Figure 2a), the(ftir, C-Br stretching Figure 2a), vibration the C-Br of stretching 2,7-dibromocarbazole vibration of at2,7-dibromocarbazole 495 cm 1 and the C Hat stretching 495 cm 1 vibration and the of C H thestretching terminal alkyne vibration (1,3,5-triethynylbenzene) of the terminal alkyne at 3270 (1,3,5-triethynylbenzene) cm 1 disappeared fromat the3270 IR spectrum cm 1 disappeared of LNU-13, from verifying the the IR completeness spectrum of LNU-13, of the Sonogashira-Hagihara verifying the completeness coupling of the reaction. Sonogashira-Hagihara The structural integrity coupling ofreaction. LNU-13The was structural further confirmed integrity of bylnu-13 C NMR was (Figure further 2b). confirmed The main by 13 peaks C NMR observed (Figure in 2b). thethe range main of peaks 120 150 observed ppm were in the attributed range of to 120 150 the substituted ppm were carbon attributed of theto aromatic the substituted ring connected carbon of to the aromatic benzene ring; connected and the resonance to the benzene around 90 ring; ppmand was the assigned resonance to the around carbons 90 ppm originated was assigned from the to C C the carbons group. originated from the C C group. Figure 1. (a) Synthesis of LNU-13 polymer; (b) schematic diagram of PAF solid for I 2 sorption.

Molecules 2021, 26, x FOR PEER REVIEW 3 of 10 Molecules 2021, 26, 5263 3 of 10 Figure 1. (a) Synthesis of LNU-13 polymer; (b) schematic diagram of PAF solid for I2 sorption. Figure 2. 2. (a) (a) FTIR spectra of of 2,7-dibromocarbazole, 1,3,5-triethynylbenzene, and and LNU-13; (b) (b) solid-state 13 C NMR 13 C NMR solidstate spectrum spectrum of LUN-13; of LUN-13; (c) powder (c) powder X-ray X-ray diffraction diffraction pattern pattern of LNU-13. of LNU-13. (d) (d) SEM SEM image image of LNU-13; (e)tem image of LNU-13; (f) TGA plot of LNU-13 at N2 condition with a ramp of LNU-13; (e)tem image of LNU-13; (f) TGA plot of LNU-13 at N 2 condition with a ramp rate of 5 C min 1 ; (g) N 2 adsorption-desorption isotherm of LNU-13; (h) pore size distribution of LNU-13.

Molecules 2021, 26, 5263 4 of 10 Powder X-ray diffraction (XRD) pattern of LNU-13 shows a characteristic broad peak, indicating they are amorphous in nature (Figure 2c). It seems that the formation of the stacked layer structure by the ordered connection among the building blocks is otherwise difficult [13,27]. Scanning electron microscopy (SEM) analysis demonstrated the stacked spherical structures of LNU-13, as shown in Figure 2d. Transmission electron microscopy (TEM) clearly confirmed the amorphous structure of LNU-13 (Figure 2e). As illustrated by thermogravimetric analysis (TGA, Figure 2f), the LNU-13 material begins to degrade at 350 C and the weight loss is about 20% at 750 C under a purified nitrogen atmosphere, indicating that LNU-13 possesses good thermal stability. All the results demonstrate that LNU-13 retains its intact skeleton under a variety of harsh conditions. The porosity of the resulting PAF material was probed using N 2 adsorption-desorption isotherms at 77 K up to 1 bar. The adsorption curve combined the features of type-i and type-iv adsorption isotherms, indicating the co-existence of a micro- and meso-pore system (Figure 2g). The BET surface area of LNU-13 was determined to be 255 m 2 g 1. LNU-13 possessed wide pore size distribution in the range of 1 6 nm calculated using a nonlocalized DFT (NL-DFT) (Figure 2h). This hierarchical porous structure made the PAF solid an excellent scaffold for the access of the I 2 guest into the internal space of LNU particle [28,29]. The iodine uptake measurement of LUN-13 was conducted by placing the PAF powder into a sealed vessel filled with iodine vapor at 348 K under normal atmosphere. As shown in Figure 3a, the iodine adsorption capacity increased significantly with the prolonging of the contact time. In the first 5 h, the adsorption capacity of LNU-13 was very fast with a value of 1.75 g g 1. No further change in iodine loading was observed after 48 h exposure, indicating that LNU-13 was basically saturated (2.10 g g 1 ). A significant color change in the powder from brown to black was observed (Figure 3a inset). Calculated by the BET surface area (255 m 2 g 1 ), the iodine uptake per specific surface area was ~ 8 mg m 2 which achieved the highest level among silver-containing zeolite [30], metalorganic frameworks (MOFs), and conjugated microporous polymers (CMPs), etc., reported by the same adsorption method, surpassing that of PAF-1 by ca. 30 times (Figure 4). Moreover, it also has a certain competitiveness compared with other forms of adsorbent, such as carbon foam, fiber adsorbent, carbon cloth, aerogel, etc., including BN foam (2.12 g g 1 ) [31], PE/PP-g-PNVP fibers (1.2378 g g 1 ) [32], C60-CC-PNP (2.4 g g 1 ) [33], CC-PNP (1.02 g g 1 ) [33], ENTDAT dried gel (1.8 g g 1 ) [34], G-TP5 (0.67 g g 1 ) [35] and G-TP6 (0.58 g g 1 ) [35]. The adsorption mechanism of iodine vapor in LNU-13 was studied through PXRD, Raman, and FT-IR spectroscopy. Curve-fitting for the I 2 adsorption isotherm was based on pseudo-second-order kinetics (Figure 3b), a high correlation coefficient (R 2 = 0.99993) suggested the chemical adsorption process of LNU-13. As shown in Figure 5a, there were no characteristic peaks of I 2 crystal diffraction peaks observed in the iodine-loaded LNU-13 (LNU-13@I 2 ). This phenomenon proved the monodispersed iodine species in the form of molecular or ionic states in the PAF architecture [27]. Raman spectroscopy of LNU-13@I 2 presented a series of bands centered at 110 and 170 cm 1 (Figure 5b). The characteristic bands in the region of 100 120 cm 1 were assigned to the symmetric stretching of the I 3 species, while the band located at 170 cm 1 was ascribed to the higher polyiodide anions, i.e., I 5 [36,37]. Comparing the FTIR spectra of pristine LNU-13 and LNU-13@I 2 (Figure 5c,d), the aromatic rings were centered at 1555 cm 1 in LNU-13 vs. 1612 cm 1 in I 2 @LNU-13. A similar shift was also observed for the band assigned to v C N (str) bond vibration (1234 cm 1 for LNU-13 and 1262 cm 1 for I 2 @LNU-13). In addition, the peak at 731 cm 1 belonged to the characteristic signal for iodine molecules. All these results indicate that the lone pair electron of the carbazole nitrogen polarizes the iodine molecule into an ionic state, and then achieves the excellent adsorption property for an iodine guest [38,39].

Molecules 2021, 26, 5263 Molecules 2021, 26, x FOR PEER REVIEW 5 of 10 5 of 10 Figure curve of of LNU-13 LNU-13 at at 348 348 K. K. Inset: Inset: the the photographs photographsreveal revealthe thecolor color Figure 3.3. (a) II22 adsorption adsorption curve change in in LNU-13 LNU-13 before before and and after after iodine adsorption; adsorption; (b) change (b) curve-fitting curve-fittingfor forthe theii22adsorption adsorptionproprocess;(c) (c)photographs photographs showing showing the the iodine-adsorbed iodine-adsorbed process cess; process in in n-hexane; n-hexane; (d) (d) photographs photographsshowing showing the iodine-released process of LNU-13@I2 in ethanol; (e) I2 release curve of LNU-13@I2 at 398 K; (f) the iodine-released process of LNU-13@I2 in ethanol; (e) I2 release curve of LNU-13@I2 at 398 K; recycling experiment of LNU-13. (f) recycling experiment of LNU-13.

Molecules 2021, 26, 5263 6 of 10 Molecules 2021, 26, x FOR PEER REVIEW 6 of 10 Molecules 2021, 26, x FOR PEER REVIEW 7 of 10 Figure4. 4. Iodine uptake capacitiesof of different adsorbents. The adsorption mechanism of iodine vapor in LNU-13 was studied through PXRD, Raman, and FT-IR spectroscopy. Curve-fitting for the I2 adsorption isotherm was based on pseudo-second-order kinetics (Figure 3b), a high correlation coefficient (R 2 = 0.99993) suggested the chemical adsorption process of LNU-13. As shown in Figure 5a, there were no characteristic peaks of I2 crystal diffraction peaks observed in the iodine-loaded LNU-13 (LNU-13@I2). This phenomenon proved the monodispersed iodine species in the form of molecular or ionic states in the PAF architecture [27]. Raman spectroscopy of LNU-13@I2 presented a series of bands centered at 110 and 170 cm 1 (Figure 5b). The characteristic bands in the region of 100 120 cm 1 were assigned to the symmetric stretching of the I 3 species, while the band located at 170 cm 1 was ascribed to the higher polyiodide anions, i.e., I 5 [36,37]. Comparing the FTIR spectra of pristine LNU-13 and LNU-13@I2 (Figure 5c,d), the aromatic rings were centered at 1555 cm 1 in LNU-13 vs. 1612 cm 1 in I2@LNU-13. A similar shift was also observed for the band assigned to vc N (str) bond vibration (1234 cm 1 for LNU-13 and 1262 cm 1 for I2@LNU-13). In addition, the peak at 731 cm 1 belonged to the characteristic signal for iodine molecules. All these results indicate that the lone pair electron of the carbazole nitrogen polarizes the iodine molecule into an ionic state, and then achieves the excellent adsorption property for an iodine guest [38,39]. Figure 5. 5. (a) PXRD spectra of II2, 2, LNU-13, and LNU-13@I2; 2 ; (b) Raman spectra ofi2, I 2, LNU-13, and LNU-13@I2; 2 ; (c,d) FTIR spectra of LNU-13 andlnu-13@i2. 2. In order to evaluate the ability of LNU-13 for the capture of elemental iodine from the solution, LNU-13 powder was immersed into a closed vial containing a pre-prepared iodine elemental n-hexane solution (300 mg L 1 1 ). ). As As depictedin in Figure3c, 3c, the colorof of the initial solution originated from iodine elemental substance changed from purple to colorless over time; after exposure for 24 h, the n-hexane solution containing both LNU-13 and iodine molecules became transparent and colorless, which proved that LNU-13 powder captured iodine from a n-hexane solution.

Molecules 2021, 26, 5263 7 of 10 the initial solution originated from iodine elemental substance changed from purple to colorless over time; after exposure for 24 h, the n-hexane solution containing both LNU-13 and iodine molecules became transparent and colorless, which proved that LNU-13 powder captured iodine from a n-hexane solution. The recyclability for I 2 capture is also a key parameter in practical usage. The iodineloaded LNU-13 powder can be activated by both thermal desorption and solvent elution. The iodine adsorbed in the PAF cavity is easily released in polar organic solvents including methanol and ethanol. After immersion in an ethanol solution for 72 h, the color of the mixture gradually changes from colorless to dark brown, correspondingly, the color of the solid varies from black to brown (Figure 3d). These results manifest that guest iodine is gradually released from the PAF structure into the organic solvent. As shown in Figure 3e, the release efficiency of LNU-13@I 2 is as high as 97% after the solid is heated in air at 398 K for 320 min. In addition, the LNU-13 sample withstands multiple adsorption-desorption cycles, and the adsorption capacity reaches 69% of the initial capacity after five cycles of iodine adsorption (Figure 3f). 3. Materials and Methods 3.1. Materials 2,7-Dibromocarbazole was purchased from Energy Chemical, Shanghai, China and 1,3,5-triethynylbenzene was received from TCI, Tokyo, Japan. Copper iodide and tetrakis (triphenylphosphine) palladium were obtained from Sigma-Aldrich, St. Louis, MO, USA. Other chemicals and solvents were purchased from commercial suppliers and used without further purification. All reactions were performed under a purified nitrogen atmosphere. 3.2. Synthesis of LNU-13 The 2,7-Dibromocarbazole (649 mg, 1.9976 mmol), 1,3,5-triethynylbenzene (200 mg, 1.3317 mmol), tetrakis (triphenylphosphine) palladium (30 mg), and copper (I) iodide (10 mg) were added into a round-bottom flask. The mixture was degassed through a N 2 bubbling process for 30 min; after that, 20 ml of anhydrous N,N-dimethylformamide (DMF) and 8 ml of anhydrous triethylamine (TEA) were added into the system. Then, the reaction mixture was heated to 80 C for 72 h under N 2 gas atmosphere. Cooling to room temperature, the precipitate was washed with each DMF, tetrahydrofuran (THF), and acetone solvents for several times to obtain a crude product. Further purification of the product was carried out via Soxhlet extraction with THF, dichloromethane, and methanol in turns for 72 h. The product was dried in a vacuum for 10 h at 90 C to obtain LNU-13. 3.3. Iodine Adsorption and Release 3.3.1. Iodine Adsorption from Volatile Iodine The iodine adsorption capacity was analyzed according to the gravimetric measurements. The LNU-13 powder (30.0 mg) was loaded into a small weighing bottle, which was then placed in a closed system at 348 K (75 C) and ambient pressure, along with excess non-radioactive solid iodine. After certain time intervals, the bottle was taken out, cooled down to room temperature and weighted, and then loaded back into the vapor of iodine to continue iodine adsorption [40,41]. The weight percentage of captured iodine was calculated using the following formula: Adsorption capacity = m 2 m 1 m 1 100% (1) where m 2 and m 1 are the masses of PAF powder after and before iodine intake, respectively. 3.3.2. Iodine Adsorption from Solution To evaluate the adsorption of dissolved iodine in cyclohexane, LNU-13 samples were immersed in n-hexane solution (300 mg L 1 ) containing iodine for 24 h, the adsorption process of iodine was photographed at selected time intervals.

Molecules 2021, 26, 5263 8 of 10 References 3.3.3. Iodine Desorption in Solution Ethanol was used as the extraction solvent to evaluate the reversibility of PAF materials iodine adsorption. Pouring five milliliters of ethanol to five milligrams of iodine-loaded polymer, the release process of iodine was photographed at selected time intervals. 4. Conclusions In summary, a carbazole-based porous aromatic framework was successfully synthesized through a one-step Sonogashira-Hagihara cross-coupling polymerization. Based on the Lewis electron pairing effect, the resulting solid achieved the highest value of iodine uptake per specific surface area. The iodine uptake per specific surface area far surpassed that of silver-containing zeolite, MOFs, and CMPs, etc. Our study firmly demonstrated the important role of electron-rich units in the open architecture for capture and the removal of iodine substance, which opened a gate for the design and synthesis of porous adsorbents for remediation of radioactive iodine to address environmental issues. Author Contributions: Z.Y., L.X. and N.B. designed and planned the project. B.C. and H.Z. conducted all of the experiments. T.Z. and Y.L. helped to characterize the samples. J.X. and N.L. helped to synthesize the materials. Z.Y. and Y.Y. helped to explain the mechanism. Z.Y., Y.Y. and B.C. analyzed the data and wrote the paper. Z.Y., L.X., N.B. and Y.Y. revised the paper. All authors have read and agreed to the published version of the manuscript. Funding: This work was supported by the National Natural Science Foundation of China (31972522, 21704037, 21671089), National Key Research and Development Project of China (2018YFC1801200), Major Science and Technology Project of Liaoning Province (2019JH1/10300001), the Scientific Research Fund of Liaoning Provincial Education Department (2020-YKLH-22), LiaoNing Revitalization Talents Program (XLYC2007032), Scientific Research Fund of Liaoning Provincial Education Department (LQN202003). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: All data related to this study are presented in this publication. Acknowledgments: All individuals appreciate the partial support of Liaoning University. Conflicts of Interest: The authors declare no conflict of interest. Sample Availability: Samples are not available from the author. 1. Chu, S.; Majumdar, A. Opportunities and challenges for a sustainable energy future. Nature 2012, 488, 294 303. [CrossRef] 2. Hoffert, M.I.; Caldeira, K.; Benford, G.; Criswell, D.R.; Green, C.; Herzog, H.; Jain, A.K.; Kheshgi, H.S.; Lackner, K.S.; Lewis, J.S. Advanced Technology Paths to Global Climate Stability: Energy for a Greenhouse Planet. Science 2002, 298, 981 987. [CrossRef] 3. Ren, F.; Zhu, Z.Q.; Qian, X.; Liang, W.D.; Mu, P.; Sun, H.X.; Liu, J.H.; Li, A. Novel thiophene-beared conjugated microporous polymer honeycomb-liked porous spheres with ultrahigh Iodine uptake. Chem. Commun. 2016, 52, 9797 9800. [CrossRef] [PubMed] 4. Yan, Z.J.; Yuan, Y.; Tian, Y.Y.; Zhang, D.M.; Zhu, G.S. Highly efficient enrichment of volatile iodine by charged porous aromatic frameworks with three sorption sites. Angew. Chem. Int. Ed. 2015, 54, 12733 12737. [CrossRef] 5. Liang, S.Y.; Fan, Z.Y.; Zhang, W.D.; Guo, M.; Cheng, F.Q.; Zhang, M. Controllable growth of Na 2 CO 3 fibers for mesoporous activated alumina ball modification towards the high-efficiency adsorption of HCl gas at low temperature. RSC Adv. 2017, 7, 53306 53315. [CrossRef] 6. Lan, Y.S.; Tong, M.M.; Yang, Q.Y.; Zhong, C.L. Computational screening of covalent organic frameworks for the capture of radioactive iodine and methyl iodide. CrystEngComm 2017, 19, 4920 4926. [CrossRef] 7. Lei, Y.; Zhan, Z.S.; Saakes, M.; Weijden, R.D.; Buisman, C.J.N. Electrochemical recovery of phosphorus from acidic cheese wastewater: Feasibility, quality of products, and comparison with chemical precipitation. ACS EST Water 2021, 1, 1002 1013. 8. Ighaloa, J.O.; Adeniyia, A.G.; Adelodun, A.A. Recent advances on the adsorption of herbicides and pesticides from polluted waters: Performance evaluation via physical attributes. J. Ind. Eng. Chem. 2021, 93, 117 137. [CrossRef] 9. Cui, P.; Jing, X.F.; Yuan, Y.; Zhu, G.S. Synthesis of porous aromatic framework with Friedel Crafts alkylation reaction for CO 2 separation. Chin. Chem. Lett. 2016, 27, 1479 1484. [CrossRef]

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