Abstract

Objective During the utilization of nuclear energy， radioactive isotopes of iodine （such as iodine-129 and iodine-131） are prevalent contaminants. Managing radioactive iodine is a critical concern for researchers. Utilizing porous materials to adsorb iodine vapor is an effective solution. However， traditional porous iodine adsorbents， including activated carbon and porous zeolite， exhibit drawbacks such as high density， limited structural versatility， low specific surface area， large pore size， low adsorption capacity， and inadequate cycling performance， significantly impeding their industrial applicability. Given these challenges， there is a necessity to develop novel porous materials for efficient iodine vapor adsorption. Porous Organic Polymers （POPs） represent a promising category of porous materials characterized by high physical and chemical stability， low density，high porosity， large specific surface area， outstanding adsorption performance， and recyclability. POPs demonstrate promising prospects in radioactive iodine treatment. Ball mills， as common crushing equipment， find widespread application in industries such as mineral processing， building materials， and chemical industry. Additionally， researchers employ ball mills for chemical synthesis due to advantages such as brief reaction times， high efficiency， simplicity， and potential for low-cost， straightforward，large-scale industrial production. In this study， tetraphenylmethane with a three-dimensional structure served as the monomer，and a high-energy planetary ball mill acted as a reactor to swiftly and efficiently construct three POPs materials. These materials were evaluated for their adsorption performance and recycling ability in a simulated radioactive iodine vapor environment. Our research offers a viable solution for large-scale POPs material production and practical iodine vapor adsorption applications.

Methods In this study， we successfully synthesized three distinct porous organic polymers （POPs）， namely T-FDA， T-DCM，and T-DCE， utilizing a rapid and efficient ball milling approach， resulting in materials characterized by high specific surface area and abundant pore structure. The synthesis process involved employing tetraphenylmethane as a three-dimensional structure monomer， along with either anhydrous ferric chloride or anhydrous aluminum trichloride as catalysts， and three different crosslinking agents （dimethoxymethane， dichloromethane， and1，2-dichloroethane） to generate the aforementioned POPs materials. The synthesis procedure commenced by introducing the requisite reagents into a 250 mL zirconia grinding jar containing 50 zirconia spheres （Diameter：10 mm）， followed by purging the jar with argon atmosphere before sealing it. Subsequently， the planetary high-energy ball mill was set to a revolution speed and rotation speed of 400 r/min， and the milling process was terminated after 2 hours of operation at room temperature. Subsequently， the iodine vapor adsorption capacity of the porous materials was evaluated. Specifically，0. 2 g of POPs powders were accurately weighed and placed into a pre-weighed small sample bottle.Additionally，2 g of iodine was introduced into another sample bottle. These two bottles were then positioned within a glass container to create a sealed system. This closed system was subsequently transferred into an oven set at 75 ℃， thereby exposing the powder to a saturated iodine vapor environment. At predetermined time intervals （1，2，3，4，5，6，8，12，16，20， and 24 hours）， the sealed container was removed from the oven and rapidly cooled， following which the mass of the sample bottle was accurately determined.

Results and Discussion The resulting porous materials T-FDA， T-DCM， and T-DCE exhibit high specific surface area （398，516， and 753 m²/g respectively）， abundant pore channels， and excellent structural stability. These materials are characterized by a significant presence of micropores （<2 nm） and even ultra-micropores （<0. 7 nm）， alongside a certain proportion of meso⁃pores. The interconnected nature of these pores confers unique advantages to the materials， particularly in the realm of adsorption， notably in the adsorption and separation of gas substances such as radioactive iodine vapor. Based on experimental findings， the iodine adsorption capacity of T-FDA， T-DCM， and T-DCE can reach up to 461%，486%， and 444% respectively.These materials achieve adsorption saturation at the 5th，8th， and 6th hour respectively. Furthermore， to assess the materials' cycling performance， iodine vapor adsorption recycling experiments were conducted five times for each of T-FDA，T-DCM， and T-DCE. The results indicate that the iodine vapor adsorption efficiency of T-FDA only slightly decreases after five cycles of use，with the iodine vapor adsorption amount reducing from 461% initially to 454% after the fifth cycling， representing a decrease of only 1. 5%. For T-DCM， its iodine vapor adsorption capacity decreases from 486% for the first time to 473% for the fifth time，corresponding to a reduction of 2. 7%. Similarly， the iodine vapor adsorption of T-DCE decreases from 444% for the first time to 414% for the fifth time， with a reduction of 6. 8%. Notably， the iodine adsorption performance of the three porous materials only slightly decreases after five cycles of use.

Conclusion In this study， utilizing the ball-milling method， three porous materials（T-FDA， T-DCM， and T-DCE） were synthesized within a remarkably short period of 2 hours. Subsequently， structural analyses and evaluated the iodine vapor adsorption performance of these materials were conducted. Our findings revealed that T-FDA， T-DCM， and T-DCE exhibited specific surface areas of 398，516， and 753 m²/g， respectively. These materials showcased abundant micropores， continuous multi-level pore distribution， and a relatively stable structure. To assess their practical utility， we applied these porous materials to iodine vapor adsorption in a closed system operating at 75 ℃， simulating the vapor evaporation environment of radioactive iodine with standard iodine elements. The experimental outcomes demonstrated impressive iodine adsorption mass fractions of 461%，486%， and 444% for T-FDA， T-DCM， and T-DCE， respectively. Remarkably， these materials exhibited reusability for up to 5cycles with only a marginal decrease in performance （≤6. 8%）. Our results underscore the exceptional iodine vapor adsorption performance of the porous materials synthesized via fast ball milling， suggesting their potential significance in the context of radioactive iodine adsorption. Moreover， the ball milling synthetic method offers advantages including short reaction time， high efficiency， low energy consumption， and avoidance of extensive energy and organic solvent usage， thereby harboring considerable potential for large-scale industrial production.

Keywords：tetraphenylmethane； ball-milling method； porous organic polymer； iodine vapor adsorption