Machine-Learning-Assisted Material Discovery of Pyridine-Based Polymers for Efficient Removal of ReO4.

Efficient capture of 99TcO4- is the focus in nuclear waste management. For laboratory operation, ReO4- is used as a nonradioactive alternative to 99TcO4- to develop high-performance adsorbents for the treatment. However, the traditional design of new adsorbents is primarily driven by the chemical intuition of scientists and experimental methods, which are inefficient. Herein, a machine learning (ML)-assisted material genome approach (MGA) is proposed to precisely design high-efficiency adsorbents. ML models were developed to accurately predict adsorption capacity from adsorbent structures and solvent environment, thus predicting and screening the 2450 virtual pyridine polymers obtained by MGA, and it was found that halogen functionalization can enhance its adsorption efficiency. Two halogenated functional pyridine polymers (F-C-CTF and Cl-C-CTF) predicted by this approach were synthesized that exhibited excellent acid/alkali resistance and selectivity for ReO4-. The adsorption capacity reached 940.13 (F-C-CTF) and 732.74 mg g-1 (Cl-C-CTF), which were better than those of most reported adsorbents. The adsorption mechanism is comprehensively elucidated by experiment and density functional theory calculation, showing that halogen functionalization can form halogen-bonding interactions with 99TcO4-, which further justified the theoretical plausibility of the screening results. Our findings demonstrate that ML-assisted MGA represents a paradigm shift for next-generation adsorbent design.

Aliquat 336 in Solvent Extraction Chemistry of Metallic ReO4- Anions.

A study of the liquid-liquid extraction of ReO4- anions from hydrochloric acid solutions using the ionic liquid Aliquat 336 (QCl: trialkyl(C8-C10)methylammonium chloride) via the well-known method of slope analysis along with the determination of the process parameters is presented. This study employs CCl4, CHCl3 and C6H12 as diluents. This study was carried out at room temperature (22 ± 2) °C and an aqueous/organic volumetric ratio of unity. The ligand effect on the complexation properties of ReO4- is quantitatively assessed in different organic media. The organic extract in chloroform media is examined through 1H, 13C and 15N NMR analysis as well as the HRMS technique and UV-Vis spectroscopy in order to view the anion exchange and ligand coordination in the organic phase solution. Final conclusions are given highlighting the role of the molecular diluent in complexation processes and selectivity involving ionic liquid ligands and various metal s-, p-, d- and f-cations. ReO4- ions have shown one of the best solvent extraction behaviors compared to other ions. For instance, the Aliquat 336 derivative bearing Cl- functions shows strongly enhanced extraction as well as pronounced separation abilities towards ReO4-.

Synthesis and performance of guanidinium-based cationic organic polymer for the efficient removal of TcO4-/ReO4.

Cationic organic polymers have found relatively extensive utility for TcO4-/ReO4- removal, but the harsh preparation conditions constrain their practical application. The bifunctional guanidinium-based cationic organic polymer (GBCOP) was successfully and facilely synthesized in benign conditions within 1 h. Batch experiments showed that GBCOP exhibited rapid removal kinetics (1 min, >98.0%) and a substantial removal capacity of 536.8 mg/g for ReO4-. Even in 1000-fold co-existing NO3- anions, the removal efficiency of GBCOP for ReO4- was 74.0%, indicating its good selectivity. Moreover, GBCOP had high removal efficiencies for ReO4- across a wide pH (3.0-10.0) range and presented remarkable stability under the conditions of strong acid and base. GBCOP could be reused four times while removing 80.8% ReO4- from simulated Hanford wastewater. SEM and XPS results revealed that the mechanism of ReO4- removal involved Cl- ion exchange within the channels of GBCOP. Theoretical calculation results supported that existing the strong electrostatic interaction between guanidinium and ReO4-. This dual-function GBCOP material is cost-effective and holds significant potential for large-scale preparation, making it a promising solution for TcO4- removal from nuclear wastewater.

Alkyl modified cationic COFs for preferential trapping of charge dispersed perrhenate: Synergistic hydrophobicity and anion-recognition effects.

Charge dispersed oxoanionic pollutants (such as TcO4- and ReO4-) with low hydrophilicity are typically difficult to be preferentially extracted. Recently, cationic covalent organic frameworks (COFs) have received considerable attention for anions trapping. Two cationic COFs, denoted as Tp-S and Tp-D, were synthesized by incorporating ethyl and cyclic alkylated diquats into 2,2'-bipyridine-based COF. A synergistic effect of hydrophobic channel and anion-recognition sites were achieved by branched chains, which effectively surmounted the Hofmeister bias. Both Tp-S and Tp-D exhibited raising removal performance for surrogate ReO4- at high acidity with adsorption capacities of 435.6 and 291.4 mg g-1, respectively. Obvious variations caused by side chains were displayed in microstructures and adsorption performance. Specially, compared with Tp-D, Tp-S demonstrated desirable priority in uptake capacity and selectivity. In a real-scenario experiment, Tp-S could remove 72.8 % of ReO4- in a simulated Hanford LAW stream, which was attributed to the spatial effects and charge distribution arising from the open and flexible side chains of Tp-S. Otherwise, the rigid cyclic chains endowed pyridine-base Tp-D material an unprecedented alkaline stability. Spectra and theoretical calculations revealed a mechanism of preferential capture based on electrostatic interaction and hydrogen bonding between charge dispersed ReO4-/TcO4- and Tp-S/Tp-D. This work provides an innovative perspective to tailored materials for the treatment of oxoanionic contaminants.

Efficient removal of perrhenate/pertechnetate by a pyridinium-based porous polymer.

The extraction of 99TcO4- from radioactive effluents is extremely crucial for the purposes of nuclear disposal and environmental remediation. Herein, utilizing a facile and low-cost synthesis method, we report a pyridinium-based cationic polymer network, CPP-Cl, with impressive adsorption performance and ultrafast adsorption kinetics towards ReO4-. The structure featuring highly density of charged pyridinium units was synthesized, making it an effective adsorbent for capturing ReO4-. The material showed fast ReO4- adsorption kinetics reaching adsorption equilibrium within 30 s, an excellent capture capability of 1069.7 mg/g, and exceptional separation efficiency of 94.3% for removing 1000 ppm ReO4-. Furthermore, it possessed excellent reusability in multiple sorption/desorption trials and good uptake capacity within a widely ranging pH values. It is noteworthy that the extraction efficiency of CPP-Cl for ReO4- from simulated nuclear waste can be up to 94.2%. The favorable performance of the material in multiple tests revealed that CPP-Cl has tremendous potential as a high-efficiency sorbent for capturing 99TcO4-/ReO4- in complex nuclear associated environmental systems.

Synthesis of cationic polymer decorated with halogen for highly efficient trapping 99TcO4-/ReO4.

The elimination of anion is of great importance from radioactive nuclear waste containing 99TcO4- by rationally designing anion-scavenging materials with high density of charge and more accessible adsorption sites. Herein, a tailor-made cationic organic polymer with donor-acceptor (D-A) structure, namely TrDCPN, was successfully synthesized by rationally modifying the benzimidazole unit for efficient trapping the perrhenate (ReO4-) as a 99Tc surrogate. Systematic control of the skeleton affect enables the material to integrate a variety of features, surmounting the long-term challenge of 99TcO4-/ReO4- remediation under extreme conditions of high acid/base and high ionic strength. Furthermore, the TrDCPN shows excellent affinity toward ReO4- in the existence of large excess of competitive anions (SO42-, NO3- and PO43-etc.) as well as promising reusability for trapping ReO4-. The excellent stability and separation were derived from the introduction of large conjugated modules, triazine core and hydrophobic. More importantly, the synthetic cationic organic polymer with D-A feature was first proved that the introduction of halogen can effectively enhance the backbone charge, and increase the adsorption capacity by synergy of ion exchange, electrostatic interaction and δ hole-anion interaction. The adsorption capacity of TrDCPN can be up to 420.3 mg/g and reach equilibrium within 20 min. It is noteworthy that TrDCPN successfully immobilizes ReO4- from simulated Hanford waste with a high separation efficiency of 93 %, providing a new paradigm for material design to dispose of the problem of radioactive pollutants in the environment.

Ultrafast and selective separation of 99mTc from molybdenum matrix using DBDGA deliberately tailored macrocyclic crown-ethers.

Technetium-99m (99mTc) is an important medical radionuclide. Due to the crisis in supply of molybdenum-99 (99Mo), production of 99mTc directly via the 100Mo (p, 2 n) reaction by cyclotron was proposed. In this process, the most critical challenge is to rapidly and efficiently separate 99mTc from high concentration of molybdenum. In this work, a novel ligand, bis(N,N-dibutyldiglycolamide)dibenzo-18-crown-6 (BisDBDGA-DB18C6) was successfully synthesized and used for extraction of TcO4- /ReO4- from molybdenum. The results demonstrated that BisDBDGA-DB18C6 expressed excellent selectivity for TcO4- with a high separation factor of 1.6 × 105 against Mo, a fast extraction kinetic (within 45 s), and a high extraction capacity of 211 mmol ReO4- (99TcO4-)/per mole of extractant. The extraction mechanism was proposed as a co-interaction of macrocyclic crown ether and N,N-dibutyldiglycolamide group through slope analysis, FT-IR, ESI-MS, 1H NMR titration and theory calculations. Importantly, 99Tc in the organic phase can be quantitatively (> 99%) and easily back-extracted using deionized water, which can be directly used for medical applications.

Olefin-linked cationic covalent organic frameworks for efficient extraction of ReO4-/99TcO4.

Efficient extraction of radioactive 99TcO4- from strong acid/base solutions by porous adsorbents is extremely desirable but remains a great challenge. To overcome the challenge, here we report the first example of an olefin-linked cationic covalent organic framework (COF) named BDBI-TMT with excellent acid, base and radiation stability is synthesized by integrating robust imidazolium salt-based linkers with triazine building blocks. BDBI-TMT shows an ultra-fast adsorption kinetics (equilibrium is reached within 1 min) and an excellent ReO4- (a non-radioactive surrogate of 99TcO4-) capture capacity of 726 mg g-1, which can be attributed to the abundance of precisely tailored imidazolium salt-based units on the highly accessible pore walls of the ordered pore channels. Furthermore, the formation of the highly conjugated bulky alkyl skeleton enhances the hydrophobicity of BDBI-TMT, which significantly improves not only the affinity toward ReO4-/99TcO4- but also the chemical stability, allowing selective and reversible extraction of ReO4-/99TcO4- even under extreme conditions. This work demonstrates the great potential of olefin-linked cationic COFs for ReO4-/99TcO4- extraction, providing a new avenue to construct high-performance porous adsorbents for radionuclide remediation.

Ultra-stable 3D pyridinium salt-based polymeric network nanotrap for selective 99TcO4-/ReO4- capture via hydrophobic and steric engineering.

Selective capture of radioactive 99TcO4- from highly alkaline nuclear waste is highly desirable for environmental remediation and waste disposal. However, the combined features of adsorbents with excellent chemical stability and high capture selectivity for 99TcO4- have not yet been achieved. Herein, we report an ultra-stable 3D pyridinium salt-based polymeric network (TMP-TBPM) nanotrap with remarkable radiation, acid and base stability for selective capture of ReO4- via hydrophobic engineering and steric hindrance, a non-radioactive surrogate of 99TcO4-. The batch capture experiments show that TMP-TBPM has high capture capacity (918.7 mg g-1) and fast sorption kinetics (94.3 % removal in 2 min), which can be attributed to the high density of pyridinium salt-based units on the highly accessible pore channels of 3D interconnected low-density skeleton. In addition, the introduction of abundant alkyl and tetraphenylmethane units into the 3D framework not only greatly enhanced the hydrophobicity and stability of TMP-TBPM, but also significantly improved the affinity toward 99TcO4-/ReO4-, enabling reversible and selective capture of 99TcO4-/ReO4- even under highly alkaline conditions. This study exhibits the great potential of 3D pyridinium salt-based polymeric network nanotrap for 99TcO4-/ReO4- capture from highly alkaline nuclear waste, providing a new strategy to construct high-performance cationic polymeric sorbents for radioactive wastewater treatment.

Halogen microregulation in metal-organic frameworks for enhanced adsorption performance of ReO4-/TcO4.

Effective and selective removal of 99TcO4-, one of the most nuisance radionuclides in nuclear waste, is highly desirable but remains a significant challenge. Herein, two isostructural MOFs, NCU-3-X (X = Cl, Br) were constructed by ZnX2 coordinated to nitrogen-containing neutral ligand tri(4-(1H-imidazole-1-l) phenyl) amine for efficient adsorption ReO4-/TcO4-. Owning to the twofold interpenetrating structure, both of them exhibit strong alkaline resistance. Consequently, NCU-3-Br exhibited superior adsorption performances with a maximum capacity as high as 483 mg/g, which is 2.23 times larger than that of NCU-3-Cl. The primary reasons accounting for the enhanced adsorption performances of NCU-3-Br are that compared to chlorine atoms, the smaller electronegativity of bromine atoms as halogen bonds donor can facilitate the formation of σ-holes, enhance positively charged skeleton, and reduce the adsorption energy associated with ReO4-/TcO4-. In addition, the one-dimensional hydrophobic channels in the NCU-3-Br framework enable NCU-3-Br to have highly selective toward ReO4-, which has a low relative charge density against interfering ions. The SRS simulation removal experiment further confirmed the excellent adsorption capacity of NCU-3-Br to ReO4-/TcO4-. This work illustrated that the halogenated new strategy incorporated different halogen atoms into MOF skeletons can dramatically modulate the adsorption performances for ReO4-/TcO4-.

CTAB assisted evaporation-induced self-assembly to construct imidazolium-based hierarchical porous covalent organic polymers for ReO4-/TcO4- removal.

Evaporation-induced self-assembly method (EISA) was a facile and reliable method to synthesize porous materials. Herein, we report a kind of hierarchical porous ionic liquid covalent organic polymers (HPnDNH2) under cetyltrimethylammonium bromide (CTAB) assisted by EISA for ReO4-/TcO4- removal. Unlike covalent organic frameworks (COFs), which usually needed to be prepared in a closed environment or with a long reaction time, HPnDNH2 in this study was prepared within 1 h in an open environment. It was worth noting that CTAB not only served as a soft template for forming pore, but also induced ordered structure, which was verified by SEM, TEM, and Gas sorption. Benefit from its hierarchical pore structure, HPnDNH2 exhibited higher adsorption capacity (690.0 mg g-1 for HP1DNH2 and 808.7 mg g-1 for HP1.5DNH2) and faster kinetics for ReO4-/TcO4- than 1DNH2 (without employing CTAB). Additionally, the material used to remove TcO4- from alkaline nuclear waste was seldom reported, because combining features of alkali resistance and high uptake selectivity was not easy to achieve. In this study, in the case of HP1DNH2, it displayed outstanding adsorption efficiency toward aqueous ReO4-/TcO4- in 1 mol L-1 NaOH solution (92%) and simulated Savannah River Site High-level waste (SRS HLW) melter recycle stream (98%), which could be a potentially excellent nuclear waste adsorbing material.

Aminomethylpyridine isomers functionalized cellulose microspheres for TcO4-/ReO4- uptake: Structure-properties relationship and their application in different aquatic systems.

Technetium-99 (99Tc) is a long-lived radioactive nuclide that poses great threat to environment, hence selective removal of 99Tc from aquatic system is always an issue. Aminomethylpyridine (AMP) equipped with pyridine and amino, is a promising receptor for TcO4- and its surrogate ReO4-, thus it is of interest to explore and understand the structure-properties relationship of ReO4- adsorption related to n-AMP structure that differ in amino methyl position. In this work, three n-AMP functionalized cellulose microspheres (n-AMPR, n = 2, 3, 4) were synthesized and employed for TcO4-/ReO4- uptake. The effect of aminomethyl position on adsorption properties of n-AMPR for ReO4- were investigated and compared. Adsorption kinetics and adsorption isotherm showed that adsorption speed and adsorption capacity were in order of 3-AMPR > 2-AMPR > 4-AMPR. DFT calculation verified that the adsorption of ReO4- by n-AMPR was attributed to electrostatic interaction and hydrogen bonding interaction, the order of adsorption abilities of n-AMPR was due to that steric effect and hydrogen bond collaborated in stabilizing n-AMPR-ReO4- complexes. The column experiments demonstrated that 3-AMPR can be selectively remove ReO4- from simulated groundwater. More importantly, 99Tc column experiments showed that 3-AMPR had a better ability for actual radioactive TcO4-.

An alkali-resistant metal-organic framework as halogen bond donor for efficient and selective removing of ReO4-/TcO4.

99Tc is one of the most problematic nuclear fuel products due to its long half-life and high environmental mobility. Direct removal of TcO4- from the highly alkaline solution of nuclear fuel is a serious and challenging environmental issue. In this work, the first efficient synthetic approach introducing halogens into a two-dimensional metal-organic framework, named Mn-MOF, is established using MnCl2·4H2O coordinating with neutral nitrogen-donor ligand, showing ultrahigh stability in alkaline aqueous even under 1 M NaOH. The luxuriant Mn-Cl bonds and ordered hydrophobic pore channels enable the Mn-MOF to have an efficient adsorption capacity for ReO4- with a large capacity (403 mg g-1), which is higher than most MOF adsorbents. More importantly, the Mn-MOF shows an excellent selectivity toward ReO4- in high-density competitive anions, such as NO3- and SO42-. Moreover, the outstanding performance of Mn-MOF in removing ReO4- endowed it successfully separated ReO4- from the simulated Savannah River Site (SRS) high-level waste (HLW) stream with high removal of 66.84% at the phase ratio of 10. The adsorption mechanism is further demonstrated by FT-IR, XPS analysis, and DFT calculation, showing that the ReO4- can selectively interact with Mn-Cl bonds and imidazole groups, forming unique halogen bonds Cl-O-Re, and a series of hydrogen bonds, respectively. This work suggests a new approach to the removal of TcO4- from nuclear fuel.

Highly Selective Adsorption of 99TcO4-/ReO4- by a Novel Polyamide-Functionalized Polyacrylamide Polymer Material.

The treatment of radioactive wastewater is one of the major problems in the current research. With the development of nuclear energy, the efficient removal of 99TcO4- in radioactive wastewater has attracted the attention of countries all over the world. In this study, a novel functional polyamide polymer p-(Amide)-PAM was synthesized by the two-step method. The experimental results show that p-(Amide)-PAM has good adsorptive properties for 99TcO4-/ReO4- and has good selectivity in the nitric acid system. The kinetics of the reaction of p-(Amide)-PAM with 99TcO4-/ReO4- was studied. The results show that p-(Amide)-PAM has a fast adsorption rate for 99TcO4-/ReO4-, the saturated adsorption capacity reaches 346.02 mg/g, and the material has good reusability. This new polyamide-functionalized polyacrylamide polymer material has good application prospects in the removal of 99TcO4- from radioactive wastewater.

Radiation synthesis of ionic liquid-functionalized silica-based adsorbents: a preliminary investigation on its application for removal of ReO4- as an analog for TcO4.

The decontamination of radioactive TcO4- from nuclear wastes is becoming increasingly crucial for spent nuclear fuel reprocessing and environmental remediation. In this work, a series of ionic liquid-immobilized silica-based adsorbents (SVIL-Cn, n = 1, 4, 8) were newly synthesized using the radiation-induced grafting of 4-vinylbenzyl chloride onto silanized silica and subsequent functionalization with 1-methylimidazole, 1-butylimidazole, or 1-octylimidazole. The synthesis conditions such as the solvent, absorbed dose, and monomer concentration were investigated in detail, and the resulting adsorbents were characterized by elemental analysis, FT-IR, SEM, and TGA. In batch experiments, the adsorbents exhibited a high ReO4- (a nonradioactive surrogate of TcO4-) removal efficiency over a wide pH range (3 ~ 8), and SVIL-C1 showed a maximum adsorption capacity of 70.62 mg g-1 towards ReO4-. In addition, their adsorption performance barely changed after 800 kGy radiation. The column experiments for treating simulated radioactive wastewater showed that the SVIL-Cn adsorbents could selectively separate TcO4-/ReO4- from a variety of fission products, and they could be recycled four times with negligible capacity loss. Lastly, XPS and FT-IR analysis confirmed that the adsorption proceeded via an ion-exchange mechanism. The results showed that these adsorbents are suitable for the efficient removal of TcO4-/ReO4- from radioactive wastewater with complex compositions.

Selective identification and separation of ReO4- by biomimetic flexible temperature-sensitive imprinted composite membranes.

A new type of temperature-sensitive imprinted composite membranes(ICMs) was developed. Poly N,N-diethylacrylamide (DEA) blocks, as temperature-sensitive polymer, were grafted onto the substrate of the imprinted polymer separation layer to endow membranes with better adsorption effect. The comprehensive properties of the imprinted composite membranes were adequately tested and evaluated in detail. Results showed that ReO4- -ICMs (Re-ICMs) with temperature-sensitive recognition sites could adjust the structure of the imprinted holes at different temperatures, which presented excellent performance in the selective separation and purification of ReO4-. The prepared Re-ICMs exhibit the maximum adsorption capacity of 0.1639 mmol/g at 35 °C with the equilibrium adsorption time of 2 h. After ten adsorption/desorption cycles, Re-ICMs could still maintain 73.5% of the original adsorption capacity, the separation degree of ReO4-/MnO4- was only reduced from the initial 24.5 to 15.9, and the desorption ratio dropped from 80.4% to 68.4%, indicating that Re-ICMs have excellent adsorption and separation performance and reusability.

Aluminum-based metal-organic frameworks (CAU-1) highly efficient UO22+ and TcO4- ions immobilization from aqueous solution.

In this research, an Al-based metal-organic framework (MOFs), CAU-1 was prepared through complexation between 2-aminoterephthalic acid and Al (III) by solvothermal approach, and simple operation and cost-effective synthetic route. The objective was to immobilize the typical positive/negative radionuclide ions (UO22+/TcO4-) in aqueous solution. The synthesized CAU-1 was characterized by XRD, FT-IR, TGA, FESEM, TEM-SAED, pHpzc, XPS and N2 physisorption analysis. The structure of CAU-1 possessed excellent thermostability, rich functional groups (‒NH2 and ‒OH groups), as well as large surface area (1636.3 m2/g) and the micropore volume (0.51 m3/g). Furthermore, batch experiments demonstrated that CAU-1 with superior adsorption capacity was 648.37 (UO22+) mg/g and 692.33 (ReO4-) mg/g calculating from Langmuir isotherm model, respectively. Thermodynamic investigation showed the adsorption process was endothermic and spontaneous. In addition, the adsorption mechanism of ReO4- ion onto CAU-1 could be electrostatic attraction and chelation effect, while for UO22+ ion, was mainly chelation effect induced by nitrogen-containing and oxygen-containing functional groups. Hence, the inexpensive and high-capacity CAU-1 could be considered as a practical material for sequestrations of radioactive pollutants from water environment.

Efficient capture of ReO4- on magnetic amine-functionalized MIL-101(Cr): Revealing from selectivity to mechanism.

The efficient decontamination of pertechnetate (99TcO4-) is an essential task for managing radioactive 99Tc in nuclear wastes. Perrhenate, (ReO4-), as a nonradioactive analog, exhibits almost identical physicochemical properties as 99TcO4-. Herein, a novel magnetic amine-functionalized MIL-101(Cr) (NH2-MIL-101(Cr)@Fe3O4) was prepared and used to efficiently remove ReO4- from solution for the facile magnetic separation. A series of environmental parameters were considered to investigate the adsorption performance of NH2-MIL-101(Cr)@Fe3O4. Experimental results suggested that NH2-MIL-101(Cr)@Fe3O4 has reached a satisfied adsorption capacity (~401 mg/g) and a very fast adsorption kinetics at pH 7.0. The selectivity for ReO4- was maintained even in the presence of interfering anions with relatively high concentrations. ReO4- were mainly captured by N-donor sites of the surface-decorated amine via complexation and were trapped in the cavities of modified MIL-101(Cr). NH2-MIL-101(Cr)@Fe3O4 exhibits satisfactory adsorption performance for ReO4- and can be conveniently separated from wastewaters after adsorption.