Rapid And Rational Synthesis Of Imidazole-based Cationic Polymers For Technetium (Rhenium) Adsorption

Energetically developing clean energy is of great practical and strategic significance.To date,the nuclear power is an important way to achieve low-carbon power generation.However,the potential harm of radioactive spent fuel and its fission products cannot be ignored.⁹⁹Tc is one of the main fission products of spent fuel.Due to its long half-life,high mobility and high volatility,the efficient removal of Tc O₄^-from the environment is an ongoing challenge.Radioactive Tc O₄^-is difficult to study in the laboratory,so Re O₄^-with similar chemical properties is often used as a substitute research object.The mainly existence form of Tc O₄^-is anion,hence cationic materials with positive charges show an excellent performance for technetium separation.However,the long preparation time,harsh preparation conditions and low reusable utilization of cationic materials remain the focus of the research in this area.In this paper,six kinds of imidazolyl cationic polymer adsorption materials with different morphologies were rapidly prepared via grinding-induced solvent-free synthesis strategy,evaporation-induced self-assembly strategy,thiol-ene click chemical strategy.In addition,the ability of them to remove Tc O₄^-/Re O₄^-was also studied.The details are as follows:（1）First,a kind of cationic polymer 1PhTNH₂ with Schiff base bond was prepared within 1 h by grinding-induced solvent-free synthesis strategy,which was carried out using the well mixed three-dimensional sphere ionic liquid polymers PhTNH₂IM IL and p-Phthalaldehyde.After ammonia aldehyde condensation reaction,the TEM image of the product 1PhTNH₂ partly showed a similar structure with COFs.The synthesis method with simple to operate,green and environmentally friendly,not only overcomes the shortcomings of the long preparation time,but also barely affected by H₂O and air.Besides,the reaction rate is fast and the yield of the product is high.Benefit from the two-dimensional hexagonal structure,which is similar with SBA-15,1PhTNH₂ gains a high structural stability and hydrophobicity,and overcome the disadvantage of ionic liquid polymers PhTNH₂IM IL being easily lost in aqueous solutions.The maximum adsorption capacity for 1PhTNH₂ towards Re O₄^-was up to 469.6 mg g^-1,which was higher than that of three-dimensional spherical ionic liquid polymers PhTNH₂IM IL.1PhTNH₂ had a fast adsorption kinetics,and reached adsorption equilibrium within 30min.Moreover,after 5 cycles,the adsorption and recovery rates for 1PhTNH₂ remained stable at more than 90%.Discussed by FTIR and XPS,we deduced that the effect of ion exchange and chelation both due to electrostatic interaction can effectively improve the adsorption efficiency of 1PhTNH₂ at p H 4.The above results fully showed that the grinding-induced solvent-free synthesis strategy is a fast and efficient adsorbent synthesis method for preparing cationic polymer,which can be used as adsorption separation study for Tc O₄^-/Re O₄^-.（2）In view of the expensive raw materials 1,3,5-tris（bromomethyl）benzene and the unobvious adsorption advantages of 1PhTNH₂,a series of cationic polymer n DNH₂and n PhDNH₂ were prepared within 1 h by evaporation-induced self-assembly method（EISA）.The cheap 3-chloropropylamine hydrochloride and 1,4-p-dichlorobenzyl were selected as raw materials to synthesize ionic liquids DNH₂IM IL and PhDNH₂IM IL by quaternary ammonium reaction with 1-aminopropylimidazole.Then the two above imidazolyl ionic liquids were respectively dissolve in 1 m L Me OH with p-Phthalaldehyde.Finally,n DNH₂ and n PhDNH₂ successfully self-assembled within 1 h by after solvent evaporation.In this work,the amount of organic solvent was just 1 m L,which is in line with the development concept of green chemistry.Moreover,the evaporation-induced self-assembly method with the advantage of assembling hundreds of alternating organic/inorganic layers in a few seconds,could accelerate the formation of Schiff base bonds and achieve an efficient and reasonable reduction in energy consumption.The maximum adsorption capacity of 1DNH₂ and 1PhDNH₂ fitted by Langmuir model were up to 598.2 and 525.9 mg g^-1 respectively,which were higher than 1PhTNH₂(469.6 mg g^-1).It indicated that imidazole ionic liquid repeating units with less steric hindrance and higher density on an adsorption material were more conducive to the improvement of adsorption capacity.FTIR and XPS were used to characterize 1.2DNH₂ before and after adsorption,and it was proved that the effect of ion exchange and chelation both due to electrostatic interaction were the internal mechanisms for effectively improving the adsorption efficiency.（3）Based on the slow adsorption kinetics（4 h）of 1DNH₂,we report a kind of hierarchical porous ionic liquid covalent organic polymers（HPn DNH₂）under cetyltrimethyl ammonium bromide（CTAB）assisted by EISA for Re O₄^-/Tc O₄^-removal.HPn DNH₂ in this study was prepared within 1 h in an open environment.Benefit from its hierarchical pore structure,HPn DNH₂ exhibited high adsorption capacity(690.0 mg g^-1 for HP1DNH₂ and 808.7 mg g^-1 for HP1.5DNH₂),and faster kinetics of HP1DNH₂than 1DNH₂.Due to the fast mass transfer rate,the adsorption equilibrium time was shortened from 4 h to 1 h.Additionally,HP1DNH₂ displayed outstanding adsorption efficiency toward simulated waste.The satisfying removal rate of Re O₄^-on HP1DNH₂at a solid/liquid ratio of 20 mg m L^-1 was 98%,which indicated that HP1DNH₂ could be a potentially excellent nuclear waste adsorbing material.In addition,the adsorption mechanism of Re O₄^-on HP1DNH₂ was discussed in detail by FTIR,XPS and DFT theoretical calculations under p H=4 HCl,p H=11 NH₃·H₂O and 1 mol L^-1 Na OH.It was further implied that anion exchange due to electrostatic attraction between Re O₄^-and imidazole group in HP1DNH₂ structures,and chelation between the nitrogen atom in Schiff’s base groups and the oxygen atoms in Re-O,were considered to play the important role in successfully adsorbing Re O₄^-on the surface of HP1DNH₂.This work provides a strategy to design new hierarchical porous materials for the removal of Tc O₄^-/Re O₄^-in alkaline nuclear waste.（4）In order to improve the adsorption efficiency of 1PhDNH₂,which could not achieve through the CTAB assisted EISA method,we design a kind of cationic polymerized microsphere B1PhDNH₂-1TMB,which was prepared within 1 h by F127/TMB-mediated EISA method.The removal percentage of B1PhDNH₂-1TMB towards Re O₄^-at a solid/liquid ratio of 10 mg m L^-1 were up to 97%in 1 mol L^-1 Na OH and 74%in 1 mol L^-1 HCl,which indicated more exceptional Re O₄^-capture ability than HP1DNH₂（92%and 60%）.Moreover,removal percentage on B1PhDNH₂-1TMB at a solid/liquid ratio of 5 mg m L^-1 was up to 97%in 1 mol L^-1 Na OH,which was also better than HP1DNH₂（83%）.Comparing the adsorption performance between irregularly shaped solid 1PhDNH₂ with B1PhDNH₂-1TMB,the maximum adsorption capacity increased from 525.92 mg g^-1 to 584.78 mg g^-1,and the adsorption equilibrium time was shortened from 20 min to 30 s.These experimental results showed that the spherical morphology could increase the specific surface area in contact with Re O₄^-,and was more conducive to adsorption.（5）Due to the powder adsorption materials was easy to be compacted in practical application,the resistance pressure of the tightly packed powder was large,and the water flux was small,resulting in limited adsorption performance.We designed a functionalize graphene oxide flexible membrane（GO-C₆）using thiol-ene click reaction,where C=C bond of graphene network can further to connect to the imidazolyl ionic liquids.Owing to preparing GO-C₆ membrane based on thiol-ene click chemical strategy,there were several typical advantages of the method,such as convenient operation,mild reaction conditions,rapid reaction rate,high atomic utilization and so on.The maximum adsorption capacity of GO-C₆ at p H 3,p H 4,p H 6 and p H 10 was evaluated as 269.17 mg g^-1,246.36 mg g^-1,252.55 mg g^-1,and 238.67 mg g^-1,respectively.GO-C₆ membrane exhibited excellent adsorption performance for Re O₄^-at a wide p H range and a large water flux.In addition,after three experimental cycles,GO-C₆ membrane still maintained the same adsorption performance compared with the original membrane.The good reusability indicated that GO-C₆ could be an economic and efficient membrane material for wastewater,and offered the basic data for the practical application.