Synthesis And Ion-exchange Properties Of Novel Chalcogenidostannate Microporous Materials

The long-lived radioactive caesium(t^Cs_1/2≈30.2 a)and strontium(t^Sr_1/2≈28.8 a)are two of the main fission products in nuclear waste.They have high radiation intensity,radioactivity and toxicity and can emitβrays and/orγrays during the decay process.They can be easily dissolved in water and exist as Cs⁺and Sr²⁺ions.Through their own strong mobility,Cs⁺and Sr²⁺ions can enter soil,forests,vegetation and then have an access to the food chain,posing a serious threat to the environment and human health.In recent years,metal chalcogenides have been attracted great attention as a variety of highly efficient ion-exchange materials.The soft basic Q（Q=S,Se）atoms in metal chalcogenides have a strong affinity to the lewis acidic metal ions,such as Cs⁺and Sr²⁺here,thus endowing these materials poetential exchange performace toward Cs⁺and Sr²⁺ions in aqueous solution.However,metal sulfide ion-exchangers still have certain drawbacks.（1）Such layered structures usually exhibit a lower mechanical strength and thereby results in possible powdering failure caused by stripping,increasing the pressure drop of the water coming through the column and thus hinder the practical application.（2）Most of them are layered materials so that the broad interlamellar spaces allow for the adsorption of both Cs⁺and Sr²⁺,making it impossible to separate these two elements.（3）The sulfide materials commonly suffer from poor adsorption performance at highly acidic conditions（usually p H<2）that are often applied for practical scenarios in HLLW partitioning.Herein,we propose to construct three-dimensional metal sulfide compounds with a higher mechanical strength,furthermore,the compositional expansion from sulfide to selenide would probably endow the framework a higher resistance to acid.This thesis is focused on synthesizing novel tin based chalcogenide microporous materials and exploring their application in adsorption and separation properties with Cs⁺and Sr²⁺ions.The contents of each chapter are summarized as follows:1.Solvothermal reaction of Na₂S?9H₂O,Sn,S,and Zn Cl₂ were in methanol led to an open framework quaternary Na-Zn-Sn-S compound,Na₅Zn_3.5Sn_3.5S₁₃?6H₂O（Zn Sn S-1）,which exhibits an effective ion exchange performance for Sr²⁺ion.According to Langmuir-Freundlich isotherm,the maximum exchange capacity q_m^Sr is124.2 mg g^-1 and ranks ahead of those of all the reported metal sulfide Sr²⁺adsorbents.Besides,high exchange activity is observed over a broad p H range of 2.5-13,and the Sr²⁺in the exchanged product can be conveniently eluted by concentrated KCl solution,highlighting the recycling potential of the exchanger for practical application.2.Deep eutectic solvents composed of Ch Cl-urea and propyltrimethylammonium bromide-urea were adopted for the preparation of two alkylammonium-templated layered Sn-Se compounds,[（CH₃）₃N（CH₂）₂OH]₂[Sn₃Se₇]·H₂O 1 and[（CH₃）₃N（CH₂）₂CH₃]₂[Sn₃Se₇]2.The choline cation and propyltrimethylammonium cation are located in the interlammler space,acting as structral direction agents and charge balancing agents.Punching the inorganic sheet with pores can lead to a lattice of quantum antidots.Compared to the bulk Sn Se₂,the bandgap of the material shows a clear blue-shift tendency,resulting in a remarkable reversibly thermochromic property.However,the large size and complex configuration of the long-chain organic amines and the strong hydrogen bonds lead to poor mobility,furthermore,hingdering the ion-exchange process with Cs⁺and Sr²⁺.3.Silver cation Ag⁺was introduced as additional metallic source to the of deep eutectic solvothermal synthesis of Sn-Se,giving rise to a novel open-framework silver selenidostannate[NH₃CH₃]_0.5[NH₂（CH₃）₂]_0.25Ag_1.25Sn Se₃（Ag Sn Se-1）.The alkylammonium cations play a significant templating role in construction appropriate microporous environments.Ag Sn Se-1 exhibits a fast and selective ion exchange toward Cs⁺against Sr²⁺with an outstanding SF_Cs/Sr of～121.4 for the separation of mixed Cs⁺/Sr²⁺.The Ag Sn Se-1-filled ion-exchange column shows an efficient separation effect for Cs⁺and Sr²⁺ions,with removal rates of～99.9%and 0±5.5%,respectively.Besides,Ag Sn Se-1 owns an excellent p H stability（1-12）and radiation resistance.Cs⁺ions in the exchanged product can be easily eluted for recycling use of the exchanger.