Deep Eutectic Solvothermal Synthesis Of Tin-based Chalcogenides And Ion Exchange Properties

Metal chalcogenides have diverse structural characteristics and special physicochemical properties,and can be widely used in photoelectric catalysis,fast ion conduction,luminescence and nonlinear optics.Among them,metal chalcogenides as ion exchange materials have excellent performance in the removal of harmful metal ions such as radioactivity,and gradually receives attention.On the one hand,the soft basic S atom in metal chalcogenides has a good affinity for Lewis soft acidic ions(such as Cs⁺,Sr²⁺,Ba²⁺ions).On the other hand,metal chalcogenide ion exchange materials exhibit flexible coordination modes,good framework flexibility,and construct windows and channels with different sizes and shapes,providing a convenient transport pathway for the exchange of ions.However,the adsorption capacity of the currently reported metal chalcogenide ion exchange materials needs to be improved.For example,the exchange capacity of Sr²⁺ions is generally at the level of 20-100 mg g^-1,which is significantly lower than that of oxide materials such as titanium silicates(such as DTS-type titanosilicates can reach 180 mg g^-1).In addition,the molecular-level ion exchange mechanism is not well studied because the material does not easily maintain good crystallinity after exchange,and the effect of the chemical environment on the adsorption selectivity is unclear.Therefore,designing and constructing stable chalcogenide frameworks with multifunctional tunnels or voids filled with mobile cations have become an important part of the research on chalcogenide ion exchange materials.The traditional synthesis methods of metal chalcogenides are electrochemical method,high temperature solid phase method,reactive molten salt method,hydro(solvo)thermal method.In comparison,deep eutectic solvothermal technology have the advantages of greenness,safety and low cost,and has gradually become one of the synthetic methods that has attracted much attention.Deep eutectic solvents(DESs)are composed of different organic amine salts(such as halides,etc.)and hydrogen bond donors(HBDs,such as carboxylic acids,amides or polyols)in specific proportions.The mixture can act as a solvent or structure directing agent.It has the characteristics of fast mass transfer,strong ionicity and low vapor pressure,and can effectively promote the dissolution,reaction and crystallization of the reaction raw materials.In view of this,the main content of this thesis is the synthesis of chalcogenide crystals by deep eutectic solvothermal technique.The ammonium or organic amines contained in DESs or generated by in situ decomposition are used as structure-directing agents to promote the coordination mode-rich Sn(or the simultaneous introduction of heterometals such as Zn,Cd)and the chalcogen Q(Q=S,Se)to assemble new Sn-Q and M-Sn-Q materials.They have isolated clusters,one-dimensional chains,two-dimensional sheets and three-dimensional microporous framework structures,and we have deeply studied the ion exchange properties and structure-activity relationship of such compounds.The details are as follows:1.A two-dimensional layered tin sulfide crystal material[CH₃CH₂NH₃]_1.2[NH₂CH₂CH₂NH₃]_0.8Sn₃S₇·0.1C₃H₆N₂O(Sn S-1)with honeycomb structure was synthesized using DES composed of ethylamine hydrochloride and ethylene urea as the reaction medium.The[Sn₃S₇]_n^2n-anion sheets of Sn S-1 are formed by{Sn₃S₁₀}clusters connected by edge-sharing,with a hexagonal window of size?11.02×13.12?~2,and the sheets are arranged in parallel stacking in ABAB form with uniform interlayers distribution,packing of ethylamine and ethylenediamine cations.Preliminary ion exchange experiments show that Sn S-1 has excellent adsorption properties for four ions of Sr²⁺,Ba²⁺,Co²⁺and Ni²⁺.Preliminary ion exchange experiments show that Sn S-1 has excellent adsorption properties for four ions of Sr²⁺,Ba²⁺,Co²⁺,Ni²⁺,and the adsorption capacity is as high as q_m^Sr=111.45 mg g^-1;q_m^Ba=175.93 mg g^-1;q_m^Co=73.42 mg g^-1;q_m^Ni=73.22 mg g^-1,which has great potential for the efficient removal of radioactive metals or heavy metal ions.2.A microporous framework compound[NH₃CH₃]₃[NH₄]₃Cd₄Sn₃Se₁₃·3H₂O(Cd Sn Se-1)assembled by vacancy supertetrahedral clusters was synthesized using DES composed of diethylamine hydrochloride and N,N'-dimethylurea as the reaction medium.The methylamine cations and ammonium radicals generated by in situ decomposition in DES act as counter cations and structure directing agents to fill the pores.Cd Sn Se-1 can efficiently remove Cs⁺and Sr²⁺ions,showing fast kinetic response and high selectivity.Meanwhile,the negative charge density of the[Cd₄Sn₃Se₁₃]_n^6n-anion framework in Cd Sn Se-1 is as high as 3.27×10^-3,which endows Cd Sn Se-1 with higher Cs⁺and Sr²⁺exchange capacities of 371.4 and 128.4 mg g^-1,respectively.More importantly,the exchange mechanism is revealed at the molecular level.The products of each link in the entire ion exchange-elution process can be structurally analyzed by single crystal diffraction,revealing the impact of the vacancy-type cluster symmetry breaking on the chemical environment of the ion adsorption site and the host-guest interaction.The energy changes during the adsorption process of Cs⁺and Sr²⁺and their effect on the adsorption selectivity were further investigated by DFT calculation.3.Three examples of Zn-Sn-S or Cd-Sn-Se compounds were synthesized using DESs composed of tetraethylammonium chloride and thiourea,dimethylamine hydrochloride and thiourea,dimethylamine hydrochloride and N,N'-dimethylurea as reaction media,respectively.namely[NH₄]₇[H₃O]₃Zn₄Sn₄S₁₇(1),[NH₄]₅[(CH₃)₂NH₂]Zn₄Sn₅S₁₇(2)and[NH₄]₂Cd Sn Se₄(3).Compound 1 contains an isolated P1-[Zn₄Sn₄S₁₇]^10-cluster,and the counter ion is the ammonium species generated in situ during the heating of DES and protonated water.Compound 2 is a three-dimensional microporous material induced by mixed ammonium and dimethylammonium cation structure-directing agents,and its anionic framework is an open structure formed by the connection of P1-[Zn₄Sn₄S₁₇]^10-clusters and Sn S₄tetrahedra connected by shared apex S atoms.Compound 3 is composed of parallel-arranged[Cd Sn Se₄]_n^2n-anion chains,with ammonium cations located between the chains,which play a role in balancing charges.The formation and crystallization conditions of compounds 1-3 were optimized through precise adjustment of the reactant ratio,temperature,time,auxiliary solvent and other parameters,which provided a reference for the application of deep eutectic solvents in the synthesis of inorganic functional materials.