| Mayenite(Ca12Al14O33)is a functional material with a cage crystal structure and wide promising applications in the CaO-A12O3 binary system.It has good room temperature stability and is easy to be doped with various ions.It has important application prospects in many fields such as electronic devices,electrochemistry,catalysis,and sensing components.Macroporous monolithic materials have been widely used in filtration,separation,adsorption,electrochemistry and optoelectronic devices because of their unique pore structure.Therefore,combining the special crystal structure of mayenite and the microscopic morphology of porous monolith is of great significance for developing macroporous mayenite monolithic materials and expanding the application of mayenite,especially in the field of ion and gas detection.In this paper,the research status and development trend of sol-gel accompanied by phase separation in the preparation of macroporous monolith and mayenite materials are discussed.The sol-gel method accompanied by phase separation is used to prepare the mayenite porous monolith.The macroporous mayenite material with conductivity is obtained after oxidation-reduction reaction.The influence of pore structure on its electrical properties is discussed,and the conductive mechanism is revealed.The macroporous mayenite monolithic material is doped with rare earth elements.The luminescence properties of doped porous mayenite monolith and its detection of silver ions are analyzed.The macroporous mayenite monolithic material was loaded with tetrastyrene(TPE),and the porous monolith of loaded TPE mayenite is investigated for formaldehyde.The detection performance of gas;the controllable preparation and doping loading mechanism of the mayenite porous monolithic material is established.The research provides an important theoretical basis for the preparation and application of macroporous mayenite monolithic material.The main research contents and conclusions are as follows:(1)Controllable preparation of macroporous mayenite monolithic material.Using inorganic salts of aluminum chloride and calcium chloride,and aluminum nitrate and calcium nitrate as precursors,ethylene glycol(EG)as a chelating agent,formamide(FA)as a drying control agent,and propylene oxide(PO)as a gel.The accelerator,polyethylene glycol(PEO)(Mw=1×105)is used as the phase separation inducer,water and ethanol are used as solvents,and the porous mayenite monolithic material is prepared by sol-gel accompanied by phase separation.Under the optimal reactant conditions,the mayenite monolithic material with macroporous and co-continuous skeleton structure can be obtained by controling the process of phase separation and sol-gel transformation.After heat-treated at 1100 0C,the crystal form Cai2Al14O32Cl2 or Ca12Al14O33,while the macroporous structure is retained.The macroporous mayenite monolith has a narrow pore size distribution before and after heat treatment;the porosity of the monolith after the heat treatment of the chloride system and the nitrate system may be up to 77.43%and 76.03%.(2)Oxidation-reduction and conductive mechanism of porous mayenite monolithic materials.The mayenite is oxidized through the process of heat-treatment in an oxygen atmosphere,and the macroporous mayenite monolith is subjected to reduction treatment by using a calcium hydride as a reducing agent.After the reduction,the macroporous mayenite monolith is transformed to conductor and the pore structure of the porous mayenite is well preserved.Due to the loss of the binding effect of the strong electronegative anion,a large number of bound electrons are converted into free electrons,thereby obtaining a macroporous mayenite monolith electronic compound with good electrical conductivity.The carrier concentration can reach 1.996×1018 cm-3.After doping with Cr element,while retaining the porous structure,the electrical properties are further improved.Finally,the conductive concentration with the carrier concentration up to 1019 is obtained.(3)Rare earth doped macroporous mayenite monolihic material and its detection of metal ions.Doping with Tb3+and Eu3+ ions in macro porous mayenite monolith,while retaining the co-continuous macroporous structure,obtains a porous mayenite monolithic material with excellent luminescence properties.Rare earth ions were incorporated into the lattice and replaced the position of Ca’+ions,which does not destroy the lattice structure of C12A7 and has good high temperature stability.The luminescence lifetimes of Tb3+ions and Eu3+ion doped mayenite can reach 2584.24 Vs and 2143.7 μs,respectively.The obtained porous C12A7:Tb3+ material has a sensitive response to Ag+and has a very good application prospect for the detection of Ag+ ions.The obtained macroporous C12A7:Eu3+ can be applied to the field of luminescence sensors,and has a good response to Pb2+ions.The relationship between the concentration of Pb(Cpb)and the fluorescence intensity(F)can be calculated using a linear equation(F0-F)/F0=1.412+0.3428Log10(Cpb).(4)TPE loaded macroporous mayenite monolithic material and its detection of formaldehyde.The TPE was loaded onto the surface of the skeleton of the macroporous mayenite monolith by physical infiltration method and the luminescence properties of the macroporous mayenite monolith loading TPE were studied.The obtained macroporous mayenite monolith has a good detection response to formaldehyde gas,the minimum detection time is 10 min,and the luminescence intensity has a good linear relationship with the concentration decrease in the 0-100 ppm formaldehyde concentration range.The formaldehyde detection material can be recycled and placed in the air for a period of time to restore the detection performance. |
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