Preparation Of Polyacrylonitrile Foam With Solar Evaporation Capacity By Thermally Induced Phase Method And Its Uranium Adsorption Performance

The development of science and technology not only brings more innovation and opportunities,but also exacerbates the energy crisis.It has become an urgent need to seek a new renewable and clean energy that can replace traditional fossil energy.Nuclear energy has entered people’s vision because of its low consumption but high productivity.Uranium is the most important nuclear raw material in nuclear energy,and its reserves on land are limited.In order to achieve the extraction and enrichment of uranium in the ocean and the recovery and purification of uranium in nuclear waste water,a new type of polyacrylonitrile material with dual adsorption and evaporation properties was designed and prepared and relevant research was carried out.In this paper,polyacrylonitrile porous foam（T-PAN）was prepared by thermally induced phase separation using polyacrylonitrile（PAN）as polymer and dimethyl sulfone（MSM）as diluent.Then it reacted with hydroxylamine to graft amidoxime group to obtain polyacrylonitrile adsorption foam（T-PAO）.The properties of the material were characterized by FT-IR,SEM,TGA,XPS,ICP and OCA.It is found that the foam has vertical capillary channels and good mechanical strength after regulating the freezing mode,and the uranium adsorption amount can reach 348.70 mg·g^-1（C₀=100 ppm,p H=6.0）.In a coexisting solution of multiple metal ions,this material has excellent selectivity for uranium ions,and the removal rate of uranium can reach 57%,which is much higher than other metal ions.The results of kinetic and thermodynamic studies indicate that the adsorption process is more in line with the pseudo-second-order kinetic model and thermodynamic Langmuir model,that is,the adsorption is dominated by chemical adsorption in a single molecular layer.When Na₂CO₃ was used as desorption agent,the material showed excellent recycling performance.On this basis,in order to further improve the uranium adsorption performance of the prepared polyacrylonitrile foam material,considering the characteristics of the foam with vertical capillary channels,an integrated polyacrylonitrile foam（T-PAO-CNT）with the dual function of adsorption and evaporation and an assembled polyacrylonitrile foam（T-PAO-CF）covered with modified carbon fiber cloth were designed.The research results indicated that both materials had good photothermal conversion ability and could quickly achieve interface temperature rise.The temperature of T-PAO-CNT foam can reach 31.80℃under 1 sun simulated light intensity.The water evaporation rate is 1.40 kg·m^-2·h^-1,and the photo thermal conversion efficiency is 73.28%.In the experiment of synchronous adsorption evaporation driven by solar energy,light accelerated the adsorption process,and the removal rate of uranium reached 46.50%.The temperature of T-PAO-CF can reach 39.90℃under 1 sun simulated light intensity,at which the water evaporation rate is 1.84 kg·m^-2·h^-1,and the photothermal conversion efficiency is 88.81%.In the experiment of synchronous adsorption evaporation driven by solar energy,the removal rate of uranium reached 94.12%under 1 sun light intensity.Compared with the disordered membrane pore structure obtained by thermally induced phase diluent crystal growth in all directions reported in most literatures,a unique induced cooling method was used in this paper to make the crystal grow perpendicular to the cooling interface to obtain T-PAO foam with vertical unidirectional pores,which greatly improved the permeability of water and was more conducive to adsorption and evaporation.The application of T-PAO-CNT and T-PAO-CF can be further expanded by adding carbon nanotubes and the coverage of photothermal fiber cloth.By making them both adsorption materials and photothermal conversion materials,the collaboration between uranium adsorption and solar water evaporation can be realized.In this way,water evaporation can be realized at the same time as uranium extraction and water purification can be obtained,which provides a new idea and data support for the research of multifunctional adsorption materials.