Preparation And U(?) Adsorption Behavior Of The Novel Three-Dimensional Porous Materials

With the rapid growth of the global population and the high speed of industrial development,global energy demand is gradually increasing.As an economic,clean,safe,and sustainable form of energy,nuclear energy has huge advantages over other traditional energy sources.Uranium is the main raw material for the development of nuclear energy,but the identified uranium reserves are quite limited.More importantly,uranium-containing wastewater discharged during uranium mining or nuclear industry operations can threaten human health through the biosphere.Therefore,to achieve ecological safety and solve the problem of limited uranium reserves,it is necessary to develop new methods that can effectively remove and recover uranium from radioactive wastewater or other aqueous solutions(e.g.,strongly acidic solutions).Based on this,four porous materials(3D AFC,3D r GOE,3D CA,and 3D GO/CA)with 3D porous structural morphologies were designed and prepared in this research with simple and inexpensive methods.Subsequently,their structural morphology and chemical composition were characterized,the effects of different factors(including solid-liquid ratio,p H and ionic strength,contact time,and initial U(VI)concentration)on the adsorption behavior of U(VI)were investigated,and the adsorption mechanism of these materials for U(VI)was analyzed to provide basic data and theoretical support for its application.The main research contents are as follows:1.A framework carbon with a three-dimensional structural morphology was successfully prepared via one-step calcination and activated by chemical oxidation(3D AFC)for the adsorption of U(VI)in aqueous solution.3D AFC showed an ultrathin,curved carbon sheet structure with a macroporous skeleton structure(50–80nm)morphology.Experimental results show that the adsorption of U(VI)on 3D AFC is highly dependent on the p H of the solution and its kinetic adsorption process can be described by the pseudo-second-order model.The maximum adsorption capacity of3D AFC on U(VI)was calculated to be 127.5 mg/g at p H=5.8.In conjunction with the FTIR and XPS results,the mechanism of U(VI)adsorption by 3D AFC was confirmed to be electrostatic interaction.With its 3D pore-like structure morphology,simple preparation method,and high adsorption capacity of U(VI),3D AFC is considered a promising candidate material for the removal of U(VI)from aqueous solution.2.A three-dimensional(3D)hierarchical reduced graphene oxide/ethylenediamine porous scaffold(3D r GOE)was successfully constructed with the aid of direct ink writing(DIW)-based 3D printing and hydrothermal treatment techniques.3D r GOE presents a pore structure with orderly aligned microstructures,good hydrophilicity,mechanical properties,and a high specific surface area.Experimental results showed that the optimized 3D r GOE exhibited higher U(VI)adsorption capacity(p H=5.8,908 mg/g).After 11 adsorption-desorption cycles,the adsorption capacity only decayed by 3.8%.In addition,the adsorbed U(VI)could be eluted in acid solution by the protonation mechanism,and the adsorption and recovery of U(VI)in aqueous solution could be achieved.Furthermore,the selective adsorption ratio of U(VI)in aqueous solution in the presence of competing cations was shown to be as high as 99.3%,where the adsorption mechanism is a synergistic interaction between electrostatic forces between uranyl ions and oxygen-containing functional groups and chelation between uranyl ions and amino functional groups.Since the prepared 3D r GOE has an optimized orderly and aligned hierarchical pore structure and abundant effective active adsorption sites,it has high selectivity and strong adsorption capacity for U(VI),and wider application prospects in recovery and reuse of U(VI)in aqueous solution.3.A three-dimensional porous calcium alginate(3D CA)scaffold was successfully constructed without the addition of additional reducing agents by means of DIW-based 3D printing and in situ calcium ion cross-linking technology.Characterization showed that the lamellar calcium alginate sheets constituted an ordered arrangement of hierarchically porous structural morphology with good structural stability and abundant active binding sites.The adsorption results demonstrate that 3D CA exhibits a wide p H working range(3.0–10),especially under strongly acidic conditions(p H=2.5),and a higher U(VI)adsorption capacity(117.3mg/g)than other previously reported porous-based adsorbents.The adsorption mechanism of 3D CA for U(VI)is both electrostatic interactions and ion exchange.The adsorbed U(VI)on 3D CA can be eluted in strong acid solution via a protonation mechanism,which provides the possibility of further enrichment and recovery of U(VI).Furthermore,3D CA is structurally stable after a 24-h immersion over a wide range of hydrochloric acid solutions(3.6×10^-3–2.0 mol/L).Therefore,3D CA presents advantages of a wide p H working range,high acid stability,and high U(VI)adsorption performance,and its removal and recovery of U(VI)in acidic solution has wide application value.4.With the help of DIW-based 3D printing technology and calcium ion cross-linking in situ technology,a three-dimensional hierarchical hybrid porous scaffold(3D GO/CA)with both 3D r GOE and 3D CA-integrated adsorption capabilities were successfully constructed using graphene oxide(GO)and sodium alginate(SA)as raw materials.In 3D GO/CA,a stable three-dimensional hierarchical structure was successfully constructed by stacking GO and CA sheets,and the pore structure was arranged in an orderly manner with highly abundant active adsorption sites(oxygen-containing functional groups/Ca²⁺binding sites).The adsorption experiment results showed that 3D GO/CA has wider p H working range(3.0–12)compared with 3D CA,especially at a higher adsorption capacity for U(VI)in strongly acidic solutions(e.g.,200.1 mg/g at p H=2.8).In addition,3D GO/CA exhibits a very high adsorption kinetic reaction rate(adsorption equilibrium was attained within 30 min),much higher than 17 h for 3D r GOE and 10 h for 3D CA.It also has a very highly selective adsorption capacity for U(VI)in strongly acidic(p H=2.8)simulated wastewater with 99.7%adsorption ratio.After eight repeated adsorption-desorption cycles,3D GO/CA maintained its stable structure and the adsorption percentage only decreased by 4.4%.Acid stability experiments showed that the stable structure of 3D GO/CA was maintained even when in immersed in across a range of strong acid solutions(1.59×10^-3–2.00 mol/L)for 24 h at different concentrations.In this experiment,the 3D printing technology used to optimize its structure(exposing more effective active adsorption sites),the Ca²⁺-based in situ cross-linking technology to retain more of the oxygen-containing functional groups at the edges of GO sheets,and the ordered microporous channel structure were all shown to enhance the adsorption capacity for U(VI).Therefore,3D GO/CA has greater application potential for the removal and recovery of U(VI)in acidic solution.In this paper,by constructing four different multistage layered pore-like adsorption materials,the structurally stable porous materials with high adsorption capacity for U(VI)removal and recovery in complex environments were obtained,and provide a new ideas and approaches for the development and research of nuclear energy.