Study On Preparation And Reaction Mechanisms Of Ag/Cu-Based Composites For The Removal Of Radioactive Iodide From Solutions

The decline of the traditional fossil fuel energy and increasing pollutions have aroused global attention.As a kind of green energy,nuclear power has long been popular in many countries,but the formed radioactive waste pollutions prevent its rapid expansion.Radioactive iodine is an inevitable product of nuclear fission,which is high radioactivity and acute toxicity,and could present a health risk upon people and environment once it is released into the environment.Thus,effective removal of radioactive iodide from solutions will play an irreplaceable important role in the rapid and healthy development of nuclear power.In this dissertation,Ag/Cu-based composites had been prepared,the morphology,chemical compositions and surface information had been determined by a series of characterization methods.The adsorption property and adsorption mechanisms were proposed.The main contributions of this dissertation are described as follows:?1?MIL-101 was chosen as a basis material because of its extra-large specific surface area.It can adsorb I-anions from solutions on its surface quickly due to its ultra-high physical adsorption performance.Then,Ag^? doped in MIL-101 can reacts with I-anions to form AgI₃?AgI+I₂?.Therefore,the adsorption capacity of Ag@MIL-101 can be up to 2.14 mmol g^-1 within only few minutes.Meanwhile,since the adsorption mechanism of adsorbent is the synergistic effect of physical adsorption and chemical adsorption,the adsorption performance of adsorbent severe dropped in alkaline environment due to the structure of MIL-101 was destroyed.In addition,desorption efficiency of adsorbent after the removal of I-anions was large because of the physical adsorption.Therefore,Ag@MIL-101 is difficult to remove the radioactive iodide from solutions completely.?2?In order to reduce the desorption efficiency,instead of MIL-101,Cu₂O was selected as a basis material.Meanwhile,to eliminate the influence of surface CuO toward the adsorption performance of Cu₂O,metallic Ag or Cu was doped into Cu₂O,respectively.Metallic Ag or Cu can reacts with the superficial CuO to generate Ag2O/Cu₂O or Cu₂O.Therefore,the adsorption capacity of Cu₂O increased from 0.02 to 0.20 and 0.18 mmol g-1.Moreover,the desorption efficiency of Cu₂O-based material after the removal of I-anions can be neglected in purified water.Besides,the research results show that the acidic environment and the strong acid radical ion are helpful for the adsorption process.Since metallic Cu and Cu₂O can be oxidized to CuO in the alkaline environment,the alkaline environment and weak acid radical ions are advantageous for the adsorption performance of Ag/Cu₂O,but are disadvantageous for the adsorption process of Cu/Cu₂O adsorbent.In addition,the possible crystalline mechanism of Cu/Cu₂O is presented.Firstly,ammonia molecules prefer to bind to Cu₂+ to form[Cu?NH₃?_n]²⁺?n=3-8?.Subsequently,Cu²⁺clusters with less ammonia molecules can be reduced to Cu₂O by formic acid,Furthermore,NH₃ can be released from reaction and bind with some of Cu2+ clusters to form stably[Cu?NH₃?₈]²⁺,resulting in the decreasing of the molar ratio of Cu²⁺ to formic acid.Therefore,Cu²⁺ can be reduced to Cu?0?by excessive formic acid.?3?In order to understand the different selectivity and adsorption mechanism of metallic Ag and Cu toward I-anions in the adsorption process,bimetallic AgCu was doped into Cu₂O.The results show that the selectivity of metallic Ag is better than that of metallic Cu,Ag₂O can reacts with I-anions to form AgI precipitate directly,but the adsorption process of Cu₂O is the a substitution of surface hydroxyl groups by I-anions.The adsorption capacity of bimetallic AgCu/Cu₂O can be up to 0.52 mmol g^-1.Meanwhile,both acidic and alkaline environment are helpful for the adsorption process.Moreover,the competitive anions(e.g.Cl^-,CO₃^2-.SO₄^2-and NO^3-),seawater environment had rare effects on the adsorption performance of adsorbent.AgCu/Cu₂O adsorbent can work well in the adsorption of radioactive iodide.In addition,desorption rate of Cu₂O-based adsorbent after the removal of I^-anions can be neglected in purified water or the presence of Cl^-anions.