AlMg Alloy-LDH Miicro-Nano Coreshell Structure Material For Nitrate Reduction In Water

Nitrate nitrogen pollution has become a global problem,posing a serious threat to human health and the ecological environment.Therefore,it is of great significance to remove nitrate nitrogen and convert it into ammonia nitrogen with higher added value for resource utilization.At present,the widely used remediation materials generally have the problems of unstable activity in wide p H,weak stability and secondary pollution.In this paper,based on the chemical reactivity and amphoteric metal properties of magnesium and aluminum,a new method for the reduction of nitrate nitrogen in water by aluminum-magnesium alloy hydrotalcite core-shell structural materials is proposed.In situ self-assembly of magnesium-aluminum hydrotalcite on the surface of aluminum-magnesium alloy,the micro-nano core-shell structure material AlMg@LDH was prepared.The effects of temperature,p H,alloy dosage,pollutant concentration,and various heavy metal ions on nitrate conversion and removal were investigated.XRD,FT-IR,SEM,TEM,BET and XPS were used to characterize the effect of AlMg@LDH on the conversion and removal mechanism of nitrate.The main results are as follows:（1）Spherical aluminum-magnesium alloy particles with a particle size of20±5μm were prepared by atomization,and the main component was Al₁₂Mg₁₇.The aluminum-magnesium hydrotalcite-coated alloy particles were formed in situ on their surface by hydrolysis.The main molecular formula of hydrotalcite is Mg₄Al₂（OH）₁₂CO₃ 3H₂O,with a small amount of Cl^-intercalation,unit cell parameters a=2.986（?）,c=22.710（?）,and interlayer channel height E=2.770（?）.The two-dimensional hydrotalcite nanosheets grow alternately and vertically on the surface of the alloy particles in a flower shape,with a layer thickness of1000±200 nm,which makes the material present a rich surface structure with a specific surface area of 6.09 m²·g^-1 and a surface mesopore diameter of 11.67nm.（2）The two-dimensional nano-hydrotalcite layer on the surface of the alloy has a good protective effect on the alloy and avoids the erosion of water molecules.The hydrogen production in water for 50 days is 0.38%of the alloy.After 460 days,the surface hydrotalcite structure is compact and regular,with Good stability.On the other hand,the surface hydrotalcite promotes the reduction rate of nitrate.The reduction and conversion of nitrate to nitrate reached more than 77.80%at p H 2-11.Under acidic conditions,the reaction rate was the fastest at 0.0063 h^-1,and the reduction removal rate was 92.00%,which decreased slightly with the increase of p H.Under the condition of neutral room temperature,compared with the alloy without hydrotalcite,the reduction and removal rate of 50 mg·L^-1 nitrate increased by 39.46%,and the reaction rate within 13 h increased by 6.85 times.The reaction rate at 30℃was 0.0014 h^-1,and the reaction rate increased by 52.40%for every 10℃increase,and the reaction rate was 0.012 h^-1 at 80℃.In the presence of Cd（II）,Mn（II）,Zn（II）and Ni（II）at a concentration of 25 mg·L^-1,the reduction and conversion rates of nitrate increased by 16.20%,13.08%,8.16%and 3.95%,respectively.（3）Reduction of nitrate by the material First,the positive charge on the surface of the two-dimensional nano-hydrotalcite layer electrostatically adsorbs nitrate anions to make it rapidly enriched.The reduction reaction occurs with the inner alloy phase Al₁₂Mg₁₇ through the surface mesoporous channels,and the nitrate is converted into ammonia and trace nitrite（<0.02%）,adsorbed on the hydrotalcite layer or into the solution.After Al₁₂Mg₁₇ loses electrons,the dissolved Al and Mg ions consume OH^-to generate new hydrotalcite in situ on the surface of the material,and the specific surface area is further increased by169.32%after 300 min.The two-dimensional nano-hydrotalcite layer on the surface of the material continues to update.This study provides a new reference for the green removal and reuse of nitrate nitrogen,and provides support for the in-situ preparation of alloy hydrotalcite core-shell structural materials using alloy materials and their application in the field of pollution remediation.