Design Of Fe-based Superstable Mineralization Materials And Exploration On Treatment Of Nickel-Containing Wastewater And Recycling Of Resources

Industrial wastewater containing heavy metals has polluted natural ecology.Therefore,it is of great significance to develop a highly efficient stabilizer to treat the wastewater containing heavy metals and realize the recovery of metal resources.In this manuscript,based on layered double hydroxides(LDHs),a stabilizer material for wastewater treatment and a high performance catalyst for electrocatalytic water oxidation were designed and synthesized.The microstructure,fine structure,free energy and energy band structure of the synthesized materials were studied by means of experimental characterization and density functional theory(DFT)calculation.The relationship between the properties of the materials and the morphology,coordination structure and coordination environment of the materials was revealed.Main works and achievements are as follows:There are a lot of Ni2+ions in electroplating wastewater.The treatment and recovery of nickel-containing wastewater pollution has attracted great attention from both environment and resources.There are many chemical bonding modes in LDHs,which makes its solubility product constant(Ksp)tens of orders of magnitude smaller than that of the corresponding metallic carbonate or hydroxide.Based on the idea of superstable mineralized structure(SSMS)proposed in the laboratory,CaFe-LDH was used as a stabilizer to anchor Ni2+ions in the crystal lattice of LDH based isomorphism substitution property to form SSMS structure with very low solubility.The maximum saturation removal rate of CaFe-LDH was 321 mg/g.Using 1 g/L CaFe-LDH,the mineralization removal effect of 300 mg/LNi2+ions solution can exceed 99.5%.By means of ex-insitu X-ray powder diffraction(XRD)and X-ray fine structure(XAFS)characterization,it was found that CaFe-LDH was transformed into NiCaFe-LDH during mineralization process.The DFT calculation further showed that the transition from CaFe-LDH to NiCaFe-LDH was spontaneous.In addition,the mineralized product NiCaFe-LDH showed good electrocatalytic OER performance,which was better than commercial RuO2 and Ni(OH)2.In this work,CaFe-LDH was used to recycle Ni2+ions from nickel-containing wastewater,which provided an idea for wastewater treatment and reuse of nickel resources to prepare high efficient OER electrocatalyst at a low price.To further optimize the performance of LDHs,the researchers found that the ultrathin LDHs material has unique physical and chemical properties.Among them,monolayer LDHs containing transition metals showed higher OER activity than bulk LDHs.However,the preparation methods of monolayer LDHs reported at present have some problems,such as low-yield and need to add organic solvents.Therefore,herein,we improved the synthesis method reported before,ammonia solution as co-precipitator,using a colloid mill reactor in a short time to synthesize monolayer NiFe-LDH in large-scale.The morphology of the prepared LDHs nanosheets was studied by high resolution transmission electron microscopy.The thickness of the obtained NiFe-LDH monolayers was less than 1 nm determined by atomic force microscopy.XAFS characterizations showed that the obtained monolayer NiFe-LDH had more vacancy defects than the bulk NiFe-LDH.Due to the existence of defects,the obtained monolayer NiFe-LDH showed better electrocatalytic OER performance.The DFT calculation further revealed that the NiFe-LDH with rich vacancy defects had a smaller band gap,which was more conducive to electron transport in the electrochemical reaction.This new synthesis method has the advantages of economy,universality and high-yeild.It will pave the way for large-scale synthesis of monolayer nanomaterials and their future industrial applications.