Preparation Of Transition Metal Oxides Based On P-d Orbital Hybridization And Adsorption Mechanism For Aqueous PO₄^3-

PO₄^3-is a typical oxyanion in the water environment,which have an important effect on aquatic plants and aquatic ecosystems.The transition metal adsorbent materials have been widely used in the projects for tail water standard raising in sewage plants and water quality improvement because of its good processing efficiency,easy separation and recovery,and simple treatment process.At present,a large number of transition metal adsorbent materials have been developed.However,there is a lack of systematic understanding of the adsorption activity of these transition metal materials.The research and development approach of adsorbent materials is still in the experimental screening stage.The structure-performance relationship of adsorbent materials needs to be deepened,including doping of metal ions,pore structure and surface ligands of materials.In this paper,firstly,aiming at the intrinsic activity of transition metal oxides for phosphate adsorption,transition metals Mn,Fe,Ni,Zr and La are selected to study the relationship between the structural characteristics of transition metal oxide materials and phosphate adsorption performance.Secondly,based on the phosphate adsorption strengthening phenomenon of some bimetal oxide materials,Fe-Ni,Fe-Zr and La-Zr are selected to prepare a series of metal molar ratio of Fe-Ni,Fe-Zr and La-Zr bimetal oxide materials,and to explore their doping characteristics of metal ions and the regulation mechanism of phosphate adsorption performance.Thirdly,considering the performance improvement of phosphate adsorption by porous materials,La/Zr composite oxide material was selected to prepare macroporous and mesoporous materials for exploring the pore structure regulation of metal oxides and its effect on phosphate adsorption efficiency.Finally,aiming at the high-efficiency phosphate adsorption of the Mn-based material,which was found during the abovementioned experiment,the phosphate adsorption strengthening mechanism will have been explored based on the ligand regulation of metal oxide.The purpose of this article is to explore the phosphate adsorption mechanism of metal ion doping,pore structure and metal ligand regulation of transition metal oxide materials,and to provide effective measures and theoretical guidance for the development of efficient phosphate adsorption materials,and the main research results obtained are:?1?The 3d-transition metal oxide materials Mn O_xH_y,Fe O_xH_y and Ni O_xH_y have high crystallinity,and the O 2p-M 3d hybrid orbital energy level is low,while the 4d/5d transition metal oxide Zr O_xH_y and La O_xH_yare amorphous or polycrystalline nanocluster,and have high p-d hybrid orbital energy level.The phosphate adsorption performance of transition metal oxide materials is in the order of Fe O_xH_y<Ni O_xH_y<Mn O_xH_y<La O_xH_y<Zr O_xH_y,the efficient phosphate adsorption performance of Zr O_xH_y and La O_xH_ymaterials may be due to the electronic configuration t⁰_2g e_g⁰ of Zr⁴⁺and La³⁺and their high coordination properties.?2?Fe-Ni and La-Zr bimetallic oxides are long-range ordered Fe-Ni and dsiordered La-Zr bimetal oxides solid solution,while Fe-Zr bimetallic oxides are a mixed oxide with Fe O_xH_y and Zr O_xH_y grains.Fe-Ni and La-Zr bimetallic oxides exhibited a bimetallic reinforcement for phosphate adsorption,while the Fe-Zr composites exhibited a Zr-dependent phosphate adsorption performance.The phosphate adsorption capacity of La-Zr bimetallic oxide reached 160 mg P·g^-1.O K-edge XANES and XPS analysis showed that the charge recombination between lanthanum and zirconium in La-Zr bimetallic oxides promoted the formation of Zr-O…PO₄ surface species.P K-edge XANES showed that phosphate coordination complexation species mainly exist on the La site of La-Zr bimetal oxide.?3?The phosphate adsorption performance of porous La/Zr composite oxides is twice that of non-porous La/Zr composite oxide.The pore structure regulation not only enhances the mass transfer of phosphate,but also the larger specific surface area increases the number of effective adsorption active sites on the surface and improves the phosphate adsorption performance.The oxygen defects of La₂O₃ in La/Zr composite oxides were produced under the pore structure regulation,which enhances the adsorption effect of La sites with phosphate.P K-edge XANES analysis showed that the main site to adsorb phosphate was La in La/Zr composite oxides,which accounted for?90%,and the La P-adsorption sites increased with the increase of oxygen vacancy content.?4?The phosphate adsorption capacity of core-shell Mn₃O₄@Mn-MOH is nearly 4 times that of Mn₃O₄(?110 vs.30 mg P·g^-1),and the maxium adsorption capacity is as high as?190 mg P·g^-1.The shell of Mn₃O₄@Mn-MOH has oxygen-containing organic ligands with higher energy than O^2-ligand,and its O2p energy band center energy is closer to the Fermi energy level,making it stronger coordination with phosphate.In-situ FTIR and Raman spectra indicate that the phosphate adsorbed species of Mn₃O₄@Mn-MOH mainly include the forms of charge transfer and coordination,and the phosphate coordination interaction of Mn-MOH shell is stronger than Mn₃O₄core material.