Surface Properties Of Kaolinite And Adsorption Of Pb(?) By Density Functional Theory

The pollution of water bodies in China is getting more and more serious,especially the pollution hazard of heavy metals is increasingly aggravated,which seriously harms the survival of humans and aquatic organisms.Due to the hard-to-degrade and deposition properties of heavy metal ions,it is generally difficult to handle.The adsorption method is an economic and efficient method for controlling heavy metal ions.In the natural world,natural kaolinite minerals have the advantages of large specific surface area,multiple surface active adsorption sites,permanent negative charge,and low cost,and are ideal for heavy metal ion adsorbents.At present,the treatment and research of heavy metal ions are basically based on experiments.The first-principles method based on density functional theory is used to calculate and analyze the mineral structure theory.The adsorption of heavy metal ions on kaolinite is less.The mechanism is not clear enough.In this dissertation,the computational simulation software,Materials Studio,using the quantum chemistry method,was used to perform calculations and analysis using the CASTEP module in the software.The binding energy and electronic properties of heavy metals adsorbed on the?001?crystal surface of kaolinite with the most stable dissociation surface were investigated.Chemical adsorption mechanism and adsorption characteristics of phenanthrene and Pb.The forbidden band width of kaolinite crystals is large,and the valence band and conduction band do not easily undergo electronic transitions.They are insulators,and their internal charges are unbalanced.The aluminum-oxygen octahedron layer shows more positive charges,and the silicon tetrahedron.The layer shows more negative charge,in which the covalence of Si-O bond is stronger than the covalent bond of Al-O bond,the action strength is higher,and it is more difficult to fracture.The layout of Si-Ob is smaller than that of Si-Oa.Si atoms have stronger attraction to O atoms than Al atoms,and the interaction between O atoms and Si atoms is stronger.Therefore,kaolinite crystals tend to dissociate along the?001?plane.The O atoms of the optimized?001?-Si crystal plane gradually move around the Fermi level,and the O atom is more active.After disassociation,the?001?-Si crystal surface is more negatively charged and more likely to adsorb with cations;the O atom located on the?001?-Si crystal plane and the?001?-Al crystallographic plane hydroxyl group?-OH?O atoms in the medium are more reactive than other atoms;perpendicular to the?001?-Al crystal surface hydroxyl?-OH?H atom has a stronger reactivity.Adsorption of single Pb ion on the top?top?and bridge?bridge?sites of the kaolinite?001?surface is relatively stable,and the adsorption of the Pb ion is more stable than the top position.Adsorption kinetics and adsorption thermodynamics fitting show that the Langmuir equation fits the adsorption kinetics better,the Bangham equation fits the adsorption thermodynamic effect better,the adsorption of Pb²⁺and kaolinite is monolayer adsorption and the adsorption capacity is larger.Adsorption of Pb²⁺on kaolinite increases with increasing pH.The chemical reaction of adsorption of Pb2+on the surface of kaolinite has a mineralized surface containing>J-OPbOH and>J-OH.Before and after the adsorption of Pb2+by kaolinite,the polarity of Si-Si/Si-O bond on the mineral surface changed to some extent,which also proved that the adsorption of Pb2+by kaolinite is stable.