Construction Of Two LDH Matrix Composites And Their Applications In Wasterwater Treatment

Layered Double Hydroxides（LDHs）are widely used in the field of adsorption because of their positively charged inorganic layers,exchangeable interlayer anions,and large specific surface area.And LDHs have attacted great attention in the field of photocatalysis because of the properties of LDHs,such as visible-light response,adjustable electronic structure and chemical composition.However,due to the few kinds of functional groups in LDHs,the adsorption performance is limited.And the low photo-generated carrier separation efficiency inhibits the photocatalytic performance of LDHs.In order to improve the performance of LDHs,LDH-based composite materials have aroused great interest from researchers.In this work,two kinds of LDH-based composite materials were prepared,which were used for adsorption and photocatalysis studies respectively.The main research contents and conclusions are as follows:（1）Construction and adsorption properties of Al-Fe₂O₃/LDH composite.Herein,a novel Al-doped iron oxide decorated layered double hydroxide nanocomposite（Al-Fe₂O₃/LDH）was synthesized by a one-step hydrothermal method.In individual systems,the Al-Fe₂O₃/LDH had high adsorption capacities of 93.06 mg/g,1363.54 mg/g and 577.42 mg/g for phosphates,Congo red（CR）and methyl orange（MO）,respectively.Adsorption capacities could be mostly achieved in the first minute.The synergistic effect between layered hydroxide nanoflakes and supported Al-doped iron oxides contributed to the enhanced removal ability,and the good dispersion of Al-Fe₂O₃/LDH contributed to the fast removal ability.The limited number of reactive sites on the surface of Al-Fe₂O₃/LDH had a greater effect on phosphate removal in the phosphate–CR system while the reactive sites had less effect on phosphate removal in the phosphate–MO system,which could be attributed to the differences in the interactions between the adsorbates and the active sites of Al-Fe₂O₃/LDH.Moreover,the special affinity for phosphates caused by the Al doping in iron oxides contributed to the enhanced competitive adsorption for phosphates.We proposed that the effective removal of phosphates could be attributed to inner-sphere formation through ligand exchange,electrostatic interaction and hydrogen-bond formation.（2）Construction and photocatalytic performance of Ti O₂-4/LDH composite.The unique layered double hydroxide coated defective Ti O₂ nanobelts（2Ti O₂-4/LDH）Z-scheme photocatalyst has been designed by the hydrothermal method.The Ti O₂-4/LDH Z-scheme photocatalyst shows excellent photocatalytic activity in the degradation of tetracycline hydrochloride（TC-H）,which has a degradation rate constant that is 5 and 2.5 times that of LDH,Ti O₂-4,respectively.The presence of Ti³⁺ions as well as associated oxygen vacancies in Ti O₂ nanobelts broadened the ultraviolet absorption range to the visible range.The visible-light response of both LDH and defective Ti O₂ nanobelts contributed to the outstanding photoactivity.The modification of band structure at the interface between LDH and Ti O₂ promoted the directional transport of charge carriers which followed the direct Z-scheme.The construction of the direct Z-scheme heterojunction promoted the separation of carriers,which also contributed to the superb photoactivity.This work provided understanding of Z-scheme heterojunction and demonstrated excellent photocatalytic ability of the 2Ti O₂-4/LDH heterostructure.