Preparation And Photocatalytic Properties Of Layered Double Hydroxides And Bismuth Based Composites

Layered double hydroxides?LDHs?,including hydrotalcites and hydrotalcite like compounds,are a kind of anionic layered functional material.At present,LDHs with unique supramolecular structure are widely used as high-performance catalytic materials,adsorption materials,separation materials,functional assistant materials,and pharmaceutical materials.However,LDHs in powder form have some deficiencies,such as easy agglomeration and difficult separation from reactants in catalytic systems.As a result,more and more studies are carried out on LDH films or immobilized LDH materials.In addition,bismuth bromide oxide?BiOBr?,which is a new visible light responsive photocatalyst with narrow band gap,has attracted extensive attention of researchers over the past decade.The low efficiency of photocatalysis still limits the development and application of narrow band gap semiconductor photocatalyst because of the short lifetime of photogenerated charge carriers.Focusing on the catalyst immobilization and reducing the recombination rate of photogenerated carriers,three-dimensional LDHs/AAO films based on porous anodic aluminum oxide?AAO?templates and LDHs/BiOBr powder catalysts with visible light activity were prepared.The main contents are as follows:1. Three-dimensional Zn Al-LDH/AAO and Ni Al-LDH/AAO films were successfully prepared by innovative in-situ growth without precipitant and the key factors affecting the formation of the two kinds of three-dimensional films were studied in detail.It was found that the p H value of reaction solution was the key factor for Zn Al-LDH/AAO preparation,while for Ni Al-LDH/AAO,both the concentration morphology and crystallinity of LDHs/AAO films could be controlled by changing the concentration of metal ions,the p H value of reaction solution and the reaction time.The growth mechanism and process of Zn Al-LDH and Ni Al-LDH on AAO first adsorbed on the inner and outer surface of hydrated AAO template,and reacted crystal nuclei grew towards the solution direction to form LDHs plates perpendicular to the substrate.Besides,Co Al-LDHs/AAO and Ni Al-LDH/AAO films were also prepared in ethanol solvent,which verified the universality of this method.Compared with Ti O₂ and two-dimensional LDHs,three dimensional LDH/AAO films showed higher photocatalytic activity of methyl orange?MO?degradation.The degradation of colorless 2,4-dichlorophenol?2,4-DCP?solution,excluding the influence of dye sensitization,proved the stability of LDH/AAO photocatalysts.2. A simple two-step method was used to prepare the BiOBr/LDHs photocatalyst.The effects of LDHs on the structure,separation efficiency of photogenerated carriers and the photocatalytic performance of BiOBr were studied systematically.It was found that the addition of LDHs increased not only the specific surface area of composite but also the adsorption for MO and Rhodamine B?Rh B?,and therefore pollutants approached the catalyst surface and reacted with active species more easily.Furthermore,the composite material contributed to the separation of photogenerated electrons and holes,resulting in a significantly lower recombination efficiency than that of pure BiOBr.Therefore,LDHs/BiOBr catalysts showed enhanced activity in degradation of MO,Rh B and bisphenol A?BPA?solutions under visible light.At the same time,the results of cyclic experiments showed that LDHs/BiOBr composite had good reusability.