LDHs And Their Nanocomposites For Adsorption/Photocatalysis Of Degradation Dye Wastewater

With the widespread use of dyes in several industries,more and more dye wastewater is being discharged into nature without up to standard treatment,causing serious harm to aquatic life and humans.Of the various treatment technologies currently available for treating dye wastewater,adsorption is the most reliable and effective separation technology because it is efficient and fast,simple to operate,cheap and easy to recover.Photocatalysis is considered to be the most promising treatment technology because it is green and breaks down pollutants into CO₂and H₂O.In this thesis,Zn-Co-Ni-LDHs nano sorbent materials with high adsorption capacity and Zn Co-LDHs/g-C₃N₄and Zn Co-LDHs/g-C₃N₄/Ag nano photocatalytic materials with good photocatalytic performance were prepared.The materials are characterized with the aid of SEM,TEM,EDS,XRD,FTIR,UV-DRS,PL,TG,BET,XPS and other characterization methods.The adsorption properties of Zn-Co-Ni-LDHs,the photocatalytic properties of Zn Co-LDHs/g-C₃N₄and Zn Co-LDHs/g-C₃N₄/Ag were systematically investigated.The mechanism of material adsorption and photocatalysis was analyzed.The recyclability and antibacterial properties of the material were tested.（1）Using zinc nitrate,cobalt nitrate,nickel nitrate and triethanolamine as raw materials,the amount of triethanolamine（1 m L-3 m L）was changed by the hydrothermal method at 120℃and the reaction time was 2 h,synthesis of three Zn-Co-Ni-LDHs nanomaterials in the form of sheets and microspheres assembled from sheets.The specific surface areas of the three materials were 80.77 m2/g,149.84m2/g and 135.40 m2/g respectively.The effect of different conditions on the adsorption of the anionic dye methyl orange by the three Zn-Co-Ni-LDHs was systematically investigated and the maximum adsorption amounts were found to be1839 mg/g,1899 mg/g and 1676 mg/g,respectively.The adsorption kinetics,adsorption isotherms and thermodynamics of the adsorption process were fitted to reveal that the adsorption process is dominated by chemisorption,which is a single molecular layer adsorption,and that the adsorption process is a heat-absorbing and spontaneous reaction.Through recycling experiments,it was confirmed that Zn-Co-Ni-LDHs have good recycling performance,and Zn-Co-Ni-LDHs have good bacterial inhibition and electrochemical properties.（2）Three heterojunction Zn Co-LDHs/g-C₃N₄materials with different doping ratios were synthesized using a simple hydrothermal method with g-C₃N₄and Zn Co-LDHs at 120°C.The test results show that the compounding of the material improves the defect of the small specific surface area of g-C₃N₄and enhances the photocatalytic performance of the material.The experimental results showed that the three Zn Co-LDHs/g-C₃N₄degraded sunset yellow at 75 mg/L with 98.4%,94.8%and93.9%respectively at the natural pH when the material was dosed at 1.25 g/L.The photocatalytic process conforms to a first-order kinetic model and the material has good cycling and bacterial inhibition properties.（3）Three Zn Co-LDHs/g-C₃N₄/Ag materials with different doping ratios were synthesized by loading Ag onto the surface of Zn Co-LDHs/g-C₃N₄using a chemical deposition method.The results of photocatalytic experiments showed that the doping of Ag nanoparticles improved the photocatalytic performance of the material,resulting in a better degradation of sunset yellow and a higher removal rate of methyl orange.Under natural pH conditions,Zn Co-LDHs/g-C₃N₄/5%Ag achieved 92.3%removal of 25 mg/L sunset yellow and 96.0%removal of 20 mg/L methyl orange when the material was dosed at 1 g/L.The photocatalytic process conforms to a first-order kinetic model and the material has good cycling and bacterial inhibition properties.