Preparation Of Hierarchical Hydrotalcite And Its Application In Dye Wastewater Treatment

The direct discharge of dye wastewater from the printing,dyeing and textile industry can cause a serious negative impact on the balance of ecological environment and human health.Therefore,it is of great significance to treat a large amount of organic dye wastewater effectively.Adsorption method is widely used in the treatment of organic dye wastewater because of its simple operation and high efficiency;Photocatalytic technology has a broad application prospect because it can completely remove the pollutants that are difficult to biodegrade and is environmentally friendly.Hydrotalcite based materials have become a research hotspot in the field of dye wastewater treatment by adsorption/photocatalysis due to their wide sources,high dispersibility,strong stability,controllable chemical composition and diversified structure and morphology.Therefore,this paper focuses on the preparation of hierarchical hydrotalcite based materials by one-step method and explores their application in the treatment of organic dye wastewater.The specific research contents are as follows.Mg-Al hydrotalcite with three-dimensional hierarchical flower-like structure and hierarchical hydrotalcite based materials containing transition metal（LDH-M,M:Co,Ni,Cu and Zn）were prepared by one-step double-drop coprecipitation usingγ-Al₂O₃ particles as sacrificial soft template agent.The preparation method is easy to operation,high yield,strong synthetic controllability and environmentally friendly.The effects of different preparation methods,kinds of transition metals,doping amount and system p H on the morphology of LDH-Ni were investigated,and a possible formation mechanism was proposed.The as-prepared hydrotalcite based materials precursor were calcined at 500℃,and the calcined product of Mg-Al hydrotalcite was used as adsorbent to investigate its adsorption performance on three organic anion dyes（Congo red,methyl orange and methyl blue）,and the adsorption mechanism was extensively studied.The experimental results showed that the adsorbent had excellent adsorption capacity and good recycling performance for three organic dyes.The adsorption process could be well described by the pseudo second-order kinetic and Langmuir isotherm models.The excellent adsorption performance is mainly determined by the surface electrostatic adsorption,the“memory effect”and three-dimensional flower-like structure of hydrotalcite.The photocatalytic degradation of organic dyes（methyl orange and methylene blue）was investigated by using the calcined product of LDH-M as photocatalysts.The results showed that the addition of transition metals did not improve the adsorption performance,but greatly improved the photocatalytic performance of the materials,and the photocatalytic process conformed to the pseudo-first-order kinetic.The transition metal Zn doped hydrotalcite based material had a good photocatalytic degradation capability to methylene blue.When the catalyst LDO-Zn was calcined at 500℃ and the dosage was 100 mg,the degradation rate of cationic dye methylene blue could reach more than 96.0%under the environment of weak acid or weak base.The photocatalytic mechanism is that the catalyst generates hydroxyl radicals and holes and other active radicals under ultraviolet light conditions and REDOX with dye molecules to degrade dyes.