Hierarchically Porous Layered Double Hydroxides: Hydrothermal Synthesis And Adsorption Performance

Layered double hydroxides?LDHs? is a kind of positively charged mental hydroxide and filling exchangeable interlayer anions layer of columnar compounds, already has been widely used in catalysis, medicine, functional materials, ion exchange, and other fields. In order to remove the toxic and harmful pollutants in the water,three different Zn₂+/Al₃+ layered double hydroxides?LDHs? and calcined zinc/aluminum layered double hydroxide, terephthalic acid?PTA? modified magn/aluminum layered double hydroxide were prepared by hydrothermal and ion exchange method. Characterization of the morphology,specific area and texture characteristics, then through the static adsorption experiment showed the adsorption performance of the material. Then study the material through the following three steps: control the morphology of materials; increase the specific surface area and pore volume; change the hydrophilic and hydrophobic in the layer, to increase the adsorption ability, the main conclusion as follow:First, different Zn₂+/Al₃+ layered double hydroxides were synthesized by using methenamine as precipitating, then calcined one of the zinc/aluminum layered double hydroxide under 300?. It was found that calcination destroy the layered structure, but it reconstruction after adsorped phosphate. The sample present hexagonal nanometer flake morphology no matter calcination or not.From the nitrogen adsorption-desorption analysis, its special surface area of the as-prepared Zn/Al-CLDH samples reached 140.55 m²·g^-1. Static adsorption experiments showed that the adsorption of this sample is conform to the pseudo-second-order kinetics equation and Langmuir isothermal model.It can know from the thermodynamic and kinetic research, in nature the adsorption process was endothermic and spontaneous. When the temperature was 303 K and the pH was around 7, the calcined sample show excellent adsorption capacity of 142.3 mg·g^-1 towards phosphate in water.Then, a simple synthesis route is reported for generation of hierarchically porous Zn/Al layered double hydroxides by using urea and trisodium citrate?TSC? as precipitating agent and structure-directing agent, respectively.It was found that the flowerlike Zn/Al-LDHs hierarchically porous assemblies were constructed from hexagonal nanosheets with different sizes. Pseudo-second-order kinetic model was turn out to fit the experimental data well. The adsorption data are better described using the Langmuir adsorption isotherm with excellent adsorption capacity of 98.7 mg·g^-1 towards parachlorophenol in water.Finally, the preparation of Mg/Al layered double hydroxides as a precursor,glycol as a dispersant to synthesis terephthalic acid intercalate Mg/Al layered double hydroxides. The interlayer spacing is increased to 1.442 nm with the modificated Mg/Al layered double hydroxides. It can found that terephthalic acid inserted into the Mg/Al layered double hydroxides and arranged by single vertical way. The SEM characterization results indicate that,the flake structure was thicker and appeared same rodlike structure in samples which added terephthalic acid. The static adsorption experiments indicate the modified and unmodified Mg/Al layered double hydroxides all comform to pseudo-second-order kinetic equation. Langmuir model also fit better to the experimental data.But the modified sample had a big promotion about theadsorption capacity of the p-nitrophenol.Langmuir model provides the best saturation adsorption reached 102.4 mg·g^-1. Secondary circulation regeneration adsorption experiments suggested that the samples which had terephthalic acid intercalated Mg/Al layered double hydroxides can be repeatedly to used in remove of organic pollutants in water, and maintain a good adsorption stability.