| Porous layered hydroxide compounds have a wide range of applications in environmental governance. It is studied that microcosmic morphology and structure of hydrotalcite were controlled by the changes of synthesis conditions. We have investigated that explored porous hydrotalcite enhancement effect in the field of environmental pollutants adsorption through the preparation of different porous zinc aluminum hydrotalcite with different morphologies, hen their adsorption capacity for pollutant p-nitrophenol in water were discussed.Firstly, porous zinc aluminum hydrotalcite were synthesized by a simple hydrothermal method using HMT as precipitating agent; sodium dodecyl benzene sulfonate(SDBS) as surfactant; sodium tartrate(ST), sodium citrate(SC), and sodium salicylate(SS) as structure-directing agent, respectively. The characterization results indicate that the morphology of zinc aluminum hydrotalcite changed from irregular nanosheets convert to spherical aggregates, sphere-like crystal assemblies and flower-like nanoarchitectures in turn by adjusting the variety of structure-directing agent. Using p-nitrophenol as model pollutant, the batch adsorption experiments were carried out in order to investigate the adsorption capacity of the prepared materials. The zinc aluminum hydrotalcite modified with odium dodecyl benzene sulfonate(SDBS) which prepared with structure-directing agent sodium salicylate(SS) has the biggest surface area of 128.9 m2/g and the best adsorption efficiency for p-nitrophonel of 101.6 m2/g.Then, porous zinc aluminum hydrotalcite were synthesized by a simple hydrothermal method using HMT as precipitating agent; sodium dodecyl benzene sulfonate(SDBS) as surfactant; sodium tartrate(ST) and sodium citrate(SC) as modifying agent, respectively. We can obtain three different kinds of zinc aluminum hydrotalcites which were intercalated by different modifier anion. The samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), and N2 adsorption-desorption techniques. The characterization results indicate that the modified zinc aluminum hydrotalcite exhibit different morphology and surface area, among them, the zinc aluminum hydrotalcite modified with sodium tartrate(ST) possess the highest surface area of 176.9 m2/g. It also has the highest adsorption efficiency of and the saturated adsorption for p-nitrophonel is 154.4 mg/g. With the presence of modifying agent, the interlamellar spacing of zinc aluminum hydrotalcite has increased from 0.757 nm to 2.94, 3.42, 3.73 nm in turn, indicating that the three kinds of modifying agents have inserted into interlayer successfully. Static adsorption experiments show that the adsorption efficiency for p-nitrophonel of zinc aluminum hydrotalcite modified bymodifying agent has increased, the adsorption process is in accordance of the second-order reaction kinetics and Langmuir model.Finally, coprecipitation and ion exchange were used to the preparation of zinc aluminum hydrotalcite intercalated by cyclodextrin(CMCD). The interlayer spacing of original ZnAl-NO3-LDH increased from 0.874 nm to 1.60 nm, indicating that cyclodextrin and nitrate anion have exchanged in the interlayer and CMCD appear as an axis vertical single layer arrangement. The batch adsorption experiments suggested that the modified ZnAl-CMCD-LDH had a faster adsorption rate, higher adsorption efficiency and larger adsorption capacity of 68.07 mg/g compared with the original ZnAl-NO3-LDH. This is because the cyclodextrin molecule has a round barrel structure, the internal cavity of molecule is hydrophobic and the surface of molecule is hydrophilic. The particularity of the molecular structure made cyclodextrin molecule act as a “host” or “principal part”, which form inclusion compound with the addition of “object” through intermolecular interactions(such as charge transfer, van der Waals force, hydrophobic function and ether oxygen keys, etc.), thus improving its adsorption capacity on nitrophenol. The experiments show that and the Freundlich isothermal model and second-order reaction kinetics are more fit for isothermal adsorption. |
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