Preparation And Oriented Assembly Of LDHs, MMO Nanoparticles And Their Applications In Waste Water Treatment

In order to realize the application of layered double hydroxides (LDHs) and mixed metal oxides (MMO) in waste water treatment, preparation and oriented assembly of LDHs and MMO nanoparticles have been investigated, and the capacities and mechanisms of removing sulfide anions (S^2-) and methyl orange (MO) have been systematically investigated. The main results are as follows:1．Based on the exchangeable property of the interlayer anions and the so-called "memory effect" of LDHs, the capacities and mechanisms of removing sulfide anions (S^2-) were studied using chloride-containing MgAl-LDHs (MgAl-Cl-LDHs) and MgAl-MMO. Structures of the products obtained by anions exchange and reconstruction respectively and the removal capacities were characterized by XRD, FT-IR, UV-Vis and ICP, and the different mechanisms for MgAl-Cl-LDHs and MgAl-MMO were proposed. The results indicated that the removal capacity for MgAl-MMO was much greater than that for MgAl-Cl-LDHs. When pH is 9, S^2- was hydrolyzed and mainly existed as HS^-in the solution. When MgAl-Cl-LDHs was used to remove S^2-, due to the weaker exchange ability for HS^-compared to Cl^-, HS^- could not enter the interlayer through anions exchange with Cl^-. Adsorption of HS^-to the sample's surface and oxidation to S₂O₃^2- are the removal mechanisms for MgAl-Cl-LDHs. While when we used MgAl-MMO, during the structure recovering, HS^-entered the interlayer qickly, and were oxidized to thiosulfate anions (S₂O₃^2-) and polysulfide anions (S₂^-and S₃^-) simultaneously because MgAl-MMO has the abilities to catalyze and oxidize. Therefore, it can remove S^2- efficiently. The products of LDHs with Mg/Al molar ratio of 2 calcined at 500℃were shown to have a high degree of removal capacity, which had reached above 98%. Therefore, it is a method with high efficiency to remove S^2- by using MgAl-MMO.2．Novel, simple and general methods for ZnAl-NO₃-LDHs and ZnAl-MMO nanoparticles oriented assembly to films have been developed. The uniform and small crystal size of LDHs nanoparticles favor not only face-to-face type interactions but also edge-to-edge type interactions between individual LDHs nanoparticles, and is the major factor in the formation of a uniform densely packed c-oriented LDHs film. Highly ordered transparent films of ZnAl-NO₃-LDHs with a size of the order of cm² have been obtained by the simple method. Furthermore, highly homogeneous oriented large crack-free nanostructured ZnAl-MMO films with narrow mesopore size distribution have been fabricated using low-cost and easily processible inorganic hydroxide as precursor.3．The capacities and mechanisms of removing MO which was simulated as organic contamination have been studied using ZnAl-NO₃-LDHs and ZnAl-MMO films. The results indicated that the removal capacity for ZnAl-NO₃-LDHs films was much greater than that for ZnAl-MMO films. When ZnAl-NO₃-LDHs films were used as the precursor to remove 20mg/L MO, due to the anionic exchange and adsorption for MO, the removal capacity could reach 97．92%, and the loading was 196．68mg/g. Though reacted for 96h, the morphology and c-oriented property of the film were preserved. Therefore, it is a method with high efficiency to remove low concentration MO by using ZnAl-NO₃-LDHs films. While when ZnAl-MMO films were used, MO was only adsorbed to the surface, thus they cannot remove MO efficiently.