The Synthesis And Properties Of Layered Hydroxide Acetates

Recently, environmental pollution is one of the hot topics that have attractedattention from all over the world. The effluent discharged by many industries containsa considerable amount of dyes. The presence of dye in water interfere with lightpenetration and thus reduce the photosynthesis of the aquatic plants which destroyaquatic ecosystems. Many dyes are toxic, and this brings about a serious hazard toaquatic organisms as well as the human health. Adsorption is an efficient way toremove dyes especially when they are non-biodegradable and has found wideapplications. Many adsorbents are used to remove dyes from wastewater. Among thedifferent adsorbents, hydrotalcite-like compounds with interlamellar reactivity arepromising adsorbents for the removal of dyes.Hydrotalcite-like compounds are those which have similar structure but differentcomposition of hydrotalcite, including layered double hydroxides ([MII1–xMIIIx(OH)2]x+(An)x/n·mH2O) and layered hydroxide salts (M(OH)2x(Am)x/m·nH2O).Due to the special layered structure, the hydrotalcite-like compounds have thefollowing characteristics: cation-exchange ability of the brucite layer andanion-exchange ability of the interlayer space. These compounds are widely used inmany areas, such as adsorption, catalyst, ion-exchange, flame retardants andbiological materials. Many studies have been carried out on layered doublehydroxides, focusing on their physicochemical properties, surface modificationreactions and applications, while relatively few publications deal with layered hydroxide salts, mainly describing their synthesis and structural characterization.Applications of layered hydroxide salts have seldom been explored. Due to the similarstructure, layered hydroxide salts have similar physical and chemical properties oflayered double hydroxides, such as good ability of ion exchange, adsorption ability,etc. In this article, we describe the synthesis and properties of layered hydroxideacetates. The major research work is as follows:1. CuZn DHS have been synthesized using a facile solution phase method, anddiscussed the adsorption behavior of MO on CuZn DHS. We found CuZn DHS withdifferent specific surface area have different adsorption capacity of MO. CuZn-1withhigh specific surface area showed the highest adsorption capacity for MO with aremoval efficiency of95.3%. However, the MO adsorption capacity of CuZn-2andCuZn-3are different although their specific surface areas are almost the same. Inorder to detect the adsorption capacity of the material with Cu/Zn molar ratio is zero,we synthesized LHS-Zn using the same method, and tested its adsorption capacity. Itshowed very low adsorption capacity with a removal efficiency of5.5%. The XRDand SEM results of LHS-Zn after adsorption indicated that LHS-Zn was unstable inaqueous solution, which led to the low adsorption capacity. The adsorption behaviorof MO onto CuZn-1was further investigated. Adsorption isotherm was fittedaccording to the Langmuir model, which indicated that adsorption sites werehomogeneous with each site accommodating one molecule only and there was nointeraction among adsorbed molecules. The adsorption process followed thepseudo-second-order kinetic model, which suggested that the rate limiting step was achemical adsorption process. Based on the XRD and IR of CuZn-1after adsorption,we studied the adsorption mechanism, combined with intraparticle diffusion model,we believed that the adsorption process of MO was a complex process. The surfaceadsorption and the interlayer ion exchange occurred concurrently. The high adsorptioncapacity of CuZn-HDS reported here demonstrates that an important role of thesematerials as potential adsorbents for removal of pollutants from wastewater.2. ZnO nanowires have been successfully obtained using a top-down methodwith LHZA nanobelts as precursors. ZnO nanowires have uniform diameters of about 3nm~5nm and lengths of several hundred nanometers. From the TEM, we could findsome NWs had the same boot due to the inadequate splitting of the NBs and somewere still connected with plate-like structures. We investigated the effect of thetemperature on the nanowires. The results showed that ZnO nanowires were obtainedonly at room temperature, the low or high temperature was not conducive. In order tounderstand the formation process of ZnO nanowires, we also investigated the effect ofthe reaction time on the growth of nanowires. When keeping the NBs in water for1day, small amount of nanowires were obtained. Long and thin NWs were obtainedafter an incubating time of2day. With the extension of incubating time, acetates inwater were gradually increased and reacted with LHZA to generate ZnO nanorods.According to the above results, we explored the formation mechanism of nanowires.The formation process of nanowires can be described as the splitting of LHZA due tothe releasing of acetates between layers. It is responsible for this novel top-downmethod to prepare other ultrathin metal oxides nanowires. We also studied themorphology and structure of the products obtained by ion exchange, and found thatthe nanowires were observed only after incubating LHZC in water.3. The Knoevenagel condensation between benzaldehyde and diethyl malonatewas used as a probe reaction to detect the catalytic ability of CuZn DHS, LHS-Zn,ZnO nanowires and commercial ZnO by comparing the conversion of diethylmalonate. The results showed that the basicity of metal-oxygen bond had an importantrole on the basicity of the materials.