Preparation And Properties Study Of Hydrotalcite-Like (Composites) Via Coprecipitation Method Using Microreactor

Hydrotalcite-like (LDH) are a class 2D nano-anionic clay made up of positively charged brucite-like layers with an interlayer region containing charge compensating anions and solvation molecules. Because of the flexibility in composition and the exchange ability of interlayer anions, LDH possess a wide range of properties. These materials have various applications, such as catalyst, absorbents, pharmaceutics, carriers for enzyme immobilization. In view of the high application value of LDH, its preparation methods have garnered much attention. However, there are still some defects in carriers for enzyme immobilization and the removal of anionic pollutants, such as poor dispersion, agglomerates and non-uniform dispersion of LDH. Recently, micro reactor has been widely used in the preparation of inorganic nano particle. Compared with the macro reactor, micro reactor has completely different geometric characteristics such as micro scale, larger specific surface area, the smaller size and unique flow behavior. In this paper, we reported a new method to synthesis a serious of LDH nanocomposites with different morphologys by using T-type microchannel reactor and surfactant-free reverse microemulsion, and then, the property of it was following been investigated.The main contents of this thesis are as follows:(1) A T-type microchannel reactor was used to prepare Hb-LDHj via the coprecipitation method, concentration of mixed salt solution on the particle size and the particle size distribution of the obtained LDH samples were examined. The results showed that the crystal structure of the LDH samples obtained using the T-type microchannel reactor were similar to those of the materials synthesized by the conventional coprecipitation method. However, the T-type microchannel reactor route could afford small particle size and very narrow distribution of particle size for the materials. XRD results indicate that the Hb connected to LDH surface by forming hydrogen bonds instead of interacted in the interlayers. The fluorescence spectra indicates the environmental polarity around the Trp- and Tyr- residues are enhanced. The results of UV and fluorescence proved that Hb keeps its native conformation in Hb-LDH. The catalytic activity of Hb was studied using H2O2 oxidation of o-phenylenediamine (OPD) to phenazine as a model reaction. Though the catalytic activity of immobilized Hb are lower than free Hb in water at 25 ℃, the catalytic activity of immobilized Hb are higher than free Hb in water at 90 ℃. The Hb-LDHT is higher than Hb intercalated LDH both in water at 25 ℃ and 90 ℃. The Hb-LDHT is 8.72 times that of free enzyme and 2.96 times that of Hb-LDHc in water at 90 ℃. The recycle capability of the materials were also assessed. After 5 repeated uses, the activity of the Hb-LDHT was maintained at 82.69% of the initial activity, not a major loss. After cold storage for 30 days, the activity of Hb-LDHT was still possessed 85.86% of its initial activity and the immobilized enzyme also remained at a high level of activity with a good stability.(2) The Mg2Al-LDH nanosheet dispersion was obtained by a double-microemulsion technique in a surfactant-free reverse microemulsion composed of bmimPF6, DMF and water. The LDH nanosheets consisted of a single brucite layer without any loading of organic molecules. Compared with the conventional coprecipitation method, LDH from reverse microemulsion exhibited smaller particle size, higher specific surface, better thermal stability, and uniform dispersion. The BET surface analysis and porosity results indicate that LDHM to be obtained with a relatively high surface area with values ranging between 78 and 202 m2/g. After calcination, layer structure of LDH was destroyed and appeared diffraction peak of mixed MgAl(O) (calcined Mg-Al-LDH, LDO); LDOg, LDHT and LDHC on phosphorus removal rate can reached 95%,75% and 57% on conditiongs of material amount 1 g/L,5mL phosphorus wastewater of 2 mg/L, initial pH=5,25 ℃, processing time 24 h. When tested as adsorbents in phosphorus removal, the LDOg showed excellent performance, and the adsorption capacities of LDOg for phosphorus were better than those of LDHT and LDHc. By comparing the results from desorption assays, it is suggested that phosphate uptake on LDOg is mainly due to the structural rebuilding of LDOg played and ion exchange between the interlayer anions and phosphate ions, while the phosphate uptake on LDH is largely attributed to physico-chemical adsorption. The recycle capability of the materials were also assessed.