Synthesis And Performance Study Of Saa-ldh Nanoplates Prepared From Lamellar Lyotropic Liquid Crystals Composed Of Anionic Surfactant

Layered double hydroxides (LDHs) are positively charged hydroxides ofdivalent and trivalent metal ions with brucite-like layered structure, whose galleriesare intercalated with charge-balancing anions and water molecules. LDHs have beenwidely used in adsorption, drug intercalation and controlled release, catalysis andflame-retardant. Lyotropic liquid crystal (LLC) is usually composed of surfactant(SAA) at a certain concentration and water, which is of liquid flowing and crystalanisotropic characters. As the repeat distance of LLC is on the nanometer scale, LLChas been widely used as microreactor or template for the synthesis of nanomaterial.Preparation and characterization of LDH nanomaterials with LLC as reaction mediumhas been the research focus of this field.In this thesis, lamellar lyotropic liquid crystals were constructed with anionicsurfactants including sodium dodecyl sulfate (SDS) or sodium di(2-ethylhexyl)sulfosuccinate (AOT), which were used as the microreactors for the preparation ofsurfactant-layered double hydroxides hybrids (L-SAA-LDHs). On this basis, thehydrophobic, non-ionic pesticide Avermectin (AVM) was intercalated into the hybridand the controlled releasing behavior was studied. With the2,4-dicholorphenol (DCP)as a model molecule, adsorption property of the hybrid was characterized. Themorphology, structure and properties of the L-SAA-LDHs product were fullyresearched in this thesis, the growth mechanism of nanostructured LDHs from LLCwas explored, which provided scientific basis for the preparation of superior LDHnanomaterials.The main contents of this thesis were as follows:(1) Preparation of layered L-SAA-MgAl-LDHs from the lamellar LLC composed of SDS or AOT. Effects of SAA concentration, inorganic salt concentration,precipitant dosage and reaction time on the product structure were studied. For thesynthesis of L-SDS-LDHs, salt solution (45mmol/L) was used as solvent to prepareSDS solution (28.6wt%). As the volume ratio of SAA solution to pentanol (Vs/Vpentanol)was fixed as7/3and the precipitant amount r (r=Vapplied volume of precipitant solution/Vtheoreticvolume of precipitant solution) was selected as10, nanoplates with average thickness of3.13±1.01nm was prepared by the reaction time of48h. The product was thin and withtypical layer-oriented character. During the synthesis of L-AOT-LDHs, the appliedconcentrations of SAA and inorganic salt solution were30wt%and90mmol/L,respectively. The amount of the precipitant r was selected as8, by the reaction time of48h, the average thickness of the product was3.28±1.32nm. According to the d003data from the XRD results, the above synthesized L-SAA-LDHs hybrids contained1-2layers of LDH sheets, indicating that the LLC microreactor controlled the productthickness effectively. As the super-thin layers could be directly prepared withoutdelamination, the LLC microreactor method is a flexible and effective method toprepare LDH nanomaterials.(2) Intercalation and sustained release behavior study of AVM. L-SAA-LDHswere used as carriers, evaporating solvent enhanced intercalation method was appliedfor the AVM intercalation. As the anionic surfactant could form hydrophobic regionsin the LDH gallery, when L-SAA-LDH was dispersed in AVM-ethanol solution, theevaporation of solvent prompted the AVM molecules to enter into the hydrophobicregion between LDH layers. As a result, the AVM-SDS-LDHs and AVM-AOT-LDHsproducts were obtained, with AVM content of10.4wt%and8.4wt%respectively. At25oC and pH=7, the AVM released percent from the SDS and AOT hybrids reached45.8wt%and43.7wt%respectively by the releasing time of1d. These resultssuggested that the L-SAA-LDHs could control the drug release so some extent.(3)2,4-dichlorphenol (DCP) adsorption property study. Using the L-SAA-LDHsas adsorbents, adsorption property of DCP was investigated. XRD, FT-IR, UV-visibletechnologies were applied to analyze the hybrid product and adsorption process. Thedynamic experimental data showed that, the adsorption equilibrium could be reachedby the adsorption time of350min. The obtained adsorption isotherms were almoststraight lines, indicating that the prepared L-SAA-LDHs were of superior adsorptioncharacter. As ordered SAA structure was formed in the liquid crystal phase, theordered structure favored the SAA adsorption on the LDHs surface. As a result, theDCP adsorption amount on the L-SDS-LDHs and L-AOT-LDHs reached as high as 1.34and1.01mmol/g respectively. These results indicated that the single-tailed SDSmoledulces were more favorable for the DCP adsorption than the double-tailed AOTmolecules.(4) Synthesis of different SAA-LDH hybrids from lamellar LLC. Lamellarmesophases composed of anionic surfactants SDS or AOT were used as reactionmedia to prepare Ni-Al, Co-Fe, Zn-Al LDHs. The synthesized SAA-NiAl-LDHs andSAA-ZnAl-LDHs were of typical diffraction peaks with high intensity, indicating anordered structure was formed in the product. Experimental results showed that theLLC microreactor method was a simple, effective and versatile method to prepareSAA-LDH hybrids.