A One-pot Approach To Prepare TiO₂/layered Double Hydroxides Complex Absorbent

Layered double hydroxides （LDH） are a class of emerging from a positive divalentmetal hydroxide layer and interlayer anions with regular layered structure. LDH has abase-catalyzed redox catalysis function because of divalent and trivalent metal cationsare many types according to different uses in a wide range modulation, thus greatlybroadens the scope of application of LDH. At the same time as the LDH interlayerexchangeable anions can be organic, inorganic anions and complexes into layers, it ispossible to achieve different functions. Preparation of LDH system is complex, thefactors affecting the structure of the products are from many aspects. So, how to get alayered structure of LDH is a prior topic.This departure was from the solution precipitation method, by controlling thecationic species, the proportion of cations as well as precipitating agent during thepreparation to get LDH with different structures. After X-ray diffraction （XRD）,scanning electron microscopy （SEM） analysis these results were characterized thatZn-Al is a cation, the ratio of3:1, NaOH-Na₂CO₃as precipitant to prepare LDH, thelayered structure was more complete and clear, the surface layer defects and lessdistortion, and the resulting LDH sheet size was about400nm. Further analysis showedthat the thermal properties of the entire structure of LDH accounted for63%of thewater content. BET adsorption tests showed surface area of the LDH was37.3m2/g,average pore size was101. The adsorption of the fuel dye showed that LDH canbasically within half an hour to reach equilibrium.A one-pot approach to prepare a hierarchically nanostructure composite ofTiO₂/ZnAl LDH was firstly reported by simply mixing the precursors of TiO₂and ZnAlLDH at optimized conditions.By adjusting the material of tetrabutyl titanate added tocontrol the amount of the compound TiO₂. XRD and SEM tests showed that by adding acertain degree of TiO₂undermined the integrity of layered structure of LDH, LDH layersurface was covered the small particles size of about50nm. At the same time we foundthat high pressure treatment resulted in serious collapse of LDH layered structure,therefore it was not applicable to the composite systems. Infrared （FITR）andX-rayphotoelectron spectroscopy （XPS） showed that composites contained a lot of metalelements and oxygen, the oxygen atom linked metal atoms, so that the whole layeredstructure intact. Adsorption tests showed that BET specific surface area of compositeswere80-100m2/g, was3.5times of pure LDH. Dye adsorption experiments showedthat the adsorption to methylene blue of TiO₂/LDH complexes was more than doubledof LDH. Bangladesh Red and methyl orange basically reached completely adsorbed. Overall the adsorption performance of TiO₂/ZnAl complex was greatly improved thanpure LDH. At the same time, we further explored the dynamic mechanism for dyeadsorption of pure LDH and TiO₂/LDH, studied the combination form of the dye andthe adsorbent. Preliminary studies indicated that the dye was maily exchanged withinterlayer anions CO₃^2-and the interlayer bound water to reach adsorption. Thesignificantly enhanced adsorption ability of LDH after incorporation of TiO₂by thisnovel strategy made the developed composites promising for diverse applications.