Study On Preparation Of NaA/Polymer Nanocomposites Using Natural Halloysite As A Starting Material

Because of its ordered three-dimensional structure, NaA zeolite has a largesurface area, a strong negative charge in lattice, which gives rise to the ion-exchangeor adsorption capability. NaA zeolite is also applied in catalytic cracking, polarity-nonpolar molecule separation, separating gas from liquid by the reason of unique poresize. Therefore, NaA zeolite is widely used in chemical industry, environmentalprotection, petroleum, metallurgy, and high-tech fields.Halloysite nanotubes (HNTs) are a cost-effective and readily available naturalmineral, consisting of SiO2and Al2O3with stoichiometric ratio of2:1. The chemicalcomposition is very close to NaA zeolite. Using halloysite as original material, NaAzeolite can be synthesized simply through adding a certain amount of sodiumhydroxide. Based on this idea, we used the natural halloysite as a starting material toprepare NaA zeolite/chitosan hybrid porous beads and NaA zeolite/PES hybridmembrane. The performance of adsorbing ammonium onto NaA zeolite/chitosanhybrid beads and separating oil from water by NaA zeolite/PES hybrid membranewere studied.(1) Synthesizing NaA zeolite/chitosan hybrid beads and investigating theadsorption properties of the as-synthesized NaA zeolite/chitosan hybrid beads forammoniumWe used the natural materials of halloysite and chitosan to prepare a newadsorbent of NaA zeolite/chitosan porous hybrid beads by in-situ hydrothermalsynthesis method. The XRD indicated that the as-synthesized NaA zeolite crystalswere perfected. SEM showed that the porous hybrid beads were composed of6~8μmsized cubic NaA zeolite particles congregated together with chitosan. The effect ofadsorbent dosage, pH, temperature, contact time, initial concentration on theadsorption behavior of NH4+from aqueous solution onto hybrid beads wasinvestigated in static conditions. The adsorption behavior predominantly followed thepseudo-second-order kinetic model The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. A maximum adsorption capacityof47.62mg/g at298K was achieved according to Langmuir model. The adsorptionwas a spontaneous and exothermic process. The regenerated or reused experimentsindicated that the adsorption capacity of the hybrid beads could maintain in90%above after10times successive adsorption/desorption cycles.The effect of bed height, initial concentration and flow rate on adsorptionbehavior of NH4+from aqueous solution onto hybrid beads was investigated indynamic conditions. As the increase of bed height, initial concentration and thedecrease of flow rate, the adsorption capacity of NH4+onto hybrid beads wasincreased. The experimental dates were fitted well to the BDST and Thomas model.The adsorption/desorption cycle experiment were carried out under the columnconditions, and the beads also showed good regeneration. Furthermore, theexperiment mentioned above lasted for long time in aqueous. The morphology andsize of the hybrid beads did not change, and the hybrid beads kept a good chemicalstability and high crushing strength. The high adsorption and reusable ability impliedpotential application of the hybrid beads for removing NH4+pollutants fromwastewater.(2) Synthesizing NaA zeolite/PES hybrid membrane and investigating theperformance of separating oil from waterUsing PES as membrane material and activated HNTs as additives, PES castingsolutions and activated HNTs/PES blending casting solutions were preparedrespectively. We prepared hybrid membrane Ⅰ and hybrid membrane Ⅱ and furthertransformed the membrane into NaA zeolite/PES hybrid membrane Ⅰ and NaAzeolite/PES hybrid membrane Ⅱ respectively through in-situ hydrothermal reactionin alkaline solution. The XRD demonstrated that pure NaA zeolite was synthesizedsuccessfully in PES membrane. The SEM showed that the NaA zeolite/PES hybridmembrane Ⅰ had obviously double layer structure. One of the layers was PESmembrane, in which there existed the interconnected finger-like pore. The other layerwas composed of1~2μm sized cubic NaA zeolite particles and PES. Nevertheless,the NaA zeolite/PES hybrid membrane Ⅱ did not have the double layer structure.The contact angle indicated that the surface of as-prepared NaA zeolite/PES hybrid membrane Ⅰ and NaA zeolite/PES hybrid membrane Ⅱ with goodhydrophilicity can be wet by pure water. Compared with the pure water flux of PESmembrane (27.45L/m2·h), the pure water flux of NaA zeolite/PES hybrid membraneⅠ and NaA zeolite/PES hybrid membrane Ⅱ could reach31.2L/m2·h and55.58L/m2·h, respectively. The test of oil-water separation showed that the free oil anddispersed oil could be rejected effectively by NaA zeolite/PES hybrid membrane Ⅰand NaA zeolite/PES hybrid membrane Ⅱ.In conclusion, using HNTs as starting material, we prepared NaA/Polymernanocomposites successfully. As-prepared NaA zeolite/CTs hybrid beads and NaAzeolite/PES hybrid membrane had good performance of adsorbing ammonium inaqueous and separating oil from water, respectively.