Preparation And Application Of Attapulgite Nanocomposites With Magnetic And Electric Properties

Attapulgite （AT） is a hydrated magnesium aluminium silicate with fibrillar geometry. Its porous crystalline structure and negative charge provide it with strong sorption capacity for the removal of pollutants from aqueous solution, especially, heavy metal ions and dyes. However, some limitations still existed, such as the difficulty in separation from aqueous dispersion and recycling, inhibiting their practical application in the environment. In this thesis, Fe₃O₄-AT magnetic nanocomposites were prepared by ultrasonic co-deposition method. The as-prepared composites were characterized systemically and the detail analyses on the adsorption properties of Methylene Blue for the nanocomposites were carried out. Generally, the work can be summarized as follows:1. Fe₃O₄ nanoparticles were synthesized on the surface of acid-treated AT in aqueous suspension by a simple ultrasonic co-deposition method. Fourier transform spectroscopy （FT-IR）, X-ray diffraction analysis （XRD）, Field Emission Scanning Electron Microscopy （FESEM）, BET specific surface area measurements and Vibrating Sample Magnetometry （VSM） were used to characterize the Fe₃O₄-AT nanocomposites. The results indicated that Fe₃O₄ nanoparticles with diameters ranging from 10nm to 30nm were well attached on the surface of AT. The specific saturation magnetization（os） of the nanocomposites was increased from 18.34 to 63.67emu/g as increasing Fe₃O₄ content. The BET surface area of as-prepared nanocomposites first increased, and then decreased when Fe₃O₄ content increased and the maximum value was 152.9m²/g.2. Through simple magnetic procedure, the studies of removal of heavy metal ions Ni（II）、Cr（III）、Zn（II）、Ag（I） and Methylene Blue from aqueous media with Fe₃O₄-AT nanocomposites were performed. The results showed that the adsorption efficiency of the nanocomposites for Ni（II） was higher than other heavy metal ions and the removal rate was above 66%. For Methylene Blue, the maximum removal rate has reached 99.93%. Moreover, we also found that the high adsorption efficiency was regained even after four cycles of acid-regeneration.3. The effect of various experiment parameters, including adsorbent dose, temperature and initial Methylene Blue concentration etc., on the adsorption property of Fe₃O₄-AT nanocomposites were investigated by using a batch adsorption technique. It was found that the fewer adsorbent dose, the higher initial Methylene Blue concentration as well as the higher temperature in the adsorption processes may result in more equilibrium adsorption capacity of the nanocomposites. The adsorption isotherms model, kinetics model and thermodynamic parameters of dyes onto nanocomposites were also proposed. The results demonstrated that the equilibrium values were fitted well by the Temkin isotherm equation and the adsorption behavior of Methylene Blue onto the nanocomposites followed pseudo-first-order kinetics, which was in according with Saeid Azizian’s theory. The thermodynamics parameters of enthalpy changes （ΔH^o） and entropy changes （ΔS^o） were: 4.93kJ/mol and 27.94J/mol·K, respectively. The Gibb’s free energy changes （ΔG^o） were negative values at different temperatures. These results further suggested that adsorption thermodynamics of Methylene Blue were a spontaneous and endothermic process and thus increasing temperature was in favor of adsorption.Additionally, we considered that Ag nanoparticles are prominent candidate in superconduction, electronics, antibacterial action and catalysis. In this thesis, AT-Ag nanocomposites were prepared via chemical reduction of silver nitrate in liquid phase, using NaBH₄ as reducing agent. By means of various characterization methods, such as FESEM, XRD, UV-Vis, Scanning Probe Microscope （SPM）, energy-dispersive spectrometers （EDS） and electrometer, the micro-morphology, chemical composition and crystallinity of the AT-Ag nanocomposites have been investigated. The electric properties of the nanocomposites for conductive materials were also studied.