Preparation And Properties Of Alumina And Its Composite Aerogels

Al₂O₃ aerogel was mostly used in the fields of heat insulation,catalyst support and adsorption due to its unique porous structure,infinite path effect in heat conduction,excellent performance as a catalyst support and the formation of AlO-OH in water to provide adsorption performance.However,the Al₂O₃ aerogel prepared via conventional method possessed relatively high density,which was the key factor to affect Al₂O₃ aerogel used as heat insulation,catalyst support and adsorbent material.Therefore,reducing the density of Al₂O₃ aerogel was the focus of broadening the application of Al₂O₃ aerogel.In this work,Al₂O₃-based aerogels with ultra-low density?about 9 mg/cm³?were prepared via solution-freeze-drying-calcination technology using AlCl₃·6H₂O as aluminum source and chitosan as the template.Meanwhile,thermal insulation property,catalytic performance as catalyst support and adsorption performance to U?VI?were researched.The researches showed that the as-prepared Al₂O₃ aerogel possessed a relatively good thermal insulation performance.Meanwhile,compared with pure Pt as a catalyst to catalyze the thermal decomposition of ammonium perchlorate?AP?,the thermal decomposition temperature of AP was reduced by nearly 30°C and the exothermic heat increased by 699 J/g using Al₂O₃aerogel as a Pt catalyst support.Moreover,the maximum adsorption capacity of U?VI?on Al₂O₃ aerogel was 769.9 mg/g and the adsorption efficiency almost remained constant after5 cycles.These results indicated that the as-prepared Al₂O₃ aerogels had excellent properties in the fields of heat insulation,catalyst support and adsorption.The adsorption property of Al₂O₃ aerogel have been studied in depth due to its high adsorption capacity.The researches indicated that Al₂O₃ aerogel prepared with different templates or different aluminum salts would have different microstructures,which could result in different adsorption property.Therefore,various Al₂O₃ aerogels were prepared using different aluminum salts and different templates and these Al₂O₃ aerogels were characterized by scanning electron microscopy,Fourier transform infrared spectrometer,thermogravimetric analysis,X-ray diffraction and X-ray photoelectron spectroscopy.The results showed that the Al₂O₃ aerogel truly copied the microstructure of chitosan.Furthermore,U?VI?was selected as an adsorbate of hexavalent actinides in this study.The adsorption properties of Al₂O₃ aerogels to U?VI?were compared and estimated,including the effect of the initial pH of the solution,the adsorption time,the initial concentration of U?VI?solution,different coexisting ions in wastewater and reusability of the adsorbents.The results showed that the adsorption of U?VI?on Al₂O₃ aerogels reached adsorption equilibrium within 180 min and the maximum adsorption capacity of Al₂O₃ was 805.58mg/g.Meanwhile,the adsorption of U?VI?on Al₂O₃ aerogel was independent of coexisting ions and the adsorption efficiency almost remained constant after 5 cycles?about 90%?.In conclusion,the results displayed that Al₂O₃ aerogels were excellent adsorbents to U?VI?.Finally,the interaction mechanism between U?VI?and Al₂O₃ aerogel was elaborated via X-ray photoelectron spectroscopy.