Controllable Synthesis Of Mesoporous Alumina And The Application Of CeO₂/Al₂O₃ Catalyst In Fenton-like Reaction

Activated alumina with mesoporous structure was commonly used as adsorbent,catalyst and catalyst support in adsorption and separation of pollutants as well as heterogeneous catalytic reactions due to its large specific surface area,high thermal stability,surface acid-base property and dispersion activity of surface species.Herein,mesoporous?-Al₂O₃ including hexagonal nanoplates and hierarchically olive-like particles were successfully architected in different synthesis systems using ionic liquid-assisted hydrothermal method.The structures of final products can be tailored by adjusting the reaction conditions,and the mechanism on the the structure construction of alumina with ionic liquid as the template was investigated in depth.Moreover,the synthesized olive-like alumina was utilized as the support for the fabrication of CeO₂/Al₂O₃ catalyst via an ultrasound-assisted deposition-precipitation route.And the catalytic activity was evaluated by Fenton-like degradation of acidic orange 7?AO7?.First,?-Al₂O₃ hexagonal nanoplates was synthesized via hydrothermal method using aluminum chloride as the aluminum source,n-butylamine as the precipitant and[Bmim]BF₄ as the template.The addition of[Bmim]BF₄ could change the crystallization mode and the growth orientation of the precursor.Meanwhile,the structural transformation from rhombohedral nanosheets to hexagonal nanoplates could be realized by adjusting the content of ionic liquid,reaction temperature and reaction time.The well-defined?-Al₂O₃ hexagonal nanoplates were finally formed with the molar ratio of[Bmim]BF₄ to aluminum source at 0.15 by reacting 24 h at 160^oC.Compared with the rhombohedral nanosheets prepared without[Bmim]BF₄template,the obtained?-Al₂O₃ hexagonal nanoplates possessed relatively larger specific surface area(203 m²g^-1)and more uniform ink bottle-shaped mesoporous structure?4.2 nm?.Well-defined olive-like alumina with hierarchical structures was successfully synthesized by the hydrothermal method with aluminum nitrate as the aluminum source,urea as the precipitant and[Bmim]BF₄ still employed as the template.The effects of ionic liquid concentrations,urea dosages,reaction temperature and reaction time on the microstructures and pore parameters of alumina products were investigated systematically.The results suggested that the synthesized olive-like alumina displayed a slit-like mesoporous structure with the BET specific surface area of 178 m² g^-1,average pore volume of 0.59 cm³g^-11 and pore diameter of 12.35 nm.Based on the above experiments,the template mechanisms how[Bmim]BF₄ induces crystal growth and structure architecture were discussed in detail.CeO₂/Al₂O₃ catalysts with different CeO₂ loadings were prepared with the synthesized olive-like alumina as the support using an ultrasound-assisted deposition-precipitation method,and then employed for Fenton-like degradation of AO7.The effects of CeO₂ loadings on the microstructure,surface properties and catalytic performance of CeO₂/Al₂O₃ catalysts were deeply investigated.The result showed that the CeO₂ nanoparticles on Al₂O₃ support were highly dispersed and possessed an average grain size of about 4-5 nm,which is smaller and more uniform than that of the pure CeO₂.The catalyst prepared with the molar ratio of CeO₂ to Al₂O₃ at 0.2 displayed the highest catalytic activity,the removal efficiency of AO7reached 98%under visible light irradiation,and the degradation rate constant was2.03×10^-22 min^-1.Besides,the catalyst also showed an excellent reusability during the cycle experiments.