Microwave-assisted Solvothermal Synthesis Of Nano Structural CeO₂for Wasterwater Treatment

As a new type of semiconductor material, nano CeO₂was widely used in electrochemical,glass polishing, clarifying agent, vehicle exhaust treatment, ultraviolet absorption and thewater pollution treatment. Due to the broad application prospect of nano CeO₂, researchershad been trying to develop CeO₂nanomaterial with good properties.Because of its unique performance, nano CeO₂was widely used in waste water treatment.Its strong oxygen storage capacity enables it easily react with organic pollutants in water toachieve the purpose of the degradation of pollutants. For this performance, differentmorphology of nano CeO₂, micro/nano structure CeO₂and nano CeO₂composite materialswere prepared in microwave solvothermal way by using cerous nitrate, ammonia and urea asreactants. The samples were characterized by scanning electron microscope （SEM）,transmission electron microscopy （TEM）, X-ray diffraction （XRD）, ultraviolet-visiblespectrum analysis methods and so on.CeO₂nanoparticles in size of about17nm were prepared by microwave solvothermalmethod using ammonia as precipitant. Extending the heat treatment time from2h to3haggravated the aggregation of CeO₂nanoparticles. Good dipersion particles were obtainedwhen the reaction time was2h. CeO₂nanoparticles in size of about13nm were prepared bymicrowave solvothermal method using ammonia as precipitant. CeO₂hollow balls withdiameter of400nm were obained through the self-assemble of CeO₂nanoparticles. Theoptimum reaction condition: the concentration of Ce³⁺was0.01mmol/mL, the heating ratewas12℃/min, the reaction temperature was170℃, the holding time was30min. A largenumber of microporous spheres CeO₂were prepared when the heating rate changed to36℃/min and other condition kept the same. The concentration of Ce³⁺had a great influence onmorphology of products with ammonia as precipitant: when the concentration of Ce³⁺is0.01mmol/mL,CeO₂were hollow spheres with diameter of approximate25nm, when Ce³⁺concentration is0.02mmol/mL,CeO₂were spheres with diameter of about400nm and sticksaround3μm in length, when concentration of Ce³⁺was0.03mmol/mL, CeO₂were balls withdiameter of about15μm and rods with length of40to60μm. Nano CeO₂prepared withammonia as precipitant and hollow nanospheres CeO₂prepared with urea as precipitant had high adsorption and catalysis properties, which were more than90%.Micro-nano structural CeO₂was synthesized by microwave solvothermal method usingPS spheres and absorbent cotton as templates. CeO₂hollow balls with the diameter of about4μm were obtained when using PS spheres as template and the grain size of its primaryparticle was about200nm; Sheet cerium oxide with the thickness of about200nm wasprepared when using absorbent cotton as template and the grain size of its primary particlewas between30nm and40nm. For the hollow balls, the degradation rate on methyl orangewas up to91.4%under visible light irradiation for1h. And the sheet cerium oxide was up toabout60%.To wipe off the impurities on the surface of diatomaceous earth, amplify the specificsurface area and increase the adsorption degradation property, the Shandong diatomaceousearth was acid modified by microwave irradiation. The property of sample which was modifiedwith10%of sulfuric acid under70℃. After modified, the nanocrystalline loaded by dippinghybrid method. After load, the adsorption and degradation properties increased, and when thethe rate of CeO₂and diatomaceous earth was20%, the absorption and degradation ability wasthe highest. The cotton wool was used as carriers. The C/CeO₂composite material with flowersglobal in size of3μm was obtained by microwave precipitation.Influenced by compositematerial,the simulated degradation rate of methyl orange solution was about85%。Small particle of silver sol was synthesized by a microwave solvothermal method. Thesize of silver particle was between10.5to15.8nm. Prepared silver nanoparticles had highadsorption capabilities of light, particularly visible light. The adorption ability of CeO₂whichwas loaded by nano-silver on its surface was higher compared with the unmodified CeO₂. Thedegradation rate of methyl orange improved after modification.