Preparation Of Spherical γ-Fe₂O₃ By Rapid Solvent Evaporation And Its Application In Oxidation Reaction

Magnetic nanomaterial have many advantages,especially in the field of environmental protection.It can not only separate and recycle products,but also catalyze the degradation of phenol and other toxic industrial waste water to meet the needs of today’s green environmental friendly chemistry.The traditional synthetic route has the disadvantages of high cost and complicated process.The research of low cost and simple operation is the current main task.In this paper,a sphericalγ-Fe₂O₃ catalyst was synthesized by rapid solvent evaporation method,which is used to catalyze the oxidation reactions.The main research contents are as follows:（1）The mixture of ferric acetylacetonate,sodium carbonate and sodium nitrate were used as precursors to prepareγ-Fe₂O₃ catalyst by rapid solvent evaporation method.The crystal phase,surface group and morphology of the catalyst were characterized by XRD,Raman,XPS,TEM,BET and FT-IR.Results showed thatγ-Fe₂O₃ catalysts were spherical formed by aggregation of small particles and its specific surface area is 87 m²·g^-1.The surface ofγ-Fe₂O₃samples contain hydroxyl and carbonyl group.By investigated the composition of the precursor,concentration ratio,solvent and solvent temperature.It was found that the highest activity catalysts areγ-Fe₂O₃which is synthesized by the ratio of 1:1:10 to acetylacetone iron,sodium carbonate and sodium nitrate,6:4 to ethanol and water as solvent under 300℃rapid evaporation.When the evaporation solvent temperature is above 400℃,part ofγ-Fe₂O₃ is converted toα-Fe₂O₃.Using acetonitrile as solvent,theγ-Fe₂O₃ is 0.0167g,benzyl alcohol is0.5m L,hydrogen peroxide is 2m L.After reaction at 78℃for 10h,the conversion of benzyl alcohol and the selectivity of benzoic acid reach 86.78%and 69.78%respectively in the catalytic reaction.Further experiments show that the solvent has a special effect on the reaction.When the solvent is n-heptane,the selectivity of benzaldehyde reaches 100%.When the solvent is dichloromethane or chloroform,the conversion rate of benzyl alcohol is up to100%.If preparating theγ-Fe₂O₃through using the conventional room temperature slowly heated to the specified temperature or the first drying and then baking heating method is non-uniform and slightly decreased of specific surface area.The activity of benzyl alcohol is decreased significantly.It can be obtainedα-Fe₂O₃when ferric chloride or ferric nitrate was used as the ferric salt instead of ferric acetylacetonate,and the activity of catalytic oxidation of benzyl alcohol is significantly lower thanγ-Fe₂O₃.Therefore,the catalytic activity of Fe（acac）₃as the iron salt through rapid solvent evaporation method was better than that of the conventional method in the catalytic oxidation of benzyl alcohol.Theγ-Fe₂O₃ is magnetic and easy to be separated and recycled.Its catalytic activity is almost negligible after three cycles.（2）Theγ-Fe₂O₃samples are synthesized by fast solvent evaporation under various conditions used in the catalytic decomposition of hydrogen peroxide.By investigating the effects of preparation and reaction conditions on the decomposition of hydrogen peroxide.It was found that theγ-Fe₂O₃which is prepared by the ratio of 1:1:10 to acetylacetone iron,sodium carbonate and sodium nitrate,6:4 to ethanol and water as solvent can reduce the activation energy of decomposition of hydrogen peroxide from 220000 J?mol^-1 to 2333 J?mol^-1.It significantly increases the rate of decomposition of hydrogen peroxide;wherein,n-heptane as solvent,the amount of catalyst is 0.01g,After reaction at 60℃,the rate constant of the decomposition of hydrogen peroxide reaches 0.127min^-1.