Study On Catalytic Performance Of Heterogeneous Fenton-like System Of CeO₂ Nanocrystals With Different Morphologies

The traditional Fenton technique(Fe2+/H2O2)is an effective and promising method for treating industrial wastewater due to the formation of HO·,which react rapidly and nonselectively with organic compounds.However,the homogeneous Fenton process has some critical disadvantages,such as the method mostly performs well in low pH condition(pH 2.0～4.0),dissolved iron recovery is difficult and ferric hydroxide sludge will be produced.The heterogeneous Fenton reaction provides an alternative to circumvent the shortcomings of homogeneous catalysis by using a solid catalyst.Among these solid catalysts,CeO2 has gained considerable attention.However,the precise pathway for the reaction between nanocerium and H2O2 remains unclear.In this work,CeO2 nanocubes and nanorods were prepared by a hydrothermal method,and their Fenton-like catalytic performance for the degradation of organic pollutant were investigated using 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS),methylene blue(MB)and Congo red(CR)as the model organic pollutant in the presence of H2O2.And then the Fenton-like properties of CuO-CeO2 and Fe3O4-CeO2 were also investigated.The main results are as follows:(1)The Fenton-like properties of CeO2 NPs were investigated under both acidic and basic conditions.Nanoceria possesses strong strong morphology-and pH-dependent Fenton-like catalytic activity for the degradation of ABTS,MB and CR.Compared with ceria nanocubes,ceria nanorods exhibited a higher peroxidase activity.Two types of oxidative species were generated in the CeO2/H2O2 systems,namely,HO· and peroxide-like intermediates.Under acidic conditions,HO-is primarily responsible for the Fenton-like catalytic activity of CeO2 NPs;under neutral and basic conditions,HO and peroxide-like intermediates are responsible for the activity.(2)The removal of MB or CR was investigated to better understand the oxidizing ability of CeO2/H2O2 system under alkaline conditions.It can be found that MB exhibited weak adsorption over the nanoceria surface via electrostatic attraction,whereas the adsorption of MB was enhanced significantly in the presence of H2O2.While CR was adsorbed through Lewis acid-base interactions and an adsorption competition existed between CR and H2O2.The degradation of CR catalyzed by CeO2 was much faster than that of MB,and nanorods degraded CR rapidly in comparison to that of nanocubes.(3)MB could be removed from aqueous solution by mixture of CuO NPs and CeO2 NPs from pH 3.0 to 9.0.The removal of MB was by the Fenton-like reaction under acidic condition or by the adsorption and Fenton-like reaction under weak alkaline condition.The Fenton-like catalytic activity of CuO NPs could be enhanced by CeO2 NPs from pH 3.0 to 9.0,which is dependent on the morphology of CeO2 NPs and the pH value of system.(4)The Fenton-like activity of Fe3O4 NPs was associated with the pH and their size and shape.Octahedral Fe3O4 NPs is more stable than spherical Fe3O4 NPs.The morphology of CeO2 NPs had a significant influence on the Fenton-like activity of Fe3O4NPs in Fe3O4-CeO2/H2O2 systems.