Synthesis Of Morphology Controllable And Property Study Of Co₃O₄ Nanomaterials

Because of their special properties,Co3O4 nanomaterials are of considerable importance in technological applications,such as electrochemistry、catalysis、magnetism and so on.In our paper,different morphology of Co3O4 nanomaterials were synthesized by a simple aqueous synthesis method at low temperature.The reaction mechanism on the synthesis of Co3O4 from Co(OH)2 were studied.Then they were used to degrade RhB,thermal decomposition of AP and electrochemical testing.First,The transformation process from Co(OH)2 to Co3O4 was invested detailly and according to this mechanism,nanoparticles of different sizes were prepared by controlling the reaction parameters.When OH-:Co2+ratio<2.0:1,α-Co(OH)2 transformed to Co3O4 with[CoⅡ1-xCoⅢx(OH)2](NO3)x.nH2O as intermediate.When OH-:Co2+ ratio is larger than 2.0:1,α-Co(OH)2 fast transformed to β-Co(OH)2 at the initial stage of the reaction,and CoOOH was the oxidation product.The crystalline size of Co3O4 nanoparticles with 40 nm,30 nm,27 nm,18 nm and 15 nm were prepared under the NaOH concentration of 2 mol·dm-3,0.25 mol·dm-3,0.2 mol·dm-3,0.1 mol·dm-3 and 0.05 mol·dm-3 respectively.Experimental results of RhB degradation showed that samples with smaller size exhibited higher photocatalytic degradation rate.Second,particle-assembled Co3O4 nanorods were successfully synthesized via a simple aqueous method by using CoC2O4 2H2O rods as self-template in basic solution.By controlling the amount of NaOH,crystal characters of Co(OH)2,and growth time,Co3O4 rods with 2～6 μm in length and 0.95 μm in diameter can be obtained.The transformation mechanism of COC2O4·2H2O→Co(OH)2→Co3O4 were also proposed.According to the FT-IR results,trace residual CoC2O4·2H2O plays a supporting role in keeping Co3O4 nanoparticles in rod-shaped assembly.Compared to the Co3O4 rods obtained by calcining CoC2O4·2H2O rods at high temperature,the solution synthesized particle-assembled Co3O4 nanorods performed higher activities on photocatalytic degradation of rhodamine B(RhB)and catalytic decomposition of ammonium perchlorate(AP):degradation efficiency of RhB can reach 70%after 120 min illumination and the high temperature of AP decomposition decreased from 450℃ to 258 ℃ when 3%of Co3O4 was involved.Third,flowerlike hierarchical Co3O4 nanostructures were prepared by wet-chemical method with the assistance of trisodium citrate(Na3Cit·2H2O)under mild conditions.Substitution-oxidation([Co2(CitH-1)2]4-→Co(OH)2→Co3O4)process was proposed for the possible evolution mechanism on the basis of the experimental results,including the amount of Na3Cit·2H2O,reaction time and H2O2 amount.Under condition of Co2+:Na3Cit= 1:1.5,the[Co2(CitH-1)2]4-complex acted as soft-template for forming flowerlike Co(OH)2,then oxidized to hierarchical Co3O4 nanostructures.The obtained flowerlike hierarchical Co3O4 nanostructures exhibited remarkable enhanced visible-light photocatalytic properties on rhodamine B(RhB)degradation and catalytic decomposition of ammonium perchlorate(AP):degradation efficiency of RhB can reach 72%after 90 min illumination and the high-temperature decomposition peak of AP decreased from 450 ℃ to 248 ℃ when 3%of flowerlike hierarchical Co3O4 was used.And after four times cycle,the material also showed good catalytic performance.Fourth,three-dimensional(3D)Co3O4 nanoclusters were fabricated with the assistance of tetrasodium ethylene diamine tetraacetic acid(EDTANa4)through a one-pot wet chemical reaction,featuring self-limiting assembly of building blocks and controlled regrowth process.A possible formation mechanism of the Co3O4-→α-Co(OH)2→Co3O4 was proposed based on the results of X-ray diffraction(XRD),Fourier-transform infrared(FT-IR)spectroscopy and scanning electron microscopy(SEM).The molar ratio range of EDTANa4 and Co2+(1:4-2:3)can build initial clusters as blocks,and the amount of NaOH affected the regrowth process ofα-Co(OH)2→Co3O4.The designed hierarchical Co3O4 nanoclusters exhibit rremarkable enhanced photocatalytic properties on RhB degradation and catalytic decomposition of AP.The RhB degradation efficiency can reach 80%after 120 min illumination and the high-temperature AP decomposition peak decreased from 450℃to 261℃ when 3%of Co3O4 nanoclusters were used.Fifth,Zn-doped Co3O4 nanomaterial was synthesized by a coprecipitation method with Zn(NO3)2 as Zn resource.The Zn-doped Co3O4 nanomaterial was called ZnCo2O4 nanomaterials.Zn:Co ratio plays a key role on the morphology and composition of final samples.When Zn:Co was lower,ZnCo2O4 nanoparticles were obtained;improving Zn:Co ratio,ZnCo2O4 nanocube can be obtained.Further increase of Zn:Co ratio content led to the formation of ZnCo2O4-ZnO nanocubes.ZnCo2O4 samples with Zn:Co ratio of 1:2 exhibited remarkable catalytic performance for H2O2 decomposition.And the ZnCo2O4 samples with Zn:Co ratios of 0:10,3:7,1:2 and 7:3 have capacitance values of 126 F g-1,219 F g-1,272 F g-1 and 85 F·g-1,respectively.Sixth,electrochemical performance of Co3O4 samples with different morphologies were evaluated for supercapacitors by cyclic voltammetry(CV)and galvanostatic charge-discharge testing.At a currert density of 2 A·g-1 in 2 mol·dm-3 KOH electrolyte,specific capacitances of the obtained Co3O4 nanoparticles,Co3O4 nanorods,Co3O4 nanoflowers,Co3O4 nanoclusters are 104,203,270 and 224 F·g-1,respectively.The results show that the hierachical Co3O4 nanomaterials(nanorods,nanoflowers and nanoclusters)display excellent performance than 0D C03O4 nanopaticles.In summary,my thesis focused on the syntheis and property study on Co3O4 nanomaterials.The aqueous strategy in this work is facil,simple,low-cost and environmental friendly.The as-prepared samples have promising applications in electrochemical,degradation of organic pollutants and AP decomposition.