Study On CO₂Decomposition Into C With NiFe₂O₄/CoFe₂O₄under Light Illumination

The greenhouse effect caused by carbon dioxide emission has attracted people attention. As a result, the research on CO2conversion is of significant theoretical value and practical implications.Oxygen-deficient MFe2O4reduced by H2can decompose CO2to C at high temperature. We choose ferrites with photocatalytic activity as catalyst for decomposition of CO2in aqueous suspensions and gas phase system, respectively. The effects of light irradiation on photocatalytic reduction of CO2were investigated. The main contents of this thesis are as follows:Firstly, NiFe2O4and CoFe2O4powder were prepared by coprecipitation method and solvothermal-thermal decomposition method, respectively. The results showed that NiFe2O4nanoparticles with a diameter of3-5nm and CoFe2O4nanoparticles with a diameter of10-15nm were prepared by coprecipiation method. NiFe2O4porous nanorods and CoFe2O4porous nanorods were prepared by solvothermal-thermal decomposition method.Secondly, oxygen deficient NiFe2O4-δ formed by NH3reduced were used to decomposes CO2to C under light irradiation in gas phase system, and the influence factors of CO2decomposition activity were discussed. NiFe2O4prepared by a coprecipitation method was reduced by NH3at320℃for80min, and then subjected to the CO2gas. The experimental results showed that CO2could convert to C under light at80℃and the carbon was deposited in forms of carbon nanotubes, carbon microspheres, etc. But CO2conversion to C took place at a temperature higher than200℃in the dark, which indicated that light could reduce CO2decomposition temperature. Compared with the dark, the amount of C at200℃,250℃,300℃under UV irradiation increased obviously. NiFe2O4prepared by solvothermal-thermal decomposition method and CoFe2O4had poor decomposition activity due to their crystallinity and atom structure.Finally, the influence factors of CO2decomposition activity in solution were discussed. The experiment results showed that NiFe2O4prepared by co-precipitation methods could convert CO2to C under the condition of light illumination and the pH=7and10. NiFe2O4showed the best activity under the condition of UV light and the pH of10, and the carbon deposited on the surface of catalysts were in the form of carbon nanoonion and carbon crystallite. CoFe2O4can convert CO2to C only under the condition of light and the pH of10. The poor decomposition activity may be due to large grain size and weak electron-donating ability.