Preparation,Characterization And CO₂ Light Conversion Performance Of The Spinel Composite Materials

CO2 is the main greenhouse gases resulted in the global warming.Thus the study of CO2 fixation and conversion presents important significance.CO2 conversion from photocatalytic is one way of CO2 conversion and utilization.Spinel oxide shows some visible light photocatalytic activity.In this paper,three kinds of spinel nano-photocatalytic materials based on cobalt chromium,cobalt aluminum and magnesium iron,are designed and prepared.By the way of different metal ions doped with spinel nano-photocatalytic materials and titanium oxide composited with the photocatalytic materials,doped and composited catalytic materials are prepared in order to reduce the recombination of photo-generated electron and hole,broaden the range of spectra effect,make full use of solar energy and improve the efficiency of photocatalytic.The structures and photochemical properties of prepared photocatalytic materials are characterized and analyzed by TG-DTA、XRD、IR、UV-Vis、SPS、SEM、NH3-TPD and BET.The condition of photocatalytic conversion CO2 are optimized used the reparation of formic acid from photocatalytic conversion CO2 as the evaluated standard of photocatalytic performance for prepared materials.The results show that CoCr2O4 displayed obvious absorption peak at visible range of 550～700 nm corresponding to gap energy of 1.61 eV.When the reaction for 5 h,the cumulative concentration of formic acid obtained from photocatalytic reducing CO2 by CoCr2O4 was 4.15mmol/g·cat。The photocatalytic performance of CoCr2O4/TiO2 composite is higher than that of CoCr2O4,indicating that the CoCr2O4/TiO2 composite material is benefits of charge transport and expands light response range of photocatalytic materials.The photocatalytic composite can efficiently reduce the recombination rate of photo-generated electron and hole,which greatly increased the utilization of solar energy.Sample of CoCr2O4/TiO2-1/2-600 shows better photocatalytic activity.When the reaction for 5 h,cumulative concentration of formic acid prepared by photocatalytic reducing CO2 by CoCr2O4/TiO2-1/2-600 was 6.82 mmol/g·cat。Compared with undoped CoCr2O4,the doping of Na and Ni leads to a tiny lattice expansion and the doping of A1 results in a lightly lattice contraction.A higher or lower doping amount would affect the activity of photocatalytic conversion of CO2.CoAl2O4 catalyst displays obvious absorption peak at visible range of 500～700 nm corresponding to gap energy of 1.68 eV.When the reaction for 5 h,the cumulative concentration of formic acid obtained from photocatalytic reducing CO2 by CoAl2O4 was 3.63 mmol/g·cat。The photocatalytic performance of CoAl2O4/TiO2 composite catalyst is higher than that of CoAl2O4.The micro morphology of MgFe2O4 material is spherical.MgFe2O4 shows clear absorption peak at visible range of 400～620 nm corresponding to gap energy of 2.07 eV.When the reaction for 5 h,the cumulative concentration of formic acid prepared by photocatalytic reducing CO2 by MgFe2O4 was 3.36 mmol/g·cat。The photocatalytic performance of MgFe2O4/TiO2 composite is higher than that of MgFe2O4,indicating that the composite can expand light response range,increase the specific surface area,improve the separation efficiency of photo-generated charge so as to efficiently increase the yield of formic acid.When the calcination temperature at 600 ℃ and the ratio of composite for 1/2,the prepared MgFe2O4/TiO2-1/2-600 composite show the best photocatalytic activity.The C-TiO2 photocatalytic materials were prepared by impregnated-roasting method used citric acid and TiO2-P25 as raw materials.Ti atoms in the TiO2 lattice are replaced by C to form a structure of Ti-O-C.The doping of C does not change crystal type.Since C atom formed a new level above the valence band,the energy of TiO2 forbidden band is narrow,which make the absorption edge red-shift.The C-TiO2 photocatalytic materials expand light response range of TiO2 and improve the separation efficiency of electron-hole.The grain size distributes uniformly,which is in favor of transmission of charge and improve obviously photocatalytic activity.The yield of formic acid formed from photocatalytic reducing CO2 reach to 2.63 mmol/g·cat。The comparison of photocatalytic activity under the same conditions:CoCr2O4/TiO2>CoAl2O4/TiO2>MgFe2O4/TiO2>C-TiO2>TiO2.The performance of photocatalytic reduction of carbon dioxide by photocatalytic materials was studied.The effect of dosage of different catalyst materials,the concentration of NaHSO3 solution and NaOH solution,irradiate time and light sources on the efficiency of reduction carbon dioxide were investigated.The best reduction process was determined through the orthogonal experiment:the catalyst dosage of 2.25 g/L,the concentration of NaHSO3 solution of 2.25 g/L and NaOH solution of 0.125 mol/L,irradiated time of 12 h and the light source of 175 W mercury lamp.