The Construction Of Based Hematite Nanotubs Electrodes And Photoelectrocatalytic Reduction Of Carbon Dioxide

The emission of CO₂has increased gradually in recent years which resulted in a series ofenvironment problems, such as rising of sea level, greenhouse effect, change of ecologicalclimate and so on. Therefore, what we can do to decrease the CO₂concentration effectively inthe atmosphere has become the first global problem in which caused researchers interest.Furthermore, CO₂is a nontoxic, low-cost and recyclable carbon resouces.Electrocatalytic and photocatalytic reduction of CO₂utilize H2O as hydrogen, sunlight asdriving force which has become the research hot field due to its clean and environmentallyfriendly techniques.On the other hand, the suitabe catalysts are important during the process of CO₂reduction. Semiconductors with narrow band （e.g. Fe₂O₃,2.2eV） have attracted considerableattention in recent years. Fe₂O₃can absorb light of wavelength up to600nm, collect up to40%energy of the solar spectrum. Moreover, Fe₂O₃behaves the advantages of non-toxic andlow-costing.CuO is a narrow band semiconductor with excellent electrocatalytic activity as well ashigh selectivity of catalytic products. CuO FCs/Fe₂O₃NTs is prepared by the pulseelectrochemical deposition method. CuO flower clusters that constituted with flaky CuO aredistributed on the surface of Fe₂O₃NTs uniformly. After CuO FCs are loaded on Fe₂O₃NTs,the absorption of visible light is enhanced noticeably, and its band gap narrowed to1.84eVfrom2.03eV. It further obtains the conduction band and valence band locating at-0.79eVand1.05eV, respectively. In the photoelectrocatalytic reduction of CO₂process, methanoland ethanol are two major products detected by chromatography. Their concentration reach1.00mmol L^-1cm^-2and107.38μmol L^-1cm^-2after6hours.SnO₂behaves better electrocatalytic activity among these catalyst species. Thesurfactant-free hydrothermal method was explored to prepare SnO₂NRs with the special facesof （110） and （101） on the surface of Fe₂O₃NTs. According to the SEM and XRD results, theformation process of the hierarchically assembled SnO₂NRs is deduced. When the reactiontime is prolonged from60mins to90mins and120mins, SnO₂chang from irregular nanorodsto nanorod crossed arrays on the4-fold and6-fold symmetrical structure ordinally. The SnO₂NRs/Fe₂O₃NTs catalyst that have reacted for120mins behaves the best photoelectrocatalyticproperties. From the view of photocatalytic reduction, the conduction band （-0.75eV） isnegative enough to drive CO₂reduction, and the valence band （1.82eV） is positive enough tooxidize H2O for H+, which is used for CO₂reduction. From the electrocatalytic reduction point, the net CO₂reduction current density of the composite is7.48times that of Fe₂O₃NTsat-1.1V, indicating that the electrocatalytic performance of Fe₂O₃NTs is greatly enhancedby the introduction of6-fold branched SnO₂NRs. Analysized from the product methanolyield, the methanol yield of the obtained catalyst under photoelectrocatalytic reduction CO₂is2.05mmol L^-1cm^-2（t=6hours）, it is much higher than the simple addition of methanol yieldobtained under soly photocatalytic and electrocatalytic reduction, it is also much higher thanthe simple addition of methanol yield obtained under photoelectrocatalytic reduction withsoly SnO₂and Fe₂O₃. Herein, there are two synergistic effects in the system, one is thesynergistic effect between the photocatalytic reduction and the electrocatalytic reduction, theother is the synergistic effect between SnO₂NRs and Fe₂O₃NTs.Cu₂O is also a narrow band semiconductor with excellent selectivity for catalyticproducts. Cu₂O MSs/Fe₂O₃NTs is prepared by the constant potential electrochemicaldeposition, Cu₂O MSs are distributed on the surface of Fe₂O₃NTs uniformly. According to aseries characterization of photoelectrical properties, Cu₂O improves the absorption of visiblelight of Fe₂O₃as well as narrow the band gap to1.96eV, which resulting the absorption ofmore sunlight. The predominant reduction product analyzed by GC is methanol. When thephotoelectrocatalytic reduction time is6hours, the methanol yield is4.94mmol L^-1cm^-2.Analysized from the product methanol yield, there is a synergistic effect between thephotocatalytic reduction and the electrocatalytic reduction.Three original kinds of catalytic materials are prepared in this paper. They obtaindistinguished effect in the application of CO₂reduction. The design of these high-efficiencycatalysts provides new idears for the development of photoelectric dual catalytic interfacescatalysts. As well as the experiment and theory basis for photoelectrocatalytic reduction CO₂to liquid carbon fuels.