The Preparation Of Lanthanum Carbonate Semiconductor Containing Oxygen And Photoelectric Synergistic Catalytic Reduction Of CO₂

Due to the large amount of fossil fuels burning and the ever-decreasing forest area,the CO₂ emissions in the air are increasing.While CO₂ is agreenhouse gas,It leads to global warming and decreasing the area of the Arctic ice and snow and rising sea level.It brings a series of problems to the life of people.How to use CO₂,has been widespread concern.CO₂ comprehensive utilization mainly includes the following three aspects: CO₂ storage utilization,CO₂ recycling and CO₂ conversion utilization.In the CO₂ conversion and utilization,CO₂ catalytic hydrogenation is an important way to use CO₂.Photocatalytic?PC?and electrocatalytic?EC?reduction of CO₂ own its shortcomings: In the PC reduction of CO₂,there is a drawback that the photogenerated electron and hole recombination rate is high and the product selectivity is poor.There is a drawback that the overpotential is high in the EC reduction of CO₂.In order to achieve the advantages of complementary,we choose the method is the PC collaborative EC reduction method.In the PC,there are shortcomings of high photoelectron recombination rate and poor product selectivity.EC can be compensated,and the shortcomings of high overpotential in EC can be enhanced.The core of photoelectric synergistic catalytic reduction is the choice of catalyst.The catalyst has a relatively negative conduction band,high utilization of visible light,and can withstand higher negative potential.Among the many catalysts,rare earth semiconductors are a good choice.In terms of PC,rare earth semiconductors have a narrow band gap and a high negative potential.The PC reduction ability is excellent.It is an excellent photoreduction catalyst.In the EC aspects,rare earth semiconductors can withstand high negative potential.Low temperature catalytic activity is high.It is not easy to inactivate.Less intermediate products,product selectivity is high.It is an excellent catalyst in EC reduction of CO₂.Since then,there is no antagonism between EC and PC on rare earth semiconductors.PC and EC achieve the effective unity.We also hope that on such a good catalyst it can achieve PC and EC reduction synergies.While rare earth lanthanum semiconductors are representative of rare earth semiconductors.In rare earth lanthanum semiconductors,its oxides and sulfide instability,and LaCO₃ OH relatively stable,so LaCO₃ OH is chosed as the research object.LaCO₃OH was prepared by hydrothermal method,and it is white powder.It is loaded onto the conductive glass to make an electrode and to test the series of photoelectric properties.From the test results,it can be seen that LaCO₃ OH has a larger band gap.It almost has no absorption in the visible light spectrum region.This is an obstacle to the next study.We have tothink out ways to reduce the LaCO₃ OH band gap.the ways are to control the growth of the crystal structure,leading to a particular orientationgrowth of the crystal surface,to reduce its bandgap width,improve the use of more light spectrum.Two methods were chosed to control the crystal structure: one is the acid regulation,the other is the surfactant regulation.In order to reduce the band gap of LaCO₃ OH and improve the utilization of light,acid was used to regulate its crystal structure grows along a particular crystal plane.For LaCO₃ OH,the trivalent lanthanum ion is a Lewis acid.It has a strong ability to combine with the hydroxide.So in the process of hydrothermal synthesis,the solution changed pH adjusted the concentration of OH-in solution,and then changed the crystalline structure and morphology of LaCO₃ OH.How to control the pH change during the hydrothermal process? Thiourea was used as the raw material,it is known that it will occur hydrolysis when the thiourea solution heated to a certain temperature,generating NH3,CO₂,H2 S.At the beginning of the reaction,the pH of the solution is adjusted to 1.With the reaction going on,thiourea hydrolysis and generates NH3.Then NH3 will react with the acid.So the pH is slowly changed,and the crystalline structure of LaCO₃ OH to be regulated.And then affect the morphology of LaCO₃ OH,it varys from the spindle structure gradually to ellipsoidal.Acid-controlled LaCO₃ OH,mainly along the?002?,?300?,?302?crystal plane grow.The band gap is decreased by 0.4eV and the light utilization efficiencyis improved.The photoelectric catalytic performance is improved and the methanol yield is improved by nearly three times.In order to reduce the band gap of LaCO₃ OH and improve the use of light,surfactant wasused to control its crystal structure.When catalysts were prepared by hydrothermal method,surfactants with different a hydrophilic group and a lipophilic group and different HLB values were added.And the surfactant aqueous solution has the interfacial adsorption characteristics.In the catalyst growth process,the surfactant will absorb on certain suface,so the crystalwill grow along a specific orientation.So that LaCO₃ OH crystal structure is regulated.Two kinds of crystal structure of LaCO₃ OH are prepared.One is hexagonal and another is hexagonal and orthorhombic.Different crystalline structures exhibit different photoelectrocatalytic properties.The band gap is decreased by 0.4eV.Photoelectric conversion efficiency increased by 20% and methanol yield increased nearly twice.LaCO₃OH band gap is 3.95 eV.It is difficult to be excited by visible light spectrum.In order to improve this defect,LaCO₃ OH is further calcined.The calcination temperature and the calcination time are screened to obtain La₂O₂CO₃.The band gap is 2.82 eV,reduced by 1.1eV.It increases the use range of visible light spectrum.Methanol yield increased nearly four times than LaCO₃OH.