Research On Preparation Of Up-conversion Nanomaterials And Application Of Photocatalytic Nitrogen Fixation

The current industrial synthesis of ammonia technology is dominated by the Haber-Bosch method using iron-based catalysts.Its reaction conditions are very harsh（250 MPa,400℃）and require huge energy consumption.Photocatalytic technology can directly convert solar energy into chemical energy,providing a very promising method for reducing the energy consumption of synthetic ammonia.However,the ultra-high bond energy of N≡N bonds makes nitrogen molecules exhibit stable chemical characteristics,which makes it difficult for conventional photocatalytic materials to activate nitrogen molecules.Therefore,the development of high-efficiency nitrogen-fixing ammonia synthesis photocatalysts still faces huge challenges.In this paper,with rare earth compounds and natural silicate attapulgite（ATP）materials as the core,Ce F₃:Yb³⁺,Er³⁺/Fe-ATP,two-dimensional CaCuSi₄O₁₀ and two-dimensional Sm VO₄ up-conversion nanomaterials,and used them as catalysts for photo-nitrogen-fixation synthesis of ammonia.The effects of its structural composition,morphology,energy band structure,luminescence characteristics and other factors on the photocatalytic nitrogen-fixation performance were investigated.Using iron-modified attapulgite as the carrier and rare earth fluoride as the matrix material,a series of different doping levels（Er:1%,2%,3%,4%,5%）were synthesized by the microwave hydrothermal method.And loading（5 wt%,10 wt%,20 wt%,30 wt%,40 wt%）Ce F₃:Yb³⁺,Er³⁺/Fe-ATP composite material.It is found that Fe has a special affinity for N₂ and can play a key role in coordinating the catalytic function.In addition,the generated fluorine vacancies（F_V）can act as charge mediators,creating an indirect Z-type heterojunction,which retains a high reduction-oxidation potential and promotes charge separation.The presence of F_V and Fe form a synergistic effect,which effectively promotes the nitrogen fixation reaction.The up-conversion effect of rare earth doping(Yb³⁺,Er³⁺)can convert near-infrared light into ultraviolet light and visible light,realizing a full-spectrum response.Nitrogen fixation experiments show that when Ce F₃:Yb³⁺,Er³⁺load is 20 wt%,the formation rate of NH₄⁺reaches the highest 69.2μmol·h^-1·g^-1.Using attapulgite,natural copper ore and egg shells and other calcium-containing biomass as raw materials,CaCuSi₄O₁₀two-dimensional nanosheets were prepared by solid-phase high-temperature calcination,and different amounts of K₂CO₃（5 wt%,10wt%,15 wt%）to optimize the morphology of CaCuSi₄O₁₀.The CaCuSi₄O₁₀ nanosheet material can up-convert near-infrared light into ultraviolet light and visible light,which greatly expands the light response range of the material.CaCuSi₄O₁₀ with a large specific surface area provides abundant active sites for the adsorption and activation of N₂molecules,and at the same time helps to increase the contact area with light and improve the utilization of sunlight.In addition,its relatively negative conduction potential provides high reduction ability for the photonitrogen fixation reaction.Under simulated sunlight and near-infrared light,the ammonia production efficiency of 10 wt%CaCuSi₄O₁₀is as high as 60.32μmol·g^-1·h^-1 and 15.60μmol·g^-1·h^-1,respectively.Compared with the traditional Silicate materials show more excellent photo-nitrogen fixation activity.The SmVO₄ two-dimensional nanosheet material was synthesized under microwave hydrothermal conditions using PVP as a template.Its large specific surface area creates more V⁵⁺reaction sites for photoreaction and enhances the adsorption and activation of nitrogen.Secondly,the thinner longitudinal dimension can improve the utilization rate of light and reduce the ineffective loss caused by the light source passing through the sample.In addition,thin Sm VO₄ can be upconverted by itself without doping with other rare earth ions,which also provides a simple advantage for its use in a wide spectral range.Photocatalytic nitrogen fixation experiments show that the nitrogen generation rate of Sm VO₄ nanosheets can reach 81.20μmol·g^-1·h^-1 under simulated sunlight.