Synthesis Of Heterogeneous Semiconductor Nanomaterials For Artificial Nitrogen Cycle

Semiconductor nanomaterials have been widely applied in the field of catalytic energy conversion and utilization because of their unique electronic structures.Compared with single-component semiconductor nanomaterials,heterogeneous semiconductor nanomaterials show flexible controllability in terms of morphology,composition and structure due to different heterogeneous materials.Moreover,electronic structure of semiconductors can be effectively regulated by the construction of heterogeneous semiconductor nanomaterials,further improving the catalytic activity.It is of great significance to design and construct heterogeneous semiconductor nanomaterials and study the influence of changes in the electronic structure of the heterojunction on its catalytic activity for developing new energy and new strategies of artificial nitrogen cycle independent on fossil energy.Therefore,this paper is guided by the development of a new artificial nitrogen cycle strategy.By constructing heterogeneous semiconductor nanomaterials and regulating the electronic structure of semiconductors,we obtained the highly active photo-electro-catalyst for photoelectrocatalytic oxidation of hydrazine hydrate to promote hydrogen evolution,effective electrocatalyst for selective electrocatalytic reduction of nitrate to ammonia and photocatalyst for photocatalytic direct oxidation of nitrogen to nitric oxide.The main research contents are summarized as follows:1.Gradient oxygen doped hierarchical CdS nanorod arrays(Grad-O CdS)were synthesized by thermal treatment under low vacuum containing trace amounts of oxygen.The gradient doping of oxygen in the CdS nanorod could not only narrow the band gap of CdS but also construct continuous built-in band bending in Grad-O CdS,which could induce directed transfer of photogenerated electrons and holes,further reduce the recombination of photogenerated carriers.When Grad-O CdS was used as the photoanode material for photoelectrocatalytic oxidation of hydrazine hydrate to promote hydrogen evolution,the photocurrent density could reach 6.0±0.1 mA cm^-2and could be stably maintained for more than 42 h.This method of conducting element gradient doping to build a built-in curved energy band of a semiconductor provides a new way to explore higher-performance photoelectrocatalytic materials.2.Metal-semiconductor heterostructures Co/CoO nanoarrays(Co/CoO NSAs)were constructed by a gas-solid phase chemical conversion method for electrocatalytic nitrate reduction to produce ammonia.In the Co/CoO NSAs heterostructures,the Schottky rectification effect existed between metal Co and semiconductor CoO due to the Schottky contact.The electrons at the interface are transferred from metal Co to semiconductor CoO,resulting in an electron-deficient Co.Co/CoO NSAs containing electron-deficient Co during electrocatalytic nitrate reduction could not only inhibit the production of H₂,but also inhibited the formation of by-products,thereby promoting the Faraday efficiency and selectivity of the product ammonia:93.8%and 91.2%,respectively.This research provides a new avenue for the development of efficient catalysts for the catalytic reduction of nitrate to ammonia by using electrical energy.3.TiO₂/WO₃ nanorods with a direct Z-scheme heterojunction were constructed for thermal-assisted photocatalytic nitrogen oxidation to synthesize nitric oxide.The photogenerated electrons on the conduction band of WO₃ would be transferred to TiO₂and combined with the photogenerated holes on its valence band,leaving the photogenerated holes to undergo an oxidation reaction on WO₃ and the photogenerated electrons to undergo a reduction reaction on TiO₂.The electron transfer at the interface of the Z-Scheme TiO₂/WO₃ heterojunction could not only promote the separation of photocarriers,but also promote the adsorption of N₂ at the interfacial WO₃ and the formation of the intermediate NO*,thereby making TiO₂/WO₃ heterostructures exhibited excellent performance.The photocatalytic NO production was also used directly to synthesize nitric acid and fine chemical?-Nitrostyrene,suggesting the broad application prospects of this work.