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Preparation of small: hexagonal tungsten oxide nanowires by molten salt method and its application in photocatalytic nitrogen fixation

wallpapers News 2020-11-25
The ultra-fine one-dimensional structure of

semiconductor materials has physical chemical properties different from bulk materials such as quantum conductivity negative magnetoresistance non Newtonian rheology etc. Wet chemistry is a common method to obtain high-quality ultra-fine one-dimensional structure that is to achieve anisotropic crystal growth obtain one-dimensional products by controlling the surface energy of nano materials in solution. In this process the selective bonding between organic ligs the surface of semiconductor materials is indispensable for controlling the morphology dispersion of the products. However it also makes it a big challenge to obtain "clean" material surface which seriously restricts the property research application exploration of ultra-fine one-dimensional structure of semiconductor materials.

to solve this problem researcher Zhao Zhigang associate researcher Congshan collaborators of Suzhou Institute of nanotechnology nanobionics Chinese Academy of Sciences reviewed the traditional salt melting method found a solution breaking the traditional cognition that the high temperature salt melting method is not suitable for the preparation of ultra-fine one-dimensional structure. The research team used ammonium tungstate ammonium molybdate binary precursors molten sodium nitrate as the reaction matrix after 1 min reaction the uniform ultra-fine nanostructures with an average diameter of less than 5 nm a length of 300-500 nm were obtained. The characterization confirmed that the product was mo doped hexagonal tungsten oxide crystal phase with high crystallinity clean surface. It is found that Mo doping plays an important role in initiating the formation of ultra-fine one-dimensional structure. Furthermore through the characterization of the intermediate products in different reaction stages it is found that the formation of ultra-fine one-dimensional structure is a melting recrystallization process that is the existence of Mo in the lattice will break the stability of the lamellar structure (kinetic product) make it break up decompose into quasi zero dimensional crystal clusters in high temperature molten salt then the final ultra-fine one-dimensional structure (thermodynamic product) is formed by directional assembly )。 The Mo doped tungsten oxide obtained by

is hexagonal phase which is usually considered as a metastable phase difficult to obtain by conventional calcination method. Compared with many thermodynamic stable phases of tungsten oxide hexagonal phase has more advantages in energy storage catalysis other applications due to its abundant hydroxyl groups on the surface internal lattice channels. The team studied the photocatalytic nitrogen fixation performance of the materials found that the ammonia synthesis efficiency under room temperature simulated sunlight conditions is as high as 370 μ molg-1h-1 which is in the leading position in the existing semiconductor photocatalytic materials. Furthermore the excellent photocatalytic properties of the above materials were described in detail from the aspects of semiconductor energy level structure photo generated carrier transport surface active sites. It was found that the one-dimensional structure of the ultra-fine structure surface is conducive to carrier transport separation the adjacent Mo W atoms are the double sites for N2 molecule adsorption activation the surface hydroxyl group is the channel for H transport which can be realized efficiently The multi electron / multi proton transport process of nitrogen fixation is described. The researchers of

believe that this research will open up a new way for the application of molten salt method in the preparation of new nanostructures provide new ideas for the physical properties exploration application development of low dimensional semiconductor structures.

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