A Method to Produce Tungsten Trioxide Nanofilm

Tungsten trioxide is an n-type semiconductor material with a narrow band gap (2.4-2.8 eV), is capable of responding to visible light, and has similar characteristics to TiO2 photocatalyst, which is stable, non-toxic, photo-resistant, and low-cost. Its valence band has a high potential and the photo-generated electron hole has strong oxidation ability.

The tungsten trioxide film has photoelectrocatalytic performance and sensing performance, and can be used for photocatalytic degradation of organic matter, photocatalytic decomposition of hydrogen produced by water, pH, CH4, NO2 sensors and etc. However, the microstructure of the tungsten trioxide film determines the photocatalytic performance, sensing performance and service life of the tungsten trioxide film. The preparation method of the existing tungsten trioxide nano film is mainly by hydrothermal synthesis.

However, in the existing hydrothermal chemical preparation method, since the substrate is made of conductive glass, the bonding between the conductive materials and the WO3 is a non-natural combination, and the mutual bonding force is poor, especially when subjected to mechanical external force. At the time of, or when the ambient temperature changes, the internal expansion stress changes due to the difference in material expansion coefficient, which causes cracking or fracture between WO3 and the conductive glass substrate, and even causes peeling of the WO3 film and the conductive glass substrate.

In this regard, some scholars have adopted a tungsten-based tungsten trioxide (W/WO3) nanofilm material that naturally combines with the same elements of the substrate, and has high catalytic activity or sensing performance and stable performance. The main methods are as follows:

The polished and cleaned tungsten flakes are dried, placed in a muffle furnace, and the temperature is controlled to be calcined at 550 ° C for 30 min. A layer of WO3 fine particles is formed on the surface of the metal tungsten as a seed crystal for subsequent crystal growth; The tungsten sheet is immersed in a hydrothermal chemical reaction system, and the hydrothermal reaction system contains a polyethylene glycol having a volume fraction of 10% and a molecular weight of 300 as a crystal growth directing agent and a sodium tungstate solution having a concentration of 0.03 mol/L as a material for crystal growth. The inner wall of the reaction vessel is a polytetrafluoroethylene material, the pH of the reaction solution is adjusted to 2.0 with hydrochloric acid, the hydrothermal reaction temperature is controlled to 180 ° C, and the reaction time is 2 h, and the directional growth of tungsten trioxide on the surface of the base tungsten can be completed; The tungsten-based tungsten trioxide reaction product is taken out, repeatedly immersed in distilled water to remove the residue on the surface of the product, and then air-dried, placed in a muffle furnace, and calcined at 550 ° C for 180 minutes to obtain a monoclinic phase W having a nano-sheet array structure. /WO3 film material, the thickness of a single nanosheet is about 70 nm, and the height is about 4 μm. The material can be used as a photoanode for photocatalytic degradation of organic pollutants and photocatalytic decomposition of water to produce hydrogen.

The tungsten-based tungsten trioxide nanofilm material prepared by the method has the same combination of the same element between the metal tungsten substrate and the tungsten trioxide seed crystal and the crystal, and is a natural combination, and uses a crystal growth directing agent to control growth. It can form thin and orderly materials with large specific surface area and excellent performance. It can be widely used in photocatalysis, photoelectrocatalysis, COD sensors, pH sensors and gas sensors.

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