Hydrothermal Method for Preparing Tungsten Oxide Nanowire Ammonia Sensor

Tungsten oxide is a transition metal oxide n-type semiconductor. Traditionally, tungsten oxide is applied in catalysts, electrochromism, battery electrodes, solar absorbing materials and radar absorbing materials (RAM). In recent years, scientists have focused on its applications as semiconductor materials such as heat-sensitive, pressure-sensitive and gas-sensitive material. The characteristics and applications of tungsten oxide nanocrystalline films in gas sensors, photocatalysis, photoconductivity, etc. are attracting more and more attentions, especially in the field of oxide semiconductor gas sensor applications, tungsten oxide-based material has been considered as one of the most promising new gas sensing materials for detecting NOx, SOx, NH3, H2S and, etc.

Tungsten oxide nanowires have a larger specific surface area than traditional tungsten oxide materials, and they have broad application prospects in gas sensors, electroluminescence, photoluminescence, conductivity electrodes and photocatalysis. Tungsten oxide nanowires have greater surface activity and stronger adsorption capacity, which accelerates the reaction with gases, thereby greatly improving the sensitivity. And further reduce the operating temperature of the sensor.

The hydrothermal preparation of a tungsten oxide nanowire gas sensitive material is prepared by the following method comprising the steps of:

1) Dissolve 1.0 to 1.5 g of sodium tungstate in 24 to 30 ml of deionized water, and magnetically stirring in an ice water bath for 1 hour to form a colorless transparent sodium tungstate solution;

2) First, slowly add 3.5 to 4 ml of 3 M/L hydrochloric acid to the solution in (1) and stir for 0.5 hour, then slowly add 4.6 to 5.2 ml of 0.3 M/L of oxalic acid and continue stirring for 0.5 hour. Light yellow micelle solution;

3) Transfer 28 to 30 ml of the micelle solution in (2) into a 50 ml reaction vessel and adding 25 to 30 g of potassium sulfate, stirring uniformly, and then hydrothermally treating at a temperature of 180 ° C for 12 to 144 hours;

4) The hydrothermal product in step 3) was repeatedly washed with deionized water and absolute ethanol, and then sufficiently dried in an air atmosphere at 65 ° C to obtain a tungsten oxide nanowire.

The tungsten oxide nanowire ammonia sensor is prepared by the following method:

1) Preparation of gas sensitive material slurry

The tungsten oxide nanowires prepared as described above are mainly composed of ethyl cellulose and terpineol as a binder, and a glass frit is added to enhance the adhesion between the sensitive material and the alumina substrate, and the above materials are mixed. And stirring evenly to prepare a sensitive material slurry.

2) Sintering of substrate

The slurry in the step 1) was screen-printed on an alumina substrate having a silver electrode and a lead, and sufficiently dried in air at 70 ° C, and sintered at a temperature of 300 to 500 ° C in a box furnace for 1~2 hours, a tungsten oxide nanowire ammonia sensor was produced.

3) Aging of the sensor

The ammonia sensor sintered in the step 2) was aged at 300 ° C for 72 hours to prepare an ammonia sensor to be tested.

The preparation method of tungsten oxide nanowire using the hydrothermal method are very simple, the process parameters in the preparation process are easy to control, the energy consumption of the whole preparation process is very small, the prepared tungsten oxide nanowire has a large specific surface area. The ammonia sensor has high sensitivity, good repeatability and high stability for low concentration ammonia (1~100ppm).

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