Tungsten Trioxide Nanoblock Sensor Element

Nitrogen oxides (NO_x) are toxic and harmful gases that cause environmental problems such as acid rain and photochemical smog and pose a great threat to human beings. It is very important for human health to study high performance gas sensitive materials and devices for accurate detection and monitoring of nitrogen oxides.

In order to improve the gas sensing performance of tungsten oxide, some scholars have designed a preparation scheme of sensor elements for detecting nitrogen oxide by solvothermal method based on the principle of tungsten oxide nano-block. The preparation steps of sensor elements with tungsten oxide nano-block structure are as follows:

(1) Cleaning of Ceramic Substrate
Ceramic wafers were used as substrates, and the substrates were placed in acetone solvent and ethanol for 15-20 minutes to remove surface organic impurities. Subsequently, the ceramic substrate was washed in deionized water, washed and dried in absolute ethanol and in an infrared oven.

(2) Preparation of Pt interdigital electrode
The ceramic substrate was placed in the vacuum chamber of DPS-III high vacuum magnetron sputtering equipment. The platinum metal with 99.99% mass purity was used as the target, and the argon with 99.999% mass purity was used as the working gas. The sputtering pressure was 2.0Pa, the sputtering power was 80-90W, the sputtering time was 8-10min, and the substrate temperature was room temperature. The interdigital platinum electrode was formed on the surface of alumina substrate.

(3) Preparation of reaction solution
Firstly, tungsten hexachloride solution of 0.025M-0.1M was disposed. Tungsten hexachloride was dissolved in 65ml deionized water, and magnetic stirring was used to dissolve it completely to form white tungsten hexachloride solution.

(4) Fabrication of gas sensor
Aluminum oxide substrate plated with platinum electrodes in step (2) was placed in a stainless steel hydrothermal reactor lined with PTFE. Meanwhile, the solution of tungsten hexachloride prepared in step (3) was transferred to the reactor and sealed. Then the reactor was placed in a constant temperature drying chamber. Tungsten oxide nano-block structure was synthesized on the surface of alumina substrate at the reaction temperature of 200 ℃. The reaction time was 6-9 h, and the reaction was completed. After that, the reactor was naturally cooled to room temperature.

(5) Alumina Substrate after Cleaning Reaction
The alumina substrates after solvothermal reaction in step (4) were repeatedly soaked in deionized water and anhydrous ethanol, and then dried in a vacuum drying chamber at 60-80 ℃ for 8-10 hours.

(6) Heat Treatment of Gas Sensor Elements
The gas sensor element with tungsten oxide nanoblock structure prepared in step (5) is heat treated in muffle furnace. The heat treatment temperature is 300-400 ℃, the holding time is 2 h, and the heating rate is 2-5 ℃/min, which is used to increase the crystallinity of tungsten oxide nanoblock.

The prepared tungsten trioxide nano-block structure sensor element has huge specific surface area and large surface activity. The nano-block structure is applied to the nitrogen oxide gas sensor. The results show that the tungsten trioxide nano-block gas sensor material can effectively detect nitrogen oxides at low temperature (~100 ℃), and detect very low concentration of nitrogen oxide gas (up to 0.1 ppm), and has a very good performance, high gas sensitivity, excellent repeatability and good stability.

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