CN104458827A

CN104458827A - NO2 gas sensor based on hollow spherical WO3 and preparation method of NO2 gas sensor based on the hollow spherical WO3

Info

Publication number: CN104458827A
Application number: CN201410778511.6A
Authority: CN
Inventors: 卢革宇; 王冲; 孙彦峰; 马健; 孙鹏
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2014-12-15
Filing date: 2014-12-15
Publication date: 2015-03-25
Anticipated expiration: 2034-12-15
Also published as: CN104458827B

Abstract

The invention discloses a NO2 gas sensor based on hollow spherical WO3 and a preparation method of the NO2 gas sensor based on the hollow spherical WO3, and belongs to the technical field of gas sensors. A developed sensor is of a heater-type structure, and mainly comprises a nickel-cadmium heating wire, an aluminum oxide ceramic pipe, a platinum wire, a gold electrode and a hollow spherical WO3 body sensitive material. The WO3 with the uniform size and a hollow structure is utilized for adsorbing and desorbing NO2 rapidly with the high sensitivity, so that a NO2 gas sensor with high performances is developed. The lower limit of detection of the sensor can reach 40ppb; additionally, the sensor also shows good long-term stability, and has a good application prospect in the aspect of environment monitoring.

Description

Based on hollow ball-shape WO 3nO 2gas sensor and preparation method thereof

Technical field

The invention belongs to gas sensor technical field, be specifically related to a kind of based on hollow ball-shape WO ₃oxide semiconductor NO ₂gas sensor and preparation method thereof.

Background technology

Along with the fast development of process of industrialization, a large amount of uses of the energy, as coal, rock gas, oil etc. burn the toxic and harmful brought, have become and have threatened one of human health and safety serious problem.NO ₂as a kind of toxic gas.Can photo-chemical smog and acid rain etc. be caused, thus endanger the growth of plant and corrosion is produced to buildings.Even in the magnitude of ppm, it also can injure digestive system and the nervous system of the mankind.The safety standard concentration that ACGIH is listed in air is 3ppm.The standard that Occupational Safety and Health Administration (OSHA) sets is 5ppm.As can be seen here, develop cheap, practical and there is highly sensitive NO ₂gas sensor is very necessary.

Based on this demand, scholars has high performance NO being devoted to exploitation ₂gas sensor is also used in environmental monitoring and the commercial production aspect such as safely.Comprise Si material, organic material, oxide semiconductor material etc.Wherein the sensor of based oxide semiconductor sensitive material have highly sensitive, response recovers fast, selectivity is good and high reliability, is well suited for in real time, continuous and on-line monitoring.WO ₃the extensive concern of researchers is being subject in recent years because meeting these characteristics.Sensitive material WO used in the present invention ₃a kind of typical n-type semiconductor, with gas NO ₂after contact, resistance rises, and namely the change of gaseous environment has been changed into detectable electric signal.Therefore exploitation has high performance WO ₃base NO ₂sensor is of great significance at every field tools such as environmental monitorings.

Summary of the invention

The object of this invention is to provide a kind of based on hollow ball-shape WO ₃the NO of oxide ₂gas sensor, and the WO that a kind of novel synthesis graded structure is provided ₃the method of hollow ball.

One of the present invention is based on hollow ball-shape WO ₃nO ₂gas sensor is heater-type structure, its by outside surface with two parallel, ring-types and the ceramic pipe substrate of gold electrode separate, the hollow ball-shape WO be coated on ceramic pipe outside surface and gold electrode ₃nano sensitive material and the nickel-chrome heater strip composition be placed in ceramic pipe; Nickel-chrome heater strip passes to direct current to provide the working temperature of sensor, realizes measuring NO by the direct current resistance resistance measured in different atmosphere between two gold electrodes ₂the function of concentration; Wherein, hollow ball-shape WO ₃nano sensitive material is prepared by following steps:

(1) first by 0.8 ~ 1.2g Na ₂wO ₄2H ₂o, 0.8 ~ 1.2g citric acid are dissolved in 30 ~ 40mL, volume ratio is the water of 2 ~ 3:1 and in the mixed solvent of glycerine, instill the HCl of 4 ~ 5mL, 3M, continue stirring 5 ~ 10min after stirring 15 ~ 30min;

(2) be encased in 50mL water heating kettle by above-mentioned solution, put into hydro-thermal baking oven subsequently, baking oven setting parameter is 160 ~ 180 DEG C, 20 ~ 30h;

(3), after reaction terminates, by products in water and the washing of ethanol alternating centrifugal, at 400 ~ 600 DEG C, calcine 2 ~ 5h after the product drying obtained, obtain hollow ball-shape WO ₃nano sensitive material.

Sensor of the present invention adopts heater-type structure, and concrete technology is as follows:

(1) hollow ball-shape WO is got ₃nano sensitive material, with ethanol in mass ratio 0.25 ~ 0.5:1 be uniformly mixed to form slurry; This slurry is evenly coated in surface with two parallel, ring-types and the Al of gold electrode separate ₂o ₃on the surface of ceramic pipe, it is made to cover gold electrode completely; Hollow ball-shape WO ₃the thickness of nano sensitive material is 15 ~ 30um; Al ₂o ₃the internal diameter of ceramic pipe is 0.6 ~ 0.8mm, and external diameter is 1.0 ~ 1.5mm, and length is 4 ~ 5mm; The width of single gold electrode is 0.4 ~ 0.5mm, and the spacing of two gold electrodes is 0.5 ~ 0.6mm; The platinum filament wire that gold electrode is drawn, its length is 4 ~ 6mm.

(2) hollow ball-shape WO will have been applied ₃the ceramic pipe of nano sensitive material sinters 2 ~ 5h at 200 ~ 350 DEG C, is then 50 ~ 60 circles by the number of turn, resistance value is that the NI-G heater coil of 30 ~ 40 Ω is through Al ₂o ₃ceramic tube inside, passes to direct current to provide working temperature, and working temperature is 85 ~ 150 DEG C; By platinum filament wire, ceramic pipe is welded on general heater-type hexagonal base again;

(3) finally by sensor in 200 ~ 400 DEG C of air ambients aging 5 ~ 7 days, thus WO is obtained ₃base NO ₂gas sensor.

Principle of work:

Work as WO ₃base NO ₂when gas sensor is placed in air, the oxygen molecule in air will from WO ₃capture electronics and with O ₂ ^-, O ^-or O ^2-mode exist, material surface formed depletion layer.When sensor contacts NO under certain suitable temperature ₂during gas, NO ₂gas molecule will be adsorbed on sensor surface.Due to NO ₂strong electron-withdrawing power, electrons is from WO ₃transfer to NO ₂, thus make WO ₃resistance increases.Here we define the sensitivity S of sensor: S=R _g/ R _a, wherein R _afor the aerial resistance of sensor, R _gfor sensor contacts NO ₂after resistance.

Advantage of the present invention:

(1) the present invention's one-step method for synthesizing has prepared the WO of the graded structure of Nano grade ₃hollow ball, possesses homogeneous Size Distribution, is exploitation high-performance NO ₂sensor provides a kind of effective sensitive material.

(2) the present invention uses the WO of size uniformity, hollow structure ₃sensitive material is to NO ₂fast absorption and desorption, high sensitivity, be conducive to gas diffusion, can realize quick adsorption and desorption.

(3) sensor stability developed is good, and reliability is strong.The Monitoring lower-cut of sensor can reach 40ppb.Sensor also shows good long-time stability in addition.

(4) WO of the present invention's making ₃base NO ₂gas sensor manufacture craft is simple, with low cost, is applicable to industrial batch production.Have a good application prospect in environmental monitoring.

Accompanying drawing explanation

Fig. 1: WO of the present invention ₃base NO ₂the structural representation of sensor.

Fig. 2: WO of the present invention ₃the SEM figure (a) and (b) of hollow ball, WO of the present invention ₃the TEM figure (c) and (d) of hollow ball, composition WO ₃one of hollow ball independently TEM figure (e), the HRTEM figure (f) of nano particle and SAED figure (g).

Under the working temperature of Fig. 3: 100 DEG C, WO of the present invention ₃base NO ₂sensor is at 40 ~ 400ppb NO ₂real-time change curve (a) of resistance in atmosphere, WO of the present invention ₃base NO ₂transducer sensitivity and NO ₂funtcional relationship (b) between concentration.

Under the working temperature of Fig. 4: 100 DEG C, WO of the present invention ₃base NO ₂the linearity curve steady in a long-term of sensor.

As shown in Figure 1, each component names is: Al ₂o ₃insulating ceramics pipe 1, platinum line 2, annular gold electrode 3, nickel-cadmium coil 4, WO ₃nano sensitive material 5.

As shown in Fig. 2 (a), WO ₃hollow ball size is more homogeneous, and the diameter of each hollow ball is 1.5 ~ 2.5um, examines the hollow ball that can find some fragmentations.Fig. 2 (b) gives the hollow ball of an independent fragmentation, and this is also for proving WO ₃hollow structure provide direct proof.Simultaneously we also can observe ball wall and are made up of some nano particles.Fig. 2 (c) and Fig. 2 (d) is the WO of synthesis ₃tEM figure, in figure, spheroid presents the hollow-core construction that obvious comparison of light and shade further demonstrates it, can observe WO ₃the wall thickness of hollow ball is 200 ~ 300nm.Again HRTEM test (Fig. 2 (f)) is carried out to independent nano particle (Fig. 2 (e)), the distance that can calculate on a direction between adjacent crystal planes according to scale is 0.34nm, another direction is 0.385nm, corresponding to monocline WO ₃(JCPDS card number .72-1465) (120) and (002) crystal face.The neat dot matrix (Fig. 2 (g)) of SEAD also reveal that these compositions WO ₃the single crystal intrinsic of the nano particle of hollow ball.

As shown in Fig. 3 (a), at working temperature is 100 DEG C, WO ₃base NO ₂the resistance of sensor is at variable concentrations NO ₂change curve under (40 ~ 400ppb) atmosphere.Initial in atmosphere time, resistance Ra is constant.When the environment component of sensor becomes NO from air ₂time, sensor resistance raises; When the environment component of sensor is by NO ₂when becoming air, resistance declines.We progressively increase NO ₂concentration (40 ~ 400ppb), sensor resistance change can be observed more and more obvious, namely along with NO ₂the rising of concentration, sensitivity increases, and by transducer sensitivity and NO ₂the funtcional relationship of concentration lists in Fig. 3 (b).It should be noted that the NO that sensor can detect ₂concentration limit is 40ppb, and corresponding sensitivity is 3.4.

Be illustrated in figure 4 WO ₃base NO ₂the linearity curve steady in a long-term of sensor.In the time of two weeks, test sensor under 100 DEG C of working temperatures, to 1ppm NO ₂sensitivity.In the time of two weeks, the fluctuation range of sensitivity is 75 ~ 85, has substantially remained in a stable scope.As can be seen here, sensor shows good stability.

Embodiment

Embodiment 1

With WO ₃hollow ball makes heater-type NO as sensitive material ₂sensor, its concrete manufacturing process:

1. first by 1g Na ₂wO ₄2H ₂o, 1.2g citric acid is dissolved in 35mL mixed solvent (water: glycerine=25mL:10mL).After stirring 20min, instillation 4mL 3M HCl, continues to stir 5min;

2. be encased in 50mL water heating kettle by above-mentioned solution, put into baking oven subsequently, baking oven setting parameter is 180 DEG C, 24h;

3., after reaction terminates, what the products in water obtained and ethanol are replaced carries out centrifuge washing.Centrifuge parameters is set to 10000r/min, 10min.Centrifugal afterproduct carries out drying.After drying terminates, product is carried out calcining 3h at 500 DEG C.

4. get appropriate obtained nano material and ethanol in mass ratio 0.4mg:1mg be uniformly mixed to form slurry.Dip appropriate slurry with hairbrush and be coated in commercially available ceramic pipe outside surface, make it cover the gold electrode of outside surface completely.(internal diameter of tubular ceramic substrate is 0.7mm, and external diameter is 1.1mm, and length is 4.5mm; Its outside surface carries two ring-type gold electrodes be parallel to each other, the single width of two electrodes is 0.4mm, and spacing is 0.5mm; The platinum filament conductor length that gold electrode is drawn is 5mm).

5. coated ceramic pipe is sintered 2h at 300 DEG C, be then 50 circles by the number of turn, resistance value is that the NI-G heater coil of 30 Ω is through Al ₂o ₃ceramic tube inside, passes to direct current to provide working temperature.Finally by platinum filament wire, ceramic pipe is welded on general heater-type hexagonal base, thus obtains WO ₃base oxide semiconductor N O ₂sensor.

6. finally by sensor in 300 DEG C of air ambients aging 6 days, stand-by.

7. at 80 DEG C testing sensor to 1ppm NO ₂sensitivity.

Embodiment 2

2. be encased in 50mL water heating kettle by above-mentioned solution, put into hydro-thermal baking oven subsequently, baking oven setting parameter is 180 DEG C, 24h;

4. get appropriate obtained nano material and ethanol in mass ratio 0.4mg:1mg be uniformly mixed to form slurry.Dip appropriate slurry with hairbrush and be coated in commercially available ceramic pipe outside surface, make it cover the gold electrode of outside surface completely.(internal diameter of tubular ceramic substrate is 0.7mm, and external diameter is 1.1mm, and length is 4.5mm; Its outside surface carries two ring-type gold electrodes be parallel to each other, the single width of two electrodes is 0.4mm, and spacing is 0.5mm; The platinum filament conductor length that gold electrode is drawn is 5mm.)

6. finally by sensor in 300 DEG C of air ambients aging 6 days, stand-by.

7. at 100 DEG C testing sensor to 1ppm NO ₂sensitivity.

Embodiment 3

6. finally by sensor in 300 DEG C of air ambients aging 6 days, stand-by.

7. at 115 DEG C testing sensor to 1ppm NO ₂sensitivity.

Embodiment 4

6. finally by sensor in 300 DEG C of air ambients aging 6 days, stand-by.

7. at 120 DEG C testing sensor to 1ppm NO ₂sensitivity.

Embodiment 5

6. finally by sensor in 300 DEG C of air ambients aging 6 days, stand-by.

7. at 150 DEG C testing sensor to 1ppm NO ₂sensitivity.

Table 1: gas sensor is at 1ppm NO ₂in atmosphere, the relation of sensitivity and working temperature

Senor operating temperature (DEG C)	Sensitivity (Rg/Ra)
		85	55.55
100	81
		115	35
120	18.6
		150	7.8

Claims

1. one kind based on hollow ball-shape WO ₃nO ₂gas sensor, is characterized in that: be heater-type structure, by outside surface with two parallel, ring-types and the ceramic pipe substrate of gold electrode separate, the hollow ball-shape WO be coated on ceramic pipe outside surface and gold electrode ₃nano sensitive material and the nickel-chrome heater strip composition be placed in ceramic pipe; Wherein, hollow ball-shape WO ₃nano sensitive material is prepared by following steps,

(2) be encased in 50mL water heating kettle by above-mentioned solution, put into baking oven subsequently, baking oven setting parameter is 160 ~ 180 DEG C, 20 ~ 30h;

2. as claimed in claim 1 a kind of based on hollow ball-shape WO ₃nO ₂gas sensor, is characterized in that: hollow ball-shape WO ₃the thickness of nano sensitive material is 15 ~ 30um.

3. as claimed in claim 1 a kind of based on hollow ball-shape WO ₃nO ₂gas sensor, is characterized in that: Al ₂o ₃the internal diameter of ceramic pipe is 0.6 ~ 0.8mm, and external diameter is 1.0 ~ 1.5mm, and length is 4 ~ 5mm; The width of single gold electrode is 0.4 ~ 0.5mm, and the spacing of two gold electrodes is 0.5 ~ 0.6mm; The platinum filament wire that gold electrode is drawn, its length is 4 ~ 6mm.

4. as claimed in claim 1 a kind of based on hollow ball-shape WO ₃nO ₂gas sensor, is characterized in that: NI-G heater coil is 50 ~ 60 circles, resistance value is 30 ~ 40 Ω.

5. one according to claim 1 is based on hollow ball-shape WO ₃nO ₂the preparation method of gas sensor, its step is as follows:

(1) hollow ball-shape WO is got ₃nano sensitive material, with ethanol in mass ratio 0.25 ~ 0.5:1 be uniformly mixed to form slurry; This slurry is evenly coated in surface with two parallel, ring-types and the Al of gold electrode separate ₂o ₃on the surface of ceramic pipe, it is made to cover gold electrode completely; And on gold electrode, draw platinum filament wire;

(2) hollow ball-shape WO will have been applied ₃the ceramic pipe of nano sensitive material sinters 2 ~ 5h at 200 ~ 350 DEG C, then NI-G heater coil is passed Al ₂o ₃ceramic tube inside, passes to direct current to provide working temperature, and working temperature is 85 ~ 150 DEG C; By platinum filament wire, ceramic pipe is welded on general heater-type hexagonal base again;