CN109850948B - A method and application of synthesizing Au-doped WO3 nanosheets from scheelite concentrate - Google Patents

Abstract

A method and application for synthesizing Au-doped WO ₃ nanosheets with scheelite concentrate, which relate to the field of semiconductor oxide gas sensors. A method for synthesizing Au-doped WO ₃ nanosheets from scheelite concentrate, the method is as follows: using NaOH leaching process to transform and preliminarily purify scheelite concentrate to obtain a leaching solution containing sodium tungstate, and dilute the solution into tungstic acid A solution with a sodium concentration of 0.019 to 0.044 mol/L is used as a precursor to be mixed with HAuCl ₄ solution and CaCl ₂ solution, and the mixing ratio is that the molar ratio of Au, W and Ca is 0.3% to 1%: 1:3 to 14 . The Au-doped WO ₃ nanosheet NO ₂ gas sensing element prepared based on the method of the present invention can realize the rapid detection of low concentration, even ppb level NO ₂ gas with high sensitivity and high selectivity. Using cheap and low-polluting scheelite concentrate as the tungsten source, the cost of raw materials and preparation process is greatly reduced.

Description

Au-doped WO synthesized by using scheelite concentrate3Methods and applications of nanoplatelets

Technical Field

The invention relates to the technical field of gas sensors of semiconductor oxides, in particular to a method for synthesizing Au-doped WO by using white tungsten concentrate₃Methods and uses of the nanoplatelets.

Background

In the past decades, with the rapid development of economic construction and the continuous acceleration of industrialization process, more and moreToxic and harmful gases are discharged into the air, so that serious air pollution is caused, and the physical and psychological health of human is seriously harmed. NO₂The gas is a corrosive strong toxic gas, mainly comes from the emission of factories and motor vehicles and the high-temperature combustion of some petroleum fuels, is the main cause of acid rain and photochemical smog, and can also cause a series of environmental problems such as the thinning of an ozone layer, the acidification of land, the eutrophication of surface water and the like. Most importantly, NO₂Is extremely harmful to human health and can damage the respiratory system of the human body at relatively low concentrations. For safety reasons, human beings have 3ppm and 5ppm NO₂The time of the reaction can not exceed 8h and 15min in the environment respectively. Therefore, for effective environmental and personal safety protection, low concentration NO is used₂The development and development of gas sensors are imperative.

WO₃Is an important n-type semiconductor functional material, has excellent gas-sensitive, photoelectric and catalytic properties, is widely applied to the fields of gas sensors, photoelectrolysis, catalysts and the like, and can be used for NO₂、H₂、 H₂S、NH₃The detection of gases such as ethanol, acetone and the like has great application prospect, and therefore, the method is widely applied to the aspects of mine safety, environmental detection, factory safety monitoring and the like. In the prior art preparation of WO₃In the research of nano materials, analytically pure or high-purity elemental tungsten metals such as sodium tungstate, ammonium paratungstate, tungsten hexachloride, tungstic acid and the like are mostly selected as tungsten sources, and the reagents are high in price and have certain pollution.

Disclosure of Invention

Aiming at the current situation, the invention takes the scheelite concentrate as the tungsten source to prepare the Au-doped WO with irregular, loose and ordered appearance₃The nanosheet breaks the limitation of the tungsten oxide raw material with high added value. Doping of WO with Au₃The gas-sensitive element prepared by using the nano-sheet as a gas-sensitive material can realize the control of low-concentration even ppb level NO₂The detection is effective.

The method takes the scheelite concentrate with the grade of 62.36 percent as a tungsten source, and adopts a NaOH leaching process to convert and preliminarily purify the scheelite concentrate to obtain the leachate containing the sodium tungstateAnd then the leaching solution is taken as a precursor to synthesize Au-doped WO by adopting a two-step method at normal temperature₃Nanosheets and doping of WO with these Au₃The nano-sheet prepared NO has the advantages of high sensitivity, good reversibility, high response/recovery speed, good selectivity and the like₂A gas sensor element. Au-doped WO obtained by the invention₃The nano sheet has the advantages of low preparation cost, simple process, high yield, large specific surface area and the like, is beneficial to industrial mass production, and has good application prospect.

Au-doped WO synthesized by using scheelite concentrate₃A method of nanoplatelets, the method comprising:

carrying out NaOH leaching on the scheelite concentrate: placing the scheelite concentrate into a NaOH solution with the concentration of 15-18 mol/L, leaching under the experimental conditions of a liquid-solid ratio of 1:1, a reaction temperature of 180 ℃, a stirring speed of 400rpm and a heat preservation time of 120min to obtain a leaching product, filtering the leaching product to obtain filtrate and leaching slag, washing the leaching slag with deionized water for 3 times to obtain a washing solution, and mixing the obtained filtrate and the obtained washing solution to obtain a leaching solution containing sodium tungstate;

secondly, diluting the solution obtained in the step one to a solution with the sodium tungstate concentration of 0.019-0.044 mol/L, and mixing with HAuCl₄Solution, CaCl₂Mixing the solutions to obtain white precipitate; the HAuCl₄The concentration of the solution is 0.014-0.02 mol/L, and the CaCl is₂The concentration of the solution is 0.2-2 mol/L, and the mixing proportion is that the molar ratio of Au, W and Ca is 0.3% -1%: 1: 3-14;

thirdly, washing the white precipitate obtained in the second step with water, drying, acidifying and carrying out heat treatment to obtain Au-doped WO₃Nanosheets.

In the second step, the solution obtained in the first step is diluted into a solution with the sodium tungstate concentration of 0.019-0.044 mol/L, and the solution and HAuCl are mixed₄Solution, CaCl₂The solutions were mixed in the order of adding HAuCl₄Adding CaCl into the solution₂Solution, adding CaCl₂White precipitate is generated instantly; the HAuCl₄The concentration of the solution is 0.014-0.02 mol/L, and the CaCl is₂The concentration of the solution is 0.2-2 mol/L, and the mixing proportion is AThe molar ratio of u, W and Ca is 0.3-1%: 1: 3-14; preferably, the grade of the scheelite concentrate is 50-63%.

Preferably, the grade of the scheelite concentrate is 62.36%.

The grade of the scheelite concentrate in the invention refers to the percentage content of tungsten in the scheelite concentrate.

Preferably, the washing, drying and acidifying process in the third step is washing the white precipitate for 5-6 times; drying at the temperature of 60-80 ℃; HNO with the concentration of 2-5 mol/L in 20mL₃And acidifying the solution at normal temperature to obtain a yellow product, washing the yellow product with water for 5-6 times, and drying at the temperature of 60-80 ℃.

Preferably, the heat treatment in the third step is heat treatment at 400 ℃ for 4-8 h.

Another object of the present invention is to provide an Au-doped WO prepared by the following method₃Nanosheets, said Au doped WO₃The thickness of the nanosheet is 10-30 nm, the length and the width of the nanosheet are less than 200nm, and the nanosheet is of a monoclinic crystal structure.

Au-doped WO synthesized by using scheelite concentrate₃A method of nanoplatelets, the method comprising:

carrying out NaOH leaching on the scheelite concentrate: placing the scheelite concentrate into a NaOH solution with the concentration of 15-18 mol/L, leaching under the experimental conditions of a liquid-solid ratio of 1:1, a reaction temperature of 180 ℃, a stirring speed of 400rpm and a heat preservation time of 120min to obtain a leaching product, filtering the leaching product to obtain filtrate and leaching slag, washing the leaching slag with deionized water for 3 times to obtain a washing solution, and mixing the obtained filtrate and the obtained washing solution to obtain a leaching solution containing sodium tungstate;

secondly, diluting the solution obtained in the step one to a solution with the sodium tungstate concentration of 0.019-0.044 mol/L, and mixing with HAuCl₄Solution, CaCl₂Mixing the solutions to obtain white precipitate; the HAuCl₄The concentration of the solution is 0.014-0.02 mol/L, and the CaCl is₂The concentration of the solution is 0.2-2 mol/L, and the mixing proportion is that the molar ratio of Au, W and Ca is 0.3% -1%: 1: 3-14;

thirdly, washing the white precipitate obtained in the second step with water, drying, acidifying and carrying out heat treatmentTo obtain Au-doped WO₃Nanosheets.

It is a further object of the present invention to provide a method for the synthesis of Au doped WO from a scheelite concentrate₃Gas sensor with nanosheet material as gas sensitive coating, the gas sensor comprising Al₂O₃Ceramic tube, gold electrode, platinum wire, Ni-Cr heater wire, and Al wire attached to gold electrode₂O₃The gas-sensitive coating on the outer surface of the ceramic tube is Au-doped WO₃Nanosheets.

Au-doped WO prepared from scheelite concentrate₃Nanosheets, said Au doped WO₃The thickness of the nanosheet is 10-30 nm, the length and the width of the nanosheet are less than 200nm, and the nanosheet is of a monoclinic crystal structure.

Au-doped WO synthesized by using scheelite concentrate₃A method of nanoplatelets, the method comprising:

carrying out NaOH leaching on the scheelite concentrate: placing the scheelite concentrate into a NaOH solution with the concentration of 15-18 mol/L, leaching under the experimental conditions of a liquid-solid ratio of 1:1, a reaction temperature of 180 ℃, a stirring speed of 400rpm and a heat preservation time of 120min to obtain a leaching product, filtering the leaching product to obtain filtrate and leaching slag, washing the leaching slag with deionized water for 3 times to obtain a washing solution, and mixing the obtained filtrate and the obtained washing solution to obtain a leaching solution containing sodium tungstate;

secondly, diluting the solution obtained in the step one to a solution with the sodium tungstate concentration of 0.019-0.044 mol/L, and mixing with HAuCl₄Solution, CaCl₂Mixing the solutions to obtain white precipitate; the HAuCl₄The concentration of the solution is 0.014-0.02 mol/L, and the CaCl is₂The concentration of the solution is 0.2-2 mol/L, and the mixing proportion is that the molar ratio of Au, W and Ca is 0.3% -1%: 1: 3-14;

thirdly, washing the white precipitate obtained in the second step with water, drying, acidifying and carrying out heat treatment to obtain Au-doped WO₃Nanosheets.

Preferably, the gas sensor is used for NO₂The detection range of the gas concentration is 50 ppb-5 ppm.

Another object of the present invention is to provide a method for synthesizing Au-doped WO from scheelite concentrate₃Made of nano-sheet materialA method of making a gas sensor that is a gas sensitive coating, the method comprising:

carrying out NaOH leaching on the scheelite concentrate: placing the scheelite concentrate into a NaOH solution with the concentration of 15-18 mol/L, leaching under the experimental conditions of a liquid-solid ratio of 1:1, a reaction temperature of 180 ℃, a stirring speed of 400rpm and a heat preservation time of 120min to obtain a leaching product, filtering the leaching product to obtain filtrate and leaching slag, washing the leaching slag with deionized water for 3 times, and combining the filtrate and a washing solution to obtain a leaching solution containing sodium tungstate;

secondly, diluting the solution obtained in the step one to a solution with the sodium tungstate concentration of 0.019-0.044 mol/L, and mixing with HAuCl₄Solution, CaCl₂Mixing the solutions to obtain white precipitate; the HAuCl₄The concentration of the solution is 0.014-0.02 mol/L, and the CaCl is₂The concentration of the solution is 0.2-2 mol/L, and the mixing proportion is that the molar ratio of Au, W and Ca is 0.3% -1%: 1: 3-14;

thirdly, washing the white precipitate obtained in the second step with water, drying, acidifying and carrying out heat treatment to obtain Au-doped WO₃Nanosheets;

fourthly, doping the Au obtained in the third step with WO₃Adding absolute ethyl alcohol into the nanosheets, and performing ultrasonic dispersion to obtain viscous slurry; uniformly brushing the viscous slurry on the gold electrode and Al₂O₃Preparing a gas-sensitive coating on the outer surface of the ceramic tube, and naturally drying for 10-30 min; Ni-Cr heating wires are transversely penetrated through Al₂O₃A ceramic tube, both ends of which are welded to the heating electrode; and connecting the gold electrode with a platinum lead, welding the platinum lead on the measuring electrode to obtain the gas sensor, and aging the obtained gas sensor on an aging table at 300 ℃ for 24-72 h.

The Au is doped with WO₃The heat treatment and aging treatment of the nano-sheet gas-sensitive material and the gas-sensitive element are both used for keeping the structure of the gas-sensitive material and the stability of the performance of the gas-sensitive element.

Compared with the prior art, the invention has the characteristics and beneficial effects that: the invention directly uses the scheelite concentrate as a tungsten source, adopts a NaOH leaching method to obtain a leaching solution containing sodium tungstate, uses the leaching solution as a precursor, and adopts a two-step method to synthesize the product with knotsGood crystal, large specific surface area, high porosity and large yield of Au-doped WO₃Nanosheets; subsequently doping Au with WO₃After the nanosheet is subjected to heat treatment in a tubular furnace, Au-doped WO is prepared on the ceramic electrode₃The nano-sheet gas-sensitive coating is subjected to heat treatment by an aging table to obtain the WO based on Au doping₃NO of nanosheet₂A gas sensor. The gas sensor can obtain 5ppm NO at the working temperature of 175 DEG C₂The maximum sensitivity of the gas is 212.3, the response/recovery time is short (9s and 108s), the reversibility and the selectivity are good, and the traditional NO is effectively solved₂The gas sensitive element has poor gas sensitive property in a low concentration area and is NO with good development prospect₂A gas sensor. Meanwhile, the preparation method takes raw material selection as a starting point, adopts cheap and low-pollution scheelite concentrate as a tungsten source, and greatly reduces functional WO (tungsten oxide) from raw materials and the whole preparation process₃The preparation cost of the nano material is low, and the obtained product has high yield and is suitable for batch production.

Drawings

The invention is illustrated in FIG. 11:

FIG. 1 is a (a) X-ray diffraction pattern and (b) scanning electron micrograph of the scheelite concentrate used in example 1;

FIG. 2 is a schematic view of gas sensors according to embodiments 1 to 3;

FIG. 3 is Au-doped WO prepared in example 1₃An X-ray diffraction pattern of the nanosheets;

FIG. 4 shows Au-doped WO prepared in example 1₃Scanning electron microscope photos of the nanosheets at high magnification;

FIG. 5 shows Au-doped WO prepared in example 1₃(ii) a transmission electron microscopy photograph and (b) a high resolution transmission electron microscopy photograph of the nanoplatelets;

FIG. 6 shows the gas sensor of example 1 for 5ppm NO at different operating temperatures₂A dynamic response profile of the gas;

FIG. 7 is a graph of gas sensor pair of example 1 for 5ppm NO₂A graph of sensitivity of the gas versus operating temperature;

FIG. 8 shows the gas sensor of example 1 for different concentrations of NO at an operating temperature of 175 deg.C₂A dynamic response profile of the gas;

FIG. 9 shows the sensitivity of the gas sensor of example 1 at an operating temperature of 175 ℃ in comparison with NO₂A graph of the relationship between gas concentrations;

FIG. 10 is a graph of the gas sensor of example 1 for 5ppm NO at different operating temperatures₂Response and recovery time profiles of the gas;

FIG. 11 shows the selectivity of the gas sensor of example 1 for different gases at an operating temperature of 175 ℃.

The reference numbers are as follows:

in FIG. 2, Al₂O₃A ceramic tube 1; a Ni-Cr heater wire 2; a gold electrode 3; a platinum wire 4; a gas-sensitive coating 5.

The scheelite concentrate adopted in the invention is obtained from mining industry Limited of Xinzhou, Gansu, from small tungstite in Nanxian county, Zhangye, Gansu province, and has a grade of 62.36%.

Detailed Description

The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way.

The test methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.

Example 1

The invention relates to a method for synthesizing Au-doped WO by using white tungsten concentrate₃Method of nanosheet and its use in NO₂Application in gas sensors. The X-ray diffraction pattern and scanning electron micrograph of the scheelite concentrate (grade 62.36%) adopted in the invention are shown in figure 1, and the result shows that the scheelite concentrate raw material consists of blocky particles with irregular shapes, and the main useful mineral of the scheelite concentrate raw material is CaWO₄. WO doped with Au as gas-sensitive coating₃The gas sensor of the nano-sheet has a structure diagram shown in figure 2, wherein a heating wire 2 is made of Al₂O₃The ceramic tube 1 is transversely welded on a heating electrode of a hexagonal base, and gold is usedThe electrode 3 is coated on the outer surface of the ceramic tube 1 and is welded on a measuring electrode of a six-pin base through a platinum lead wire 4, and the gas-sensitive coating 5 is coated on the gold electrode 3 and Al₂O₃The outer surface of the ceramic tube 1. The gas-sensitive coating 5 is formed by doping Au with WO with a monoclinic crystal structure₃The thickness of the nanosheet is 10-30 nm, the length and the width of the nanosheet are less than 200nm, and the nanosheet has high porosity and large specific surface area.

Au-doped WO₃The X-ray diffraction pattern of the nanosheet is shown in FIG. 3, and the result shows that the Au-doped WO with the single monoclinic crystal structure prepared in the embodiment₃The nano-sheet has no other impurity peak, and has excellent crystallization condition. Au-doped WO₃The high-magnification scanning electron micrograph of the nanosheet is shown in FIG. 4, from which it can be seen that the resulting product is a product of WO which is in a staggered, loosely ordered arrangement₃The nano-sheets are stacked, the thickness of the nano-sheets is 10-30 nm, the length and the width of the nano-sheets are less than 200nm, and the nano-sheets have high porosity and specific surface area. Au-doped WO₃The transmission electron microscope photograph and the high resolution transmission electron microscope photograph of the nanoplatelets are shown in fig. 5, further demonstrating the loosely ordered sheet shape of WO₃A nanostructure.

Au-doped WO synthesized by using scheelite concentrate₃The preparation method of the nanosheet comprises the following steps:

firstly, carrying out NaOH leaching on the white tungsten concentrate under the conditions of NaOH concentration of 17.57mol/L, liquid-solid ratio of 1:1, reaction temperature of 180 ℃, heat preservation time of 120min and stirring speed of 400rpm to obtain a leaching product, filtering the leaching product to obtain filtrate and leaching slag, washing the leaching slag with deionized water for 3 times to obtain washing liquid, and mixing the filtrate and the washing liquid to obtain a leaching solution containing sodium tungstate;

and secondly, diluting the solution obtained in the step I, adding 70mL of deionized water into 5mL of leaching solution containing sodium tungstate, wherein the W concentration is 0.66mol/L, diluting the solution, wherein the concentration of the sodium tungstate is 0.044mol/L, and magnetically stirring the solution for 5 min.

③ adding 1.65mL HAuCl into the leaching solution containing sodium tungstate diluted in the step II₄The solution was magnetically stirred and mixed for 10min to obtain Au in moleIs 0.7% of the molar amount of W. The HAuCl₄The concentration of the solution was 0.014 mol/L.

Fourthly, 20mL of CaCl with the concentration of 0.9mol/L is added into the solution obtained in the third step₂The solution was magnetically stirred for 10min, at which time the reaction produced a white precipitated product. The white precipitated product was washed with deionized water, filtered 5 times, and then dried at 60 ℃.

Taking 0.3g of the dried product in 20mL of HNO with the concentration of 4mol/L₃Acidifying the solution, and magnetically stirring at normal temperature for 24 h. Washing the acidified yellow precipitate with deionized water, filtering for 5 times, drying the washed product at 60 deg.C, transferring the product into a tubular furnace, and heat treating at 400 deg.C for 4 hr to obtain Au-doped WO₃Nanosheets.

Sixthly, doping the Au obtained in the fifth step with WO₃Adding absolute ethyl alcohol into the nanosheets, and performing ultrasonic dispersion to obtain viscous slurry; uniformly brushing the viscous slurry on the gold electrode 3 and Al₂O₃Preparing a gas-sensitive coating 5 on the outer surface of the ceramic tube 1, and coating Al of the gas-sensitive coating 5 on the outer surface of the ceramic tube₂O₃Placing the ceramic tube 1 in the air for natural drying for 30min, and heating the Ni-Cr heating wire 2 from Al₂O₃The ceramic tube 1 penetrates through and is welded on a heating electrode of the hexagonal base; connecting a platinum lead wire 4 with a gold electrode 3 on the outer surface of the ceramic tube 1, and welding the platinum lead wire on a measuring electrode of the hexagonal base; placing the obtained gas-sensitive element on an aging table, aging for 24h at 300 ℃, and finally obtaining the gas-sensitive coating which is Au-doped WO₃NO of nanosheet₂A gas sensor.

In the working temperature range of 100 ℃ to 225 ℃, Au is doped with WO₃Nanosheet gas sensor pair 5ppm NO₂The dynamic response curve of the gas is shown in fig. 6. As can be seen from the figure, the gas sensor of the present invention is for NO₂The gas has good reaction reversibility and a fast response/recovery speed, and the resistance change of the gas is most obvious at 175 ℃. As the operating temperature continues to rise, the resistance change becomes progressively smaller.

FIG. 7 shows Au-doped WO₃Nanosheet gas sensor pair 5ppm NO₂Sensitivity and operation of gasesGraph of the relationship between temperatures. As can be seen from the graph, the gas sensitivity first gradually increases with increasing operating temperature, and the maximum sensitivity is obtained at an operating temperature of 175 ℃; as the operating temperature continues to increase, the gas sensitivity gradually decreases.

Au-doped WO₃The nano-sheet gas sensitive element can be used for treating NO with different concentrations at the working temperature of 175 DEG C₂The dynamic response curve of the gas is shown in fig. 8. As can be seen from the figure, the gas sensor is used for different concentrations of NO in 7 consecutive reaction cycles₂The gas has good response reversibility, and high response and recovery speed; resistance change of gas sensor with NO₂The gas concentration increased and showed a tendency to increase, indicating that the gas sensitivity was dependent on NO₂The concentration increases.

FIG. 9 shows WO with gas-sensitive coating doped with Au₃Sensitivity of gas sensor of nano-sheet at working temperature of 175 ℃ and NO₂Graph of relationship between gas concentrations. As can be seen from FIG. 9, the gas-sensitive coating is Au-doped WO₃Gas sensor of nano-sheet for 50ppb, 100ppb, 300ppb, 500ppb, 1 ppm, 3ppm and 5ppm NO₂The sensitivity of the gas was 2.6, 6.2, 32.5, 56.9, 108.9, 171.8 and 212.3, respectively, indicating that the Au-doped WO₃The nano-sheet gas-sensitive element can be used for detecting low-concentration even ppb level NO₂Gas, which is the greatest advantage of the gas sensor of the present invention.

FIG. 10 shows the gas sensor of the present invention for 5ppm NO at different operating temperatures₂Response and recovery time profiles of the gas. As can be seen from the graph, the response and recovery time of the gas sensor both show a decreasing trend with increasing operating temperature. When the working temperature is lower than 175 ℃, the response and recovery time has a remarkable descending trend; as the operating temperature continues to rise, the response and recovery times decrease. The gas-sensitive coating is Au-doped WO₃The gas sensor of the nano sheet is used for detecting 5ppm NO at the optimal working temperature of 175 DEG C₂The response and recovery time of the gas are fast, 9s and 108s respectively.

The gas-sensitive coating is Au-doped WO₃The gas sensor of the nano sheet is used for detecting 5ppm NO at the working temperature of 175 DEG C₂And 100ppm of xylene, formaldehyde, acetone, NH₃And SO₂The gas sensitivity of (2) is shown in fig. 11. As can be seen from the figure, the sensitivity of the gas sensor of the present invention to six detected gases is NO in the order of magnitude₂>Xylene>Formaldehyde (I)>Acetone (II)>NH₃>SO₂Description of the gas sensor for NO under the same detection conditions₂Gas selectivity is best, and for SO₂The selectivity of the gas is poor.

Example 2

WO doped with Au as gas-sensitive coating₃The structural schematic diagram of the gas sensor of the nano-sheet is shown in fig. 2.

Au-doped WO synthesized by using scheelite concentrate₃Preparation method of nanosheet and NO₂The gas sensor is carried out according to the following steps:

firstly, carrying out NaOH leaching on the scheelite concentrate under the conditions of NaOH concentration of 17.57mol/L, liquid-solid ratio of 1:1, reaction temperature of 180 ℃, heat preservation time of 120min and stirring speed of 400rpm to obtain a leaching product, filtering the leaching product to obtain filtrate and leaching slag, washing the leaching slag with deionized water for 3 times to obtain washing liquid, and combining the filtrate and the washing liquid to obtain a leaching solution containing sodium tungstate;

and secondly, diluting the solution obtained in the step I, adding 70mL of deionized water into 2mL of leaching solution containing sodium tungstate, wherein the W concentration is 0.7mol/L, diluting the solution, wherein the concentration of the sodium tungstate is 0.019 mol/L, and magnetically stirring the solution for 5 min.

③ adding 0.29mL HAuCl into the diluted sodium tungstate leaching solution₄The solution was mixed with magnetic stirring for 10min so that the number of moles of Au was 0.3% of the number of moles of W. The HAuCl₄The concentration of the solution was 0.014 mol/L.

Fourthly, 20mL of CaCl with the concentration of 0.2mol/L is added into the mixed solution₂The solution was magnetically stirred for 10min, at which time the reaction produced a white precipitated product. The white precipitated product was washed with deionized water, filtered 5 times, and then dried at 60 ℃.

Taking 0.3gThe dried product is treated with 20mL of HNO with the concentration of 2mol/L₃Acidifying the solution, and magnetically stirring at normal temperature for 6 h. Washing the acidified yellow precipitate with deionized water, filtering for 5 times, drying the washed product at 60 deg.C, transferring the product into a tubular furnace, and heat treating at 400 deg.C for 8 hr to obtain Au-doped WO₃Nanosheets.

Sixthly, doping the Au obtained in the fifth step with WO₃Adding absolute ethyl alcohol into the nanosheets, and performing ultrasonic dispersion to obtain viscous slurry; uniformly brushing the viscous slurry on the gold electrode 3 and Al₂O₃Preparing a gas-sensitive coating 5 on the outer surface of the ceramic tube 1, and coating Al of the gas-sensitive coating 5 on the outer surface of the ceramic tube₂O₃Placing the ceramic tube 1 in the air for natural drying for 30min, and heating the Ni-Cr heating wire 2 from Al₂O₃The ceramic tube 1 penetrates through and is welded on a heating electrode of the hexagonal base; connecting a platinum lead wire 4 with a gold electrode 3 on the outer surface of the ceramic tube 1, and welding the platinum lead wire on a measuring electrode of the hexagonal base; placing the obtained gas sensitive element on an aging table, aging for 24h at 300 ℃, and finally obtaining the gas sensitive element based on Au doping WO₃NO of nanosheet₂A gas sensor.

By detection, the Au-doped WO prepared in the example₃The nano-sheet gas-sensitive element is used for NO at the working temperature of 100-225 DEG C₂The gas has good response recovery performance.

Example 3

WO doped with Au as gas-sensitive coating₃The structural schematic diagram of the gas sensor of the nano-sheet is shown in fig. 2.

Au-doped WO synthesized by using scheelite concentrate₃Preparation method of nanosheet and NO₂The gas sensor is carried out according to the following steps:

firstly, carrying out NaOH leaching on the scheelite concentrate under the conditions of NaOH concentration of 17.57mol/L, liquid-solid ratio of 1:1, heat preservation time of 120min, stirring speed of 400rpm and reaction temperature of 180 ℃ to obtain a leaching product, filtering the leaching product to obtain filtrate and leaching slag, washing the leaching slag with deionized water for 3 times to obtain washing liquid, and combining the filtrate and the washing liquid to obtain a leaching solution containing sodium tungstate;

and secondly, diluting the solution obtained in the step I, adding 70mL of deionized water into 10mL of the leaching solution containing the sodium tungstate, wherein the W concentration is 0.3mol/L, diluting the solution, wherein the concentration of the sodium tungstate is 0.038 mol/L, and magnetically stirring the solution for 5 min.

③ adding 1.52mL of HAuCl into the diluted sodium tungstate leaching solution₄The solution was mixed with magnetic stirring for 10min so that the number of moles of Au in the mixed solution was 1% of the number of moles of W. The HAuCl₄The concentration of the solution was 0.020 mol/L.

Fourthly, 20mL of CaCl with the concentration of 2mol/L is added into the mixed solution₂The solution was magnetically stirred for 10min, at which time the reaction produced a large amount of white precipitated product. The white precipitated product was washed with deionized water, filtered 5 times, and then dried at 80 ℃.

Taking 0.3g of the dried product in 20mL of HNO with the concentration of 5mol/L₃Acidifying the solution, and magnetically stirring at room temperature for 30 h. Washing the yellow precipitate product after acidification with deionized water, filtering for 5 times, drying the washed product at 80 ℃, transferring the product to a tubular furnace, and carrying out heat treatment at 400 ℃ for 4h to obtain the required Au-doped WO₃Nanosheets.

Sixthly, doping the Au obtained in the fifth step with WO₃Adding absolute ethyl alcohol into the nanosheets, and performing ultrasonic dispersion to obtain viscous slurry; uniformly brushing the viscous slurry on the gold electrode 3 and Al₂O₃Preparing a gas-sensitive coating 5 on the outer surface of the ceramic tube 1, and coating Al of the gas-sensitive coating 5 on the outer surface of the ceramic tube₂O₃Placing the ceramic tube 1 in the air for natural drying for 30min, and heating the Ni-Cr heating wire 2 from Al₂O₃The ceramic tube 1 penetrates through and is welded on a heating electrode of the hexagonal base; connecting a platinum lead wire 4 with a gold electrode 3 on the outer surface of the ceramic tube 1, and welding the platinum lead wire on a measuring electrode of the hexagonal base; placing the obtained gas sensitive element on an aging table, aging for 72h at 300 ℃, and finally obtaining the WO based on Au doping₃NO of nanosheet₂A gas sensor.

By detection, the Au-doped WO prepared in the example₃The nano-sheet gas-sensitive element is used for NO at the working temperature of 100-225 DEG C₂Gas utensilHas good response recovery performance.

Claims (9)

1. a method for synthesizing Au _- doped WO nanosheets with scheelite concentrate, is characterized in that, described method is as follows: ①The scheelite concentrate is leached with NaOH: the scheelite concentrate is placed in a NaOH solution with a concentration of 15-18mol/L at a liquid-solid ratio of 1:1, a reaction temperature of 180°C, a stirring speed of 400rpm, and a holding time of 120min. Leach under the experimental conditions to obtain the leaching product, filter the leaching product to obtain the filtrate and the leaching residue, wash the leaching residue with deionized water 3 times to obtain the washing solution, and mix the obtained filtrate and the obtained washing solution to obtain sodium tungstate containing sodium tungstate. Leachate; ② Dilute the solution obtained in step ① into a solution with a sodium tungstate concentration of 0.019 to 0.044 mol/L, and mix with HAuCl ₄ solution and CaCl ₂ solution to obtain a white precipitate; the HAuCl ₄ solution has a concentration of 0.014 to 0.02 mol/L , the concentration of the CaCl ₂ solution is 0.2-2 mol/L, and the mixing ratio is that the molar ratio of Au, W and Ca is 0.3%-1%: 1:3-14; ③ Wash the white precipitate obtained in step ② with water, dry, acidify and heat treat to obtain Au-doped WO ₃ nanosheets. 2 . The method according to claim 1 , wherein the grade of the scheelite concentrate is 50-63%. 3 . 3. The method according to claim 1, wherein the grade of the scheelite concentrate is 62.36%. 4. method according to claim 1, is characterized in that, described step 3. in water washing, drying, acidifying process is to wash white precipitate 5～6 times with water; Dry under 60～80 ℃ of conditions; In 20mL concentration is 2 Acidification at room temperature is carried out in ~5mol/L HNO ₃ solution to obtain a yellow product, which is washed with water for 5 to 6 times, and then dried at 60 to 80°C. 5 . The method according to claim 1 , wherein the heat treatment in step ③ is heat treatment at 400° C. for 4 to 8 hours. 6 . 6 . The Au-doped WO ₃ nanosheets prepared by the method of claim 1 , wherein the Au-doped WO ₃ nanosheets have a thickness of 10 to 30 nm, a length and a width of less than 200 nm, and a monoclinic crystal structure. 7 . . 7. A gas-sensing element using the Au-doped WO3 nanosheets of claim 6 as a gas-sensing coating, wherein the gas-sensing element comprises Al ₂ O ₃ ceramic tubes, gold electrodes, platinum wires, Ni -Cr heating wire and gas-sensitive coating attached to the gold electrode and the outer surface of the Al ₂ O ₃ ceramic tube. 8 . The gas sensor according to claim 7 , wherein the detection range of the concentration of NO ₂ gas by the gas sensor is 50ppb˜5ppm. 9 . 9. The preparation method of a gas sensor according to claim 7, wherein the method is as follows: ①The scheelite concentrate is leached with NaOH: the scheelite concentrate is placed in a NaOH solution with a concentration of 15-18mol/L at a liquid-solid ratio of 1:1, a reaction temperature of 180°C, a stirring speed of 400rpm, and a holding time of 120min. Leach under the experimental conditions to obtain the leaching product, filter the leaching product to obtain the filtrate and the leaching residue, wash the leaching residue with deionized water 3 times to obtain the washing solution, and mix the obtained filtrate and the obtained washing solution to obtain sodium tungstate containing sodium tungstate. Leachate; ② Dilute the solution obtained in step ① into a solution with a sodium tungstate concentration of 0.019 to 0.044 mol/L, and mix with HAuCl ₄ solution and CaCl ₂ solution to obtain a white precipitate; the HAuCl ₄ solution has a concentration of 0.014 to 0.02 mol/L , the concentration of the CaCl ₂ solution is 0.2-2 mol/L, and the mixing ratio is that the molar ratio of Au, W and Ca is 0.3%-1%: 1:3-14; ③ Wash the white precipitate obtained in step ②, dry, acidify and heat treat to obtain Au-doped WO ₃ nanosheets; ④ The Au-doped WO ₃ nanosheets obtained in step ③ were added to anhydrous ethanol for ultrasonic dispersion to obtain a viscous slurry; the viscous slurry was evenly brushed on the outer surface of the gold electrode and the Al ₂ O ₃ ceramic tube to make gas Sensitive coating, dry naturally for 10-30min; pass the Ni-Cr heating wire across the Al ₂ O ₃ ceramic tube, and weld both ends to the heating electrode; connect the gold electrode to the platinum wire, and weld the platinum wire A gas sensor was obtained on the measuring electrode, and the obtained gas sensor was placed on an aging table at 300° C. for aging for 24 to 72 hours.

Images