Porous ZnO nanobelt, ZnOHF nanobelt, method for manufacturing porous ZnO nanobelt, and gas sensor

Abstract

To provide a new ZnO-containing nano structure useful as a material for a gas sensor, and a manufacturing method thereof, and a gas sensor containing the ZnO-containing nano structure.SOLUTION: A porous ZnO nano belt includes a porous structure which is composed from ZnO particles and has a porosity of 1% to 50%, and is long-sized. Further, in the porous ZnO nano belt, a cross-sectional shape has a rectangular form, a width is 10nm to 200nm, a thickness is 1nm to 50nm, and a length in the longer direction is 100nm to 1000 μm.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to porous ZnO nanobelts, ZnOHF nanobelts, a method for producing porous ZnO nanobelts, and gas sensors.

Background Art

[0002] Zinc oxide (ZnO) is widely known for its properties and can be used, for example, in gas sensors, microelectronics, optoelectronics, piezoelectric devices, photochemical devices, and photovoltaic devices. Therefore, it is required to control the crystallinity, microstructure, crystal plane, surface area, etc. of ZnO nanostructures.

[0003] Also, for example, ZnO nanostructures are known to have crystal forms such as nanowire-type ZnO, nanorod-type ZnO, nanorod-type ZnO, and nanowhisker-type ZnO. The present inventor has also proposed a method for synthesizing nanorod-type ZnO and nanowhisker-type ZnO that can be used as gas sensors (Non-Patent Document 1).

[0004] Also, for example, Patent Document 1 describes a gas sensor including a semiconductor nanowire aggregate layer. Further, ZnO is exemplified as one of the compounds forming the nanowires, and it is described that "nanowires" include short fibers, long fibers (nanofibers), hollow filamentous (nanotubes), short columnar fibers (nanorods), and flat plate fibers (nanobelts).

[0005] Furthermore, for example, Patent Document 2 describes a method for producing nanosheets and nanobelts of crystals of basic zinc acetate (LBZA), and it is said that ZnO nanostructures obtained by heat-treating (annealing) these can be used in gas sensors and the like.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-165682 [Patent Document 2] Special Publication No. 2016-531104 [Non-patent literature]

[0007] [Non-Patent Document 1] J Am Ceram Soc., 105, 2150-2160 (2022) Effect of oxygen vacancy sites in exposed crystal facet on the gas sensing performance of ZnO nanomaterial [Non-Patent Document 2] AD McNaught and A. Wilkinson., IUPAC Compend. Chem. Terminol., 1997, 3540. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in Patent Document 1, the gas sensor performance is actually examined using selenium nanowires, and no specific examination is conducted regarding methods for obtaining new ZnO nanostructures or gas sensors utilizing them.

[0009] On the other hand, Patent Document 2 does not disclose, in particular, the crystal structure, size, and constituent components of ZnO nanostructures in the form of nanobelts, nor does it examine the performance of gas sensors using these ZnO nanostructures. In other words, Patent Document 2 does not clarify whether the ZnO nanostructures manufactured by the prescribed method possess properties useful as materials for gas sensors.

[0010] This invention has been made in view of these circumstances, and aims to provide a novel Zn-containing nanostructure, a method for producing the same, and a gas sensor containing a ZnO-containing nanostructure, which are useful as materials for gas sensors that detect flammable gases and reducing gases such as acetone, isoprene, toluene, ammonia, and hydrogen, as well as oxidizing gases and combustion-supporting gases such as nitrogen dioxide. [Means for solving the problem]

[0011] To solve the above problems, the following porous ZnO nanobelt, ZnOHF nanobelt, method for manufacturing the porous ZnO nanobelt, and gas sensor are provided.

[0012] [1] It is composed of ZnO particles and has a porous structure with a porosity of 1% to 50%, It is long and has a rectangular cross-sectional shape. The width is between 10 nm and 200 nm. The thickness is between 1 nm and 50 nm. The length in the longitudinal direction is between 100 nm and 1000 μm. A porous ZnO nanobelt characterized by the following features.

[0013] [2] The porous ZnO nanobelt according to [1], characterized in that the ratio of length to width in the longitudinal direction (length / width) is greater than 1 and 10,000 or less.

[0014] [3] The porous ZnO nanobelt according to [1] or [2], characterized in that the ZnO particles have an average particle size of 1 nm or more and 50 nm or less.

[0015] [4] The ZnO particles include elongated particles, The longitudinal direction of the porous ZnO nanobelt coincides with the longitudinal direction of the elongated particles. A porous ZnO nanobelt characterized by any of the above [1] to [3].

[0016] [5]Having atomic layer steps on the crystal surface The porous ZnO nanobelt according to any one of [1] to [4] above, characterized in that.

[0017] [6] The porous ZnO nanobelt according to any one of [1] to [5] above, characterized in that it contains 33.3 at.% or less of fluorine.

[0018] [7] Containing a single crystal of ZnOHF, Being long and having a rectangular cross-sectional shape, The longitudinal direction being the b-axis direction of the ZnOHF crystal, The width being 10 nm or more and 200 nm or less, The thickness being 1 nm or more and 50 nm or less, The length in the longitudinal direction being 100 nm or more and 1000 μm or less The ZnOHF nanobelt characterized by that.

[0019] [8] The ZnOHF nanobelt according to [7] above, characterized in that the ratio of the length in the longitudinal direction to the width (length / width) is greater than 1 and 10000 or less.

[0020] [9] A method for producing the porous ZnO nanobelt according to any one of [1] to [6] above, The following steps: In a solvent, A zinc compound, a fluorine compound and an alkali source compound, Or, A fluorine-containing zinc compound and an alkali source compound Adding to synthesize a ZnOHF nanobelt; and, A second step of heat-treating the ZnOHF nanobelt to obtain a porous ZnO nanobelt Containing The method for producing a porous ZnO nanobelt characterized by that.

[0021]

[10] In the first step, the solvent is water and the alkali source compound is hexamethylenetetramine The method for producing the porous ZnO nanobelt described above [9], characterized by the above.

[0022]

[11] The temperature of the heat treatment in the second step is 100 to 1000°C. A method for producing the porous ZnO nanobelt according to [9] or

[10] , characterized by the above.

[0023]

[12] Substrate and A pair of electrodes provided on the substrate, A conductive coating film formed on the electrode and connecting the pair of electrodes, Equipped with, The gas sensor is characterized in that the conductive coating film contains any of the porous ZnO nanobelts described in [1] to [6] above.

[0024]

[13] The gas sensor according to

[12] , characterized in that it is capable of detecting one or more of the following gases: acetone, isoprene, toluene, ammonia, hydrogen, and nitrogen dioxide.

[0025]

[14] The gas sensor according to

[12] or

[13] , characterized in that it exhibits a resistance change rate (Ra / Rg or Rg / Ra) greater than 1.0 and 16.5 or less for a reducing gas or an oxidizing gas at a concentration of 500 ppb.

[0026]

[15] The rate of change in resistance to acetone (Ra / Rg), The rate of change in resistance to isoprene, toluene, ammonia, or hydrogen (Ra / Rg), or the rate of change in resistance to nitrogen dioxide (Rg / Ra) and The gas sensor according to any of the above

[12] to

[14] , characterized in that, when compared, an acetone selectivity ratio of 1.0 or higher can be obtained.

[0027]

[16] Any of the gas sensors described in

[12] to

[15] above, characterized in that, in response to acetone gas at a concentration of 500 ppb, the maximum rate of change in resistance (Ra / Rg) is observed at a sensor element temperature of 450°C, among the sensor element temperatures of 375°C, 400°C, 425°C, 450°C, 475°C, and 500°C. [Effects of the Invention]

[0028] The porous ZnO nanobelts and ZnOHF nanobelts of the present invention have novel structures not found in conventional ZnO-containing nanostructures, and can be suitably used as materials for sensors such as gas sensors, molecular sensors, and solution sensors.

[0029] According to the method for producing porous ZnO nanobelts of the present invention, ZnOHF nanobelts can be synthesized in an aqueous solution without using pressure vessels or high-temperature equipment, and porous ZnO nanobelts can also be synthesized by heat treatment of ZnOHF nanobelts in air.

[0030] The gas sensor of the present invention can detect flammable gases, reducing gases, oxidizing gases such as nitrogen dioxide, and combustion-supporting gases. Specifically, the gas sensor of the present invention can detect gases such as acetone, isoprene, toluene, ammonia, hydrogen, and nitrogen dioxide with high sensitivity. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic diagram showing examples of the synthesis of ZnOHF nanobelts and porous ZnO nanobelts. [Figure 2] This is a scanning electron microscope image of a ZnOHF nanobelt. [Figure 3] This is a transmission electron microscope image of a ZnOHF nanobelt. [Figure 4] Figure 3 shows the electron diffraction pattern of the ZnOHF nanobelt. [Figure 5] This figure shows the X-ray diffraction patterns of (a) ZnOHF nanobelts and (b) porous ZnO nanobelts. [Figure 6] This is a scanning electron microscope image of a porous ZnO nanobelt. [Figure 7] This is a transmission electron microscope image of a porous ZnO nanobelt. [Figure 8] This is a high-resolution transmission electron microscope image of a porous ZnO nanobelt. [Figure 9] This is a high-resolution transmission electron microscope image of a porous ZnO nanobelt. [Figure 10] This is a high-resolution transmission electron microscope image of a porous ZnO nanobelt. [Figure 11] This is a high-resolution transmission electron microscope image of a porous ZnO nanobelt. [Figure 12] This graph shows the effect of sensor element temperature on the response of a gas sensor made of porous ZnO nanobelts to acetone gas at a concentration of 500 ppb. [Figure 13] This graph shows the response of a gas sensor made of porous ZnO nanobelts to acetone gas at concentrations of 10 to 500 ppb. [Figure 14] This graph shows the response of a gas sensor made of porous ZnO nanobelts to acetone gas at concentrations of 200 to 1000 ppt. [Figure 15] This graph shows the response of a gas sensor made of porous ZnO nanobelts to various gases. [Modes for carrying out the invention]

[0032] The inventors have succeeded in synthesizing a long, belt-shaped ZnO-containing nanostructure (hereinafter referred to as "ZnOHF nanobelt" and "porous ZnO nanobelt") having a novel structure.

[0033] The following describes an embodiment of the ZnOHF nanobelt, porous ZnO nanobelt, and a method for producing them according to the present invention.

[0034] (ZnOHF nanobelt) The ZnOHF nanobelt of the present invention contains a single crystal of ZnOHF, is elongated, and has a rectangular cross-sectional shape. The ZnOHF nanobelt of the present invention has a one-dimensional structure and a belt-like shape extending in one direction.

[0035] Here, "cross-section" refers to a cross-section that includes a direction perpendicular to the longitudinal direction of the ZnOHF nanobelt (the b-axis direction of the ZnOHF crystal).

[0036] Generally, a "rectangle" refers to a quadrilateral in which two pairs of opposite sides (long and short sides) are parallel to each other and of equal length. However, in this invention, this definition is not strictly followed, and it includes shapes where opposite sides are approximately parallel to each other or where the lengths are approximately equal. In other words, in this invention, a "rectangle" includes shapes that are recognized as substantially rectangular, for example, when observed with an electron microscope, and deformations of opposite sides or fine irregularities on the surfaces constituting the opposite sides are permissible.

[0037] Furthermore, in the ZnOHF nanobelt of the present invention, the longitudinal direction of the overall shape coincides with the b-axis direction of the ZnOHF crystal.

[0038] The width of the ZnOHF nanobelt (the length of the longer side of the rectangular cross-section) is between 10 nm and 200 nm. Furthermore, from the viewpoint of application in gas sensors and other applications, the width of the ZnOHF nanobelt (the length of the longer side of the rectangular cross-section) is preferably between 10 nm and 100 nm, and more preferably between 10 nm and 50 nm.

[0039] The thickness of the ZnOHF nanobelt (length of the shorter side of the rectangular cross-section) is between 1 nm and 50 nm. Furthermore, from the viewpoint of application in gas sensors and other applications, the thickness of the ZnOHF nanobelt (length of the shorter side of the rectangular cross-section) is preferably between 1 nm and 30 nm, and more preferably between 1 nm and 10 nm.

[0040] The longitudinal length of the ZnOHF nanobelt is between 100 nm and 1000 μm. Furthermore, from the viewpoint of application in gas sensors and other applications, the longitudinal length of the ZnOHF nanobelt is preferably between 1 μm and 1000 μm, and more preferably between 10 μm and 100 μm.

[0041] Furthermore, the ratio of the longitudinal length to the width (length / width) of the ZnOHF nanobelt is preferably greater than 1 and 10,000 or less, more preferably between 10 and 10,000, and even more preferably between 200 and 10,000, from the viewpoint of application to gas sensors and the like.

[0042] The ratio of width to thickness (width / thickness) of the ZnOHF nanobelt is preferably greater than 1 and 200 or less, more preferably between 2 and 200, and even more preferably between 10 and 200, from the viewpoint of application in gas sensors and the like.

[0043] In this invention, the width (length of the longer side of the rectangular cross-section), thickness (length of the shorter side of the rectangular cross-section), and longitudinal length of the ZnOHF nanobelt can be calculated from observation images such as scanning electron microscope images, transmission electron microscope images, and optical microscope images.

[0044] The ZnOHF nanobelt of the present invention can be used in gas sensors, molecular sensors, solution sensors, battery materials, artificial photosynthesis materials, and the like.

[0045] (Method for manufacturing ZnOHF nanobelts) The method for producing ZnOHF nanobelts according to the present invention is:

[0046] (Form 1) A step of adding a zinc compound, a fluorine compound, and an alkali source compound to a solvent, or

[0047] (Form 2) A step of adding a fluorine-containing zinc compound and an alkali source compound to a solvent. Includes.

[0048] In Forms 1 and 2, the solvent is not particularly limited, but examples include water, alcohols such as methanol and ethanol, organic solvents such as acetone, hexane, and toluene, and acids such as acetic acid and formic acid. Among these, water is preferred as the solvent. In addition, both highly polar solvents (hydrophilic) and less polar solvents (hydrophobic) can be used. Polar solvents include protic polar solvents and aprotic polar solvents, and both can be used. Alternatively, mixed solvents of these can also be used.

[0049] Other solvents include, for example, acetaldehyde, acetic anhydride, acetonitrile, acetophenone, acetylacetone, allyl alcohol, ethanolamine, aniline, benzaldehyde, benzene, benzyl alcohol, benzyl benzoate, 1-butanol, 2-butanol, methyl ethyl ketone, butyl acetate, tert-butyl alcohol, dibutyl ether, carbon disulfide, chloroform, epichlorohydrin, o-cresol, m-cresol, p-cresol, cyclohexane, cyclohexanol, 1,2-dichloroethane, dichloromethane, diethyl carbonate, diethylene glycol, diethylene glycol monobutyl ether, butyl carbitol acetate, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, diethyl ether, dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, 1,4-dioxane, ethyl acetate, ethyl benzoate, 2-chloroethanol, ethylene glycol, 1,2-dimethyl Xyethane, 2-butoxyethanol, ethylene glycol monobutyl ether acetate, 2-ethoxyethanol, ethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, ethyl formate, 2-ethylhexanol, ethyl acetoethyl, ethyl propionate, formamide, furfuryl alcohol, glycerin, heptane, 1-hexanol, ligroin, 2,6-lutidine, 2-methoxyethanol, methyl acetate, 2-methyl-2-butanol, 3-methyl-1-butanol Thanol, isoamyl acetate, methyl propionate, triethanolamine, nitrobenzene, nitromethane, n-octane, 1-octanol, 2-octanol, pentane, 1-pentanol, 3-pentanol, n-pentyl acetate, petroleum benzine, phenol, 1-propanol, n-propyl acetate, propylene glycol, propylene oxide, propylene oxide, n-propyl ether, pyridine, 1,1,2,2-tetrachloroethane, tetrachloroethylene, tetrahydrofuran, tetralin, 1,1,Examples include one or more of the following: 2-trichloroethane, trichloroethylene, triethylamine, trifluoroacetic acid, xylene, o-xylene, m-xylene, and p-xylene.

[0050] Furthermore, the alkali source compound is not particularly limited as long as it is a compound that hydrolyzes and releases an alkaline component, but for example, urea, ethylenediamine, and hexamethylenetetramine (C6H 12 Examples of N4) include one or more of the following: sodium hydroxide, potassium hydroxide, barium hydroxide, ammonia, calcium hydroxide, sodium carbonate, sodium borate, potassium carbonate, methylamine, dimethylamine, ethylamine, diethylenetriamine, triethylenetetramine, dimethylhydrazine, methylhydrazine, potassium sulfide, sodium sulfide, caustic alkalis, sodium aluminate, sodium oxide, tetramethylammonium hydroxide, soda lime, pyrrolidine, hydrazine, potassium oxide, sodium hydrogen sulfide, tetraethylenepentamine, 1,3-dimethylbutylamine, 1,2-dimethylhydrazine, N-ethylpiperidine, N-methylpiperidine, piperidine, ethanolamine, piperazine, aminopyridine, rubidium hydroxide, lithium hydroxide, cesium hydroxide, ammonium sulfide, amines or polyamines, polyammonium sulfide, vinylpyridine, sodium metasilicate, and mixtures of sodium borohydride and sodium hydroxide. Among them, alkali source compounds include hexamethylenetetramine (C6H 12 It is preferable that it be N4.

[0051] (Form 1) The zinc compounds are not particularly limited, but examples include zinc fluoride, zinc fluoride tetrahydrate, zinc oxide, ZnOHF, zinc, zinc chloride, zinc nitrate hexahydrate, zinc acetate dihydrate, zinc citrate dihydrate, zinc hydroxide carbonate, zinc telluride, zinc bromide, zinc thiocyanate, zinc stearate, zinc diphosphate, zinc phosphate tetrahydrate, pt-butylbenzoate zinc, bacitracin zinc, zinc acetate, zinc sulfide, zinc iodide, zinc trifluoromethanesulfonate, creatinine zinc chloride, zinc terephthalate, zinc laurate, zinc acrylate, zinc carbonate, zinc protoporphyrin, zinc tert-butoxide, zinc meso-tetraphenylporfin, zinc i-propoxide, zinc bis(trifluoromethylsulfonyl)imide, zinc 2-methoxyethoxide, zinc 2,4-pentanedione monohydrate, zinc-copper pair, zinc 2-methylimidazole MOF (ZIF-8), zinc dibutyldithiocarbamate, zinc diethyldithiocarbamate, zinc peroxide, zinc 5,10,15,20-tetraphenylporphyrinatozinc, zinc protoporphyrinatozinc, zinc 2-mercaptobenzothiazole, zinc diphenyl, zinc bis(2,2,6,6-tetramethyl-3,5-heptanedionato)zinc, zinc neodecanoate, zinc iron oxide, 2,5-dibutoxy-4-morpholinobenzene Azonium chloride zinc chloride, 2,5-diisopropoxy-4-morpholinobenzenediazonium chloride zinc chloride, zinc undecylenate, zinc propionate, p-(dimethylamino)benzenediazonium chloride zinc chloride, acridine orange, zinc pyrithione, zinc naphthenate / mineral spirit solution, polaprezinc, mancozeb, ziram, zineb, methylam, zinc gluconate n hydrate, propineb (dicarbamate), ethylenediamine-N,N,N',N'-Zinc(II) tetraacetate disodium tetrahydrate, dimethylzinc, zinc selenide, zinc tetrafluoroborate, zinc phthalocyanine, zinc diethyldithiocarbamate, tert-butylzinc bromide, zinc naphthenate, zinc dibutyldithiocarbamate, zinc diethyldithiocarbamate, zinc hexafluoroacetylacetonate hydrate, zinc gluconate, diethylzinc, Zn(BTZ)2[Bis[2-(2-hydroxyphenyl)benzothiazolato]zinc(II)], ethyl violet G (Zinc chloride double salt), zinc sulfate heptahydrate, zinc perchlorate hexahydrate, zinc acetylacetonate hydrate, Fast Violet B salt, bis(2-ethylhexanoate) zinc, Fast Blue RR salt, Fast Blue BB salt, bis(3-acetyl-6-methyl-2H-pyran-2,4(3H)-dionato) zinc dihydrate, zinc 2-ethylhexanoate, zinc borate 3.5 hydrate, toluene-3,4-dithiol zinc salt hydrate, zinc oxide tungsten, zinc molybdate, Examples include one or more of the following: cyclohexanezinc butyrate dihydrate, zinc cyanide, zinc arsenide, cyclopropylzinc bromide, oxo[hexa(trifluoroacetato)]tetrazinc trifluoroacetic acid adduct, zinc nitride, 3-cyanopropylzinc bromide, zinc molybdenum oxide, Devalda alloy, diethylzinc, zinc salicylate trihydrate, zinc lactate trihydrate, isopropylmagnesium chloride-zinc(II) ate complex, superoxide dismutase, etc.

[0052] Fluorine compounds are not particularly limited, but examples include hydrofluoric acid, ammonium hydrogen fluoride, sodium fluoride, potassium fluoride, lithium fluoride, ammonium fluoride, calcium fluoride, cesium fluoride, magnesium fluoride, potassium hydrogen fluoride, sodium hydrogen fluoride, potassium fluoride dihydrate, lutetium fluoride, fluoride ion standard solution, aluminum fluoride, tin fluoride, antimony fluoride, barium fluoride, lead fluoride, strontium fluoride, lanthanum fluoride, europium fluoride, dysprosium fluoride, neodymium fluoride, and fluorine. Praseodymium fluoride, erbium fluoride, gadolinium fluoride, holmium fluoride, ytterbium fluoride, samarium fluoride, nickel fluoride, iron fluoride, boron fluoride, silver fluoride, cerium fluoride, tetra-n-butylammonium trihydrate fluoride, copper fluoride, rubidium fluoride, gallium fluoride, bismuth fluoride, zinc fluoride, zirconium fluoride, cobalt fluoride, vanadium fluoride, titanium fluoride, xenon fluoride, yttrium fluoride, manganese fluoride, niobium fluoride, tantalum fluoride, chromium fluoride, perfluoro-2,5,8 fluoride ,11,14,17-Hexamethyl-3,6,9,12,15,18-Hexaoxaneicosane oil, Scandium fluoride, Zinc fluoride tetrahydrate, Aluminum fluoride trihydrate, Iron(II) fluoride trihydrate, Iron(III) fluoride trihydrate, Rubidium fluoride hydrate, Hydrogen pyridine fluoride, Aluminum fluoride hydrate, Perfluorooctanoyl fluoride, Acetate complex, 2,3,4,6-Tetra-O-acetyl-α-D-Glucopyranosyl fluoride, Trityl fluoride, Phenacyl fluoride, Octyl fluoride, 4-Methoxymethanilyl fluoride, Fluoride Examples include one or more of the following: pentyl fluoride, cerium(IV) hydrate, pyridine hydrogen fluoride complex, n-tetradecyl fluoride, mercury fluoride, indium fluoride, thallium fluoride, phenylmethylsulfonyl fluoride, 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl fluoride, 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl fluoride, boron trifluoride diethyl ether complex, potassium tetrafluoroborate, sodium hexafluorosilicate, ammonium hexafluoride phosphate, etc.

[0053] (Form 2) Fluorine-containing zinc compounds are not particularly limited, but examples include zinc fluoride, zinc fluoride tetrahydrate, ZnOHF, and zinc hexafluoroacetylacetonate hydrate.

[0054] The method for producing the ZnOHF nanobelt of the present invention preferably involves dissolving the above-mentioned material in distilled water at normal pressure (atmospheric pressure, 1 atm) at a temperature of approximately 0 to 100°C and holding it for approximately 10 minutes to 24 hours. This allows for the synthesis of the ZnOHF nanobelt of the present invention. The ZnOHF nanobelt synthesized in the solvent can be separated, dried, or otherwise treated as appropriate.

[0055] (Porous ZnO Nanobelt) The porous ZnO nanobelt of the present invention has a porous structure composed of ZnO particles, is elongated, and has a rectangular cross-sectional shape. Furthermore, the porous ZnO nanobelt of the present invention has a one-dimensional structure and a belt-like shape extending in one direction.

[0056] Here, "cross-section" refers to a cross-section that includes a direction perpendicular to the longitudinal direction of the porous ZnO nanobelt. Furthermore, "rectangle" is defined similarly to that used for ZnOHF nanobelts, including shapes that are substantially recognized as rectangles, for example, when observed with an electron microscope, and is acceptable for deformation of opposite sides or fine irregularities on the surfaces constituting opposite sides.

[0057] Furthermore, when using porous ZnO nanobelts as gas sensors, it is desirable that they have many reaction sites with the target gas molecules, a high resistance change rate, and conductivity. From this perspective, the following characteristics should be considered.

[0058] Porous ZnO nanobelts have a porosity of 1% to 50%. Furthermore, from the viewpoint of applications such as gas sensors, a porosity of 5% to 50% is preferable for porous ZnO nanobelts. Porosity can be calculated from the area ratio of the zinc oxide (ZnO) region to the void region in observation images such as transmission electron microscope images.

[0059] The width of the porous ZnO nanobelt (the length of the longer side of the rectangular cross-section) is between 10 nm and 200 nm. Furthermore, from the viewpoint of application in gas sensors and other applications, the width of the porous ZnO nanobelt (the length of the longer side of the rectangular cross-section) is preferably between 10 nm and 100 nm, and more preferably between 10 nm and 50 nm.

[0060] The thickness of the porous ZnO nanobelt (the length of the shorter side of the rectangular cross-section) is between 1 nm and 50 nm. Furthermore, from the viewpoint of application in gas sensors and other applications, it is preferably between 1 nm and 30 nm, and more preferably between 1 nm and 10 nm.

[0061] The longitudinal length of the porous ZnO nanobelt is between 100 nm and 1000 μm. Furthermore, from the viewpoint of application in gas sensors and other applications, the longitudinal length is preferably between 1 μm and 1000 μm, and more preferably between 10 μm and 100 μm.

[0062] Furthermore, the ratio of the length to width in the longitudinal direction of the porous ZnO nanobelt (length / width) is preferably greater than 1 and 10,000 or less, more preferably between 10 and 10,000, and even more preferably between 200 and 10,000, from the viewpoint of application to gas sensors and the like.

[0063] The ratio of width to thickness (width / thickness) of the porous ZnO nanobelt is preferably greater than 1 and 200 or less, more preferably between 2 and 200, and even more preferably between 10 and 200, from the viewpoint of application in gas sensors and the like.

[0064] In this invention, the width (length of the long side of the rectangular cross-section), thickness (length of the short side of the rectangular cross-section), and longitudinal length of the porous ZnO nanobelt can be calculated from observation images such as scanning electron microscope images, transmission electron microscope images, and optical microscope images.

[0065] Furthermore, from the viewpoint of applications such as gas sensors, the average particle size of the ZnO particles in the porous ZnO nanobelt is preferably 1 nm to 50 nm, more preferably 1 nm to 30 nm, and even more preferably 1 nm to 20 nm. The average particle size of the ZnO particles can be calculated, for example, from the particle size of the ZnO particles in observation images such as hyperformed electron microscope images.

[0066] Furthermore, the ZnO particles constituting the porous ZnO nanobelt preferably include elongated particles that are long in one direction, and it is preferable that the longitudinal direction of the porous ZnO nanobelt coincides with the longitudinal direction of these elongated particles. In addition, the elongated particles include particles (elliptical particles) whose cross-section along the longitudinal direction is approximately elliptical. The inclusion of elongated particles in the ZnO particles can improve the response of the sensor, for example, when the porous ZnO nanobelt is used in a gas sensor.

[0067] Furthermore, porous ZnO nanobelts have atomic layer steps (atomic steps) on their crystal surface. Therefore, they possess dangling bonds (unbonded areas) and steps at the atomic level. Dangling bonds are known to be highly reactive. It is thought that these dangling bonds promote the adsorption of the target gas onto the ZnO surface, promote the adsorption of oxygen molecules, promote the reaction between the target gas molecules and oxygen, and promote the transfer of electrons between the target molecules, oxygen, and ZnO. Additionally, it is thought that the adsorption of oxygen molecules and the target gas is promoted at the locations of the atomic-level steps. Due to these effects, when porous ZnO nanobelts are used in gas sensors, the sensor's response can be improved.

[0068] Furthermore, porous ZnO nanobelts can contain 33.3 at.% or less of fluorine. Specifically, porous ZnO nanobelts preferably contain 0.33 to 33.3 at.% or less of fluorine. The presence of fluorine in porous ZnO nanobelts improves conductivity, and when porous ZnO nanobelts are used in gas sensors, it is thought that the sensor characteristics will improve. In addition, because oxygen and fluorine have different ionic radii, the crystal structure is distorted, crystal defects are more likely to occur, and oxygen vacancies are more easily formed within the ZnO. Therefore, it is thought that these oxygen ions contribute to the reaction with the target gas molecules, improving the sensor response.

[0069] The porous ZnO nanobelt of the present invention can be used in gas sensors, molecular sensors, solution sensors, battery materials, artificial photosynthesis materials, and the like. In particular, the porous ZnO nanobelt of the present invention is suitable for gas sensor applications.

[0070] (Method for manufacturing porous ZnO nanobelts) The present invention provides a method for producing porous ZnO nanobelts, comprising: a first step of synthesizing ZnOHF nanobelts by adding a zinc compound, a fluorine compound, and an alkali source compound, or a fluorine-containing zinc compound and an alkali source compound, to a solvent; and, The second step involves heat-treating the ZnOHF nanobelt to obtain a porous ZnO nanobelt. Includes.

[0071] The first step is the same as the manufacturing method for ZnOHF nanobelts described above, so we will omit the explanation.

[0072] In the second step, the ZnOHF nanobelt is heat-treated to obtain a porous ZnO nanobelt. The heat-treatment conditions are not particularly limited, but for example, by heat-treating the ZnOHF nanobelt at around 100 to 1000°C for about 10 minutes to 24 hours, a porous ZnO nanobelt can be synthesized.

[0073] Figure 1 is a schematic diagram showing examples of the synthesis of ZnOHF nanobelts and porous ZnO nanobelts. In Figure 1, zinc tetrahydrate is shown as an example of a fluorine-containing zinc compound, and hexamethylenetetramine (C6H) is shown as an alkali source compound. 12 N4) is given as an example.

[0074] (Gas sensor) The porous ZnO nanobelt of the present invention described above can be suitably used in gas sensors. In particular, the gas sensor of the present invention can detect one or more of the following: flammable gases such as acetone, isoprene, toluene, ammonia, and hydrogen; reducing gases such as NO2 (nitrogen dioxide); oxidizing gases such as NO2 (nitrogen dioxide); or combustion-supporting gases such as NO2 (nitrogen dioxide).

[0075] An embodiment of the gas sensor of the present invention will be described below.

[0076] The gas sensor of the present invention comprises a substrate, a pair of electrodes provided on the substrate, and a conductive coating formed on the electrodes that connects the pair of electrodes.

[0077] The base material is not particularly limited, but examples include silicon single crystal substrates, semiconductor substrates, and resin materials.

[0078] The electrode material is not particularly limited, but examples include Pt (platinum), Ir (iridium), Pd (palladium), Ag (silver), Ni (nickel), W (tungsten), Cu (copper), Al (aluminum), Ta (tantalum), Ti (titanium), TiN (titanium nitride), TaN (tantalum nitride), and TiAlN (titanium aluminum nitride). The method for forming the pair of electrodes is also not particularly limited, and known methods can be used.

[0079] The conductive coating film contains the porous ZnO nanobelts of the present invention. The content of the porous ZnO nanobelts is not particularly limited, but is preferably 50 to 100% by mass.

[0080] A gas sensor can be made into a sensor element by forming a conductive coating (particle film) from a porous ZnO nanobelt-containing paint on a substrate such as a substrate having metal electrodes, using a coating method or the like.

[0081] The method for forming the conductive coating film is not particularly limited and can be used, for example, by coating methods such as slit coating, spin coating, bar coating, or spray coating.

[0082] The solvent used in the paint that forms the conductive coating film can be any solvent capable of dispersing porous ZnO nanobelts, such as water or alcohol. As for alcohols, one or more can be selected from isopropanol, ethanol, methanol, n-propanol, isobutanol, and n-butanol.

[0083] Furthermore, a binder may be added to the paint as appropriate. The binder is not limited, but examples include one or more types selected from organic binders or inorganic binders. Examples of organic binders include cellulose derivatives, vinyl resins, fluororesins, silicone resins, acrylic resins, epoxy resins, polyester resins, melamine resins, urethane resins, alkyd resins, etc. Examples of inorganic binders include products obtained by decomposing hydrolyzable silicon compounds such as alkyl silicates, silicon halides, and their partial hydrolysates, organic polysiloxane compounds and their polycondensates, silica, colloidal silica, water glass, silicon compounds, phosphates such as zinc phosphate, metal oxides such as zinc oxide and zirconium oxide, biphosphates, cement, gypsum, lime, enamel frit, etc.

[0084] Furthermore, paints can also contain various other additives besides the binder. Examples of these other additives include defoamers, crosslinking agents, curing catalysts, pigment dispersants, emulsifiers, film-forming aids, thickeners, neutralizing agents, and preservatives.

[0085] The thickness of the conductive coating can be appropriately set according to the detection target and characteristics of the gas sensor, for example, a range of approximately 10 μm to 5 mm can be exemplified.

[0086] Air is a mixed gas consisting of 20% oxygen and 80% nitrogen. If we denote the resistance of the gas sensor in air as Ra and the resistance of the gas to be detected as Rg, then the rate of change in electrical resistance (resistance change rate) when switching from air to the gas to be detected can be expressed as Ra / Rg for reducing gases and as Rg / Ra for oxidizing gases.

[0087] The gas sensor of the present invention exhibits a change in resistance value relative to air for target gases such as reducing gases represented by acetone, isoprene, toluene, ammonia, and hydrogen, or oxidizing gases represented by nitrogen dioxide.

[0088] Specifically, the gas sensor of the present invention preferably exhibits a resistance change rate of 1.0 to 16.5 (Ra / Rg for reducing gases, Rg / Ra for oxidizing gases) for reducing gases (concentration 500 ppb) such as acetone, isoprene, toluene, ammonia, and hydrogen, or for oxidizing gases (concentration 500 ppb) such as nitrogen dioxide, more preferably 2.0 to 16.5 (Ra / Rg or Rg / Ra), and even more preferably 10.0 to 16.5 (Ra / Rg or Rg / Ra).

[0089] The gas sensor of the present invention can detect acetone gas at concentrations of, for example, 70 ppt to 200 ppt. Furthermore, for example, the gas sensor of the present invention preferably exhibits a resistance change rate (Ra / Rg or Rg / Ra) of 1.0 to 2.5 for low-concentration acetone (10 ppb).

[0090] Furthermore, when comparing the rate of change of resistance for acetone (Ra / Rg) with the rate of change of resistance for isoprene, toluene, ammonia, hydrogen, and nitrogen dioxide (Ra / Rg or Rg / Ra), the gas sensor of the present invention achieves an acetone selectivity of 1.0 or higher, preferably 2.0 or higher, 3.0 or higher, or 4.0 or higher. When comparing the rate of change of resistance for acetone (Ra / Rg) with the rate of change of resistance for isoprene, toluene, ammonia, hydrogen, and nitrogen dioxide (Ra / Rg or Rg / Ra), for example, an acetone selectivity of 1.0 to 10.0, and practically speaking, 1.0 to 3.5, is exemplified.

[0091] Furthermore, the gas sensor of the present invention preferably exhibits the maximum resistance change rate (Ra / Rg) at a sensor element temperature of 450°C, among the sensor element temperatures of 375°C, 400°C, 425°C, 450°C, 475°C, and 500°C, in response to acetone gas at a concentration of 500 ppb.

[0092] The ZnOHF nanobelt, porous ZnO nanobelt, method for producing the same, and gas sensor of the present invention are not limited to the embodiments described above. [Examples]

[0093] The ZnOHF nanobelt, porous ZnO nanobelt, methods for producing them, and gas sensors of the present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0094] <Example 1> Synthesis of ZnOHF nanobelts 300 mg of zinc fluoride tetrahydrate (ZnF2·4H2O) and 240 mg of hexamethylenetetramine (C6H 12 N4) was dissolved in 200 mL of distilled water at 80°C. The prepared solution was placed in a polypropylene container and held at 80°C for 3 hours to synthesize ZnOHF nanobelts. The ZnOHF nanobelts were recovered by centrifugation, washed with ethanol, and then dried at 80°C. The powder consisting of ZnOHF nanobelts was white in color.

[0095] Figure 2 is a scanning electron microscope image of a ZnOHF nanobelt. Figure 3 is a transmission electron microscope image of a ZnOHF nanobelt. Figure 4 shows the electron diffraction pattern of the ZnOHF nanobelt shown in Figure 3.

[0096] Figure 2 shows the one-dimensional shape and size of the ZnOHF nanobelt.

[0097] As shown in Figures 2 and 3, the ZnOHF nanobelt was confirmed to be a belt-like structure that is long and has a rectangular cross-sectional shape. Furthermore, as shown in Figure 3, it was confirmed that the longitudinal direction of the ZnOHF nanobelt is the b-axis direction of ZnOHF.

[0098] As shown in Figure 4, it was confirmed that the ZnOHF nanobelt exhibits an electron diffraction pattern attributed to ZnOHF, as well as an electron diffraction pattern attributed to a single crystal, and that the longitudinal direction of the ZnOHF nanobelt is the b-axis direction of the ZnOHF crystal.

[0099] As shown in the data for PDF card number (Inorganic, ICSD Pattern) 01-076-7466, the ZnOHF crystal is known to be orthorhombic. The Crystallographic Society of Japan has proposed that "orthorhombic" should be translated as "orthorhombic system" rather than "orthorhombic system," so "orthorhombic" is now often translated as "orthorhombic system," whereas it was traditionally translated as "orthorhombic." The space group is known to be Pna21(33). The lattice constants are a = 10.2276 Å (angstroms), b = 4.7161 Å (angstroms), and c = 3.1130 Å (angstroms), and the angles are known to be α = 90°, β = 90°, and γ = 90°. In other words, the ZnOHF crystal is orthorhombic, and as indicated by the fact that the lattice constants are different for all three sides and the three angles are 90°, it has a rectangular crystal structure. Therefore, ZnOHF nanobelts, which have a crystalline structure in which the ZnOHF crystal extends in the uniaxial (b-axis) direction, have a rectangular cross-sectional shape when cut perpendicular to the longitudinal axis.

[0100] Furthermore, as shown in Figures 2 and 3, scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) observations confirmed that the ZnOHF nanobelt has a rectangular cross-section, with a width (length of the long side of the rectangular cross-section) ranging from 10 nm to 200 nm, a thickness (length of the short side of the rectangular cross-section) ranging from 1 nm to 50 nm, and a longitudinal length ranging from 100 nm to 1000 μm. In particular, the ZnOHF nanobelts, which were observed in greater numbers, were found to have a width (length of the long side of the rectangular cross-section) ranging from 20 nm to 100 nm, a thickness (length of the short side of the rectangular cross-section) ranging from 10 nm to 30 nm, and a longitudinal length ranging from 1 μm to 10 μm. Furthermore, as shown in Figure 3, TEM observation confirmed that the longitudinal direction of the ZnOHF nanobelts was the b-axis direction.

[0101] Furthermore, as shown in Figure 4, diffraction spots at 020, 0-20, 600, -600, 610, -610, -6-10, and 1200 were observed. Electron diffraction indicated that it was a single crystal. It also confirmed that it has a dense structure.

[0102] Furthermore, compositional analysis using energy-dispersive X-ray spectroscopy (EDS) during TEM observation revealed that the proportion of constituent elements in the ZnOHF nanobelt was calculated as atomic percentages (atomic %). Zinc: 32.0 at.% Oxygen: 34.5 at.% Fluorine: 33.5 at.% That was the case.

[0103] Figure 5 shows the X-ray diffraction pattern of (a) a ZnOHF nanobelt and (b) a porous ZnO nanobelt.

[0104] In Figure 5(a), the X-ray diffraction (XRD) pattern of the white powder matched the data from PDF card number (Inorganic, ICSD Pattern) 01-076-7466, indicating that it was ZnOHF. Furthermore, no X-ray diffraction patterns of other components were observed. Therefore, it was determined that the white powder was ZnOHF and contained no other components, representing a single phase of ZnOHF.

[0105] The crystallite sizes calculated using Scherrer's formula from the full width at half maximum of the X-ray diffraction peaks 110, 310, 201, 111, and 221 were 22.1 nm, 23.6 nm, 29.6 nm, 27.4 nm, and 20.9 nm, respectively.

[0106] <Example 2> Synthesis of porous ZnO nanobelts Porous ZnO nanobelts were synthesized by heat-treating the ZnOHF nanobelts prepared in Example 1 at 500 °C for 2 hours. During this process, the color of the powder changed from white to pale yellow.

[0107] As shown in Figure 5(b), the X-ray diffraction pattern of the pale yellow powder was consistent with the data from JCPDS No. 36-1451, confirming that it was ZnO. Furthermore, no X-ray diffraction patterns of other components were observed. Therefore, it was confirmed that the pale yellow powder was ZnO and contained no other components, forming a single phase of ZnO.

[0108] The crystallite sizes calculated using Scherrer's formula from the full width at half maximum of the X-ray diffraction peaks 100, 002, 101, 110, and 103 were 19.0 nm, 16.0 nm, 17.2 nm, 16.7 nm, and 13.8 nm, respectively.

[0109] Figure 6 is a scanning electron microscope image of a porous ZnO nanobelt. Figure 7 is a transmission electron microscope image of a porous ZnO nanobelt. Figure 8 is a high-resolution transmission electron microscope image of a porous ZnO nanobelt. Figure 9 is a high-resolution transmission electron microscope image of a porous ZnO nanobelt, and is an enlarged view of the dotted line area in Figure 8. Figure 10 is a high-resolution transmission electron microscope image of a porous ZnO nanobelt. Figure 11 is a high-resolution transmission electron microscope image of a porous ZnO nanobelt.

[0110] Figure 6 shows the one-dimensional shape and size of the porous ZnO nanobelt.

[0111] As shown in Figures 6, 7, and 8, it was confirmed that the porous ZnO nanobelt is porous, composed of ZnO nanoparticles, and is a belt-like structure that is long and has a rectangular cross-sectional shape. Furthermore, it was confirmed that the ZnO nanoparticles include elongated particles (elliptical particles), and that the longitudinal direction of these particles is the same as the longitudinal direction of the porous ZnO nanobelt.

[0112] As shown in Figure 9, it was confirmed that the ZnO nanoparticles constituting the porous ZnO nanobelt have regular ZnO lattice fringes.

[0113] As shown in Figure 10, it was confirmed that the surface of the ZnO nanoparticles constituting the porous ZnO nanobelt has atomic layer steps (atomic step structure).

[0114] As shown in Figure 11, it was confirmed that the ZnO nanoparticles constituting the porous ZnO nanobelt have regular ZnO lattice fringes, and that the spacing of their atomic arrangement is 0.335 nm, which is attributed to the interplanar spacing of the (001) plane of ZnO.

[0115] In other words, the porous ZnO nanobelt had a porous structure composed of ZnO particles, and a polycrystalline structure composed of ZnO particles. Furthermore, the ZnO particles constituting the porous ZnO nanobelt included elongated particles (elliptical particles), and the average particle size was between 1 nm and 50 nm.

[0116] Furthermore, the porous ZnO nanobelt is long and has a rectangular cross-sectional shape, with a width (the longer side of the rectangular cross-section) ranging from 10 nm to 200 nm. The thickness (the shorter side of the rectangular cross-section) is in the range of 1 nm to 50 nm. Length range is 100 nm to 1000 μm. Porosity of 1% to 50% That was the case.

[0117] The ZnO particles constituting the porous ZnO nanobelts, which were observed in greater numbers, had an average particle size of 10 nm to 30 nm.

[0118] The porous ZnO nanobelts that were observed in greater numbers were The width (the longer side of the rectangular cross-section) is in the range of 20 nm to 100 nm. The thickness (the shorter side of the rectangular cross-section) is in the range of 10 nm to 30 nm. The length range is between 1 μm and 10 μm. Porosity is between 1% and 30%. That was the case.

[0119] Furthermore, TEM observation confirmed that the longitudinal direction of the porous ZnO nanobelt is the b-axis direction.

[0120] Furthermore, when the composition of the porous ZnO nanobelt was analyzed by EDS analysis under TEM observation, Zinc: 49.51 at.% Oxygen: 50.16 at.% Fluorine: 0.33 at.% That was the case.

[0121] (Example 1 of calculating fluorine content) As is clear from its chemical formula, the composition of a ZnOHF nanobelt is Zn:O:H:F = 1:1:1:1, and when expressed as atomic percentages, Zinc: 25 at.% Oxygen: 25 at.% Hydrogen: 25 at.% Fluorine: 25 at.% That is the case.

[0122] Since porous ZnO nanobelts are synthesized by heat-treating ZnOHF nanobelts in air, no other elements are introduced. The amount of zinc ions is maintained, while the amounts of hydrogen and fluorine ions are maintained or decreased. The amount of oxygen ions is maintained, increased, or decreased. Considering the heat-treating of a material composed of Zn, O, H, and F in air, and the results of the X-ray diffraction pattern, more specifically, it is thought that the amount of zinc is usually maintained, the amounts of hydrogen and fluorine ions decrease, and the amount of oxygen ions becomes equivalent to or slightly less than that of ZnO. Here, the case in which the amount of oxygen ions becomes less than the amount of Zn ions is when oxygen vacancies are formed. For example, if the amount of oxygen decreases to one-tenth, the ion ratio Zn:O=1:1 before heat treatment becomes Zn:O=1:0.1 after heat treatment.

[0123] Based on these considerations, in the case where oxygen vacancies are not formed, the fluorine content of porous ZnO nanobelts synthesized by heat-treating ZnOHF nanobelts in air is a maximum of 33.3 at.%. This calculation assumes that hydrogen ions are eliminated by heating, the zinc ion content is maintained, the oxygen ion content is maintained to match the composition of ZnO, and the fluorine ions remain unchanged. Ratio of ion amounts in ZnOHF nanobelts Zn:O:H:F=1:1:1:1 Ratio of ion content in porous ZnO nanobelt Zn:O:H:F=1:1:0:1 Atomic percentage calculated from the ratio of ions in the porous ZnO nanobelt described above Zinc: 33.3 at.% Oxygen: 33.3 at.% Hydrogen: 0 at.% Fluorine: 33.3 at.% Considering that the atomic percentage of fluorine in the EDS analysis results obtained from TEM observation is 0.33 at.%, the fluorine content in porous ZnO nanobelts can take values ​​of 0.33 to 33.3 at.%.

[0124] (Example 2 of calculating fluorine content) Furthermore, for example, if the fluorine content of a ZnOHF nanobelt is reduced by 90% through heat treatment, the fluorine content in the porous ZnO nanobelt will be a maximum of 4.76 at.% as shown below. Ratio of ion amounts in ZnOHF nanobelts Zn:O:H:F=1:1:1:1 Ratio of ion content in porous ZnO nanobelt Zn:O:H:F=1:1:0:0.1 Ratio of ion content in the porous ZnO nanobelt described above Atomic percentages calculated from Zinc: 47.6 at.% Oxygen: 47.6 at.% Hydrogen: 0 at.% Fluorine: 4.76 at.% Considering that the atomic percentage of fluorine in the EDS analysis results obtained from TEM observation is 0.33 at.%, if the fluorine content of the ZnOHF nanobelt is reduced by 90% due to heat treatment, the fluorine content in the porous ZnO nanobelt can take values ​​of 0.33 to 4.76 at.%.

[0125] (Example 3 of calculating fluorine content) Furthermore, for example, if the fluorine content of a ZnOHF nanobelt is reduced by 99% through heat treatment, the fluorine content in a porous ZnO nanobelt will be a maximum of 0.50 at.% as shown below. Ratio of ion amounts in ZnOHF nanobelts Zn:O:H:F=1:1:1:1 Ratio of ion content in porous ZnO nanobelt Zn:O:H:F=1:1:0:0.01 Atomic percentage calculated from the ratio of ions in the porous ZnO nanobelt described above Zinc: 49.8 at.% Oxygen: 49.8 at.% Hydrogen: 0 at.% Fluorine: 0.50 at.% Considering that the atomic percentage of fluorine in the EDS analysis results from TEM observation is 0.33 at.%, if the fluorine content of the ZnOHF nanobelt is reduced by 99% through heat treatment, the fluorine content in the porous ZnO nanobelt can take values ​​of 0.33 to 0.50 at.%.

[0126] <Example 3> Characterization of a gas sensor made of porous ZnO nanobelt A gas sensor was fabricated by coating a porous ZnO nanobelt onto a substrate equipped with a pair of platinum electrodes using a coating method, thereby forming a conductive coating that connects the two electrodes. Specifically, 10 mg of porous ZnO nanobelt powder was added to 3 mL of ethanol and dispersed by sonication for 30 minutes. 5 μL of this dispersion solution was coated onto a 3 × 3 mm substrate to form a conductive coating and fabricate a gas sensor.

[0127] Figure 12 is a graph showing the effect of sensor element temperature on the response of a gas sensor to acetone gas at a concentration of 500 ppb.

[0128] The response values ​​at sensor element temperatures of 375°C, 400°C, 425°C, 450°C, 475°C, and 500°C were 9.16, 11.4, 12.9, 16.1, 13.3, and 12.4, respectively.

[0129] At the evaluated measurement temperatures, it was confirmed that the sensor element showed the maximum response at a temperature of 450°C.

[0130] Figure 13 is a graph showing the response of the gas sensor to acetone gas at concentrations of 10 to 500 ppb.

[0131] The response time and recovery time of porous ZnO nanobelts to 500 ppb of acetone gas were 20 seconds and 240 seconds, respectively. Here, response time (τres) is defined as the time it takes for the response value to reach 90% of its maximum value from exposure to the target gas, and recovery time (τrec) is defined as the time required for the response value to recover to 10%.

[0132] The sensor response values ​​for flammable and reducing gases such as acetone, isoprene, toluene, ammonia, and hydrogen were calculated using the Ra / Rg formula, based on the sensor resistance value Ra in air and the sensor resistance value Rg in the target gas.

[0133] The sensor response values ​​for oxidizing gases such as nitrogen dioxide and combustion-supporting gases were calculated using the Rg / Ra formula, based on the sensor resistance value Ra in air and the sensor resistance value Rg in the target gas.

[0134] The sensor response (resistance change rate (Ra / Rg)) for acetone concentrations of 500 ppb, 250 ppb, 100 ppb, 50 ppb, 25 ppb, and 10 ppb was 16.3, 10.7, 6.0, 3.9, 2.9, and 2.2, respectively.

[0135] Figure 14 is a graph showing the response of the gas sensor to acetone gas at concentrations of 200 to 1000 ppt.

[0136] The sensor response (resistance change rate (Ra / Rg)) for acetone concentrations of 1000 ppt, 800 ppt, 600 ppt, 400 ppt, and 200 ppt was 1.9, 1.7, 1.5, 1.3, and 1.2, respectively. The gas sensor was confirmed to be capable of detecting acetone gas at a concentration of 200 ppt.

[0137] It shows good linearity in the range of 1000ppt to 200ppt, and the Root Mean Squared Error (RMSE) is R 2 The result was 0.996. The detection limit (LOD) was calculated to be 73 ppt. Here, the detection limit is defined as "the smallest amount (value) that can be detected." The detection limit was calculated by multiplying the standard deviation by 3. The detection limit (LOD) was calculated using the formula 3.3 × σ / S, where σ is the standard deviation of the blank signal and S is the slope of the linear fit (Non-Patent Literature 1). The values ​​of σ and S in the calculation of the detection limit were 0.021384 and 0.000972, respectively. The calculation of the detection limit showed that the gas sensor containing porous ZnO nanobelts can detect acetone gas at a concentration of 73 ppt.

[0138] Figure 15 is a graph showing the response of a gas sensor using a porous ZnO nanobelt to various gases: acetone, isoprene, toluene, ammonia, hydrogen, and nitrogen dioxide.

[0139] The sensor response values ​​(resistance change rate (Ra / Rg or Rg / Ra)) for acetone, isoprene, toluene, ammonia, nitrogen dioxide, and hydrogen at 500 ppb were 16.0, 8.1, 6.2, 5.6, 5.4, and 4.6, respectively. It was confirmed that the gas sensor containing the porous ZnO nanobelt can detect various gases including acetone, isoprene, toluene, ammonia, hydrogen, and nitrogen dioxide.

[0140] When comparing the resistance change rate (Ra / Rg) for acetone with that for isoprene, toluene, ammonia, nitrogen dioxide, or hydrogen (Ra / Rg or Rg / Ra), the values ​​were 2.0, 2.6, 2.9, 3.0, and 3.5, respectively. This demonstrated that the gas sensor made of porous ZnO nanobelts exhibits acetone selectivity.

[0141] <Example 4> Comparison of the gas sensor from Example 3 with a commercially available gas sensor For comparison, when compared to the TGS2602, a representative semiconductor gas sensor manufactured by Figaro Engineering Co., Ltd., the catalog for the TGS2602 states that, if Rs = sensor resistance value in gases of various concentrations and Ro = sensor resistance value in clean air, then at 10 ppm hydrogen, Rs / Ro = 0.80. Converting this to Ra / Rg, the reciprocal of 0.80 is Ra / Rg = 1.25.

[0142] The sensor response of the porous ZnO-containing gas sensor in Example 3 to 500 ppb of hydrogen was 4.6, which was 3.68 times higher than that of the TGS2602 manufactured by Figaro Technology Co., Ltd., despite the hydrogen concentration being 1 / 20th.

[0143] Assuming that the sensor response is proportional to the hydrogen concentration in the range of 500 ppb to 10 ppm, the sensor response for 10 ppm of hydrogen in the porous ZnO nanobelt gas sensor of Example 3 is calculated to be 72, which is 20 times the increase of 3.6 from 1 to 4.6. This is calculated to be 57.6 times the sensor response of 1.25 for the TGS2602 manufactured by Figaro Technology Co., Ltd.

[0144] Although the type of gas is different, the sensor sensitivity of the porous ZnO nanobelt gas sensor in Example 3 to 500 ppb of acetone was 16.0, which was 12.8 times higher than that of the TGS2602 manufactured by Figaro Technology Co., Ltd., despite the gas concentration being 1 / 20th.

[0145] Assuming that the sensor response is proportional to the acetone concentration in the range of 500 ppb to 10 ppm, the sensor response of the porous ZnO nanobelt gas sensor of Example 3 for 10 ppm of acetone is calculated to be 300, which is 20 times the increase from 1 to 16.0 (15.0). This is calculated to be 240 times the sensor response of the TGS2602 manufactured by Figaro Technology Co., Ltd., which is 1.25.

[0146] Product TGS2602 catalog website: https: / / www.figaro.co.jp / product / entry / tgs2602.html Product TGS2602 catalog website: https: / / www.figaro.co.jp / product / docs / tgs2602_product%20information%28jp%29_rev04.pdf

Claims

1. It is composed of ZnO particles and has a porous structure with a porosity of 1% to 50%. It is long and has a rectangular cross-sectional shape. The width is between 10 nm and 200 nm. The thickness is between 1 nm and 50 nm. The length in the longitudinal direction is between 100 nm and 1000 μm. The ZnO particles include elongated particles, The longitudinal direction of the porous ZnO nanobelt coincides with the longitudinal direction of the elongated particles. A porous ZnO nanobelt characterized by the following features.

2. The ratio of length to width in the longitudinal direction (length / width) is greater than 1 and less than or equal to 10,000. A porous ZnO nanobelt according to feature 1.

3. The ZnO particles have an average particle size of 1 nm or more and 50 nm or less. A porous ZnO nanobelt according to feature 1.

4. A crystal surface has a step in the atomic layer. A porous ZnO nanobelt according to feature 1.

5. It is composed of ZnO particles and has a porous structure with a porosity of 1% to 50%. It is long and has a rectangular cross-sectional shape. The width is between 10 nm and 200 nm. The thickness is between 1 nm and 50 nm. The length in the longitudinal direction is between 100 nm and 1000 μm. Contains 0.33 to 33.3 at.% fluorine. A porous ZnO nanobelt characterized by the following features.

6. A method for producing a porous ZnO nanobelt according to any one of claims 1 to 5, The following steps: In the solvent, Zinc compounds, fluorine compounds and alkali source compounds, or Fluorine-containing zinc compounds and alkali source compounds The first step involves adding to synthesize ZnOHF nanobelts; and, The second step involves heat-treating the ZnOHF nanobelt to obtain a porous ZnO nanobelt. including A method for producing porous ZnO nanobelts, characterized by the above.

7. In the first step, the solvent is water, and the alkali source compound is hexamethylenetetramine. A method for producing porous ZnO nanobelts according to feature 6.

8. The heat treatment temperature in the second step is 100 to 1000°C. A method for producing porous ZnO nanobelts according to feature 6.

9. Substrate and A pair of electrodes provided on the substrate, A conductive coating film formed on the electrode and connecting the pair of electrodes, Equipped with, The conductive coating film comprises a porous ZnO nanobelt according to any one of claims 1 to 5. A gas sensor characterized by the following features.

10. It can detect one or more of the following gases: acetone, isoprene, toluene, ammonia, hydrogen, and nitrogen dioxide. The gas sensor according to feature 9.

11. A resistivity change rate (Ra / Rg or Rg / Ra) greater than 1.0 and less than or equal to 16.5 for a reducing gas or an oxidizing gas at a concentration of 500 ppb. The gas sensor according to feature 9.

12. The rate of change in resistance to acetone (Ra / Rg), The rate of change in resistance to isoprene, toluene, ammonia, or hydrogen (Ra / Rg), or the rate of change in resistance to nitrogen dioxide (Rg / Ra) When comparing these, an acetone selectivity ratio of 1.0 or higher can be obtained. The gas sensor according to feature 9.

13. Substrate and A pair of electrodes provided on the substrate, A conductive coating film formed on the electrode and connecting the pair of electrodes, Equipped with, The conductive coating film is It is composed of ZnO particles and has a porous structure with a porosity of 1% to 50%. It is long and has a rectangular cross-sectional shape. The width is between 10 nm and 200 nm. The thickness is between 1 nm and 50 nm. It contains porous ZnO nanobelts with a longitudinal length of 100 nm to 1000 μm. In response to acetone gas at a concentration of 500 ppb, the maximum resistance change rate (Ra / Rg) is observed at a sensor element temperature of 450°C, out of the sensor element temperatures of 375°C, 400°C, 425°C, 450°C, 475°C, and 500°C. A gas sensor characterized by the following features.

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