Method for decomposing hydroxyapatite and volatile organic substances

Abstract

To provide hydroxyapatite capable of efficiently decomposing VOC, and to provide a method for producing the hydroxyapatite and a method for decomposing VOC using the hydroxyapatite.SOLUTION: A hydroxyapatite of the present invention is characterized by a ratio of a peak intensity IP=O of P=O bonds to a peak intensity IP-O of P-O bonds analyzed from the O1 s spectrum (IP=O / IP-O) being 0.8 or more when measured by X-ray photoelectron spectroscopy (XPS).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to hydroxyapatite. [Background technology]

[0002] Gases emitted from automobiles and chemical plants contain various volatile organic compounds (VOCs), such as toluene, xylene, ethyl acetate, and isopropanol, which are the cause of suspended particulate matter and photochemical oxidants that can affect human health. The emission levels of many of these VOCs are regulated by the Air Pollution Control Act, and various efforts are being made to reduce VOC emissions.

[0003] Various methods are known for decomposing harmful components in gases, including combustion (direct combustion, catalytic combustion), adsorption, plasma decomposition, and photocatalysis. Of these methods, catalytic combustion allows decomposition to proceed even at relatively low temperatures (e.g., below 500°C) by using a catalyst, thus preventing the generation of nitrogen compounds. This method also has the advantage of allowing the use of relatively small-scale equipment and requiring infrequent catalyst replacement.

[0004] While some catalytic combustion methods utilize catalysts made by supporting expensive metal elements on metal oxides such as zeolites or zirconia, these methods are costly and difficult to reuse after use. For example, Patent Document 1 discloses a method for decomposing volatile organic substances in a gas by catalytic combustion, characterized by the use of hydroxyapatite as the catalyst. Hydroxyapatite can be reused after catalyst use, thus avoiding the problem of adverse environmental impacts from disposal. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-188652

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the above Patent Document 1, it is disclosed that VOC can be decomposed by bringing hydroxyapatite into contact with a gas containing VOC under heating conditions.

[0007] Therefore, an object of the present invention is to provide hydroxyapatite capable of decomposing VOC more efficiently, and a method for producing the same, and a method for decomposing VOC using the hydroxyapatite.

Means for Solving the Problems

[10] A method for decomposing volatile organic substances by catalytic combustion, A method for decomposing volatile organic substances, characterized by using hydroxyapatite as described in any of [1] to [7] as a catalyst.

[11] The decomposition method according to

[10] , wherein the heating temperature during the decomposition of the volatile organic substance is 150°C or higher. [Effects of the Invention]

[0009] According to the hydroxyapatite of the present invention, the peak intensity of the PO bond I P-O Peak intensity I of the P=O bond P=O The ratio (I P=O / I P-O Since ) is 0.8 or higher, I P=O / I P-OCompared to hydroxyapatite, which has a VOC ratio of less than 0.8, it can either decompose VOCs at low temperatures or, when compared at the same temperature, achieve a higher VOC decomposition rate. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows the spectra obtained by XPS measurement in the example. [Figure 2] This graph shows the spectra obtained by ESR measurement in the example. [Figure 3] This graph shows the spectra obtained by XRD measurement in the example. [Figure 4] This is a photograph used as a substitute for a drawing, showing an SEM image of hydroxyapatite in the example. [Figure 5] This graph shows the decomposition efficiency when VOCs were decomposed using hydroxyapatite in the examples. [Modes for carrying out the invention]

[0011] The hydroxyapatite of the present invention, when measured by X-ray photoelectron spectroscopy (XPS), exhibits a peak intensity of PO bond I, which is analyzed from the O1s spectrum. P-O Peak intensity I of the P=O bond P=O The ratio (I P=O / I P-O ) is 0.8 or higher. Hydroxyapatite (hereinafter sometimes referred to as HAp) is elemental calcium phosphate, and [Ca 10 The basic composition is (HPO4)6(OH)2, and it also includes compounds with a different composition in which the molar ratio of Ca to P (Ca / P) is in the range of 1.55 to 2.50. The molar ratio of Ca to P may change depending on differences in conditions such as the manufacturing method. In the present invention, the above I P=O / I P-O If it is 0.8 or higher, then PO4 3- This means that surface defects are being generated at the site, and the relative composition of PO is decreasing. P=O / I P-OHAp with a value of 0.8 or higher is I P=O / I P-O Compared to HAp, which has a value of less than 0.8, it can efficiently decompose VOCs and can be suitably used as a thermal catalyst. Specifically, being able to efficiently decompose VOCs means that decomposition of VOCs can be initiated even at low temperatures, or that VOCs can be decomposed at a higher rate when compared at the same temperature.

[0012] I P=O / I P-O The value of is preferably 1.0 or higher, more preferably 1.05 or higher, and even more preferably 1.1 or higher. There is no particular upper limit, but it may be 1.4 or lower, or 1.3 or lower.

[0013] Peak intensity of PO binding I P-O and the peak intensity I of the P=O bond P=O These are all analyzed from the O1s spectrum when measured by X-ray photoelectron spectroscopy (XPS). The peak corresponding to the PO bond can be identified at a bond energy of 529.50 ± 0.5 eV (more precisely, between 529.00 eV and 530.00 eV), and the peak corresponding to the P=O bond can be identified at a bond energy of 530.50 ± 0.5 eV (more precisely, between 530.00 eV and 531.00 eV).

[0014] The HAp of the present invention is capable of generating O2 radicals when heated at high temperatures. The generation of O2 radicals can be confirmed by electron spin resonance spectroscopy (ESR). In a preferred embodiment of the present invention, the generation of O2 radicals in the HAp is specifically confirmed by measuring the electron spin resonance spectrum of the HAp at 400°C in an oxygen-containing atmosphere using a standard sample Mn marker, when the g value = 2.003. HAp and the peak intensity of the Mn marker I Mn The ratio (I HAp / I Mn ) 400℃ However, it can be identified as being 0.3 or higher. The O2 radical is PO4 3-It is thought that numerous electrons are trapped in surface defects or oxygen vacancies that form at the site, and these trapped electrons react with O2 molecules adsorbed on the surface to generate O2 radicals. These O2 radicals can decompose VOCs into CO2, CO, and H2O.

[0015] (I HAp / I Mn ) 400℃ The value of is preferably 0.4 or higher, more preferably 0.5 or higher, and even more preferably 0.6 or higher. There is no particular upper limit, but it may be 1.5 or lower, or 1.4 or lower.

[0016] The generation of O2 radicals upon heating can be evaluated at heating temperatures of 100°C, 200°C, and 300°C. Other than heating temperature, (I HAp / I Mn ) 400℃ The peak intensity of HAp at 100°C, 200°C, and 300°C was measured in the same manner as the measurement of HAp I. HAp and the peak intensity of the Mn marker I Mn The ratio (I HAp / I Mn ) to each (I HAp / I Mn ) 100℃ , (I HAp / I Mn ) 200℃ , (I HAp / I Mn ) 300℃ Expressed as, (I HAp / I Mn ) 100℃ (I HAp / I Mn ) 200℃ (I HAp / I Mn ) 300℃ It is preferable that the value is between 0.2 and 0.9.

[0017] The HAp of the present invention is the peak intensity I of the (002) plane, measured by X-ray diffraction. (002) Peak intensity I on the (300) plane relative to (300) The ratio (I(300) / I (002) It is preferable that ) is 1.1 or higher. As will be described later, the HAp of the present invention can be manufactured by mechanochemical treatment, and it is thought that in mechanochemical treatment, the amorphization of the surface proceeds preferentially and selectively on the (002) plane (i.e., the c plane) of HAp compared to the (300) plane (i.e., the a plane). (300) / I (002) Preferably, the value is 1.15 or higher, more preferably 1.20 or higher, and even more preferably 1.25 or higher. The upper limit is not particularly limited, but may be, for example, 2.0 or lower, or 1.7 or lower.

[0018] Furthermore, it is preferable that the HAp of the present invention has secondary particles formed by the aggregation of primary particles. The average particle diameter of the secondary particles is preferably 1 to 40 μm, and the BET specific surface area is 35 m². 2 It is preferable that the amount is less than or equal to / g. By satisfying these requirements, VOCs can be efficiently decomposed. The average particle size of the secondary particle diameter refers to the cumulative 50% diameter (D50) based on the number of particles and can be measured by a laser diffraction particle size distribution analyzer. The average particle size of HAp in the present invention is preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and also preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. The BET specific surface area is 33 m². 2 It is more preferable that it be less than or equal to / g, and even more preferably 30m 2 The lower limit is not particularly limited, but for example, 10m 2 It is / g.

[0019] As described above, the molar ratio of Ca to P (Ca / P) in HAp is variable depending on conditions such as the production method, and as described above, it is preferably 1.55 or more and 2.50 or less, more preferably 10 / 6 or more (i.e., 1.67 or more) and 2.50 or less, and even more preferably 1.67 or more and less than 1.74. That the molar ratio of Ca to P (Ca / P) is 1.67 or more is preferable because the catalytic function of HAp is more effectively exhibited, and that it is less than 1.74 is also preferable because the catalytic function is more effectively exhibited.

[0020] The HAp of the present invention can be produced by mechanochemical treatment. More specifically, when measured by X-ray photoelectron spectroscopy (XPS), the peak intensity I of the P-O bond analyzed from the O1s spectrum P-O of the P=O bond with respect to P=O is obtained by subjecting HAp having a ratio (I P=O / I P-O ) less than 0.8 to mechanochemical treatment.

[0021] Mechanochemical treatment is a treatment that induces changes in the physicochemical properties of a substance by applying mechanical energy such as compressive force, shear force, frictional force, and impact force to the substance, resulting in changes in the crystal structure of the substance, activation of the surface of the substance, and subsequent chemical reactions. Hereinafter, in this specification, for convenience, HAp having I P=O / I P-O less than 0.8 is referred to as non-activated HAp, and HAp having I P=O / I P-O of 0.8 or more is referred to as activated HAp.

[0022] The mechanochemical treatment is not particularly limited as long as it can impart mechanical energy to the substance, and may be a pulverizer that uses pulverizing media or a pulverizer that does not use pulverizing media, but a pulverizer that uses pulverizing media is preferred. Examples of pulverizers that use pulverizing media include ball mills such as planetary ball mills and bead mills. Examples of pulverizers that do not use pulverizing media include vibratory mills, jet mills, turbo mills, etc. The mechanochemical treatment may be dry or wet, but a dry treatment is preferred.

[0023] Examples of grinding media include zirconia, alumina, titania, silicon nitride, stainless steel, and chromium steel, with zirconia being particularly preferred. The diameter of the crushed media is preferably 1 to 20 mm, and more preferably 3 to 10 mm.

[0024] Inactive HAp preferably has secondary particles formed by the aggregation of primary particles, with an average particle diameter of, for example, 1 to 10 μm. The average particle diameter of the secondary particles can be measured by a laser diffraction particle size distribution analyzer, similar to that of activated HAp. The BET specific surface area of ​​inactive HAp is, for example, 35 m². 2 / g is greater than 38m 2 It may be 45m or more. 2 It may be less than / g.

[0025] The ratio of the diameter of the grinding media to the average particle size of the secondary particles of inactive HAp is, for example, 0.5 × 10⁻⁶. 3 ~2.8×10 3 That is the case.

[0026] MeThe rotation speed of the grinder used during the mechanochemical treatment may vary depending on the shape or size of the device, etc. For example, it may be set to 200 to 500 rpm. When using the planetary ball mill described later, the rotation speed of the self-rotation may be within the above range. Also, when using a planetary ball mill, the ratio of the self-rotation speed to the revolution speed is preferably 0.275 or more, preferably 17.5 or less, more preferably 10 or less, and even more preferably 2.19 or less. Further, the amount of the grinding medium with respect to the inactive HAp at the start of the mechanochemical treatment is preferably 10 times by mass or more, more preferably 13 times by mass or more, even more preferably 15 times by mass or more, and preferably 30 times by mass or less, more preferably 27 times by mass or less, and even more preferably 25 times by mass or less.

[0027] Inactive HAp can be produced by a usual method of reacting calcium ions and phosphate ions in a neutral or alkaline aqueous solution (such as by a neutralization reaction, a reaction between salts, etc.). For example, an aqueous solution of calcium hydroxide and an aqueous solution of phosphoric acid are mixed, and the produced precipitate is dried, or dicalcium phosphate and calcium carbonate are mixed, dispersed in water, heated, stirred for a predetermined time, and the produced precipitate is dried. Also, the synthetic method can be changed to produce plate-like crystals, or it can be dried with a spray dryer or the like to change the shape to spherical. Also, commercially available products such as the product name "Spherical HAP", the product name "HAP-100", and the product name "HAP-200" manufactured by Taihei Chemical Industry Co., Ltd. may be used.

[0028] The atmosphere for the mechanochemical treatment is not particularly limited, and it may be carried out under an air atmosphere. The temperature may be started at about 20 to 40 °C, and it is allowed for the atmosphere temperature to rise due to heat generation during the mechanochemical treatment.

[0029] As described above, P=O / P-O The HAp of the present invention with I / I being 0.8 or more can efficiently decompose VOCs, and a method for decomposing volatile organic substances by catalytic combustion using the HAp of the present invention is also included in the present invention.

[0030] In the VOC decomposition method of the present invention, VOCs can typically be decomposed by bringing a gas containing VOCs into contact with the HAp of the present invention under an oxygen-containing atmosphere and heating conditions. The equipment for carrying out the decomposition method of the present invention can be the same as that conventionally applied to catalytic combustion methods. That is, the equipment should include a container for placing the catalyst, a means for heating the container, an inlet for the gas to be treated (VOC-containing gas), and an outlet for the treated gas, and should be configured so that the gas to be treated and the catalyst can come into contact within the container.

[0031] The shape of HAp is not particularly limited and can be in the form of powder, granules, lumps, or molded bodies formed from powdered HAp. The ratio of the gas to be treated to the catalyst, the introduction rate of the gas to be treated, etc., can be set as appropriate. Furthermore, the concentration of VOCs in the gas to be treated should be, for example, around 1 to 2000 ppm.

[0032] The heating temperature during VOC decomposition is preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 250°C or higher. The upper limit of the heating temperature is not particularly limited, but it may be 500°C or lower. Because the HAp of the present invention exhibits a high VOC decomposition rate even at lower temperatures, it is possible to lower the heating temperature. The aforementioned heating temperature may also be the maximum temperature during the VOC decomposition reaction. Note that the aforementioned heating temperature refers to the temperature of the catalyst.

[0033] Furthermore, since the HAp of the present invention initiates the decomposition reaction of VOCs at a lower temperature compared to conventional HAp, the temperature at which the decomposition of VOCs begins (the heating temperature mentioned above) is, for example, above 100°C and 200°C or less, preferably above 100°C and 180°C or less, and more preferably above 100°C and 150°C or less. The temperature at which decomposition begins means the temperature at which at least one of CO2, CO, and H2O is generated by the decomposition of VOCs. According to the decomposition method of the present invention, the conversion rate of VOCs to CO+CO2 at a heating temperature of 400°C is, for example, 75% or more, preferably 80% or more, and most preferably 100%.

[0034] VOCs are organic compounds that exist as gases in the atmosphere, for example, substances with a boiling point of 50°C to 260°C. Examples of VOCs that can be decomposed using HAp in the present invention include monoalcohols such as methyl alcohol, isopropanol, n-butanol, and isobutanol; glycols such as ethylene glycol; aliphatic hydrocarbons such as n-butane, isobutane, n-pentane, and n-hexane; aromatic hydrocarbons such as toluene, xylene, and 1,3,5-trimethylbenzene; esters such as ethyl acetate, butyl acetate, and propyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and alkyl halides such as chloromethane, dichloromethane, chloroethane, and 1,2-dichloroethane. Among these, methyl alcohol, isopropanol, n-butane, n-hexane, toluene, xylene, ethyl acetate, methyl ethyl ketone, and dichloromethane are preferred, with ethyl acetate being particularly preferred. [Examples]

[0035] The present invention will be described in more detail below with reference to examples. The present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit described below, and all such modifications are included within the technical scope of the present invention.

[0036] Example 1-1 Hydroxyapatite spherical HAP manufactured by Taihei Chemical Industry Co., Ltd. was vacuum-dried at 60°C for 24 hours in an air atmosphere to remove moisture physically adsorbed on the surface, and 4 g of HAp (inactivated HAp) was prepared by weight after drying. The above spherical HAP is a spherical HAp with a stoichiometric composition (i.e., Ca / P molar ratio is 1.67), and I P=O / I P-O The value is 0.73. 4g of HAp and 80g of 3mm diameter zirconia balls were placed in a Fritsch Japan Co., Ltd. planetary ball mill, Premium Line 7 (container size 80mL), and the mixture was left at room temperature in an air atmosphere. , YongThe planetary ball mill was operated at a rotational speed of 300 rpm and a rotational speed of 300 rpm to perform mechanochemical treatment and obtain activated HAp1.

[0037] Examples 1-2 Activated HAp2 was obtained in the same manner as in Example 1-1, except that the diameter of the zirconia ball was changed to 10 mm.

[0038] Examples 1-3 Activated HAp3 was obtained in the same manner as in Example 1-1, except that the diameter of the zirconia ball was changed to 15 mm.

[0039] The obtained activated HAp1-3 and inactive HAp were evaluated using the following method.

[0040] (1-1) X-ray photoelectron spectroscopy (XPS) measurement Using an M-probe from Surface Science Instruments, monochromatic AlKα was used as the excitation X-ray, with an X-ray output of 500W and a photoelectron escape angle of 30°. The peak intensity of the PO bond was analyzed from the O1s spectra of activated HAp1-3 and inactive HAp. P-O Peak intensity I of the P=O bond relative to (529.50±1eV) P=O The ratio of (530.50 ± 1 eV) was calculated.

[0041] (1-2) Electron spin resonance (ESR) spectroscopy Measurements were performed using a JEOL JES-FA200 under the following conditions. Microwave output: 1mW Magnetic field sweep width: 2.5 Width*10mT Sweep time: 0.1 Time constant: 0.1 Measurement time: 2 min Measurement temperature: RT / 100 / 200 / 300 / 400 Method for determining the g-value: The basic formula is g = Hf / mB (H: Planck's constant, f = frequency, m: Bohr magneton, B: magnetic field), and it is automatically calculated using JEOL's analysis software.

[0042] (1-3) X-ray diffraction (XRD) measurement Using a powder X-ray diffractometer (PXRD: Ultima IV, manufactured by Rigaku Corporation), the operating current was set to 40 mA and the voltage to 40 kV. Using CuKα rays, the peak intensities of the (002) and (300) planes of activated HAp1-3 and inactive HAp were determined, and their ratio I (300) / I (002) The result was calculated.

[0043] (1-4) Measurement of average particle size by laser diffraction Using a Shimadzu SALD-2300 laser particle size distribution analyzer, the particle size distribution of activated HAp1-3 and inactive HAp was measured by laser diffraction, and the particle size D50 equivalent to 50% cumulative percentage by volume was determined. As the sample for measurement, a dispersion was used, in which HAp was placed in water and dispersed using an ultrasonic disperser.

[0044] (1-5) Measurement of BET specific surface area The specific surface area of ​​HAp was evaluated by the BET method using a nitrogen adsorption / desorption device (BELSORP miniX, MicrotracBEL) after vacuum drying the sample at 120°C for 180 minutes.

[0045] (1-6) Observation of shape The morphology of activated HAp1-3 and inactive HAp was observed at 80x magnification using a scanning electron microscope (SEM: JCM-6000 NeoScope, JEOL Ltd.).

[0046] The results are shown in Table 1.

[0047] [Table 1]

[0048] Figure 1 shows the spectra obtained by the above-mentioned "(1-1) X-ray photoelectron spectroscopy (XPS) measurement". In Figure 1, "Raw" represents inactive HAp, while 3 mm, 10 mm, and 15 mm represent activated HAp1 to HAp3, respectively. From Figure 1, it can be seen that the relative intensity of PO has decreased.

[0049] Figure 2 shows the spectra obtained by the above-mentioned "(1-2) Electron Spin Resonance Spectrum (ESR) Measurement". Figure 2(a) is inactive HAp, Figure 2(b) is activated HAp1, Figure 2(c) is activated HAp2, and Figure 2(d) is activated HAp3. In inactive HAp, a signal of g=2.002 was observed when the temperature exceeded 200°C. Such a signal is thought to be a trap electron induced in HAp by the dehydration of hydroxyl groups on the surface, which reacts with O2 molecules adsorbed on the surface to generate superactive O2 radicals. Looking at the spectra in Figures 2(b) to (d), even at a low temperature of 200°C, peaks with higher spin density and sharper signals were detected.

[0050] Figure 3 shows the spectrum obtained from the "(1-3) X-ray diffraction (XRD) measurement" described above. In Figure 3, "Raw" represents inactive HAp, while 3 mm, 10 mm, and 15 mm represent activated HAp1 to HAp3, respectively. From Figure 3, it can be seen that the relative peak intensity of the (002) plane is reduced.

[0051] Furthermore, the morphological observations of activated HAp1-3 and inactive HAp are shown in Figure 4. Figure 4(a) is inactive HAp, Figure 4(b) is activated HAp1, Figure 4(c) is activated HAp2, and Figure 4(d) is activated HAp3. In all cases, secondary particles formed by the aggregation of primary particles were observed. In inactive HAp, the primary particles were loosely packed, whereas in activated HAp1-3, aggregates (secondary particles) in which the primary particles were tightly packed were observed.

[0052] The average particle size for inactive HAp is 5.45 μm, while the average particle size for Example 1-1 is 4.26 μm, and for Example 1-2 it is 2.70 μm, indicating a decrease in average particle size. In Example 1-3, the average particle size is 9.32 μm, suggesting particle aggregation. However, regardless of the average particle size, the activation of the HAp surface achieves the objective of the present invention, as shown in the examples described later.

[0053] Example 2 Ethyl acetate at a concentration of 100 ppm was used as the VOC source. It was mixed with air at a constant flow rate of 250 mL / min in a 1:1 volume ratio using a mass spectrometer and brought into contact with 1 g of activated HAp1-3 or inactive HAp at a temperature range of 100-400°C. The concentrations of the inorganic substances CO2 and CO among the decomposed VOCs were detected using an infrared absorption type CO2 monitor (RI-215D: Riken Keiki Co., Ltd.) and a CO monitor (UM-300: Kitagawa Industries Co., Ltd.). The VOC conversion efficiency was calculated using the following formula. Conversion efficiency (%) = (Detected CO2 and CO) / (Theoretical CO2 and CO) × 100

[0054] Figure 5 shows the results of CO2 / CO conversion of VOCs in the temperature range of 100°C to 400°C using activated HAp1-3 or inactive HAp. Figure 5(a) is inactive HAp, Figure 5(b) is activated HAp1, Figure 5(c) is activated HAp2, and Figure 5(d) is activated HAp3. Compared to inactive HAp, which exhibits catalytic activity at temperatures above 200°C, all activated HAp begin decomposing VOCs in the lower temperature range below 200°C, demonstrating a clear improvement in catalytic performance. In particular, activated HAp1 treated with 3mm balls achieved the highest conversion efficiency of 100%. Cycle testing was also performed on activated HAp1 treated with 3mm balls, and the results are shown in Figure 5(e). It can be seen that activated HAp1 treated with 3mm balls maintained a conversion efficiency of nearly 90% even in the fifth test.

[0055] Furthermore, in activated HAp obtained by mechanochemical treatment, PO4 3-In addition to the formation of surface defects or oxygen vacancies at the site, it is thought that radical generation, changes in surface basicity, and changes in VOC adsorption affinity preferably occur. It is believed that the activated HAp treated with 3mm balls had an optimal balance of these factors, which resulted in the highest VOC conversion efficiency.

Claims

1. When measured by X-ray photoelectron spectroscopy (XPS), the peak intensity of the P-O bond analyzed from the O1s spectrum is I P-O Peak intensity I of the P=O bond P=O The ratio (I P=O / I P-O A hydroxyapatite thermal catalyst characterized by having a coefficient of 0.8 or higher.

2. When the electron spin resonance spectrum was measured at 400°C in an oxygen-containing atmosphere using a standard Mn marker, the peak intensity I of the hydroxyapatite when the g value = 2.003 was measured. HAp and the peak intensity of the Mn marker I Mn Ratio to (I HAp / I Mn The hydroxyapatite according to claim 1, wherein the ratio is 0.3 or more.

3. The peak intensity I of the (002) plane measured by X-ray diffraction (002) to the peak intensity I of the (300) plane (300) ratio (I (300) / I (002) ) is 1.1 or more, the hydroxyapatite according to claim 1 or 2.

4. It has secondary particles formed by the aggregation of primary particles, The average particle size is 1 to 40 μm, and the BET specific surface area is 35 m². ２ The hydroxyapatite according to any one of claims 1 to 3, wherein the amount is less than or equal to / g.

5. The hydroxyapatite according to any one of claims 1 to 4, wherein the molar ratio of Ca to P (Ca / P) in the hydroxyapatite is 1.67 to 2.

50.

6. The hydroxyapatite according to claim 5, wherein the molar ratio of Ca to P (Ca / P) in the hydroxyapatite is 1.67 or more and less than 1.

74.

7. A method for decomposing volatile organic substances by catalytic combustion, A method for decomposing volatile organic substances, characterized by using hydroxyapatite as described in any one of claims 1 to 6 as a catalyst.

8. The decomposition method according to claim 7, wherein the heating temperature during the decomposition of the volatile organic substance is 150°C or higher.

Images