JP5756740B2 - Photocatalyst, method for producing the same, and method for treating nitrate-containing water - Google Patents
Photocatalyst, method for producing the same, and method for treating nitrate-containing water Download PDFInfo
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- JP5756740B2 JP5756740B2 JP2011263605A JP2011263605A JP5756740B2 JP 5756740 B2 JP5756740 B2 JP 5756740B2 JP 2011263605 A JP2011263605 A JP 2011263605A JP 2011263605 A JP2011263605 A JP 2011263605A JP 5756740 B2 JP5756740 B2 JP 5756740B2
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- 239000011941 photocatalyst Substances 0.000 title claims description 214
- 229910002651 NO3 Inorganic materials 0.000 title claims description 39
- 238000000034 method Methods 0.000 title claims description 37
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 title claims description 31
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims description 31
- 238000004519 manufacturing process Methods 0.000 title claims description 10
- 239000000463 material Substances 0.000 claims description 82
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 claims description 64
- -1 hydroxide ions Chemical class 0.000 claims description 39
- 239000007864 aqueous solution Substances 0.000 claims description 29
- 239000006185 dispersion Substances 0.000 claims description 28
- MMDJDBSEMBIJBB-UHFFFAOYSA-N [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] Chemical compound [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] MMDJDBSEMBIJBB-UHFFFAOYSA-N 0.000 claims description 22
- 229910021645 metal ion Inorganic materials 0.000 claims description 19
- 244000191761 Sida cordifolia Species 0.000 claims description 14
- 150000001875 compounds Chemical class 0.000 claims description 14
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 13
- 239000004202 carbamide Substances 0.000 claims description 13
- 229910052782 aluminium Inorganic materials 0.000 claims description 10
- VKYKSIONXSXAKP-UHFFFAOYSA-N hexamethylenetetramine Chemical compound C1N(C2)CN3CN1CN2C3 VKYKSIONXSXAKP-UHFFFAOYSA-N 0.000 claims description 10
- 150000001450 anions Chemical class 0.000 claims description 8
- 229910052751 metal Inorganic materials 0.000 claims description 7
- 239000002184 metal Substances 0.000 claims description 7
- 150000003839 salts Chemical class 0.000 claims description 6
- 239000004312 hexamethylene tetramine Substances 0.000 claims description 5
- 235000010299 hexamethylene tetramine Nutrition 0.000 claims description 5
- 238000000354 decomposition reaction Methods 0.000 claims description 4
- 238000000151 deposition Methods 0.000 claims description 4
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 3
- 229910002367 SrTiO Inorganic materials 0.000 claims description 3
- 229910010413 TiO 2 Inorganic materials 0.000 claims description 3
- 230000001678 irradiating effect Effects 0.000 claims description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Substances N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 64
- 238000002360 preparation method Methods 0.000 description 47
- 238000006243 chemical reaction Methods 0.000 description 45
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 33
- 229910052757 nitrogen Inorganic materials 0.000 description 32
- 230000001699 photocatalysis Effects 0.000 description 32
- 238000006722 reduction reaction Methods 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 19
- 239000000126 substance Substances 0.000 description 18
- 239000001257 hydrogen Substances 0.000 description 17
- 229910052739 hydrogen Inorganic materials 0.000 description 17
- 239000011777 magnesium Substances 0.000 description 17
- 230000000694 effects Effects 0.000 description 16
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 16
- 238000010438 heat treatment Methods 0.000 description 15
- 239000010936 titanium Substances 0.000 description 13
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 12
- 238000012986 modification Methods 0.000 description 12
- 230000004048 modification Effects 0.000 description 12
- 239000000243 solution Substances 0.000 description 11
- 238000011068 loading method Methods 0.000 description 10
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 9
- 238000001354 calcination Methods 0.000 description 9
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 9
- 229910052753 mercury Inorganic materials 0.000 description 9
- 239000001301 oxygen Substances 0.000 description 9
- 229910052760 oxygen Inorganic materials 0.000 description 9
- 239000000843 powder Substances 0.000 description 9
- 229910052749 magnesium Inorganic materials 0.000 description 8
- MFUVDXOKPBAHMC-UHFFFAOYSA-N magnesium;dinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[Mg+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MFUVDXOKPBAHMC-UHFFFAOYSA-N 0.000 description 8
- 230000009467 reduction Effects 0.000 description 8
- 239000004317 sodium nitrate Substances 0.000 description 8
- 235000010344 sodium nitrate Nutrition 0.000 description 8
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 7
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 7
- 239000003054 catalyst Substances 0.000 description 7
- 230000008569 process Effects 0.000 description 7
- DNIAPMSPPWPWGF-UHFFFAOYSA-N Propylene glycol Chemical compound CC(O)CO DNIAPMSPPWPWGF-UHFFFAOYSA-N 0.000 description 6
- AYJRCSIUFZENHW-UHFFFAOYSA-L barium carbonate Chemical compound [Ba+2].[O-]C([O-])=O AYJRCSIUFZENHW-UHFFFAOYSA-L 0.000 description 6
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 6
- 150000002431 hydrogen Chemical class 0.000 description 6
- 238000002715 modification method Methods 0.000 description 6
- 229910052759 nickel Inorganic materials 0.000 description 6
- 239000002245 particle Substances 0.000 description 6
- 239000010453 quartz Substances 0.000 description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 5
- 238000010304 firing Methods 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- KBJMLQFLOWQJNF-UHFFFAOYSA-N nickel(ii) nitrate Chemical compound [Ni+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O KBJMLQFLOWQJNF-UHFFFAOYSA-N 0.000 description 5
- 238000006116 polymerization reaction Methods 0.000 description 5
- 238000003786 synthesis reaction Methods 0.000 description 5
- XNDZQQSKSQTQQD-UHFFFAOYSA-N 3-methylcyclohex-2-en-1-ol Chemical compound CC1=CC(O)CCC1 XNDZQQSKSQTQQD-UHFFFAOYSA-N 0.000 description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 4
- 239000007795 chemical reaction product Substances 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000000634 powder X-ray diffraction Methods 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 3
- 239000004327 boric acid Substances 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 239000003673 groundwater Substances 0.000 description 3
- 230000007062 hydrolysis Effects 0.000 description 3
- 238000006460 hydrolysis reaction Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 239000004570 mortar (masonry) Substances 0.000 description 3
- 229910000480 nickel oxide Inorganic materials 0.000 description 3
- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 238000010298 pulverizing process Methods 0.000 description 3
- 238000010532 solid phase synthesis reaction Methods 0.000 description 3
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 239000000872 buffer Substances 0.000 description 2
- YHWCPXVTRSHPNY-UHFFFAOYSA-N butan-1-olate;titanium(4+) Chemical compound [Ti+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] YHWCPXVTRSHPNY-UHFFFAOYSA-N 0.000 description 2
- 239000003638 chemical reducing agent Substances 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 238000000921 elemental analysis Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 150000004679 hydroxides Chemical class 0.000 description 2
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 description 2
- GJKFIJKSBFYMQK-UHFFFAOYSA-N lanthanum(3+);trinitrate;hexahydrate Chemical compound O.O.O.O.O.O.[La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O GJKFIJKSBFYMQK-UHFFFAOYSA-N 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 239000003002 pH adjusting agent Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000012827 research and development Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 238000000967 suction filtration Methods 0.000 description 2
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 description 1
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 241000894006 Bacteria Species 0.000 description 1
- JVMRPSJZNHXORP-UHFFFAOYSA-N ON=O.ON=O.ON=O.N Chemical compound ON=O.ON=O.ON=O.N JVMRPSJZNHXORP-UHFFFAOYSA-N 0.000 description 1
- 229910002668 Pd-Cu Inorganic materials 0.000 description 1
- 230000010757 Reduction Activity Effects 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000001342 alkaline earth metals Chemical class 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 230000001580 bacterial effect Effects 0.000 description 1
- 238000010170 biological method Methods 0.000 description 1
- 230000000711 cancerogenic effect Effects 0.000 description 1
- 231100000357 carcinogen Toxicity 0.000 description 1
- 239000003183 carcinogenic agent Substances 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000000909 electrodialysis Methods 0.000 description 1
- 239000011532 electronic conductor Substances 0.000 description 1
- 238000012851 eutrophication Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000003895 groundwater pollution Methods 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 239000010842 industrial wastewater Substances 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 231100000053 low toxicity Toxicity 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 208000005135 methemoglobinemia Diseases 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- XKLJHFLUAHKGGU-UHFFFAOYSA-N nitrous amide Chemical compound ON=N XKLJHFLUAHKGGU-UHFFFAOYSA-N 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 239000006174 pH buffer Substances 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 238000011197 physicochemical method Methods 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 239000011164 primary particle Substances 0.000 description 1
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- 238000000746 purification Methods 0.000 description 1
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- 238000001223 reverse osmosis Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000000527 sonication Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 239000008399 tap water Substances 0.000 description 1
- 235000020679 tap water Nutrition 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Description
本発明は、光触媒およびその製造方法、並びに光触媒を用いた硝酸性窒素含有水の処理方法に関する。 The present invention relates to a photocatalyst, a method for producing the same, and a method for treating nitrate nitrogen-containing water using the photocatalyst.
例えば工場や農場から排出される硝酸性窒素は、湖などの富栄養化の原因になるばかりでなく、生体内でニトロソアミンのような発がん性物質になったり、メトヘモグロビン血症を引き起こしたりするなど、人体に害を及ぼすものである。また、硝酸イオンによる地下水の汚染は、１９７０年頃より世界的に深刻になり、ＷＨＯ（世界保健機関）は、窒素イオンの許容濃度を５０ｐｐｍ（理想的には２５ｐｐｍ）に定めている。また、平成１１年に日本国内で定められた水道水中の硝酸態窒素および亜硝酸態窒素の水質基準値は、１０ｐｐｍ以下であるが、すべての環境基準項目の中で、未だに最も高い環境基準超過率を示しているのが現状である（非特許文献１参照。）。 For example, nitrate nitrogen discharged from factories and farms not only causes eutrophication of lakes and the like, but also becomes a carcinogen such as nitrosamine in the body and causes methemoglobinemia. , Harm the human body. In addition, the contamination of groundwater by nitrate ions has become serious worldwide since around 1970, and the WHO (World Health Organization) sets the allowable concentration of nitrogen ions to 50 ppm (ideally 25 ppm). Moreover, the water quality standard value of nitrate nitrogen and nitrite nitrogen in tap water established in Japan in 1999 is 10 ppm or less, but it still exceeds the highest environmental standard among all environmental standard items. The current rate shows the rate (see Non-Patent Document 1).
地下水へ流れ込む硝酸性窒素を除去する方法としては、従来、イオン交換法、電気透析法、逆浸透膜法、触媒などによる物理化学的方法や、細菌を用いて還元する生物学的方法について実用化の検討が行われている。
しかしながら、これらの方法によって硝酸性窒素を除去する場合には、高濃度硝酸イオンの二次処理の問題や細菌の維持管理の問題など、多くの課題が残されている。
一方、近年、Ｐｄ−Ｃｕ担持触媒などの熱触媒の研究開発が進み、その耐久性向上のための検討が行われている（特許文献１および特許文献２参照。）。また、層状複水酸化物（ＬＤＨ）を用いた触媒も開発されており、層間に白金、パラジウム、ロジウム、ルテニウムなどの貴金属をインターカレートした多孔性複合体が、１００℃以下で窒素酸化物を還元することが見だされている（特許文献３参照）。
しかしながら、これらの固体触媒反応を用いるプロセスでは、還元剤として水素ガスを用いることが必要であるため、水素を製造するために多大なエネルギーが必要となる。
Conventional methods for removing nitrate nitrogen flowing into groundwater include ion exchange, electrodialysis, reverse osmosis membranes, physicochemical methods using catalysts, and biological methods for reduction using bacteria. Is being studied.
However, when nitrate nitrogen is removed by these methods, many problems remain, such as the problem of secondary treatment of high concentration nitrate ions and the problem of bacterial maintenance.
On the other hand, in recent years, research and development of thermal catalysts such as Pd—Cu supported catalysts have progressed, and studies for improving their durability have been conducted (see
However, in processes using these solid catalytic reactions, it is necessary to use hydrogen gas as a reducing agent, and thus a great deal of energy is required to produce hydrogen.
そこで、本発明者らは、水素製造用光触媒の研究開発を重ねた結果、水を全分解することができる高活性なＮａＴａＯ3 や、層状ペロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15などの紫外光応答型酸化物光触媒が、硝酸イオンの還元反応にも高活性であることを見いだした。この紫外光応答型酸化物光触媒は、紫外光をエネルギー源、水を還元剤として、硝酸イオンを無害な窒素にまで還元することができるため、地下水あるいは工業廃水の硝酸性窒素の浄化への応用が期待される。そして、これらの光触媒の高活性化の検討を行った結果、ニッケルを助触媒として含浸法で担持した場合に、最も助触媒の効果が高いことが確認された。また、ｐＨ調整剤としてホウ酸を添加することにより、高効率化が可能であることが確認された（非特許文献２、非特許文献３および特許文献４参照。）。
しかしながら、これらの触媒調製法の最適化は、３〜１０ｍｍｏｌ／Ｌまでの硝酸イオン濃度（２５５〜８５０ｐｐｍに相当）でしか行われておらず、実用化を目的とするためには、より高濃度の硝酸イオン溶液で最適化を行う必要がある。
Therefore, as a result of repeated research and development of a photocatalyst for hydrogen production, the present inventors have developed an ultraviolet light responsive type such as highly active NaTaO 3 capable of completely decomposing water and a layered perovskite compound BaLa 4 Ti 4 O 15. The oxide photocatalyst was found to be highly active in the reduction reaction of nitrate ions. This ultraviolet light-responsive oxide photocatalyst can reduce nitrate ions to harmless nitrogen using ultraviolet light as an energy source and water as a reducing agent, so it can be applied to the purification of nitrate nitrogen in groundwater or industrial wastewater. There is expected. As a result of studying high activation of these photocatalysts, it was confirmed that the cocatalyst was most effective when it was supported by the impregnation method using nickel as the cocatalyst. Moreover, it was confirmed that high efficiency can be achieved by adding boric acid as a pH adjuster (see Non-Patent Document 2,
However, optimization of these catalyst preparation methods has been carried out only at nitrate ion concentrations up to 3 to 10 mmol / L (corresponding to 255 to 850 ppm), and for the purpose of practical use, higher concentrations are required. It is necessary to perform optimization with a nitrate ion solution.
ところで、光触媒による硝酸イオンの還元反応は、水の還元反応と競争的に反応が進行することがわかっているが、Ｌａやアルカリ土類金属をドーピングしたＮａＴａＯ3 光触媒は非常に高い水分解活性を示すが、そのメカニズムとして、表面のナノステップ構造が、酸化反応サイトと還元反応サイトを分離した有効な反応場をつくり、この水分解反応を促進すると考えられる（非特許文献４および非特許文献５参照。）。また、ＬａドープＮａＴａＯ3 光触媒に担持された酸化ニッケルは、Ｌａ未ドープの試料と比べて分散性が著しく高く（非特許文献６参照。）、光触媒の表面状態が助触媒に与える影響は大きいと考えられる。
すなわち、Ｎｉ助触媒上に吸着した活性水素が効率的に使われているこのような状態は、同時に進行する硝酸イオンの還元にも有利であると考えられる。つまり、ナノステップ構造のような表面状態が硝酸イオンの還元活性に寄与するとすれば、光触媒そのものの性能を保持したまま、何らかの方法で表面の形状あるいは化学的性質を変化させることにより、還元サイトと酸化サイトとを分離し、光触媒の性能を向上させることができると考えられる。
By the way, it is known that the reduction reaction of nitrate ions by the photocatalyst proceeds competitively with the reduction reaction of water, but the NaTaO 3 photocatalyst doped with La or alkaline earth metal has a very high water splitting activity. As shown, the nanostep structure on the surface creates an effective reaction field in which the oxidation reaction site and the reduction reaction site are separated, and this water splitting reaction is promoted (Non-Patent
That is, it is considered that such a state in which active hydrogen adsorbed on the Ni promoter is used efficiently is advantageous for the reduction of nitrate ions that proceed simultaneously. In other words, if a surface state such as a nanostep structure contributes to the reduction activity of nitrate ions, the surface shape or chemical properties can be changed by some method while maintaining the performance of the photocatalyst itself. It is considered that the performance of the photocatalyst can be improved by separating the oxidation site.
本発明は、以上のような事情に基づいてなされたものであって、その目的は、優れた硝酸イオンの還元反応に対する活性を有し、高濃度の硝酸性窒素を含有する水溶液中において、硝酸イオンを高い効率で還元することができる新規な光触媒およびその製造方法並び硝酸性窒素含有水の処理方法を提供することである。 The present invention has been made on the basis of the circumstances as described above, and the object thereof is to provide nitric acid in an aqueous solution having excellent nitrate ion reduction reaction and containing a high concentration of nitrate nitrogen. To provide a novel photocatalyst capable of reducing ions with high efficiency, a method for producing the photocatalyst, and a method for treating nitrate-containing water.
本発明の光触媒は、層状ペロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15、ＳｒＴｉＯ3 、ＮａＴａＯ3 またはＴｉＯ2 よりなる紫外光応答型酸化物光触媒材料の表面に、下記一般式（１）で表される層状複水酸化物が部分的に修飾された構造を有することを特徴とする。 The photocatalyst of the present invention comprises a layered perovskite compound BaLa 4 Ti 4 O 15 , SrTiO 3 , NaTaO 3 or TiO 2 on the surface of an ultraviolet photoresponsive oxide photocatalytic material represented by the following general formula (1). The hydroxide is characterized by having a partially modified structure.
〔一般式（１）において、Ｍ2+は、Ｍｇ 2+ よりなる２価の金属イオン、Ｍ3+は、Ａｌ 3+ よりなる３価の金属イオン、Ａn-は、硝酸イオン、炭酸イオンおよび水酸化物イオンから選ばれた少なくとも一種の陰イオンを示し、ｎは陰イオンの価数、ｘは０以上で１未満の値、ｙは０以上の値である。〕
In [Formula (1), M 2+ is a divalent metal ion consisting Mg 2+, M 3+ is a trivalent metal ions consisting of Al 3+, A n-is, nitrate ion, carbonate ion And at least one anion selected from hydroxide ions, n is the valence of the anion, x is 0 or more and less than 1, and y is 0 or more. ]
本発明の光触媒においては、前記層状複水酸化物は、前記一般式（１）においてｘが０〜０．３３のものであることが好ましい。
また、前記紫外光応答型酸化物光触媒材料の表面にＮｉ助触媒が担持されていることが好ましい。
また、本発明の光触媒は、硝酸イオンを含有する水溶液中において、紫外光照射により硝酸イオンを還元するものであってもよい。
また、本発明の光触媒は、水中において、紫外光照射により水の全分解反応をするものであってもよい。
In the photocatalyst of the present invention, the layered double hydroxide is preferably one in which x is 0 to 0.33 in the general formula (1).
Further, it is preferable that a Ni promoter is supported on the surface of the ultraviolet light responsive oxide photocatalyst material.
The photocatalyst of the present invention may be one that reduces nitrate ions by irradiation with ultraviolet light in an aqueous solution containing nitrate ions.
In addition, the photocatalyst of the present invention may undergo a total decomposition reaction of water by irradiation with ultraviolet light in water.
本発明の光触媒の製造方法は、上記の紫外光応答型酸化物光触媒材料を、尿素またはヘキサメチレンテトラミンと所定の金属塩とを含む水溶液に分散し、得られた分散液を加熱して加水分解処理することにより、前記紫外光応答型酸化物光触媒材料の表面に、上記一般式（１）で表される層状複水酸化物を析出させる工程を有することを特徴とする。 The method for producing a photocatalyst according to the present invention comprises dispersing the ultraviolet light-responsive oxide photocatalyst material in an aqueous solution containing urea or hexamethylenetetramine and a predetermined metal salt, and heating the resulting dispersion to hydrolyze it. It has the process of depositing the layered double hydroxide represented by the general formula (1) on the surface of the ultraviolet light responsive oxide photocatalyst material by the treatment.
本発明の硝酸性窒素含有水の処理方法は、硝酸イオンを含有する水溶液中において、上記の光触媒に紫外光を照射することにより、当該硝酸イオンを還元することを特徴とする。 The method for treating nitrate-nitrogen-containing water of the present invention is characterized in that nitrate ions are reduced by irradiating the photocatalyst with ultraviolet light in an aqueous solution containing nitrate ions.
本発明の光触媒によれば、特定の紫外光応答型酸化物光触媒材料の表面に上記一般式（１）で表される層状複水酸化物が部分的に修飾されているため、優れた硝酸イオンの還元反応に対する活性が得られ、高濃度の硝酸性窒素を含有する水溶液中において、硝酸イオンを高い効率で還元することができる。
本発明の光触媒の製造方法によれば、優れた硝酸イオンの還元反応に対する活性を有し、高濃度の硝酸性窒素を含有する水溶液中において、硝酸イオンを高い効率で還元することができる光触媒を製造することができる。
本発明の硝酸性窒素含有水の処理方法によれば、高濃度の硝酸性窒素を含有する水溶液について、硝酸イオンを高い効率で還元することができる。
According to the photocatalyst of the present invention, the layered double hydroxide represented by the above general formula (1) is partially modified on the surface of a specific ultraviolet light-responsive oxide photocatalyst material, so that excellent nitrate ions Activity in the reduction reaction, and nitrate ions can be reduced with high efficiency in an aqueous solution containing a high concentration of nitrate nitrogen.
According to the method for producing a photocatalyst of the present invention, a photocatalyst having excellent activity for reduction reaction of nitrate ions and capable of reducing nitrate ions with high efficiency in an aqueous solution containing a high concentration of nitrate nitrogen. Can be manufactured.
According to the method for treating nitrate nitrogen-containing water of the present invention, nitrate ions can be reduced with high efficiency in an aqueous solution containing a high concentration of nitrate nitrogen.
以下、本発明の実施の形態について説明する。
［光触媒］
本発明の光触媒は、紫外光応答型酸化物光触媒材料（以下、単に「光触媒材料」ともいう。）の表面に、上記一般式（１）で表される層状複水酸化物（以下、「特定の層状複水酸化物」という。）が部分的に修飾された構造を有するものである。
Embodiments of the present invention will be described below.
[photocatalyst]
The photocatalyst of the present invention has a layered double hydroxide represented by the above general formula (1) (hereinafter referred to as “specific”) on the surface of an ultraviolet light responsive oxide photocatalyst material (hereinafter also simply referred to as “photocatalytic material”). Is a layered double hydroxide ") having a partially modified structure.
本発明において、光触媒材料としては、層状ペロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15、ＳｒＴｉＯ3 、ＮａＴａＯ3 またはＴｉＯ2 よりなるものが用いられ、これらの中では、層状ペロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15、が好ましい。
層状ペロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15の合成法は、特に限定されず、固相法あるいは錯体重合法を用いることができるが、高い活性を有する光触媒材料が得られる点で、錯体重合法が好ましい。錯体重合法による具体的な合成法としては、特開２００９−２１４０３３号公報に記載の方法を利用することができる。
In the present invention, as the photocatalyst material, a layered perovskite compound BaLa 4 Ti 4 O 15 , SrTiO 3 , NaTaO 3 or TiO 2 is used, and among these, the layered perovskite compound BaLa 4 Ti 4 O 15 is used. preferable.
The method for synthesizing the layered perovskite compound BaLa 4 Ti 4 O 15 is not particularly limited, and a solid phase method or a complex polymerization method can be used, but a complex polymerization method is preferable in that a photocatalytic material having high activity can be obtained. . As a specific synthesis method by the complex polymerization method, a method described in JP2009-214033A can be used.
特定の層状複水酸化物の組成を示す一般式（１）において、Ｍ2+は、Ｚｎ2+、Ｍｎ2+、Ｎｉ2+、Ｃｏ2+、Ｆｅ2+、Ｃｕ2+、Ｃａ2+およびＭｇ2+から選ばれた少なくとも一種の２価の金属イオン（以下、「特定の２価の金属イオン」という。）である。これらの特定の２価の金属イオンは、単独でまたは２種以上組み合わせて用いることができるが、これらの特定の２価の金属イオンの中では、Ｍｇ2+、Ｚｎ2+、Ｎｉ2+、Ｆｅ2+が好ましい。
また、一般式（１）において、Ｍ3+は、Ａｌ3+、Ｃｒ3+、Ｆｅ3+、Ｃｏ3+、Ｃｅ3+およびＧａ3+から選ばれた少なくとも一種の３価の金属イオン（以下、「特定の３価の金属イオン」という。）である。これらの特定の３価の金属イオンは、単独でまたは２種以上組み合わせて用いることができるが、これらの特定の３価の金属イオンの中では、Ａｌ3+、Ｆｅ3+が好ましい。
また、特定の２価の金属イオンおよび特定の３価の金属イオンの組み合わせとしては、Ｍｇ2+およびＡｌ3+の組み合わせ、Ｚｎ2+およびＡｌ3+の組み合わせが、毒性が小さく、安定性が高く、製造コストが低く、紫外光吸収性が低い特定の層状複水酸化物が得られる点で好ましい。
In the general formula (1) showing the composition of a specific layered double hydroxide, M 2+ is Zn 2+ , Mn 2+ , Ni 2+ , Co 2+ , Fe 2+ , Cu 2+ , Ca 2+. And at least one divalent metal ion selected from Mg 2+ (hereinafter referred to as “specific divalent metal ion”). These specific divalent metal ions can be used alone or in combination of two or more thereof. Among these specific divalent metal ions, Mg 2+ , Zn 2+ , Ni 2+ , Fe 2+ is preferred.
In the general formula (1), M 3+ represents at least one trivalent metal ion selected from Al 3+ , Cr 3+ , Fe 3+ , Co 3+ , Ce 3+ and Ga 3+ ( Hereinafter, it is referred to as “specific trivalent metal ion”. These specific trivalent metal ions can be used singly or in combination of two or more. Among these specific trivalent metal ions, Al 3+ and Fe 3+ are preferable.
As combinations of specific divalent metal ions and specific trivalent metal ions, a combination of Mg 2+ and Al 3+ and a combination of Zn 2+ and Al 3+ have low toxicity and stability. It is preferable in that a specific layered double hydroxide is obtained that is high, has a low production cost, and has a low ultraviolet light absorbability.
また、一般式（１）において、Ａn-は、硝酸イオン，炭酸イオンおよび水酸化物から選ばれた少なくとも一種の陰イオン、ｎは陰イオンの価数であり、これらの陰イオンは、単独でまたは組み合わせて用いることができる。
また、一般式（１）において、ｘは、０以上で１未満の値であるが、好ましくは０〜０．４４、より好ましくは０〜０．３３であり、特にこのｘの値が大きいほど、層状複水酸化物の陰イオン吸着能が増すため、高い活性が得られる。
また、ｙは０以上の値である。
In the general formula (1), A n− is at least one anion selected from nitrate ion, carbonate ion and hydroxide, n is the valence of the anion, and these anions are each independently Or in combination.
Further, in the general formula (1), x is a value of 0 or more and less than 1, preferably 0 to 0.44, more preferably 0 to 0.33. Since the anion adsorption ability of the layered double hydroxide is increased, high activity can be obtained.
Y is a value of 0 or more.
本発明の光触媒における特定の層状複水酸化物の割合は、１〜３０質量％であることが好ましく、より好ましくは５〜１０質量％である。この割合が過小である場合には、活性点の量が少なくなり、硝酸イオンの吸着能も低下する。一方、この割合が過大である場合には、光触媒の表面を覆うため、光触媒による酸化還元反応が起こり難く、活性が低下する。 The ratio of the specific layered double hydroxide in the photocatalyst of the present invention is preferably 1 to 30% by mass, more preferably 5 to 10% by mass. When this ratio is too small, the amount of active sites decreases, and the adsorption ability of nitrate ions also decreases. On the other hand, when this ratio is excessive, the surface of the photocatalyst is covered, so that the redox reaction by the photocatalyst hardly occurs and the activity is reduced.
光触媒材料の表面を特定の層状複水酸化物によって修飾する方法としては、尿素またはヘキサメチレンテトラミンによる均一沈殿法を利用することができる。
具体的には、尿素またはヘキサメチレンテトラミンと、特定の２価の金属イオンおよび／または特定の３価の金属イオンによる金属塩とが溶解された水溶液中に、光触媒材料を分散することにより、分散液を調製し、得られた分散液を加熱して加水分解処理することにより、光触媒材料の表面に特定の層状複水酸化物を析出させることにより、光触媒材料の表面が特定の層状複水酸化物によって修飾される。
このような尿素またはヘキサメチレンテトラミンによる均一沈殿法を利用することにより、粒度分布が狭く、結晶子がそれぞれ分離したプレート状の結晶を有する特定の層状複水酸化物が得られるため、特定の層状複水酸化物の有効表面積の高い表面修飾が可能になる。また、光触媒材料の結晶粒子の隙間にも特定の層状複水酸化物が析出し、当該特定の層状複水酸化物が光触媒材料の表面に強固に固着されるため、優れた耐久性が得られる。また、中性の水溶液中において、光触媒材料の表面は負に帯電しているのに対して、特定の層状複水酸化物の表面は正に帯電していることから、特定の層状複水酸化物の安定性を高める要因となると考えられる。
但し、この方法では、加水分解前の溶液が酸性であるため、使用前に光触媒材料がその溶液中で安定に分散することを予め確かめることが好ましい。
As a method for modifying the surface of the photocatalytic material with a specific layered double hydroxide, a uniform precipitation method using urea or hexamethylenetetramine can be used.
Specifically, the photocatalytic material is dispersed in an aqueous solution in which urea or hexamethylenetetramine and a specific divalent metal ion and / or a metal salt of the specific trivalent metal ion are dissolved. The surface of the photocatalyst material is made to have a specific layered double hydroxide by precipitating a specific layered double hydroxide on the surface of the photocatalytic material by preparing a liquid and subjecting the obtained dispersion to a hydrolysis treatment. It is modified by things.
By utilizing such a uniform precipitation method with urea or hexamethylenetetramine, a specific layered double hydroxide having a narrow particle size distribution and plate-like crystals with separated crystallites can be obtained. Surface modification with a high effective surface area of the double hydroxide becomes possible. In addition, the specific layered double hydroxide precipitates in the gaps between the crystal particles of the photocatalytic material, and the specific layered double hydroxide is firmly fixed to the surface of the photocatalytic material, so that excellent durability is obtained. . In addition, in the neutral aqueous solution, the surface of the photocatalyst material is negatively charged, whereas the surface of the specific layered double hydroxide is positively charged. It is thought to be a factor that increases the stability of things.
However, in this method, since the solution before hydrolysis is acidic, it is preferable to confirm beforehand that the photocatalytic material is stably dispersed in the solution before use.
以上において、金属塩の使用量は、光触媒材料１ｇに対して金属イオン成分（特定の２価の金属イオンおよび特定の３価の金属イオンの和）が０．５〜５ｍｍｏｌとなる量であることが好ましい。金属塩の使用量が過小である場合には、析出する特定の層状複水酸化物の量が減少し、十分な活性点が構築することができない。一方、金属塩の使用量の過大である場合には、特定の層状複水酸化物が多量に析出し、光触媒の表面を覆い尽くすため、光触媒活性が消失する。
また、尿素またはテトラメチレンテトラミンの使用量は、光触媒材料１ｇに対して１００〜５００ｍｍｏｌであることが好ましく、テトラメチレンテトラミンを用いる場合には、５０〜２５０ｍｍｏｌであることがより好ましい。尿素またはテトラメチレンテトラミンの使用量が過小である場合には、ｐＨが低すぎるため析出が起こらない。一方、尿素の使用量が過大である場合には、ｐＨの上昇速度を上げることができるが、合成操作上、扱いが難しくなる。
また、加水分解処理における処理温度は、例えば９０〜１００℃であり、処理時間は、例えば２〜２０時間である。
In the above, the amount of the metal salt used is such that the metal ion component (the sum of the specific divalent metal ion and the specific trivalent metal ion) is 0.5 to 5 mmol with respect to 1 g of the photocatalytic material. Is preferred. When the amount of the metal salt used is too small, the amount of the specific layered double hydroxide precipitated is reduced, and a sufficient active point cannot be established. On the other hand, when the amount of the metal salt used is excessive, the specific layered double hydroxide precipitates in a large amount and covers the surface of the photocatalyst, so that the photocatalytic activity is lost.
Moreover, it is preferable that the usage-amount of urea or tetramethylenetetramine is 100-500 mmol with respect to 1 g of photocatalyst materials, and when tetramethylenetetramine is used, it is more preferable that it is 50-250 mmol. When the amount of urea or tetramethylenetetramine used is too small, precipitation does not occur because the pH is too low. On the other hand, when the amount of urea used is excessive, the rate of increase in pH can be increased, but handling becomes difficult in the synthesis operation.
Moreover, the processing temperature in a hydrolysis process is 90-100 degreeC, for example, and processing time is 2 to 20 hours, for example.
また、上記の方法は、特定の層状複水酸化物を光触媒材料の表面に直接析出させることにより、当該光触媒材料の表面を特定の層状複水酸化物によって修飾する方法であるが、水溶液中において特定の層状複水酸化物を予め核析出させた後、当該特定の層状複水酸化物を光触媒材料の表面に修飾することも可能である。但し、特定の層状複水酸化物を光触媒材料の表面に直接析出させる方法が、高い活性を有する光触媒が得られるため好ましい。 In addition, the above method is a method in which a specific layered double hydroxide is directly deposited on the surface of the photocatalyst material to modify the surface of the photocatalyst material with the specific layered double hydroxide. It is also possible to nucleate a specific layered double hydroxide in advance and then modify the specific layered double hydroxide on the surface of the photocatalytic material. However, a method of directly depositing a specific layered double hydroxide on the surface of the photocatalyst material is preferable because a photocatalyst having high activity can be obtained.
本発明の光触媒においては、光触媒材料の表面にＮｉ助触媒が担持されていることが好ましい。
本発明の光触媒におけるＮｉ助触媒の担持量は、０．２〜３質量％、特に０．５〜３質量％であることが好ましい。Ｎｉ助触媒の担持量が過小である場合には、十分な光触媒上の還元サイトが得られない。一方、Ｎｉ助触媒の担持量が過大である場合には、焼成時にシンタリングが起こるために粒径が増し、Ｎｉ助触媒の分散性を低下させる。また、高濃度のＮｉ助触媒により光触媒に当たる光が遮蔽され、光触媒活性が低下する。
In the photocatalyst of the present invention, a Ni promoter is preferably supported on the surface of the photocatalytic material.
The supported amount of Ni promoter in the photocatalyst of the present invention is preferably 0.2 to 3% by mass, particularly 0.5 to 3% by mass. When the supported amount of Ni promoter is too small, sufficient reduction sites on the photocatalyst cannot be obtained. On the other hand, when the supported amount of Ni promoter is excessive, sintering occurs during firing, resulting in an increase in particle size and a decrease in dispersibility of the Ni promoter. In addition, light hitting the photocatalyst is shielded by the high concentration Ni promoter, and the photocatalytic activity is reduced.
光触媒材料の表面にＮｉ助触媒を担持する方法としては、光触媒材料に、所定の量のニッケルを含有する硝酸ニッケル水溶液を添加して焼成処理した後、水素雰囲気下において加熱することによって還元処理する方法を利用することができる。
以上において、焼成処理の条件としては、例えば焼成温度が２７０〜５００℃、焼成時間が１〜５時間である。
また、還元処理の条件としては、例えば処理温度が３００〜５００℃、処理時間が１〜３時間である。
As a method for supporting the Ni promoter on the surface of the photocatalyst material, a nickel nitrate aqueous solution containing a predetermined amount of nickel is added to the photocatalyst material, followed by firing treatment, followed by heating in a hydrogen atmosphere for reduction treatment. The method can be used.
In the above, as conditions for the baking treatment, for example, the baking temperature is 270 to 500 ° C., and the baking time is 1 to 5 hours.
Moreover, as conditions for the reduction treatment, for example, the treatment temperature is 300 to 500 ° C., and the treatment time is 1 to 3 hours.
本発明の光触媒によれば、光触媒材料の表面に特定の層状複水酸化物が部分的に修飾されているため、優れた硝酸イオンの還元反応に対する活性が得られ、高濃度の硝酸性窒素を含有する水溶液中において、硝酸イオンを高い効率で還元することができる。 According to the photocatalyst of the present invention, the specific layered double hydroxide is partially modified on the surface of the photocatalyst material, so that an excellent activity for reduction reaction of nitrate ions is obtained, and high concentration of nitrate nitrogen is obtained. In the aqueous solution to be contained, nitrate ions can be reduced with high efficiency.
［硝酸性窒素含有水の処理方法］
本発明の硝酸性窒素含有水の処理方法においては、硝酸イオンを含有する水溶液中において、上記の光触媒に紫外線を照射することにより、当該硝酸イオンを還元する。
以上において、処理対象である硝酸性窒素含有水としては、濃度が１００ｍｍｏｌ／Ｌ以下、特に５０ｍｍｏｌ／Ｌ以下の硝酸イオンを含有する水溶液であることが好ましい。 また、処理対象である硝酸性窒素含有水は、緩衝剤（ｐＨ調整剤）によって、ｐＨが６〜１０、特に６〜９に調整されることが好ましい。緩衝剤としては、ホウ酸、リン酸、酢酸などを用いることができる。
また、紫外光光源としては、高圧水銀灯などを用いることができる。
また、硝酸性窒素含有水に対する光触媒の量は、例えば１〜３０ｇ／Ｌであり、硝酸性窒素含有水の処理時間は、例えば２〜４８時間である。
[Method of treating nitrate-containing water]
In the method for treating nitrate nitrogen-containing water of the present invention, the nitrate ions are reduced by irradiating the photocatalyst with ultraviolet rays in an aqueous solution containing nitrate ions.
In the above, the nitrate nitrogen-containing water to be treated is preferably an aqueous solution containing nitrate ions having a concentration of 100 mmol / L or less, particularly 50 mmol / L or less. Moreover, it is preferable that nitrate nitrogen containing water which is a process target is adjusted to pH 6-10, especially 6-9 by a buffer (pH adjuster). As the buffer, boric acid, phosphoric acid, acetic acid and the like can be used.
Moreover, a high pressure mercury lamp etc. can be used as an ultraviolet light source.
Moreover, the quantity of the photocatalyst with respect to nitrate nitrogen containing water is 1-30 g / L, for example, and the processing time of nitrate nitrogen containing water is 2 to 48 hours, for example.
本発明の硝酸性窒素含有水の処理方法によれば、上記の光触媒を用いるため、高濃度の硝酸性窒素を含有する水溶液について、硝酸イオンを高い効率で還元することができる。 According to the method for treating nitrate nitrogen-containing water of the present invention, since the above photocatalyst is used, nitrate ions can be reduced with high efficiency in an aqueous solution containing a high concentration of nitrate nitrogen.
以下、本発明の具体的な実施例について説明するが、本発明はこれらの実施例に限定されるものではない。 Specific examples of the present invention will be described below, but the present invention is not limited to these examples.
〈光触媒材料の合成〉
［合成例１］
以下のようにして、層状ベロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15を錯体重合法により合成した。
炭酸バリウム（関東化学社製；純度９９．０％）０．８７８ｇと、チタン酸テトラブチル（関東化学社製；純度９７．０％）６．０５３ｇと、硝酸ランタン６水塩（和光純薬社製；純度９９．９％）７．７０２ｇと、錯化剤としてのプロピレングリコール（関東化学社製；純度９９．０％）６０．９ｇおよびクエン酸（Ｓｉｇｍａ−Ａｌｄｒｉｃｈ社製；純度９９．５％）３８．４４ｇと、溶剤としてのエタノール（関東化学社製；純度９９．５％）３０ｍｌとを、温度が８０℃の条件下において混合することにより、すべての原料を溶剤に溶解させた後、温度が１２０℃の条件下で３時間かけて反応させた。得られた反応生成物をマントルヒーターにより、４００℃に加熱することによって有機物を分解除去することにより、白色物質を得た。この白色物質を、電気炉により、加熱温度が１１００℃、加熱時間が１０時間の条件で焼成処理することにより、白色粉末４．９ｇを得た。
得られた白色粉末は、Ｘ線回折装置「ＭｉｎｉＦｌｅｘ」（Ｒｉｇａｋｕ社製）を用いた粉末Ｘ線回折により、組成式がＢａＬａ4 Ｔｉ4 Ｏ15である層状ベロブスカイト化合物であると同定された。以下、この白色粉末を「光触媒材料（ａ）」とする。
この光触媒材料（ａ）の紫外−可視−近赤外拡散反射スペクトル（ＤＲＳ）を、紫外可視赤外分光光度計「ＵｂｅｓｔＶ−５７０」（Ｊａｓｃｏ社製）を用いて測定したところ、得られた拡散反射スペクトルから、光触媒材料（ａ）は紫外吸収能を有することが確認された。
<Synthesis of photocatalytic materials>
[Synthesis Example 1]
A layered velovskite compound BaLa 4 Ti 4 O 15 was synthesized by a complex polymerization method as follows.
Barium carbonate (manufactured by Kanto Chemical Co., Inc .; purity 99.0%) 0.878 g, tetrabutyl titanate (manufactured by Kanto Chemical Co., Ltd .; purity 97.0%) 6.053 g, lanthanum nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) Purity of 99.9%) 7.702 g, propylene glycol (manufactured by Kanto Chemical Co .; purity 99.0%) 60.9 g and citric acid (Sigma-Aldrich; purity 99.5%) 38.44 g and 30 ml of ethanol (manufactured by Kanto Chemical Co., Inc .; purity: 99.5%) as a solvent were mixed at a temperature of 80 ° C. to dissolve all raw materials in the solvent. Was allowed to react at 120 ° C. over 3 hours. The obtained reaction product was heated to 400 ° C. with a mantle heater to decompose and remove organic substances, thereby obtaining a white substance. This white material was baked in an electric furnace under the conditions of a heating temperature of 1100 ° C. and a heating time of 10 hours, to obtain 4.9 g of white powder.
The obtained white powder was identified as a layered velovskite compound having a composition formula of BaLa 4 Ti 4 O 15 by powder X-ray diffraction using an X-ray diffractometer “MiniFlex” (manufactured by Rigaku). Hereinafter, this white powder is referred to as “photocatalytic material (a)”.
When the ultraviolet-visible-near infrared diffuse reflection spectrum (DRS) of this photocatalyst material (a) was measured using an ultraviolet-visible infrared spectrophotometer “UbestV-570” (manufactured by Jasco), the obtained diffusion From the reflection spectrum, it was confirmed that the photocatalytic material (a) has an ultraviolet absorbing ability.
［合成例２］
以下のようにして、層状ベロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15を錯体重合法により合成した。
炭酸バリウム（関東化学社製；純度９９．０％）０．８７８ｇと、チタン酸テトラブチル（関東化学社製；純度９７．０％）６．０５３ｇと、硝酸ランタン６水塩（和光純薬社製；純度９９．９％）７．７０２ｇと、錯化剤としてのプロピレングリコール（関東化学社製；純度９９．０％）６０．９ｇおよびクエン酸（Ｓｉｇｍａ−Ａｌｄｒｉｃｈ社製；純度９９．５％）３８．４４ｇと、溶剤としてのエタノール（関東化学社製；純度９９．５％）３０ｍｌとを、温度が８０℃の条件下において混合することにより、すべての原料を溶剤に溶解させた後、温度が１２０℃の条件下で３時間かけて反応させた。得られた反応生成物をマントルヒーターにより、４００℃に加熱することによって有機物を分解除去することにより、白色物質を得た。この白色物質を、電気炉により、温度が５００℃、加熱時間が１時間の条件で仮焼成処理した後、アルミニウム乳鉢中で３０分間粉砕処理し、更に、加熱温度が１１００℃、加熱時間が１０時間の条件で焼成処理することにより、白色粉末を得た。
得られた白色粉末は、Ｘ線回折装置「ＭｉｎｉＦｌｅｘ」（Ｒｉｇａｋｕ社製）を用いた粉末Ｘ線回折により、組成式がＢａＬａ4 Ｔｉ4 Ｏ15である層状ベロブスカイト化合物であると同定された。以下、この白色粉末を「光触媒材料（ｂ）」とする。
また、光触媒材料（ｂ）をＳＥＭ像で観察したところ、粉砕処理を行ったことにより、光触媒材料（ａ）に比較して、一次粒子が著しく凝集し、光触媒材料の表面は削れて結晶面が見えにくい状態のものであった。
[Synthesis Example 2]
A layered velovskite compound BaLa 4 Ti 4 O 15 was synthesized by a complex polymerization method as follows.
Barium carbonate (manufactured by Kanto Chemical Co., Inc .; purity 99.0%) 0.878 g, tetrabutyl titanate (manufactured by Kanto Chemical Co., Ltd .; purity 97.0%) 6.053 g, lanthanum nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) Purity of 99.9%) 7.702 g, propylene glycol (manufactured by Kanto Chemical Co .; purity 99.0%) 60.9 g and citric acid (Sigma-Aldrich; purity 99.5%) 38.44 g and 30 ml of ethanol (manufactured by Kanto Chemical Co., Inc .; purity: 99.5%) as a solvent were mixed at a temperature of 80 ° C. to dissolve all raw materials in the solvent. Was allowed to react at 120 ° C. over 3 hours. The obtained reaction product was heated to 400 ° C. with a mantle heater to decompose and remove organic substances, thereby obtaining a white substance. The white material was calcined in an electric furnace under the conditions of a temperature of 500 ° C. and a heating time of 1 hour, and then pulverized in an aluminum mortar for 30 minutes. Further, the heating temperature was 1100 ° C. and the heating time was 10 A white powder was obtained by baking under time conditions.
The obtained white powder was identified as a layered velovskite compound having a composition formula of BaLa 4 Ti 4 O 15 by powder X-ray diffraction using an X-ray diffractometer “MiniFlex” (manufactured by Rigaku). Hereinafter, this white powder is referred to as “photocatalytic material (b)”.
In addition, when the photocatalyst material (b) was observed with an SEM image, the primary particles were significantly aggregated compared to the photocatalyst material (a) due to the pulverization treatment, and the surface of the photocatalyst material was scraped and the crystal plane was changed. It was difficult to see.
［合成例３］
以下のようにして、層状ベロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15を固相法により合成した。
ルチル型の酸化チタン（添川理化学社製）０．５８２ｇ（１０．７ｍｍｏｌ）、酸化ランタン（関東化社学製）１．７３８ｇ（５．３ｍｍｏｌ）、および炭酸バリウム（関東化社学製）０．５２６ｇ（２．７ｍｍｏｌ）を，アルミナ乳鉢中で十分に混合し、得られた混合物に対して、加熱温度が１１００℃、加熱時間が１０時間の条件で焼成処理を行うことにより、白色物質を得た。この白色物質を粉砕混合処理した後、ペレット成形し、更に加熱温度が１４００℃、加熱時間が１０時間の条件で焼成処理した。得られた固形物をアルミナ乳鉢中で十分に粉砕処理することにより、白色粉末を得た。
得られた白色粉末は、Ｘ線回折装置「ＭｉｎｉＦｌｅｘ」（Ｒｉｇａｋｕ社製）を用いた粉末Ｘ線回折により、組成式がＢａＬａ4 Ｔｉ4 Ｏ15である層状ベロブスカイト化合物であると同定された。以下、この白色粉末を「光触媒材料（ｃ）」とする。
[Synthesis Example 3]
A layered velovskite compound BaLa 4 Ti 4 O 15 was synthesized by the solid phase method as follows.
0.582 g (10.7 mmol) of rutile-type titanium oxide (manufactured by Soekawa Rikagaku), 1.738 g (5.3 mmol) of lanthanum oxide (manufactured by Kanto Kagaku), and barium carbonate (manufactured by Kanto Kagaku) 526 g (2.7 mmol) was thoroughly mixed in an alumina mortar, and the resulting mixture was subjected to a firing treatment under the conditions of a heating temperature of 1100 ° C. and a heating time of 10 hours to obtain a white substance. It was. After this white substance was pulverized and mixed, it was pelletized and further fired under the conditions of a heating temperature of 1400 ° C. and a heating time of 10 hours. The obtained solid was sufficiently pulverized in an alumina mortar to obtain a white powder.
The obtained white powder was identified as a layered velovskite compound having a composition formula of BaLa 4 Ti 4 O 15 by powder X-ray diffraction using an X-ray diffractometer “MiniFlex” (manufactured by Rigaku). Hereinafter, this white powder is referred to as “photocatalytic material (c)”.
〈光触媒の調製〉
［調製例１］
（１）層状複水酸化物の修飾工程
硝酸マグネシウム６水和物（和光純薬社製；純度９９．０％）０．７７０ｇおよび硝酸アルミニウム９水和物（和光純薬社製；純度９８．０％）０．３７７ g（マグネシウムおよびアルミニウムのモル数の和が４ｍｍｏｌ）と、尿素（和光純薬社製；純度９９．０％）２４．０４ｇ（４００ｍｍｏｌ）とを、３００ｍｌの耐熱ガラス容器に入れ、純水２４０ｍｌを加えて撹拌した。得られた水溶液に光触媒材料（ａ）１．４００ｇを加え、超音波処理を行うことによって分散させた。この分散液を、９０℃で５時間の条件（分散液のｐＨ＝８．５）で加熱・撹拌した後、放冷してから吸引濾過して回収し、乾燥することにより、特定の層状複水酸化物によって修飾された光触媒材料（ａ）を得た。以下、この工程による特定の層状複水酸化物の修飾法を「修飾法（１）」とする。
<Preparation of photocatalyst>
[Preparation Example 1]
(1) Modification step of layered double hydroxide 0.770 g of magnesium nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd .; purity 99.0%) and aluminum nitrate nonahydrate (manufactured by Wako Pure Chemical Industries, Ltd .; purity 98. 0%) 0.377 g (sum of moles of magnesium and aluminum is 4 mmol) and urea (manufactured by Wako Pure Chemical Industries, Ltd .; purity 99.0%) 24.04 g (400 mmol) in a 300 ml heat-resistant glass container Then, 240 ml of pure water was added and stirred. 1.400 g of photocatalyst material (a) was added to the obtained aqueous solution and dispersed by sonication. The dispersion is heated and stirred at 90 ° C. for 5 hours (dispersion pH = 8.5), allowed to cool, then collected by suction filtration, and dried to obtain a specific layered composite. A photocatalytic material (a) modified with hydroxide was obtained. Hereinafter, the modification method of the specific layered double hydroxide by this process is referred to as “modification method (1)”.
(２）助触媒の担持工程
磁性るつぼに、特定の層状複水酸化物によって修飾された光触媒材料（ａ）０．７ｇを入れた後、光触媒材料（ａ）に対する担持量が０．５質量％となる量のニッケルを含有する硝酸ニッケル水溶液を滴下し、湯浴上において混合しながら蒸発乾固させた。次いで、電気炉を用い、加熱温度が２７０℃、加熱時間が１時間の条件で焼成処理し、更に水素雰囲気下において、温度が５００℃、処理時間が２時間の条件で水素還元処理を施すことにより、光触媒材料（ａ）の表面に０．５質量％のＮｉ助触媒が担持された光触媒を調製した。得られた光触媒を光触媒（１）とする。
(2) Cocatalyst loading step After 0.7 g of the photocatalytic material (a) modified with a specific layered double hydroxide is put in the magnetic crucible, the loading amount with respect to the photocatalytic material (a) is 0.5 mass%. An aqueous nickel nitrate solution containing a quantity of nickel was added dropwise and evaporated to dryness while mixing on a hot water bath. Next, using an electric furnace, a baking treatment is performed under the conditions of a heating temperature of 270 ° C. and a heating time of 1 hour, and further a hydrogen reduction treatment is performed in a hydrogen atmosphere at a temperature of 500 ° C. and a treatment time of 2 hours. Thus, a photocatalyst having 0.5% by mass of Ni promoter supported on the surface of the photocatalytic material (a) was prepared. Let the obtained photocatalyst be a photocatalyst (1).
［調製例２］
助触媒の担持工程において、焼成時間を１時間から５時間に変更したこと以外は、調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（２）とする。
この光触媒（２）について、ＩＣＰ元素分析を行ったところ、ＭｇとＡｌとの原子比（Ｍｇ／Ａｌ）の値が１．７５であり、また、粉末Ｘ線回折法により分析したところ、Ｍｇ4 Ａｌ2 （ＯＨ）12ＣＯ3 ・３Ｈ2 Ｏに帰属される回折ピークが観察された。従って、光触媒（２）における層状複水酸化物は、上記一般式（１）において、Ｍ2+がＭｇ2+、Ｍ3+がＡｌ3+、Ａn-がＣＯ3 - 、ｘの値が約０．３３、ｙの値が０．５であるものと推定される。
[Preparation Example 2]
A photocatalyst was prepared in the same manner as in Preparation Example 1 except that the calcination time was changed from 1 hour to 5 hours in the cocatalyst loading step. Let the obtained photocatalyst be a photocatalyst (2).
This photocatalyst (2), was subjected to ICP elemental analysis, the value of the atomic ratio of Mg and Al (Mg / Al) is 1.75 where, also, were analyzed by powder X-ray diffraction method, Mg 4 A diffraction peak attributed to Al 2 (OH) 12 CO 3 .3H 2 O was observed. Therefore, layered double hydroxide in a photocatalyst (2), in the above-mentioned general formula (1), M 2+ is Mg 2+, M 3+ is Al 3+, A n-is CO 3 -, the value of x It is estimated that the value of about 0.33 and y is 0.5.
［調製例３］
助触媒の担持工程において、焼成温度を２７０℃から５００℃に変更したこと以外は調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（３）とする。
[Preparation Example 3]
A photocatalyst was prepared in the same manner as in Preparation Example 1 except that the calcination temperature was changed from 270 ° C. to 500 ° C. in the cocatalyst loading step. Let the obtained photocatalyst be a photocatalyst (3).
［調製例４］
層状複水酸化物の修飾工程において、硝酸マグネシウム６水和物および硝酸アルミニウム９水和物の使用量を、マグネシウムおよびアルミニウムのモル数の和が４ｍｍｏｌから４０ｍｍｏｌとなる量に変更した（分散液のｐＨ＝８）こと以外は、調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（４）とする。
[Preparation Example 4]
In the modification step of the layered double hydroxide, the amount of magnesium nitrate hexahydrate and aluminum nitrate nonahydrate used was changed from 4 mmol to 40 mmol in terms of the total number of moles of magnesium and aluminum (dispersion of the dispersion). A photocatalyst was prepared in the same manner as in Preparation Example 1 except that pH = 8). Let the obtained photocatalyst be a photocatalyst (4).
［調製例５］
助触媒の担持工程において、焼成温度を２７０℃から５００℃に変更したこと以外は調製例４と同様にして光触媒を調製した。得られた光触媒を光触媒（５）とする。
[Preparation Example 5]
A photocatalyst was prepared in the same manner as in Preparation Example 4 except that the calcination temperature was changed from 270 ° C. to 500 ° C. in the cocatalyst loading step. Let the obtained photocatalyst be a photocatalyst (5).
［調製例６］
層状複水酸化物の修飾工程において、尿素使用量を４００ｍｍｏｌから４０ｍｍｏｌに変更した（分散液のｐＨ＝８）こと以外は、調製例３と同様にして光触媒を調製した。得られた光触媒を光触媒（６）とする。
[Preparation Example 6]
In the layered double hydroxide modification step, a photocatalyst was prepared in the same manner as in Preparation Example 3, except that the amount of urea used was changed from 400 mmol to 40 mmol (dispersion pH = 8). Let the obtained photocatalyst be a photocatalyst (6).
［調製例７］
層状複水酸化物の修飾工程および助触媒の担持工程の順序を逆にした、すなわち、光触媒材料（１）について、層状複水酸化物の修飾工程を行う前に、助触媒の担持工程を行い、その後、層状複水酸化物の修飾工程を行ったこと以外は、調製例４と同様にして光触媒を調製した。得られた光触媒を光触媒（７）とする。
[Preparation Example 7]
The order of the step of modifying the layered double hydroxide and the step of supporting the cocatalyst was reversed, that is, the step of supporting the cocatalyst was performed on the photocatalyst material (1) before the step of modifying the layered double hydroxide. Thereafter, a photocatalyst was prepared in the same manner as in Preparation Example 4 except that the step of modifying the layered double hydroxide was performed. Let the obtained photocatalyst be a photocatalyst (7).
［調製例８］
層状複水酸化物の修飾工程において、尿素使用量を４００ｍｍｏｌから４０ｍｍｏｌに変更した（分散液のｐＨ＝８）こと以外は、調製例３と同様にして光触媒を調製した。得られた光触媒を光触媒（８）とする。
[Preparation Example 8]
In the layered double hydroxide modification step, a photocatalyst was prepared in the same manner as in Preparation Example 3, except that the amount of urea used was changed from 400 mmol to 40 mmol (dispersion pH = 8). Let the obtained photocatalyst be a photocatalyst (8).
［調製例９］
層状複水酸化物の修飾工程において、尿素使用量を４００ｍｍｏｌから４０ｍｍｏｌに変更した（分散液のｐＨ＝８）こと以外は、調製例７と同様にして光触媒を調製した。得られた光触媒を光触媒（９）とする。
[Preparation Example 9]
A photocatalyst was prepared in the same manner as in Preparation Example 7 except that in the step of modifying the layered double hydroxide, the amount of urea used was changed from 400 mmol to 40 mmol (dispersion pH = 8). Let the obtained photocatalyst be a photocatalyst (9).
［調製例１０］
（１）層状複水酸化物の修飾工程
硝酸マグネシウム６水和物（和光純薬社製；純度９９．０％）０．７７０ｇおよび硝酸アルミニウム９水和物（和光純薬社製；純度９８．０％）０．３７７ｇ（マグネシウムおよびアルミニウムのモル数の和が４ｍｍｏｌ）と、尿素（和光純薬社製；純度９９．０％）２４．０４ｇ（４００ｍｍｏｌ）とを、３００ｍｌの耐熱ガラス容器に入れ，純水２４０ｍｌを加えて撹拌した。得られた水溶液を加熱して、水溶液のｐＨを８．５に上げて、層状複水酸化物を核析出させ、水溶液の温度が９０℃を超えてから３０分間経過した後、純水中に光触媒材料（ｂ）１．４００ｇが分散された分散液を添加し、温度９０℃で４．５時間の条件で加熱・撹拌した後、放冷してから吸引濾過して回収し、乾燥することにより、層状複水酸化物によって修飾された光触媒材料（ｂ）を得た。以下、この工程による層状複水酸化物の修飾法を「修飾法（２）」とする。
[Preparation Example 10]
(1) Modification step of layered double hydroxide 0.770 g of magnesium nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd .; purity 99.0%) and aluminum nitrate nonahydrate (manufactured by Wako Pure Chemical Industries, Ltd .; purity 98. 0%) 0.377 g (sum of moles of magnesium and aluminum is 4 mmol) and urea (manufactured by Wako Pure Chemical Industries, Ltd .; purity 99.0%) 24.04 g (400 mmol) are put in a 300 ml heat-resistant glass container. , 240 ml of pure water was added and stirred. The obtained aqueous solution is heated to raise the pH of the aqueous solution to 8.5 to cause the layered double hydroxide to nucleate, and after 30 minutes have passed since the temperature of the aqueous solution exceeded 90 ° C, Add a dispersion in which 1.400 g of photocatalyst material (b) is dispersed, heat and stir at 90 ° C. for 4.5 hours, allow to cool, collect by suction filtration, and dry. Thus, a photocatalytic material (b) modified with a layered double hydroxide was obtained. Hereinafter, the modification method of the layered double hydroxide in this step is referred to as “modification method (2)”.
(２）助触媒の担持工程
磁性るつぼに、層状複水酸化物によって修飾された光触媒材料（ｂ）０．７ｇを入れた後、光触媒材料（ｂ）に対する担持量が０．５質量％となる量のニッケルを含有する硝酸ニッケル水溶液を滴下し、湯浴上において混合しながら蒸発乾固させた。次いで、電気炉を用い、加熱温度が２７０℃、加熱時間が１時間の条件で焼成処理し、更に水素雰囲気下において、温度が５００℃、処理時間が２時間の条件で水素還元処理を施すことにより、光触媒材料（ｂ）の表面に０．５質量％のＮｉ助触媒が担持された光触媒を調製した。得られた光触媒を光触媒（１０）とする。
(2) Cocatalyst loading step After 0.7 g of the photocatalytic material (b) modified with the layered double hydroxide is put in the magnetic crucible, the loading amount with respect to the photocatalytic material (b) becomes 0.5 mass%. An aqueous nickel nitrate solution containing a quantity of nickel was added dropwise and evaporated to dryness while mixing on a hot water bath. Next, using an electric furnace, a baking treatment is performed under the conditions of a heating temperature of 270 ° C. and a heating time of 1 hour, and further a hydrogen reduction treatment is performed in a hydrogen atmosphere at a temperature of 500 ° C. and a treatment time of 2 hours. Thus, a photocatalyst having 0.5% by mass of Ni promoter supported on the surface of the photocatalytic material (b) was prepared. Let the obtained photocatalyst be a photocatalyst (10).
［調製例１１］
光触媒材料（ａ）の代わりに光触媒材料（ｂ）を用い、層状複水酸化物の修飾工程において、分散液の温度を９０℃から８０℃に変更した（分散液のｐＨ＝７）こと以外は、調製例３と同様にして光触媒を調製した。得られた光触媒を光触媒（１１）とする。
[Preparation Example 11]
Except for using the photocatalyst material (b) instead of the photocatalyst material (a) and changing the temperature of the dispersion from 90 ° C. to 80 ° C. in the layered double hydroxide modification step (dispersion pH = 7). A photocatalyst was prepared in the same manner as in Preparation Example 3. Let the obtained photocatalyst be a photocatalyst (11).
［調製例１２］
光触媒材料（ａ）の代わりに光触媒材料（ｂ）を用い、層状複水酸化物の修飾工程において、分散液の温度が９０℃に上昇した時点で、３％アンモニア溶液２ｍｌずつ５回添加した（ｐＨ＝１０）こと以外は、調製例６と同様にして光触媒を調製した。得られた光触媒を光触媒（１２）とする。
[Preparation Example 12]
The photocatalyst material (b) was used instead of the photocatalyst material (a), and when the temperature of the dispersion rose to 90 ° C. in the layered double hydroxide modification step, 2 ml of 3% ammonia solution was added five times ( A photocatalyst was prepared in the same manner as in Preparation Example 6 except that pH = 10). Let the obtained photocatalyst be a photocatalyst (12).
［調製例１３］
光触媒材料（ａ）の代わりに光触媒材料（ｂ）を用いたこと以外は、調製例６と同様にして光触媒を調製した。得られた光触媒を光触媒（１３）とする。
[Preparation Example 13]
A photocatalyst was prepared in the same manner as in Preparation Example 6 except that the photocatalyst material (b) was used instead of the photocatalyst material (a). Let the obtained photocatalyst be a photocatalyst (13).
［調製例１４］
光触媒材料（ａ）の代わりに光触媒材料（ｃ）を用い、助触媒の担持工程において、硝酸ニッケル水溶液として、光触媒材料に対する担持量が０．２質量％となる量のニッケルを含有するものを用いたこと以外は、調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（１４）とする。
[Preparation Example 14]
The photocatalyst material (c) is used in place of the photocatalyst material (a), and in the cocatalyst support step, an aqueous nickel nitrate solution containing nickel in an amount of 0.2% by mass with respect to the photocatalyst material is used. A photocatalyst was prepared in the same manner as in Preparation Example 1 except that Let the obtained photocatalyst be a photocatalyst (14).
［調製例１５］
光触媒材料（ａ）の代わりに光触媒材料（ｃ）を用いたこと以外は、調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（１５）とする。
[Preparation Example 15]
A photocatalyst was prepared in the same manner as in Preparation Example 1 except that the photocatalyst material (c) was used instead of the photocatalyst material (a). Let the obtained photocatalyst be a photocatalyst (15).
［調製例１６］
層状複水酸化物の修飾工程において、硝酸アルミニウム９水和物を用いず、硝酸マグネシウム６水和物の使用量を、マグネシウムのモル数が４ｍｍｏｌとなる量に変更した（分散液のｐＨ＝９）こと以外は、調製例２と同様にして光触媒を調製した。得られた光触媒を光触媒（１６）とする。この光触媒（１６）について、ＩＣＰ元素分析を行ったところ、Ｍｇの量は、光触媒（２）におけるＭｇの量の１／１００以下であった。
[Preparation Example 16]
In the modification process of the layered double hydroxide, the amount of magnesium nitrate hexahydrate used was changed to an amount such that the number of moles of magnesium was 4 mmol without using aluminum nitrate nonahydrate (dispersion pH = 9). The photocatalyst was prepared in the same manner as in Preparation Example 2 except that. Let the obtained photocatalyst be a photocatalyst (16). When ICP elemental analysis was performed on this photocatalyst (16), the amount of Mg was 1/100 or less of the amount of Mg in the photocatalyst (2).
［比較調製例１］
層状複水酸化物の修飾工程を行わなかったこと以外は、調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（１７）とする。
[Comparative Preparation Example 1]
A photocatalyst was prepared in the same manner as in Preparation Example 1 except that the step of modifying the layered double hydroxide was not performed. Let the obtained photocatalyst be a photocatalyst (17).
［比較調製例２］
助触媒の担持工程において、焼成時間を１時間から５時間に変更したこと以外は、比較調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（１８）とする。
[Comparative Preparation Example 2]
A photocatalyst was prepared in the same manner as in Comparative Preparation Example 1 except that the calcination time was changed from 1 hour to 5 hours in the cocatalyst loading step. Let the obtained photocatalyst be a photocatalyst (18).
［比較調製例３］
助触媒の担持工程において、焼成温度を２７０℃から５００℃に変更したこと以外は、比較調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（１９）とする。
[Comparative Preparation Example 3]
A photocatalyst was prepared in the same manner as in Comparative Preparation Example 1 except that in the step of supporting the cocatalyst, the calcination temperature was changed from 270 ° C. to 500 ° C. Let the obtained photocatalyst be a photocatalyst (19).
［比較調製例４］
光触媒材料（ａ）の代わりに光触媒材料（ｂ）を用いたこと以外は、比較調製例１と同様にして光触媒を調製した。得られた光触媒を光触媒（２０）とする。
[Comparative Preparation Example 4]
A photocatalyst was prepared in the same manner as in Comparative Preparation Example 1 except that the photocatalyst material (b) was used instead of the photocatalyst material (a). Let the obtained photocatalyst be a photocatalyst (20).
［比較調製例５］
層状複水酸化物の修飾工程を行わなかったこと以外は、調製例１４と同様にして光触媒を調製した。得られた光触媒を光触媒（２１）とする。
[Comparative Preparation Example 5]
A photocatalyst was prepared in the same manner as in Preparation Example 14 except that the step of modifying the layered double hydroxide was not performed. Let the obtained photocatalyst be a photocatalyst (21).
［比較調製例６］
助触媒の担持工程において、硝酸ニッケル水溶液として、光触媒材料に対する担持量が０．５質量％となる量のニッケルを含有するものを用いたこと以外は、比較調製例５と同様にして光触媒を調製した。得られた光触媒を光触媒（２２）とする。
[Comparative Preparation Example 6]
In the cocatalyst supporting step, a photocatalyst was prepared in the same manner as in Comparative Preparation Example 5 except that an aqueous nickel nitrate solution containing nickel in an amount of 0.5% by mass with respect to the photocatalyst material was used. did. Let the obtained photocatalyst be a photocatalyst (22).
調製例１〜１６および比較調製例１〜６の各々における各工程の諸条件、および調製例１〜１６で得られた光触媒における特定の層状複水酸化物の割合を、下記表１にまとめて示す。 The conditions of each step in each of Preparation Examples 1 to 16 and Comparative Preparation Examples 1 to 6, and the ratio of specific layered double hydroxides in the photocatalysts obtained in Preparation Examples 1 to 16 are summarized in Table 1 below. Show.
〈光触媒の評価〉
［実験例１］
図１に示す閉鎖循環系の反応装置を用い、以下のようにして、光触媒（１）について、硝酸イオンの還元反応に対する活性の評価を行った。ここで、図１において、１は石英製内部照射型反応管、２は真空ライン、３はスターラー、４は撹拌子、５は循環器、６は圧力計、７はガスクロマトグラフ、８はリービッヒ冷却管、９は４００Ｗ高圧水銀灯、１０は反応溶液である。
<Evaluation of photocatalyst>
[Experimental Example 1]
Using the closed circulation system reactor shown in FIG. 1, the activity of the photocatalyst (1) with respect to the reduction reaction of nitrate ions was evaluated as follows. Here, in FIG. 1, 1 is a quartz internal irradiation reaction tube, 2 is a vacuum line, 3 is a stirrer, 4 is a stirrer, 5 is a circulator, 6 is a pressure gauge, 7 is a gas chromatograph, and 8 is Liebig cooling. A tube, 9 is a 400 W high-pressure mercury lamp, and 10 is a reaction solution.
濃度が１０ｍｍｏｌ／Ｌの硝酸ナトリウム水溶液３５０ｍｌ中に、濃度が１０ｍｍｏｌ／ＬとなるようにｐＨ緩衝剤であるホウ酸を添加すると共に、光触媒（１）０．５６４ｇ（層状ペロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15０．５００ｇ含有）を懸濁することにより、光触媒分散液を調製した。この分散液のｐＨは、６．９である。この光触媒分散液を、図１に示す反応装置における石英製内部照射型反応管１の反応管本体内に仕込み、さらに、この反応管本体内に、光源として４００Ｗの高圧水銀灯が収容された石英管を挿入した。そして、この高圧水銀灯を点灯することにより、当該高圧水銀灯からの光を光触媒分散液に２１時間照射した。ここで、光照射中において発生する水素、酸素、窒素の量をガスクロマトグラフ「ＧＣ−８Ａ」（島津製作所製；ＭＳ−５Ａカラム；Ａr キャリアー）により定量した。光照射が終了した後に、光触媒分散液中の硝酸イオン残存量を、イオンクロマトグラフ「ＩＣＡ−２０００」（東亜ＤＫＫ社製）により定量した。そして、得られた測定値に基づいて、下記の式（１）〜（４）に従って、硝酸イオン除去率、硝酸イオン除去量、窒素転化率、窒素転化量をそれぞれ算出した。下記結果を表２に示す。
式（１）：硝酸イオン除去量（ｍｏｌ）＝初期硝酸イオン量−硝酸イオン残存量
式（２）：硝酸イオン除去率（％）＝（硝酸イオン除去量／初期硝酸イオン量）×１００式（３）：窒素転化量（ｍｏｌ）＝窒素ガス生成量×２
式（４）：窒素転化率（％）＝（窒素転化量／初期硝酸イオン量）×１００
式（１）、式（２）および式（４）において、「初期硝酸イオン量」とは、硝酸ナトリウム水溶液中の硝酸イオンのモル量である。
Boric acid as a pH buffer was added to 350 ml of an aqueous sodium nitrate solution having a concentration of 10 mmol / L, and 0.564 g of a photocatalyst (1) (layered perovskite compound BaLa 4 Ti 4 O 15 containing 0.500 g) was prepared to prepare a photocatalyst dispersion. The pH of this dispersion is 6.9. This photocatalyst dispersion is charged into a reaction tube main body of a quartz internal irradiation
Formula (1): nitrate ion removal amount (mol) = initial nitrate ion amount−nitrate ion residual amount formula (2): nitrate ion removal rate (%) = (nitrate ion removal amount / initial nitrate ion amount) × 100 formula ( 3): Nitrogen conversion amount (mol) = nitrogen gas production amount × 2
Formula (4): Nitrogen conversion rate (%) = (nitrogen conversion amount / initial nitrate ion amount) × 100
In the formulas (1), (2) and (4), the “initial nitrate ion amount” is the molar amount of nitrate ions in the aqueous sodium nitrate solution.
［実験例２〜１６および比較実験例１〜７］
光触媒（１）の代わりに下記表２に示す光触媒または光触媒材料を用いたこと以外は、実験例１と同様にして光照射中において発生する水素、酸素、窒素の量を定量すると共に、光照射が終了した後における光触媒分散液中の硝酸イオン残存量を定量し、反応２１時間後の硝酸イオン除去率、硝酸イオン除去量、窒素転化率、窒素転化量をそれぞれ算出した。下記結果を表２に示す。
[Experimental Examples 2-16 and Comparative Experimental Examples 1-7]
Except that the photocatalyst or photocatalyst material shown in Table 2 below was used instead of the photocatalyst (1), the amounts of hydrogen, oxygen, and nitrogen generated during light irradiation were quantified in the same manner as in Experimental Example 1, and light irradiation was performed. The amount of nitrate ions remaining in the photocatalyst dispersion after the completion of the process was quantified, and the nitrate ion removal rate, nitrate ion removal amount, nitrogen conversion rate, and nitrogen conversion amount after 21 hours of reaction were calculated. The following results are shown in Table 2.
［比較実験例８］
光触媒（１）を用いなかったこと以外は、実験例１と同様にして光照射中において発生する水素、酸素、窒素の量を定量すると共に、光照射が終了した後における光触媒分散液中の硝酸イオン残存量を定量し、反応２１時間後の硝酸イオン除去率、硝酸イオン除去量、窒素転化率、窒素転化量をそれぞれ算出した。下記結果を表２に示す。
[Comparative Experimental Example 8]
Except that the photocatalyst (1) was not used, the amounts of hydrogen, oxygen, and nitrogen generated during the light irradiation were quantified in the same manner as in Experimental Example 1, and the nitric acid in the photocatalyst dispersion after the light irradiation was completed. The remaining amount of ions was quantified, and the nitrate ion removal rate, nitrate ion removal amount, nitrogen conversion rate, and nitrogen conversion amount after 21 hours of reaction were calculated. The following results are shown in Table 2.
［実験例１７］
濃度が１０ｍｍｏｌ／Ｌの硝酸ナトリウム水溶液の代わりに濃度が１００ｍｍｏｌ／Ｌの硝酸ナトリウム水溶液を用いたこと以外は、実験例１と同様にして光照射中において発生する水素、酸素、窒素の量を定量すると共に、光照射が終了した後における光触媒分散液中の硝酸イオン残存量を定量し、反応２１時間後の硝酸イオン除去率、硝酸イオン除去量、窒素転化率、窒素転化量をそれぞれ算出した。下記結果を表２に示す。
[Experimental Example 17]
Quantify the amount of hydrogen, oxygen, and nitrogen generated during light irradiation in the same manner as in Experimental Example 1, except that a sodium nitrate aqueous solution with a concentration of 100 mmol / L was used instead of a sodium nitrate aqueous solution with a concentration of 10 mmol / L. At the same time, the remaining amount of nitrate ions in the photocatalyst dispersion after the light irradiation was finished was quantified, and the nitrate ion removal rate, nitrate ion removal amount, nitrogen conversion rate, and nitrogen conversion amount after 21 hours of reaction were calculated. The following results are shown in Table 2.
［実験例１８］
濃度が１０ｍｍｏｌ／Ｌの硝酸ナトリウム水溶液の代わりに濃度が１００ｍｍｏｌ／Ｌの硝酸ナトリウム水溶液を用いたこと以外は、実験例３と同様にして光照射中において発生する水素、酸素、窒素の量を定量すると共に、光照射が終了した後における光触媒分散液中の硝酸イオン残存量を定量し、反応２１時間後の硝酸イオン除去率、硝酸イオン除去量、窒素転化率、窒素転化量をそれぞれ算出した。下記結果を表２に示す。
[Experiment 18]
Quantify the amounts of hydrogen, oxygen, and nitrogen generated during light irradiation in the same manner as in Experimental Example 3, except that a sodium nitrate aqueous solution with a concentration of 100 mmol / L was used instead of a sodium nitrate aqueous solution with a concentration of 10 mmol / L. At the same time, the remaining amount of nitrate ions in the photocatalyst dispersion after the light irradiation was finished was quantified, and the nitrate ion removal rate, nitrate ion removal amount, nitrogen conversion rate, and nitrogen conversion amount after 21 hours of reaction were calculated. The following results are shown in Table 2.
［比較実験例９］
濃度が１０ｍｍｏｌ／Ｌの硝酸ナトリウム水溶液の代わりに濃度が１００ｍｍｏｌ／Ｌの硝酸ナトリウム水溶液を用いたこと以外は、比較実験例１と同様にして光照射中において発生する水素、酸素、窒素の量を定量すると共に、光照射が終了した後における光触媒分散液中の硝酸イオン残存量を定量し、反応２１時間後の硝酸イオン除去率、硝酸イオン除去量、窒素転化率、窒素転化量をそれぞれ算出した。下記結果を表２に示す。
[Comparative Experiment 9]
The amounts of hydrogen, oxygen, and nitrogen generated during light irradiation in the same manner as in Comparative Experimental Example 1, except that a sodium nitrate aqueous solution with a concentration of 100 mmol / L was used instead of a sodium nitrate aqueous solution with a concentration of 10 mmol / L. The amount of nitrate ions remaining in the photocatalyst dispersion after the light irradiation was quantified, and the nitrate ion removal rate, nitrate ion removal amount, nitrogen conversion rate, and nitrogen conversion amount after 21 hours of reaction were calculated. . The following results are shown in Table 2.
実験例１〜３および比較実験例１〜３の結果から以下のことが理解される。
助触媒の担持工程において、焼成温度が低温（２７０℃）である光触媒（１）および光触媒（２）によれば、焼成温度が高温（５００℃）である光触媒（３）より高い窒素転化率が得られるが、光触媒（３）によれば、水分解反応の生成物である水素および酸素の生成量が、光触媒（１）および光触媒（２）より著しく増加している。これは、高温で焼成することにより、Ｎｉ助触媒の状態がかわり、窒素への還元反応の選択性が低下し、水の還元反応の方が有利になったためであると考えられる。また、焼成温度が低い（２７０℃）と、Ｎｉ助触媒は、粒径の小さい酸化ニッケルになるか、あるいは層状複水酸化物の一部に組み込まれカチオンの状態で表面に残ることが考えられる。これに対して、焼成温度が高い（５００℃）と、粒径の大きい酸化ニッケルになり、還元処理後のＮｉ金属の粒径も大きくなる傾向があると考えられる。
一方、層状複水酸化物によって修飾されていない光触媒（１８）〜光触媒（２０）では、助触媒の担持工程において、焼成温度が低温（２７０℃）で短時間（１時間）の光触媒（１８）が最も窒素転化率が高かった。これらの結果は、硝酸イオンの還元反応も、Ｎｉ助触媒の分散性に大きく依存している可能性が高いことを示している。
The following can be understood from the results of Experimental Examples 1 to 3 and Comparative Experimental Examples 1 to 3.
In the cocatalyst loading step, the photocatalyst (1) and photocatalyst (2) having a low calcination temperature (270 ° C.) have a higher nitrogen conversion rate than the photocatalyst (3) having a high calcination temperature (500 ° C.). Although it is obtained, according to the photocatalyst (3), the production amounts of hydrogen and oxygen which are products of the water splitting reaction are remarkably increased as compared with the photocatalyst (1) and the photocatalyst (2). This is considered to be because the state of the Ni promoter is changed by baking at a high temperature, the selectivity of the reduction reaction to nitrogen is lowered, and the reduction reaction of water becomes more advantageous. Further, when the calcination temperature is low (270 ° C.), the Ni promoter may be nickel oxide having a small particle size or may be incorporated into a part of the layered double hydroxide and remain on the surface in a cation state. . On the other hand, when the firing temperature is high (500 ° C.), nickel oxide having a large particle size is obtained, and the particle size of Ni metal after the reduction treatment tends to be large.
On the other hand, in the photocatalyst (18) to the photocatalyst (20) not modified by the layered double hydroxide, the photocatalyst (18) having a low firing temperature (270 ° C.) and a short time (1 hour) in the cocatalyst supporting step. Has the highest nitrogen conversion. These results indicate that there is a high possibility that the reduction reaction of nitrate ions is highly dependent on the dispersibility of the Ni promoter.
また、実験例１〜６の結果から以下のことが理解される。
光触媒材料に対してマグネシウムおよびアルミニウムの使用量が少ない光触媒（１）〜光触媒（３）および光触媒（６）によれば、高い窒素添加率が得られる。一方、光触媒材料に対してマグネシウムおよびアルミニウムの使用量が多い光触媒（４）および光触媒（５）においては、窒素への転化が著しく低い。光触媒（４）および光触媒（５）の表面をＳＥＭで観察したところ、光触媒材料の表面の大部分が層状複水酸化物によって修飾されていることが確認された。このことから、硝酸イオンの窒素への還元反応は、光触媒材料の表面でのみ起こっており、光触媒材料の表面が露出していなければ窒素への転化は起こらないと考えられる。また、層状複水酸化物は電子伝導体ではないため、反応は光触媒材料上に担持されたＮｉ助触媒や、層状複水酸化物上に担持されたＮｉ助触媒と、光触媒材料との境界で起こっていると考えられる。
Moreover, the following is understood from the results of Experimental Examples 1 to 6.
According to the photocatalyst (1) to the photocatalyst (3) and the photocatalyst (6), which use less magnesium and aluminum than the photocatalyst material, a high nitrogen addition rate can be obtained. On the other hand, in the photocatalyst (4) and the photocatalyst (5) in which the amounts of magnesium and aluminum used are large relative to the photocatalytic material, the conversion to nitrogen is extremely low. When the surfaces of the photocatalyst (4) and the photocatalyst (5) were observed with an SEM, it was confirmed that most of the surface of the photocatalyst material was modified with a layered double hydroxide. From this, it is considered that the reduction reaction of nitrate ions to nitrogen occurs only on the surface of the photocatalytic material, and conversion to nitrogen does not occur unless the surface of the photocatalytic material is exposed. In addition, since the layered double hydroxide is not an electronic conductor, the reaction takes place at the boundary between the Ni catalyst supported on the photocatalyst material, the Ni promoter supported on the layered double hydroxide, and the photocatalyst material. It seems that it is happening.
また、実験例４〜９の結果から、層状複水酸化物の修飾を行う前にＮｉ助触媒を担持しても、窒素への添加が促進されないことが確認された。特に、マグネシウムおよびアルミニウムの使用量が多い場合には、光触媒材料の表面の大部分が層状複水酸化物によって修飾されるため、層状複水酸化物の修飾工程および助触媒の担持工程の順序を変えても差が認められなかった。
また、実験例１０および実験例１３の結果から、光触媒材料の表面に直接析出させる修飾法（１）によれば、光触媒材料の表面を予め核析出させた層状複水酸化物によって修飾する修飾法（２）に比較して、硝酸イオン除去率および窒素転化率のいずれも高い値を示すことが理解される。
また、実験例３および実験例１３の結果から、粉砕処理を行った光触媒触媒（１３）を用いた場合（実験例１３）には、粉砕を行っていない光触媒材料（３）を用いた場合（実験例３）と比べて窒素の転化率が低下することが理解される。
また、実験例１４〜１５および比較実験例５の結果から、固相法によって合成された光触媒材料（ｃ）を使用した場合でも、当該光触媒材料（ｃ）の表面が層状複水酸化物によって修飾されることにより、得られる光触媒の活性が向上することが理解される。
Further, from the results of Experimental Examples 4 to 9, it was confirmed that the addition to Ni was not promoted even when the Ni promoter was supported before the modification of the layered double hydroxide. In particular, when the amount of magnesium and aluminum used is large, most of the surface of the photocatalyst material is modified by the layered double hydroxide, so the order of the layered double hydroxide modification step and the cocatalyst loading step is reduced. Even if it changed, the difference was not recognized.
Further, from the results of Experimental Example 10 and Experimental Example 13, according to the modification method (1) for directly depositing on the surface of the photocatalyst material, the modification method for modifying the surface of the photocatalyst material with a layered double hydroxide that has been nucleated in advance. It is understood that both the nitrate ion removal rate and the nitrogen conversion rate are higher than (2).
From the results of Experimental Example 3 and Experimental Example 13, when the photocatalyst catalyst (13) subjected to the pulverization treatment was used (Experimental Example 13), the photocatalyst material (3) not subjected to pulverization was used ( It is understood that the conversion rate of nitrogen is lower than in Experimental Example 3).
Further, from the results of Experimental Examples 14 to 15 and Comparative Experimental Example 5, even when the photocatalytic material (c) synthesized by the solid phase method is used, the surface of the photocatalytic material (c) is modified with the layered double hydroxide. It is understood that the activity of the resulting photocatalyst is improved.
また、実験例１７および比較実験例９の結果から、光触媒材料の表面が層状複水酸化物によって修飾されることにより、硝酸イオンの濃度が高い水溶液に対しても、得られる光触媒の活性が向上することが理解される。
また、実験例１７〜１８の結果から、助触媒の担持工程において、焼成温度が低温（２７０℃）である光触媒を用いることにより、硝酸イオンの濃度が高い水溶液に対しても、得られる光触媒の活性が向上することが理解される。
また、実験例１６の結果から、層状複水酸化物の修飾工程において硝酸アルミニウムを用いない場合（上記一般式（１）においてｘが０）でも、得られる光触媒の活性が向上することが理解される。
Further, from the results of Experimental Example 17 and Comparative Experimental Example 9, the surface of the photocatalyst material is modified with the layered double hydroxide, so that the activity of the obtained photocatalyst is improved even for an aqueous solution having a high nitrate ion concentration. To be understood.
Further, from the results of Experimental Examples 17 to 18, by using a photocatalyst having a low calcination temperature (270 ° C.) in the cocatalyst supporting step, the photocatalyst obtained can be obtained even for an aqueous solution having a high concentration of nitrate ions. It is understood that the activity is improved.
Further, from the results of Experimental Example 16, it is understood that the activity of the obtained photocatalyst is improved even when aluminum nitrate is not used in the modification step of the layered double hydroxide (x in the general formula (1) is 0). The
［実験例１９］
図１に示す閉鎖循環系の反応装置を用い、以下のようにして、光触媒（１）について、水の全分解反応に対する活性の評価を行った。
純水３５０ｍｌ中に、光触媒（１）０．５６４ｇ（層状ペロブスカイト化合物ＢａＬａ4 Ｔｉ4 Ｏ15０．５００ｇ含有）を懸濁することにより、光触媒分散液を調製した。この光触媒分散液を、図１に示す反応装置における石英製内部照射型反応管１の反応管本体内に仕込み、さらに、この反応管本体内に、光源として４００Ｗの高圧水銀灯が収容された石英管を挿入した。そして、この高圧水銀灯を点灯することにより、当該高圧水銀灯からの光を光触媒分散液に２１時間照射した。ここで、光照射中において発生する水素、酸素の量をガスクロマトグラフ「ＧＣ−８Ａ」（島津製作所製；ＭＳ−５Ａカラム；Ａr キャリアー）により定量した。反応３時間後の反応生成物量の測定結果を下記表３に示す。
[Experimental Example 19]
The activity of the photocatalyst (1) with respect to the total decomposition reaction of water was evaluated in the following manner using the closed circulation system reactor shown in FIG.
A photocatalyst dispersion was prepared by suspending 0.564 g of photocatalyst (1) (containing 0.500 g of the layered perovskite compound BaLa 4 Ti 4 O 15 ) in 350 ml of pure water. This photocatalyst dispersion is charged into a reaction tube main body of a quartz internal irradiation
［比較実験例１０］
光触媒（１）の代わりに光触媒（２０）を用いたこと以外は、実験例１９と同様にして光照射中において発生する水素、酸素の量を定量した。反応３時間後の反応生成物量の測定結果を下記表３に示す。
[Comparative Experimental Example 10]
Except that the photocatalyst (20) was used instead of the photocatalyst (1), the amounts of hydrogen and oxygen generated during light irradiation were quantified in the same manner as in Experimental Example 19. The measurement results of the reaction product amount after 3 hours of reaction are shown in Table 3 below.
表３の結果から、本発明に係る光触媒（１）によれば、水の全分解反応に対して高い活性を有するものであることが理解される。 From the results of Table 3, it is understood that the photocatalyst (1) according to the present invention has high activity for the total decomposition reaction of water.
１ 石英製内部照射型反応管
２ 真空ライン
３ スターラー
４ 撹拌子
５ 循環器
６ 圧力計
７ ガスクロマトグラフ
８ リービッヒ冷却管
９ ４００Ｗ高圧水銀灯
１０ 反応溶液
DESCRIPTION OF
Claims (7)
A method for treating nitrate nitrogen-containing water, wherein the nitrate ion is reduced by irradiating the photocatalyst according to any one of claims 1 to 3 with ultraviolet rays in an aqueous solution containing nitrate ions. .
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