JP2013000673A - Technology for enhancing performance of photocatalyst - Google Patents
Technology for enhancing performance of photocatalyst Download PDFInfo
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- JP2013000673A JP2013000673A JP2011135250A JP2011135250A JP2013000673A JP 2013000673 A JP2013000673 A JP 2013000673A JP 2011135250 A JP2011135250 A JP 2011135250A JP 2011135250 A JP2011135250 A JP 2011135250A JP 2013000673 A JP2013000673 A JP 2013000673A
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Abstract
Description
本発明は、光触媒無機材料等の光機能無機材料を高機能化する技術に関する。より具体的には、基材に固定化された酸化物あるいは酸窒化物、窒化物、亜硫酸化物、硫化物などの光触媒材料または化学溶液法で作製された光触媒材料の前駆体へ紫外線パルスレーザーを照射することによる高い光触媒特性無機材料の形成に関するものである。 The present invention relates to a technique for enhancing the functionality of a photofunctional inorganic material such as a photocatalytic inorganic material. More specifically, an ultraviolet pulse laser is applied to a photocatalyst material such as an oxide or oxynitride, nitride, sulfite oxide or sulfide immobilized on a base material or a precursor of a photocatalyst material produced by a chemical solution method. The present invention relates to the formation of inorganic materials having high photocatalytic properties by irradiation.
近年、環境浄化や水からの水素製造など環境問題解決に資する材料開発が盛んに行われ、中でも光触媒材料を用いた研究が非常に盛んである。光触媒を用いれば太陽光あるいはＵＶランプ光源などを利用した紫外線照射によって大気中あるいは水環境中の汚染物質の除去が可能であり、出来る限り環境負荷を減らして環境浄化を行うことが出来るうえ、水分解による水素製造などクリーンエネルギー創出にも大きな役割を果たす。 In recent years, material development that contributes to solving environmental problems such as environmental purification and hydrogen production from water has been actively carried out, and research using photocatalytic materials is particularly active. If a photocatalyst is used, it is possible to remove pollutants in the atmosphere or water environment by irradiating with ultraviolet rays using sunlight or a UV lamp light source. It also plays a major role in clean energy creation, such as hydrogen production by decomposition.
高特性を持つ光触媒材料等の光の照射を受け各種の機能を果たす光応答材料は社会的に極めて大きなインパクトを与えるため、これまで多くの開発が行われている（特許文献１、２参照）。紫外線励起によって大きな効果を発揮するアナターゼ型ＴｉＯ２を主とする酸化物材料において多くの研究が行われ、これまでに可視光利用への対応やナノテクノロジーを利用した材料の高特性化など多分野にまたがっての精力的な開発が行われてきた（特許文献３、非特許文献１参照）。 Photo-responsive materials that perform various functions when irradiated with light, such as photocatalyst materials with high properties, have a great impact on society, so much development has been carried out so far (see Patent Documents 1 and 2). . Much research has been conducted on oxide materials mainly composed of anatase-type TiO 2 that exerts a great effect by ultraviolet excitation, and so far various fields such as correspondence to the use of visible light and enhancement of properties of materials using nanotechnology. Energetic development has been performed over the past (see Patent Document 3 and Non-Patent Document 1).
実際の光触媒材料等の光応答材料は、薄膜の形態で利用する場合が多く、薄膜化は通常粉砕した小粒径光触媒を基材に塗布して固定化する場合が多い。粒子の粉砕にはボールミルやビーズミルなどメカニカルな粉砕手法が容易に利用しやすい。塗布粒子は水熱反応法などによってナノ粒子を合成して利用することも出来る。塗布された粒子はセラミック基板であれば熱アニール手法が一般的で、プラスチック基板であればレーザーアニールを用いる手法が開発されている（特許文献４、５）。これらのプロセスによって光触媒粒子は基材に固定化されて実際の光触媒材料として応用されるが、いくつかの問題点があることが本発明者らによって知見された。すなわち、（１）メカニカル手法によって粉砕された粒子はメカノケミカル的反応や表面のガラス化によって光触媒粒子としての機能が著しく損なわれる場合がある。（２）レーザーアニール手法による触媒粒子固定化は光照射条件の最適化を行わなければ光触媒機能を十分に向上させることが出来ない。すなわち弱すぎるレーザーフルエンス（例えば特許文献４に示されるような３０ｍＪ／ｃｍ２より弱いフルエンス）では十分な結晶成長が望めないし、強すぎるレーザーフルエンス（例えば特許文献５に示されるような１００ｍＪ／ｃｍ２より強いフルエンス）ではレーザーアブレーションの効果などによって材料の幾何学的構造を損なったり、アニオンの欠損などの恐れもある。後者の問題に関しては言い換えれば光照射条件の最適化によって触媒機能を高めることが出来る。 Photoresponsive materials such as actual photocatalyst materials are often used in the form of a thin film, and thinning is usually performed by applying a pulverized small particle size photocatalyst to a substrate and fixing it. For the pulverization of particles, a mechanical pulverization method such as a ball mill or a bead mill is easily used. The coated particles can be used by synthesizing nanoparticles by a hydrothermal reaction method or the like. If the coated particles are ceramic substrates, a thermal annealing method is generally used. If a plastic substrate is used, methods using laser annealing have been developed (Patent Documents 4 and 5). By these processes, the photocatalyst particles are immobilized on a substrate and applied as an actual photocatalyst material, but the present inventors have found that there are some problems. That is, (1) the function of the photocatalyst particles may be significantly impaired by the mechanochemical reaction or vitrification of the surface of the particles pulverized by the mechanical method. (2) The catalyst particle immobilization by the laser annealing method cannot sufficiently improve the photocatalytic function unless the light irradiation conditions are optimized. That is, if the laser fluence is too weak (for example, a fluence weaker than 30 mJ / cm 2 as shown in Patent Document 4), sufficient crystal growth cannot be expected, and the laser fluence is too strong (for example, 100 mJ / cm 2 as shown in Patent Document 5). At higher fluences, there is a risk of damage to the material's geometric structure due to the effect of laser ablation, or anion loss. Regarding the latter problem, in other words, the catalytic function can be enhanced by optimizing the light irradiation conditions.
これまでにある種の金属酸化物膜を作製する方法として、金属有機酸塩ないし有機金属化合物を可溶性溶媒に溶かし、あるいは液体のものはそのまま、該溶液を基板上に分散塗布した後、大気圧下でエキシマレーザを照射することを特徴とし、オンデマンド性の高い製膜手法であるエキシマレーザによる金属酸化物および金属酸化物薄膜の製造方法（光ＭＯＤ法）が知られている（特許文献６）。ここでは、金属有機化合物を溶媒に溶解させて溶液状とし、これを基板に塗布した後に、乾燥させ、波長４００ｎｍ以下の紫外線レーザ光、例えば、ＡｒＦ、ＫｒＦ、ＸｅＣｌ、ＸｅＦ、Ｆ２から選ばれるエキシマレーザを用いて照射することにより基板上に金属酸化物を形成することを特徴とする金属酸化物の製造方法が記載され、波長４００ｎｍ以下のレーザ光の照射を、複数段階で行い、最初の段階の照射は金属有機化合物を完全に分解させるに至らない程度の弱い照射で行い、次に酸化物にまで変化させることができる強い照射を行うことも記載されている。また、金属有機化合物が異なる金属からなる２種以上の化合物であり、得られる金属酸化物が異なる金属からなる複合金属酸化物となるものを作製可能であることも知られている。 As a method for producing a certain type of metal oxide film so far, a metal organic acid salt or an organic metal compound is dissolved in a soluble solvent, or a liquid is left as it is, and the solution is dispersed and coated on a substrate, and then atmospheric pressure is applied. A method for producing metal oxides and metal oxide thin films using an excimer laser (optical MOD method) is known, which is characterized by irradiating an excimer laser underneath and is a film forming method with high on-demand characteristics (Patent Document 6). ). Here, a metal organic compound is dissolved in a solvent to form a solution, which is applied to a substrate, dried, and then selected from ultraviolet laser light having a wavelength of 400 nm or less, for example, ArF, KrF, XeCl, XeF, F 2 A method for producing a metal oxide is described in which a metal oxide is formed on a substrate by irradiating with an excimer laser. Irradiation with a laser beam having a wavelength of 400 nm or less is performed in a plurality of stages. It is also described that the stepwise irradiation is performed with weak irradiation that does not lead to complete decomposition of the metal organic compound, and then strong irradiation that can be changed to an oxide. It is also known that two or more kinds of compounds in which the metal organic compound is composed of different metals and that the resulting metal oxide is a composite metal oxide composed of different metals can be produced.
一例を挙げればペロブスカイト型酸化物については、Ｌａ、ＭｎおよびＣａ、ＳｒもしくはＢａの各酸化物の原料成分を含む前駆体塗布液を被塗布物の表面に塗布して成膜した後、被塗布物表面に形成された薄膜を結晶化させて、組成式（Ｌａ1-ｘＭx）ＭｎＯ3-δ（Ｍ：Ｃａ，Ｓｒ、Ｂａ、０．０９≦ｘ≦０．５０）で表わされる複合酸化物膜（超電導を示さない）を形成する複合酸化物膜の製造方法において、前記前駆体塗布液を被塗布物の表面に塗布して成膜した後、被塗布物表面に形成された薄膜に対し波長が３６０ｎｍ以下である光を照射して薄膜を結晶化させることを特徴とする複合酸化物膜の製造方法が知られている（特許文献７）。ここでは、被塗布物の表面に形成された薄膜に対して光を照射する光源が、ＡｒＦエキシマレーザ、ＫｒＦエキシマレーザ、ＸｅＣｌエキシマレーザ、ＸｅＦエキシマレーザ、ＹＡＧレーザの３倍波光またはＹＡＧレーザの４倍波光が用いられ、被塗布物の表面に塗布される前駆体塗布液が、Ｌａのアルカノールアミン配位化合物と、Ｍｎのカルボン酸塩と、Ｍの金属またはアルコキシドとを、炭素数が１〜４である一級アルコール中で混合させ反応させて調整することが記載されている。最近では前駆体溶液にナノ粒子を混ぜ反応を促進させるナノ粒子光反応法を用いた手法も開発が進んでいる（特許文献８、９）。ポリシリコンを成膜する手法として一般的なレーザーアニール法では、１００ｍＪ／ｃｍ２以上のフルエンスを用いたレーザー照射がよく用いられ、その結晶成長は主にレーザー照射時の溶融再結晶によって進行するが、本発明者らは、光ＭＯＤ法、ナノ粒子光反応法いずれの場合も溶融再結晶が主な結晶成長の駆動要因ではなく、反応界面・粒子界面における光化学的反応（光加熱効果も含む）を積極的に利用する手法である。つまり材料の融解温度以上の温度に達しなくても効率的に結晶成長が進行することを知見した。 For example, for a perovskite oxide, a precursor coating liquid containing raw material components of La, Mn, and Ca, Sr or Ba is applied to the surface of the object to be coated, and then coated. The thin film formed on the surface of the material is crystallized to obtain a composite represented by the composition formula (La 1-x M x ) MnO 3-δ (M: Ca, Sr, Ba, 0.09 ≦ x ≦ 0.50). In the method for producing a composite oxide film for forming an oxide film (not showing superconductivity), the thin film formed on the surface of the object to be coated after the precursor coating solution is coated on the surface of the object to be coated On the other hand, there is known a method for producing a complex oxide film characterized by irradiating light having a wavelength of 360 nm or less to crystallize a thin film (Patent Document 7). Here, the light source for irradiating the thin film formed on the surface of the object to be coated is an ArF excimer laser, a KrF excimer laser, a XeCl excimer laser, a XeF excimer laser, a triple wave of a YAG laser, or 4 of a YAG laser. A precursor coating solution that is applied to the surface of an object to be coated using double wave light is an alkanolamine coordination compound of La, a carboxylate of Mn, and a metal or alkoxide of M having 1 to 1 carbon atoms. No. 4 is prepared by mixing and reacting in a primary alcohol. Recently, a technique using a nanoparticle photoreaction method in which nanoparticles are mixed with a precursor solution to promote the reaction has been developed (Patent Documents 8 and 9). In a general laser annealing method as a method for forming a polysilicon film, laser irradiation using a fluence of 100 mJ / cm 2 or more is often used, and crystal growth proceeds mainly by melt recrystallization at the time of laser irradiation. In the case of either the optical MOD method or the nanoparticle photoreaction method, the present inventors do not rely on melt recrystallization as the main driving factor for crystal growth, but the photochemical reaction at the reaction interface / particle interface (including the photoheating effect). Is a method of actively using. That is, it was found that crystal growth proceeds efficiently even if the temperature does not reach the melting temperature of the material.
基材上に固定化された光触媒材料もしくは、化学溶液法で作製された光触媒材料の前駆体に紫外線パルスレーザーを照射し、材料を溶融させずに表面形状を維持して結晶性を向上させることによって高い光触媒能を有する無機材料の形成方法を提供する。主として光触媒材料のナノ粒子を塗布して薄膜化し、表面に紫外線レーザー照射を行うことによって高機能化させる技術であるが、例えば、光触媒機能を有する無機材料のナノチューブ、ナノロッドなどのナノ構造を形成させた後に結晶性を向上させる後処理方法としても使用できる。また、化学溶液法で作製した前駆体膜からの光触媒材料の形成へも適用できる。これらはすなわち、形成した前駆体となる薄膜表面形状、あるいは構造体形状を大きく損なうことなく、光触媒材料表面近傍（深さ５００ｎｍ以内）の範囲に対して結晶成長かつ結晶子成長の促進を可能にすることを意味する。基板の耐熱温度を考慮して基板温度と照射フルエンスの制御を行えば基板材料にプラスチックなどの有機基板を用いることもできる。従来のレーザー照射による方法では、これら目的を満たすためのレーザー照射条件の限定が困難であった。本手法による光触媒材料の高機能化は光電気化学電池など光応答によって駆動する種々の光応答材料に展開することも可能である。つまり光応答性を有する材料は主として材料表面近傍の電子授受・輸送現象であり、本手法によって表面の結晶成長・粒成長が進めば、励起光照射時の電子輸送に有利であるため、広義の光応答材料に対して有効であると考えることは自明である。光触媒材料は表面の防曇効果を発現することも良く知られており、本発明の表面改質は防曇材料にも適用可能である。以下、光応答材料の一つとして光触媒を例に挙げて本発明の説明を記すが、その適用材料範囲は光化学電池、フォトクロミック材料などの光応答材料を含む。 Irradiate a photocatalyst material immobilized on a base material or a photocatalyst material precursor prepared by a chemical solution method with an ultraviolet pulse laser to maintain the surface shape without melting the material and improve crystallinity. Provides a method for forming an inorganic material having high photocatalytic activity. This is a technology that mainly applies photocatalyst material nanoparticles to form a thin film and irradiates the surface with ultraviolet laser irradiation to increase the functionality. For example, nanostructures such as nanotubes and nanorods of inorganic materials that have a photocatalytic function are formed. After that, it can be used as a post-treatment method for improving crystallinity. It can also be applied to the formation of a photocatalytic material from a precursor film produced by a chemical solution method. In other words, crystal growth and crystallite growth can be promoted in the vicinity of the surface of the photocatalyst material (within a depth of 500 nm) without greatly degrading the shape of the thin film surface or the structure as a precursor. It means to do. If the substrate temperature and irradiation fluence are controlled in consideration of the heat-resistant temperature of the substrate, an organic substrate such as plastic can be used as the substrate material. In the conventional laser irradiation method, it is difficult to limit the laser irradiation conditions to satisfy these purposes. The functional enhancement of the photocatalyst material by this method can be applied to various photoresponsive materials that are driven by photoresponse such as photoelectrochemical cells. In other words, photoresponsive materials are mainly electron transfer / transport phenomena near the surface of the material, and if crystal growth / grain growth on the surface proceeds by this method, it is advantageous for electron transport during excitation light irradiation. It is obvious to think that it is effective for photoresponsive materials. It is well known that the photocatalytic material exhibits a surface antifogging effect, and the surface modification of the present invention can be applied to the antifogging material. Hereinafter, the present invention will be described by taking a photocatalyst as an example of a photoresponsive material. The range of applicable materials includes photoresponsive materials such as photochemical cells and photochromic materials.
本発明は紫外レーザー照射を用いて光触媒材料前駆体の幾何学的構造を保ったまま表面の結晶成長、結晶子成長を促進させる。特に作製する光触媒材料のナノ粒子を含むコーティング剤を塗布した後、紫外レーザー照射を行う手法を説明するが、この手法によって用いられるレーザー照射条件は、薄膜以外にも、例えば陽極酸化法で得られた光触媒ナノチューブなどにも適用可能で形成された構造体表面の結晶成長を促進する。紫外レーザー照射のエネルギーの決定にはレーザー照射時における表面からの温度分布を一次元熱拡散モデルに従って計算し、光触媒材料の融解温度以下の温度に抑えるように基板温度とレーザーフルエンスを調整する。（本手法において実現するナノ秒パルス加熱では極めて短時間（１マイクロ秒以下）の加熱となるため、材料の融解温度は必ずしも一般的な対象材料の融点と一致せず、実際の融解温度は一般的融点の値を上回ると考えられるが、参考値として一般的な固体融点温度を利用し、その値を下回るようにフルエンス設定することが望ましい。）計算方法は次の偏微分方程式を用いる。
次に代表的な光触媒材料の一つである酸化タングステンを例に最適なレーザーフルエンスの決定法について説明する。酸化タングステンナノ粒子をガラス基板上に塗布し塗布膜厚を１２０ｎｍとした場合、基板温度を室温とすれば２６ｎｓのパルス幅を持つＫｒＦレーザーを５０ｍJ／ｃｍ２のフルエンスで照射したとき前駆体膜表面は４４ｎｓ後に最高温度に達し、おおよそ１０００℃程度に昇温すると計算される（図１）。この温度は酸化タングステンの融点、１４７３℃を大きく下回っているが、薄膜近傍では熱アニール処理では見られない著しい結晶子成長が確認され（図１）、Ｘ線の回折強度も増大した（図２）。これは所謂レーザーアニール処理で利用されるような溶融成長とは異なり、溶融を避けたフルエンス調整を行っている。そのため前述した前駆体の幾何学的構造を著しく損なうことなく結晶子増大を含む結晶性の向上を実現するものである。この利点は例えば光触媒材料のナノチューブ構造を形成した後、後処理方法として結晶性の向上を行うことが可能である。以上の最適なレーザーフルエンスの決定は材料と基材に関して上記の熱拡散方程式中の熱物性値と融解温度、材料厚によって制御されるべきものであるが、本発明においては照射レーザー波長に対して作製する材料の吸収が十分にある場合に（例えば５０％以上の照射光が吸収されるように材料に合わせて照射レーザー波長を選択）、そのフルエンスを３０〜１００ｍＪ／ｃｍ２に限定する。融解温度が１５００℃程度の場合にはフルエンスは３０〜８０ｍＪ／ｃｍ２に抑制することが好ましく、融解温度が１５００℃を超え２５００℃以下の材料に対しては５０〜１００ｍＪ／ｃｍ２の範囲でフルエンスを選択することができる。照射レーザー光を吸収すれば、上記の昇温が発生するため、材料表面にレーザー光が当たれば原理的に温度が上昇する。また、温度上昇は限定した３０〜１００ｍＪ／ｃｍ２の範囲内で表面から５００ｎｍ程度の範囲における温度上昇を融解温度以下の範囲内に収める制御が可能であるため、例えば２００ｎｍ以上径を持つ光触媒ナノチューブなどの構造体にもレーザー照射による表面改質プロセスは適用が可能である。 Next, a method for determining the optimum laser fluence will be described taking tungsten oxide, which is one of typical photocatalytic materials, as an example. When tungsten oxide nanoparticles are coated on a glass substrate and the coating thickness is 120 nm, the surface of the precursor film is irradiated with a KrF laser with a pulse width of 26 ns at a fluence of 50 mJ / cm 2 when the substrate temperature is room temperature. Is calculated to reach the maximum temperature after 44 ns and raise the temperature to about 1000 ° C. (FIG. 1). Although this temperature is much lower than the melting point of tungsten oxide, 1473 ° C., remarkable crystallite growth not observed in the thermal annealing treatment was confirmed in the vicinity of the thin film (FIG. 1), and the X-ray diffraction intensity increased (FIG. 2). ). This is different from melt growth used in so-called laser annealing treatment, and performs fluence adjustment that avoids melting. Therefore, it is possible to improve the crystallinity including crystallite increase without significantly deteriorating the geometric structure of the precursor described above. This advantage is that, for example, after the nanotube structure of the photocatalytic material is formed, the crystallinity can be improved as a post-treatment method. The determination of the optimum laser fluence as described above should be controlled by the thermophysical value, melting temperature, and material thickness in the above thermal diffusion equation for the material and the substrate. When the material to be manufactured has sufficient absorption (for example, the irradiation laser wavelength is selected according to the material so that 50% or more of the irradiation light is absorbed), the fluence is limited to 30 to 100 mJ / cm 2 . In the range of 50~100mJ / cm 2 for the fluence is preferably suppressed to 30~80mJ / cm 2, 2500 ℃ following materials melting temperature exceeds 1500 ° C. If the melting temperature is about 1500 ° C. A fluence can be selected. If the irradiation laser beam is absorbed, the above temperature rises. Therefore, if the laser beam hits the material surface, the temperature rises in principle. In addition, since the temperature rise can be controlled within a limited range of 30 to 100 mJ / cm 2 so that the temperature rise in the range of about 500 nm from the surface falls within the melting temperature or less, for example, a photocatalytic nanotube having a diameter of 200 nm or more The surface modification process by laser irradiation can also be applied to such a structure.
以上のような本願発明の特徴をまとめると、次のとおりである。
（１）紫外線パルスレーザー照射により基材上の光機能無機材料を処理する工程又は基材上の前駆体を処理して光機能無機材料とする工程で、対象材料が溶融しないようにレーザー照射フルエンスを３０〜１００ｍＪ／ｃｍ２の範囲で制御することを特徴とする光機能無機材料の表面改質方法。
（２）基材上の光機能無機材料の前駆体が、有機金属塩又はアルコキシド塩の塗布熱分解法又はゾルゲル法のいずれかにより作製された、アモルファス化していてもよい薄膜であり、有機金属塩又はアルコキシド塩の有機化合物は、β−ジケトナト、炭素数６以上の長鎖のアルコキシド、ハロゲンを含んでもよい有機酸塩から選ばれる１種であることを特徴とする（１）に記載した光機能無機材料の表面改質方法。
（３）基材上の光機能無機材料の前駆体が、対象材料のナノ粒子を分散させた溶液を塗布して形成された薄膜であることを特徴とする（１）に記載した光機能無機材料の表面改質方法。
（４）光機能無機材料が、酸化物、酸窒化物、窒化物、亜硫酸化物、又は硫化物の一種である（１）から（３）のいずれか１項に記載した光機能無機材料の表面改質方法。
（５）光機能無機材料が酸化タングステンＷＯ３である（１）から（３）のいずれか１項に記載した光機能無機材料の表面改質方法。
（６）レーザー照射フルエンスが３０〜８０ｍＪ／ｃｍ２であることを特徴とする（１）から（５）のいずれか１項に記載した光機能無機材料の表面改質方法。
（７）（１）から（６）のいずれか１項に記載の方法によって材料表面幾何学的構造を維持したまま、結晶子サイズを増大させて光機能が向上した光機能材であって、基材と基材上の光機能無機材料膜とを含み、該光機能無機材料膜は、レーザー照射部において表面部の結晶子サイズが内部に比して大きくなる傾斜的な結晶子サイズ分布を持つことを特徴とした光機能材。
（８）（７）に記載された光機能材を用い、光機能無機材料が光触媒である環境改善装置。
（９）（７）に記載された光機能材を用い、光機能無機材料が光触媒である光化学電池。
（１０）（７）に記載された光機能材を用い、光機能無機材料がフォトクロミック材料又はエレクトロクロミック材料である調光装置。
（１１）（７）に記載された光機能材を用い、光機能無機材料が光触媒であり、防曇性を具備する透光材。
The characteristics of the present invention as described above are summarized as follows.
(1) Laser irradiation fluence so that the target material does not melt in the process of processing the optical functional inorganic material on the substrate by ultraviolet pulse laser irradiation or the process of processing the precursor on the base material to make the optical functional inorganic material Is controlled in the range of 30 to 100 mJ / cm 2. A method for modifying the surface of an optical functional inorganic material.
(2) The precursor of the optically functional inorganic material on the substrate is a thin film which may be amorphized, prepared by either a coating pyrolysis method or a sol-gel method of an organic metal salt or alkoxide salt, and an organic metal The organic compound such as a salt or an alkoxide salt is one kind selected from β-diketonato, a long-chain alkoxide having 6 or more carbon atoms, and an organic acid salt that may contain a halogen. Surface modification method for functional inorganic materials.
(3) The optical functional inorganic described in (1), wherein the precursor of the optical functional inorganic material on the substrate is a thin film formed by applying a solution in which nanoparticles of the target material are dispersed Material surface modification method.
(4) The surface of the optical functional inorganic material according to any one of (1) to (3), wherein the optical functional inorganic material is one of oxide, oxynitride, nitride, sulfite oxide, or sulfide. Modification method.
(5) surface modification method of the optical functional inorganic material described in any one of the optical functional inorganic material is tungsten oxide WO 3 (1) (3).
(6) The surface modification method for an optically functional inorganic material according to any one of (1) to (5), wherein the laser irradiation fluence is 30 to 80 mJ / cm 2 .
(7) An optical functional material having an improved optical function by increasing the crystallite size while maintaining the material surface geometric structure by the method according to any one of (1) to (6), A substrate and a light functional inorganic material film on the substrate, wherein the light functional inorganic material film has a gradient crystallite size distribution in which a crystallite size of a surface portion is larger than that in a laser irradiation portion. Optical functional material characterized by having.
(8) An environment improvement device using the optical functional material described in (7), wherein the optical functional inorganic material is a photocatalyst.
(9) A photochemical battery using the optical functional material described in (7), wherein the optical functional inorganic material is a photocatalyst.
(10) A light control device using the optical functional material described in (7), wherein the optical functional inorganic material is a photochromic material or an electrochromic material.
(11) A translucent material using the optical functional material described in (7), wherein the optical functional inorganic material is a photocatalyst, and has antifogging properties.
本発明は、固定化された光触媒材料等の光機能無機材料に対して紫外線パルスレーザーを照射し光触媒能等の光機能を向上させることを可能にする発明である。本発明によれば、材料溶融を避けた照射レーザーのフルエンス制御を行い、材料表面の幾何学構造を大きく変化させることなく材料表面近傍の結晶成長を促進し結晶子サイズを増大させる。表面近傍の結晶子サイズの増大は光励起による電子の輸送を促進し、光触媒能を高めることが出来る。 The present invention is an invention that makes it possible to improve the optical functions such as the photocatalytic ability by irradiating the photofunctional inorganic material such as the immobilized photocatalytic material with an ultraviolet pulse laser. According to the present invention, the fluence control of the irradiation laser avoiding material melting is performed, crystal growth near the material surface is promoted and crystallite size is increased without greatly changing the geometric structure of the material surface. Increasing the crystallite size in the vicinity of the surface promotes electron transport by photoexcitation and can enhance the photocatalytic ability.
本発明を実施するための１つの好ましい形態は、基材上にコーティングされた光機能無機材料薄膜又は光機能無機材料の前駆体薄膜にパルス紫外レーザー光を照射することを特徴として表面結晶成長を行うものである。
光機能無機材料としては、光触媒無機材料、フォトクロミック無機材料等のように、照射される光に応答して所定の機能を果たす光応答性無機材料が挙げられるが、エレクトロクロミック無機材料のように、電気的な操作等によって所定の光機能を果たすものであっても良い。
光機能無機材料は、金属の酸化物、酸窒化物、窒化物、亜硫酸化物、硫化物の一種で、前述のような光機能を発揮するものであれば良い。該金属としては、例えば、Ｔｉ、Ｚｒ、Ｈｆ、Ｖ、Ｎｂ、Ｔａ、Ｃｒ、Ｍｏ、Ｗ、Ｍｎ、Ｔｃ、Ｒｅ、Ｆｅ、Ｃｏ、Ｎｉ、Ｒｕ、Ｒｈ等が挙げられる。特に酸化物が好適に使用でき、そのうちタングステン酸化物ＷＯ３を好適に用いることができる。
光機能無機材料の前駆体薄膜は、パルス紫外レーザー光の照射により光機能無機材料となるものであり、基材に有機金属溶液やゾルゲル溶液を塗布した後に乾燥、仮焼を経たアモルファス膜やあらかじめ作製された光触媒ナノ粒子を溶液化して基材に塗布したものでも良い。また、陽極酸化法などを用いて作製した光触媒ナノチューブなどの構造体であっても良い。
本発明で用いる紫外光としては、パルスレーザ光であるエキシマレーザを挙げることができる。エキシマレーザとしては、波長４００ｎｍ以下のＡｒＦ、ＫｒＦ、ＸｅＣｌ、ＸｅＦ、Ｆ２等から選ぶことができる。紫外光照射は、目的に応じて、所定の工程途中や各工程の前後を選ぶことが出来る。
One preferred mode for carrying out the present invention is to perform surface crystal growth by irradiating a light functional inorganic material thin film coated on a substrate or a precursor thin film of a light functional inorganic material with a pulsed ultraviolet laser beam. Is what you do.
Examples of the photofunctional inorganic material include a photoresponsive inorganic material that performs a predetermined function in response to irradiated light, such as a photocatalytic inorganic material, a photochromic inorganic material, and the like. A predetermined optical function may be achieved by electrical operation or the like.
The optical functional inorganic material is one of metal oxides, oxynitrides, nitrides, sulfites, and sulfides, as long as it exhibits the optical functions as described above. Examples of the metal include Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Co, Ni, Ru, and Rh. In particular, an oxide can be preferably used, and tungsten oxide WO 3 can be preferably used.
The precursor thin film of the optical functional inorganic material becomes an optical functional inorganic material by irradiation with pulsed ultraviolet laser light. After applying an organic metal solution or a sol-gel solution to the base material, an amorphous film or a preliminarily dried and calcined film is used. The produced photocatalyst nanoparticles may be made into a solution and applied to a substrate. Further, it may be a structure such as a photocatalyst nanotube produced by using an anodic oxidation method or the like.
As the ultraviolet light used in the present invention, an excimer laser which is a pulse laser beam can be exemplified. The excimer laser can be selected from ArF, KrF, XeCl, XeF, F 2 and the like having a wavelength of 400 nm or less. Irradiation with ultraviolet light can be performed during a predetermined process or before and after each process depending on the purpose.
紫外レーザー照射条件は前述したパルス光照射時における熱拡散をシミュレートして決定することが望ましく、対象材料の融解温度以下の温度になるようにフルエンスを設定する。本発明においてはレーザーフルエンスを３０〜１００ｍＪ／ｃｍ２と限定する。照射レーザー波長に対して作製する材料の吸収が例えば５０％以上の吸収を持つ場合には、対象材料の融解温度が１５００℃程度の場合にはフルエンスは３０〜８０ｍＪ／ｃｍ２に抑制することが好ましく、融解温度が１５００℃を超え２５００℃以下の材料に対しては５０〜１００ｍＪ／ｃｍ２の範囲でフルエンスを選択することが望ましい。１００ｍＪ／ｃｍ２を超えるフルエンスは特に低融点材料の場合、強いレーザーアブレーションを引き起こし表面形状を損なう恐れがある。また、３０ｍＪ／ｃｍ２以下のフルエンスの場合、多くの場合、十分な結晶子サイズの増大に寄与しない場合が多く、本発明の目的に対しては好ましくない。 The ultraviolet laser irradiation conditions are desirably determined by simulating the thermal diffusion during the pulse light irradiation described above, and the fluence is set so that the temperature is equal to or lower than the melting temperature of the target material. In the present invention, the laser fluence is limited to 30 to 100 mJ / cm 2 . In the case where the absorption of the material to be produced with respect to the irradiation laser wavelength has absorption of 50% or more, for example, when the melting temperature of the target material is about 1500 ° C., the fluence is suppressed to 30 to 80 mJ / cm 2. Preferably, it is desirable to select a fluence in the range of 50 to 100 mJ / cm 2 for a material having a melting temperature exceeding 1500 ° C. and not more than 2500 ° C. A fluence exceeding 100 mJ / cm 2 may cause strong laser ablation and damage the surface shape, particularly in the case of a low melting point material. Further, in the case of a fluence of 30 mJ / cm 2 or less, in many cases, it does not contribute to a sufficient increase in crystallite size, which is not preferable for the purpose of the present invention.
例えば、基材上に前駆体薄膜を形成する手段としては、塗布熱分解法等、ゾルゲル法などの化学溶液法が金属有機化合物の光反応が結晶成長を促進させること、製膜雰囲気の制限が少なく大面積化が容易なこと等から、化学溶液法が望ましい。化学溶液法は、スピンコート法、ディップ法、スプレー法、インクジェット法を含む化学溶液法を基にした前駆溶液塗布手法を用いるものであり、上記組成を生成する金属有機化合物の溶液をスピンコート、スプレー等の塗布法やインクジェット法等により基板上に塗布、乾燥後、金属有機化合物中の有機成分を分解して非晶質薄膜を形成する。金属有機化合物としては、好ましくは、有機金属塩やアルコキシド塩が挙げられ、その有機化合物としては、β−ジケトナト、炭素数６以上の長鎖のアルコキシド、ハロゲンを含んでもよい有機酸塩が挙げられる。そのような有機酸としては、２−エチルヘキサン酸、ナフテン酸、カプリル酸、ステアリン酸等が挙げられる。金属有機化合物中の有機成分の分解は、例えば、３００〜６００℃の温度に加熱保持することによる仮焼成、紫外ランプによる紫外光照射等により行うことができる。また、前駆体溶液は対象材料自身のナノ粒子を含んでいた方が好ましい。もしくは対象材料の結晶成長を促進する、すなわち結晶格子ミスマッチの小さな類似結晶構造を持つ材料のナノ粒子を導入することも有効である。コーティングによって形成した前駆体膜（あるいは構造体）に紫外線レーザーを照射すれば照射レーザー強度にも依存するが、５００ｎｍ以下の深さに対して結晶子サイズの増大が期待できる。コーティング厚を増大させる必要がある場合には塗布と光照射を繰り返し行うことによって膜厚を増大させることが望ましい。また、レーザー照射後には照射表面から結晶子サイズが増大し深部はそれに比して結晶子サイズが小さくなることが本手法を用いた場合の材料の特徴となる。例えば、膜厚を増大させるために複数回コーティングと照射を繰り返した場合においても結晶子サイズは最深部が最も小さくなることが特徴となる。
本発明の表面改質方法により得られた光機能無機材料膜を含む光機能材は、各種の用途に用いることが可能である。光機能無機材料が光触媒である場合、空気浄化機能、浄水機能、抗菌機能、防汚機能、脱臭機能等を奏するので、各種の環境改善装置として使用できることは勿論、光触媒の親水性化機能を利用した防曇性を有する各種透明材や、光触媒機能を利用した光化学電池等にも使用できる。また、光機能無機材料がフォトクロミック材料やエレクトロクロミック材料である場合、各種の調光装置として使用することができる。
For example, as a means for forming a precursor thin film on a substrate, a chemical solution method such as a coating pyrolysis method, such as a sol-gel method, promotes the crystal growth by the photoreaction of a metal organic compound, and limits the film forming atmosphere. The chemical solution method is desirable because it is easy to increase the area and is small. The chemical solution method uses a precursor solution coating method based on a chemical solution method including a spin coating method, a dip method, a spray method, and an ink jet method, and spin-coats a solution of a metal organic compound that generates the above composition. After applying and drying on a substrate by a coating method such as spraying or an inkjet method, the organic component in the metal organic compound is decomposed to form an amorphous thin film. The metal organic compound is preferably an organic metal salt or an alkoxide salt, and examples of the organic compound include β-diketonato, a long-chain alkoxide having 6 or more carbon atoms, and an organic acid salt which may contain a halogen. . Examples of such an organic acid include 2-ethylhexanoic acid, naphthenic acid, caprylic acid, stearic acid, and the like. The decomposition of the organic component in the metal organic compound can be performed by, for example, temporary baking by heating and holding at a temperature of 300 to 600 ° C., ultraviolet light irradiation by an ultraviolet lamp, or the like. Moreover, it is preferable that the precursor solution contains nanoparticles of the target material itself. Alternatively, it is also effective to introduce nanoparticles of a material that promotes crystal growth of the target material, that is, has a similar crystal structure with a small crystal lattice mismatch. If the precursor film (or structure) formed by coating is irradiated with an ultraviolet laser, an increase in crystallite size can be expected for a depth of 500 nm or less, depending on the irradiation laser intensity. When it is necessary to increase the coating thickness, it is desirable to increase the film thickness by repeating application and light irradiation. In addition, after laser irradiation, the crystallite size increases from the irradiated surface, and the crystallite size becomes smaller in the deep part compared to that, which is a feature of the material when this method is used. For example, even when coating and irradiation are repeated a plurality of times in order to increase the film thickness, the crystallite size is characterized in that the deepest part is the smallest.
The optical functional material including the optical functional inorganic material film obtained by the surface modification method of the present invention can be used for various applications. When the photofunctional inorganic material is a photocatalyst, it has air purification function, water purification function, antibacterial function, antifouling function, deodorization function, etc. It can also be used for various transparent materials having antifogging properties, photochemical cells utilizing a photocatalytic function, and the like. Further, when the optical functional inorganic material is a photochromic material or an electrochromic material, it can be used as various light control devices.
以下、本発明の具体例を示し、さらに詳しく説明するが、本発明はこれら実施例に限定されるものではない。本発明の実施例で使用した基板は、無アルカリガラス基板であり、原料溶液は、ＷＯ３溶液を用いた。紫外光照射は、ＫｒＦエキシマレーザを用いた。 Hereinafter, specific examples of the present invention will be shown and described in more detail, but the present invention is not limited to these examples. The substrate used in the examples of the present invention was a non-alkali glass substrate, and the raw material solution was a WO 3 solution. For irradiation with ultraviolet light, a KrF excimer laser was used.
（実施例１）
ＷＯ３粉末（粒径数ミクロン以上）を湿式ビーズミル粉砕し、ナノ粒子溶液（粒子形状１０−３０ｎｍ）とした後、ガラス基板上に塗布、乾燥後、室温でＫｒＦエキシマレーザを５０ｍＪ／ｃｍ２のエネルギーで７５００パルス照射することにより、結晶化が促進され、形成したＷＯ３薄膜表面近傍の結晶子サイズが前駆体として導入したナノ粒子径と比較して２倍以上に増大した。（図３）一方、同ＷＯ３ナノ粒子溶液を塗布した前駆体膜を５００℃の炉中で焼成して得られたＷＯ３薄膜では粒界の固着はあっても粒子サイズを増大させるような成長には至っていない。（図３）両者の光触媒能を太陽光強度に近い１００ｋＬｕｘの可視光（３００Ｗキセノン光源の４００ｎｍ以上の波長を利用）を励起光源として評価した。ＷＯ３薄膜表面は硫酸銅水溶液中で処理しＣｕイオンで修飾した。評価にはメチレンブルー水溶液を用い、その分解速度を検討したところ、レーザー照射によって得られたＷＯ３膜において熱処理膜と比較して約２.８倍以上分解速度が向上した。（図４）
Example 1
A WO 3 powder (particle size of several microns or more) is pulverized by wet bead milling to form a nanoparticle solution (particle shape 10-30 nm), coated on a glass substrate, dried, and then subjected to KrF excimer laser at 50 mJ / cm 2 at room temperature. By irradiating 7500 pulses with energy, crystallization was promoted, and the crystallite size in the vicinity of the surface of the formed WO 3 thin film increased more than twice compared with the nanoparticle diameter introduced as a precursor. (FIG. 3) On the other hand, in the WO 3 thin film obtained by firing the precursor film coated with the WO 3 nanoparticle solution in a furnace at 500 ° C., the particle size increases even though the grain boundary is fixed. It has not reached growth. (FIG. 3) The photocatalytic ability of both was evaluated using 100 kLux visible light (using a wavelength of 400 nm or more of a 300 W xenon light source) close to sunlight intensity as an excitation light source. The surface of the WO 3 thin film was treated with an aqueous copper sulfate solution and modified with Cu ions. When the methylene blue aqueous solution was used for evaluation and the decomposition rate was examined, the decomposition rate was improved about 2.8 times or more in the WO 3 film obtained by laser irradiation as compared with the heat-treated film. (Fig. 4)
（実施例２）
市販ＷＯ３粉末とイソプロパノールを混合した溶液（Ｃ１）を作製した。Ｃ１溶液をビーズミルで湿式粉砕して得られたＷＯ３ナノ粒子溶液（粒子サイズ１０−３０ｎｍ）を無アルカリガラス基板に３０００ｒｐｍ、１０秒間でスピンコートし、１００℃で１０分間乾燥した。この工程を５回繰り返した後、室温、大気中で２６ｎｓのＤｕｒａｔｉｏｎを持つＫｒＦパルスレーザをフルエンス:５０ｍＪ／ｃｍ２（５０Ｈｚ）で１５０秒照射した。このようにして作製した膜についてレーザー照射部のみ結晶成長が確認された。得られたＷＯ３膜は薄膜表面の結晶子が原料粒子の２倍以上に粗大成長していることが明らかになった。作製したＷＯ３膜表面を硫酸銅水溶液で処理することによって表面をＣｕイオンで修飾した後、太陽光強度に近い１００ｋＬｕｘの可視光（３００Ｗキセノン光源の４００ｎｍ以上の波長を利用）を励起光源とし、メチレンブルー水溶液を用いて光触媒能を評価したところ熱処理膜（５００℃）の約２.８倍の分解速度が得られた。
(Example 2)
A solution (C1) obtained by mixing commercially available WO 3 powder and isopropanol was prepared. A WO 3 nanoparticle solution (particle size: 10-30 nm) obtained by wet pulverizing the C1 solution with a bead mill was spin-coated on an alkali-free glass substrate at 3000 rpm for 10 seconds and dried at 100 ° C. for 10 minutes. After this process was repeated 5 times, a KrF pulse laser having a duration of 26 ns was irradiated at a fluence of 50 mJ / cm 2 (50 Hz) for 150 seconds in the air at room temperature. In the film thus produced, crystal growth was confirmed only in the laser irradiated portion. It was revealed that the obtained WO 3 film had crystallites grown on the surface of the thin film as coarse as twice or more of the raw material particles. After the surface of the prepared WO 3 film is modified with Cu ions by treating with a copper sulfate aqueous solution, 100 kLux visible light (using a wavelength of 400 nm or more of a 300 W xenon light source) close to sunlight intensity is used as an excitation light source, When the photocatalytic activity was evaluated using an aqueous methylene blue solution, a decomposition rate about 2.8 times that of the heat-treated film (500 ° C.) was obtained.
（実施例３）
実施例２において、レーザの照射時間を３０秒にした場合、照射部のみ結晶成長が確認され、実施例２同様の後処理及び光触媒能を測定したところ熱処理膜（５００℃）の約２.７倍の分解速度が得られた。
(Example 3)
In Example 2, when the laser irradiation time was 30 seconds, crystal growth was confirmed only in the irradiated part, and post-treatment and photocatalytic activity as in Example 2 were measured. As a result, about 2.7 of the heat-treated film (500 ° C.) was measured. Double degradation rate was obtained.
（実施例４）
実施例２において、レーザの照射時間を６秒にした場合、照射部のみ結晶成長が確認され、実施例２同様の後処理及び光触媒能を測定したところ熱処理膜（５００℃）の約２.１倍の分解速度が得られた。
Example 4
In Example 2, when the laser irradiation time was set to 6 seconds, crystal growth was confirmed only in the irradiated part, and post-treatment and photocatalytic activity as in Example 2 were measured. As a result, about 2.1 of the heat-treated film (500 ° C.) was measured. Double degradation rate was obtained.
（実施例５）
実施例４において、基板をＰＥＴ（ポリエチレンテレフタラート）にした場合、照射部のみ結晶成長が確認された。
(Example 5)
In Example 4, when the substrate was made of PET (polyethylene terephthalate), crystal growth was confirmed only in the irradiated area.
（参考例１）
実施例２において、レーザのフルエンス: ２０ｍＪ／ｃｍ２で照射した場合、照射部の有意な結晶成長は確認できなかった。
(Reference Example 1)
In Example 2, when irradiation was performed at a laser fluence of 20 mJ / cm 2 , significant crystal growth in the irradiated portion could not be confirmed.
（参考例２）
実施例２において、レーザのフルエンス: １１０ｍＪ／ｃｍ２で照射した場合、照射部はレーザーアブレーションによって失われ、Ｘ線の回折強度は減少した。
(Reference Example 2)
In Example 2, when irradiation was performed at a laser fluence of 110 mJ / cm 2 , the irradiated portion was lost by laser ablation, and the X-ray diffraction intensity decreased.
（参考例３）
実施例２において、レーザー照射工程の変わりに電気炉中で１００℃で加熱処理を行ったところＸ線回折強度も増大せず処理前と変化は確認できなかった。
(Reference Example 3)
In Example 2, when heat treatment was performed at 100 ° C. in an electric furnace instead of the laser irradiation step, the X-ray diffraction intensity did not increase and no change from before the treatment could be confirmed.
（参考例４）
実施例２において、レーザー照射工程の変わりに電気炉中で５００℃で加熱処理を行ったところＸ線強度は増大し、塗布前と比して結晶性は向上したものの結晶子サイズの著しい増大は観測されなかった。実施例２同様の後処理と光触媒能を測定したところ実施例２と比較して３５％の分解速度であった。
(Reference Example 4)
In Example 2, when the heat treatment was performed at 500 ° C. in an electric furnace instead of the laser irradiation process, the X-ray intensity increased, and although the crystallinity was improved as compared with before coating, the crystallite size was significantly increased. Not observed. The post-treatment and photocatalytic ability as in Example 2 were measured and the decomposition rate was 35% compared with Example 2.
本発明により現在用いられている光触媒材料に対して表面改質による光触媒能の向上が期待される。光触媒は既に広く応用されているとおり、水素製造などのエネルギー創出や環境浄化、表面親水化による防曇材料などに用いることが出来る。光触媒材料の光応答性を使った光化学電池やフォトクロミック材料などの高機能化も可能である。 The photocatalytic material currently used by the present invention is expected to improve the photocatalytic performance by surface modification. As already widely applied, the photocatalyst can be used for energy creation such as hydrogen production, environmental purification, and antifogging material by surface hydrophilization. It is possible to enhance the functionality of photochemical batteries and photochromic materials that use the photoresponsiveness of photocatalytic materials.
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