JP3980370B2 - Method for producing Ni porous body having nanopore structure - Google Patents
Method for producing Ni porous body having nanopore structure Download PDFInfo
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- JP3980370B2 JP3980370B2 JP2002037761A JP2002037761A JP3980370B2 JP 3980370 B2 JP3980370 B2 JP 3980370B2 JP 2002037761 A JP2002037761 A JP 2002037761A JP 2002037761 A JP2002037761 A JP 2002037761A JP 3980370 B2 JP3980370 B2 JP 3980370B2
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Description
【０００１】
【産業上の利用分野】
本発明は、Ｎｉの活性度を最大限利用して機能性を格段に向上させ、触媒，吸着剤，ガス吸蔵材，コンデンサ，選択透過膜等の機能材料として有用なＮｉ多孔質体を製造する方法に関する。
【０００２】
【従来の技術】
炭化水素の分解，付加，置換反応に使用されるＮｉ触媒は、表面反応によって分解，付加，置換反応が律速されることから比表面積の大きなものほど触媒活性が高くなる。比表面積の大きなＮｉ触媒は、高分子マトリックスに原子，イオン，分子等の化学種を分散させ，高温焼成することにより製造されている。得られたＮｉ触媒は、スポンジ状の化学種／高分子複合体，化学種／炭素複合体，化学種の酸化物になっており、大きな比表面積をもつ。
比表面積の大きなＮｉ多孔質体は、他の触媒反応や有害ガスの分解・吸着，天然ガスの改質反応，各種ガスセンサ，エネルギー蓄積用コンデンサ，選択透過膜等としても使用されている。これらの用途でも、比表面積が高いほどＮｉ多孔質体の機能性が向上する。
【０００３】
【発明が解決しようとする課題】
従来の方法でＮｉ多孔質体を製造するとき、高温焼成時にＮｉ粒子が相互に凝集しやすい。Ｎｉ粒子の凝集により多孔質化に制約が加わり、ナノメータオーダの微細孔をもつＮｉ多孔質体になりがたい。また、化学種の分散用マトリックスとして用いた高分子が高温焼成時に炭化してＮｉ多孔質体に残留し、機能低下を引き起こしやすい。高分子化合物の残留なくＮｉ多孔質体をナノ細孔構造にできると、比表面積が飛躍的に大きくなり、従来の多孔質機能材料に比較して格段に優れた性能の発現が予想される。
【０００４】
たとえば、Ｎｉ多孔質体を触媒に使用する場合、大きな比表面積のため表面反応が活発に進行し、反応の促進，分解・合成の効率化が図られる。次世代エネルギーとして有望視されている水素の貯蔵材にあっては、大きな比表面積に起因して貯蔵可能な水素量が増加し、車載用燃料電池用水素貯蔵材として適用できる程度に小型・高性能化が達成される。水素燃料電池のセパレータとしても単位面積当りの水素処理能力が大きくなり、高出力の水素燃料電池が得られる。
【０００５】
【課題を解決するための手段】
本発明は、このような要求に応えるべく案出されたものであり、熱分解が容易なポリビニルアルコールを分散用マトリックスに使用し、ポリビニルアルコールの熱分解で生じた空間を微細孔とすることにより、触媒，吸着剤，ガス吸蔵材，コンデンサ，選択透過膜等の機能性向上に有効なナノ細孔構造をもち、残留炭素のないＮｉ多孔質体を得ることを目的とする。
【０００６】
本発明のＮｉ多孔質体製造方法は、その目的を達成するため、ポリビニルアルコールの乾燥フィルムにニッケル化合物を分散吸着させた後、還元性又は非酸化性雰囲気中で加熱することによりポリビニルアルコールフィルムを消失させると共にニッケル化合物を金属Ｎｉに還元することを特徴とする。
ポリビニルアルコールとしては、側鎖官能基の８０％以上がヒドロキシル基で、鹸化度８０％以上，数平均分子量５００〜２００００のポリビニルアルコールが好ましい。ニッケル化合物には、酢酸ニッケル，蓚酸ニッケル，酪酸ニッケル等の有機酸塩の他に、硫酸ニッケル，硝酸ニッケル，塩化ニッケル，リン酸ニッケル等の無機酸塩も使用できる。
【０００７】
ニッケル化合物を分散吸着させたポリビニルアルコールフィルムを５００℃以上の温度で加熱焼成すると、還元反応が促進されニッケル化合物が効率よく金属Ｎｉまでに還元される。ポリビニルアルコールを消失させる加熱焼成工程とは別工程で多孔質体を加熱還元することによっても、ニッケル化合物が金属状態に還元されたＮｉ多孔質体を製造できる。
【０００８】
【作用】
ポリビニルアルコールは、比較的低温で熱分解を開始し、分解残渣が少なく造膜製に優れた材料である。本発明では、このような特徴を活用してポリビニルアルコールを分散用マトリックスに使用した。ポリビニルアルコールは、原子，イオン，分子等に対して強い吸着場を与える上でも有効な分散用マトリックスである。そのため、ポリビニルアルコールにＮｉソースを含浸させると、Ｎｉソースは互いに凝集することなく均質分散される。
【０００９】
Ｎｉイオンをポリマー側鎖に選択的に取り込むためには、ポリビニルアルコールをフィルム化する必要がある。ポリマーのフィルム化にはポリビニルアルコールの重合度，鹸化度を高くして溶媒に溶けてしまうことを防止することが重要であるが、過度に重合度を高くすると溶媒に対するポリビニルアルコールの分散度が劣り、取扱いも困難になる。そのため、ポリビニルアルコールの数平均分子量が５００〜２００００となるように重合度を調整し、鹸化度を８０％以上に調整することが好ましい。重合度、鹸化度が適正に調整されたポリビニルアルコールから造膜されたフィルムは、側鎖官能基にＮｉイオンを選択的に結合させ、後工程の加熱処理時においてもＮｉ相互の焼結凝集を防止し、ナノ細孔構造の形成に働く。
【００１０】
Ｎｉイオンは、ヒドロキシル基にＮｉイオンが配位結合することによりポリビニルアルコールに選択結合される。Ｎｉイオンの効果的な選択結合を実現させる上では、ポリビニルアルコールの側鎖官能基がアルキル基等で置換されておらず、８０％以上がヒドロキシル基の側鎖が好ましい。
【００１１】
分散用マトリックスは、ガラス等の適宜の基板上にポリビニルアルコール溶液を展開し、室温乾燥で造膜するキャスト法で用意される。ポリビニルアルコール溶液には、ポリマー分子間の相互作用に起因するゲル化を防止するため、ヒドロキシル基の保護剤として (ＮＨ4)2ＨＰＯ4が必要に応じ添加される。得られたポリビニルアルコールフィルムは多数のミクロ孔，メソ孔をもち、分子吸着能が強化された細孔壁が無数に形成される。
【００１２】
ポリビニルアルコールフィルム（分散用マトリックス）を洗浄，乾燥した後、Ｎｉソースを含浸させる。Ｎｉソースとしては、比較的マイルドな環境下で金属Ｎｉに還元される有機酸塩，無機酸塩が挙げられる。具体的には、酢酸ニッケル，蓚酸ニッケル，酪酸ニッケル等の有機酸塩や、硫酸ニッケル，硝酸ニッケル，塩化ニッケル，リン酸ニッケル等の無機酸塩がある。
【００１３】
Ｎｉソースの含浸に際しては、Ｎｉソース含有溶液にポリビニルアルコールフィルムを浸漬する方法，ポリビニルアルコールフィルムを透過してＮｉソース含有溶液を流動させる方法等の液相法が採用される。或いは、蒸気化したＮｉソースをポリビニルアルコールフィルムに送り込み、ポリビニルアルコールとＮｉソースとの接触でＮｉソースをポリビニルアルコールフィルムに吸着させる気相法も採用可能である。
【００１４】
Ｎｉソースを含浸させたポリビニルアルコールフィルムを還元性又は非酸化性雰囲気下で加熱焼成すると、ポリビニルアルコールが熱分解して消失する。還元性雰囲気には水素ガス，水素含有ガス等が使用される。ポリビニルアルコールの熱分解で生じる炭化物が還元作用を呈するため、窒素ガス，不活性ガス等の非酸化性雰囲気も使用できる。
【００１５】
Ｎｉソース含浸ポリビニルアルコールフィルムから熱分解によってポリビニルアルコールが消失すると、ポリビニルアルコールの消失個所が微細孔になる。このとき、高度の分散性でＮｉソースが吸着しているポリビニルアルコールフィルムを還元焼成するため、Ｎｉソース又は金属Ｎｉが凝集することなく、ポリビニルアルコールの痕跡が微細孔として確保されたナノ細孔構造が現出する。また、比表面積の大きな金属は一般的に酸化されやすいが、金属表面の活性点がポリビニルアルコールの熱分解で生成した炭素で終端するため、得られるＮｉ多孔質体の耐酸化性が極めて高くなる。金属表面の活性点が炭素で終端していることは、還元反応で生じた金属Ｎｉの凝集が抑制される原因の一つとも推察される。
【００１６】
【実施例】
ポリビニルアルコールに１０質量％の割合で(ＮＨ4)2ＰＯ4を混合し、蒸留水に溶解することにより濃度１０質量％のポリビニルアルコール水溶液を用意した。ポリビニルアルコール水溶液８０ｍｌをガラス基板上に滴下し、室温で１週間静置させて乾燥することにより、膜厚２ｍｍのポリビニルアルコールフィルムを作製した。次いで、ポリビニルアルコールフィルムを１Ｎ−ＮａＯＨ水溶液に２４時間浸漬し、Ｎｉ化合物：Ｎｉ(ＯＨ)2としてポリマー中に固定した。その後，常温下、純水で洗浄し、室温で乾燥させた。
【００１７】
造膜されたポリビニルアルコールフィルムは、弾力性のある緑色のフィルムであった。フィルムの弾力性は、ポリビニルアルコール側鎖のヒドロキシル基と水素結合を介して相互作用する水分子の残存を示唆している。ヒドロキシル基と相互作用している水分子は室温乾燥で除去されないので、次の含浸過程におけるポリビニルアルコールとニッケル溶液との馴染み性を向上させ、ポリビニルアルコールフィルムへのＮｉイオンの取込みをスムーズに進行させる。
【００１８】
硝酸ニッケルをＮｉソースに用い、濃度３０質量％の硝酸ニッケル水溶液を用意した。硝酸ニッケル水溶液にポリビニルアルコールフィルムを７２時間浸漬し、Ｎｉイオンをポリビニルアルコールフィルムに吸着させた。次いで、１Ｎ−ＮａＯＨ水溶液にポリビニルアルコールフィルムを７２時間浸漬した後、蒸留水で洗浄し、室温で乾燥することによりＮｉ(ＯＨ)2が分散したポリビニルアルコールフィルムを得た。
Ｎｉ(ＯＨ)2分散ポリビニルアルコールフィルムを石英管に装入し、流量１０ｃｃ／ｍｌで窒素ガスを石英管に送り込みながら加熱焼成した。得られるＮｉ多孔質体に及ぼす焼成温度の影響を調査するため、２００〜６５０℃の範囲で焼成温度を変更した。
【００１９】
焼成後の各試料について容量法（−１９６℃）で窒素吸収等温線を求めると共に、Ｘ線吸収スペクトルから微細構造を測定し、Ｘ線光電子分光法で分光スペクトルを測定した。
窒素吸収等温線の測定結果を示す図１にみられるように、何れの焼成温度で得られたＮｉ多孔質体も低相対圧部で窒素吸収等温線が急激に立ち上がっていた。窒素吸収等温線の急激な立上りは、口径２ｎｍ以下のミクロ孔が存在していることを意味する。また、吸着時（図中、黒点で示す）と脱着時（図中、白点で示す）で窒素吸収等温線が一致しないヒステリシスが観測され、口径２〜５０ｎｍのメソ孔が共存することが確認された。メソ孔は、ＤＨ法（Dollimore-Heal法）で求められたメソ細孔分布（図２）から細孔口径約４ｎｍをピークとし、３〜７.４ｎｍ程度の細孔分布をもっていた。
窒素吸収等温線から決定した表面積を表１に示す。表１から，本発明で得られたＮｉ多孔質体は、非常に大きな表面積をもつことが判る。
【００２０】
Ｘ線吸収微細構造の測定結果を示す図３にみられるように、２００〜４００℃の焼成温度で得られた多孔質体がＮｉＯの電子状態と同じ構造をもっていたが、５００〜６５０℃の焼成温度で得られた多孔質体では金属Ｎｉと同じ電子状態になっていた。この結果は、焼成温度を５００℃以上に設定するとき、ＮｉＯが還元されて金属Ｎｉになることを示している。焼成温度６５０℃で得られたＮｉ多孔質体をＸ線光電子分光法でスペクトル分析したところ、表面酸素官能基に由来するＯ１ｓピークがほとんど観測されなかった。図４の結果は、酸素に対する表面の反応性が極めて低く、耐酸化性に優れたＮｉ多孔質体であることを示している。
【００２２】
【発明の効果】
以上に説明したように、本発明においては、原子，イオン，分子等に対して強い吸着場を与える物質にポリビニルアルコールフィルムを使用することにより、高度な分散状態でニッケル化合物がポリビニルアルコールフィルムに吸着される。しかも、ポリビニルアルコールが加熱消失する際に生成する炭素が還元作用を呈するので、還元性雰囲気で加熱焼成しなくてもニッケル化合物が金属Ｎｉに還元される。このようにして得られるＮｉ多孔質体は、ポリビニルアルコールの痕跡がナノメータオーダの微細孔となり、従来のスポンジ状ニッケルに比較して格段に比表面積の大きなナノ細孔構造をもつ。そのため、Ｎｉ本来の活性作用が効果的に発現され、機能性が大幅に改善された触媒，吸着剤，ガス吸蔵材，コンデンサ，選択透過膜等の機能材料として使用される。
【図面の簡単な説明】
【図１】 Ｎｉ(ＯＨ)2分散ポリビニルアルコールフィルムを加熱焼成して得られた薄膜の窒素吸収等温線に焼成温度が及ぼす影響を表したグラフ
【図２】 焼成温度がメソ細孔分布に及ぼす影響を表したグラフ
【図３】 Ｎｉ(ＯＨ)2分散ポリビニルアルコールフィルムを加熱焼成して得られた薄膜（ａ）のＸ線吸収微細構造を標準試料（ｂ）と対比したグラフ
【図４】 Ｎｉ(ＯＨ)2分散ポリビニルアルコールフィルムを加熱焼成して得られた薄膜（ａ）のＸ線光電子分光法スペクトルを標準試料（ｂ）と対比したグラフ[0001]
[Industrial application fields]
The present invention remarkably improves functionality by making maximum use of the activity of Ni, and manufactures a Ni porous body useful as a functional material such as a catalyst, an adsorbent, a gas storage material, a capacitor, and a permselective membrane. Regarding the method.
[0002]
[Prior art]
Ni catalysts used for hydrocarbon decomposition, addition, and substitution reactions are rate-determined by surface reactions, so that the larger the specific surface area, the higher the catalytic activity. Ni catalysts having a large specific surface area are produced by dispersing chemical species such as atoms, ions, and molecules in a polymer matrix and firing them at a high temperature. The obtained Ni catalyst is a sponge-like chemical species / polymer composite, chemical species / carbon composite, or chemical species oxide, and has a large specific surface area.
Ni porous bodies having a large specific surface area are also used as other catalytic reactions, decomposition / adsorption of harmful gases, natural gas reforming reactions, various gas sensors, capacitors for energy storage, permselective membranes, and the like. Even in these applications, the functionality of the Ni porous body improves as the specific surface area increases.
[0003]
[Problems to be solved by the invention]
When a Ni porous body is produced by a conventional method, Ni particles tend to aggregate together during high-temperature firing. Due to the aggregation of Ni particles, restrictions are imposed on the porous structure, and it is difficult to obtain a Ni porous body having fine pores on the order of nanometers. In addition, the polymer used as the matrix for dispersing the chemical species is carbonized during high-temperature firing and remains in the Ni porous body, which tends to cause functional deterioration. If the Ni porous body can be made to have a nanopore structure without the polymer compound remaining, the specific surface area is remarkably increased, and it is expected that the performance will be remarkably superior to that of the conventional porous functional material.
[0004]
For example, when a Ni porous body is used as a catalyst, the surface reaction actively proceeds due to the large specific surface area, thereby promoting the reaction and improving the efficiency of decomposition and synthesis. Hydrogen storage materials, which are considered promising as next-generation energy, increase the amount of hydrogen that can be stored due to the large specific surface area, and are small and high enough to be applicable as hydrogen storage materials for automotive fuel cells. Performance is achieved. As a separator of a hydrogen fuel cell, the hydrogen processing capacity per unit area is increased, and a high output hydrogen fuel cell can be obtained.
[0005]
[Means for Solving the Problems]
The present invention has been devised to meet such demands. By using polyvinyl alcohol, which is easily pyrolyzed, as a dispersion matrix, the space generated by the pyrolysis of polyvinyl alcohol is made into micropores. An object of the present invention is to obtain a Ni porous body having a nanopore structure effective for improving the functionality of a catalyst, an adsorbent, a gas storage material, a capacitor, a permselective membrane and the like and having no residual carbon.
[0006]
In order to achieve the object of the method for producing a porous Ni body of the present invention, after a nickel compound is dispersed and adsorbed on a dry film of polyvinyl alcohol, the polyvinyl alcohol film is heated by heating in a reducing or non-oxidizing atmosphere. It is characterized in that it is eliminated and the nickel compound is reduced to metallic Ni.
As polyvinyl alcohol, 80% or more of the side chain functional groups are hydroxyl groups, and polyvinyl alcohol having a saponification degree of 80% or more and a number average molecular weight of 500 to 20000 is preferable. In addition to organic acid salts such as nickel acetate, nickel oxalate, and nickel butyrate, inorganic acid salts such as nickel sulfate, nickel nitrate, nickel chloride, and nickel phosphate can also be used as the nickel compound.
[0007]
When the polyvinyl alcohol film on which the nickel compound is dispersed and adsorbed is heated and fired at a temperature of 500 ° C. or higher, the reduction reaction is promoted and the nickel compound is efficiently reduced to metal Ni. A Ni porous body in which the nickel compound is reduced to a metal state can also be produced by subjecting the porous body to heat reduction in a step separate from the heating and baking step for eliminating polyvinyl alcohol.
[0008]
[Action]
Polyvinyl alcohol is a material that starts thermal decomposition at a relatively low temperature, has few decomposition residues, and is excellent in film formation. In the present invention, using such characteristics, polyvinyl alcohol is used for the matrix for dispersion. Polyvinyl alcohol is a dispersion matrix that is effective in providing a strong adsorption field for atoms, ions, molecules, and the like. Therefore, when polyvinyl alcohol is impregnated with Ni source, the Ni source is homogeneously dispersed without agglomeration.
[0009]
In order to selectively incorporate Ni ions into the polymer side chain, it is necessary to form a film of polyvinyl alcohol. It is important to increase the degree of polymerization and saponification of polyvinyl alcohol to prevent it from dissolving in a solvent for polymer film formation. However, if the degree of polymerization is excessively high, the degree of dispersion of polyvinyl alcohol in the solvent is poor. , Handling becomes difficult. Therefore, it is preferable to adjust the polymerization degree so that the number average molecular weight of polyvinyl alcohol is 500 to 20000, and to adjust the saponification degree to 80% or more. A film formed from polyvinyl alcohol having a properly adjusted degree of polymerization and saponification selectively binds Ni ions to the side chain functional groups and causes Ni to sinter and agglomerate during the subsequent heat treatment. Prevent and work in the formation of nanopore structure.
[0010]
Ni ions are selectively bonded to polyvinyl alcohol by coordination of Ni ions to hydroxyl groups. In order to realize effective selective bonding of Ni ions, the side chain functional group of polyvinyl alcohol is not substituted with an alkyl group or the like, and 80% or more is preferably a hydroxyl group side chain.
[0011]
The matrix for dispersion is prepared by a casting method in which a polyvinyl alcohol solution is spread on an appropriate substrate such as glass and is formed into a film by drying at room temperature. In order to prevent gelation due to the interaction between polymer molecules, (NH 4 ) 2 HPO 4 is added to the polyvinyl alcohol solution as a hydroxyl group protecting agent as required. The obtained polyvinyl alcohol film has numerous micropores and mesopores, and innumerable pore walls with enhanced molecular adsorption ability are formed.
[0012]
The polyvinyl alcohol film (dispersion matrix) is washed and dried, and then impregnated with Ni source. Examples of the Ni source include organic acid salts and inorganic acid salts that are reduced to metallic Ni in a relatively mild environment. Specific examples include organic acid salts such as nickel acetate, nickel oxalate, and nickel butyrate, and inorganic acid salts such as nickel sulfate, nickel nitrate, nickel chloride, and nickel phosphate.
[0013]
When impregnating the Ni source, a liquid phase method such as a method of immersing a polyvinyl alcohol film in a Ni source-containing solution or a method of allowing the Ni source-containing solution to flow through the polyvinyl alcohol film is employed. Alternatively, a vapor phase method in which vaporized Ni source is fed into a polyvinyl alcohol film and Ni source is adsorbed on the polyvinyl alcohol film by contact between the polyvinyl alcohol and the Ni source can be employed.
[0014]
When the polyvinyl alcohol film impregnated with the Ni source is heated and fired in a reducing or non-oxidizing atmosphere, the polyvinyl alcohol is thermally decomposed and disappears. Hydrogen gas, hydrogen-containing gas, or the like is used for the reducing atmosphere. Since the carbide generated by the thermal decomposition of polyvinyl alcohol exhibits a reducing action, a non-oxidizing atmosphere such as nitrogen gas or inert gas can also be used.
[0015]
When polyvinyl alcohol disappears from the Ni source-impregnated polyvinyl alcohol film by thermal decomposition, the disappeared portions of the polyvinyl alcohol become micropores. At this time, since the polyvinyl alcohol film on which Ni source is adsorbed with high dispersibility is reduced and fired, the nanopore structure in which traces of polyvinyl alcohol are ensured as fine pores without aggregation of Ni source or metal Ni Appears. Metals with a large specific surface area are generally easily oxidized, but the active sites on the metal surface are terminated with carbon generated by the thermal decomposition of polyvinyl alcohol, so that the resulting Ni porous body has extremely high oxidation resistance. . The fact that the active sites on the metal surface are terminated with carbon is presumed to be one of the causes for suppressing the aggregation of metal Ni generated by the reduction reaction.
[0016]
【Example】
(NH 4 ) 2 PO 4 was mixed with polyvinyl alcohol at a ratio of 10% by mass and dissolved in distilled water to prepare a polyvinyl alcohol aqueous solution having a concentration of 10% by mass. A polyvinyl alcohol film having a thickness of 2 mm was prepared by dropping 80 ml of an aqueous polyvinyl alcohol solution onto a glass substrate, allowing the solution to stand at room temperature for 1 week and drying. Next, the polyvinyl alcohol film was immersed in a 1N-NaOH aqueous solution for 24 hours, and fixed in the polymer as Ni compound: Ni (OH) 2 . Thereafter, it was washed with pure water at room temperature and dried at room temperature.
[0017]
The formed polyvinyl alcohol film was an elastic green film. The elasticity of the film suggests the survival of water molecules that interact with the hydroxyl groups of the polyvinyl alcohol side chain via hydrogen bonds. Since water molecules interacting with hydroxyl groups are not removed by drying at room temperature, the compatibility of polyvinyl alcohol and nickel solution in the next impregnation process is improved, and the incorporation of Ni ions into the polyvinyl alcohol film proceeds smoothly. .
[0018]
Nickel nitrate was used for the Ni source, and an aqueous nickel nitrate solution having a concentration of 30% by mass was prepared. The polyvinyl alcohol film was immersed in an aqueous nickel nitrate solution for 72 hours, and Ni ions were adsorbed on the polyvinyl alcohol film. Next, the polyvinyl alcohol film was immersed in a 1N-NaOH aqueous solution for 72 hours, washed with distilled water, and dried at room temperature to obtain a polyvinyl alcohol film in which Ni (OH) 2 was dispersed.
A Ni (OH) 2 -dispersed polyvinyl alcohol film was placed in a quartz tube and heated and fired while feeding nitrogen gas into the quartz tube at a flow rate of 10 cc / ml. In order to investigate the influence of the firing temperature on the obtained Ni porous body, the firing temperature was changed in the range of 200 to 650 ° C.
[0019]
For each sample after firing, a nitrogen absorption isotherm was determined by a volume method (−196 ° C.), a fine structure was measured from the X-ray absorption spectrum, and a spectrum was measured by X-ray photoelectron spectroscopy.
As can be seen in FIG. 1 which shows the measurement results of the nitrogen absorption isotherm, the nitrogen absorption isotherm suddenly rose at the low relative pressure portion in the Ni porous body obtained at any firing temperature. The rapid rise of the nitrogen absorption isotherm means that micropores having a diameter of 2 nm or less exist. In addition, a hysteresis in which nitrogen absorption isotherms do not match is observed during adsorption (indicated by black dots in the figure) and during desorption (indicated by white dots in the figure), confirming the coexistence of mesopores having a diameter of 2 to 50 nm. It was done. The mesopores had a pore distribution of about 3 to 7.4 nm with a peak of about 4 nm from the mesopore distribution (FIG. 2) determined by the DH method (Dollimore-Heal method).
The surface area determined from the nitrogen absorption isotherm is shown in Table 1. From Table 1, it can be seen that the Ni porous body obtained by the present invention has a very large surface area.
[0020]
As can be seen in FIG. 3 which shows the measurement result of the X-ray absorption fine structure, the porous body obtained at the firing temperature of 200 to 400 ° C. had the same structure as the electronic state of NiO, but was fired at 500 to 650 ° C. The porous body obtained at the temperature was in the same electronic state as metal Ni. This result shows that when the firing temperature is set to 500 ° C. or higher, NiO is reduced to become metallic Ni. When the Ni porous body obtained at a calcination temperature of 650 ° C. was spectrally analyzed by X-ray photoelectron spectroscopy, almost no O1s peak derived from the surface oxygen functional group was observed. The results of FIG. 4 indicate that the Ni porous body has extremely low surface reactivity to oxygen and excellent oxidation resistance.
[0022]
【The invention's effect】
As described above, in the present invention, by using a polyvinyl alcohol film as a substance that provides a strong adsorption field for atoms, ions, molecules, etc., the nickel compound is adsorbed on the polyvinyl alcohol film in a highly dispersed state. Is done. Moreover, since the carbon produced when the polyvinyl alcohol disappears by heating exhibits a reducing action, the nickel compound is reduced to metallic Ni without being heated and fired in a reducing atmosphere. The Ni porous body obtained in this way has traces of polyvinyl alcohol as micropores on the order of nanometers, and has a nanopore structure with a significantly larger specific surface area than conventional sponge-like nickel. Therefore, it is used as a functional material such as a catalyst, an adsorbent, a gas occlusion material, a capacitor, and a selectively permeable membrane in which the original active action of Ni is effectively expressed and the functionality is greatly improved.
[Brief description of the drawings]
FIG. 1 is a graph showing the effect of baking temperature on the nitrogen absorption isotherm of a thin film obtained by heating and baking a Ni (OH) 2 -dispersed polyvinyl alcohol film. FIG. 2 shows the baking temperature on the mesopore distribution. Graph showing the effect [Fig. 3] Graph comparing the X-ray absorption fine structure of the thin film (a) obtained by heating and baking the Ni (OH) 2- dispersed polyvinyl alcohol film with the standard sample (b) [Fig. 4] The graph which compared the X-ray photoelectron spectroscopy spectrum of the thin film (a) obtained by heat-firing a Ni (OH) 2- dispersed polyvinyl alcohol film with the standard sample (b).
Claims (4)
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| CN1296427C (en) * | 2004-06-11 | 2007-01-24 | 武汉大学 | Reinforced polyvinyl alcohol composite membrane, preparing method and use thereof |
| KR100680889B1 (en) | 2005-07-19 | 2007-02-08 | 한국화학연구원 | Nanoporous multi metal-incorporated nickel phosphate molecular sieves and their preparation methods |
| JP5445991B2 (en) * | 2007-08-09 | 2014-03-19 | 独立行政法人物質・材料研究機構 | Nano-flaked metal composite material, method for producing the same, and surface-enhanced Raman scattering active substrate |
| WO2012063591A1 (en) * | 2010-11-09 | 2012-05-18 | 国立大学法人大阪大学 | Processes for producing porous metal body and porous metal-containing body, and porous metal body and porous metal-containing body |
| CN113398885B (en) * | 2021-06-29 | 2023-03-24 | 哈尔滨理工大学 | Adsorb H 2 Preparation method of S lignin carbon film |
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