A protocol for the synthesis of moisture-responsive luminescent Ag-zeolite composites is described in this report.
Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film.
閉じ込められたゼオライトマトリックス中に自己組織化によって形成された小サブナノメートルoligoatomic銀クラスターは、独自の光学特性を示す。1-5このような銀-ゼオライト複合材料は、高い化学的及び光安定性を有します。しかしながら、それらの光ルミネセンス特性は銀クラスターのローカル環境に大きく依存しています。銀ゼオライト複合体に光学的特徴に影響を与える環境条件に内因性および外因性の特性に分けることができます。固有特性は、ゼオライトトポロジー、カウンターバランスするイオンの種類、および銀の負荷に関連している。1一方、外因性の性質は、そのような中で吸着物や水分子の存在などの合成後の変化に関連していますゼオライトの空洞。3,4後者の特性は、銀ゼオライトに与えるには、光学的に、このようなゼオライト足場6-8内の水分の変動のような外部刺激に応答する能力を合成します</suP>または決定されたガスの存在。したがって、水蒸気およびガスセンサーとしてのそれらの使用が提案されている。9,10
最近の研究では、湿気に銀ゼオライトの光学応答が唯一の彼らの放射の吸収または消光の変化にも、それらの含水量に対して異なる発光色の外観に相関されていないことを実証している。5安定化部分的にLiがLTAゼオライトは、それぞれ、脱水および水和試料中の緑/黄色発光する青色から動的な色の変化に反映された相対湿度の低いスケールで変化する水分応答性材料の形成につながっ交換で銀クラスターの。したがって、発光ベース湿度センサとして、これらの材料を使用することが提案されました。今日まで、このような電解質、セラミック、ポリマー、およびナノ構造複合材料などの材料の異なるタイプの湿度Bにおける監視変更が提案されています電気的および光学的応答に関するASED。11,12この詳細なプロトコルでは、我々は、湿度センサとしてLTA(李)-Agゼオライトの応用のために、さらにプロトタイプの開発に、概念実証を実証することを目指しています。 LTA(李)-Agゼオライトの汎用性のために、異なる基板に組み込まれるように、彼らの潜在的な拡張性と費用対効果の製造は、プロトタイプの設計を容易にする可能性があります。13このようなセンサは、のように、異なる産業分野での適用可能性を持つことができます農業だけでなく、自動車、製紙産業。14
A simple device to demonstrate the proof of concept of using LTA(Li)-Ag as a luminescence based humidity sensor was produced by spray coating the LTA(Li)-Ag powder suspended in a PEI solution onto a quartz plate. The PEI solution produces a polymer layer with homogenous thickness when the water is evaporated. The polymer-zeolite composite layer displays similar luminescent properties as that of the zeolite in powder form. The PEI/LTA(Li)-Ag zeolite composite displays the expected water-responsive luminescent properties, whose emission color changes upon variations in the water content present in the composite at relatively low humidity scale.
Replacing Na with Li ions in LTA zeolites (calculated exchange rate 33%) has a notable impact on the self-assembly and stabilization of luminescent silver clusters in the LTA(Li) scaffolds leading to unique optical properties. The EQE of LTA(Li)-Ag as compared to LTA(Na)-Ag samples is enhanced by more than one order of magnitude. Moreover, the emission colors displayed by the LTA(Li)-Ag samples have a water-dependence, providing a potential application of the samples as luminescence based humidity sensors.
We have thus demonstrated an easy method to fabricate a luminescent film-like humidity sensor through which changes in hydration levels can be visually monitored simply by using a UV lamp. The availability of the raw materials, the direct visualization of the color changes correlated with humidity content, the photo-stability of the films, and the relative ease of fabricating cost-effective devices make these luminescent materials potential candidates to compete with state-of-the-art humidity sensors based upon electrical responses. The procedure described in this report could also be applied and extended to different substrates, at different micro and macro scales, to make the sensor more flexible. Additionally, several critical steps during the fabrication of Ag-zeolites, which play an important role in determining the final optical properties of such materials, were discussed in this protocol. For instance, the pre-cleaning of the raw zeolite material leads to the removal of optical and chemical impurities, as well as to homogenous zeolite crystal size distribution. This is crucial for the incorporation of zeolites into functional devices. One limitation of the present methodology is the restriction on the use of thin film sensors beyond 75 °C. This is mainly due to the decomposition of the PEI polymer, rather than to the degradation of the LTA(Li)-Ag zeolites, which can withstand up to 500 °C. The use of heat-resistant polymers, such as polyvinyl alcohol, could expand the temperature range up to 200 °C. We expect that further investigations will be directed to the development of methodologies for the synthesis of nanostructured Ag-zeolite composites with (multi)functional properties and finally to the design of advanced sensor prototypes.
The authors have nothing to disclose.
The authors gratefully acknowledge financial support from the Belgian Federal government (Belspo through the IAP VI/27 and IAP-7/05 programs), the European Union’s Seventh Framework Programme (FP7/2007-2013 under grant agreement no. 310651 SACS), the Flemish government in the form of long-term structural funding “Methusalem” grant METH/08/04 CASAS, the “Strategisch Initiatief Materialen” SoPPoM program, and the Fund for Scientific Research Flanders (FWO) grant G.0349.12. W.B. gratefully acknowledge the chemistry department of the KU Leuven for a FLOF-scholarship. The authors thank UOP Antwerp for the kind donation of zeolite samples and the mechanical workshop of the KU Leuven for helping with the design and construction of the heating/vacuum cell used in this study.
LTA(Na) zeolite | UOP | Molsiv adsorbent 4A | |
Silver nitrate | Sigma Aldrich | 209139 | ≥99,0% |
Lithium nitrate | Sigma Aldrich | 62574 | ≥99,0%, calc. on dry substances |
Polyethyleneimine solution | Sigma Aldrich | 3880 | ~50% H2O |
Scanning electron microscope (SEM) | JEOL | JSM-6010LV | |
Thermogravimetric analyzer | TA instruments | Q500 | |
Spectrofluorimeter | Edinburgh instruments | FLS980-s | |
Integrating sphere | Labsphere | 4P-GPS-033-SL |