Наноструктурные Ag-цеолита композиты как люминесценция на основе датчиков влажности
Summary
A protocol for the synthesis of moisture-responsive luminescent Ag-zeolite composites is described in this report.
Abstract
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.
Introduction
Малый субнанометровым oligoatomic кластеры серебра , образованные самосборки в замкнутых матриц цеолита представлены уникальные оптические свойства. 1-5 Такие серебро-цеолит композиты обладают высокой химической и фото-стабильность. Тем не менее, их свойства фотолюминесценции сильно зависят от локального окружения кластеров серебра. Условия окружающей среды, которые влияют на оптические характеристики в серебристо-цеолита композитов можно разделить на внутренние и внешние свойства. Внутренние свойства связаны с топологией цеолита типа противоионов балансировки, и серебро нагрузки. 1 С другой стороны, внешние свойства связаны с пост-синтетических изменений, таких , как наличие адсорбатов или молекул воды в полостях цеолита. 3,4 последние свойства придают серебру-цеолита композитов способность оптически реагировать на внешние раздражители, такие как вариации влаги внутри цеолита эшафот 6-8 </suр> или наличие определенных газов; Поэтому их применение в качестве датчиков водяного пара и газа было предложено. 9,10
В недавнем исследовании мы показали , что оптический отклик Ag-цеолиты к влаге не только коррелируют с изменениями в абсорбции или тушением их эмиссии , но и к появлению разных излучаемых цветов в отношении их содержания воды. 5 Стабилизация кластеров серебра в частично Ли обменялись LTA цеолиты привело к образованию материала влаги отзывчивым, в котором изменяется в относительном масштабе с низкой влажностью воздуха были отражены в динамическом изменении цвета от синего до зеленого / желтого излучения в обезвоженных и гидратированных образцов, соответственно , Поэтому было предложено использование этих материалов в качестве датчиков влажности свечения на основе. На сегодняшний день различные типы материалов, такие как электролиты, керамики, полимеров и композитов наноструктурных были предложены для мониторинга изменений в влажности бAsed на электрических и оптических откликов. 11,12 В этом подробном протоколе мы стремимся , чтобы продемонстрировать доказательство правильности концепции для применения LTA (Li) -ag цеолиты в качестве датчиков влажности и для дальнейших разработок прототипа. Благодаря универсальности LTA (Li) -ag цеолиты должны быть включены в различные подложки, их потенциал масштабируемости и экономически эффективное изготовление, конструкция прототипа может быть облегчено. 13 Такие датчики могут иметь потенциальное применение в различных отраслях промышленности, таких как сельское хозяйство, а также автомобильной и бумажной промышленности. 14
Protocol
Representative Results
Discussion
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.
Disclosures
The authors have nothing to disclose.
Acknowledgements
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.
Materials
| 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 |
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