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.
밀폐 된 제올라이트 행렬에 자기 조립에 의해 형성된 작은 서브 나노 미터 oligoatomic 실버 클러스터는 독특한 광학적 성질을 표시합니다. 1-5 이러한 실버 – 제올라이트 복합체가 높은 화학 및 광 안정성을 가지고있다. 그러나, 그들의 광 발광 특성은 실버 클러스터의 지역 환경에 크게 의존한다. 실버 제올라이트 복합체의 광학 특성에 영향을 미치는 환경 조건은 극한과 외적 특성으로 나눌 수있다. 고유 특성이 제올라이트 토폴로지 카운터 밸런싱 이온의 유형 및 실버 로딩에 관련된다. 한 반면, 외인성 특성 등의 흡착 물 또는 물 분자의 존재로 이후 합성의 변화에 연관된 제올라이트 공동. 3,4- 후자의 성질은 제올라이트에 부여하는 광학적 같은 제올라이트 골격 6-8 내의 수분의 변화와 같은 외부 자극에 반응하는 능력을 합성물 </sup> 또는 측정 가스의 존재; 따라서, 수증기 및 가스 센서로서의 용도가 제안되었다. 9,10-
최근 연구에서는 수분 AG-제올라이트의 광학 응답이 그들의 발광의 흡수 또는 소광의 변화뿐만 아니라, 그들의 수분 함량에 대하여 서로 다른 발광색의 외관과 상관되지 않는다는 것을 보여 주었다. 5 안정화 부분적으로 리 LTA 제올라이트 각각 탈수 수화 샘플 녹색 / 황색 발광 푸른에서 동적 색상 변화에 반영 상대 습도가 낮은 배율의 변화하는 수분 – 반응성 물질의 형성을 이끌어 교환 실버 클러스터 . 따라서, 발광 계 습도 센서와 같은 이들 재료의 사용이 제안되었다. 지금까지, 예컨대 전해질, 세라믹, 폴리머 및 나노 복합체와 같은 물질의 종류는 습도 B의 변화를 모니터링 제안되어있다전기 및 광 반응에 ased. (11, 12)이 상세한 프로토콜에서 우리는 습도 센서와 같은 LTA (리) – AG 제올라이트의 응용 프로그램에 대한 추가 프로토 타입 개발에 대한 개념 증명을 입증하는 것을 목표로하고 있습니다. LTA (리튬) – AG 제올라이트의 다양성으로 인해 서로 다른 기판에 통합하는 잠재 성 및 비용 효율적인 제조는 프로토 타입 설계는 용이하게 될 수있다. (13)와 같은 센서는 마찬가지로 다른 산업 분야에서 잠재적 인 응용 성을 가질 수있다 농업뿐만 아니라 자동차 산업 용지. 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 |