The implemented experimental details for targeting above-mentioned individual objectives are reported below.
The implementation of MOF-CVD technique for MOF film deposition was only demonstrated on ZIF-8, a prototypical zeolitic-imidazolate framework (ZIF). The first objective is to demonstrate the feasibility of this technique for other MOF films deposition. A variety of characterization techniques were employed to evaluate the film deposition, including grazing-incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), atomic layer deposition (AFM), ellipsometry and quartz crystal microbalance (QCM). As the ZIF family is big based on the large variety of imidazolate ligands, the extension of MOF-CVD method to other ZIFs was first investigated. Several deposition parameters were studied including thickness of precursor layer, temperature, reaction time and vapor additives. Some of the ZIFs such as ZIF-7-III and ZIF-72 can be successfully deposited by MOF-CVD. The possibility of this technique for other metal based MOFs were also investigated. The selected MOF is MOF-74 which consists of metal nodes connected by 2,5-dihydroxyterephtalic acid (DOBDC). The metal centers can vary from alkaline earth metal Mg to transition metals Zn, Fe, Ni, Co, Mn and Cu. Here, with the optimization of the reactor setup together with deposition parameters (e.g. temperature, time and additives), the deposition of MOF-74 (Zn, Co and Mg) through MOF-CVD technique was demonstrated.
As targeting the applications of LG@MOFs for solid-state light and chemical sensing, the first important task is to develop an efficient method to load LGs in the pores of MOFs. Therefore, we developed the MOF-CVD technique for the efficient loading of LGs inside MOFs with tunable loading amount. Several types of LGs were demonstrated to be able to be loaded in the MOF pores, such as polycyclic aromatic hydrocarbon and metal-organic complex. The successful loading were demonstrated by powder x-ray diffraction (PXRD), N2 physisorption, nuclear magnetic resonance spectroscopy (NMR) and thermal gravimetric analysis (TGA). Interestingly, different fluorescence colors can be achieved by just loading one LG with different loading amount. Importantly, as these organic LGs were encapsulated inside the MOF pores, the thermal stability are dramatically enhanced.
As the encapsulation of LGs inside MOFs can be readily achieved through MOF-CVD technique, the obtained LG@MOFs were introduced on the top of the UV emitter. The fluorescence emission color can be tuned from blue to orange. Importantly, carefully control the loading amount, white light emission can be achieved. Also, some LGs loaded MOFs show yellow fluorescence light via the blue light excitation, thus, have the potential for blue light converted WLED. Interestingly, when the LG@MOFs exposed to some VOCs, the photoluminescence properties changed, such as fluorescence intensity and spectrum shift, thus, showing high potential for VOC sensing.
