Preparation, Characterization And Luminsecent Properties Of Organic-inorganic Dense Nano-silica Hybrid Materials

Since the discovery of luminescent by George Gabriel Stokes in1852, it has awide range of applications in agriculture, industry and the biomedical field.Particularly, the luminescent materials have been widely used as a fluorescent tracerin the drug delivery fields. Although the property of luminescent material is excellent,there are also some defects. Recently, the applications of luminescent materials arelimited, due to the inferior thermostability, mechanical performance and toxic nature.Especially, the luminescent characteristics of the resultant organic-inorganic hybridsare usually hindered because of the “self-quenching fluorescence”. Combining theinorganic material with the luminescent molecules is the effective solution.In our study, a novel luminescent density nano-silica hybrid materials （DNSS）modified with different amount of （3-aminopropyl）triethoxysilane （APTES） andvarious capacity of1,8-naphthalic anhydride （NA）,4-amino-1,8-naphthalic anhydride（4NH₂-NA） and perylene-3.4.9.10-tetracarboxylic-dianhydride （PTD） have beensuccessfully synthesized via two steps post-grafting methods. Powder X-raydiffraction （XRD）, N2sorption analysis, Fourier transform infrared （FT-IR）,Transmission electron microscopy （TEM）, Thermogravimetric analysis （TGA）,Photoluminescence spectroscopy （PL） and elemental analysis were employed tocharacterize the resultant hybrid materials. The main results are summarized asfollow:1. The density nano-silica hybrids material have been successfully synthesizedthrough post grafting method without disturbing of the structure and morphology ofthe density nano-silica. The modification with different amount of APTES and thegrafting with different additives of NA have weak effects on the structure propertiesbut significant influences on luminescent properties. When the loading amount of NAis below3wt%, the peak around390nm is ascribed to the spectra of monolayeradsorption, while the loading amount of NA greater than3wt%, the other one （about450nm） is due to the characteristic of aggregation of NA molecule.2. In order to explore the relationship between aminopropyl and luminescentmolecules loaded on the density nano-silica spheres, it is necessary to characterize therelated samples via thermoanalysis. The accurate and trustworthy apparent activationenergy has been calculated through the Kissinger equation and Ozawa equation. Inaddition, the decomposition behaviors of NA-DNSS-0.05-10represent thediffusion-based control at low temperature stage and the dynamic-based control at the high temperature range. Furthermore, we can also deduce that both dynamic-basedcontrol and diffusion-based control play an important role during the wholedecomposition process of hybrid DNSS with nonporous structures. Thedecomposition process of pure NA at low temperature （445⁵78K） correspondingdecomposition mechanism belongs to branch shape nucleation. Meanwhile, thedecomposition mechanism at high temperature （615⁶69K） follows two dimensionaldiffusion. In addition, for APTES-DNSS-0.05, the related decomposition mechanismunder different heating rate （5K/min,10K/min and15K/min） all obey nucleation&growth in respectively. Comparably, for NA-DNSS-0.05-10, the decompositionmechanism in low temperature （597⁷02K） follows nucleation and growth. With thetemperature rising （731⁹00K）, the decomposition mechanism changes into phaseboundary reaction, while there is an interesting observation about the decompositionby a heating rate of15K/min, whereas kinetic model belongs to Mampel Powerduring low temperature periods.3. In order to make our research more integrity and systemic, the large-sizeluminescent molecules of4NH₂-NA and PTD, which have the same element andstructure, are chosen to explore the luminescent properties. It is found that with thegradually increasing additive loading amount of luminescent molecules in hybridmaterials, the intensity of emission peaks of4NH₂-NA-APTES-0.05series areincreasing. When the loading amount of4NH₂-NA is below3wt%, the luminescentmolecules of hybrid materials are ascribed to the spectra of monolayer adsorption.While the loading amount of4NH₂-NA is greater than3wt%, it is due to thecharacteristic of aggregation of4NH₂-NA molecules. However, the intensity ofemission peaks of PTD-APTES-0.05series are reducing when the increasing gradualadditive amount of PTD. Additionally, it is noteworthy that the lifetime was increasedfrom3.99ns to4.49ns and to9.85ns via the different size of luminescent molecules（the size of luminescent molecules: PTD>4NH₂-NA> NA）.