Design,Preparation And Application Of Organic-Inorganic Hybrid Mesoporous Materials With Riboflavin As The Framework

Regularly arranged ordered mesopores(2-50 nm)were a major breakthrough for molecular sieves in materials science.Since then,mesoporous materials have attracted extensive attention and research in the field of nanoscience.Among them,the bridged organic-inorganic hybrid mesoporous materials,also known as periodic mesoporous organosilica(PMO)materials,are an important branch of mesoporous sieves.The PMO materials use micelles formed by surfactants as soft templates to prepare porous materials with controllable structure.Therefore,PMO materials have adjustable pore size,relatively large surface area,and excellent biocompatibility,and can modify the surface functional groups through a variety of chemical reactions.At present,PMO materials have been used in many fields,such as chemical sensing,cell imaging,molecular adsorption,drug delivery and catalysis..Flavins,as a series of rare photosensitizers and coenzymes,can participate in redox processes through electron transfer in many biochemical reactions.Flavins are a class of organic compounds containing isoalloxazine ring,where the heterocyclic system with N atom has large ? coordination plane,thus generally possessing high absorption and intense emission.Therefore,flavins are frequently applied to design fluorescent probes with fast response,low cost and simple operation.Riboflavin,one of the most important compounds in flavins,as an organic fluorophore,has attracted much attention due to its good biological relevance and sensitive chemical sensing properties.By integrating riboflavin(fluorescent probe)into PMO to construct a solid-state fluorescence sensor,it can provide a stable and non-toxic carrier,and improve the fluorescence intensity and lifetime.In this paper,a novel riboflavin-5'-phosphate sodium salt organic siloxane precursor(Rf-Si)was designed and synthesized by using riboflavin-5'-phosphate sodium salt(Rf).Rf-Si was mixed with tetraethyl orthosilicate(TEOS)to obtain organic-inorganic hybrid silicon source,then the Rf bridged periodic mesoporous organosilica(Rf-PMO)was prepared by co-condensation reaction.The results show that Rf-PMO not only maintains good ordered mesoporous structure,but also has excellent fluorescence emission characteristics.Strong fluorescence can be applied for the highly sensitive detection of ferbam residues,and the detection limit is as low as nanomoles.The specific research contents are as follows:(1)The new organic siloxane precursor compound Rf-Si was synthesized from Rf,which was water-soluble.The Rf-Si was confirmed to be the target compound by various characterizations.The newly prepared Rf-Si has typical fluorescence properties like Rf,which can be used for sensitive detection of the ferbam in aqueous solution.(2)The bridged Rf-PMO was prepared by utilizing the newly synthesized precursor Rf-Si.The Rf-PMO is a new practical optical nanosensor with high-sensitivity,low-cost,whichi can be used for detection of pesticide ferbam residue.The morphology,structure and surface chemistry of Rf-PMO materials were characterized by Fourier transform infrared,thermogravimetric analysis,high-resolution transmission electron microscopy,X-ray small-angle diffraction,nitrogen adsorption-desorption isotherms.It was also proved that the organic fluorophore Rf was successfully embedded in the mesoporous materials.The Rf-PMO materials exhibit strong fluorescence emission due to the steric hindrances of Rf embedded within the silica skeleton,making the large ?-conjugate planer platforms of each Rf molecules separate.This strategy avoids the fluorescence self-quenching by stacking aggregation of Rf and enhances the fluorescence emission.The electron spin resonance(ESR)spectra proves that the free radicals in Rf exist stably in the Rf-PMO material.The prepared Rf-PMO materials can participate in the redox reaction between Rf and the ferbam through electron transfer process.The X-ray absorption near-edge spectroscopy(XANES)of Fe K-edge shows the coordination structure through the interaction between iron ions from ferbam and O and N atoms in Rf-PMO.X-ray photoelectron spectroscopy(XPS)further reveals the changes in the valence state of the redox mechanism.Based on the mechanism and fluorescence characteristics of Rf-PMO,ferbam can be detected in aqueous solution with a limit of detection(LOD)as low as 6.97×10-9 M.Therefore,the design and preparation of Rf-PMO materials with hypersensitivity and selectivity for the detection of ferbam has potential value and important theoretical significance in food safety monitoring.