Preparation And Application Of Polyhedral Oligomeric Silsesquioxgne-Based Fluorescence Sensing Materials

Among various organosilicon functional materials,organosilicon fluorescent materials including silanes and siloxanes are developing rapidly,and widely used in chemical sensors,biomedicine,optoelectronic devices and other fields.Polyhedral oligomeric sesquisiloxane(POSS)-based fluorescent materials,as a class of organosilicon fluorescent materials with unique structures,not only have the excellent properties of traditional organosilicon fluorescent materials,such as non-toxicity,good,biocompatibility,high-temperature resistance,and abundant species,but also have their unique advantages:1.POSS has a regular three-dimensional spatial structure,which suppresses the π-πstacking of conjugated fluorescent groups.2.POSS has a well-defined nanometer size,and can be further made into nanoparticle with controlled structure and precise size,which is an excellent carrier for constructing fluorescent nanomaterials.3.The rigidity of the Si-O-Si core of POSS is conducive to improving the mechanical properties of fluorescent materials.4.The five empty 3d orbitals of silicon atom and the two lone pairs of electrons of oxygen atom on POSS interact with each other,which constitutes a unique electron cloud distribution and has unique photoelectric properties.Fluorescence sensing is one of the important applications of fluorescent materials.The existing fluorescent sensing materials are abundant,but there are still problems such as aggregation burst,poor biocompatibility,high toxicity,and poor stability.In contrast,POSS has the advantages of large spatial potential resistance,biodegradability,non-toxicity,good photo-thermal stability,etc.Combining POSS with fluorescent moieties in a suitable way and taking advantage of the unique advantages of POSS can overcome the problems in the field of fluorescent sensing materials,endowing POSS-based fluorescent sensing materials with excellent performance.In this thesis,from the perspective of solving practical detection problems,four kinds of POSS-based fluorescent sensing materials were designed and synthesized,and their functions and applications were explored in depth.The main works are,as follows.1.Imidazole selenone-modified POSS-based fluorescent sensor was prepared to detect and absorb mercury ions.Firstly,the POSS-based compound peripherally modified with imidazolium(M-2)was prepared by quaternization reaction of octa((benzyl chloride)vinyl)sesquisiloxane(M-1)and 1-methylimidazole,and then the imidazoloselenone-modified POSS-based fluorescent compound(POSS-Se)was synthesized by reacting M-2 with selenium powder.POSS could improve the stability and fluorescence emission efficiency of material.It was found that the aqueous dispersion of acidified POSS-Se could efficiently detect mercury ions by color change and "turn on" fluorescence phenomenon,and POSS-Se showed high removal ability for highly toxic mercury ions in aqueous solution.By comparison,its detection and adsorption capacity was better than most similar materials.2.Imidazole thione-modified POSS-based fluorescent sensor was prepared to detect and adsorb gold ions.Firstly,imidazolium-modified POSS compound(POSS-1)was prepared via the thiol-ene click reaction of octamercaptopropylsilsesquioxane(POSS-SH)and 1-methyl-3-(2-propenyl)imidazolium bromide,and then the imidazole thione-modified POSS-based fluorescent molecule(POSS-2)was prepared by the reaction of POSS-1 with sulfur.Experiments showed that POSS-2 exhibited a sensitive quenching effect and good selectivity for gold ions.At the same time,POSS-2 was able to selectively and rapidly adsorb gold ions in water.The actual adsorption amount of gold ions was higher than the theoretical adsorption value calculated by coordination interaction between POSS-2 and gold ions.Given this phenomenon,we investigated the adsorption mechanism of POSS-2,and the results showed that there is a redox reaction between gold ions and POSS-2 in addition to the coordination interaction,leading to a higher adsorption capacity of POSS-2.Furthermore,we successfully applied POSS-2 to extract gold from a waste CPU,indicating that POSS-2 has good prospects for secondary use in electronic waste.3.A POSS-based fluorescent sensor was prepared for the detection of iodide ions.By taking advantage of the lightweight and low density of POSS,the POSS-based ionic porous framework(IPF)was obtained by quaternization reaction of octa((benzylchloride)ethenyl)silsesquioxane and 1,4-bis(lH-imidazole-1-yl)benzene.Traditional iodine ion sensors usually require a suitable pseudocavity,but designing pseudocavity is complicated and tedious.We replaced the traditional pseudocavity with porosity in the IPF to interact with iodine ions,providing a more versatile and simple method for detecting iodine ions.In addition,IPF suspension could effectively detect iodide ions in pure and actual water with high sensitivity and good selectivity.To facilitate and visualize the detection of iodide ions,we prepared portable IPF fluorescent test papers by loading IPF onto filter paper by vacuum filtration method,which can detect iodide ions rapidly and visually.4.A POSS-based fluorescent sensor was prepared to detect ammonia gas.This sensor,a POSS-based fluorescent porous framework(FPF),was synthesized by Heck reaction of octavinyl POSS and tetrabromofluorescein potassium salt.The introduction of POSS suppressed the π-π stacking of the tetrabromofluorescein potassium salt and imparted the strong fluorescence emission and good porous properties to FPF.FPF exhibited a sensitive color response to hydrochloric acid gas and ammonia gas.Furthermore,a portable acidified FPF-based test paper with good detection sensitivity and reusability was developed to detect trace amounts of ammonia gas in air,which provides an effective method for rapidly and visually detecting ammonia gas.In addition,acidified FPF ethanol suspension could sensitively detect ammonia aqueous solution with detection limit as low as 27 ppb.