Functionalization And Application Of Cyclomatrix Polyphosphazene Micro/Nano Materials

In recent years, with the continuously developing and expanding of nano technology,preparation of functional polyphosphazene micro/nano materials (PMNM) hasgradually been one of the research focuses of phosphazene chemistry. The presentstudies on PMNM are mainly based on linear polyphosphazenes. However, thesynthesis of linear polyphosphazenes is difficult, together with the disadvantages onthermostability, structural stability, and solvent resistance compared to cross-linkedpolymers, which seriously limits the preparation and functionalization of PMNM, aswell as their application extensions in other fields besides biomedicine. Cyclomatrixpolyphosphazene micro/nano materials (CPMNM) based onhexachlorocyclotriphosphazene (HCCP) are a novel class of PMNM, which have thefeatures of simple preparation, mild synthetic condition, and highly cross-linkedstructure. They not only show excellent thermostability, structural stability, and solventresistance, but also possess the characteristics of remarkable molecular structuredesignability, template induced self-assembly, and hetero-atoms doped porous carbonprecursor. These features endow CPMNM with the good prospects of functionalizationand application. This study is mainly focused on the design and preparation offunctional CPMNM based on the above-mentioned features, and further investigatestheir possible applications. The detailed research contents and results are as follows:Based on the remarkable molecular structure designability of CPMNM, a fluorinatedcyclomatrix polyphosphazene microsphere is designed and prepared by thepolycondensation between6F-bisphenol A and HCCP, and its possible applications areinvestigated. On the one hand, the super-hydrophobic surface with water contact angle as high as (157±1.5)°is produced by this microsphere on silicon wafer. On the otherhand, based on the characteristic of template induced self-assembly, a noncovalentfunctionalization of MWCNTs with the fluorinated cyclomatrix polyphosphazenecoating and its application as the supporter of Pt for electro-catalytic oxidation ofmethanol are studied. The Pt nanoparticles on polyphosphazene-coated MWCNTsshow an even smaller particle size (1.8nm) and better dispersion compared with thenaked MWCNTs, which further brings about the higher electrochemical surface area(80.9m2g-1) of Pt nanoparticles and finally leads to the much better electrocatalyticperformance (the oxidation peak current achieves143mA mg-1Pt) inelectro-catalytic oxidation of methanol compared with the Pt/MWCNTs.Based on the remarkable molecular structure designability of CPMNM, anintrinsically fluorescent cyclomatrix polyphosphazene microsphere bearing primaryamine groups on the surface is designed and prepared by the polycondensation betweenbenzidine and HCCP, and its application as fluorescence-based explosive sensor todetect trace nitroaromatics is investigated. The microsphere exhibits remarkablethermal stability, photobleaching stability, solvent resistance, and dispersion ability invarious solvents.2,4,6-trinitrotoluene (TNT),2,4-dinitrotoluene (DNT), and picric acid(PA) can be effectively and sensitively detected by the microsphere sensor, and thesensitivity reaches ppb level. Especially for PA, a surprising superquenching efficiencyis observed, and its quenching constant is as high as38134M-1. The main mechanismfor detection of TNT and DNT is electron transfer. For PA, the fluorescence quenchingprocess predominantly obeys resonance energy transfer mechanism besides commonelectron transfer. The nitroaromatic analytes can be effectively enriched on the surfaceof microspheres by the charge-transfer complexing interaction betweenelectron-deficient aromatic rings and electron-rich amino groups, which facilitates theelectron transfer and energy transfer from microspheres to nitroaromatics, and finallyleads to a significant and sensitive fluorescence quenching response. Based on the feature of CPMNM as hetero-atoms doped porous carbon precursor, anamorphous MnO2·nH2O/microporous carbon spheres composite electrode material isdesigned and prepared, and its electrocapacitive performance is investigated. Theelectrochemical measurements reveal the composite electrode material presents muchmore stable and reversible capacitor behavior compared with the pure α-MnO2·nH2O in1M Na2SO4electrolyte. The composite also shows a relatively high electrode-specificcapacitance of3.13F cm-2and a long cycle life. The remarkable enhancement ofelectrochemical performance is mainly attributed to the good deposition of MnO2particles on the surface of carbon spheres, and the uniquely developed porous networkof the composite facilitating the rapid transport of electrolyte, which result in highelectrochemical utilization of MnO2, great reduction of the equivalent series resistance.Based on the two features of CPMNM as template induced self-assembly andhetero-atoms doped porous carbon precursor, a nano-TiO2@carbon core-shell structurecomposite photocatalyst is designed and prepared, and its photocatalytic activity isinvestigated. The results show that the carbon layer is amorphous, microporous, andheteroatom (N, O, P, and S)-doped. Compared to original TiO2, the compositephotocatalyst shows remarkable adsorption capacity and photocatalytic activity tomethylene blue, a model organic pollutant. In addition, the composite also shows goodseparability and cycle use performance.