Controlled Preparation Of Fluorescent Nanofilms At The Gas-liquid Interface And Their Applications

Film-based fluorescent sensors have attracted great attentions due to their excellent performances in sensing,such as high sensitivity,good selectivity,absence of a radiation source,and ease of operation.Therefore,they have been widely used in the detections of hazardous chemicals,monitoring of environmental quality,food safety supervision and management and so on.The key part of a film-based fluorescent sensor is the sensing film,so the creation of fluorescent sensitive films is the key technology for high-performance sensor devices.Traditional preparation strategies to fabricate fluorescent sensitive films are mainly based on loading fluorophores on different substrates（including particles）,which can be divided into two types.One strategy is to load fluorescent molecules onto the substrate surface by physical methods,such as physical coating method and layer by layer self-assembly method.Although these methods have the advantages of excellent adaptability,convenient and quick implementation,the resulting films usually demonstrate poor stability,which greatly limits their applications in the practical uses.Another is to attach fluorescent molecules on the substrate surface by chemical bonding.Although this method can endow the sensors with stable film structures,the chemical reactions are usually difficult to carry out and the efficiency of preparation is rather insufficient.Therefore,it is of great significance to develop a new preparing strategy for sensitive films for the development of film-based fluorescent sensors.In recent years,nanofilms have become a research hotspot due to their unique structural characteristics,and thus are widely used in sensing,separation,catalysis and many other fields.Based on the above considerations,we attempted to prepare a kind of fluorescent nanofilms to solve the problems that are existed in the traditional film preparing strategies.At the same time,it is noted that pyrrole has become one of the ideal building blocks for the construction of supramolecular self-assembly materials as a result of its various modification sites,flexible conformation,and rich host-guest chemistry.Therefore,we considered using calix[4]pyrrole as the core module to prepare a new fluorescent nanofilm by self-assembling of CPTH at humid air/liquid interface,and explore its potential applications in sensing and separation.The thesis is mainly composed of the following two parts:（1）The controlled preparation of fluorescent nanofilms at gas/liquid interface and their applications in biogenic amine sensing.In this work,we designed and synthesized two compounds,tetra-hydrazide functionalized calix[4]pyrrole derivative（CPTH）and tetra-aldehyde functionalized tetraphenylethylene derivative（TPEBA）.Based on the formation of the dynamic hydrazone bond using the Schiff base reaction between the acylhydrazine group in CPTH and the aldehyde group in TPEBA and the advantage of self-assembling,the fluorescent nanofilm was prepared successfully at the humid air/DMSO interface,which are integrated,flexible,smooth and uniform.The thickness of the films can be controlled in the range of 12～58 nm by controlling the concentration of the precursor solution.Owing to the aggregation-induced emission（AIE）property of TPEBA,the nanofilm is highly emissive with a Stokes shift of～175 nm.The typically designed chemical composition and nanostructure endow the film-preferable affinity to amine vapors,and the networked structure allows fast mass transfer,which lays foundation for high-performance sensing.With an optimized nanofilm-based sensor,biogenetic amines were sensitively,selectively,and reversibly detected.The detection limit（DL）for trimethylamine（TMA）is 0.89 ppm.Typically,interference from water can be neglected,thus,the nondestructive evaluation of fish freshness was realized successfully at 25℃and 4℃.Moreover,a portable seafood freshness detector was conceptually built.（2）The preparation of the nanofilms and their applications in molecular separation.Based on the work mentioned in the previous chapter,we continued to use the same method to fabricate the separation membrane.We have chosen a relatively simple small molecule tetrachuronic tetrastyrene（TPEA）as the aldehyde building block which is to be cross-linked with CPTH to form the C[4]P-TPEA nanofilm.Preliminary characterization results showed that the amorphous film also had excellent integrity,surface flatness.It was found that the membrane could be formed at the concentration of 0.1%～3%,and the membrane formation rate was relatively faster.For the membrane separation process,the lower the thickness of the film,the better the separation efficiency,but the extremely thin thickness will lead to weak mechanical strength,which is also not conducive to the membrane separation process.Therefore,we chose 0.5%thin film（thickness of about 85 nm）to study the molecular separation performance.A PET/C[4]P-TPEA composite nanofilm which is suitable for forward osmosis process was obtained by compacting the prepared C[4]P-TPEA nanofilm with the commercial PET track-etched membrane.The separation performance of the film was studied from two aspects which are flux and rejection.It was found that C[4]P-TPEA nanofilms had higher permeability to water with a water flux of 25.65 LMH when 2 M NaCl aqueous solution was used as extraction liquid.The fluxes of methanol and ethanol are 17.74 LMH and 11.65 LMH respectively,indicating that the membrane is more suitable for the separation process with water as the medium.Furthermore,six water-soluble dyes with different molecular weights were selected to study the molecular interception properties of C[4]P-TPEA nanofilms.The results showed that the retention molecular weight of C[4]P-TPEA nanofilms is about 400 Da based on the rejection rate of 90%.The flux and rejection rate of the C[4]P-TPEA nanofilms were investigated.The results showed that the prepared C[4]P-TPEA nanofilms could intercept molecules with a molecular weight of about 400 Da in the aqueous phase through forward osmosis,which laid foundation for its practical application in the field of molecular separation.