Study On Catalytic Preparation Of 5-hydroxymethylfural And Fluorescence Detection Of Nitro Explosives Based On Nitrogen-riched Covalent Organic Polymers

Nitrogen-riched covalent organic polymers are a special class of covalent organic polymers(COPs).They have a wide range of applications in the field of catalysis and fluorescence detection because of its good hydrothermal stability and rich nitrogen active sites which could be attached to active metal/metal oxide components or interact with hydrophilic molecules through hydrogen bonds.This paper aims to develop its application in the field of biomass conversion and nitro explosives detection based on the fluorescence response.Firstly,based on the reactive active groups in nitrogen-riched covalent organic polymers,this paper provides a new strategy for effective 5-hydroxymethylfurfural(HMF)production from fructose via constructing a non-acidic triazine-based porous organic polyurea network(TPU-Br)with bromine as the catalytic sites.The successful synthesis of TPU-Br was demonstrated in terms of FT-IR,XRD,EDS and N2 adsorption-desorption isotherms,among which the catalyst exhibited the hierarchical porosity as well as the uniform dispersion of bromine active sites in the TPU-Br.Catalytic results indicated that a high HMF yield for 96.0%and selectivity for 99.2%were achieved at 120? in DMSO for 1 h,although the TPU-Br loading was lower than that of most literature(only 4 wt%).Meanwhile,the TPU-Br exhibited HMF selectivity higher than 93%after four catalytic cycles.Compared with the majority of acid catalysts which only show a moderate HMF selectivity of 80%to 90%under optimized conditions,the high HMF yield and selectivity catalyzed by TPU-Br in this study made up for the limited tolerance of products to strong acidic catalytic sites and provided a new strategy to developing non-acidic catalysts for effective HMF production.Secondly,based on the electron-riched nature of nitrogen-riched covalent organic polymers,a series of fluorescence probes trz-COPs(trz-COP-1,-2 and-3)were firstly designed and synthesized in this paper as well as used for the detection of electron-deficient nitroaromatic explosives.Fluorescence quenching experiments showed that trz-COP-3 showed high sensitivity for detecting TNP,which is owing to the extended ? conjugated systems and abundant hierarchical porosity in trz-COP-3.Further study demonstrated that the detection limit of trz-COP-3 probe for TNP was down to 212 ppb and without interference by other competitive nitroaromatic compounds,both indicating the potential of high selectivity and sensitivity of trz-COP-3 for TNP detection.Additionally,the emission wavelength of trz-COP-3 was obviously red-shifted with the increase of TNP concentration in quenching process,which makes the detection of TNP expands from one-dimensional fluorescence intensity change to the two-dimensional fluorescence map with wavelength,intensity as variables.The above unique phenomenon is of great significance for the precise positioning of TNP in practically complex applications.