Rapid Fluorescent Sensing And Efficient Iodine Adsorption Of Conjugated Porous Materials

Nitrophenols are important members of the nitroaromatic compound family,known for their environmental pollution characteristics and classification as hazardous explosives,posing a severe threat to human health and the environment.Additionally,radioactive iodine is widely present in the nuclear energy industry and medical applications.Due to its high reactivity and solubility,radioactive iodine can rapidly spread through air and water,causing significant harm to human health and the environment.Therefore,our study focuses on the potential applications of porous conjugated materials in fluorescence sensing and adsorption.Porous conjugated materials possess extended conjugated structures and porosity,exhibiting excellent properties.Through Schiff base chemistry and Sonogashira-Hagihara coupling reactions,we successfully synthesized a series of conjugated microporous polymers(CMPs)and fully flexible covalent organic frameworks(COFs).We investigated the influence of synthesis methods and linker lengths on the structural characteristics of CMPs and COFs,as well as their applications in fluorescence sensing and iodine adsorption.Our research revealed that the polymerization methods and linker lengths significantly impact the specific surface area,crystallinity,fluorescence sensing performance,and I2 adsorption capacity.The principal findings of this research are as follows:(1)Carbazole-based amorphous fluorescent CMPs powder(DCZP)and nanoparticles(DCZN)were successfully synthesized via the Sonogashira-Hagihara coupling reaction using solution polymerization and miniemulsion polymerization methods.Experimental results demonstrate that both DCZP and DCZN are amorphous powders,By adsorbing nitrogen molecules on the surface of the sample and performing adsorption and desorption at different relative pressures,the Brunauer-Emmett-Teller(BET)specific surface areas of 688 and 97 m2 g-1,respectively,belonging to mesoporous and microporous materials.The DCZN nanoparticles are easily dispersed in organic solvents,and DCZP and DCZN exhibit excellent fluorescence properties in certain organic solvent dispersions.Regarding their potential in fluorescence sensing of quinine(PA),both DCZP and DCZN exhibit excellent sensitivity,with quenching constants(Ksv)of 3.94×103(DCZP-THF),6.63×103(DCZN-THF),and 1.99×103 L·mol-1(DCZN-acetone).It was discovered that the fluorescence quenching of DCZP and DCZN by PA follows a photoinduced electron transfer mechanism.(2)Three fully flexible cyclophosphazene-based COFs(HDADE,HBAPB,and HBPDA)were synthesized via Schiff base chemistry reaction using solvothermal method.These COFs are entirely built by flexible building blocks.Results indicate that HDADE,HBAPB,and HBPDA are crystalline,with HBPDA being a spherical structure and HDADE and HBAPB being porous network structures.Their crystallinity gradually increases with the increase in the length of connecting units.The synthesized fully flexible COFs are mesoporous materials with BET surface areas of 87.6、47.7and 18.2 m2·g-1,respectively,which are higher than the corresponding COFs constructed by rigid linkers.These COFs exhibit excellent fluorescence properties in organic solvent dispersions.They can sense PA or p-nitrophenol(p-NP)in real-time with excellent sensitivity and selectivity,The quenching constants of HDADE by PA,HBAPB and HBPDA by p-NP are 6.29× 104,2.17×105 and 2.48×105 L·mol-1,respectively.The LODs of PA and p-NP are 1.19×10-11,6.91×10-12 and 6.05×10-12 mol·L-1,and their sensitivity increases with the length of their linkers,and higher than that of the corresponding COFs composed of rigid linkers.There are only photoinduced electron transfer mechanism in the fluorescence quenching of HBPDA by p-NP;while there are both photoinduced electron charge transfer and resonance energy transfer mechanisms in both fluorescence quenching of HDADE by PA and fluorescence quenching of HBAPB by p-NP.(3)Fully flexible COFs can adsorb iodine in either the gas or liquid phase.Due to their high nitrogen content,abundant electron-rich π-conjugation system and their advantages in flexibility and self-adaptability,the prepared fully flexible COFs showed highly efficient and ultra-high adsorption capacity for volatile iodine.Among them,HDADE,HBAPB and HBPDA capture 5.22,4.55,and 3.86 g·g-1 of iodine,respectively.As the length of the flexible linker increases,the crystallinity increases,but the specific surface area and iodine adsorption decreases.The iodine adsorbed either in the gas phase or in solution can be released by heating or by the addition of a solvent.The prepared fully flexible COFs exhibit reversible adsorption of volatile iodine and can therefore be recycled.(4)The fully flexible COFs can fluorescence sense iodine with high sensitivity.Their quenching constants(Ksv)are 2.22×104,7.07×104,and 1.04×104 L·mol-1.Their LODs are 1.35×10-10,4.24×10-11,and 2.88×10-1 mol·L-1,respectively.The fluorescence quenching of iodine to the fully flexible COFs has both photo-induced charge transfer and resonant energy transfer processes.