Synthesis And Photoelectrical Properties Study Of Novel Triazine-based Covalent Organic Polymers

Over the past two decades,the emergence of new porous materials with exceptional porosity has been one of the most exciting outcomes in scientific research.This research area is still growing rapidly aiming at their primary applications in gas storage/separation,catalysis,sensing,drug delivery,and energy conversions.Among these,the triazine-based covalent organic polymers family is particularly interesting,because the covalent organic polymers have higher nitrogen contents in the frameworks than others as well as higher porosity comprised of both micropores and mesopores,which can be prepared economically using easily available chemical precursors.Based on the above characteristics,this study has selected the triazine-based structuring units as precursors,designed and synthesized two cases of triazine-based covalent organic polymers(named COP-1 and COP-NT).The applications of COP-1 in sensing and applications COP-NT in catalysis have been studied.We have synthesized a fluorescent triazine-based covalent organic polymer(named COP-1)sensor toward HCl and NH₃ gases.Both solvent-dispersed COP-1 powders and microporous COP-1 film exhibit stable fluorescence and sensitive HCl/NH₃ response.The COP-1 powders were used to successively detect HCl and NH₃ in liquid medium.The as-prepared COP-1 film was applied for reversible detection of HCl and NH₃ gases.The detection limit for HCl gas was calculated to be 1.0967×10^-4,and the detection limit for NH₃ gas was determined to be 5.8925×10^-4.Quantum chemical calculations show that the weak and red-shifted fluorescence response of the COP-1 powders/film to HCl originates from the adsorption of proton/HCl to the N atoms of triazine rings.The interaction between negative N of the triazine ring and positive H of proton/HCl could lead to a charge-transfer(CT)state.Subsequent exposure of the HCl-pretreated COP-1powders/film to NH₃ cause deprotonation/desorption and recovers the fluorescence.As a visible and easy-operating detection strategy,it paves a new way for continuous detection of acidic and alkaline gases.A new triazine-based covalent organic polymer(named COP-NT),which showed high catalytic activities for the degradation of acidic and basic dyes(MO,Rh B and MB)under LED or natural light irradiation,is synthesized.COP-NT itself exhibits excellent chemical stability toward acid and base,and also excellent thermostability.The degradation conditions were carefully selected to obtain the optimized efficiencies.The kinetics of degradation of dyes by COP-NT is studied,and it is determined that the photocatalytic degradation of MO,Rh B or MB is a pseudo-first order reaction.The Ea values of COP-NT for MO,Rh B and MB degradation were obtained to be 9.40 k J mol^-1,30.94 k J mol^-1 and 17.54 k J mol^-1,respectively.Furthermore,COP-NT showed excellent reusability in degrading all the above dyes without obvious performance decay.The successful application of COP-NT in the photocatalytic field may also provide useful insight into the development of other covalent organic polymers.