Design, Syntheses And Properties Of Heptazine-based Porous Organic Polymers

Porous organic polymers have attracted extensive attention owing to their low skeleton density,high surface area,good stability and diverse synthesis methods and have been applied in many areas such as gas adsorption and speration,catalysis,sensor,photovoltaic devices and biochemistry.By selecting functional building units,task-specific porous organic framework with unique properties can be prepared.Heptazine,construction unit of g-C3N4,have attractive prospects in aspects of photocatalysis,electrode materials,biology,etc.In this dissertation we sythesized two series of heptazine-based polymers using cyameluric chloride as basic building blocks via direct coupling of cyameluric chloride and piperazine or aromatic compounds.The structures and morphology of the polymers have been explored.Further we studied their properties of gas adsorption,photocatalytic degradation of dye and catalytic organic reactions.The thesis is divided into four parts:In the first part,we ntroduced the development and application of the porous organic polymers.The aims and main work are also outlined.In the second part,a new heptazine-based porous organicframework(Cy-pip)has been prepared under mild condition via catalyst-free direct coupling of synthetically accessible cyameluric chloride and piperazine(Pip).The framework showed good thermal and chemical stability.N2adsorption-desorption isotherms indicated that BET surface area is 105.8 m2g-1.The pore size centered at 1.37,2.73,and 3.43 nm,respectively.The high nitrogen content of the framework may enhance the interaction between adsorbent and CO2 molecules.Cy-pip exhibited large CO2 uptake of103.4 mg/g(9.4 wt %)at 1bar/273 K and good selectivity of 117 toward CO2over N2.Moreover,the rich nitrogen in the network served as Lewis basic sites,which prompt us to investigate heterogeneous catalytic performance toward Knoevenagel reaction.Catalytic results revealed that high yields could be achieved with only 1mol% of catalyst at room temperature for 4 h.Cy-pip could be recycled at least for four times with only a minor loss of catalytic activity.Then we studied the heterogeneous catalysis properties of Pd-loaded Cy-pip towards Suzuki coupling reaction.Cy-pip-Pd showed good catalytic performance and general applicability for Suzuki reaction.Cy-pip-Pd can be reused for three times without significant loss of catalytic activity.In the third part,two new heptazine-based porous organic polymers Teph-Cl and Quph-Cl have been achieved by Friedel-Crafts reaction of cyameluric chloride and aromatic compounds in the presence of aluminum chloride.UV-visible diffuse-reflectance spectroscopy results gave the band-gap values(Eg)were 2.0 and2.1e V for Teph-Cl and Quph-Cl.Firstly,we evaluated the photocatalytic activities for RhB and MO degradation under visiblelight irradiation and compared with graphitic carbon nitride g-C3N4.Teph-Cl and Quph-Cl catalysts performed good degradation results,which could be apply in clean energy area.Secondly,the polymers have been used as photocatalyst for the selective oxidation of sulfides to sulfoxides.Teph-Cl and Quph-Cl both could achieve selective oxidation of sulfides to sulfoxides and showed good general applicability.The catalysts can be efficiently recycled for five times without significant loss of catalytic activity.In the last part,a concise conclusion was drawn and an outlook of porous organic frameworks was expected.