Investigations On The Synthesis Of Covalent Organic Polymers With Redox Activity And Their Photocatalytic Properties

As an important branch of porous organic polymers,covalent organic polymers(COPs)are a class of polymer framework materials composed of light elements(C,N,H,O,B,etc.)and each structural unit is connected by covalent bonds.Due to its large specific surface area,adjustable pore size,simple processability,and designed skeleton functions,it has been widely used in many fields such as gas adsorption and separation,water purification,fuel cells,electrochemical energy storage,and photocatalysis.Among them,COPs with redox activity provide the possibility for non-metal-involved photocatalytic processes due to their excellent photogenerated electron ability and suitable electron transport channels.It is of great significance for the low-carbon synthesis of fine chemicals to develop green,stable,environmentally friendly,highly active,and selective COPs-based photocatalysts and reduce the use of precious metals.In this paper,two kinds of redox-active COPs materials with anthraquinone and polycyanoanthracene units were designed and synthesized.The catalytic performance of these materials in non-metal-involved photocatalytic oxidation reactions was studied in detail.The research work of this paper mainly includes the following two parts:In the first part,the crystalline COP material AQ-COP with anthraquinone as the core structural unit was synthesized and used for selective photocatalytic oxidation of sulfide.Using 2,6-diamineanthraquinone and 2,4,6-trihydroxy benzene-1,3,5-tricarboxaldehyde as building blocks,a covalent organic framework AQ-COP with good crystalline structure was obtained by solvothermal method.The AQ-COP has a high specific surface area(892m2·g-1),CO2 adsorption capacity(1.269mmol·g-1),and CO2/N2 static ideal gas selectivity IAST of 39.5.In particular,cyclic voltammetry tests showed that AQ-COP had paired redox peaks at 0.21 V and 0.52V.Under air atmosphere and visible light,AQ-COP exhibits excellent metal-free catalytic selective catalytic oxidation of sulfides,with a conversion rate of 99%and a selectivity of 98%,and the catalyst is recycled 10 times without significant activity reduction.The intermediate capture experiments and spectroscopic experiments showed that the main active species for the selective oxidation of sulfides by photocatalytic AQ-COP was1 1O2.In the second part,the novel COP material TD-COP with tetracyanoanthraquinone as the core structural unit was synthesized and used for selective photocatalytic oxidation of sulfide.The cyano group has a strong electron-withdrawing ability brought by its own unique electronic structure.When replacing organic molecules,especially aromatic molecules,it can greatly change its electronic structure and is widely used in the field of small-molecule organic optoelectronics.In this paper,2,6-diamine-11,11,12,12-tetracyanoanthraquinodimethane was synthesized on the basis of 2,6-diamineanthraquinone.The novel multi-cyano covalent organic polymer TD-COP with spherical nanofiber structure was prepared by the solvothermal reaction.TD-COP has a high specific surface area(544m2·g-1),CO2 adsorption capacity(0.637mmol·g1),and CO2/N2 static ideal gas selectivity IAST(125.6).In particular,cyclic voltammetry tests showed that TQ-COP had paired redox peaks at 0.23V and 0.53V.Under air atmosphere and visible light,the protonated TD-COP-1 exhibits excellent metal-free catalytic selective catalytic oxidation of sulfides,with a conversion rate of 99%and a selectivity of 97%,and the catalyst is recycled 6 times without significant activity reduction.Free radical capture experiments,spectral analysis,and theoretical calculations show that the most favorable protonation position of TD-COP is the carbonyl O atom,and 1O2 is the main active substance in photocatalytic oxidation.