Construction And Properties Of Functionalized Polythiophene Semiconductor Composite Photocatalysts

The development of high-performance photocatalytic materials has always been a research focus of photocatalytic technology.Polythiophene semiconductors have formed heterojunction photocatalysts with many wide band gap semiconductor materials due to their flexible and variable structure,low cost,chemical resistance,strong stability,easy synthesis and unique photoelectrochemical properties,and have been used in the field of photocatalytic degradation of organic pollutants.The purpose of the paper is to design and develop a new type of polythiophene conjugated polymer.By modifying different functional groups,adjusting the band gap of the polymer,extending the π-π conjugation effect,and recombining with TiO₂ and g-C₃N₄,a series of polythiophene semiconductor composite photocatalytic systems were investigated for their photocatalytic degradation of organic pollutants under visible light.This work mainly includes four aspects as following:1.Two novel linear conjugated polymers,poly[（thiophene-ethylene-thiophene）-thiophene]（PTET-T）and poly[（thiophene-ethylene-thiophene）-thiophene-3-carboxylic acid]（PTET-T-COOH）,were synthesized by stille coupling reactions.Heterogeneous photocatalysts PTET-T/TiO₂（C1）and PTET-T-COOH/TiO₂（C2）were prepared with different polymer proportions.Under visible light,the photocatalytic degradation performance of organic pollutants modeled by Rhodamine B（RhB）was investigated.Experimental results showed that 15%C2 exhibited the best photocatalytic performance and good chemical stability.RhB was almost completely removed within 80 min,and its kinetic rate constant is 41.7 times that of TiO₂.That was due to the "lock-in effect" between PTET-T-COOH and TiO₂ through the interaction of carboxyl and hydroxyl groups,which greatly improved the interface charge transfer ability and inhibited the recombination of electrons and holes of PTET-T-COOH/TiO₂,thus improved photocatalytic degradation activity.2.A series of PTET-T-COOH/g-C₃N₄ heterostructures were fabricated successfully.Compared with pure g-C₃N₄,the prepared PTET-T-COOH/g-C₃N₄ heterostructure had excellent photocatalytic degradation activity and superior stability.Among them,the performance of 1%PTET-T-COOH/g-C₃N₄ was the best,the degradation eff-iciency of RhB was 90%within 120 min.The kinetic constant was 0.0184 min-1,which was about 3.83 times that of pure g-C₃N₄.The enhancement of photocatalytic performance was ascribed to the three aspects:one was the strong interaction between PTET-T-COOH and g-C₃N₄;the second was the larger surface area of PTET-T-COOH/g-C₃N₄ heterostructure compared to that of the pure g-C₃N₄;the third was the effectively improved the transferability of photogenerated carriers.3.A novel polythiophene semiconductor Poly[(4,8-（6,9-bis（2-octy1-dodecyl）-dithiophene-pyrrolopyrroledione）-alt-（2,5-（3-carboxy）-thiophene）]（PDPPT-T-COOH）was designed and synthesized.Steady heterojunction photocatalysts PDPPT-T-COOH/TiO₂ were prepared and their photocatalytic degradation activity for tetracycline（TC）were researched under visible light.Experimental results showed that 3%PDPPT-T-COOH/TiO₂ heterojunction photocatalyst had a good visible light response at 400-750 nm.The degradation rate of TC was 65.8%,and the kinetic rate constant was 0.00652 min-1,which was 5.48 and 11.6 times that of single PDPPT-T-COOH and TiO₂,respectively.Through the photoelectric performance experiment,it was found that the formation of heterojunction between PDPPT-T-COOH and TiO₂ was more conducive to the separation and transfer of carriers,thus improving the photocatalytic performance.The experiments of active species capture showed that superoxide radical（·O₂-）played a major role,while hydroxyl radical（·OH）and hole（h+）played a secondary role.4.Heterogeneous photocatalysts of PDPPT-T-COOH/g-C₃N₄ with different mass ratios were prepared.The maximum absorption edge of DRS was extended to 800 nm,covering almost the entire visible light range.Under visible light irradiation,2%PDPPT-T-COOH/g-C₃N₄ had the optimal photocatalytic activity of 69.1%and mineralization rate of 69.0%,and had good chemical stability in 7 cycles.The larger specific surface area of heterojunction photocatalyst could provide more active sites.There was a strong interfacial interaction between PDPPT-T-COOH and g-C₃N₄,which effectively promoted the transfer of photogenerated charge,inhibited the recombination of electron holes,and ultimately improved the photocatalytic activity.In addition,three active species were produced in the process of photocatalytic degradation,the importance of which was:h+>·O₂->·OH.