| The survival of mankind and the sustainable development of society are inseparable from the continuous source of energy supply.At present,fossil energy is the most important source of energy in human production and life.The limited reserves of fossil energy and the uncontrolled large-scale exploitation of human beings not only make mankind face energy The shortage problem has also brought serious environmental pollution and climate change problems.Scientists from various countries have been committed to finding and developing clean and sustainable new energy sources that can replace fossil fuels.Inspired by the process of plant photosynthesis,people have developed a series of semiconductor photocatalysts,these materials can directly use the energy of sunlight to split water to produce environmentally friendly and renewable energy-hydrogen energy.Among the many photocatalysts,the emerging organic conjugated polymer photocatalysts have flexible structure and optical properties,adjustable porosity and framework structure,environmental friendliness,good photo-thermal stability,and unique photo-generated current.Sub-transmission performance and other advantages have attracted widespread attention from researchers in recent years.Dibenzothiophene sulfone is an electrondeficient aromatic heterocyclic ring,which has attracted extensive research interest due to its high charge separation ability and high electron affinity.In addition,the very good hydrophilicity of sulfonyl groups increases the possibility of excitons diffusing to the interface between the photocatalyst and water.These characteristics make dibenzothiophene sulfone one of the current photocatalyst building units with development potential.Previous studies have shown that the D-A structure can significantly enhance the photocatalytic activity of the polymer,but the asymmetric electronic push-pull effect of the D-A structure easily causes the rapid recombination of photogenerated electrons and holes,which limits the photocatalytic activity of the photocatalyst.Therefore,by adjusting the ratio of push-pull electron units in the polymer backbone to balance the push-pull effect of electrons,the rapid recombination of photo-generated electrons and holes can be effectively reduced,thereby improving the photocatalytic activity of the photocatalyst.Based on this,this thesis uses spirobifluorene and pyrene as the electrondonating unit and dibenzothiophene sulfone as the electron-accepting unit.By adjusting the molar ratio of D/A,a series of conjugated polymers with different structures and properties are prepared.To systematically study the influence of the ratio of push-pull electronic units and different electron donating units(spirobifluorene,pyrene)on the photocatalytic hydrogen production performance of materials,explore the factors that can effectively improve the photocatalytic hydrogen production performance of materials,and design new photocatalysts Provide theoretical basis.The main research contents of this paper are as follows:(1)Based on the highly twisted spiral structure of the spirobifluorene unit,the material can have a larger specific surface area.Therefore,spirobifluorene is used as the electron donor unit and dibenzothiophene sulfone is the electron acceptor unit to synthesize a series of different push-pull electrons.The role of conjugated polymers.The influence of the ratio of push-pull electronic units on the photocatalytic hydrogen production performance of the photocatalyst was studied by adjusting the molar ratio of D/A.The experimental results show that with the increase of the D/A molar ratio,the hydrogen production activity of the polymer first increases and then decreases.The polymer Spso-3 with a D/A molar ratio of 1:20 has the best hydrogen production activity,which can reach 22.4 mmol g-1 h-1,almost 3 times that of polymers with a D/A ratio of 1:2.The results of fluorescence spectroscopy and photocurrent test showed that the photogenerated carrier separation efficiency of polymer Spso-3 was improved.In addition,the SEM results show that the polymer Spso-3 has a sheet-like structure.Compared with bulk materials,the sheet-like structure not only provides more active sites for the reaction,but also shortens the distance from the photogenerated electrons to the surface of the material,effectively suppressing electrons.-Bulk recombination of hole pairs.This result shows that changing the ratio of push-pull electronic units can change the push-pull electronic interactions inside the polymer,thereby affecting the separation and transport efficiency of carriers,which is an effective strategy to improve the performance of photocatalytic hydrogen production.(2)Since the visible light absorption range of the above-mentioned polymers is relatively narrow,in order to further improve the visible light utilization of conjugated polymers,we choose large plane,highly conjugated and electron-rich pyrene as the electron donating unit,and dibenzothiophene sulfone is Accept the electron unit,adjust the molar ratio of the donor unit and the acceptor unit to synthesize a series of conjugated polymers with different push and pull electron effects.The experimental results show that with the increase of the proportion of electron-donating units in the polymer backbone,the light absorption of the polymer gradually redshifts,the crystallinity gradually decreases,the morphology has a significant difference,and the photocatalytic activity first increases and then decreases.When the D/A molar ratio is1:20,the polymer Pyso-3 has the highest photocatalytic hydrogen production activity,reaching 23.3 mmol h-1 g-1,which is almost the D/A molar ratio of 1:2 Compared with the polymer Spso-3,the hydrogen production activity has been improved.The fluorescence lifetime and photocurrent test results of the polymer show that the polymer Pyso-3 has a higher carrier separation efficiency.In addition,the SEM results show that Pyso-3 has a flake structure.The flake structure not only provides more active sites for the reaction,but also promotes the rapid migration of photogenerated electrons to the surface of the polymer,inhibiting the bulk recombination of electron-hole pairs.This result shows that changing the electron donating unit to pyrene and changing the ratio of push-pull electron units will also affect the morphology of the polymer and the efficiency of carrier separation and migration,thereby improving the performance of photocatalytic hydrogen production. |
