| Nowadays human society is facing two serious problems of chemical fuel shortage and environmental pollution,and the development and utilization of green energy can effectively solve these problems,especially solar energy,the photocatalysis of semiconductors is an important technology to effectively use solar energy.Semiconductor catalysts have been used in environmental treatment,energy production,organic synthesis.However,there are two key problems for semiconductor catalysts: the low utilization of visible light and high recombination of photogenerated electron-hole.The photocatalytic performance depends on the light absorption efficiency,photogenerated charge separation efficiency,transfer efficiency and recombination efficiency.The band gap of the photocatalyst with the conjugated structure falls within the absorption range of visible light,and thus has excellent visible-light absorption efficiency,but also increases the recombination efficiency of electron-hole.Under the ?-? stacking interaction,perylene diimide spontaneously forms self-assembly with ?-conjugated structure in a certain proportion of medium solvent,and the photogenerated charge transfers in the structural unit along the ?-? stacking direction,reducing the recombination of electron and hole.Perylene diimide self-assembly can achieve photocatalytic degradation and photocatalytic water spill under the driving of visible light.However,there are still two important problems: 1,the length of ?-? stacking of self-assembly is too long to cause the recombination of electron and Hole;2,self-assembly forms a band-like electronic energy level structure,which greatly reduces its redox capacity.Around these two issues,we mainly carried out two aspects of the study as following:The separation of photogenerated charge is closely related to the photocatalytic efficiency.The complex can effectively realize the separation of electrons and holes,forming cluster charges to reduce the electrostatic interaction of electrons and holes.The PDI/P25 core-shell structure with PDI self-assembly as the shell and P25 as the core was prepared by pH-induced aggregation method,which enhanced the visible light photocatalytic activity of PDI,especially EDTA as the sacrificial agent,with activity increased by 7 times.We have revealed that the improvement of its photocatalytic performance is due to the electron transfer from PDI to P25 through the Ti-O=C electron channel,and the formation of breakpoint-controlled ?-? stacking short-range ordered structures.This study provides a thought to improve the photocatalytic performance of the assembly.The electronic-coupling interactions between noble-metal cocatalysts and host semiconductor nanocrystals have been found to be effective for the utilization of solar energy.However,the electronic-coupling mechanisms between the noble metals and self-assemblies have not been addressed.Here,we reveal a mechanism of back-electron-transfer-enhanced photocatalysis,which contributes to the visible-light photocatalytic improvement of perylene diimide(PDI)assembly for phenolic degaradation and hydrogen generation.The absorption spectra showed that an additional electronic state exists above the conduction band of PDI assembly resulting from PDI radical anion.Under the interfacial electric-field interaction,the system composed by PDI and palladium quantum dots(QDs)distributed inside the PDI assembly provided the light-driven dissipative structure stable energy and material flow.Continuous electron transfer caused the quasi-Fermi level of the palladium QDs to be higher in energy to overcome the interfacial energy barrier.Back-electron transfer from the palladium QDs to neutral PDI molecules resulted in the formation of more PDI radical anions that are important for phenolic oxidation and hydrogen generation revealed by DFT calculation.These findings provide a new strategy for the development of highly efficient visible-light photocatalysts based on self-assembly for energy production. |
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