Synthesis And Photocatalytic Acativty Study Of Pyrene-based Conjugated Polymers

Since the discovery of solar-driven water splitting for hydrogen evolution on the n-type Ti O₂ electrode which was presented by Fujishima in 1972,photocatalytic H₂generation technology has attracted enormous attention as a platform for figuring out the worldwide energy crisis.Over the past decades,substantial efforts have been made to develop ideal photocatalytic systems for hydrogen production,which contain inorganic semiconductors including metal oxides,sulfides,oxynitrides,and nitrides.However,such metal-based inorganic semiconductors still faced to the relatively low photocatalytic activity as well high-cost.Till 2009,g-C₃N₄ was firstly utilized for visible-light photocatalytic water splitting,which lead to a continuous attention on organic semiconductor-based photocatalyst.Nowadays,conjugated polymers?CPs?was emerged as the shining star for various novel organic semiconductor-based photocatalysts.As reported,compared to the other materials,CPs are recognized as an ideal choice for understanding the photocatalytic process structurally and making them appealing candidates for scale-up due to because of their tunable band gaps,high carrier mobility,various preparation methods,visible light driven property and so on.Herein,to investigate the key factors of photocatalytic performance for H₂generation,we have designed a series of pyrene-based donor-acceptor?D-A?conjugated polymers and characterized them reasonably.The main content of our work was consisted with the following three aspects:?1?At first,we have designed and synthesized a series of conjugated polymers with either a one-or three-dimensional framework consisting of pyrene and benzothiadiazole with different numbers of fluorine substitutions?0 or 2?.The effect of molecular structure and fluorine substitution on their catalytic activity was investigated.It was found that the linear non-fluorinated polymer L-Py BT exhibited the highest hydrogen evolution rate up to 83.7?mol h^-1 under visible light irradiation among the prepared polymers because of its broad light absorption,suitable energy bandgap,and enhanced charge generation and separation process.?2?Based on the last work,two analogous positional polymers P16Py SO and P27Py SO have been synthesized via the copolymerization from dibenzothiophene-S,S-dioxide and pyrene building blocks.The effect of the linking pattern on the molecular packing,photophysical and photocatalytic properties of the two isomers was investigated.It was interestingly found that a minor change at the substitution position of pyrene unit was demonstrated to largely influence the photocatalytic properties of the two isomers.P16Py SO exhibited an encouraging average hydrogen evolution rate?HER?of 619.5?mol h^-1 and the maximum HER of774?mol h^-1,much higher than that of 2,7-counterpart with a moderate rate of 282?mol h^-1.The enhanced photocatalytic activity of P16Py SO is mainly ascribed to its more ordered molecular packing,broader absorption region,better wettability,and higher photo-generated charge mobilities.?3?In the second work,we carried out an simple investigation on the effect of Pt co-catalyst to the photocatalytic activity of the polymer.As reported,the deposition of noble-metal Pt co-catalyst on the surface of polymeric photocatalysts can increase the efficiency of photo-generated charge separation.Typically,low Pt planting will be helpful for hydrogen production because of its high dispersion and increased reactive sites on the surface of polymer.However excessively amounts of Pt nanoparticles will affect the light absorption.In this work,we have prepared a Pt coordinated3,8-dibromo-1,10-phenanthroline?Pt DBP?and synthesized a series of pyrene-contained conjugated polymer of 27Py DBP,27Py Pt_0.03DBP.In that case,the Pt co-catalyst was planting in the substrate without any obstacle for light absorption.As the results shown,compare to the unmetallized polymer,27Py Pt_0.03DBP exhibited higher hydrogen evolution rate up to 140?mol h^-1 without additional deposition of co-catalyst.In comparation,an analogous HER with 152?mol h^-1 of 16Py DBP were present in the presence of 3 wt%Pt.