Conjugated Porous Polymers Semiconductor For Photocatalytic Hydrogen Production By Solvent Assist

Photocatalytic hydrogen production from water provides a promising strategy for converting solar energy into chemical energy and decreasing the dependence of fossil fuels.Conjugated porous polymers（CPPs）materials,which possess high specific surface area and broad tunability in the aspects of structure,optical bandgaps,and good light absorption,have emerged as one kind of the substitute materials.CPPs also exhibited high exciton binding energy consistent with most organic photocatalysts.Most researchers have made great efforts to improve the photocatalytic performance of CPPs,among which most focus on how to construct donor-acceptor conjugated system into the conjugated skeleton of CPPs to improve the dipole moment and carrier separation efficiency,but ignored the influence of the reaction media on the physicochemical properties of CPPs.It is known that reaction media has critical effects on inorganic&organic reactions,such as the aprotic solvent can promote the nucleophilic substitution reaction of SN2.The significance of reaction media for photocatalytic hydrogen production reactions has not yet been investigated.Choosing an appropriate cosolvents as the media for photocatalytic hydrogen production of CPPs can not only improve the dispersion of CPPs in water,but also kinetic effects on the reactive intermediates,and accelerate hydrogen evolution rates.The aim of this paper is to select suitable solvents to assist CPPs in photocatalytic hydrogen production from water.Exfoliated2D CPPs nanosheets to shorten the carrier migration distance and increase the active site for highly efficient of photocatalytic hydrogen production.The main research contents of this paper are as follows:（1）The effects of varied C–C couplings synthetic methods,including direct C–H arylation,Suzuki and Stille reaction,on the morphology,S_BET,opto-electronic properties and photocatalytic hydrogen production activity of CPP materials have been systematically studied,which shows that the Stille coupling derived CP-St has highest activity.In addition,the introduction of an aprotic dipolar cosolvents can greatly improve its photocatalytic activity.The hydrogen evolution rate（HER）of CP-St in NMP/H₂O/AA system reaches an unprecedented 190.7 mmol g^-1h^-1,and the average electron turnover number is as high as 502.Excitingly,under the same system condition loaded with of 0.5 wt%Pt as synergistic catalyst,its HERs further increased to 303.7 mmol g^-1h^-1,which is the highest reported HERs in organic semiconductors.This result shows that the introduction of NMP can improve the wettability and dispersion of CPP materials,and can also reduce the activation energy of photocatalytic hydrogen production reaction by forming hydrogen bonds with water molecules.Moreover,NMP can exfoliate CPP into ultra-thin nanosheets,thus reducing the carrier migration distance.（2）Solvents were used to conduct ultrasonic liquid-phase exfoliation of B-B、B-T、Py-B、Py-T、Py-Tt and Py-Ttt,which included three or four directions of extension,to obtain the corresponding 2D CPP nanosheets with tunable E_g and luminescence properties.By analyzing the exfoliation effect of CPPs in different solvents,it was found that the matching degree of density and dispersion force between CPPs and solvent played a key role in the exfoliation process.In addition,CPPs showed the best exfoliation effect in NMP,with the yield of exfoliated CPPs ranged from 6%to 20%and the thickness ranged from 5 to 18 nm.The fully-exfoliated 2D Py-Tt showed the highest HER of 87.1 mmol g^-1h^-1,which was 3times that of the bulk Py-Tt.It has been shown that when these CPPs were exfoliated into two-dimensional nanosheets,the exposed more active sites and the shorten carrier migration distance,thus showing higher hydrogen production activity.（3）The BTTT nanosheets,Na₂S and（CH₃COO）₂Zn were separated by solvent-assisted liquid phase in situ to obtain BTTT@Zn S organic-inorganic heterojunction photocatalyst,which was applied to the field in photocatalytic hydrogen production from water.The formation of heterojunction is beneficial to expand the light absorption range of Zn S,and can const internal electric field to promote charge separation.Through a series of characterization methods,it was found that 10 wt%BTTT@Zn S showed the best photocatalytic performance,and its HER was 15.8 mmol g^-1h^-1,which was two times of pure Zn S.