Imidazolium-based Ionic Porous Organic Polymers Constructed By Yamamoto Reaction And Their Applications

Porous Organic Polymers(POPs)have received considerable attentions due to their high surface areas,low framework density,high stability and flexible synthetic strategy.Introducing ionic groups into POPs can generate ionic porous organic polymers(IPOPs),which usually integrate the advantages of ionic compounds and POPs.Specific functional groups can be incorporated purposefully into IPOPs through ion exchange,which endows IPOPs with unique functions and properties.Imidazolium group is one of typical cationic groups,which not only can stabilize metal nanoparticles through electrostatic interaction or form metal-carbene complexes with metal ions,but also can capture the heavy metal ions in water through ion exchange.However,IPOPs containing imidazolium group are mainly used in CO2 adsorption and catalytic CO2 conversion,the applications in other heterogeneous catalytic reactions and pollutant disposal have been rarely reported to date.Hence,it is of great significance for expanding the application of IPOPs.This dissertation presents series of imidazolium-based IPOPs,which were synthesized through Yamamoto reaction between imidazolium-based building unit and tetrakis(4-bromophenyl)ethylene or tetrakis(4-bromophenyl)methane,The properties of IPOPs can be modulated through adjusting the molar ratio of two types of building units.The detailed research works are summarized as follows:1.Three imidazolium-based IPOPs(POP-Iml,POP-Im2 and POP-Im3)were prepared through Yamamoto reaction between 1,3-bis(4-bromophenyl)imidazolium bromide and tetrakis(4-bromophenyl)ethylene with the molar ratio of 2:1,1:1 and 1:2,respectively.Imidazolium group is totally in the host backbone of IPOPs,and the bromide resides in the cavities of IPOPs as a counter anion.IPOPs can detect and capture dichromate(Cr2O72-)in water through ion exchange.The following results have been demonstrated:the capture capacity and removal efficiency of Cr2O72-are in close correlation with the density of the imidazolium group.POP-Iml with the highest density of the imidazolium group shows the highest capture capacity and the best efficiency in removing Cr2O72-.Meanwhile,POP-Iml also exhibits excellent enrichment ability and remarkable selectivity in capturing Cr2O72-.Notably,these imidazolium-based IPOPs hold great promises for enrichment and removal of Cr2O72-in acid electroplating wastewater.As a sharp contrast,the non-ionic analogue(POP-TBE),synthesized by Yamamoto reaction of tetrakis(4-bromophenyl)ethylene under the same conditons,is incapable of capturing Cr2O72-.In additon,IPOPs can serve as a luminescent probe for Cr2O72-detection due to dramatic luminescence quenching effect after capturing Cr2O72-.2.Yamamoto reaction between 1,3-bis(4-bromophenyl)imidazolium bromide and tetrakis(4-bromophenyl)methane with the molar ratio of 2:1 and 1:2 gave rise to Im-POP-1 and Im-POP-2,respectivley.Anion exchange of bromide in these imidazolium-based IPOPs with chloroauric acid,followed by the reduction with NaBH4,generated IPOPs-supported gold nanoparticles.Their application in the catalytic reaction of nitroarenes reduction was investigated.The following results have been demonstrated:the BET specifc surface area of IPOPs is associated with the density of the imidazolium group.With the increase of the density of the imidazolium group,the BET specific surface area decreases.The non-ionic analogue(POP-TPM),synthesized by Yamamoto reaction of tetrakis(4-bromophenyl)methane under the same conditons possesses the highest BET specific surface area.Comparing with Im-POP-1 and POP-TPM,Im-POP-2 exhibits the highest catalytic activity,which reveals imidazolium moieties and specific surface area of IPOPs are concertedly responsible for the catalytic reaction.Au@Im-POP-2 also displays excellent recyclabilities.The size,distribution and crystallinity of Au nanoparticles in Au@Im-POP-2 have no obvious change after consecutive reaction for four runs,while apparent agglomeration and leaching of Au nanoparticles after catalytic reaction was observed in Au@POP-TPM.The results show imidazolium group can effectively stabilize metal nanoparticles.