Facile And Template-free Preparation Of Tannic Acid-based Hierarchical Porous Adsorbent

The Large amount of carbon dioxide emission has been considered as main reason for the global warming.Therefore,carbon capture and storage(CCS)is widely regarded to be an important topic in the twenty-first century not only for restraining global warming but also further CO2 utilization.Porous materials have potential applications in capture due to their low density,large specific surface area and high porosity.In recent years,the design and synthesis of porous materials,especially porous organic polymers,have achieved remarkable results.However,so far,the synthesis of most materials requires careful design of monomer structures and appropriate reaction paths.In addition,expensive transition metal catalysts or toxic solvents are often used in the reaction.All these factors will increase the production cost of materials,which will restrict the industrial production of porous polymer materials and their large-scale application in carbon capture.Therefore,the synthesis of porous polymer materials with high specific surface area by low cost method has become one of the important problems that material scientists and chemists urgently need to solve.How to effectively employ widespread natural polymers to develop novel material has attracted interests from scientist.Tannic acid,as a typical polyphenol,possesses many advantages such as low cost,abundant resources in nature,multiple reactive sites,capable of interact with other substances through physical,chemical or supramolecular interactions.However,as we know,research on developing novel porous polymer materials based on tannic acid has not been reported.This thesis introduces two kinds of tannic acid-based novel porous polymers for carbon dioxide capture,and preliminarily evaluated their dye sorption and heavy metal loading capacity,respectively.The synthesis process was performed under facile condition,as no energy was required for heating,and noble metal catalysts were also avoided.The main research contents are as follows:(1)The large number of phenol hydroxyl groups in tannic acid were used for condensation with cyanuric chloride under weak basic condition to obtain ether-linked porous polymer,while triazine was also introduced into the polymer network.The chemical composition and morphology of the obtained porous polymer were characterized.Nitrogen sorption analysis under 77 K proved that pore structures of the polymers were influenced by ratio of reactants,higher ratio of cyanuric chloride can give highly porous products,whose specific surface area calculated by BET model was 129 m2/g,and the BJH pore size distribution revealed existence of mesoporosity.CO2 sorption analysis under 273 K showed that carbon dioxide uptake at 1 bar was around 29.4 cm3/g,and specific surface area calculated by Grand Canonical Monte Carlo(GCMC)model was 300 m2/g,which is much larger than the corresponding BET value.It could be attributed to contribution of ultramicroporous structures(<0.8 nm).Meanwhile,adsorption capacity of the polymer towards nitrogen under 273 K/1 bar was only 0.884 cm3/g,indicating that the polymer is an ideal candidate for selectively adsorption of carbon dioxide.And the isosteric heat of adsorption calculated by Clausius-C lapeyron equation was about 50 k J/mol,meaning that the polymer indeed has good affinity towards carbon dioxide,due to largely existence of the triazine groups.(2)Tannic acid was co nverted into porous polymers by using compounds with diamino groups as crosslinker.The amino groups were connected to benzene rings of tannic acids by formation of azo bond.The procedure was also applied on another kind of natural polyphenol-lignin,to verify universality of the strategy.N itrogen sorption analysis under 77 K proved that pore structures of the polymers were influenced by the types of crosslinker,specific surface area of 4,4'-diaminodiphenyl crosslinked tannic acid calculated by BET model was 195 m2/g,and the BJH pore size distribution revealed that the pore structures are mainly mesopores while micropores also exist.But 4,4'-diaminodiphenyl sulphone crosslinked tannic acid showed higher CO2 uptake(c.a.23.1 cm3/g)under 273 K/1 bar.Thermogravimetric analysis results revealed that the porous polymer have high residue mass after heating to around 800? in nitrogen,indicating that the porous polymer is an ideal precursor of porous carbon material.After pyrolysis at 900? in nitrogen,the mesoporosity was reduced but microporosity was increased,and the highest BET specific surface areas from 4,4'-diaminodiphenyl crosslinked polymer was 290 m2/g.The CO2 uptake was significantly increased after pyrolysis,and the maximum value was 70.3 cm3/g and specific surface area calculated by Grand Canonical Monte Carlo(GCMC)model was 690 m2/g,and large amount of ultramicropores exist.The isosteric heat of adsorption was about 24 k J/mol,and the X-ray photoelectron spectroscopy(XPS)results showed that weight percent of carbon content after pyrolysis was higher than 90% meaning that the porous carbon capture carbon dioxide mainly by physical sorption.