| "Survival of the fittest",perpetual evolution and natural selection have endowed the living organisms in nature with unparalleled multi-level functional structures,which are capable of completing complex functions and diverse life activities such as material exchange,information transmission and energy conversion in the most efficient and flexible manner.While we awe at their sophistication,we are constantly learning and looking for inspirations from nature that can be utilized by ourselves.For example,taking inspiration from the lotus leaf,a self-cleaning surface was developed;giant panda’s enamel material facilitated the formulation of a self-repairing nanocomposite;pterostigma found on the wings of dragonflies informed the construction of anti-vibration aircraft wing balance weight structures.“Learning from nature”has become one of the most effective approaches to advance the development of high-performance materials and devices.In the view of this phenomenon,in recent years,inspired by the transmembrane ion transport on the membrane of living somatic cells,which can be precisely controlled to realize a variety of functions,a series of studies on biomimetic artificial nano-channels have been carried out,and in preliminary studies,regulation of ion motions in confined areas has been achieved.However,with as research progresses,it has been found that the implementation of a single structural composition in a homogeneous nanoporous system restricts the system’s ability to regulate ion-transport,while the high processing costs and cumbersome preparation processes limit the practical applications of this approach.Thus,it is imperative to develop a new and stable multi-functional heterogeneous composite membrane system.In the light of previous research,this thesis entails the preparation of a new stable high performance nanoporous heterogeneous membrane,a study of its unique ion transport properties and its applications in the field of energy conversion.The main contents are as follows:Based on the understanding of the structure-function relationship of polymeric molecules and taking inspiration from the ion channels of living organisms as well as literature precedents,we chose the stable polyaryl ether system as the hydrophobic backbone and introduced hydrophilic side chains through synthesis.Taking advantage of the difference in hydrophilicity and hydrophobicity between the main chain and the side chain,the polymer is phase-separated through self-assembly via hydrophobic interactions to form a three-dimensional nanoporous film,which can be prepared on a large scale.With this construction as the foundation,a series of porous heterogeneous membranes were constructed,and their transmembrane ion transport properties were studied.The resulting membranes were also applied to the salt-difference power generation devices,and ideal results were obtained.First,we prepared a pyridine-containing hydroquinone monomer Py-OH by Suzukicross-couplingusing4-pyridylboronicacid.Thenucleophilic terpolymerization of this monomer with biphenyldiol and difluorodiphenyl sulfone successfully introduced the pH-responsive group pyridine into Polyphenylene sulfone(PPSU),and by controlling the ratio of monomers,the synthesis of PPSU-Pyx with any pyridine proportions can be achieved.The 2D/3D-GO/Py nanoporous heterogeneous membrane was constructed by simple filtration and spin coating using this series of polymers and graphene oxide.GO formed negatively charged two-dimensional nanopores of about 0.8 nm;the Py layer self-assembles due to hydrophobic interactions to form three-dimensional interpenetrating nanopores of about 8 nm with a single positive charge.The dual-asymmetry in both the pores’surface charges and region-confined structures allows such porous heterogeneous membranes to exhibit superior ion rectification properties.The pyridyl group on the surface of the channel is sensitive to the pH of the environment,becoming positively charged and more hydrophilic in an acidic environment while becoming uncharged and hydrophobic in an alkaline environment.This synergistic effect of charge and wetting gives the nanopores an excellent pH-responsive ion gating effect.We can control the transmembrane ion transport effect of heterogeneous membranes by controlling the key factors such as charge density and channel length.In addition,we have also constructed a nano saline gradient power generation device based on this series of membranes,which has a power output of 0.76 W/m~2.The Janus membrane with rectifying effect can be used as an“ion highway”from seawater to rivers,which significantly improves the efficiency of salt-difference power generation.Due to the high concentration of seawater,in order to ensure high energy conversion efficiency of the system,it is necessary to maintain good ion rectification and selectivity effect of the Janus porous membrane device in a high salinity environment.By increasing the surface charge and porosity,the working concentration range(maximum rectification ratio appears at 1 M KCl)is increased by at least an order of magnitude compared to previously reports in literature,breaking the original concentration limit.The effective ion selectivity and ion rectification in high salinity solutions ensure energy conversion efficiency and high power density of saline gradient power generation devices.The device’s output power is as high as 2.66 W/m~2(by mixing seawater and river water with an efficiency of 35.7%)and 5.10 W/m~2(with a salinity gradient of 500 times).In addition,practical application matters are also taken into consideration.The polyaryl ether polymer is selected to achieve the desired ion transport function while maintaining a sufficient mechanical property through chemical molecular design,which lays the foundation for future practical applications.We boldly speculate that nanoporous membranes with ion rectification effects have great potential for collecting blue energy. |
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