Preparation And Ion Transport Properties Study Of Nanoporous Membranes

Nanoporous membranes possess unique transport behaviors beyond the macro/micro scales,thereby potentially having extensive applications,especially in ion sieving and osmotic energy conversion.However,there are still some challenges in the field of nanoporous membranes:(1)nanoporous membranes cannot distinguish ions of similar size(such as Na+,K+,and Cl-);(2)the trade-off between ion selectivity and ion conductivity obstructs the development and widespread adoption of nanoporous membranes;and(3)the detailed mechanisms of confined ion transport properties are not fully understood,which cannot provide further design guidelines for synthetic membranes.To this end,we elaborately design and construct nanoporous membranes to meet the demand of diverse applications.The impact of structures and properties of nanochannels on ion transport,including channel size,charge density,and tailored binding affinity,are systematically explored.The structure-property-performance relationships of nanoporous membranes are also discussed,providing a theoretical basis for the design of advanced membranes.The main contents are as follows:(1)The membrane-based technology used to extract osmotic energy is hindered by inadequate membrane selectivity and fails in harvesting energy from diverse water sources.A sulfonated intrinsically ultramicroporous polymer(SPX)membrane is fabricated,targeting specifically the extraction of osmotic energy.The SPX membrane with negatively charged sub-l-nm channels shows charge-governed ion transport and high ion selectivity,thereby leading to satisfactory power density and record conversion efficiency.Combining concentration and thermal gradients yields a power output of 1.2 W m’2,along with an exceptional efficiency of 48.7%.This is the highest efficiency reported under a 50-fold NaCl gradient.The strong size effect also enables power generation from solutions with equimolar concentrations,a conceptually new energy extraction system.It extends the concept of osmotic energy extraction from seawater/river water to industrial wastewater.This work focuses on the ion transport behaviors in nanochannels.It demonstrates that it is possible to extract energy from industrial wastewater at a high temperature,at various pH conditions,and has multiple cations.(2)Breaking the trade-off between ion selectivity and conductivity remains challenging.We construct oppositely charged covalent triazine frameworks(QCTF and SCTF)membranes by superacid-catalyzed trimerization reaction of functional nitrile monomers.The rigid sub-nanochannels can confer high selectivity,and the enhanced interaction between ion and channel wall accelerates ion transfer.Under a 50-fold NaCl gradient,a power output of 11.6 W m-2 and an energy conversion efficiency of 32.3%can be obtained,which surpasses the current trade-off between power and efficiency in osmotic energy harvesting.The impact of channel properties on ion transport behavior and power generation performance is also investigated.The stable framework structure enables power generation with salinity gradients in water/organic solvent mixtures.A power density of up to 16.4 W m-2 in a MeOH/H2O mixed solvent is obtained.This work provides a new approach to the design of new high-performance polymer membranes for salinity gradient power generation.(3)Realizing high monovalent ion selectivity in nanoporous membranes is highly desirable but remains a challenge.Inspired by biological sodium channels,we report a sodium selective isoporous membrane(NaSIM)derived from lyotropic liquid crystals.This membrane consists of uniform ion conductive channels lined with carboxylate groups.These negatively charged ion channels demonstrate charge-governed ion transport,pH responsiveness,and Na+selectivity.The Na+ selectivity is 2.10 against K+as revealed by the ion permeation experiment.The prominent Na+ selectivity may arise from specific interactions between Na+ ions and the carboxylate groups inside the channels,which regulate the energy barriers for monovalent cation transfer.Furthermore,the NaSIM may be used for high-precision separation and energy-related processes.Our results provide a new avenue for studying biomimetic ion transport and a cornerstone for designing a new generation of ion-selective membranes.(4)To achieve ionic current rectification in the nanoporous membrane,we prepare an asymmetric ion diode membrane(LC-IDM)by combining a liquid crystal membrane and a polyacrylonitrile membrane.The LC-IDM possesses charge-governed ion transport behavior and an apparent ionic rectification effect.It is confirmed that the opposite charge distribution and an asymmetric structure formed in LC-IDM result in asymmetric ionic flow.When applied to osmotic energy conversion,the power density of the LC-IDM-based generator reaches 3.85 W m-2(seawater/river water).LC-IDM exhibits an ion diode characteristic in alternating current circuits,which have potential applications in signal modulation and rectification.