Preparation And Properties Of Porous Materials By Ion-Regulated Ice Templating

Porous materials show promising prospects in the fields of catalysis,energy,adsorption separation,biomedicine,and so on,due to their unique properties and wide application.However,it still remains great challenges to fabricate porous materials with controllable porous structure.Ice templating has become one of the important methods for fabricating porous materials owing to its universality,environmental friendliness and easy regulation of porous structure.This reaction mechanism,using oriented ice crystals as a template,can regulate the structure of porous materials via controlling the nucleation and growth of ice crystals.Recently,studies have shown that ions can regulate the heterogeneous nucleation,ice transport and recrystallization of ice.Also,ions can specifically influence the icing behavior.Therefore,the ion-specific effect shows potentials for realizing the regulation of the ice template.Given all the above,based on the controllable preparation of porous materials,four different halogen ions F~-、Cl~-、Br~-、and I~-were chosen as additives to control the ice templating to fabricate graphene conductive film and poly(3,4-benzenedioxythiophene)-polystyrene sulfonic acid(PEDOT:PSS)aerogels using by different freezing techniques.Herein,a series of studies on its structure regulation and properties were carried out.The main research work is presented as follows:Graphene conductive films were fabricated by recrystallization ice templating.Firstly,the effects of F~-、Cl~-、Br~-、and I~-ions on the process of ice recrystallization were investigated,the regulation factors of ions on recrystallized ice crystals were also studied,and the preparation methods and control measures of recrystallized ice templates were concluded.Given these,four different halogen ion sodium salts such as F~-、Cl~-、Br~-、and I~-were employed as additives based on graphene oxide solution.Graphene oxide grid was prepared by sputtering freezing method,and graphene conductive thin films were obtained after reduction with hydroiodic acid and packaging.The results show that the ice crystal size can be controlled by changing the type of ions or annealing temperature.Besides,the graphene oxide was assembled into a two-dimensional mesh porous material with controllable pore size by using recrystallized ice as a template.The grid size of graphene oxide could be adjusted from 48.5±4.6μm to 178.5±26.8μm.After reduction,the grid conductivity of graphene was regulated due to the difference of grid size,and the conductive film was prepared by encapsulating it with polydimethylsiloxane(PDMS).The conductive film shows impressive conductive stability at small-scale stretching.High strength and high recovery PEDOT:PSS aerogels.Based on the ion-regulated directional freezing,a novel PEDOT:PSS aerogel with controllable multi-scale structure was prepared,which had an ordered layered structure with thick pore wall.Besides,there were lines embedded in the layer wall and protruding on the surface.In addition,by adding different ions or changing the freezing temperature,the morphology of the pore structure was transformed from the layered structure with bridging to the intercellular structure with thicker pore wall,and then to dense layered structure.Thus,the control of layer thickness and pore size were realized.On this basis,the differences of the morphology and mechanical performance between layered structure and conventional porous structure were revealed.Also,it is confirmed that this unique multi-scale three-dimensional structure afforded PEDOT:PSS aerogel the characteristics of high strength and high recovery at the same time.Besides,the pronounced compression-electrical properties of aerogels also highlight the potential applications in flexible electronics.This study also provides a novel idea for the preparation of porous materials with controllable microstructure and significantly improved mechanical properties by the ice templating based on the ion-specific effect.Moreover,it further expands the applications of the ion-specific effect and opens a venue for the regulation technology of ice templating.