Preparation And Performance Regulation Of Functional Composite Materials Based On Plant Polyphenol-metal Coordination

As a natural product,vegetable tannins are abundant and rank only second to the three components in wood,cellulose,lignin and hemicellulose.Attributed to their special structures characters,which endow the vegetable tannins with some unique properties,such as protein binding,free radical scavenging ability,and UV resistance.Recently,more and more functional materials based on plant tannins have been reported,due to in-depth research developed on vegetable tannins.Based on the abundant hydroxyl groups of vegetable tannins and their ease to complexation with metal ions,this paper explored their applications in metal ions detection,adsorption,photothermal conversion materials,and atom transfer radical polymerization.Firstly,ellagic acid（EA）with a relatively simple structure was selected as the research object.Based on their rich hydroxyl groups and the color change when coordinated with Fe（III）ions,they were compounded with PVA matrix to prepare a composite film that could detect iron ions.The morphologies of the composite films with different EA contents were observed by SEM.The basic properties of the composite films were analyzed by contact angle measuring instrument,XRD,FT-IR and universal mechanical testing machine.Furthermore,the optical properties of the composite films and their changes after complexation with Fe（III）were tested by fluorescence spectrometer and UV-vis.The results showed that Fe（III）ions could effectively quench the fluorescence emission of the composite films as well as reduce the lifetime.In addition,it was shown that the composite film could effectively detect Fe（III）ions,then produce a color change visible to the naked eye.Finally,the composite film exhibited an excellent detection performance in the invisible corrosion detection of the iron plate surface.Then,the research going to tannin acid since its relatively clear structure and easy chemical modification.Here,tannin acid was modified to composite cellulose aerogel framework.Based on the chelation of plant tannins and metal ions,the solar-driven pump for uranium adsorption in seawater was prepared by combined with a solar steam generation device.The composite cellulose aerogel had a complex pore structure and excellent hydrophilicity,combined with carbon nanotubes（CNTs）,and the water evaporation rate reached 1.2 kg m^-2 h^-1.It could still maintain a good interfacial water evaporation rate after 15 cycles of experiments.Adsorption experiments showed that the prepared aerogel had good selective adsorption for uranyl ions,and the adsorption process was well fitted to the second-order kinetic equation and Langmuir adsorption model.Combined with theoretical calculation and XPS analysis,the possible adsorption mechanism was given.Under sunlight irradiation,the adsorption capacity of the composite aerogel was 48.6%higher than that of the control group,indicating that this strategy could successfully promote the adsorption of metal ions in water.The above-mentioned results confirmed that vegetable tannins with a relatively simple structure could effectively interact with metal ions.Therefore,the research was further extended to extracts of larch bark,named larch bark condensed tannin.HPLC results indicated that extracts contained part of catechin monomers and some more polar condensation products.Photothermal materials were synthesized by coordination with different metal ions.The results showed that the complexation made by Fe（III）had the best performance both in photothermal conversion and stability.Also,the photothermal efficiency was comparable to reduced graphene oxide（r GO）.In addition,the mechanism was elucidated by using UV-vis,fluorescence spectroscopy,etc.Furthermore,the photothermal composite film was prepared by mixing the complex with PVA,and its photothermal conversion effect was examined,and it was successfully used in photothermal drive Stirling engine.The electron transfer from ligand to metal ions occurred when larch bark condensed tannins coordinated with Fe（III）ions.Inspired by this,the carbon dots of larch bark condensed tannins applied in photo-induced atom transfer radical polymerization（ATRP）were explored.In this paper,condensed tannin carbon dots,N-doped,and B-doped carbon dots were prepared,respectively.SEM confirmed that their sizes ranged from 10 to 15 nm.The basic physical and chemical properties of carbon dots were determined by FT-IR,XPS,XRD,and so on.The absorption and luminescence characteristics were analyzed by UV-vis and fluorescence spectroscopy,which indicated that photoelectron transfer between carbon dots and metal ions could occur.Cyclic voltammetry tests further demonstrated the thermodynamic feasibility of electron transfer.The synthesized carbon dots were designed as photosensitizers and successfully used to sensitize Cu-catalyzed,Fe-catalyzed and metal-free catalyzed ATRP systems.