Preparation And Properties Of Lignin-loaded CuS Photothermal Materials

Copper sulfide(CuS)has excellent photothermal properties and has broad application prospects in the biomedical field.Lignin is a natural amorphous polymer that can be used as a metal ion adsorbent due to its stability,biocompatibility and abundance in the plant kingdom.At the same time,polyhydroxy-containing lignin can form supramolecules through intermolecular hydrogen bonds,which can be used to guide the growth of nano-CuS.More importantly,due to its good biodegradability and compatibility,it is not necessary to separate the lignin from the CuS,which solves the application problem.In this paper,enzymatic lignin was used as raw material,and its catalytic modification was used to prepare a good photothermal conversion material.The research work carried out is as follows:In the study,we modified the refined enzymatic lignin by using formaldehyde modification with perfluorosulfonic acid resin(PFSA),using infrared spectroscopy(FT-IR)and two-dimensional nuclear magnetic resonance(2D NMR).The modified lignin was characterized and its structural characteristics were determined.The molecular weight change of the modified lignin was judged by gel permeation chromatography(GPC).The effects of the amount of resin added,the amount of formaldehyde added,and the reaction time on the total hydroxyl content of the modified lignin were investigated.The experimental data show that the modified lignin retains the basic structure of lignin and the molecular weight is reduced.When the mass ratio of PFSA to lignin is 1:2,the volume ratio of formaldehyde to solution is 1:20,the reaction time is 5h,the total hydroxyl content of modified lignin reaches 14.87%,and the corresponding total hydroxyl content reaches 8.75mmol/g.Compared with the measured total hydroxy content of refined lignin 5.16 mmol/g,the total hydroxyl content increased by-70%.The PFSA resin catalyzes the formaldehyde modified modified lignin to increase its total hydroxyl content.Using modified lignin as raw material,we prepared lignin microspheres(LMs)in ethanol-water solution by self-assembly method.The microspheres were characterized by transmission electron microscopy(TEM)and dynamic laser particle size analyzer(DLS)to determine the microstructure and size.The effects of preparation conditions such as water content of solution,lignin concentration and pH value of solution on the average particle size of microspheres were investigated.The prepared LMs were used to adsorb metal copper ions in water,and the effects of lignin adsorbent concentration and copper ion concentration in the initial solution on the adsorption amount of metal Cu2+ were investigated.The results show that when the water content of the solution increases from 20%to 90%;the average particle size of LMs increases continuously;when the content of modified lignin increases from 0.05mg/mL to 0.8 mg/mL,the average particle size of LMs is from-250nm is continuously increased to-650nm;however,the average particle size of LMs does not change much with the pH of the solution.When the lignin concentration reached 0.4 mg/mL,the adsorption amount of the adsorbent reached a maximum of 62.45 mg/g.The adsorption amoint of the lignin adsorbent increases as the initial concentration of Cu2+in the solution increases.Modified LMs can be used as a good biomass-based adsorbent for the adsorption of metallic copper ions in water.We prepared LMs/CuS photothermal conversion materials in aqueous solution by using LMs/Cu2+ as copper source and Na2S·9H2O as sulfur source.It was characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)to determine its microstructure and elemental composition.The optical properties were characterized by visible absorption spectroscopy(vis)and fluorescence spectroscopy,and the fluorescence stability of the samples was tested.The sample was irradiated with 808 nm laser,and the infrared thermal imager was used to measure the photothermal effect of the temperature difference change test LMs/CuS,and compared with the separately prepared copper sulfide,and the photothermal conversion efficiency of the sample was calculated.The characterization results show that LMs/CuS mainly contain four elements of C,O,Cu and S,and the content ratio of Cu and S is close to 1:2.LMs/CuS have absorption in the near NIR region,LMs/CuS liquid samples emit blue fluorescence,and have fluorescence excitation dependence,and the fluorescence of LMs/CuS is mainly attributed to the lignin component.Compared to DAPI,LMs/CuS show very good fluorescence stability.Photothermal experiments show that LMs/CuS can be rapidly heated in a short time,and the photothermal conversion efficiency can reach 22.1%,which is greater than CuS prepared separately.