Preparation And Application Of Two-dimensional Porous Carbon Materials Based On CDC Principle

As a typical two-dimensional carbon material,graphene has excellent physical and chemical properties,such as unique electronic conductivity,excellent thermodynamic and chemical stability.It is widely used in electrochemical energy storage,water purification,catalysis,biology and other fields.However,due to the lack of in-plane pore structure,the material transmission path is less,the transmission efficiency is low,and the performance is still unsatisfactory.In contrast,two-dimensional porous carbon materials have a more developed pore structure,especially the existence of in-plane holes,which makes it more advantageous in the application of electrochemical energy storage,water purification and other fields.Unfortunately,the currently developed methods for preparing two-dimensional porous carbon materials have problems,such as complex operations,high costs,and under-developed pore structures.Based on this,this dissertation aims at developing new principles and technologies for the preparation of two-dimensional porous carbon materials.A system-atic study was conducted on the technical conditions,influencing factors,and synthesis mechanism of two-dimensional porous carbon materials with well-developed pore struc-tures using a special two-dimensional carbide-MXene as a precursor based on the principle of carbide derived carbon（CDC）.And further explored the performance of the prepared two-dimensional porous carbon material in micro-supercapacitor（MSC）and dye wastewater purification.The main research contents are as follows:（1）Using MAX phases（Nb₂AlC,Ti₃AlC₂ and Nb₄AlC₃）as objects,MXene（Nb₂C,Ti₃C₂ and Nb₄C₃）was prepared by chemical etching,and then MXene was etched by high temperature chlorine gas to explore the feasibility of preparing two-dimensional porous car-bon materials（PCF）based on CDC principle.Based on the successful preparation of PCF,the effects of etching conditions and precursor types on the morphology and structure of PCF were systematically studied,and the formation process and mechanism of PCF were analyzed.The results show that:The chemical etching parameters for preparing precursor MXene have a significant impact on the successful synthesis of PCF.Appropriate reduction of chemical etching time can ensure successful PCF in high temperature chlorine etching of the prepared MXene.Due to the conomorphism of CDC transformation,PCF obtained from different precursor MXene by chlorine gas etching showed two-dimensional lamellar struc-ture.Based on the incomplete chlorine gas etching samples of MXene and the PCF layer thickness test results,it is speculated that the chlorine gas etching of MXene is carried out simultaneously at multiple sites,which are related to the F groups on MXene.As the etching process progresses,the remaining carbon atoms in MXene are mainly recombination to form a two-dimensional porous carbon sheet with an intra layer combination manner.In addition,the formation of in-plane mesopores with larger pore sizes on PCF can be attributed to ex-cessive etching of carbon atoms adjacent to etching sites.The higher the content of F groups on MXene,the more etching sites there are,and ultimately the more mesopores on PCF obtained.（2）Using Nb₂C-PCF,Ti₃C₂-PCF and Nb₄C₃-PCF as electrode materials and graphene as metal-free collector,MSC was assembled by mask vacuum filtration.The results show that Nb₂C-PCF-MSC,Ti₃C₂-PCF-MSC and Nb₄C₃-PCF-MSC all exhibit excellent double layer capacitance,with specific capacitance up to 76.3,102.1 and 65.1 m F cm^-2,respectively,which is much higher than that of carbon based MSC reported in previous literature.The high specific surface area and developed hierarchical pore structure of PCF bring rich active sites,shorten the ion transport distance and improve the transport efficiency,so that MSC has excellent capacitive properties.The highest specific capacitance of Ti₃C₂-PCF-MSC is attributed to the larger pore size of Ti₃C₂-PCF compared to Nb₂C-PCF and Nb₄C₃-PCF.In addition,Ti₃C₂-PCF-MSC also exhibits excellent series parallel integration ability,mechan-ical flexibility and long cycle stability.（3）The two-dimensional porous carbon membrane（PCF membrane）was assembled by vacuum filtration of Nb₂C-PCF,Ti₃C₂-PCF,and Nb₄C₃-PCF for the purification and treat-ment of dye wastewater.The results show that the Ti₃C₂-PCF membrane has a rejection rate of 99.9%for large molecule sized CR and RB,while the Nb₂C-PCF membrane and Nb₄C₃-PCF membrane not only have high rejection rates for large molecule sized dyes,but also have a rejection rate of 99.9%for small molecule sized MO and MB.At the same time,the PCF membrane has ultra-high throughput up to 3952.0 L m^-2 h^-1 bar^-1.The water flux of PCF membrane is two to three times higher than that of the currently reported two-dimensional carbon membrane with the same molecular weight cut off.In addition,the PCF membrane still has a high rejection rate（99.9%）for RB solution after soaking in harsh en-vironments for 90 days,demonstrating excellent structural stability.Long-term soaking treatment in acidic solutions also imparts a significantly increased water flux to PCF mem-branes,which can provide a simple strategy for preparing membranes with excellent dye sieving properties.（4）Ti₃C₂-PCF was modified by nitric acid oxidation at room temperature to obtain two-dimensional oxidation modified porous carbon（OPCF）,and self-assembled into an OPCF membrane.After nitric acid oxidation modification,the OPCF membrane achieved 99.9%retention of large molecules RB in RB/MO and RB/MB mixed dye solutions,and the per-meability of small molecules MO and MB was up to 91.0%and 99.5%,respectively,and the water flux was higher than 6000.0 L m^-2 h^-1 bar^-1.The separation effect of mixed solution and water flux are obviously superior to the two-dimensional carbon membrane reported so far.In addition,soaking in harsh environments for 45 days still showed a 99.9%permeate rate for RB and 99.5%permeate rate for MB in RB/MB mixed dyes,demonstrating excel-lent structural stability.