Controllable Preparation Of Carbon-based Two-dimensional Nanomaterials For Photo/electrocatalytic Hydrogen Production And Antibiotics Degradation

Since the discovery of graphene,two-dimensional nanomaterials have aroused great interest from researchers due to their monoatomic layer structure,large specific surface area and unique anisotropy.In recent years,two-dimensional materials have performed well in photoelectric catalytic energy conversion and environmental applications.However,in the actual application process,there are still problems that are difficult to solve:1.The two-dimensional materials obtained by stripping are difficult to maintain independence from each other in the actual catalytic process,and there are serious problems of aggregation and stacking.2.The active site of the two-dimensional material with complete shape is limited,and it is difficult to fully expose the catalytic active site to achieve high performance catalysis.3.The rate of the redox reaction is related to the concentration of the reactants.How to achieve high-efficiency catalysis under the condition of low reactant concentration has become an urgent technical issue.Based on the above scientific issues,this paper designed and completed the following four tasks:(1)A new type of transition metal phosphide composite nanostructure,Fe ₂P nanoparticles/reduced graphene oxide(rGO)nanosheets/Fe ₂P,was synthesized in situ on the surface of titanium foil by one-step electrodeposition and subsequent low-temperature phosphorylation Nanoparticles(Fe ₂P@rGO)sandwich-structured nanosheet array.The Fe₂P@rGO nanosheet array can maximize the exposure of the catalytic sites of the material,and its structure is conducive to the efficient transmission of electrons and electrolytes on the surface of the material,and has strong stability,so it exhibits excellent electrocatalytic hydrogen evolution(HER)performance.The overpotential of the Fe₂P@rGO composite at a current density of10 m A cm^-2 is 101 m V,the slope of the Tafel is 55.2 m V dec^-1,and the exchange current density is 0.146 m A cm^-2.More importantly,after 12 hours of durability testing,the Fe₂P@rGO composite has a catalytic activity retention rate of 72%,while the commercially available Pt/C catalys t has an activity retention rate of only 55%.This study proposes a new material preparation idea,which can be extended to the preparation of more types of high-performance transition metal phosphide-based HER catalysts.(2)Using cobalt-based nanosheets prepared by electrodeposition as a substrate,a porous carbon skeleton is induced by self-assembly ZIF-67,and then phosphatized at low temperature to produce a C@CoP multi-level nanosheet array.The introduction of the carbon skeleton effectively increase s the specific surface area of the material,fully exposes the active sites,and at the same time makes it have good electrical conductivity,making it also have excellent electrocatalytic HER and oxygen evolution(OER)performance.In the HER reaction a lone,the overpotential of the C@CoP catalyst at a low current density of 10 m A cm^-2 is 72 m V;the overpotential at 100 m A cm^-2 at a high current density is 216 m V,and the overpotential at a high current density is low For commercial Pt/C catalysts;Tafel slope is 65 m V dec^-1.In the OER reaction alone,the overpotential of the C@CoP catalyst at a current density of 10 m A cm^-2 is 329 m V,and the slope of the Tafel is 107 m V dec^-1.Use two C@CoP electrodes as positive and negative poles to assemble into a f ully hydrolyzed electrolysis cell C@CoP||C@CoP,10 m A cm^-2 The electrolysis voltage at full hydrolysis current density is only 1.63 V,100 m A cm^-2 The electrolytic voltage at the high current density is 1.94 V,which is better than the electrolytic cell assembled by the commercial catalyst Pt/C||Ir/C.In the durability test of HER alone,OER alone and total hydrolysis,C@CoP all performed well.This study proposes a method for preparing catalytic materials with a novel structure,which can be used for t he preparation of more types of electrochemical reaction catalysts and multifunctional materials.(3)Through a simple two-step thermal process,single-layer/less-layer carbon nitride nanosheets(Cv-CNNs)with carbon vacancies were synthesized.The porous two-dimensional nitrogen carbide nanosheets are constructed by the gas template method,which provides a large reactive area for the photocatalytic reaction,which is beneficial to the efficient transmission of photogenerated electrons and reactants on the catalyst surface.Construct carbon vacancies,fully expose the reactive sites,effectively inhibit the recombination of photo-generated electrons-holes,and increase the reaction rate.Compared with traditional bulk carbon nitride samples,Cv-CNNs have excellent visible light photocatalytic hydrogen evolution capacity and catalytic stability.With no bias applied,the photocurrent density of Cv-CNNs is 1.22?A cm^-2,and the photocatalytic HER rate under visible light conditions is 2.03 mmol h^-1 g^-1,which is much better than the bulk measured under the same conditions Properties of nitrogen carbide materials.This study provides a method for mass-produced metal-free photocatalysts,which has reference significance for the preparation and development of other two-dimensional materials.(4)Prepare the nanofiltration membrane modified by graphene oxide(GO)and Cv-CNNs through the two-step pressurized cross-flow filtration method,using PVDF as the supporting membrane.The introduction of GO effectively improves the pore size of the support layer and increases the rejection rate of organic pollutants;the introduction of Cv-CNNs to achieve the selective adsorption and degradation of the antibiotic sulfadiazine(SDZ)by the membrane and the construction o f membrane filtration photocatalytic degradation of coupled antibiotics Sewage treatment system.Quantum mechanical simulation results show that C vacancies can effectively change the planar structure of carbon nitride nanosheets,enhance the adsorption ca pacity of Cv-CNNs to SDZ,and promote the release of photocatalytic hydrogen and the degradation of SDZ.The removal rate of SDZ(5 mg L^-1)reached almost 100%within20 minutes under visible light irradiation.A series of experimental designs validated different reactive species and explained the potential photocatalytic mechanism.This study designed a new type of coupled wastewater treatment reminder to provide new ideas for the treatment of low-concentration antibiotic wastewater.