Design,Synthesis And Photocatalysis Of Nickel-Iron Hydrotalcite Derived Sulfide-Based Composites

In recent years,the problem of antibiotics and heavy metal pollution has become a major challenge in the process of green and sustainable development of human society,and become an urgent problem to be solved.Therefore,how to deal with these environmental pollutants efficiently should be the focus of the current research work.As one of the effective means to remove environmental pollutants,semiconductor photocatalysis technology can use cheap and easily available sunlight as the driving force to induce and stimulate the production of active species for the mineralization treatment of organic pollutants and detoxification of heavy metal ions,which has become a hot topic in the field of environmental photocatalysis research.In view of the advantages of the method of photocatalytic removal of environmental pollutants,such as green and sustainable,no secondary pollution and so on,this paper takes the nickel-iron hydrotalcite functional materials as the precursors,designs and synthesis a variety of photocatalyst materials with abundant catalytic activity through the strategies of in situ vulcanization or construction heterostructure.The removal behavior and mechanism of antibiotics and heavy metals in water environment by nickel-iron hydrotalcite and its derived sulfide-based composites were systematically explored.The main research contents of this paper are as follows:（1）A novel nickel-iron hydrotalcite/carbon nitride composite（Ni Fe-LDH/g-C₃N₄）was synthesized via the calcination and hydrothermal methods.Its micromorphology,optical properties and physicochemical properties were characterized and analyzed by XRD,FT-IR,SEM,TEM,UV-vis DRS,XPS and other characterization methods.Subsequently,tetracycline,methyl orange and rhodamine B were selected as probe pollutant molecules to evaluate the photocatalytic activity of Ni Fe-LDH/g-C₃N₄ composite.The results showed that the removal rates of 20 mg/L tetracycline probe contaminant molecules by Ni Fe-LDH/g-C₃N₄ reached 96.81%under 60 min visible light irradiation,and the removal rates of methyl orange and rhodamine B within 120 min and 60 min were95.71%and 96.26%.The reason is that the Ni Fe-LDH can be used as a hole storage layer to store and enrich a large number of the photogenerated holes,which inhibits the photogenerated charge carriers’recombination,and improves the photocatalytic activity of the catalysts.Therefore,the designed and synthesized Ni Fe-LDH/g-C₃N₄ composites should have a potential application prospect in the field of environmental pollutants wastewater purification due to its excellent photocatalytic degradation performance.（2）In view of the shortcomings of the hydrotalcite functional materials such as lower visible light response and poor conductivity,this experiment took the nickel-iron hydrotalcite materials as the research object and constructed the nickel-iron hydrotalcite derived sulfides（Ni Fe S_x）via an in-situ solvothermal vulcanization strategy,and then combined with the g-C₃N₄ to obtain the Ni Fe S_x/g-C₃N₄ photocatalyst via the hydrothermal self-assembly methods.Subsequently,the tetracycline was used as the probe contaminant molecules to evaluate the photocatalytic performance of Ni Fe S_x/g-C₃N₄ photocatalyst.Specifically,the Ni Fe S_x/g-C₃N₄ photocatalyst showed the optimal photocatalytic performance under the optimal ratio of 3%（the mass ratio of Ni Fe S_x to g-C₃N₄was 3%）,and the removal rate of the tetracycline probe contaminant molecules was 92.54%within 70 min,which was 2.61 times higher than that of the pure g-C₃N₄.The experimental data exhibited that the constructed heterojunction between the Ni Fe S_x and g-C₃N₄ can play a synergistic effect to enhance the visible light utilization efficiency,inhibit the charge carriers’recombination,and thus improve the photocatalytic degradation efficiency.The development of this experiment also provides some references for the design and synthesis of the aimed photocatalyst for the removal of the relevant water pollutants.（3）In view of the shortcomings such as the unideal separation and migration efficiency of the photogenerated electrons and photogenerated holes in the photocatalytic process of the Ni Fe S_x/g-C₃N₄ composites,this experiment took g-C₃N₄ materials as the research object and constructed the oxalate induced oxygen-doped g-C₃N₄ materials via the oxalate-melamine co-calcination strategy and then coupled with the nickel-iron hydrotalcite derived sulfides to obtained the nickel-iron hydrotalcite derived sulfides/oxygen-doped g-C₃N₄ photocatalysts（NFS/OCN）.Subsequently,the tetracycline and Cr（Ⅵ）were selected as the probe contaminant molecules to evaluate the photocatalytic performance of NFS/OCN composites.The results showed that the removal rates of tetracycline and Cr（Ⅵ）probe contaminant molecules by the target catalysts were 85.88%and 93.69%,respectively,under the visible light irradiation.The corresponding photocatalytic rates were 0.01054 min^-1 and 0.02207 min^-1,respectively,which were 9.50 and2.95 times higher than that of NFS and OCN for the removal of tetracycline probe contaminant molecules,2.82 and 1.53 times higher than that of NFS and OCN for the removal of Cr（Ⅵ）probe contaminant molecules,respectively.The reason for the improvement of photocatalytic performance may be attributed to the formation of the Z-type heterostructure structure between NFS and OCN materials,which promotes the separation and migration of the photogenerated charge carriers,thus improving the photocatalytic activity of the aimed materials.The development of this experiment provides technical reserve for the design and synthesis of materials for the treatment of energy and environmental pollutants.（4）In view of the effects of oxygen doping g-C₃N₄ on lattice symmetry,inducing the recombination of the photogenerated electrons and hole pairs and reducing the oxidation capacity of the photogenerated holes,an element self-doping strategy was proposed to change the electronic structure and surface properties of g-C₃N₄ matrix materials in order to improve its photocatalytic performance.This experiment took g-C₃N₄ materials as the research object and constructed the nitrogen self-doped g-C₃N₄ photocatalyst by using the hydrazine hydrate pretreated melamine powders as the precursors via one-step calcination method,and then coupled with the nickel-iron hydrotalcite derived sulfides to synthesize the nickel-iron hydrotalcite derived sulfides/nitrogen-doped g-C₃N₄photocatalysts（NFS/NCN）.Subsequently,Cr（Ⅵ）was selected as the probe contaminant molecules to evaluate the photocatalytic performance of the NFS/NCN composites.Under the best conditions,the photocatalytic removal efficiencies of Cr（Ⅵ）probe contaminant molecules by the NFS/NCN-2composites were 90.52%under visible light irradiation,which was much higher than that of NFS（73.88%）and NCN（57.50%）,respectively.This was due to the interface between the NFS and NCN materials formed a Z-type heterojunction structure,which inhibited the photogenerated charge recombination and ensured that the aimed catalysts had strong photocatalytic reduction ability,thus contributing to improving the photocatalytic performance of the target catalyst.The results of this experiment can provide some references for the subsequent design of the related Z-type heterojunction catalysts and can be extended to other reaction systems.（5）In view of the poor visible light response of carbon nitride materials,the narrow-bandgap visible light response type cadmium sulfide material was selected to replace it to improve the catalytic activity of the aimed catalysts.This experiment took nickel-iron hydrotalcite derived sulfides materials as the research object and constructed the nickel-iron hydrotalcite derived sulfides/cadmium sulfide heterojunction photocatalysts（NFS/Cd S）via one-step hydrothermal method.Subsequently,tetracycline was selected as the probe contaminant molecules to evaluate the photocatalytic performance of the NFS/Cd S composites.The results showed that the removal rate of the tetracycline probe contaminant molecules by the NFS/Cd S composites was 85.77%,which was 3.10 and 2.42times higher than that of NFS and Cd S,respectively.The improvement of photocatalytic performance may be attributed to the synergistic effect between the two catalyst components,which enhanced the utilization rate of the visible light photons and promoted the separation and migration rate of the photogenerated charge carriers.In addition,the NFS/Cd S composites also had good photocatalytic removal effects on methylene blue and rhodamine B,with the removal rates of 92.09%and 92.8%,respectively.After five cycles of experiments,the target catalyst photocatalytic removal efficiency of the tetracycline probe contaminant molecules still remained above 80%,which also proved that the NFS/Cd S composites have good photocatalytic stability.The results of this experiment can provide some ideas for the further synthesis of the hydrotalcite derived sulfides-based photocatalysts and expand its application in the purification of other water environmental pollutants.