Preparation And Adsorption Properties Of Two-dimensional Nanocomposites

In recent years,the problems of food safety seriously affect people’s health,resulting in economic losses and the development of national economy.Heavy metals,as a ubiquitous environmental pollutant,have great influence to food safety.Food can be contaminated by heavy metal ions,including lead,arsenic,mercury,cadmium and tin,through various ways along the food chain into the human body.These can cause the damage of human organs,which have a destructive effect and even can induce cancer.With the development of nanotechnology,as a new type of pollutant adsorbent,two-dimensional nanomaterials such as graphene has been extensively developed.In this paper,molybdenum disulfide（MoS₂）with similar structure as graphene was selected as the research object,and the composite of molybdenum disulfide-chitosan nanosheets（MoS₂-CS）and magnetic molybdenum disulfide composites（MnFMC and CoFMC）were prepared as heavy metal adsorbents,and these materials were characterized and evaluated for heavy metal removal.This paper mainly carried out in the following research work:1.MoS₂-CS nanosheet material was synthesized by a one-step synthesis by simple SiO2-assisted grinding at room temperature with high yield.The as-prepared nanomaterials were characterized by transmission electron microscopy,Fourier transform infrared spectroscopy,Raman spectroscopy,thermogravimetric analysis.The process of nanocomposites preparation was proved by means of scanning electron microscopy and UV-visible spectroscopy,and the exfoliation process of molybdenum disulfide was further analyzed.The yield of molybdenum disulfide exfoliation efficiency can be increased from 16.23% to 58.59% with the addition of auxiliary agent of SiO2.The as-synthesized MoS₂-CS is uniform monolayer and has good dispersibility in aqueous,and with a high chitosan loading about 20 wt%.2.The adsorption performance of MoS₂-CS nanomaterials were studied with a series of experiments.Compared with the bulk molybdenum disulfide,the exfoliated molybdenum disulfide nanosheet shows better adsorption effect,and the adsorption capacity of heavy metal can be increased from 6.47 mg/g to 80.03 mg/g.MoS₂-CS exhibits a larger specific surface area and provide more surface active sites arising from the functionalization of chitosan.The adsorption performance for Pb2+ at different pH values shows that MoS₂-CS nanosheets can maintain good adsorption effect during 4-6.The kinetic study shows that the adsorption process is chemisorption,and the reaction rate is mainly affected by the surface functional sites.The adsorption isotherm results show that the adsorption process can be well fitted to the Langmuir adsorption isotherm model,which proves the monolayer adsorption,and the maximum adsorption capacity can reach to 104.17 mg/g.Upon the thermodynamic study,the calculated enthalpy change ΔH0 is 25.432 KJ/mol,the entropy change ΔS0 is 103.562 J/mol K,and the Gibbs free energy ΔG0 decreases with the increase of temperature,which further proves the adsorption process is endothermic and spontaneous.Furthermore,the as-prepared MoS₂-CS adsorbent can be recycled for several times and still maintain a good adsorption effect.3.This work demonstrates a one-pot solvothermal synthetic method for fabricating MFe2O4（M=Mn,Co）-MoS₂-carbon dot（CDs）nanohybrid composites（MnFMC,CoFMC）with excellent Pb（II）removal ability.Detailed characterization through SEM,XRD,UV-vis spectra,fluorescence spectra and VSM confirmed the formation of the nanohybrid composites.On the one hand,the introduction of carbon and ferrite itself with abundant oxygen-containing functional groups effectively improve the adsorption capacity of MoS₂ nanosheets for heavy metal ions;on the other hand,MoS₂ nanosheets as the substrate for the loading of CDs overcome its difficult for separation.Moreover,the modification of ferrite nanoparticles makes the hybrid adsorbent material with the ability to separate and recycle.4.The adsorption study of MnFMC and CoFMC for heavy metal ios was carried out through kinetics,isotherm and thermodynamics study.It was proved that the adsorption process can be well fitted to pseudo-second-order kinetic model and Langmuir adsorption model.The maximum adsorption capacity of Pb2+ can reach 588.24 mg/g MnFMC and 660.67 mg/g for CoFMC,and can be reused for several times.The adsorption mechanism was further revealed using XPS and FTIR,and the results show that the adsorption is mainly contribute to the oxygen-containing groups on the surface of Mo S2.Moreover,these nanohybrid adsorbents exhibit excellent reusability,lower the effluent Pb（II）contents down to the ppb level,which satisfies the drinking water standard recommended by the World Health Organization,and are promising candidates for water purification.