The Preparation Of Interlayer-expanded MoS₂ Nanosheets For The Simultaneous Removal Of Toxic Metals And Cationic Dyes

Heavy metals and organic pollutants are commonly present in a variety of industrial effluents.For example,effluents from the textile industry and dye-making industries often contain heavy metals,which generally act as mordant during dyeing.Heavy metals and organic pollutants have serious ecological and toxicological impacts due to their high bioaccumulation,high toxicity and persistence in the environment.Therefore,it is urgent and important to study how to remove heavy metals and organic pollutants from industrial wastewater and avoid the discharge of these pollutants into the receiving water.In this paper,the preparation of interlayer expanded Mo S₂?IE-Mo S₂?nanosheets and their simultaneous adsorption of heavy metal ions and cationic dyes in water were studied.Specific research contents were as follows:?1?IE-Mo S₂nanosheets were prepared from ammonium molybdate and thiourea simply via the one-pot hydrothermal method and characterized by scanning electron microscope?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?;?2?The adsorption behaviors of heavy metal ions?i.e.,Cu???and Pb????and cationic dyes?i.e.,methylene blue?MB?,rhodamine B?Rh?and malachite green?MG??on IE-Mo S₂nanosheets were systematically studied by adsorption batch experiment in a single system;?3?The adsorption behaviors of heavy metals and cationic dyes on IE-Mo S₂nanosheets were also investigated in the mixed pollutant systems;?4?The possible mechanism of heavy metal adsorption Pb???on IE-Mo S₂nanosheets was discussed;?5?The regeneration and recycling properties of IE-Mo S₂nanosheets were studied;?6?Finally,the adsorption properties of IE-Mo S₂nanosheets on Pb???and MB in simulated textile wastewater were investigated.This study draws the following conclusions:?1?SEM and TEM images showed that the prepared IE-Mo S₂nanosheets was ultra-thin nanosheets with obvious ripples on the surface and the average transverse size was 200-300 nm.XRD and high resolution TEM results showed that the layer spacing of IE-Mo S₂nanosheets was extended to 9.4?compared with that of ordinary Mo S₂nanosheets?2.98??.The IE-Mo S₂nanosheets showed relatively disordered atomic arrangement on the surface,which contained more defects.These defects lead to more cracks and holes in the nanosheet,which can be used as an additional diffusion channel in the adsorption process,so that more pollutants can enter the interior,which is conducive to improving the adsorption performance of IE-Mo S₂nanosheet.?2?In a mono-contaminant system,the results of batch adsorption experiment showed that the adsorption rates of heavy metal ions?Cu???and Pb????and cationic dyes?MB,Rh and MG?by IE-Mo S₂nanosheets and layered bulk Mo S₂?B-Mo S₂?increased first and then remained steady with the increase of solution p H.In addition,in the studied p H,the adsorption efficiency of IE-Mo S₂nanosheets towards these five target pollutants was significantly higher than that of B-Mo S₂,indicating that increasing the layer spacing of Mo S₂could indeed improve the adsorption efficiency of Mo S₂.?3?In the mono-contaminant system,the adsorption of Pb???and Cu???at the initial concentration of 40 mg/L by IE-Mo S₂nanosheets can be completed within 50 min,and the adsorption equilibrium time of cationic dyes?MB,MG and Rh?at a initial concentration of150 mg/L was about 60 min.The adsorption behaviors of IE-Mo S₂nanosheets towards these five pollutants were well fitted by pseudo-second-order kinetic model.?4?In the mono-contaminant system,the adsorption of heavy metal ions?Pb???and Cu????and cationic dyes?MB,Rh and MG?by IE-Mo S₂nanosheets increased significantly with the increase of the initial pollutant concentration,and finally reached the saturation adsorption equilibrium.The Freundlich and Langmuir adsorption isothermal models were used to simulate these adsorption behaviors,and the results showed that the adsorption of heavy metal ions and cationic dyes on IE-Mo S₂nanosheets was more consistent with the Langmuir adsorption phenomenon,indicating that the active sites for the pollutant adsorption by IE-Mo S₂nanosheets were evenly distributed.The saturated adsorption capacities of IE-Mo S₂nanosheets for Pb???,Cu???,MB,Rh and MG at 298 K were 499,423,500,355 and 276 mg/g,respectively.?5?In the mixed Pb???-dye system,when the initial pollutant concentration?C₀?was relatively low,that is,when C_0Pb???was 2 and 40 mg/L,the presence of cationic dye slightly inhibited the adsorption of Pb???by IE-Mo S₂nanosheets.when the C₀was high,that is,when C_0Pb???were 200 and 250 mg/L,the adsorption amount of Pb???by IE-Mo S₂nanosheets was significantly increased.One possible reason for this phenomenon was that the adsorption of Pb???and cationic dyes by IE-Mo S₂nanosheets is carried out through different active sites.Cationic dyes adsorbed on the surface of IE-Mo S₂nanosheets can provide additional nitrogen-containing or oxygen-containing groups,thus providing new active sites for Pb???adsorption.?6?In the mixed Pb???-dye system,the presence of the heavy metal Pb???ions hardly affected the adsorption of the cationic dyes?MB,Rh and MG?by IE-Mo S₂nanosheets.?7?XPS technology was used to characterize the IE-Mo S₂nanosheets before and after the adsorption of heavy metal Pb???.The results showed that the sulfur atoms on the IE-Mo S₂nanosheets had a strong affinity with Pb???,and the formation of Pb S was the driving force for the adsorption of Pb???on the IE-Mo S₂nanosheets.?8?After the treatment with 0.5 mol/L EDTA or Na OH,the used IE-Mo S₂nanosheets could be regenerated and still showed a high adsorption level for Pb???and MB after 6adsorption-desorption processes.?9?Through the adsorption performance test of IE-Mo S₂nanosheets on simulated textile wastewater,it is shown that IE-Mo S₂nanosheets can remove 93.24%Pb???and92.18%MB in sewage.In addition,there was no significant loss in the adsorption efficiency of recycled IE-Mo S₂nanosheets.The simultaneous adsorption of Pb???and MB in simulated textile wastewater by IE-Mo S₂nanosheets was further tested.IE-Mo S₂nanosheets have a good comprehensive treatment effect for wastewater containing heavy metals and cationic dyes.?10?At last,we investigated the scalable preparation method of IE-Mo S₂nanosheets,and simulated the adsorption performance of IE-Mo S₂nanosheets by filling the purification column with IE-Mo S₂nanosheets and sand.The results show that IE-Mo S₂nanosheets effectively removed Pb???from the simulated Pb???contaminated Dongpu water,indicating that IE-Mo S₂nanosheets has a wide range of practical application prospects.