Study On The Preparation,Activization,Adsorption And Reduction Property Of Two-dimensional Molybdenite

As a kind of layered transition metal dichalcogenite mineral,molybdenite is rich in S atoms and possesses semiconductor property,which makes it have extraordinary potential in heavy metals adsorption and photocatalysis.However,because of the drawbacks in low specific surface area,low chemical activity and narrow indirect band gap,natural molybdenite cannot fully play crucial parts in its adsorption and catalysis properties.To overcome the mentioned problems,two-dimensional molybdenite nanosheets(2DM)were successfully prepared by exfoliating natural molybdenite in this work.The adsorption behavior of two-dimensional molybdenite on heavy metal ions in water was systematically investigated.Meanwhile,the adsorption mechanism of heavy metals on two-dimensional molybdenite was proposed.Two-dimensional molybdenite surface was activated through thermal modification.The effect of oxidation and defects of two-dimensional molybdenite surface on complexing heavy metals were revealed.Combining the photocatalysis reduction of two-dimensional molybdenite and Fenton technology,the degradation of organic pollutants was realized by two-dimensional molybdenite/Fe²⁺composite.This study established basic theory for the application of molybdenite materials in the field of water treatment,which has important significance for molybdenite utilization.The main contents and conclusions are as follows:(1)The results of AFM and TEM demonstrated that two-dimensional molybdenite was successfully prepared through electrochemical/ultrasonic exfoliation method.The adsorption experiments indicated that two-dimensional molybdenite had a dramatic efficiency for Pb²⁺removal from water with a 1479 mg/g adsorption capacity at 35?.Basing on the results of XPS,the adsorption mechanism might be described as follow:Pb²⁺was firstly attracted by the negatively charged two-dimensional molybdenite surface due to electrostatic adsorption.Then,the S sites and O sites could complex with Pb²⁺so that removing heavy metals from water.(2)Thermal treatment led to partial oxidation and edge defects on the surface of two-dimensional molybdenite.The batch tests indicated that Hg²⁺adsorption rate and capacity on 500?heated two dimensional molybdenite were 17.6 times faster and 11-fold higher compared to that of two-dimensional molybdenite without thermal modification.The tremendous enhancement of Hg²⁺adsorption was significantly related to two points:The defects greatly improved the migration rate of Hg²⁺to two-dimensional molybdenite surface by stronger electronegativity and dispersity of the adsorbent,and the oxidation could provide O active sites to strongly adsorb Hg²⁺through the formation of Hg-O.(3)The degradation experiments showed that two-dimensional molybdenite/Fe²⁺composite could eliminate all the methylene blue within 60 minutes,which was faster than some clay-and carbon-based Fenton catalyst.In addition,this material showed strong stability and nearly 100%degradation efficiency even after five cycles.During degradation process,the photocatalysis of two-dimensional molybdenite could reduce Fe³⁺which was generated by Fenton reaction to Fe²⁺so that achieving the recycle of Fenton reactants without external supplement.