MoS₂-Based Nanomaterials:Preparation And Application For Cr??? Removal From Aqueous Solution

The environmental pollutions have been eliciting numerous concerns,which are closely related to daily lives as well as directly determined the safety of human survive.The heavy metal pollution,such as chromium,has brought a serious threat to the ecological environment and to human survival,especially.It has become an urgent problem to solve heavy metal contaminant.In this study,a series of MoS₂-based nanomaterials,such as MoS₂/GO,Fe₃O₄/MoS₂,and TiO₂/Fe₃O₄/MoS₂),were prepared by hydrothermal method and used for removing of Cr?VI?from aqueous solution.The samples were characterized by SEM,XRD,BET and FITR respectively.Cr?VI?was used as the target heavy metal contaminant,and the adsorption performance of the MoS₂-based nano-adsorbent was verified by batch experiments under different conditions.The adsorption process and its mechanism were investigated.1.MoS₂ nano-sheets,fabricated by a facile hydrothermal synthesis,was used for Cr?VI?removal from contaminate water.The removal efficiency of MoS₂ for Cr?VI?was 97% in no more than 150 min and the maximum adsorption capacity was36.22 mg·g^-1.The investigation on adsorption kinetics and isotherm showed that the pseudo-second-order kinetic and Langmuir isotherm models could well fit the adsorption experimental process.Adsorption thermodynamics investigation proved that the Cr?VI?adsorption on the surface of MoS₂ was a spontaneous endothermic physic-chemical process,in which the rate of adsorption was controlled by exterior surface diffusion step.It illustrated that MoS₂ nano-sheets can be used as excellent adsorbent for heavy metal ions removal from wastewater.2.The rod-like nano-MoS₂/graphene oxide?GO?nanocomposite was fabricated by a facile hydrothermal method,which was used as adsorbent to remove heavy metal contaminate,such as Cr?VI?,from aqueous solution.The investigations on adsorption kinetics and isotherms showed that the pseudo-second-order kinetic and Langmuir isotherm model could well fit the experimental data.The adsorption rate was controlled by both exterior and interior surface diffusion steps.Further investigations on the activation energy and thermodynamics of the adsorption process elucidated that the Cr?VI?adsorption on MoS₂/GO was an endothermic and spontaneous chemi-sorption process.The maximum adsorption capacity was 43.95mg·g^-1and the adsorption efficiency of Cr?VI?was enhanced significantly by the coexistence of organic contamination.After recycling five times,the decline of adsorption capacity of MoS₂/GO was about 8.0%,which indicated that the adsorbents could be reused in Cr?VI?removal.The MoS₂/GO nanocomposite has been proved to be a low-cost,efficient and promising adsorbent used for heavy metal ions removal from wastewater.3.The cubic nano-Fe₃O₄ and Fe₃O₄/MoS₂ composite were prepared via a simple solvothermal synthesis by using FeCl₃?6H₂O as the iron source.The adsorption efficiency of adsorbent under different pH conditions was discussed.It was found that the adsorption efficiency of Fe₃O₄/MoS₂ was the best when pH = 3.0,and the removal efficiency of 50mg/L Cr?VI?was up to 99.8%.The investigations on adsorption kinetics and isotherms showed that the adsorption process was in accordance with the pseudo-second-order kinetic and the experimental data fit the Langmuir adsorption isotherm model well.The adsorption rate was only controlled by the intra-particle diffusion.The maximum adsorption capacity was 30.14 mg?g^-1.According to adsorption thermodynamics,indicated that the adsorption process was spontaneous and endothermic chemical absorption.The co-existence of HA promoted adsorption reaction,Fe₃O₄ enhanced the adsorption performance of MoS₂ for the removal of Cr?VI?from water and it was convenient for magnetic recovery.4.The spherical nano-TiO₂/Fe₃O₄ composite was formed by using FeCl₃?6H₂O as the iron source and butyltitanate?TBOT?as a titanium source,then TiO₂/Fe₃O₄/MoS₂ composite adsorbent was obtained by combined with MoS₂ sheet,which was used to remove Cr?VI?from water.The adsorption performance of TiO₂/Fe₃O₄/MoS₂ for the removal of 100 mg/L Cr?VI?could up to 80% in the first10 min,reached 99.9% at 40 min,and then the adsorption reached equilibrium.Theadsorption process was in accordance with the pseudo-second-order kinetic and the experimental data fit the Langmuir adsorption isotherm model well.The adsorption rate was controlled by both exterior and interior surface diffusion steps.The maximum adsorption capacity was 57.30 mg?g^-1.According to adsorption thermodynamics investigation,the adsorption process was spontaneous,endothermic and physical absorption.The addition of anions obviously inhibited the adsorption performance of TiO₂/Fe₃O₄/MoS₂ for high concentration of Cr?VI?.And the influence degree was according to the order of PO₄^3-> Cl^-> SO₄^2-.the coexistence of HA significantly reduced the reaction efficiency and inhibited the adsorption.The specific surface area of TiO₂/Fe₃O₄/MoS₂ was 43.05 m²?g^-1,the complexes of TiO₂ and Fe₃O₄ greatly improved the adsorption performance of MoS₂,and the adsorption behavior was better than MoS₂/GO and Fe₃O₄/MoS₂.