Preparation And Adsoption Properties Of MoSe₂ And Its Composites

With the rapid development of economic, dye wastewater has bring about serious environmental threats. Most dyes are toxic, they do great harm to humans, animals and plants. So it is of great significance to deal with these dyes wastewater effectively. MoSe₂, a kind of transition metal dichalcogenides, has similar layed structure with graphene, so it is a potential adsorbent for dye removal in wastewater treatment. In this study, flower-like MoSe₂ nanostructures were synthesized by mild and simple hydrothermal method, and MoSe₂/Fe₃O₄ magnetic composites, MoSe₂/AC composites were also synthesized by hydrothermal method. The obtained materials were characterized and the adsorption performance were investigated. This dissertation mainly included the following parts:（1） Flower-like MoSe₂ nanostructures were fabricated via hydrothermal method under 200℃ in ethanol-water mixed solvent（1:1） using sodium molybdate, Se powder as source and sodium borohydride as reductant. XRD, SEM, TEM and BET results indicated that as-prepared products were composed of nanosheets with thickness of 5-10 nm. The products was hexagonal phase MoSe₂ and the specific surface area and pore volume are all larger than solid-state synthesized MoSe₂. The results of adsorption performance showed that flower-like MoSe₂ exhibited better adsorption capability and displayed high removal ratio for dyes methylene blue（MB）, methyl orange（MO） and Rhodamine B（Rh B）, suggesting that flower-like MoSe₂ can be used as an effective adsorbent in wastewater treatment. The adsorption performance of flower-like MoSe₂ was evaluated systematically and factors influencing adsorption and sorption mechanism was also studied. The results showed that the adsorption data can be well described by pseudo-second-order equation. Langmuir isotherm model was more suitable for adsorption than Freundlich, theoretical maximum monolayer adsorption capacity was 67.29 mg/g. Adsorption thermodynamic study showed that the adsorption was spontaneous and endothermic, physisorption and chemisorption all existed in the process. The sorbent could be regenerated and used repeatedly. The main forces between MoSe₂ and MB may be π-π interaction, while Vander Waals forces, electrostatic and hydrophobic interactions also existed.（2） Magnetic MoSe₂/Fe₃O₄ composite was prepared via hydrothermal method and characterized by XRD, SEM and BET techniques. Factors affecting adsorption property, such as, adsorption time, initial dye concentration, p H, temperature, were studied.The results showed that the composite can be separated and recovered under a magnetic field. The adsorption data were modeled using the pseudo-first-order, pseudo-secondorder kinetics equations, indicating that kinetic curve conformed the pseudo-secondorder kinetic model. The adsorption process fixed Langmuir isotherm well,implying it was monolayer adsorption, the maximum theoretical amount was 52.88 mg/g. Thermodynamic parameters（-20<ΔG<-0 k J/mol,ΔH<40 k J/mol） suggested that adsorption was spontaneous and endothermic, physisorption and chemisorption coexisted.（3） In order to improve the adsorption capacity MoSe₂, MoSe₂/activated carbon（AC） composites with different AC contents were synthesized by hydrothermal method and the adsorption capacities were evaluated. It was found that the composite with 5wt% AC had the highest removal efficiency. Effect of adsorption time, initial dye concentration, p H and temperature was investigated. The results showed that adsorption process was more fit to the pseudo-second-order kinetic model. Langmuir isotherm model provided the best match to the adsorption data with the maximum adsorption capacity of 105.2 mg/g at room tempeture. Thermodynamic results showd that the adsorption process was spontaneous and favorable at hieher temperatur. The adsorption mechanism was deduced to be π-π interaction.