The Preparation Of Graphene Quantum Dots/magnetic Montmorillonite And Its Adsorption Properties For Methylene Blue

Organic dyes are widely used in the textile,paper,tanning and pigment industries.The organic dye remaining in the water is a typical pollutant,which is difficult to be biodegraded and has high toxicity.The wastewater containing such substances has deep chroma and high chemical oxygen demand and is difficult to degrade.At present,the organic dye wastewater discharged by a large amount has not only seriously damaged the ecological environment but also threatened human health.The adsorption method is simple,economical and efficient.The necessary conditions for the large-scale treatment of organic dye wastewater by this method are:low-cost,excellent adsorption/desorption performance,easy to separate solid-liquid separation adsorbents.The traditional block adsorbent(activated carbon)is difficult to regenerate,and the powder adsorbent(natural clay)is difficult to separate from solid and liquid.The large-scale practical application of the conventional adsorbent has been severely limited by the above disadvantages.Montmorillonite has the advantages of low cost,easy availability,green environmental protection and good adsorption performance.The montmorillonite modified by magnetic nanomaterial can overcome the shortcomings of difficult solid-liquid separation of powder adsorbent,and is expected to be used as a material for large-scale treatment of organic dye wastewater.Graphene quantum dots have an ultra-high specific surface area and a rich oxygen-containing functional group,and have excellent adsorption properties.However,its application in adsorption has been severely limited by its good water dispersibility.In view of this,this study aims to combine the advantages of montmorillonite,magnetic ferroferric oxide(Fe3O4)and graphene quantum dots to prepare a magnetic powder adsorbent with excellent adsorption performance,good regeneration performance and easy separation.The preparation conditions,morphology,physicochemical properties and adsorption properties of methylene blue(MB)of magnetic powder adsorbent were studied systematically.The main contents are as follows:(1)In this chapter,a graphene quantum dots(GQDs),magnetic montmorillonite(Fe3O4/MMT)and a graphene quantum dots/magnetite/montmorillonite nanocomposite(GQDs/Fe3O4/MMT)were prepared firstly.At the same time,the optimal preparation conditions for the optimized GQDs/Fe3O4/MMT powder adsorbent are as follows:Fe3O4 accounts for 50%(mass fraction)in Fe3O4/MMT,and GQDs solution accounts for 30%(volume fraction)in GQDs/Fe3O4/MMT suspension.The preparation temperature is 80?and the preparation time is 120 min.The crystal structure,morphology and physicochemical properties of GQDs/Fe3O4/MMT were characterized and analyzed by FT-IR,XRD,SEM,TEM,XPS,TGA,BET and VSM.The results are as follows:Nano-Fe3O4 was deposited on the surface of the MMT.GQDs are deposited on the surface of the material by chemical bonding in place of the hydroxyl groups.GQDs/Fe3O4/MMT is a nano-adsorbent with superparamagnetic properties,rich oxygen-containing functional groups on the surface and excellent thermal stability.(2)Research by adsorption experiments shows that:when the temperature is 20?,the pH is 7,the adsorption time is 20 min,the adsorption amount is 0.4 g/L,and the initial concentration of dye is 100 mg/L,the maximum adsorption capacity of GQDs/Fe3O4/MMT to MB is 224.9 mg/g.The removal rate of MB varies greatly with pH and the maximum removal rate occurs in the alkaline range.The removal rate of MB decreases with increasing ionic strength.Ultrasound can significantly shorten the adsorption equilibrium time without changing the adsorption amount,which can also promote the rapid selective adsorption of MB from GQDs/Fe3O4/MMT from mixed dyes.The desorption experiments showed that when the ratio of hydrochloric acid to ethanol was 1:3,the dye desorption efficiency reached a maximum of 72.8%.The MB adsorption/desorption efficiency decreased slightly after six replicate experiments.At the same time,it is concluded that the adsorption of MB by GQDs/Fe3O4/MMT conforms to the the pseudo-second-order kinetic model and the Langmuir isotherm model and the adsorption process is a spontaneous endothermic reaction.The chemical adsorption process is revealed by adsorption activation energy analysis.The MB was adsorbed on the surface of GQDs/Fe3O4/MMT by analyzing the XRD spectra before and after adsorption of MB.The change of FT-IR spectrum before and after MB adsorption and the removal rate of anion/cation dye at different pH values of GQDs/Fe3O4/MMT were obtained:electrostatic attraction,?-? stacking and hydrogen bonding have been confirmed Electrostatic attraction,?-? stacking and hydrogen bonding have been confirmed between GQDs/Fe3O4/MMT and MB,in which electrostatic interaction plays a major role.