Synthesis Of G-C₃N₄/Fe₃O₄/ZIF-8 Nanocomposites And Study On Their Adsorption Properties For Malachite Green And Cd²⁺

At present,with the rapid growth of population and rapid economic development,the global water consumption is gradually increasing.However,a large part of the water source is polluted every day.Among them,the pollution of heavy metals and organic dyes in water has become a serious environmental pollution problem.Malachite green?MG?is commonly used in the textile industry.It is also widely used as a disinfectant in the fish hatchery and aquaculture industry.MG can cause mutagenic,teratogenic and carcinogenic effects on humans.The exposure to Cd²⁺can cause skeletal deformation and poisoning of the blood system.Therefore,it is necessary to remove MG and Cd²⁺from water to avoid their negative effect on human health and the environment.Up to now,many methods had been applied to remove MG and Cd²⁺from aqueous medium,such as coagulation and flocculation,biotherapy,precipitation and adsorption.Among them,adsorption is an effective,and simple method because of its easy operation.The key point of adsorption method is to find an adsorbent with high adsorption capacity.Carbon nanomaterials are widely used as adsorbents because of their large specific surface area.Among them,g-C₃N₄ as a newly developed carbon nanomaterials is a chemically stable metal-free semiconductor.The in-built functional groups?–NH2/–NH–/=N–?of g-C3N4 allowed it to be an effective adsorbent for the elimination of heavy metal ions and organic pollutants.However,there exist some problems such as quick separation and easy recyclability in the use of g-C₃N₄ as adsorbents.Magnetic adsorbents have preferable properties such as quick separation and easy regeneration.As we all know,composites could combine the advantages of each component,thus possessing synergistic effect.We synthesized magnetic carbon nitride based nanocomposites to achieve efficient adsorption of MG and Cd²⁺.The main contents are as follows:1.g-C₃N₄ nanosheets were prepared by calcining urea at high temperature followed by ultrasonic stripping.g-C₃N₄/Fe₃O₄ were synthesized by an alcohol-thermal method and g-C3N4/Fe3O4/ZIF-8 were further prepared.The structure,morphology,specific surface area and magnetic properties of g-C3N4/Fe3O4/ZIF-8 nanocomposites were characterized by X-ray diffraction?XRD?,Fourier transform infrared?FTIR?,Transmission electron microscopy?TEM?,Nitrogen adsorption-desorption and room temperature hysteresis loop.The g-C₃N₄/Fe₃O₄/ZIF-8 possessed large specific surface area and good magnetic properties.The nanocomposites could be separated easily under an external magnetic field.2.The obtained g-C₃N₄/Fe₃O₄/ZIF-8 nanocomposites was used as a novel adsorbent for the removal of MG,bath absorption experiments for MG were done to explore the influence?pH,adsorbent dosage and initial concentration?on its absorption process.The adsorption isotherm and kinetics followed Langmuir model and pseudo-second-order kinetic model,respectively.The thermodynamic datas??G^°<0,?H^°>0,?S^°>0?showed that the adsorption process for MG was feasible,endothermic and spontaneous.The g-C₃N₄/Fe₃O₄/ZIF-8 nanocomposites showed excellent removal properties for MG.The maximum equilibrium adsorption capacity could reach as high as 3412 mg/g.The g-C3N4/Fe3O4/ZIF-8 nanocomposites could be easily separated using an external magnet,and the nanocomposites could be repeatedly utilized after five cycles.3.For the removal of Cd²⁺,the influence?pH,adsorbent dosage and initial concentration?on the Cd²⁺removal was studied.The adsorption isotherm followed Freundlich model and the adsorption kinetics was fitted by pseudo-second-order kinetic mode.The thermodynamic datas??G^°<0,?H^°>0,?S^°>0?indicated that the Cd²⁺adsorption was an endothermic and spontaneous process.The adsorption capacity of MG by g-C3N4/Fe3O4/ZIF-8 was nearly the same after five adsorption-desorption cycles,suggesting the nanocomposites could be repeatedly utilized.