Preparation Of Magnetic Graphene Composites And Adsorption Properties For Environmental Pollutants

With the development of economy,the environmental pollution caused by industrial and agricultural wastewater become a major problem in the world.The commonly used method for the removal of pollutants in environmental water samples is adsorption,and the core of the adsorption is an efficient adsorbent.Many materials such as activated carbon,carbon nanotube and resin are used as adsorbents for the removal of pollutants,graphene oxide as a kind of carbon nanomaterials has attracted much attention because of its large specific surface area and easy modification.However,graphene oxide is difficult to recover because it need to high speed centrifugation,so its widely application is limited.Magnetic graphene material can be recovered by external magnetic field,which overcomes the disadvantages of graphene.However,there are still some problems in the use of adsorbents:(1)The loaded Fe3O4 nanoparticles on the graphene oxide are not firmly immobilized and tend to fall off,which decreases the stability and reusability of the adsorbent;(2)The adsorption capacity of adsorbent is lower,which still needs to be improved;(3)The selectivity of the adsorbent is poor;(4)The reuse and practicability of adsorbent is poor.Therefore,this study focused on the preparation of the magnetic graphene composite adsorbent which is high capacity,high selectivity and not easy to fall off,and carry out the following work:these adsorbents were prepared,which including magnetic calcium silicate graphene oxide composite materials,imidazole chloride ionic liquid modified magnetic graphene oxide composite materials,triethylene tetramine modified magnetic graphene oxide composite materials and magnetic cucurbituril graphene oxide composites,and the adsorption properties of dyes,phosphate and phenols on these adsorbents were studied.The main contents are as follows:1.A novel magnetic calcium silicate graphene oxide composite adsorbent(MGSi)was synthesized using a two-phase coprecipitation method.MGSi adsorbent was characterized by Transmission electron microscopy(TEM),Field emission transmission electron microscopy(HRTEM),X-ray powder diffraction(XRD)and Fourier transform infrared spectrometry(FTIR).The results showed that the coated Fe3O4 nanoparticles with calcium silicate were firmly immobilized on the surface of graphene oxide,and were not easy fall off in the adsorption process compared to normal magnetic graphene oxide(MGO)synthesized using the coprecipitation method.Acridine orange(AO)was the selected as target to be absorbed by MGSi,and batch studies were conducted to evaluate the effects of various parameters,such as the contact time,temperature,initial concentration and solution pH on the adsorption performance of AO on the MGSi.The results indicated that the MGSi composite exhibited selective adsorption of the alkaline dye.The adsorption of AO on the MGSi followed pseudo-second-order kinetics,and the equilibrium adsorption was well described by the Freundlich isotherm model.The adsorption capacity can reach 70%of the initial adsorption capacity after repeated adsorption-desorption cycles for three times.Therefore,the adsorbent could be effectively used to remove alkaline dye from wastewater.2.Magnetic graphene oxide modified by 1-amine-3-methyl imidazole chloride ionic liquid(IL-MGO)was prepared by modified by 1-amine-3-imidazolium chloride ionic liquid and subsequently by chemical co-precipitation.The as-prepared IL-MGO was characterized by X-ray diffraction(XRD),Transmission electron microscopy(TEM)and Fourier infrared spectrometry(FT-IR).The adsorption property was evaluated by adsorption experiments of two kinds of anionic dyes including orange IV(OIV)and glenn black R(GR)and two kinds of cationic dyes including acridine orange(AO)and crystal violet(CV).The results indicated that the adsorption data followed the pseudo-second-order kinetics and Langmuir isotherm model.The maximum adsorption capacities of OIV,GR,AO and CV on IL-MGO were 588.2,57.37,132.8 and 69.44 mg·g-1 at 298 K,respectively.The IL-MGO has better selective adsorption on anionic dyes than magnetic graphene oxide(MGO).It demonstrated that IL-MGO would have great potential as an efficient adsorbent for removal of anionic dyes in water treatment.3.A novel triethylene tetramine-functionalized magnetic graphene oxide composite material(TETA-MGO)was prepared by modified by triethylene tetramine and subsequently by chemical co-precipitation.TETA-MGO was characterized by FT-IR,TEM,XRD,TG and specific surface analyses.The adsorption experiments of TETA-MGO for phosphate were compared with magnetic graphene oxide(MGO).Effects of pH,initial concentration of phosphate,adsorption time and adsorption temperature were studied.The results indicated that the adsorption capacity of the four adsorbents were highly pH dependent and reached optimum at pH 3.0.The adsorption mechanism of phosphate on TETA-MGO could be mainly related to electrostatic interaction.Adsorption processes reached the equilibrium within 50 min.The adsorption data of the TETA-MGO was well fitted with the pseudo-two-order kinetics model and the Langmuir isotherm model.The maximum adsorption capacity of TETA-MGO was 339.7 mg·g-1 at 298 K.The adsorption capacity of phosphate on the TETA-MGO was greatly improved compared with MGO.Moreover,phosphate ions adsorbed onto TETA-MGO could be desorbed and can be reused for four times.It indicated that TETA-MGO can be used as a renewable adsorbent with high capacity for the adsorption of phosphate.4.The magnetic cucurbituril[6]graphene oxide composite material(CB[6]-MGO)and magnetic cucurbituril[7]graphene oxide composite material(CB[7]-MGO)were prepared by the improved co-precipitation.CB[6]-MGO and CB[7]-MGO were characterized by FT-IR,TEM and XRD.The adsorption properties of phenol,resorcinol and 2-naphthol on the CB[6]-MGO and CB[7]-MGO were studied,respectively.The effect of the solution of pH,time and adsorbent dosage on the adsorjption performance were investigated.The adsorption data of phenol,resorcinol and 2-naphthol on CB[6]-MGO and CB[7]-MGO were well fitted with the pseudo-two-order kinetics model and Freundlich isotherm model.The experimental results showed that the adsorption of 2-naphthol on CB[6]-MGO and CB[7]-MGO are selective,the maximum adsorption capacity of 2-naphthol on CB[6]-MGO and CB[7]-MGO were 2.342 mmol·L-1 and 2.504 mmol·L-1,respectively.The adsorption capacity of phenols on the CB[7]-MGO and the number of cycles of CB[7]-MGO are higher than CB[6]-MGO.Therefore,CB[7]-MGO can be used as an envirornmentally friendly adsorbent for the removal of phenols from wastewater.