Synthesis And Application Of Graphene Oxide Based Functional Materials In Adsorption Of Heavy Metal Copper?Nickel Ions

The water contamination has become one of the key environmental problems for humanity.Among all water contaminations,the most vital menace is heavy metal ions which can damage tissues and organs of human beings and animals by enrichment.Various treaments have been used to remove heavy metal ions from wastewaters.Sorption is by far the most useful and economical method for the treatment of contaminated wastewater,which has distinct advantages of low operating cost,high efficiency,and minimal volume of sludge.The adsorbent materials must have high specific surface area,more adsorption sites and chemical stability.In recent years,graphene oxide?GO?has shown remarkable potential in the field of environmental protection.Graphene oxide is a two-dimensional?2D?nanomaterial with large specific surface and abundant oxygen-containing functional groups.Compared to conventional adsorbents,GO has a much higher effciency of adsorption to metal ion by chelation,due to its oxygen-containing functional groups like carboxyl,hydroxyl,and epoxide functional groups on the sheet.It is an important way to improve the adsorption capacity of GO by increasing the oxygen-containing functional groups of GO via chemical modification.The thesis focuses on preparation of a series of graphene oxide-based functional materials by using various methods.The morphologies and structures of the as-prepared functional materials were well characterized,and the adsorption performances to Cu²⁺?Ni²⁺of the graphene oxide-based functional materials were investigated.The main contents in this thesis are summarized as follows:?1?Graphene oxide?GO?with different oxidation degree was prepared by modified hummers method and used as adsorbent for removal of Cu²⁺?Ni²⁺in aqueous solution.The morphology,structure and composition of the GO with different oxidation degree were characterized by X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Fourier Transform Infrared Spectoscopy?FT-IR?,scanning electron microscope?SEM?,Brunauer Emmett Teller?BET?,Thermogravimetric?TG?,and a superior GO preparation technology was determined.The effects of the parameters such as p H value,contact time,initial concentration of Cu²⁺,Ni²⁺and adsorbent dosage on adsorption performance were examined.The reuse performance of GO was investigated by adsorption-desorption experiments.The XRD and XPS spectra of GO obtained at different oxidation time showed that the diffraction peak of the original graphite disappeared,and the maximum interlayer spacing of GO was 1.02 nm and the O/C ratio was the highest after 48 hours of secondary oxidation,indicating that the oxidation degree was the best.The GO prepared by this method showed the infrared activity,indicating that the oxygen-containing functional groups such as carboxyl group,hydroxyl group and epoxy group were bonded on the graphite substrate after oxidation.The TG curve also showed this.SEM and BET showed that GO surface presented a clear two-dimensional planar structure,but its surface area was not large.When the solution p H=5.3 and the adsorption time was 120 min,the copper ion reached its adsorption equilibrium,and the maximum adsorption value was110.5 mg/g.When the solution p H was 6.5 and the adsorption time was 120 min,the nickel ion reached its adsorption equilibrium,and the maximum adsorption value reached 102.7 mg/g.The adsorption of GO is in accordance with Freundlich adsorption.The results of adsorption-desorption experiments showed that the adsorption capacity still kept 61%of its initial capability after 10 cycles.The results suggested that GO is an effective adsorbent for heavy metal ions removal in water treatment.?2?Tartaric acid modified graphene oxide functional materials?t GO?were prepared by esterification,and t GO was characterized by X-ray photoelectron spectroscopy?XPS?,FourierTransformInfraredSpectoscopy?FT-IR?,Thermogravimetric?TG?,scanning electron microscope?SEM?and Brunauer Emmett Teller?BET?.The effects of p H,adsorption time,temperature and initial concentration on the adsorption of copper and nickel ions were investigated.The XPS shows that the surface functional groups of the composite change,and the FT-IR spectra show a new absorption peak.SEM and BET show that the basic form of tartaric acid modified composite material is consistent with GO.In the adsorption test,the environment p H has a great influence on the adsorption performance of the functional materials,while the ion concentration has little effect on it.When the environment p H is 6.0-6.5,the maximum adsorption capacity of Ni²⁺and Pb²⁺was147.8 mg/g and 409.2 mg/g,respectively.When the solution p H is 5.5,the maximum adsorption capacity of Cu²⁺could reach 164.2 mg/g,and the adsorption balance reached in 90 minutes.The experimental results show that the adsorption of t GO is in accordance with the second-order kinetics equation,that is,t GO is monomolecular layer adsorption,and mainly depends on chemical adsorption.Tartaric acid modified graphene can also be recycled.Experiments show that the grafted functional groups can improve the GO adsorption performance,which makes t GO more excellent than GO.?3?The cross-linked chitosan?CS?and cross-linked chitosan/fumed graphene functional materials?CS/GO?were prepared and characterized by XPS,FT-IR,SEM and BET.Effects of p H value,adsorption time,temperature and initial concentration on the adsorption properties of copper,nickel and cadmium ions were studied.The diffraction peak of N appears in the XPS spectrum.The absorption peak of-NH in the infrared spectrum demonstrates that there is an amine group in the graphene-based functional material.SEM and BET show that the combination of GO and CS can significantly increase the surface area of the material,providing more active sites for adsorption.When the environment p H was 6.0-6.5,the maximum adsorption capacity of Ni²⁺and Cd²⁺was 179.3mg/g and 360.2mg/g,respectively.When the p H was 5.5,the maximum adsorption capacity of Cu²⁺could reach 189.mg/g,the adsorption balance reached in 120 minutes.The adsorption of CS/GO is in accordance with the Langmuir equation,that is,CS/GO is monomolecular layer adsorption.The results of adsorption-desorption experiments showed that the adsorption capacity still remained65%of its initial capability after 8 cycles.?4?The EDTA was successfully introduced into the graphene oxide substrate by the reaction of the isocyanate?-NCO?group on the diphenylmethane diisocyanate?MDI?with the active hydrogen on GO and diethylamine tetraacetic acid?EDTA?,and the new functionalized materials were characterized by XPS,FT-IR,SEM and BET.Effects of p H value,adsorption time,temperature and initial concentration on the adsorption properties of copper and nickel ions were studied.The absorption peaks of the amide group and carbamate group appear in the XPS spectrum.The absorption peaks of N-Hand C-N at 1573cm^-11 and 1411cm^-1 in the FI-IR spectum demonstrate that the graphene oxide-based functional materials were successfully prepared.The SEM results show that the composite exhibits a similar structure to GO,and the surface area of the material is higher than that of GO.These are beneficial to improve the adsorption performance of the composite.When the adsorption time is 100 min,the adsorption equilibrium is reached.When the p H is about 6.5,the maximum adsorption capacity of Ni²⁺could reach 92.2 mg/g.When the p H is about 5.5,the maximum adsorption capacity of Cu²⁺could reach 101.5 mg/g.The adsorption of EDTA/MDI/GO is in accordance with the Langmuir equation,that is,EDTA/MDI/GO is monomolecular layer adsorption.The results of adsorption-desorption experiments showed that the adsorption capacity to Cu²⁺,Ni²⁺still remained 61%,56%of its initial capability after 8 cycles.?5?The Hydroxymethyl urea modified graphene oxide?UF-GO?was prepared by GO and Hydroxymethyl urea based on alkali-acid-alkali process of producing urea-formaldehyde resin.The adsorption-desorption capacities of UF-GO to Cu²⁺and Ni²⁺were investigated.UF-GO was characterized by XPS,FT-IR,XRD,SEM,BET and TG.The new peak of the amide group appears in the XPS spectrum,the new absorption peak at 1260 cm^-1 in the FI-IR spectum and the new diffraction peak in XRD demonstrated that UF-GO was obtained via amidation reaction between GO and Hydroxymethyl urea.The TG result indicates that the temperature resistance performance of UF-GO was superior to that of GO due to the existence of hydrogen bond and amide bond.The SEM and BET results show that UF-GO displayed porous,rough surface,and the surface area of the material is higher than that of GO.In the adsorption test,we found that UF-GO spent 150 min reaching equilibrium.When the solution p H=6.5,the maximum adsorption capacity of Ni²⁺is 94.1 mg/g.When the solution p H=5.5,the maximum adsorption capacity of Cu²⁺is 96.9 mg/g.UF-GO retains around 60%of the adsorption effect after 8 cycles,and the experimental results show that the adsorption of UF-GO is in accordance with Freundlich adsorption,which means UF-GO is a multi-molecular layer adsorption.Experiments show that methylol urea can effectively immobilize GO and retain the adsorption capacity in a degree,so that solid-liquid separation becomes easier,which makes UF-GO exhibit better comprehensive application performance than GO.?6?UF-GO adsorption column was prepared and the removal effects of UF-GO to low concentration copper and nickel ions in waste water were studied.The influence factors such as adsorption column height,flow velocity,initial copper and nickel ions concentrations were explored.The adsorption capacity of adsorption column was fitted by Bohart-Adams model and the ideal adsorption capacity was predicted.The regenerating method and effect of adsorption microspheres were studied in detail.The results show that the penetration time increased with the increase of packing height and decreased with the increase of flow velocity and initial concentration.The unit adsorption capacity decreased with increasing filler height and flow rate and increased with increasing initial concentration.The experimental data of different packing height were fitted by Bohrat-Adams model.The fitted parameters show that the GO modified urea-formaldehyde resin has good adsorption capacity.According to the D-A model,the theoretical adsorption capacity to Cu²⁺and Ni²⁺was 148.84 mg/L and 289.839 mg/L when the height of packed column is 2.104 cm and 2.153 cm respectively.After 10 cycles,the total adsorption capacity to Cu²⁺and Ni²⁺is 42.3%and 23.4%respectively of the value of the first time.The results show that UF-GO adsorption column has good reproducibility.