| Due to the frequent oil spills caused serious damage to the marine ecosystem and huge loss of resources,and the discharge of a large amount of toxic and high-concentration of organic dyes in the textile industry caused damage to water resources,it is in urgent need of an efficient and environmentally friendly material for oil-water separation and dye wastewater purification.As one of the most important carbon-based adsorption materials in the family,expanded graphite(EG)has attracted much attention in the field of water treatment due to its low cost,large specific surface area,rich porous structure,weak polarity,non-toxic,and light weight.However,expanded graphite is usually prepared by chemical oxidation with strong inorganic acid in harsh conditions,with high energy consumption,large consumption of strong acid,large amounts of acidic tailings and low expansion rate.At the same time,due to the strong hydrophobic surface,poor mechanical properties,and low efficiency in the sewage treatment,it is difficult to effectively recover.Therefore,in order to fulfill the better application of the expanded graphite in this field,the surface and structure modification of the expanded graphite has been a hot spot in the research of carbon-based adsorption materials in recent years.Graphite in low cost was selected as the adsorbent matrix.In view of the energy consumption and pollution problems of conventional preparation methods,expanded graphite with higher expansion rate was prepared in this study with an environmentally friendly and convenient one-step method at room temperature,and its oil absorption performance was explored and optimized.Then,in view of the poor dispersibility of EG applied to dye wastewater and the difficulty in separation and recovery of adsorbent,the compound modification and surfactant modification method by integrating with gelatin,magnetic Fe3O4 or poly(vinylidene fluoride)(PVDF)was used to improve its hydrophily/hydrophobicity,adsorption performance,and separation and recovery performance.Three composite materials,EG-xGel,Fe3O4/xMEG,and EG-PVDF were prepared and applied to the treatment of simulated dye wastewater and oily wastewater,respectively.The influences of various factors on adsorption performance were studied,and the possible adsorption mechanism between adsorbent and dye was analyzed with a variety of characterization methods.The application prospect of the prepared materials in the field of oily and dye wastewater treatment was outlooked.The main research contents were as follows:(1)In order to improve the expanded ratio of expanded graphite(EG)at the low-energy and environmentally friendly conditions,a semi-soild phase and one-step method under mild temperature was developed on the base of the traditional oxidization intercalation process for EG preparation.To improve the hydrophilicity,separation and adsorption properties of EG in dye wastewater treatment,a binary composite microbeads adsorbent(EG-xGel)with various gelatin dosages was prepared.The synthesized EG and EG-xGel were characterized by SEM,FTIR,XRD,TG,BET,VSM and their adsorption capability toward oily and dyes in wastewater were evaluated.In the oily system,with a temperature of 20? and NaCl concentration of 15 g·L-1,maximum absorption of expanded graphite toward engine oil and edible oil within 30 min can reach 23.97 and 30.92 g·g-1,respectively.The highest removal of 68.2%and 87.2%were observed for 50 mg·L-1 methylene blue(MB)and Congo red(CR)respectively,with 0.1 g EG-64Gel microbeads by air dried applied at room temperature.The pseudo-second-order kinetics described MB and CR adsorption process better.Moreover,EG-64Gel exhibited excellent separation performance under acidic condition with CR dye almost removed completely in the binary MB/CR system.(2)To enhance the surface hydrophilicity,adsorption capacity and recovery efficiency to various ionic dyes,modified expanded graphite(MEG)was fabricated by surfactant-based intercalating reagent CTAB/KBr modification of EG.Then two magnetic composite adsorbents Fe3O4/xMEG were successfully prepared by introduction of Fe3O4 magnetic component with immersion(?)or hydrothermal method(H),respectively.The adsorption properties of Fe3O4/3MEG-? on Orange ? were investigated.The adsorption mechanism and behavior were investigated by kinetic and isothermal adsorption models,and the adsorption properties toward the dye substrates with different structures were compared.At the same time,the influence of the regeneration mode on the reusability of the adsorbent was investigated.The Fe3O4/3MEG-? exhibited a rapid adsorption efficiency(47%ORII removal within 2 min)and tunable adsorption properties with adjusting MEG amount,the adsorption process fitted better to the Langmuir isotherm and pseudo-second-order kinetic models.The excellent removal efficiencies of a variety of dyes suggested that Fe3O4/3MEG-? could efficiently adsorb both the anionic and cationic dyes under neutral condition.After 6 consecutive adsorption-desorption cycles,it can still maintain good adsorption performance.In addition,Fe3O4/3MEG-I can be efficiently collected by an external magnetic,suggesting it a promising candidate for dyes effluent treatment in practical application.(3)In order to improve the separation,recovery efficiency and oil absorption performance of expanded graphite by enhancing the hydrophobicity,poly(vinylidene fluoride)(PVDF)with low surface energy,high mechanical strength and good thermal stability was chosen to prepare a 3D multi-porous structured foam by a hard template and solvent-free process.The obtained EG-PVDF composite foam exhibited excellent hydrophobicity(water contact angle at 126±3.5°)and absorption capacity to a variety of oil components,the absorption amount of 5.339 g·g-1 toward soybean oil was obtained within 1 min.Moreover,it can be conveniently recovered by detaching in ethanol or merely extruding by hand.This extraordinary absorption and separation performance maintained even in harshness environments after several recycles,verifying the efficiency of the EG-PVDF porous composite foam for various oil spillage and industrial sewage treatment. |
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