| Being a novel and mutifunctional carbon material,expanded graphite（EG）with an exfoliated volume of 200-300 m L/g can be obtained via the conventionally chemical oxidation process using sulfuric acid as the intercalating reagent.However,this process has some drawbacks,for example,the residual sulfur in the gallery of EG can cause side effects such as corrosion and catalyst deactivation,also,during the exfoliation process,sulfur dioxide will be generated which can deteriorate the air quality.Therefore,the major issue of this paper is aim to the preparation of sulfur-free EG with high expansion volume and the development of expanded graphite functional materials.Based on this,the target of this research is to design and fabricate a new preparation process of sulfur-free EG with high expansion volume,explore its adsorption for oil pollutants and performance of hydrogen evolution material prepared from waste EG,fabricate catalytic ozone catalyst on EG carrier and composite filler for biological aerated filter,evaluate the performance in engineering applications of various functional EG materials.This work will provide a valuable guidance for development and application of EG.The contents and main conclusions are reported as follows:（1）Sulfur-free EG were fabricated by two-step chemical oxidation method with potassium permanganate（KMn O4）as oxidant,perchloric acid（HCl O4）and phosphoric acid（H3PO4）as primary intercalation agent and sodium nitrate（Na NO3）as secondary intercalation agent.The process parameters were optimized by orthogonal test and sulfur-free EG with expansion volume of 480 m L/g was obtained.The optimum parameters were as follows:the mass of natural flake graphite was 5 g,KMn O4was 1 g,Na NO3was 7.5 g,mixed acid volume was 24 m L,and the intercalation temperature was60°C.The characterization analysis showed that the intercalation agent had entered the graphite layer during the preparation process,rich network pore structure with main large and medium pores was observed and a certain graphite crystal structure was retained for the prepared EG.（2）The adsorption test of sulfur-free EG for pure oil,hydrocarbon organics and oil slick were carried out,and the application research of field adsorption test were accomplished.The adsorption performance,regeneration performance and adsorption mechanism were analyzed.The results showed that the adsorption capacity of EG for pure oil was better than that of commercial EG and felt.The adsorption capacity was directly proportional to oil viscosity and inversely proportional to temperature.The adsorption capacity for hydrocarbon organics was inversely proportional to the polarity of organics.It was verified that EG had good adsorption effect on oil slick.The field experiment realized the rapid disposal of oil leakage on site,further developing its foundation of engineering applications.The regeneration performance revealed that the vacuum suction filtration method was better than the compression method.The adsorption mechanism displayed that the adsorption character depended on the non-polar property of EG,rich storage space for oils and the viscosity and polarity of oils.（3）Two kinds of composite hydrogen evolution materials（MoS2/EG-gasoline and Mo S2/EG-diesel）with molybdenum disulfide（Mo S2）supported on waste EG after adsorption saturation were successfully fabricated.The apparent morphology,crystal structure and chemical composition of two materials were characterized and the electrochemical hydrogen evolution properties were evaluated.The results indicated that Mo S2 can be successfully prepared and and loaded on EG by hydrothermal synthesis method.The electrocatalytic hydrogen evolution performance of the two composite materials were better than that of pure Mo S2.（4）The fabrication of catalytic ozonation catalyst（CaCO3/EG）with EG as carrier and calcium as active component was excuted.The crystal structure,apparent morphology,chemical composition and specific surface area were characterized.The experiments of catalytic ozonation degradation of EDTA were carried out.Characterization analysis illustrated that Ca CO3 as the active component was successfully loaded on EG.When the dosage of catalysts was 1g/L,the ozone concentration was 12 mg/L and the initial p H was4.9,the mineralization degradation of EDTA in terms of TOC removal efficiency could reach 80%and 92%within 60 and 120 min respectively.After three cycles of reuse,the TOC removal rate could still be maintained at 83%within 120 min,indicating that the catalysts have good stability and reusability.The result of free radical scavengers confirmed that·OH was involved in the catalytic mechanism of the Ca CO3/EG–O3 system and the degradation of EDTA can be deduced by O3 direct oxidation and indirect oxidation of free radicals.（5）Based on the exfoliation of EG,the experimental study on the preparation of composite filler for biological aerated filter was conducted.The preparation process was optimized by orthogonal test and the performance prameters of composite filler were tested.Compared with commercial fly ash ceramsite filler,the experimental study on the composite filler for degradation of domestic sewage were implemented.When the dosage of the diatomite,the zeolite and the expandable graphite was 10 g,5 g and 0.10 g respectively,the volume of H3PO4 was 18 m L,the calcination temperature was 500°C,the performance parameters of the optimum filler were better than those of commercial filler.In the experiments of treatment for domestic sewage,the film hanging time and the removal rates of COD,NH4+and SS of the composite filler were also better than those of the commercial filler,proving that the biodegradability and interception capacity of the self-made composite filler were capable than those of the commercial filler and the self-made filler will have good application prospects in the field of wastewater biodegradation and purification. |
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