Green Preparation Technology And Application Of Graphite Derivatives

Graphene has been widely studied and applied due to its excellent properties.At present,the preparation methods of graphene have disadvantages of low yield,high energy consumption,complicated operation and environmental pollution,so it is necessary to develop a novel and efficient green preparation method to solve the problems above.The hydroxyl radical?·OH?has strong oxidizing capacity,its oxidation characteristics are non-selective and can react with almost all kinds of substances.However,in the application process,·OH has the disadvantages of low concentration,short life and can not continuous production.In our research,we have designed and setup a continuous·OH generation apparatus for the first time,and achieved the facile exfoliation of graphite to give graphene.The maximal yield of graphene can reach to 90%.The mechanism of the preparation of graphene was also proposed.By studyed the kinetic law of·OH concentration change,the law of·OH concentration changes with the reaction process factors was predicted.The process flow of·OH exfoliation of graphite to prepare graphene was designed.·OH exfoliation method has the advantages of simple process,low energy consumption?normal pressure and room temperature?,no pollution to the environment,and effectively solves the shortcomings of the existing preparation methods of graphene.It is expected to be a practical and efficient method for graphene large-scale production.In order to expand the application of the obtained graphene product,the high concentration of graphene dispersion was prepared by the combination of ultrasonic dispersion and surfactant component formulation.The process flow sheet for high concentration graphene dispersion preparation was designed.Expandable graphite is one of the important derivatives of graphite and has extremely important industrial application.At present,the main preparation method of expandable graphite are often use aggressive reagents and restricted by the relatively high energy consumption,complex operation,environmental pollution,and low product quality,which greatly limits its application.We for the first time developed mechano-chemical method to produce the expandable graphite to solve the problems above.The process flow sheet of mechano-chemical process was designed.1.We achieved the facile exfoliation of graphite to prepare graphene by using the laboratory-made·OH continuous generation apparatus.The process parameters were optimized by the single factor experiments,the optimal process parameters were obtained as follows:NaCl concentration 5.0%?w/w?,4.0g graphite dosage,the applied current strength 10mA,the air flow rate 1.0L/h for 3h.Under the conditions,the yield of graphene is 77.5%.The morphology and structure of the graphene products were characterized by TEM,XRD,Raman,FT-IR,AFM and XPS.The results showed the products have the characteristic peaks and absorption peaks of graphene,the layers number of graphene product is 3,the carbon element content of the graphene was 82.18%,and the oxygen element content was 17.82%.The good quality of graphene product can be attributed to the synergistic effect between strong oxidation of hydroxyl radicals and electrical exfoliation.Further mechanism analysis shows that the mechanism of·OH exfoliation graphite is the synergistic effect between strong oxidation of·OH and electrical effect:The strong oxidation of·OH,etching the edges of the graphite sheet and opening the edge layer of the lattice,causing·OH inserted into the graphite sheet by the edge layer,At the same time,under the effect of electricity,the ions of the electrolyte and the·OH inserted into the graphite sheet.The above processes effectively increase the graphite layer spacing,weakening the van der waals force between the sheets,and graphite is eventually exfoliated into graphene.2.Through the optimization design of different electrolyte systems in the exfoliation process,the control of the number of layers of graphene products is realized.The optimal process parameters were obtained as follows:SDBS solution concentration 10.0%?w/w?,5.0 g graphite dosage,the applied current strength 10 mA,the air flow 1.0 L/h and the exfoliation time 3 h.At this time,the yield of the graphene product was 90%.The morphology and structure of the graphene products were characterized by TEM,XRD,Raman,FT-IR,AFM and XPS.The results showed that the carbon element content of the graphene product was 89.8%,and the oxygen element content was 10.2%,which indicated that the obtained graphene product has no impurities and the product quality is good.The layer number of graphene product obtained is about 2,while the layers of graphene products from NaOH,PVP,DTAB and NaCl systems were 30,20,4 and 3 at the same experimental conditions,respectively.At the same time,the process flow sheet of graphene preparation by·OH exfoliation was designed.3.The kinetic study of·OH formation in the preparation process was investigated.The·OH concentration change is in accordance with the following model equation:C?·OH?=0.0048+0.000894₁+0.0016₂-0.000374₃-0.0068₄-0.0000691₂²-0.0000353₃²+0.0018₄².The concentration of·OH was firstly increased with the concentration of SDBS,graphite dosage,applied current strength,the air flow rate,and then decreased.The degree of influence of different process parameters on the change of·OH concentration is:SDBS concentration>air flow rate>graphite dosage>applied current strength.The highest concentration of hydroxyl radicals was 7.98×10^-3 mol/L,at the following conditions:SDBS concentration 10.0%?w/w?,graphite dosage 5.0 g,the applied current strength 10 mA,and the air flow rate 1.0 L/h.4.The high concentration of graphene dispersion was prepared by the combination of ultrasonic dispersion and surfactant components formulation.The effects of the dispersants and preparation parameters on the quality of graphene dispersion were studied.The optimal dispersant and optimal process parameters were as follows:SDBS solution concentration5.0%?w/w?,0.25 g graphene dosage,80%ultrasonic power,and ultrasonic for 30 minutes,at this case,the concentration of the obtained graphene dispersion is 1.98g/L.The graphene dispersion remains stable for 90 days.5.Sulfur-free expandable graphite was successfully prepared by mechano-chemical method.The effects of different factors on the preparation process were studied.The optimal process parameters were as follows:stainless steel ball mill media,ball milling media size 6 mm in diameter,ball milling time 4 hours,ball mill speed 500 r/min,thermal decomposition time 4 hours,thermal decomposition temperature 200°C,ratio of graphite to sodium bicarbonate 1:1.The expanded volume of the obtained expandable graphite product was 142 mL/g.The morphology and structure of the obtained expandable graphite samples were characterized by SEM,XRD,Raman;etc.This work has important academic and industrial references for the preparation of non-sulfur expanded graphite.