Standardization System Construction And Applied Research Of Graphene-Based Two-Dimensional(2D) Material

Graphene,known as supermaterial,leads to the development of two-dimensional（2D）material due to its superior properties in light,electricity,force,heat and magnetism,etc.In practical applications,graphene prepared by different methods has a variety of structures and properties,forming a"class"of graphene material,including single layer graphene,bilayer graphene,few-layer graphene,graphene oxide（GO）,reduced graphene oxide（r GO）,etc.referred to as Graphene-based Two-Dimensional（2D）Material（hereinafter referred to as Graphene Material）which has very promising applications in many aspects such as water-treatment,sensors,battery energy storage,biomedicine,etc.However,the structure and properties of graphene material produced and applied in practice are very different from that of graphene in theory.The lack of standard system of graphene material has become a common key problem restricting the development of graphene material industry.Formulation of the measurement standards,quality evaluation methods and application rules helps to characterize the graphene material based on scientific and unified procedures,which makes different graphene material comparable.Further,there is of great significance in scientifically exploring various graphene material,improving graphene industry chain and promoting the high-quality development of graphene industry.Based on this point,the research focus of this thesis is organized as follows:（1）Firstly,due to the varying difference factor of graphene material’s intra-layer structure,a variety of instruments were used to develop the structure measurement methods,establishing a measurement system based on the intra-layer relationship.Such a system can determine the type of graphene material by directly analyzing the structure difference factors from the aspects of layer number distribution,defect level,functional group,heteroatom,and impurity content.Atomic force microscope（AFM）and Raman spectrometer were applied to measure layers of graphene material based on location-and grade-specific approach.Data statistics and analysis can really reflect the characteristics of the samples,circumventing the problem of insufficient representative micro area in TEM measurement.This also helps to reduce the measuring costs of graphene material in industry.Based on the work,the author of this paper developed a group standard as the first complete adult（refer to the attached Table Two（4））.The intensity ratio of D+D’peak and 2D peak in Raman was used to characterize the defect level of graphene powder,which replaced the originally used but inaccurate method of using the intensity ratio of D peak and G peak.The group standard has been developed based on the work by author as the first complete adult（refer to the attached Table Two（5））.Thermogravimetric-fourier transform infrared spectroscopy（TGA-FTIR）was adopted to both qualitatively and quantitatively characterize the functional groups of graphene powder material.The analysis accuracy can be traced back to the level of thermogravimetric analysis,enabling a high-level quantitative structure analysis of graphene material possible.Such a method also circumvented the problem of low measurement accuracy and poor repeatability present in traditional chemical titration method.As an important supporting material,the author participates in the development of an international IEC standard as an international expert with equal contribution（refer to the attached Table Three（2））.The usage of CS analyzer and ONH analyzer based on high-temperature combustion/pyrolysis can measure the element content of graphene powder material.The measurement challenges due to insufficient combustion and splashing of graphene material were solved by expelling air in the sample through tablet preparation,and thus realizing the accurate measurement of elemental contents.Subsequently,an international standard was developed by the author as equal contributors（refer to the attached Table Three（1））.Considering the non-easy digestion and low impurity contents of graphene material,inductively coupled plasma mass spectrometry（ICP-MS）was used to measure the contents of metal impurity in graphene material,which showed a high measurement precision.In the mean while,the author participates in a national standard development program using this work as an important support material.A number of measurement standards have been obtained the National CNAS qualification and have been widely applied in inspection and measurement area.This plays an important role in sorting out different types of graphene material and effectively analyzing the structure of graphene material.（2）Secondly,based on the classification of structure difference factors,the methods of measuring macroscopic physical properties of graphene material were systematically studied and a measurement system was established.The measurement methods of physicochemical indicators of graphene material was carried on in terms of surface morphology,specific surface area and real density.In the case of measuring surface morphology,the problem of insufficient representation in SEM measurement was solved by designing a nine-grid substrate for sample preparation and using a region-specific approach and distribution statistics.The Ar gas,which fits with the physical adsorption model of graphene material,was used as the adsorbent to measure the specific surface area of graphene material.This solved poor repeatability and reproducibility of current measurement methods in graphene industry.The author participates in a national standard development program using this work as an important support material.By standardizing the measurement conditions and the measurement procedures,the real density of graphene material was measured by a real density meter,and a general measurement method was formed.The measurement methods of conductivity,sheet resistance,and carrier mobility were studied from the aspects of electrical properties of graphene material.A four-point probe was used to measure the conductivity of graphene powder by simultaneous pressing.Therefore,the conductivity of graphene powder under different pressures was measured in situ which can be used to quickly evaluate the conductivity of graphene powder and guide its production process.The conductivity and uniformity of graphene film can be evaluated by measuring the sheet resistance of graphene film and calculating their average,average percentage change and maximum percentage change.The quality of graphene films can be evaluated by measuring the carrier mobility of graphene films by van der Pauw method,which also allows the carrier mobility of different graphene films to be effectively compared.At present,the measurement methods of thermophysical properties of graphene material is not unified,and the measurement results can be poorly compared.Based on the industrial fact,the methods of measuring the thermal conductivity and thermal performance of products were studied based on graphene powder or graphene films.Numerous experiments have been conducted to explore the sample pretreatment,sample preparation and the measurement conditions of graphene powder and graphene films.Apparatus like laser thermal meter,guided heat flow meter and hemispherical emissivity meter,were employed to characterize the thermal conductance and heat dissipation performance of graphene powder and thin films.The measurements are stable,repeatable and maneuverable.with high penetration rate of instruments.The author as the first complete adult developed and completed one local standard（refer to the attached Table Two（1））and two group standards（refer to the attached Table Two（2,3））.And these standards obtained national CNAS qualification,with wide application in inspection and measurement work,and great significance to the application of graphene powder materials in the field of heat conduction and heat dissipation.（3）Thirdly,in order to more reasonably use the measurement method and measurement standard system of the microstructure and macroscopic physical properties of the graphene material,one selection method of graphene material for transformation from scientific research to application is proposed through systematic study from micro level to macro level.The basic common relationship between the microstructure and macroscopic physical properties of graphene material should be fully investigated and analyzed before studying graphene material and their applications.The matrix of application selection parameters was proposed and designed so that the specific structure-activity relationship should be studied in depth according to the existing research results in different specific application fields,and the core key parameters and their weights should be determined.One material quality homogeneity evaluation matrix is put forward and designed,which gave the material quality uniformity coefficient and the calculation formula.By jointly using the multi-parameter,macro analysis and micro measurement way,the quality uniformity coefficient can be calculated from the formula by measuring various parameters and properties.It can be used to evaluate the quality uniformity of graphene material.A material optimization target matrix and matching coefficient was put forward,which provides the calculation formula of matching coefficient.The computed material matching coefficient over come the traditional trial and error mode,comparable to reasonable material selection and allocation,increasing research efficiency,and promoting the transformation of scientific research to application effectively.（4）Finally,in order to better understand the graphene material selection method for transformation from scientific research to application,the application of ion rejection water treatment was carried out.Based on present research achievements,four types of commercial graphene material was characterized according to the measurement methods and measurement standard system,to determine the four key selection parameters including oxygen content,thickness,diameter size and defect level.It was proved that higher the graphene material uniformity coefficient,more stable the sodium ion rejection.This provides a case for the graphene material selection of transformation from scientific research to application.Further,in order to combine with the MXene water treatment in the research group,the selected graphene material GR3 was used as an additive in MXene to compound GR3-MXene pristine composite membrane.After heat treatment,the carboxyl group in GR3 nanosheet and hydroxyl group in MXene nanosheet were cross-linked to form-COO-by esterification,which increased the swelling resistance of the composite membrane.XPS,Raman,FTIR and XRD measurements were performed to verify the formation of stable nanochannels between the nanosheets.The penetration rate of Li⁺（the diameter of hydrated ion was 7.64?）,Na⁺（diameter of hydrated ion was 7.16?）,K⁺（hydrated ion diameter 6.62?）and Al³⁺（the diameter of hydrated ion was 9.50?）in the GR3-MXene composite membrane were（0.395,0.191,0.0833 and 0.226）mol·m^-2·h^-1respectively.The ion penetration rate of GR3-MXene pristine composite membrane decreased significantly after cross-linking,and Li⁺,Na⁺,K⁺,and Al³⁺were（5.71,0.688,1.58 and 0.57）×10^-2mol·m^-2.h^-1,respectively.This provides a new solution for the development of high performance two-dimensional water purification membrane.This thesis revealed the graphene material has not only"a single formality of material",but"one family type of material".The studies help to establish general measurement system of graphene material with wide applicability and strong universality,and to establish standard systems bridging material structure,macrophysical properties,quality evaluation and selection application.This indeed provides new scheme on promoting the transformation of graphene material from research to application.