| Electrospinning is one of the most commonly used methods to prepare carbon fibers.It has the advantages of widespread resources,easy processibility,and simple equipments.It can be used directly prepare self-supporting membranes and has shown good potential for application in many aspects.However,the mechanical properties of electrospun carbon fibers are still unsatisfactory compared to wet spinning or dry-jet wet spinning.Carbon nanofiber fabrics are of hydrophobicity,porosity and chemical stability,allowing them to be used to separate water and oil mixtures.However,the hydrophobicity of carbon nanofiber fiber fabrics are still insufficient,which limits the application.For the above two key issues,the main research content of this paper is as follows:1.The coal-based graphene quantum dots?CGQDs?with abundant oxygen-containing functional groups were prepared by liquid phase oxidation mixture acid system from bituminous coal.The CQGDs are of good the surface hydrophilicity and chemical reactivity.In order to explore the influence of oxygen-containing functional groups in the electrospinning process,we used hydrazine hydrate as reducing agent to prepare reduced coal-based graphene quantum dots by chemical reduction.The Fourier-transform infrared spectroscopy spectra,X-ray photoelectron spectroscopy and thermogravimetry results indicate that chemical reduction can effectively remove the oxygen-containing functional groups on the surface of CGQDs.The reduced coal-based graphene quantum dots exhibit higher crystallinity and lower defect density than the CGQDs.2.The CGQDs were added into the PAN-based spinning solution,and carbon nanofibers with controlled diameter and good mechanical properties were prepared by electrospinning.We found that with the increase in CGQDs content,the average diameters of the carbon nanofibers gradually increase from 141.5 to 773.3 nm.The interior of the carbon nanofibers becomes dense along with increasing of CGQDs dosage.And the mechanical properties of the carbon nanofiber fabric are also gradually enhanced.Under the optimized condition,the tensile strength of the carbon fiber fabric is 2.2 MPa and the Young's modulus is about 70 MPa,which is nearly 7times higher than that of the carbon nanofiber without the CGQDs.However,the tensile strength and the Young's modulus of the carbon nanofiber fabric with the reduced coal-based graphene quantum dots were lower than those of the pure PAN carbon fiber film.From this,we propose that the improvement mechanism is due to the cross-linking effect of the introduced CGQDs.Abundant oxygen-bearing functional groups of the CGQDs endow their high surface polarity and chemical reactivity.The strong interaction between oxygen-bearing functional groups and the polar PAN molecules induces the PAN molecules to be tightly adsorbed around the CGQD nanosheets,thereby leading to the formation of compact electrospun PAN fiber precursors.Moreover,the CGQDs also act as cross-linkers toward the PAN molecules during carbonization because of their good chemical reactivity originated from the oxygen-bearing functional groups,thus resulting in the formation of dense and non-porous carbon nanofibers with improved mechanical properties.3.We investigated in detail the effects of polymer concentration,carbonization temperature,and the addition of CGQDs on the morphology and surface wettability of carbon nanofibersSeveral important results have been obtained.?1?When the polymer concentration in the spinning solution is low,the morphology is beaded.With the increase of the concentration,beading gradually disappeared,and the fiber diameter increased significantly.?2?As the carbonization temperature increases,the carbon content on the carbon fiber surface gradually increases,the content of oxygen-containing functional groups decreases,and the surface non-polarity increases.?3?The fiber diameter are increased significantly as the increasing of CGQDs,?4?The hydrophobicity of carbon fibers increases significantly with the increase of carbonization temperature,polymer concentration,and the addition of CGQDs.The contact angle of the carbon nanofiber fabric prepared under optimized conditions was142.6±1.1°,and the oil flux reached 324 L m-2 h-1.The ECNFs had good chemical stability,endurability,and high separation efficiency when used for gravity-driven oil/water separation.The strong polarity and excellent chemical reactivity of CGQDs ensuring them to act as cross-linking agents for the formation of dense,strong,and flexible carbon skeleton.This work provides a useful way for the preparation of high-performance electrospun carbon nanofibers and the design of coal-based advanced carbon materials. |
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