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摘要: 超声剥离法被认为是由石墨制备石墨烯最方便、最清洁的方法,但在溶剂中大量处理石墨时,其产率较低,且超声剥离后的石墨难以进一步再被剥离为石墨烯,造成大量的资源浪费。因此本文提出了一种超声与研磨相结合的高效剥离石墨制石墨烯的新策略。结果表明,超声剥离后不能再被剥离的石墨经超声和研磨处理后,可进一步剥离为石墨烯,石墨烯收率可达4.73%。产生这种现象的原因可能是由于石墨层的规则堆叠被破坏,且产生了卷曲的石墨边缘,这些均为溶剂进入石墨层间克服作用力提供了“楔入点”。获得的石墨烯片层均小于10层。该工作为石墨大规模高效剥离制少缺陷石墨烯提供了一种新策略。Abstract: Ultrasonication is regarded as the most convenient and cleanest approach for graphene preparation from graphite. However, the yields are low in large scale preparation because after ultrasonication the exfoliated graphite is difficult to exfoliate into graphene, which leads to a great deal of waste. A new strategy for the efficient exfoliation of the exfoliated graphite into graphene was investigated by combining ultrasonication and grinding treatments. Results indicated that the exfoliated graphite produced by ultrasonication could be further exfoliated into graphene by combining ultrasonication and grinding. The obtained graphene sheets were all comprised of fewer than 10 layers with a yield of 4.73%. This was attributed to the destruction of the regular stacking of the graphite layers and scrolling and folding their edges to provide entry points for the solvent to overcome the interlayer forces between adjacent layers. This work provides a new strategy for the efficient exfoliation of graphite into few-defect graphene on a large scale.
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Key words:
- Graphene /
- Exfoliation /
- Grinding /
- Ultrasonication /
- Graphite
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Figure 3. SEM images of (a, b) pristine graphite, (c, d) exfoliated graphite after ultrasonication for 30 min, (e, f) grinded exfoliated graphite (sample (c, d)) for 1 h. Experimental conditions: graphite, 0.5 g; NMP for ultrasonication, 50 mL; NMP for grinding, 5 mL; ultrasonication time, 30 min; grinding, 1 h; centrifugation at 600 r/min for 90 min.
Figure 4. XRD patterns of graphene and graphite with different treatment. (a) pristine graphite, (b) sample treated with ultrasonication and exfoliation by pristine graphite, (c) sample treated with ultrasonication, exfoliation and grind by pristine, (d) sample treated with ultrasonication, exfoliation, grind, ultrasonication, and exfoliation by pristine graphite, (e) sample treated with ultrasonication and extraction filtration by pristine graphite, (f) sample treated with ultrasonication, exfoliation, grind, ultrasonication and extraction filtration by pristine graphite. Experimental conditions: graphite, 0.5 g; NMP for ultrasonication, 50 mL; NMP for grinding, 5 mL; ultrasonication time, 30 min; grinding, 1 h; centrifugation at 600 r/min for 90 min.
Table 1. Effect of ultrasonication time and the grinding treatment on the yield of graphene*
Entry Experimental details Yield (%) Photo 1 1st ultrasonication
from pristine graphite1.68 2 2nd ultrasonication 1.53 3 3rd ultrasonication 0.66 4 4th ultrasonication 0.56 5 5th ultrasonication 0.59 6 Grinding followed by
ultrasonication treatment
of pristine graphite.3.42 7 Grinding followed by
ultrasonication treatment
of exfoliated graphite after the 1st ultrasonication.3.58 8 Grinding followed by
ultrasonication treatment
of exfoliated graphite
after the 5th ultrasonication.4.73 Note: *Experimental conditions: pristine graphite (0.5 g) in NMP (50 mL) was treated by the 1st ultrasonication (30 min), after ultrasonication, the mixture was sent to centrifuge at 600 r/min for 90 min to obtained the graphene suspension, and the residual exfoliated graphite was directly resent to the next time of ultrasonication or grinding for 1 h. The volume of NMP for grinding treatment was 5 mL. The 2nd, 3rd, 4th and 5th ultrasonication were treated as the same centrifugation and ultrasonication conditions. Table 2. Characteristics of graphene and graphite with different treatments*
Samples FWHMi 2θ/°ii d/nmiii D/nmiv a 0.12 26.6 0.34 1.72 b 0.15 26.5 0.35 1.72 c 0.14 26.6 0.35 1.38 d 0.10 26.5 0.35 2.30 e 0.14 26.5 0.35 1.38 f 0.12 26.5 0.35 1.72 Note: (a) pristine graphite, (b) sample treated with ultrasonication and exfoliation by pristine graphite, (c) sample treated with ultrasonication, exfoliation and grind by pristine, (d) sample treated with ultrasonication, exfoliation, grind, ultrasonication, and exfoliation by pristine graphite,
(e) sample treated with ultrasonication and extraction filtration by pristine graphite, (f) sample treated with ultrasonication, exfoliation, grind, ultrasonication and extraction filtration by pristine graphite.
Experimental conditions: graphite, 0.5 g; NMP for ultrasonication, 50 mL; NMP for grinding, 5 mL; ultrasonication time, 30 min; grinding, 1 h; centrifugation at 600 r/min for 90 min.
i FWHM: full width at a half maximum according to the peaks in Fig. 4; ii 2θ: typical diffraction angle; iii d: the d-spacing between the graphite layers; iv D: the vertical distance along the plane of (002) for each sample. -
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