National Institute of Aerospace, 100 Exploration Way, Hampton, VA 23666-6147, USA.
Nanoscale. 2013 Sep 7;5(17):7814-24. doi: 10.1039/c3nr02135a.
Structural manipulation of the two dimensional graphene surface has been of significant interest as a means of tuning the properties of the nanosheets for enhanced performance in various applications. In this report, a straightforward and highly scalable method is presented to prepare bulk quantities of "holey graphenes", which are graphene sheets with holes ranging from a few to tens of nm in average diameter. The approach to their preparation takes advantage of the catalytic properties of silver (Ag) nanoparticles toward the air oxidation of graphitic carbon. In the procedure, Ag nanoparticles were first deposited onto the graphene sheet surface in a facile, controllable, and solvent-free process. The catalyst-loaded graphene samples were then subjected to thermal treatment in air. The graphitic carbons in contact with the Ag nanoparticles were selectively oxidized into gaseous byproducts, such as CO or CO2, leaving holes in the graphene surface. The Ag was then removed by refluxing in diluted nitric acid to obtain the final holey graphene products. The average size of the holes on the graphene was found to correlate with the size of the Ag nanoparticles, which could be controlled by adjusting the silver precursor concentration. In addition, the temperature and time of the air oxidation step, and the catalyst removal treatment conditions were found to strongly affect the morphology of the holes. Characterization results of the holey graphene products suggested that the hole generation might have started from defect-rich regions present on the starting graphene sheets. As a result, the remaining graphitic carbon structures on the holey graphene sheets were highly crystalline, with no significant increase of the overall defect density despite the presence of structural holes. Preliminary experiments are also presented on the use of holey graphene sheets as fillers for polymeric composites. The results indicated that these sheets might be better reinforcing fillers than the starting graphene sheets due to their perforated structure. Other unique potentials of these materials, such as for energy storage applications, are also discussed.
二维石墨烯表面的结构调控一直是人们关注的焦点，因为它可以通过调节纳米片的性质来提高各种应用的性能。在本报告中，提出了一种简单且高度可扩展的方法来制备大量的“多孔石墨烯”，即具有平均直径为几到几十纳米的孔的石墨烯片。这种制备方法利用了银（Ag）纳米粒子对石墨碳的空气氧化的催化性质。在该过程中，首先通过一种简单、可控且无溶剂的方法将 Ag 纳米粒子沉积在石墨烯片表面上。然后将负载催化剂的石墨烯样品在空气中进行热处理。与 Ag 纳米粒子接触的石墨碳被选择性地氧化成气态副产物，如 CO 或 CO2，在石墨烯表面留下孔。然后通过在稀释的硝酸中回流将 Ag 去除，以获得最终的多孔石墨烯产物。发现石墨烯上孔的平均尺寸与 Ag 纳米粒子的尺寸相关，通过调整银前驱体的浓度可以控制 Ag 纳米粒子的尺寸。此外，空气氧化步骤的温度和时间以及催化剂去除处理条件强烈影响孔的形态。多孔石墨烯产物的表征结果表明，孔的生成可能始于起始石墨烯片上存在的富缺陷区域。因此，尽管存在结构孔，但孔状石墨烯片上剩余的石墨碳结构仍然高度结晶，整体缺陷密度没有明显增加。还初步介绍了将多孔石墨烯片用作聚合物复合材料的填充剂的实验。结果表明，由于其穿孔结构，这些片可能比起始石墨烯片更好的增强型填充剂。还讨论了这些材料的其他独特潜力，例如用于储能应用。
