Russo Paola, Hu Anming, Compagnini Giuseppe, Duley Walter W, Zhou Norman Y
Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Ave., West Waterloo, Ontario N2L 3G1, Canada.
Nanoscale. 2014 Feb 21;6(4):2381-9. doi: 10.1039/c3nr05572h. Epub 2014 Jan 16.
Porous graphene (PG) and graphene quantum dots (GQDs) are attracting attention due to their potential applications in photovoltaics, catalysis, and bio-related fields. We present a novel way for mass production of these promising materials. The femtosecond laser ablation of highly oriented pyrolytic graphite (HOPG) is employed for their synthesis. Porous graphene (PG) layers were found to float at the water-air interface, while graphene quantum dots (GQDs) were dispersed in the solution. The sheets consist of one to six stacked layers of spongy graphene, which form an irregular 3D porous structure that displays pores with an average size of 15-20 nm. Several characterization techniques have confirmed the porous nature of the collected layers. The analyses of the aqueous solution confirmed the presence of GQDs with dimensions of about 2-5 nm. It is found that the formation of both PG and GQDs depends on the fs-laser ablation energy. At laser fluences less than 12 J cm(-2), no evidence of either PG or GQDs is detected. However, polyynes with six and eight carbon atoms per chain are found in the solution. For laser energies in the 20-30 J cm(-2) range, these polyynes disappeared, while PG and GQDs were found at the water-air interface and in the solution, respectively. The origin of these materials can be explained based on the mechanisms for water breakdown and coal gasification. The absence of PG and GQDs, after the laser ablation of HOPG in liquid nitrogen, confirms the proposed mechanisms.
多孔石墨烯（PG）和石墨烯量子点（GQDs）因其在光伏、催化及生物相关领域的潜在应用而备受关注。我们提出了一种大规模生产这些有前景材料的新方法。采用飞秒激光烧蚀高度定向热解石墨（HOPG）来合成它们。发现多孔石墨烯（PG）层漂浮在水 - 空气界面，而石墨烯量子点（GQDs）分散在溶液中。这些薄片由一到六层海绵状石墨烯堆叠而成，形成不规则的三维多孔结构，其孔隙平均尺寸为15 - 20纳米。几种表征技术证实了所收集层的多孔性质。对水溶液的分析证实了尺寸约为2 - 5纳米的石墨烯量子点的存在。发现PG和GQDs的形成都取决于飞秒激光烧蚀能量。当激光能量密度小于12 J cm⁻²时，未检测到PG或GQDs的迹象。然而，在溶液中发现了每条链含有六个和八个碳原子的聚炔。对于20 - 30 J cm⁻²范围内的激光能量，这些聚炔消失，而分别在水 - 空气界面和溶液中发现了PG和GQDs。这些材料的形成原因可以基于水分解和煤气化的机制来解释。在液氮中对HOPG进行激光烧蚀后未出现PG和GQDs，证实了所提出的机制。
