Horizontally Aggregation of Monolayer Reduced Graphene Oxide Under Deep UV Irradiation in Solution

Nanoscale Research Letters, Apr 2019

Graphene has been widely used in novel optoelectronic devices in decades. Nowadays, fabrication of large size monolayer graphene with spectral selectivity is highly demanded. Here, we report a simple method for synthesizing large size monolayer graphene with chemical functionalized groups in solution. The few layer nano-graphene can be exfoliated into monolayer nano-graphene under short time UV irradiation in protic solution. The exfoliated monolayer nano-graphene could experience deoxygenation during long time UV exposure. At the same time, the edge of nano-graphene could be activated under deep UV exposure and small size nano-graphene sheets further aggregate horizontally in solution. The size of aggregated rGO increase from 40 nm to a maximum of 1 μm. This approach could be one promising cheap method for synthesizing large size monolayer reduced graphene oxide in the future.

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Horizontally Aggregation of Monolayer Reduced Graphene Oxide Under Deep UV Irradiation in Solution

Nanoscale Research Letters December 2019, 14:117 | Cite as Horizontally Aggregation of Monolayer Reduced Graphene Oxide Under Deep UV Irradiation in Solution AuthorsAuthors and affiliations Xiaoxiao HeSanjun ZhangHaifeng PanJinquan ChenJianhua Xu Open Access Nano Express First Online: 02 April 2019 89 Downloads Abstract Graphene has been widely used in novel optoelectronic devices in decades. Nowadays, fabrication of large size monolayer graphene with spectral selectivity is highly demanded. Here, we report a simple method for synthesizing large size monolayer graphene with chemical functionalized groups in solution. The few layer nano-graphene can be exfoliated into monolayer nano-graphene under short time UV irradiation in protic solution. The exfoliated monolayer nano-graphene could experience deoxygenation during long time UV exposure. At the same time, the edge of nano-graphene could be activated under deep UV exposure and small size nano-graphene sheets further aggregate horizontally in solution. The size of aggregated rGO increase from 40 nm to a maximum of 1 μm. This approach could be one promising cheap method for synthesizing large size monolayer reduced graphene oxide in the future. KeywordsUV exfoliation Aggregation of rGO Monolayer Few layer nano-graphene  Abbreviations AFM Atomic force microscopy CVD Chemical vapor deposition FTIR Fourier-transform infrared GO Graphene oxide PL Photoluminescence TEM Transmission electron microscope Background Graphene is a potential material for ultrathin optoelectronic and photodetection devices because of its high carrier mobility and high optical transparency [1, 2]. The key to the high photoresponse of graphene-based devices is the fermi level shifting that induced by the injunction of carriers [3]. With the development of chemical vapor deposition (CVD), growth of large size graphene as well as fabrication of graphene-based devices becomes convenient. However, graphene-based photoresponse device usually has weak absorption and poor spectral selectivity. The common method used to overcome this drawback is hybridizing graphene with quantum dots [4], plasmonic nanostructure [5], or other 2D materials with energy gaps [6] in order to achieve photo-induced carrier injection. Although CVD method promotes the fabrication of growth of large size graphene, the deposition process commonly happens in extreme environment, such as high vacuum, highly selected substrate, and so on. This limits the enlargement fabrication for commercial manufacture. New and low-cost methods are urgent to be developed. Solvent-mediated exfoliation for few layer flakes is one of the efficient and low-cost methods in graphene fabrication [7, 8, 9, 10, 11, 12, 13, 14, 15]. The most widely used method is modified Hummer’s method. The graphite can be oxidized and exfoliated into few layer graphene. Meanwhile, graphene fabricated via chemical oxidized exfoliation usually contains various functional groups which can enhance the optical absorption and spectral selectivity. On the other hand, the oxidized exfoliation process usually damages the crystallinity of sp2 domain [16], which requires extremely high temperature for recovery. Although the thermal reaction process could recover the sp2 domain, almost all the functional groups are also removed, leading to weak absorption and poor spectral selectivity again. Herein, we report a new strategy to fabricate large size chemical functionalized monolayer graphene by deep UV irradiation. The layered nano-graphene can be exfoliated to monolayer under short time UV exposure. The new sp2 domain can be restored during long time UV exposure. Furthermore, the edge carbon atom can be activated during UV irradiation, leading several monolayer nano-graphene sheets to aggregate horizontally to form large size monolayer graphene. Experimental Method Fabrication of Graphene Oxide Graphene oxide (GO) was synthesized from natural graphite by modifying the Hummer’s method as reported in our previous work [17]. The resulting mixture was washed by 5% HCl solution and DI for dozens of times. Finally, GO solid was obtained after freeze-drying. Synthesis of Few Layer Nano-Graphene and Growth for Large Size Reduced Graphene Oxide 4.4 mg GO solid was transferred to Teflon-lined autoclave and 12 mL ethanol (or N,N-dimethylformamide (DMF)) was added. The mixture was heated to 176 °C for 5 h. The supernatant was filtered through a 0.22-μm microporous membrane. Finally, the colloidal solution was the few layer nano-graphene solution. 4.4 mg GO solid was transferred to Teflon-lined autoclave and 15 mL DI added. The mixture was heated at 176 °C for 5 h. Then the supernatant was filtered through a 0.22-μm microporous membrane. The colloidal solution was the monolayer nano-graphene solution. The exfoliation of few layer nano-graphene and growth for large size reduced graphene oxide (rGO) were obtained by deep UV light (3 W, 254 nm) irradiating, a (...truncated)


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Xiaoxiao He, Sanjun Zhang, Haifeng Pan, Jinquan Chen, Jianhua Xu. Horizontally Aggregation of Monolayer Reduced Graphene Oxide Under Deep UV Irradiation in Solution, Nanoscale Research Letters, 2019, pp. 117, Volume 14, Issue 1, DOI: 10.1186/s11671-019-2940-z