Fluorescent graphene oxide (GO) nanoparticles were obtained from the thermal carbonization of citrate acid. Depending on the synthesizing temperature, the size of GO varied from several to several hundred nanometers. Owing to the confinement from the size, green and blue emissions at around 504 and 450 nm were observed from the GO suspension. These emissions could be dynamically quenched by titrating against copper (II) (Cu2+) ions, and the emission intensity was reduced exponentially as a function of Cu2+ concentration. The quenching mechanism was ascribed to the bridging of the surface –COOH and –OH groups by Cu2+, which restricted the vibration of edge atoms or clusters and reduced the number of luminophores of GO nanosheets. As a result, the concentration of Cu2+ was detectable with the fluorescent intensity of GO.

中文翻译：

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来自碳化柠檬酸的荧光氧化石墨烯用于铜 (II) 离子检测

荧光氧化石墨烯 (GO) 纳米颗粒是通过柠檬酸的热碳化获得的。根据合成温度的不同，GO 的尺寸从几纳米到几百纳米不等。由于尺寸的限制，从 GO 悬浮液中观察到大约 504 和 450 nm 处的绿色和蓝色发射。这些发射可以通过滴定铜 (II) (Cu2+) 离子来动态淬灭，并且发射强度作为 Cu2+ 浓度的函数呈指数降低。猝灭机制归因于表面–COOH和–OH基团被Cu2+桥接，这限制了边缘原子或簇的振动并减少了GO纳米片的发光团数量。因此，可以通过 GO 的荧光强度检测 Cu2+ 的浓度。