Photoluminescence of graphene quantum dots doped with different elements

Graphene oxide and its derivatives as promising In-vitro bio-imaging platforms

“…The dual role of GO, as a fluorophore and quencher, introduces that as a potential polymer for developing new sensors with multiplex detection capability, however, the broad fluorescence emission restricted its bio-imaging performances 39 , 40 . Proper modification of GO, using polymers, noble-metal nanoparticles and molecules, improves its fluorescence emission for definite detection/biosensing purposes 41 , 42 . For targeting delivery purposes, the modification with polymers increases the hydrophilicity and circulation of GO through the biological environment and reduces the steric hindrance between the targeting ligand and biomarker 43 , 44 .…”

Yellow Fluorescent Nitrogen and Bromine Co-doped Graphene Quantum Dots for Bioimaging

“…It is found that the energy level differences between the excited singlet states are further reduced when Br atoms are introduced. Moreover, Br atoms contain more electrons in their outer layers than N atoms, promoting the excitation of more electrons and thus enriching the excited electrons in the excited singlet state, resulting in an enhanced QY of NBr-GQDs . Furthermore, the doping of large-sized Br atoms can partly transfer the sp 2 hybrid structure of GQDs to the sp 3 hybrid structure, leading to a narrow energy gap of NBr-GQDs resulting from the uneven orbital distribution .…”

“…Moreover, Br atoms contain more electrons in their outer layers than N atoms, promoting the excitation of more electrons and thus enriching the excited electrons in the excited singlet state, resulting in an enhanced QY of NBr-GQDs. 52 Furthermore, the doping of large-sized Br atoms can partly transfer the sp 2 hybrid structure of GQDs to the sp 3 hybrid structure, 53 leading to a narrow energy gap of NBr-GQDs resulting from the uneven orbital distribution. 54 This is why NBr-GQDs emit a bright yellow fluorescence rather than the green or blue fluorescence usually emitted by GQDs and N-GQDs.…”

Solution-processable GO/rGO: Preparation, functionalization, self-assembly and applications in smart information devices

“…GO 与石墨烯都是二维碳纳米材料，但结构明显不相同。组成石墨烯的只有 sp 2 杂化碳 原子，而 GO 的碳结构却有很大程度的 sp 3 杂化，源于其接有一系列含氧官能团 [16,17] 。而常 https://engine.scichina.com/doi/10.1360/TB-2019-0060 [20] 。图 2 目前，GO 的精确原子和电子结构仍无定论 [22][23][24] ，被普遍接受的是 Lerf-Klinowski 非化 学计量无定形模型。其特征是 GO 碳平面和边缘接有大量羟基(-OH)、羧基(-COOH)、羰 基(C=O)和环氧基(C-O-C)等含氧官能团 [25] 。其中羟基和环氧基主要连接在片层中间，羧基 和羰基主要修饰在片层边缘。 1.3 GO 的性质 不同掺杂态的石墨烯具有不同的光电性质 [26] ，不同含氧官能团也会给 GO 带来不同的 光电性质和化学特性。GO 含氧基团往往随制备方法的差异有所变化，通常以 MnO 4 -氧化得 到的 GO 含较多羧基，以 ClO 3 -氧化得到的 GO 含较多羟基和环氧基团 [27,28] 。总体来说，GO 的电子传导性强烈依赖于它的化学结构，或者说取决于其 sp 3 碳部分带来的结构无序化程度 [29] 。作为一种接近绝缘的材料，GO 的导电性表现在两个方面：低氧化 GO 表现为电子/空穴 的导电性；而高氧化 GO 则表现出混合导电行为(电子/空穴导电和质子导电)，受水分影 响十分明显。高氧化 GO 在缺水时，主要是电子/空穴导电；水分多时则主要由质子导电。 尤为重要的是环氧基团对 GO 的导电性的影响：它会影响带隙、层间距离和水的插层过程， 成为电子和空穴传导的障碍，但同时它也是质子传导的活性位点 [30] 。在 100%湿度环境下， GO 的质子导电性可以高至 10 -2 S cm -1 ，远超块状的石墨氧化物(10 -4 S cm -1 )和用盐酸质子 化的氧化石墨烯(10 -5 S cm -1 )，这主要是由于 GO 上的-O-，-OH 和-COOH 等官能团能吸 引质子，并通过沿着水膜形成的氢键网络传送开来 [31] 。这种微妙的电学特性是 GO 在智能 信息器件领域应用的基础。 1.4 rGO 的制备 GO 本身电子传导性很差，需要通过还原处理才能得到导电良好的 rGO。常见还原方法 主要有化学还原法、光还原法、热还原法和电化学还原法等 [15,32] 。最常用的还原方法是化 学还原，用到的还原剂主要有卤代酸、氢化物、氨基还原剂、金属-酸/碱、羟基还原剂、硫 化物、生物还原剂等七大类，详见 Pumera 课题组的相关综述 [33] 。GO、rGO 与石墨烯的关 系见图 3。 图 3 石墨烯与 GO、rGO 的转换关系…”