不同元素掺杂的石墨烯量子点的光致发光行为
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摘要
石墨烯量子点(graphenequantumdots,GQDs)作为一种新型石墨烯材料,具有许多优异的物理化学性质,尤其是其独特的光致发光(photoluminescence,PL)特性以及低毒性的本质,在生物成像以及医学分析等领域展示出很好的应用前景,但是目前制备的GQDs存在发光效率低、发光机理不明确、缺乏有效的发光调控手段等问题.为提高GQDs的PL性能和进一步明确其发光机理以及增加发光调控手段,本文以电化学法和水热法制备了GQDs以及Cl, N, P, S 4种元素掺杂的GQDs,通过X射线光电子能谱分析(X-ray photoelectron spectroscopy, XPS)、傅里叶转换红外光谱(Fourier-transform infrared spectroscopy, FT-IR)、拉曼光谱(Raman spectra)等测试手段,表征了不同元素掺杂的GQDs的元素组成和结构缺陷,分析了杂原子在GQDs中的位置以及成键模式.通过荧光光谱仪测试了其PL性能并分析了各种GQDs的发光增强和减弱机制.Cl以及N的掺杂能够形成发光中心,提高GQDs的发光强度,相比未掺杂GQDs,Cl-GQDs发光强度增加了1倍;S元素的掺杂则形成少量猝灭中心,发光强度较未掺杂GQDs略有下降;而P的掺杂形成大量猝灭中心,导致P-GQDs几乎无发光.
Graphene quantum dots(GQDs), as a new graphene material, possess advantageous chemical-physical properties. Owing to their distinctive photoluminescence(PL) property and low biological toxicity, GQDs have been shown to be good candidates for applications in bioimaging and medical analysis. However, the prepared GQDs have their own slew of problems, including low luminescent efficiency, uncertain luminescent mechanism and lack of effective methods to tuning the luminescence property. Heteroatom doping is a good strategy, which could partially address these above problems. Because the doping atoms will be located in the internal structure of carbon nanomaterials thus change their local electronic configuration, polarizability, defect degree and band structure, etc., the physical and chemical properties of GQDs could be well tuned. At present, GQDs doped with Cl, F, N, S, B, P, etc. have been prepared. These obtained GQDs with heteroatom doping not only exhibited tunable optical properties, but also showed enormous potential applications in the field of photocatalysis. Herein, in order to further improve the PL performance of GQDs and extend their application, we prepared pure GQDs and single elemental-doped GQDs with Cl, N, P and S by using the electrochemical method and hydrothermal method. Fourier-transform infrared spectroscopy(FT-IR), X-ray photoelectron spectroscopy,(XPS) and Raman measurements were used to characterize their elemental composition, surface element state and structural defect. Based on the experimental results, the position and bonding state of heteroatoms in doped GQDs were analyzed. The doping amounts in these doped GQDs are different, i.e., 1.35% of Cl-GQDs, 7.95% of N-GQDs, 10.08% of P-GQDs and 3.25% of S-GQDs, respectively. The degree of defect state is decreased in the order as follows: P-GQDs>S-GQDs>GQDs>Cl-GQDs>N-GQDs. Meanwhile, the PL performance was tested, and the fluorescent quantum efficiencies were calculated to be 8.2% for Cl-GQDs, 5.3% for N-GQDs, 4.0% for GQDs, 2.8% for S-GQDs, and 0.037% for P-GQDs, respectively. It can be concluded that the diverse doping atoms play different roles for the improvement of PL performance. The doping of Cl and N can form the luminescent center, which improves the fluorescent intensity of GQDs. Especially for the Cl doping, the fluorescent intensity of Cl-GQDs is increased twice compared to the pure GQDs, due to larger atomic radius and more outer shell electron of Cl than that of the others doped elementals. In the S-GQDs, the doped S could become small quenching centers, which decreased the fluorescent intensity slightly compared to that of pure GQDs. However, different from the above doped GQDs, P-GQDs showed the negligible fluorescence. Because the P atoms mainly are present in the surface functional groups of P-GQDs, these P-atoms induced defects may become the large fluorescent quenching center and greatly decrease their PL intensity. Besides the measurement and analysis of luminescence intensity, the emission peak positions and corresponding excitation wavelengths of these doped GQDs were also well studied. The excitation wavelength of pure GQDs is located at 340 nm, while the doped GQDs are all located at 360 nm. The strongest emission peaks of Cl-GQDs and N-GQDs are around 450 nm, while the strongest emission peaks of S-GQDs and pure GQDs are around 430 nm. These results indicate that the doping of heteroatoms could change the band gap of GQDs to some extent.
Graphene quantum dots(GQDs), as a new graphene material, possess advantageous chemical-physical properties. Owing to their distinctive photoluminescence(PL) property and low biological toxicity, GQDs have been shown to be good candidates for applications in bioimaging and medical analysis. However, the prepared GQDs have their own slew of problems, including low luminescent efficiency, uncertain luminescent mechanism and lack of effective methods to tuning the luminescence property. Heteroatom doping is a good strategy, which could partially address these above problems. Because the doping atoms will be located in the internal structure of carbon nanomaterials thus change their local electronic configuration, polarizability, defect degree and band structure, etc., the physical and chemical properties of GQDs could be well tuned. At present, GQDs doped with Cl, F, N, S, B, P, etc. have been prepared. These obtained GQDs with heteroatom doping not only exhibited tunable optical properties, but also showed enormous potential applications in the field of photocatalysis. Herein, in order to further improve the PL performance of GQDs and extend their application, we prepared pure GQDs and single elemental-doped GQDs with Cl, N, P and S by using the electrochemical method and hydrothermal method. Fourier-transform infrared spectroscopy(FT-IR), X-ray photoelectron spectroscopy,(XPS) and Raman measurements were used to characterize their elemental composition, surface element state and structural defect. Based on the experimental results, the position and bonding state of heteroatoms in doped GQDs were analyzed. The doping amounts in these doped GQDs are different, i.e., 1.35% of Cl-GQDs, 7.95% of N-GQDs, 10.08% of P-GQDs and 3.25% of S-GQDs, respectively. The degree of defect state is decreased in the order as follows: P-GQDs>S-GQDs>GQDs>Cl-GQDs>N-GQDs. Meanwhile, the PL performance was tested, and the fluorescent quantum efficiencies were calculated to be 8.2% for Cl-GQDs, 5.3% for N-GQDs, 4.0% for GQDs, 2.8% for S-GQDs, and 0.037% for P-GQDs, respectively. It can be concluded that the diverse doping atoms play different roles for the improvement of PL performance. The doping of Cl and N can form the luminescent center, which improves the fluorescent intensity of GQDs. Especially for the Cl doping, the fluorescent intensity of Cl-GQDs is increased twice compared to the pure GQDs, due to larger atomic radius and more outer shell electron of Cl than that of the others doped elementals. In the S-GQDs, the doped S could become small quenching centers, which decreased the fluorescent intensity slightly compared to that of pure GQDs. However, different from the above doped GQDs, P-GQDs showed the negligible fluorescence. Because the P atoms mainly are present in the surface functional groups of P-GQDs, these P-atoms induced defects may become the large fluorescent quenching center and greatly decrease their PL intensity. Besides the measurement and analysis of luminescence intensity, the emission peak positions and corresponding excitation wavelengths of these doped GQDs were also well studied. The excitation wavelength of pure GQDs is located at 340 nm, while the doped GQDs are all located at 360 nm. The strongest emission peaks of Cl-GQDs and N-GQDs are around 450 nm, while the strongest emission peaks of S-GQDs and pure GQDs are around 430 nm. These results indicate that the doping of heteroatoms could change the band gap of GQDs to some extent.
引文
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2 Zhang R, Qi S, Jia J, et al. Size and refinement edge-shape effects of graphene quantum dots on UV-visible absorption. J Alloy Compd,2015, 623:186–191
3 Zhou X, Zhang Y, Wang C, et al. Photo-fenton reaction of graphene oxide:A new strategy to prepare graphene quantum dots for DNA cleavage. ACS Nano, 2012, 6:6592–6599
4 Liu Q, Guo B, Rao Z, et al. Strong two-photon-induced fluorescence from photostable, biocompatible nitrogen-doped graphene quantum dots for cellular and deep-tissue imaging. Nano Lett, 2013, 13:2436–2441
5 RisticBZ,MilenkovicMM,DakicIR,etal.Photodynamicantibacterialeffectofgraphenequantumdots.Biomaterials,2014,35:4428–4435
6 Zheng X T, Ananthanarayanan A, Luo K Q, et al. Glowing graphene quantum dots and carbon dots:Properties, syntheses, and biological applications. Small, 2015, 11:1620–1636
7 Ma C, Zhu Z, Wang H, et al. A general solid-state synthesis of chemically-doped fluorescent graphene quantum dots for bioimaging and optoelectronic applications. Nanoscale, 2015, 7:10162–10169
8 ZhuS,ZhangJ,QiaoC,etal.Stronglygreen-photoluminescentgraphenequantumdotsforbioimagingapplications.ChemCommun,2011, 47:6858–6860
9 Zhu S, Song Y, Wang J, et al. Photoluminescence mechanism in graphene quantum dots:Quantum confinement effect and surface/edge state. Nano Today, 2017, 13:10–14
10 Zhu S, Song Y, Zhao X, et al. The photoluminescence mechanism in carbon dots(graphene quantum dots, carbon nanodots, and polymer dots):Current state and future perspective. Nano Res, 2015, 8:355–381
11 PanD,GuoL,ZhangJ,etal.Cuttingsp2clustersingraphenesheetsintocolloidalgraphenequantumdotswithstronggreenfluorescence. J Mater Chem, 2012, 22:3314–3318
12 GongK,DuF,XiaZ,etal.Nitrogen-dopedcarbonnanotubearrayswithhighelectrocatalyticactivityforoxygenreduction.Science,2009, 323:760–764
13 Ma L, Hu H, Zhu L, et al. Boron and nitrogen doping induced half-metallicity in zigzag triwing graphene nanoribbons. J Phys Chem C,2011, 115:6195–6199
14 ChoiCH,ParkSH,WooSI,etal.Binaryandternarydopingofnitrogen,boron,andphosphorusintocarbonforenhancingelectrochemical oxygen reduction activity. ACS Nano, 2012, 6:7084–7091
15 SahraieNR,ParaknowitschJP,GoebelC,etal.Noble-metal-freeelectrocatalystswithenhancedORRperformancebytask-specific functionalization of carbon using ionic liquid precursor systems. J Am Chem Soc, 2014, 136:14486–14497
16 KarimzadehA,HasanzadehM,ShadjouN,etal.ElectrochemicalbiosensingusingN-GQDs:Recentadvancesinanalyticalapproach.Trac Tend Anal Chem, 2018, 105:484–491
17 LiY,LiS,WangY,etal.Electrochemicalsynthesisofphosphorus-dopedgraphenequantumdotsforfreeradicalscavenging.Phys Chem Chem Phys, 2017, 19:11631–11638
18 Zhao J, Tang L, Xiang J, et al. Fabrication and properties of a high-performance chlorine doped graphene quantum dot based photovoltaic detector. RSC Adv, 2015, 5:29222–29229
19 WangH,ReviaR,WangK,etal.Paramagneticpropertiesofmetal-freeboron-dopedgraphenequantumdotsandtheirapplicationfor safe magnetic resonance imaging. Adv Mater, 2017, 29:1605416–1605423
20 Li X, Lau S P, Tang L, et al. Sulphur doping:A facile approach to tune the electronic structure and optical properties of graphene quantum dots. Nanoscale, 2014, 6:5323–5328
21 FengQ,CaoQ,LiM,etal.Synthesisandphotoluminescenceoffluorinatedgraphenequantumdots.ApplPhysLett,2013,102:013111–013115
22 Li Y, Zhao Y, Cheng H, et al. Nitrogen-doped graphene quantum dots with oxygen-rich functional groups. J Am Chem Soc, 2012, 134:15 –18
23 Feng Y, Zhao J, Yan X, et al. Enhancement in the fluorescence of graphene quantum dots by hydrazine hydrate reduction. Carbon, 2014,66 :334–339
24 GanZ,XiongS,WuX,etal.Mechanismofphotoluminescencefromchemicallyderivedgrapheneoxide:Roleofchemicalreduction.Adv Opt Mater, 2013, 1:926–932