氨基修饰石墨烯量子点的制备及应用研究

采用强酸氧化单壁碳纳米管制得石墨烯量子点(GQDs),然后在氨水中进行水热处理,得到氨基功能化石墨烯量子点(N-GQDs)。通过荧光光谱(PL)、傅里叶红外光谱(FTIR)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、原子力显微镜(AFM)对所制备的N-GQDs进行结构和光学性质的表征。结果表明,N-GQDs粒径分布为3. 5 nm,高度小于0. 6 nm,能够均匀分散在水溶液中,并发出蓝色荧光。研究还发现,在p H=7. 0磷酸盐缓冲溶液中,所制备的N-GQDs对Hg2+具有猝灭作用。     

氮掺杂石墨烯量子点的激发波长依赖性发光研究

激发波长依赖发光是碳基荧光材料中有趣的光学性质之一,其在不同激发波长下呈现的多彩发光对某些实际应用很重要.本文以氧化石墨烯为碳源,采用酸氧化法制备了尺寸约为3~5nm的少层石墨烯量子点(GQDs),然后将其与乙二胺(EDA)在160℃下进行水热反应,得到了石墨烯边缘氮掺杂的石墨烯量子点(NGQDs).采用傅立叶变换红外光谱(FTIR)证实了N-GQDs中酰胺键和胺C-N键的形成.GQDs的吸收主要来自C=C的π-π*跃迁(265nm)和C-O相关的n-π*跃迁(340nm),而N-GQDs中出现了C(=O)NHR相关的新能级(386nm).GQDs荧光峰随着激发光波长的移动Δλem/Δλex呈现线性变化,斜率约为0.43,而N-GQDs的Δλ_(em)/Δλ_(ex)出现两段线性变化,激发波长在420nm以后斜率增大到0.78,表明C(=O)NHR相关的荧光偶极子具有更强的激发波长依赖性发光特性.     

纳米银粒子在氨基注入氧化铟锡玻璃基体表面的高密度吸附

研究了纳米银（AgNPs）在氨基注入氧化铟锡（ITO）薄膜表面的吸附.通过氨基注入的疗法得到了氨基功能化的ITO表面（NH₂/ITO）,并将纳米银直接吸附在NH₂/ITO上得到纳米银修饰NH₂/ITO基体（AgNPs/NH₂/ITO）.使用傅里叶红外光谱、X射线光电子能谱、原子力显微镜、扫描电镜、紫外可见光谱和电化学方法对AgNPs/NH₂/ITO制备过程进行了表征.结果显示纳米银可在NH₂/ITO表面高密度地吸附,并且纳米银有良好的电化学活性.这种不借助于有机连接分子吸附纳米银的方法为制备纳米银修饰材料提供了新的选择.     

水溶性氮掺杂石墨烯量子点的合成及其对Pb~(2+)的选择性识别研究

以氧化剥离碳纤维法制备的石墨烯量子点(GQDs)为原料,以N,N-二甲基甲酰胺(DMF)为氮源和溶剂,采用溶剂热法,制备了氮掺杂的水溶性石墨烯量子点(N-GQDs)。当反应时间小于24h时,N-GQDs的氮掺杂量和发光量子效率随反应时间的延长而增大,同时其荧光颜色逐渐从黄色向绿、蓝转变。N-GQDs的发光量子效率最高可从GQDs的4.0%增加到30.1%。氮掺杂一方面增加了N-GQDs中C—N键含量,另一方面增强了N-GQDs的结构有序性,从而提高了其发光量子效率。作为荧光探针,N-GQDs对水溶液中的Pb~(2+)具有良好的识别作用。荧光滴定实验证明,在8.0×10-7 mol/L~1.5×10-4 mol/L的线性范围内,以NGQDs为荧光探针,可以有效测定水溶液中Pb~(2+)的浓度。与未掺杂的GQDs相比,氮掺杂显著提高了石墨烯量子点对Pb~(2+)的选择性。     

溶剂热插层法制备荧光石墨相氮化碳量子点及其在Fe3+检测中的应用

利用溶剂热法, 基于氢氧化钾的插层作用制备了荧光氮化碳量子点(g-C₃N₄ QDs). 所获得的氮化碳量子点具有良好的水溶性和荧光稳定性. 透射电子显微镜(TEM)照片显示, 氮化碳量子点的粒径约为2.3 nm; X射线光电子能谱(XPS)和红外光谱(FTIR)结果表明, 氮化碳量子点表面存在大量的亲水基团; 荧光发射光谱(PL)结果表明, 氮化碳量子点具有激发波长依赖性. 基于三价铁离子(Fe³⁺)对荧光氮化碳量子点荧光的猝灭现象, 构建了一种用于检测Fe³⁺的荧光传感器, 在Fe³⁺浓度为5~100 μmol/L范围内, 检测体系表现出良好的线性关系, 检出限约为0.5 μmol/L, 实现了对Fe³⁺的高效、 灵敏、 选择性检测.     

石墨烯负载MnOx催化剂的制备及其低温NH3-SCR活性

通过改进的Hummers法合成氧化石墨烯(GO), 随后采用水热法制备石墨烯负载锰氧化物(MnO_x/GR)催化剂. 考察了催化剂的低温NH₃选择性催化还原(NH₃-SCR)去除NO_x的性能, 并通过傅里叶变换红外(FTIR)光谱, 拉曼(Raman)光谱, X射线衍射(XRD), 透射电镜(TEM), N₂吸附-脱附, X射线光电子能谱(XPS)及H₂程序升温还原(H₂-TPR)等多种表征手段对催化剂的结构及NH₃-SCR性能进行分析. 结果显示, 不同MnO_x负载量的MnO_x/GR催化剂均展现了较好的低温SCR催化活性, 且在负载量为20%(w)时活性最优. 表征分析结果表明, 制备的GO表面含有丰富的含氧基团, 锰可以通过与含氧基团结合而负载到GO上; MnO_x/GR催化剂中MnO_x以纳米颗粒分散于石墨烯载体表面, 且以多种氧化物(MnO、Mn₃O₄和MnO₂)共同存在; 负载量为20%(w)的催化剂中高价锰和表面吸附氧含量增加, 低温区氧化还原能力增强及活性位点数量增加是其SCR活性提高的原因.     

发光碳量子点的合成、性质和应用

基于碳量子点具有良好的水溶性、化学惰性、低毒性、易于功能化和抗光漂白性等优异性能,碳量子点和其它的碳纳米材料（如富勒烯、碳纳米管和石墨烯等）同样引起了研究者广泛的关注。 碳量子点可以通过很多较为廉价的一步法进行大规模的制备,包括化学氧化法、超声法、微波法和激光烧蚀法等。 本文主要介绍了不同碳量子点的合成方法,以及依赖于碳量子点尺寸和波长等性质的发光性能,并且讨论了碳量子点在生物成像、光催化、能量转换/储存、光电子、光限幅和传感器等方面的应用。     

组氨酸和五乙烯六胺功能化掺硼石墨烯量子点的合成及荧光检测中草药中姜黄素

将柠檬酸、组氨酸、五乙烯六胺和硼酸混合后热解，制备组氨酸和五乙烯六胺功能化掺硼石墨烯量子点（HPB-GQD）。所形成的HPB-GQD由片径4.17±0.12 nm的石墨烯片组成。石墨烯片边缘含有丰富的功能基团。HPB-GQD的荧光发射依赖于激发波长，375 nm的紫外光激发产生最强蓝色荧光发射。荧光量子产率达到87.4%，发光效率优于传统GQD以及单一组氨酸、五乙烯六胺或硼酸功能化GQD，证明组氨酸和五乙烯六胺以及硼的引入提高了GQD发光效率。基于姜黄素对HPB-GQD的荧光猝灭作用，建立了测定姜黄素的荧光分析方法。线性范围和检出限分别是0.05～20.0μmol/L和0.017μmol/L。方法已应用于中草药中姜黄素的荧光检测，结果与液相色谱-质谱法（LC-MS）结果基本一致，加标回收率在96.0%～104.0%之间。     

中温煤沥青基碳量子点的制备与结构解析

以中温煤沥青为碳源，采用HNO₃预处理结合球磨过程及双氧水氧化刻蚀的方法制备沥青基荧光碳量子点，以CQDs的收率和荧光量子产率为目标，获得最优制备条件：反应时间6 h、H₂O₂加入量100 mL （c-CQDs），此时，CQDs收率和荧光量子产率分别为6.3%和11.2%，且尺寸均匀、粒径分布在4-14 nm。延长反应时间至8 h （a-CQDs），碳量子点团聚；H₂O₂用量增加至120 mL （b-CQDs）则导致碳量子点氧化过度，颗粒小且杂乱无章。对不同条件下所制备的CQDs进行XPS、红外光谱、热重、¹³C NMR、Raman和晶相分析，探究反应条件对CQDs结构的影响规律。结果表明，就碳含量而言，a-CQDs > b-CQDs > c-CQDs，氧元素含量则为b-CQDs > c-CQDs > a-CQDs。各CQDs结构中C主要以芳碳形式存在，c-CQDs的C=O、O-C=O含量最高，而b-CQDs的C-O含量最高，¹³C NMR分析发现CQDs中表征平均芳环尺寸大小的X_b约为0.5，相应地，其平均芳环数约为3。     

大尺寸石墨烯量子点组装体的制备及电化学发光性能

对氧化石墨烯纳米材料进行HNO₃氧化处理, 制备了水溶性好且具有强电化学发光(ECL)活性的大尺寸石墨烯量子点组装体(Large-sized graphene quantum dot assemblies, LSGQD-NAs). 利用透射电子显微镜(TEM)、 原子力显微镜(AFM)、 傅里叶变换红外光谱(FTIR)和拉曼光谱(Raman)等方法对其进行了表征, 结果表明, 石墨烯量子点组装体的平均高度为20 nm, 且富含大量的羟基和羧基. 电化学测试结果显示, 在共反应物K₂S₂O₈存在下, LSGQD-NAs在阴极产生很强的ECL(峰值约在685 nm); 并推测了其ECL反应机理, 发现LSGQD-NAs容易通过中心未氧化的石墨烯π-π作用于GC电极表面进行组装修饰. 本研究为基于石墨烯量子点ECL传感器的研究提供了新方法.     

Preparation and formaldehyde sensitive properties of N-GQDs/SnO2 nanocomposite

Graphene quantum dots (GQDs) have both the properties of graphene and semiconductor quantum dots, and exhibit stronger quantum confinement effect and boundary effect than graphene. In addition, the band gap of GQDs will transform to non-zero from 0 eV of graphene by surface functionalization, which can be dispersed in common solvents and compounded with solid materials. In this work, the SnO₂ nanosheets were prepared by hydrothermal method. As the sensitizer, nitrogen-doped graphene quantum dots (N-GQDs) were prepared and composited with SnO₂ nanosheets. Sensing performance of pristine SnO₂ and N-GQDs/SnO₂ were investigated with HCHO as the target gas. The response (R_a/R_g) of 0.1% N-GQDs/SnO₂ was 256 for 100 ppm HCHO at 60 °C, which was about 2.2 times higher than pristine SnO₂ nanosheet. In addition, the material also had excellent selectivity and low operation temperature. The high sensitivity of N-GQDs/SnO₂ was attributed to the increase of active sites on materials surface and the electrical regulation of N-GQDs. This research is helpful to develop new HCHO gas sensor and expand the application field of GQDs.     

Enhancement of electro-optical response of ferroelectric liquid crystal: the role of graphene quantum dots

We present a pioneer study depicting a significant improvement in the photoluminescence (PL) intensity and display of an expeditious electro-optic response of ferroelectric liquid crystal (FLC) when doped with graphene quantum dots (GQDs). Significant threefold enhancement in PL intensity of GQDs/FLC composite material can be ascribed to the additive combination of emissions from GQDs and FLCs. Furthermore, promptness in electro-optical response by a factor of 34% can be attributed to the lowering of rotational viscosity of the FLC material due to the incorporation of GQDs. These results would certainly be helpful in realisation of highly luminescent and faster generation of LC systems.     

g-CN体系的准粒子能带结构和光学特性

利用多体格林函数理论,本文研究了二维CN体系(包括triazine和tri-s-triazine)的激发态特性。通过GW方法,我们计算了准粒子的能量。考虑电子-空穴相互作用,通过求解Bethe-Salpeter方程,我们获得了激发态能量和光谱。我们发现,在这两种CN体系的价带中,σ轨道和π轨道之间的交换作用非常强烈。由于占据的σ轨道和π轨道之间的准粒子修正量非常不同,因此,为了得到准确的带隙值和光谱,我们需要对这两种轨道开展精确的GW计算。与单层的CN体系相比,双层结构中层与层之间的范德华相互作用使带隙值降低了0.6 eV,而光吸收谱红移了0.2 eV,这是由于双层结构具有更小的激子束缚能。我们计算的吸收峰的位置与实验结果符合很好。实验中的吸收峰主要是由深能级的π轨道到π^*轨道的跃迁形成的。π→π^*跃迁和σ→π^*跃迁之间的耦合能够在长波长范围产生弱的吸收尾巴,如果调整入射光的极化方向,由σ→π^*跃迁产生的高强度的吸收峰将会在更低能量处出现。     

Preparation of Excitation‐Independent Photoluminescent Graphene Quantum Dots with Visible‐Light Excitation/Emission for Cell Imaging

We report the first pyrrole‐ring surface‐functionalized graphene quantum dots (p‐GQDs) prepared by a two‐step hydrothermal approach under microwave irradiation in an ammonia medium. The most distinct feature of the functionalized GQDs is that both the excitation and emission wavelengths fall into the visible‐light region. The p‐GQDs are excited by visible light at λ_ex 490 nm (2.53 eV) to emit excitation‐independent photoluminescence at a maximum wavelength of λ_em 550 nm. This is thus far the longest emission wavelength reported for GQDs. Stable photoluminescence is achieved at pH 4–10 with an ionic strength of 1.2 mol L^?1 KCl. These features make the p‐GQDs excellent probes for bio‐imaging and bio‐labeling, which is demonstrated by imaging live HeLa cells.     

Nitrogen-doped graphene quantum dots with oxygen-rich functional groups

Graphene quantum dots (GQDs) represent a new class of quantum dots with unique properties. Doping GQDs with heteroatoms provides an attractive means of effectively tuning their intrinsic properties and exploiting new phenomena for advanced device applications. Herein we report a simple electrochemical approach to luminescent and electrocatalytically active nitrogen-doped GQDs (N-GQDs) with oxygen-rich functional groups. Unlike their N-free counterparts, the newly produced N-GQDs with a N/C atomic ratio of ca. 4.3% emit blue luminescence and possess an electrocatalytic activity comparable to that of a commercially available Pt/C catalyst for the oxygen reduction reaction (ORR) in an alkaline medium. In addition to their use as metal-free ORR catalysts in fuel cells, the superior luminescence characteristic of N-GQDs allows them to be used for biomedical imaging and other optoelectronic applications.     

Strongly green-photoluminescent graphene quantum dots for bioimaging applications

Strongly fluorescent graphene quantum dots (GQDs) have been prepared by one-step solvothermal method with PL quantum yield as high as 11.4%. The GQDs have high stability and can be dissolved in most polar solvents. Because of fine biocompatibility and low toxicity, GQDs are demonstrated to be excellent bioimaging agents.     

Synthesis and surface photochemistry of graphitized carbon quantum dots

Graphitized carbon quantum dots (CQDs) were synthesized by a simple hydrothermal process with cetyltrimethylammonium bromide (CTAB) as the starting material and nitric acid as surface oxidant. The photoluminescent quantum yield (QY) of CQDs could be greatly enhanced through surface esterification with glycol. Based on the structure characterization, we proposed that the CQDs consisted of the stack of graphene sheets sized several nanometers and their excitation-dependent photoluminescence (PL) should be attributed to the n→π* transition of CO bond of surface carboxylic groups. And the PL of CQDs was obviously enhanced by the esterification of carboxylic groups, possibly due to the increase of the molecular coplanarity or the rigidity.     

Size Effect of Graphene Quantum Dots on Photoluminescence

High-photoluminescence (PL) graphene quantum dots (GQDs) were synthesized by a simple one-pot hydrothermal process, then separated by dialysis bags of different molecular weights. Four separated GQDs of varying sizes were obtained and displayed different PL intensities. With the decreasing size of separated GQDs, the intensity of the emission peak becomes much stronger. Finally, the GQDs of the smallest size revealed the most energetic PL intensity in four separated GQDs. The PL energy of all the separated GQDs shifted slightly, supported by density functional theory calculations.     

Fabrication and characterization of upconversion N-doped graphene quantum dots for improving photoelectrocatalytic performance of rutile hierarchical TiO₂ nanowires under visible and near-infrared light irradiations

The development of well-organized and low-priced photoelectrocatalysts for the clean and efficient water splitting reaction is crucial. In this context, novel nitrogen-doped graphene quantum dots (N-GQDs) with high photoluminescence and upconversion emission have been synthesized as excellent light harvester. Subsequently, ordered hierarchical TiO? nanowires were decorated with upconversion N-GQDs as a photoanode by a simple preparation method to improve the photocatalytic performance in the visible and near-infrared (NIR) regions of solar light, not otherwise absorbable by bare TiO? nanostructures. Moreover, the enhancement of charge transfer efficiency and electron–hole separation according to the energy states of N-GQDs and TiO? are considered for the improved photocatalytic performance of water splitting. N-GQDs/TiO₂ shows superior photoelectrocatalytic (PEC) performance, achieving a photocurrent density of 3.0 mA.cm^?2 in 1.0 M KOH solution, which is eight times that of unmodified TiO? at an applied voltage of 1.23 V vs. RHE. The high stability and photoelectrocatalytic activity of oxygen evolution reaction in the presence of newly synthesized N-GQDs are confirmed by chronoamperometry, open-circuit potential measurement, and electrochemical impedance spectroscopy. The as-fabricated photoanode provides an increased solar light harvesting from UV–Vis to NIR due to the application of newly synthesized upconversion GQDs, which increase energy conversion with an appealing perspective.     

Separation of Spectroscopically Uniform Nanographenes

Excitation‐dependent photoluminescence (PL) is a well‐known property of graphene quantum dots (GQDs). For the development of carbon‐based photofunctional materials, GQDs possessing uniform PL properties are in high demand. A protocol has been established to separate spectroscopically uniform lipophilic GQD‐ 1 a from a mixture of GQD‐ 1 mainly composed of GQD‐ 1 a and GQD‐ 1 b . The mixture of GQD‐ 1 was synthesized through the reaction of p‐methoxybenzylamine with GQD‐ 2 prepared from graphite by common oxidative exfoliation. Size‐exclusion chromatography gave rise to GQD‐ 1 a and GQD‐ 1 b , with diameters of 19.8 and 4.9 nm, respectively. Large GQD‐ 1 a showed that the PL was fairly independent of the excitation wavelengths, whereas the PL of small GQD‐ 1 b was dependent on excitation. The excitation‐dependent nature is most likely to be associated with the structures of sp² domains on the graphene surfaces. The large sp²‐conjugated surface of GQD‐ 1 a is likely to possess well‐developed and large sp² domains, the band gaps of which do not significantly vary. The small sp²‐conjugated surface of GQD‐ 1 b produces small sp²‐conjugated domains that generate band gaps differing with domain sizes.