Near-UV-emitting graphene quantum dots from graphene hydrogels

We report a novel method to prepare graphene quantum dots (GQDs) from graphene hydrogels. Graphene hydrogels were prepared using a hydrothermal technique, and GQDs were released from the hydrogels on immersion of the hydrogels in low-polarity organic solvents. This method did not require additional treatments such as the centrifugation, filtration and dialysis typical of the general hydrothermal method. These GQDs were observed to fluoresce, with their strongest emission in the near-UV region, at ∼347 nm. Moreover, these GQDs, when in their pure state, formed a highly viscous liquid insoluble in water due to their lack of many oxygen-containing functional groups.     

Enhanced photoresponse and photocatalytic activities of graphene quantum dots sensitized Ag/TiO2 thin film

TiO₂ thin films were fabricated through hydrothermal method. Silver nanoparticles were loaded on TiO₂ thin films via photoreduction technique. Subsequently, the graphene quantum dots (GQDs) were spin‐coated on the Ag/TiO₂ nanocomposites thin films. The crystal structure, surface morphology and UV‐vis absorbance were tested by XRD, SEM and ultraviolet‐visible spectrophotometer. These results indicated that Ag nanoparticles and GQDs are anchored on the TiO₂ nanorods. Absorbance of Ag/TiO₂ and GQDs/Ag/TiO₂ nanocomposite thin films have been extended into the visible region. Visible‐light response of the samples were investigated by electrochemical workstation. The photoresponse of the sample can be enhanced by sensitization of the Ag nanoparticles and GQDs. The enhanced visible‐light response may be due to the surface plasmon resonance of silver nanoparticles and visible absorbance of GQDs. The highest photocatalytic activity has been observed in the 9‐GQDs/Ag/TiO₂ composite thin film. The efficient charge separation and transportation can be achieved by introducing the Ag nanoparticles and GQDs in the TiO₂ thin film.     

Effect of l-cysteine modified ZnS quantum dots on the growth of Aspergillus oryzae

l-cysteine (L-cys) modified ZnS (LZS) quantum dots (QDs) were synthesized by a two-step way. The effects of LZS QDs on the phenotype, biomass, morphology and extracellular protein content of Aspergillus oryzae (A. oryzae) were studied in detail for the first time. The results illustrated that both uncoated and coated QDs had a cubic blend ZnS structure, and the particle size was about 4.0 and 4.3 nm, respectively. It was found that LZS QDs acted as an activator to stimulate the growth of A. oryzae in both solid and liquid media, and the biomass with 50 μg/mL (25 μg/mL) QDs in solid (liquid) medium was the highest and was about 1.65 (3.74) times higher than that in control medium (without QDs). The data of ultraviolet–visible (UV–Vis) revealed that the protein concentration of A. oryzae was 824.904 and 467.748 μg/mL relating to liquid medium with and without QDs, respectively. This work can provide a new way to increase the production of A. oryzae or microorganisms.     

Nanopatterned graphene quantum dots as building blocks for quantum cellular automata

Quantum cellular automata (QCA) is an innovative approach that incorporates quantum entities in classical computation processes. Binary information is encoded in different charge states of the QCA cells and transmitted by the inter-cell Coulomb interaction. Despite the promise of QCA, however, it remains a challenge to identify suitable building blocks for the construction of QCA. Graphene has recently attracted considerable attention owing to its remarkable electronic properties. The planar structure makes it feasible to pattern the whole device architecture in one sheet, compatible with the existing electronics technology. Here, we demonstrate theoretically a new QCA architecture built upon nanopatterned graphene quantum dots (GQDs). Using the tight-binding model, we determine the phenomenological cell parameters and cell-cell response functions of the GQD-QCA to characterize its performance. Furthermore, a GQD-QCA architecture is designed to demonstrate the functionalities of a fundamental majority gate. Our results show great potential in manufacturing high-density ultrafast QCA devices from a single nanopatterned graphene sheet.     

N,N-二(2-氯乙基)-N'-乙酰基-1,4-苯胺的合成

以4-氯硝基苯及二乙醇胺为原料,K_2CO_3为缚酸剂,合成了N,N-二(2-羟基乙基)-4-硝基苯胺,在三乙胺的催化下,利用氯化亚砜将其转化为氮芥关键中间体N,N-二(2-氯乙基)-4-硝基苯胺。在强酸介质中用氯化亚锡将氮芥中间体还原为氮芥类抗肿瘤药效体N,N-二(2-氯乙基)-1,4-苯二胺,以乙酰氯为酰基化试剂,通过酰基化反应合成了芳胺氮芥衍生物N,N-二(2-氯乙基)-N'-乙酰基-1,4-苯胺,并利用元素分析、IR、¹H NMR确证了新化合物的结构。     

Luminescent graphene quantum dots fabricated by pulsed laser synthesis

Graphene has been the subject of intense research in recent years due to its unique electrical, optical and mechanical properties. Furthermore, it is expected that quantum dots of graphene would make their way into devices due to their structure and composition which unify graphene and quantum dots properties. Graphene quantum dots (GQDs) are planar nano flakes with a few atomic layers thick and with a higher surface-to-volume ratio than spherical carbon dots (CDs) of the same size. We have developed a pulsed laser synthesis (PLS) method for the synthesis of GQDs that are soluble in water, measure 2–6 nm across, and are about 1–3 layers thick. They show strong intrinsic fluorescence in the visible region. The source of fluorescence can be attributed to various factors, such as: quantum confinement, zigzag edge structure, and surface defects. Confocal microscopy images of bacteria exposed to GQDs show their suitability as biomarkers and nano-probes in high contrast bioimaging.     

Blue and green luminescence of reduced graphene oxide quantum dots

We report on a new method for synthesising strongly blue and green photoluminescent graphene quantum dots (GQDs). Graphene was prepared by a new feasible method using an intensive cavitation field in a pressurised ultrasonic batch reactor. The prepared graphene was quantitatively converted to graphene oxide using our modified, safer Hummer’s method. Graphene oxide was characterised by microscopic (AFM and TEM) and spectral (infrared and Raman) methods, and the thermal stability of graphene oxide was determined using thermal analysis (DTA-TG). GQDs were prepared by a one-pot reaction, refluxing graphene oxide in different solvents (ethylene glycol, polyethylene glycol, dimethylformamide, dimethyl sulfoxide and N-methyl-2-pyrrolidone) at atmospheric pressure. The synthesised GQDs were characterised by infrared, UV–Vis absorption and photoluminescence spectroscopy, X-ray photoelectron spectroscopy (XPS) and AFM microscopy.     

石墨烯量子点纳滤膜的仿生修饰及稳定性研究

亲水修饰是提高纳滤膜抗污染性能的重要方法。采用氯化胆碱（ChC）对石墨烯量子点（GQDs-TMC）纳滤膜进行后处理仿生修饰,模拟细胞膜上磷酰胆碱的两性离子抗污染表面。红外光谱（FTIR）和表面元素分析（EDS）表明ChC以共价键结合在纳滤膜分离层上。提高反应温度和氯化胆碱溶液浓度,可以增加纳滤膜的仿生修饰程度。ChC的季铵基团与GQDs-TMC纳滤膜分离层羧基基团形成两性离子结构,提高了仿生修饰（GQDs/ChC-TMC）纳滤膜的亲水性,降低了表面电势,提高了对染料分子和二价盐离子的截留率,并且显著增强了抗污染性能。经过酸、碱和氧化剂溶液浸泡处理及高温纳滤膜分离实验,GQDs/ChC-TMC纳滤膜的渗透率和截留率均未发生较大改变,表明仿生纳滤膜具有优异的化学稳定性和耐热稳定性。     

Viscoelastic and mechanical characterization of graphene decorated with graphene quantum dots reinforced epoxy composites

The article explores viscoelastic and mechanical property analysis of graphene decorated with graphene quantum dots (GDGQD) reinforced epoxy composite. Tensile, nanoindentation, and nano-dynamic mechanical analysis (DMA) tests were conducted on the composite with 0 to 1 wt% filler variation (an interval of 0.25 wt% maintained). The hardness and elastic modulus for two different loading conditions under a frequency range of 10 to 250 Hz were performed. The viscoelastic properties described through loss tangent and storage modulus graphically and the various factors such as modulus and depth of penetration were influenced by force frequency and mobility of the molecular chain. The results revealed the role of GDGQDs as filler material for enhancing the nanomechanical and tensile properties of the epoxy matrix. The differences in the properties can be ascribed to the filler interfacial bonding with the polymer matrix at the molecular level. The macro-level properties like tensile properties following the same trend as that of the micro-level properties like nano-indentation and nano-DMA results. Further, with the GDGQD aspect ratio, and assuming three-dimensionally filled randomly orientation of filler, the Halpin-Tsai model was satisfied with the experimental tensile modulus values.     

ZnS量子点/纤维素复合材料的制备及光催化性能

采用硝酸锌和硫化钠为原料,通过水热法制备ZnS量子点的过程中同步负载于纤维素纤维上,得到具有优良性能的光催化纤维素纤维。探究了前驱体溶液浓度、水热温度、水热时间等对量子点纤维素材料的荧光强度、量子点负载率及光催化性能的影响。结果表明,最佳反应条件为:Zn⁽²⁺⁾浓度为75 mmol/L,反应温度180℃,反应时间12 h。在此条件下,ZnS量子点的负载率为9.4%。浓度10 mg/L的甲基橙(MO)模型污染物,量子点纤维素材料添加量2.5 g/L,以紫外灯(λ=365 nm)为光源,30 min内其光催化降解效率可达到83%。量子点纤维素材料具有良好的循环使用性能,经循环使用5次后,30 min内甲基橙的光催化降解率仍可达到59%。     

ZnS量子点/纤维素复合材料的制备及光催化性能

采用硝酸锌和硫化钠为原料,通过水热法制备ZnS量子点的过程中同步负载于纤维素纤维上,得到具有优良性能的光催化纤维素纤维。探究了前驱体溶液浓度、水热温度、水热时间等对量子点纤维素材料的荧光强度、量子点负载率及光催化性能的影响。结果表明,最佳反应条件为:Zn~(2+)浓度为75 mmol/L,反应温度180℃,反应时间12 h。在此条件下,ZnS量子点的负载率为9.4%。浓度10 mg/L的甲基橙(MO)模型污染物,量子点纤维素材料添加量2.5 g/L,以紫外灯(λ=365 nm)为光源,30 min内其光催化降解效率可达到83%。量子点纤维素材料具有良好的循环使用性能,经循环使用5次后,30 min内甲基橙的光催化降解率仍可达到59%。     

氮和硫双掺杂石墨烯量子点的合成及其性能研究

以来源丰富的大豆蛋白为前体,采用水热法和乙醇沉淀的分离方法合成了氮和硫双掺杂的石墨烯量子点（N,S-GQDs）。通过红外光谱（FTIR）、X射线光电子能谱（XPS）、紫外-可见光光谱（UV-vis）、高分辨率透射电镜（HRTEM）、原子力显微镜（AFM）和荧光光谱表征了N,S-GQDs的结构,及其对铁离子的检测性能。结果表明：大豆蛋白-柠檬酸-尿素水溶液在220℃水热温度下反应10 h,获得荧光量子效率为9.23%的N,S-GQDs,其水分散液具有明亮的蓝色荧光。N, S-GQDs具有0.34 nm的石墨烯晶格并展现出清晰的快速傅里叶变换图像,其厚度为2~5 nm。N, S-GQDs对Fe³⁺的检测限为0.95 μmol/L。本工作乙醇沉淀的简便方法将是一种快速获得N,S-GQDs固体的方法。     

Construction of quantum-scale catalytic regions on anatase TiO2 nanoparticles by loading TiO2 quantum dots for the photocatalytic degradation of VOCs

We constructed quantum-scale catalytic regions on the surfaces of TiO₂ nanoparticles by loading TiO₂ quantum dots (QDs) with a two-step method. The removal rate and mineralization efficiency of toluene were measured and then used in evaluating the oxidation performance of the prepared samples. A home-built atmospheric surface photovoltage spectrometer and X-ray photoelectron spectrometer were used in analyzing band alignment across the interface between TiO₂ QD and TiO₂ particle and the transfer of charge carriers at the surface. Results showed that an upward band bending formed from the TiO₂ particle to the TiO₂ QD and promoted the accumulation of holes at the QD side. Moreover, the QD and surrounding substrate TiO₂ formed a quantum-scale catalytic region, improving the reaction probability of electron-hole pairs and corresponding intermediates. The mineralization efficiency of toluene in QD-loaded TiO₂ reached 95.8%. The synthetic method is green and simple, showing potential in scale production and industrial application.     

Cu2ZnSnS4 nanocrystals and graphene quantum dots for photovoltaics

Semiconductor quantum dots exhibit great potential for applications in next generation high efficiency, low cost solar cells because of their unique optoelectronic properties. Cu(2)ZnSnS(4) (CZTS) nanocrystals and graphene quantum dots (GQDs) have recently received much attention as building blocks for use in solar energy conversion due to their outstanding properties and advantageous characteristics, including high optical absorptivity, tunable bandgap, and earth abundant chemical composition. In this Feature Article, recent advances in the synthesis and utilization of CZTS nanocrystals and colloidal GQDs for photovoltaics are highlighted, followed by an outlook on the future research efforts in these areas.     

Enhancement in the fluorescence of graphene quantum dots by hydrazine hydrate reduction

A simple and effective chemical method was reported to enhance the fluorescence of graphene quantum dots (GQDs). Specifically, water-soluble GQDs, prepared by solvothermal synthesis from graphene oxide, are chemically reduced by hydrazine hydrate to produce reduced GQDs (rGQDs). The results show that the hydrazine hydrate reduction not only decreases the O/C atomic ratio of GQDs, also changes the bonding type of N atoms. Such surface/edge chemical bond change of GQDs results in that as-made rGQDs exhibit more than two times fluorescence intensity as strong as that of the pristine GQDs.     

Cellular distribution and cytotoxicity of graphene quantum dots with different functional groups

Graphene quantum dots (GQDs) have been developed as promising optical probes for bioimaging due to their excellent photoluminescent properties. Additionally, the fluorescence spectrum and quantum yield of GQDs are highly dependent on the surface functional groups on the carbon sheets. However, the distribution and cytotoxicity of GQDs functionalized with different chemical groups have not been specifically investigated. Herein, the cytotoxicity of three kinds of GQDs with different modified groups (NH₂, COOH, and CO-N (CH₃)₂, respectively) in human A549 lung carcinoma cells and human neural glioma C6 cells was investigated using thiazoyl blue colorimetric (MTT) assay and trypan blue assay. The cellular apoptosis or necrosis was then evaluated by flow cytometry analysis. It was demonstrated that the three modified GQDs showed good biocompatibility even when the concentration reached 200 μg/mL. The Raman spectra of cells treated with GQDs with different functional groups also showed no distinct changes, affording molecular level evidence for the biocompatibility of the three kinds of GQDs. The cellular distribution of the three modified GQDs was observed using a fluorescence microscope. The data revealed that GQDs randomly dispersed in the cytoplasm but not diffused into nucleus. Therefore, GQDs with different functional groups have low cytotoxicity and excellent biocompatibility regardless of chemical modification, offering good prospects for bioimaging and other biomedical applications.     

Cytotoxicity of quantum dots and graphene oxide to erythroid cells and macrophages

Great concerns have been raised about the exposure and possible adverse influence of nanomaterials due to their wide applications in a variety of fields, such as biomedicine and daily lives. The blood circulation system and blood cells form an important barrier against invaders, including nanomaterials. However, studies of the biological effects of nanomaterials on blood cells have been limited and without clear conclusions thus far. In the current study, the biological influence of quantum dots (QDs) with various surface coating on erythroid cells and graphene oxide (GO) on macrophages was closely investigated. We found that QDs posed great damage to macrophages through intracellular accumulation of QDs coupled with reactive oxygen species generation, particularly for QDs coated with PEG-NH₂. QD modified with polyethylene glycol-conjugated amine particles exerted robust inhibition on cell proliferation of J744A.1 macrophages, irrespective of apoptosis. Additionally, to the best of our knowledge, our study is the first to have demonstrated that GO could provoke apoptosis of erythroid cells through oxidative stress in E14.5 fetal liver erythroid cells and in vivo administration of GO-diminished erythroid population in spleen, associated with disordered erythropoiesis in mice.     

Preparation of WO3-reduced graphene oxide nanocomposites with enhanced photocatalytic property

In this work, WO₃-reduced graphene oxide (RGO) nanocomposite was synthesized via a simple one-pot hydrothermal method. The synthesized nanocomposite was characterized by SEM, XRD, EDX, UV–vis spectroscopy, N₂ adsorption/desorption, photocurrent response, electrochemical impedance spectroscopy and Raman spectroscopy. The superior contact between WO₃ and RGO sheets in the nanocomposite facilitates the photocatalytic degradation of methylene blue and evolution of oxygen. The cause of the enhanced photocatalytic performance could ascribe to the highly facilitated electron transport by the synergistic effect between WO₃ and RGO sheets, as well as suppressing the electron hole pair recombination in the nanocomposite.