Improving singlet oxygen generating abilities of phthalocyanines: aluminum tetrasulfonated phthalocyanine in the presence of graphene quantum dots and folic acid

Glutathione-capped graphene quantum dots (GQDs@GSH) were covalently linked to folic acid (FA). Aluminum tetrasulfonated phthalocyanine (ClAlTSPc) was then adsorbed on the GQDs@GSH-FA conjugate to form GQDs@GSH-FA/ClAlTSPc or on GQDs@GSH and pristine GQDs alone to form GQDs@GSH/ClAlTSPc and GQDs/ClAlTSPc, respectively. We report for the first time on the photophysicochemical behavior of the resulting nanoconjugates. The fluorescence quantum yields of pristine GQDs, GQDS@GSH, or GQDs@GSH-FA conjugate were quenched upon non-covalent interaction (π–π) with ClAlTSPc. There was an increase in triplet quantum yields from 0.38 for ClAlTSPc alone to 0.60, 0.75, and 0.73 when ClAlTSPc was linked to pristine GQDs, GQDs@GSH, and GQDs@GSH-FA, respectively. The singlet oxygen quantum yields also increased from 0.37 for ClAlTSPc alone to 0.42 (for ClALTSPc with pristine GQDs), 0.52 (for ClAlTSPc with GQDs@GSH), and 0.54 (for ClAlTSPc with GQDs@GSH-FA). Thus, the present work may lead to a new generation of carbon-based nanomaterial photodynamic therapy agents with overall performance superior to conventional agents in terms of singlet oxygen generation, water dispersibility, and biocompatibility.     

Simultaneous determination of Hg(II) and Cu(II) in water samples using fluorescence quenching sensor of N-doped and N,K co-doped graphene quantum dots

The present study was aimed to use of N doped graphene quantum dots (N-GQDs) and N,K co-doped graphene quantum dots (N,K-GQDs) as a fluorescence quenching sensor to determine both mercury and copper in water sample, simultaneously using simple fluorescence protocol. Each of N-GQDs or N,K-GQDs was optimized separately with 1–5% (w/v) HNO₃ or KNO₃, respectively, and their quantum yields were determined and compared. It was found that N-GQDs, obtained from 3% (w/v) HNO₃ doped resulted higher fluorescence intensity at the maximum excitation and emission wavelengths of 370 and 460 nm, respectively, with higher quantum yield (QY = 83.42%) compared with that of undoped GQDs (QY = 16.35%). While N,K-GQDs obtained from 5%(w/v) KNO₃ gave somewhat different fluorescence spectrum, but still had the same maximum excitation and emission wavelengths with rather highest QY (94.07%). However, it is interesting that detection sensitivity expressed as slope of their calibration curve (y = 5.43x − 19.48; r² = 0.9971) of the N-GQDs is rather higher than that (y = 1.29x + 17.66; r² = 0.9977) of the N,K-GQDs for Hg²⁺ fluorescence quenching sensor, and the fluorescence intensity of N-GQDs had better selectively quenching effect only by both Hg²⁺ and Cu²⁺. Thus, their quenching effects were selected to develop the fluorescence turn-off sensor for trace level of both metal ions in real water samples. For method validation, the N-GQDs exhibited high sensitivity to detect both Hg²⁺ and Cu²⁺ with wide linear ranges of 20–100 μM and 100–500 μM, respectively. Limit of detection (LOD) and limit of quantitation (LOQ) were 0.42 μM & 1.41 μM for Hg²⁺ and 13.19 μM & 43.97 μM for Cu²⁺, respectively, with their precision expressed as an intra-day and an inter-day analysis of 6.98% & 11.35% for Hg²⁺ and 11.78% & 9.43% for Cu²⁺, respectively. Also the study of matrix analysis of the water samples (drinking water and tap water), was carried out using N-GQDs and N,K-GQDs resulted good percentage recoveries in comparison with those using undoped GQDs under the same optimum conditions.     

氨基功能化石墨烯量子点表面缺陷钝化及其发光增强

通过酸氧化法将氧化石墨烯进一步“切割”制备石墨烯量子点（GQDs）,在100℃水热条件下,用氨水处理石墨烯量子点制备得到氨基功能化石墨烯量子点（N-GQDs）。傅里叶变换红外光谱证明NH₃可以有效地进攻环氧基碳和羧基碳,形成羟胺和酰胺基。原子力显微镜结果表明NH₃不仅能够有助于产生更小的量子点,还对石墨烯纳米片有致孔作用。氨基功能化之后,由于C-O-C相关的n-π^*跃迁受到抑制,N-GQDs发光具有更弱的激发波长依赖性,并使其荧光量子产率从0.3%提高至9.6%。时间分辨发光光谱表明,相比含氧基团,含氮基团相关的局域电子激发态具有更长的荧光寿命和更弱的发射光谱依赖性。     

Bottom-Up Synthesis,Dispersion and Properties of Rectangular-Shaped Graphene Quantum Dots

Carbon nanomaterials have attracted the attention of the scientific community for more than 30 years now; first with fullerene, then with nanotubes and now with graphene and graphene related materials. Graphene quantum dots (GQDs) are nanoparticles of graphene that can be synthesized following two approaches, namely top-down and bottom-up methods. The top-down synthesis used harsh chemical and/or physical treatments of macroscopic graphitic materials to obtain nanoparticles, while the second is based on organic chemistry through the synthesis of polycyclic aromatic hydrocarbons exhibiting various sizes and shapes that are perfectly controlled. The main drawback of this approach is related to the low solubility of carbon materials that prevents the synthesis of nanoparticles containing more than few hundreds of sp² carbon atoms. Here we report on the synthesis of a family of rectangular-shaped graphene quantum dots containing up to 162 sp² carbon atoms. These graphene quantum dots are not functionalized on their periphery in order to keep the maximum similarity with nanoparticles of pure graphene. We chose water with sodium deoxycholate surfactant to study their dispersion and their optical properties (absorption, photoluminescence and photoluminescence excitation). The electronic structure of the particles and of their aggregates are studied using Tight-Binding (TB). We observe that the larger particles ( GQD 3 and GQD 4 ) present a slightly better dispensability than the smaller ones, probably because the larger GQDs can accommodate more surfactant molecules on each side, which helps to stabilize their dispersion in water.     

Graphene Quantum Dots Assembled with Metalloporphyrins for “Turn on” Sensing of Hydrogen Peroxide and Glucose

Noncovalent and multifunctional hybrids have been generated via π–π stacking and electrostatic interactions by combining the nanometer‐scale graphene structure of graphene quantum dots (GQDs) with Fe^III 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)porphine (FeTMPyP). The inner filter effect (IFE) of FeTMPyP on the GQDs results in substantial PL quenching of the GQDs. The quenched PL of GQDs by the FeTMPyP can be switched back “on” in response to the reaction between FeTMPyP and H₂O₂, which causes rupture of the cyclic tetrapyrrolic nucleus with consequential loss of iron from FeTMPyP, and then proceeds further to produce colorless dipyrroles and monopyrroles. This “turn on” system can be applied for simple and convenient H₂O₂ sensing and can be further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase (GOx) through the oxidation of glucose and formation of H₂O₂. Because of the inherent synthetic control available for the design of metalloporphyrins, the GQDs‐based optical sensing approach described here has the potential to be highly versatile for other target analytes.     

Cu(II)‐supported graphene quantum dots modified NiFe2O4: A green and efficient catalyst for the synthesis of 4H‐pyrimido[2,1‐b]benzothiazoles in water

NiFe₂O₄ nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe₂O₄) for green formation of 4H‐pyrimido[2,1‐b]benzothiazoles. The prepared catalyst can be isolated assisted by an outer magnet and recovered for five courses without significant reduction in its efficiency. The as‐prepared magnetic heterogeneous nanocomposite was characterized by UV–Vis, FT‐IR, XRD, EDS, VSM, TEM, and ICP. Performing the reactions in environmentally friendly and affordable conditions (water), the low catalyst percentage, high yield of products, short reaction times, and easy workup are the merits of this protocol.     

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.     

水热法制备MoO3-GQDs的三甲胺气敏性能

采用水热法制备了一系列具有不同碳量子点(GQDs)含量的MoO3?GQDs纳米复合材料,利用X射线衍射、扫描电子显微镜、透射电子显微镜、FTIR等对MoO3?GQDs复合材料进行了表征,研究了其气敏性能。结果表明,复合材料中GQDs的含量对MoO3?GQDs复合材料的气敏响应和选择性有显著影响。MoO3?GQDs纳米复合材料(S?6,GQDs悬浮液的含量为6 mL)传感器在230℃时对三甲胺(TMA)表现出高的气敏响应和好的气敏选择性;该传感器对1000μL·L^-1 TMA的响应为74.08;对1000μL·L^-1 TMA的响应时间和恢复时间分别为73和34 s;S?6复合材料气敏传感器在230℃时可以检测到1μL·L^-1的TMA。     

Fluorescent blood glucose monitor by hemin-functionalized graphene quantum dots based sensing system

In the present work, a highly sensitive and specific fluorescent biosensor for blood glucose monitoring is developed based on hemin-functionalized graphene quantum dots (GQDs) and glucose oxidase (GOx) system. The GQDs which are simply prepared by pyrolyzing citric acid exhibit strong fluorescence and good water-solubility. Due to the noncovalent assembly between hemin and GQDs, the addition of hemin can make hydrogen peroxide (H₂O₂) to destroy the passivated surface of GQDs, leading to significant fluorescence quenching of GQDs. Based on this effect, a novel fluorescent platform is proposed for the sensing of glucose. Under the optimized conditions, the linear range of glucose is from 9 to 300 μM, and the limit of detection is 0.1 μM. As unique properties of GQDs, the proposed biosensor is green, simple, cost-efficient, and it is successfully applied to the determination of glucose in human serum. In addition, the proposed method provides a new pathway to further design the biosensors based on the assembly of GQDs with hemin for detection of biomolecules.     

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.     

S-doped graphene quantum dots as nanophotocatalyst for visible light degradation

S-doped graphene quantum dots (S-GQDs) with well crystallization and monodispersity were prepared and applied as novel nanophotocatalyst for visible light degradation of basic fuchsin.     

Electrocatalytic Behavior of Manganese and Cobalt Porphyrins Attached to Graphene Quantum Dots: Applied in the Oxidation of Hydrazine

Manganese and cobalt metalated 5, 10, 15-tris(aminophenyl)-20-(4-carboxyphenyl) porphyrins (ClMnTA₃CPP and CoTA₃CPP) were synthesized and attached to graphene quantum dots (GQDs) via π-π interaction and electrostatic interaction. The electrochemical oxidation of hydrazine was performed via cyclic voltammetry and chronoamperometry. The CoTA₃CPP showed good electrocatalytic activity towards the oxidation of hydrazine in terms of catalytic rate constants and limits of detection (LoD). ClMnTA₃CPP showed lower overpotential 0.60 V. The introduction of GQDs improved the electrocatalytic ability when combined with CoTA₃CPP and ClMnTA₃CPP with the lowest LoD (0.0025 mM CoTA₃CPP–GQDs) followed by ClMnTA₃CPP–GQDs with 0.0033 mM.     

Synthesis of Fluorinated and Nonfluorinated Graphene Quantum Dots through a New Top‐Down Strategy for Long‐Time Cellular Imaging

Herein, a new strategy has been developed through combining a microwave‐assisted technique with hydrothermal treatment to reduce graphene waste and improve production yield of graphene quantum dots (GQDs) prepared by top‐down methods. By using fluorinated graphene oxide (FGO) as a raw material, fluorinated GQDs and nonfluorinated GQDs can be synthesized. Additionally, in the fluorinated GQDs, the protective shell supplied by fluorine improves the pH stability of photoluminescence and the strong electron‐withdrawing group, ?F, reduces the π‐ electron density of the aromatic structure; thus inhibiting reactivity toward singlet oxygen produced during irradiation and improving the photostability. Therefore, the as‐prepared fluorinated GQDs with excellent photo‐ and pH stability are suitable for long‐term cellular imaging.     

基于柠檬酸的石墨烯量子点的制备及其应用

石墨烯量子点（GQDs）是一种新型碳基准零维材料,不但具有石墨烯的独特平面结构,同时具备碳点的量子限制效应和边界效应。GQDs具有独特的光学性质、低毒性、高荧光稳定性和高生物相容性,被广泛应用于检测、传感、催化、细胞成像、药物递送和污染治理等领域。GQDs的合成分为自上而下法和自下而上法,前者将大尺寸的石墨烯、石墨、碳材料切割成纳米级的量子点,后者使用不同的前驱体,通过水热法、热裂解法等方法合成石墨烯量子点。柠檬酸（CA）是一种重要的有机酸,室温下是白色结晶状粉末,是自下而上法合成GQDs的一种常用前驱体,近年来有许多关于以CA为前驱体合成不同GQDs的研究,以CA为前驱体合成的GQDs（CA-GQDs）在生物医药、荧光检测、成像等领域均有应用,具有较好的应用前景。对近年来基于CA的合成方法和具体应用进行了总结和回顾,旨在将现有CA-GQDs的相关成果尽可能汇总和展现,以对相关领域研究工作者提供一定参考,并对未来CA-GQDs较有前景的研究方向进行了展望。     

氮掺杂石墨烯量子点/MOF衍生多孔碳纳米片构筑高性能超级电容器

首先采用溶液法在碳布上生长Co-MOF二维纳米片,通过高温退火和刻蚀后得到MOF衍生多孔碳纳米片。以Co-MOF衍生的多孔碳纳米片/碳布(CNS/CC)作为碳基骨架,采用电化学沉积法负载高活性氮掺杂石墨烯量子点(N-GQDs),制备得到分级多孔结构的N-GQD/CNS/CC复合材料。组装成自支撑且无粘结剂的N-GQD/CNS/CC电极,当电流密度为1 A·g~(-1)时,其比电容高达423 F·g~(-1)。通过储能机制和电容贡献机制的研究表明,在碳纤维上原位生长的具有高双电层电容的CNS和表面负载具有高赝电容的N-GQDs之间相互协同作用,使得N-GQD/CNS/CC电极具有高电容性能,是一种理想的超级电容器电极材料。电极材料的高导电、分级多孔结构有利于电子的传输和电解质离子的扩散,具有良好的动力学性能,能快速充放电和具有优异的倍率特性。将电极组装成对称型超级电容器,功率密度为250 W·kg~(-1)时对应的能量密度达到7.9 Wh·kg~(-1),且经过10 000次循环后电容保持率为91.2%,说明氮掺杂石墨烯量子点/MOF衍生多孔碳纳米片复合材料是一种电化学性能稳定的具有高电容性能的全碳电极材料。     

Experimental study and modelling of effective parameters on removal of Cd(II) from water by halloysite/graphene quantum dots magnetic nanocomposite as an adsorbent using response surface methodology

Graphene quantum dots (GQDs) were covalently immobilized onto the NiFe₂O₄-halloysite nanotubes (NiFe₂O₄-HNTs) surface to fabricate a nanocomposite material utilized as an active adsorbent to eliminate Cd(II) ions from water. NiFe₂O₄ nanoparticles were synthesized and simultaneously deposited on HNTs. Then, the material surface was coated by APTES (aminopropyltriethoxysilane) to cause GQDs be connected to the external layer via an amide bond. The prepared nanomaterial structure was identified by TEM, XRD, FT-IR, BET isotherm, EDS analysis and VSM (vibrating sample magnetometry). Box–Behnken design incorporated with response surface method (RSM) was utilized to find out the impact of pH, time, initial concentration of Cd(II) and adsorbent dose on cadmium removal. Study discovered that adsorption operation is the quasi-second-order kinetic model and adapted more precisely with Langmuir adsorption model. The Langmuir highest uptake capacity of 34.72 mg/g at 298 K was acquired. The Elovich model recommended that the process is a kind of chemisorption. The calculated thermodynamic variables verified that the uptake process is endothermic and spontaneous. Additionally, the adsorbent can be simply separated with the aid of a magnet. In this study, we have suggested a practical method for the synthesis of the NiFe₂O₄/halloysite nanotubes/graphene quantum dots magnetic nanoparticles for cadmium removal from water.     

Effects of Substituents on the Electrocatalytic Activity of Cobalt Phthalocyanines when Conjugated to Graphene Quantum Dots

We report on the π–π interactions between graphene quantum dots (GQDs) and the following cobalt phthalocyanine derivatives: cobalt monocarboxyphenoxy phthalocyanine (complex 1 ), cobalt tetracarboxyphenoxyphthalocyanine (complex 2 ), and cobalt tetraaminophenoxy phthalocyanine (complex 3 ). The conjugates (conj) with GQDs are represented as 1 @GQDs(conj), 2 @GQDs(conj) and 3 @GQDs(conj), respectively. The resulting phthalocyanine/GQDs conjugates were adsorbed on containing a glassy carbon electrode (GCE) using the drop and dry method. We explore the electrochemical properties of phthalocyanines functionalized with both electron withdrawing groups and electron donating groups when non‐covalently linked to the π‐electron rich graphene quantum dots. GCE/ 3, GCE/ 2 @GQDs(conj) and GCE/ 1 @GQDs(conj) had the lowest limits of detection (LOD). Sequentially modified electrodes showed less favourable detection limits compared to the conjugates.     

氮掺杂石墨烯量子点/钯纳米复合材料的研究

铂基催化剂因具有高催化活性、高稳定性而成为极其重要的能源转化催化剂。本文采用水热法合成氮掺杂石墨烯量子点支撑的钯纳米复合材料(Pd@N-GQDs),并将其用于碱性介质中甲醇的电催化氧化反应。实验结果表明,相比同类型材料钯负载于石墨烯纳米片(Pd@GS)、钯负载于石墨烯量子点(Pd@GQDs)和商业钯黑催化剂(Pd@C),Pd@N-GQDs纳米材料具有很高的催化活性和稳定性,并可减少催化剂材料中贵金属的使用量。     

Chemical Functionalisation and Photoluminescence of Graphene Quantum Dots

Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD–organic hybrid materials. Three peripherally functionalised GQDs having a third‐generation dendritic wedge (GQD‐ 2 ), long alkyl chains (GQD‐ 3 ) and a polyhedral oligomeric silsesquioxane group (GQD‐ 4 ) were prepared by the Cu^I‐catalysed Huisgen cycloaddition reaction of GQD‐ 1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD‐ 1 – 4 and on the five‐membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO–LUMO bandgaps of GQD‐ 1 – 4 were estimated to be approximately 2 eV, and their low‐lying LUMO levels (<?3.9 eV) were lower than that of phenyl‐C₆₁‐butyric acid methyl ester, an n‐type organic semiconductor. The solubility of GQD‐ 1 – 4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD‐ 2 , both GQD‐ 3 and GQD‐ 4 emitted white light upon excitation at 360 nm. Size‐exclusion chromatography demonstrated that white‐light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.     

A biocompatible electrochemical sensor based on PtNi alloy nanoparticles-coupled N-GQDs for in situ monitoring of dopamine in glioma cells

We report the design and construction of enzyme-free sensor using platinum–nickel (PtNi) bimetallic alloy nanoparticle-conjugated nitrogen-doped graphene quantum dots (N-GQDs) for the highly specific in situ monitoring of dopamine (DA) secreted by glioma cells (C6). PtNi@N-GQDs nanocomposites were synthesized using a simple ultrasonication method. The resulting hybrid material was an excellent electrocatalyst for the redox activity of DA owing to the combined properties of PtNi alloys and highly conductive N-GQDs. The PtNi@N-GQDs-based sensing platform demonstrated substantial sensing ability with a detection range of 0.0125–952 μM, a sensitivity of 0.279 μA/μM/cm², and a limit of detection of 0.005 μM (S/N = 3). The sensing performance of PtNi@N-GQDs was highly stable, selective, and reproducible. We successfully showed the practical application of the PtNi@N-GQDs sensor by quantifying DA in the blood serum and human urine samples. Finally, we used the PtNi@N-GQDs biocompatible platform to quantify DA released from C6 cells.