Effects of Coal Rank and High Organic Sulfur on the Structure and Optical Properties of Coal-based Graphene Quantum Dots

Coal-based graphene quantum dots(GQDs) were successfully produced via a one-step chemical synthesis from six different coal ranks, from which two superhigh organic sulfur(SHOS) coals were selected as natural S-doped carbon sources for the preparation of S-doped GQDs. The effects of coal properties on coal-based GQDs were analyzed by means of high-resolution transmission electron microscopy(HRTEM), X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, X-ray photoelectron spectroscopy(XPS), ultraviolet-visible(UV-Vis) absorption spectroscopy, and fluorescence emission spectra. It was shown that all coal samples can be used to prepare GQDs, which emit bluegreen and blue fluorescence under ultraviolet light. Anthracite-based GQDs have a hexagonal crystal structure without defects, the largest size, and densely arranged carbon rings in their lamellae; the highrank bituminous coal-based GQDs are relatively reduced in size, with their hexagonal crystal structure being only faintly visible; the low-rank bituminous coal-based GQDs are the smallest, with sparse lattice fringes and visible internal defects. As the metamorphism of raw coals increases, the yield decreases and the fluorescence quantum yield(QY) initially increases and then decreases. Additionally, the surface of GQDs that were prepared using high-rank SHOS coal(high-rank bituminous coal) preserves rich sulfur content even after strong oxidation, which effectively adjusts the bandgap and improves the fluorescence QY. Thus, high-rank bituminous coal with SHOS content can be used as a natural S-doped carbon source to prepare S-doped GQDs, extending the clean utilization of low-grade coal.

Novel Formaldehyde Sensor based on Hydrogen Peroxide/Melamine Modulated Photoluminescence of Nitrogen-doped Graphene Quantum Dots

A modulated photoluminescence nanosensor was developed for the quantitative detection of formaldehyde with nitrogen-doped graphene quantum dots and melamine. The sensing system was based on the different activated effects of melamine and hydrogen peroxide on the photoluminescence intensity of nitrogendoped graphene quantum dots. Under the optimal conditions, the modulated photoluminescence sensing system can be used to detect formaldehyde with a good linear relationship between the nitrogen-doped graphene quantum dots photoluminescence difference and the concentration of formaldehyde. The novel sensing system provided new directions for the detection of formaldehyde with high selectivity and quick response.

Effective exposure of nitrogen heteroatoms in 3D porous graphene framework for oxygen reduction reaction and lithium–sulfur batteries

The introduction of nitrogen heteroatoms into carbon materials is a facile and efficient strategy to regulate their reactivities and facilitate their potential applications in energy conversion and storage. However,most of nitrogen heteroatoms are doped into the bulk phase of carbon without site selectivity, which significantly reduces the contacts of feedstocks with the active dopants in a conductive scaffold. Herein we proposed the chemical vapor deposition of a nitrogen-doped graphene skin on the 3D porous graphene framework and donated the carbon/carbon composite as surface N-doped grapheme(SNG). In contrast with routine N-doped graphene framework(NGF) with bulk distribution of N heteroatoms, the SNG renders a high surface N content of 1.81 at%, enhanced electrical conductivity of 31 S cm^(-1), a large surface area of 1531 m^2 g^(-1), a low defect density with a low I_D/I_G ratio of 1.55 calculated from Raman spectrum, and a high oxidation peak of 532.7 ℃ in oxygen atmosphere. The selective distribution of N heteroatoms on the surface of SNG affords the effective exposure of active sites at the interfaces of the electrode/electrolyte, so that more N heteroatoms are able to contact with oxygen feedstocks in oxygen reduction reaction or serve as polysulfide anchoring sites to retard the shuttle of polysulfides in a lithium–sulfur battery. This work opens a fresh viewpoint on the manipulation of active site distribution in a conductive scaffolds for multi-electron redox reaction based energy conversion and storage.

Graphene quantum dots modulated solution-derived InGaO thin-film transistors and stress stability exploration

Graphene quantum dots(GQDs)doped InGaO(IGO)thin film transistors(TFTs)have been fabricated based on solution-driven ZrO_(x) as gate dielectrics.Compare to pure IGO TFTs,superior electrical performance of the GQDs-IGO TFTs can be achieved by adjusting the doping concentration.It has been demonstrated that GQDs-modified IGO TFTs devices with GQDs doping content of0.3 mg·ml^(-1)have the optimized performances,including field-effect mobility(μ_(FE))of 22.02 cm^(2)·V^(-1)·s^(-1),on/off current ratio(I_(on)/I_(off))of 7.06×10^(7),subthreshold swing(SS)of 0.09 V·dec^(-1),hysteresis of 0.04 V and interfacial trap states(D_(it))of 1.03×10^(12)cm^(-2).In addition,bias stress and illumination stress tests have been performed and excellent stability has been achieved for optimized GQDs-IGO-TFTs.The GQDs-IGO TFTs device showed smaller threshold voltage shift of 0.12 and 0.04 V under positive bias stress(PBS)test and negative bias stress(NBS)test for 3600 s,respectively.And it showed smaller threshold voltage shift of 0.27 and 0.34 V for red light under the PBS and NBS test for 3600 s,respectively.Meanwhile,it showed smaller threshold voltage shift of0.20 and 0.22 V for green light under PBS and NBS test for3600 s,respectively.It also showed smaller threshold voltage shift of 0.17 and 0.12 V for blue under the positive bias illumination stress(PBIS)test and negative bias illumination stress(NBIS)test for 3600 s,respectively.Lowfrequency noise(LFN)characteristics of GQDs-IGO/ZrO_(x)TFTs indicated that the noise source came from the fluctuations in mobility.Finally,a low voltage resistor-loaded unipolar inverter has been built based on GQDs-IGO/ZrO_(x)TFT,demonstrating good dynamic response behavior and a maximum gain of 7.4.These experimental results have suggested that solution-processed GQDs-IGO/ZrO_(x)TFT may envision potential applications in low-cost and large-area electronics.

UV light driven high-performance room temperature surface acoustic wave NH_(3) gas sensor using sulfur-doped g-C_(3)N_(4) quantum dots

Nanomaterials integrated surface acoustic wave(SAW)gas sensing technology has emerged as a promising candidate for realtime toxic gas sensing applications for environmental and human health safety.However,the development of novel chemical interface based on two-dimensional(2D)sensing materials for SAW sensors for the rapid and sensitive detection of NH_(3)gas at room temperature(RT)still remains challenging.Herein,we report a highly selective RT NH_(3)gas sensor based on sulfur-doped graphitic carbon nitride quantum dots(S@g-C_(3)N_(4)QD)coated langasite(LGS)SAW sensor with enhanced sensitivity and recovery rate under ultraviolet(UV)illumination.Fascinatingly,the sensitivity of the S@g-C_(3)N_(4)QD/LGS SAW sensor to NH_(3)(500 ppb)at RT is dramatically enhanced by~4.5-fold with a low detection limit(~85 ppb),high selectivity,excellent reproducibility,fast response/recovery time(70 s/79 s)under UV activation(365 nm)as compared to dark condition.Additionally,the proposed sensor exhibited augmented NH_(3)detection capability across the broad range of relative humidity(20%–80%).Such remarkable gas sensing performances of the as-prepared sensor to NH_(3)are attributed to the high surface area,enhanced functional groups,sulfur defects,UV photogenerated charge carriers,facile charge transfer in the S@g-C_(3)N_(4)QD sensing layer,which further helps to improve the gas molecules adsorption that causes the increase in conductivity,resulting in larger frequency responses.The gas sensing mechanism of S@g-C_(3)N_(4)QD/LGS SAW sensor is ascribed to the enhanced electroacoustic effect,which is supported by the correlation of resistive type and COMSOL Multiphysics simulation studies.We envisage that the present work paves a promising strategy to develop the next generation 2D g-C_(3)N_(4)based high responsive RT SAW gas sensors.

Layered MoS2@graphene functionalized with nitrogen-doped graphene quantum dots as an enhanced electrochemical hydrogen evolution catalyst

A novel three-dimensional (3D) layered MoS2@graphene functionalized with nitrogen-doped graphene quantum dots (MoS2@N-GQDs-GR) composites as an enhanced electrochemical hydrogen evolution catalyst. The few layered MoS2 nanoflowers supported on N-GQDs-GR surface were elaborately fabricated by one-pot hydrothermal method, which MoS2 and N-GQDs-GR exist in a bonding manner of Mo-N. In addition, due to the layered MoS2 sheet edge exposes more hydrogen evolution active sites and N-GQDs-GR have high conductivity, the composites exhibit prominent electrocatalytic activity with a low overpotential 99 mV, a small Tafel slope 49.3 mV/dec. Therefore, that the current work will develop HER catalysts may replace Pt.

氮掺杂碳量子点荧光法检测猪肉中的四环素

四环素(TC)作为一种广谱抗生素,用于预防和治疗细菌性疾病,以及作为饲料添加剂促进动物生长。本文旨在建立一种菠萝皮来源的氮掺杂碳量子点(N-CQDs)荧光猝灭法快速检测TC。以菠萝皮和二乙烯三胺为原料,通过水热法制备高量子产率的蓝色荧光N-CQDs。通过透射电子显微镜、傅里叶红外光谱、X射线光电子能谱对N-CQDs进行结构表征。结果表明,N-CQDs的平均粒径为3.53 nm,主要由C、N、O 3种元素组成,表面具有含氧和含氮基团。主要猝灭机理为静态猝灭和内滤效应。在最优试验条件下,该方法在0.3~40μg/mL范围线性良好,检出限为89.26μg/L。该检测方法被用于猪肉中四环素的检测,回收率在98.40%~106.02%之间,相对标准偏差1.29%~3.88%。

基于量子化学计算优化的氮掺杂碳量子点缓蚀剂制备及其缓蚀性能

[目的]氮掺杂碳量子点(N-CQDs)作为一种绿色高效的新型缓蚀剂,在腐蚀控制领域具有巨大的应用潜力。但由于其结构无法精确调控,很难对制备N-CQDs的众多前驱体进行筛选。[方法]依据密度泛函理论(DFT),通过Fukui指数计算各前驱体分子的优先反应活性位点,确定前驱体分子间一步脱水缩合反应产物的分子结构,并进行全局参量和局部参量的计算,分析了采用柠檬酸分别与乙二胺、尿素和氨基胍盐酸盐作为前驱体所合成的3种N-CQDs的缓蚀性能,再通过称重法对水热法合成的3种N-CQDs的缓蚀性能进行验证,优选出缓蚀性能最佳的缓蚀剂。采用紫外可见吸收光谱、荧光光谱和高分辨率场发射透射电镜表征优选缓蚀剂的荧光性能和表面形貌,并以电化学方法和表面分析方法研究此缓蚀剂对Q235碳钢在0.5 mol/L硫酸溶液中的缓蚀机理。[结果]以柠檬酸和氨基胍盐酸盐为前驱体制备的N-CQDs-3缓蚀性能最佳,且试验结果和理论计算结果一致。N-CQDs-3在紫外激发光下显示蓝绿光,平均粒径为(2.5±0.8)nm。该缓蚀剂是一种混合型缓蚀剂,主要通过物理和化学吸附同时抑制金属在酸溶液中腐蚀反应的发生,其对Q235碳钢在0.5 mol/L硫酸溶液中的缓蚀效率最高可达95.3%。[结论]通过量子化学计算方法对制备N-CQDs所用的前驱体进行筛选,提前预测其缓蚀性能,可提高试验效率。

抗生素亚胺培南探针分子设计及传感性能研究

抗生素亚胺培南(imipenem,IPM)用药治疗败血症患者感染需要快速做出反应,目前的血药监测方法严重延迟药物注射。设计金属元素掺杂型石墨烯量子点(graphene quantum dots,GQDs),可实现荧光法快速测定IPM和开辟荧光法检测抗生素的新途径。采用水热法制备了铁掺杂GQDs(Fe-GQDs),用于快速探测IPM。采用透射电子显微镜(transmission electron microscopy,TEM)、X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)以及荧光光谱等方法,探讨不同铁源起始剂对GQDs荧光性能及传感性能的影响,并分析了乙酸铁为铁源制备的Fe-GQDs的微观结构及荧光性能。结果表明:以乙酸铁为起始剂制备的Fe-GQDs荧光性能最佳,且对IPM具有显著的荧光淬灭效应。所制备的Fe-GQDs荧光淬灭强度(F/F_(0))与IPM浓度(concentration,C)呈线性关系,线性方程为F/F_(0)=0.983-4.23×10^(-3)C,线性相关系数(R 2)为0.997,线性范围为0.007~0.073 g/L。Fe-GQDs探针分子对血浆中常见有机分子和金属离子具有良好的抗干扰性,检测IPM误差为1.6%~4.6%。

氮掺杂碳量子点的制备及在细胞温度传感中的应用

该研究以生物质西红柿为碳源和氮源,通过微波法制备了氮自掺杂碳量子点(N-CQDs)。通过场发射透射电子显微镜(TEM)、X射线光电子能谱仪(XPS)和荧光光度计等对其形貌、结构、稳定性、光电性能、温敏性及细胞毒性进行考察,并用于活细胞温度传感研究。实验结果表明,所制备的N-CQDs稳定性强,光电性能优异,对温度具有较强的敏感性。在25~65℃范围内,N-CQDs的荧光强度随着温度的升高而降低,两者呈良好的线性关系。N-CQDs能穿透4T1细胞的细胞膜,显示出低毒性和生物相容性,在4T1细胞中具有良好的温度传感性能。该N-CQDs在活细胞荧光温度传感领域具有较大的应用潜能,有望作为温敏型纳米荧光探针在细胞研究等生物医学领域得到广泛应用。

氮掺杂碳量子点与牛血清白蛋白相互作用的研究

采用光谱法研究了掺氮碳量子点(N-CQDs)与牛血清白蛋白(BSA)的相互作用机理。光谱分析表明,N-CQDs能有效猝灭BSA的内源性荧光,属于静态猝灭机制。N-CQDs的加入导致色氨酸残基微环境的疏水性降低,继而引起BSA的构象产生变化。N-CQDs与BSA可能是以1∶1的比例相互结合形成了稳定的复合物。结合热力学参数进行分析,N-CQDs与BSA相互结合的作用力主要为静电吸引力,反应为自发进行。同步荧光光谱也表明,N-CQDs与BSA的结合改变了BSA的构象。此研究数据可为进一步了解N-CQDs纳米颗粒在生物体内的应用提供参考。

Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

Unlike inorganic quantum dots,fluorescent graphene quantum dots(GQDs)display excitation-dependent multiple color emission.In this study,we report N-doped GQDs(N-GQDs)with tailored single color emission by tuning p-conjugation degree,which is comparable to the inorganic quantum dot.Starting from citric acid and diethylenetriamine,as prepared N-GQDs display blue,green,and yellow light emission by changing the reaction solvent from water,dimethylformamide(DMF),and solvent free.The X-ray photoelectron spectroscopy,ultraviolet-visible spectra results clearly show the N-GQDs with blue emission(N-GQDs-B)have relatively short effective conjugation length and more carboxyl group because H_(2)O is a polar protic solvent,which tends to donate proton to the reagent to depress the H_(2)O elimination reaction.On the other hand,the polar aprotic solvent(DMF)cannot donate hydrogen,the elimination of H_(2)O is promoted and more nitrogen units enter GQD framework.With the increase of effective p-conjugation length and N content,the emission band of N-GQDS red-shifts to green and yellow.We also demonstrate that N-GQDs could be a potential great biomarker for fluorescent bioimaging.

Enhanced photocatalytic hydrogen production from Co-MOF/CN by nitrogen and sulfur co-doped coal-based carbon quantum dots

A novel composite photocatalyst for photocatalytic decomposition of water for hydrogen evolution was successfully synthesized by in-situ growth of nitrogen and sulfur co-doped coal-based carbon quantum dots(NSCQDs)nanoparticles on the surface of sheet cobalt-based metal-organic framework(Co-MOF)and graphitic carbon nitride(g-C_(3)N_(4),CN).The structure and properties of the obtained catalysts were systematically analyzed.NSCQDs effectively broaden the absorption of Co-MOF and CN in the visible region.The new composite photocatalyst has high hydrogen production activity and the hydrogen production rate reaches 6254μmol/(g·h)at pH=9.At the same time,NSCQDs synergy Co-MOF/CN composites have good stability.After four cycles of hydrogen production,the performance remains relatively stable.The tran sient photocurrent response and Nyquist plot experimental results further demonstrate the improvement of carrier separation efficiency in composite catalysts.The semiconductor type(n-type semico nductor)of the single-phase catalyst was determined by the Mott-Schottky test,and the band structure was analyzed.The conductive and valence bands of CN are-0.99 and 1.72 eV,respectively,and the conduction and valence bands of Co-MOF are-1.85 and 1.33 eV,respectively.Th e mechanism of the photocatalytic reaction can be inferred,that is,Z-type heterojunction is formed between CN an d Co-MOF,and NSCQDs was used as cocatalyst.

A nanoporous nitrogen-doped graphene for high performance lithium sulfur batteries

A nanoporous N-doped reduced graphene oxide(p-N-rGO) was prepared through carbothermal reaction between graphene oxide and ammonium-containing oxometalates as sulfur host for Li-S batteries.The p-N-rGO sheets have abundant nanopores with diameters of 10-40 nm and the nitrogen content is 2.65 at%.When used as sulfur cathode,the obtained p-N-rGO/S composite has a high reversible capacity of 1110mAhg^1 at 1C rate and stable cycling performance with 781.8 mAhg^1 retained after 110 cycles,much better than those of the rGO/S composite.The enhanced electrochemical performance is ascribed to the rational combination of nanopores and N-doping,which provide efficient contact and wetting with the electrolyte,accommodate volume expansion and immobilize polysulfides during cycling.

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

Graphene quantum dots(GQDs) recently emerge as the new and appealing nanophotocatalyst because of their low-cost, environmental compatibility and the ability to facilitate the charge migration and prolong the charge lifetimes. In this work, a visible photocatalyst of S-doped graphene quantum dots(S-GQDs)was prepared by a facile hydrothermal synthesis using 1,3,6-trinitropyrene and Na_2 S as precursors. The well crystallization and monodispersity as well as the chemical environment of S-GQDs were characterized by transmission electron microscopy, atom force microscopy and X-ray photoelectron spectrum. A superior photocatalytic performance of S-GQDs was demonstrated for degradation of basic fuchsin under visible light irradiation. Furthermore, the possible photocatalytic mechanism was proposed based on the trapping experiments of active species.

掺氮荧光碳量子点的制备及性能研究

以柠檬酸为碳源、对氨基苯甲酸为氮源,通过一步水热法制备了氮掺杂荧光碳量子点(N-CQDs),采用透射电子显微镜、傅里叶变换红外光谱仪、稳态瞬态荧光磷光光谱仪对其形貌、结构和光谱进行表征,研究了反应温度、反应时间、酸碱度对N-CQDs荧光性能的影响。结果表明:N-CQDs呈球形,具有良好的分散性;N-CQDs的荧光强度较碳量子点增强约17倍,N-CQDs最佳激发波长为404nm,最佳发射波长为480nm,说明氮的掺杂有助于碳量子点荧光强度的增强;反应温度为180℃、反应时间为6h,酸碱度为中性时,N-CQDs荧光强度最强。

氮硫共掺杂荧光碳点的光热效应研究

碳点具有合成简单、光学性能良好、生物相容性优异以及制备成本低廉等优点。本工作以柠檬酸为碳源,硫脲为氮源和硫源,用溶剂热法合成了氮硫共掺杂碳点。制备的碳点具有蓝色荧光,且展现出高的光热转换能力,其光热转换效率达40.86%,可同时作为光敏剂和光热剂使用。

红外成像研究PLLA/N-CQDs复合薄膜的结晶性能

将水热法制得的氮掺杂碳量子点(N-CQDs)加入聚乳酸(PLLA)基质中,以溶剂浇铸法制备了PLLA/N-CQDs复合薄膜,并通过红外成像分析了N-CQDs的加入对PLLA结晶性能的影响。结果显示,加入N-CQDs可以显著提高PLLA的结晶性能。

氮硼共掺杂碳量子点的制备及其对六价铬的检测

目的建立一种基于荧光碳量子点的快速检测方法,定量检测饮用水和食品中的六价铬[hexavalent chromium,Cr(Ⅵ)]。方法以无水柠檬酸和3-氨基苯硼酸分别作为碳、氮和硼源,通过一步水热法合成氮硼共掺杂碳量子点(nitrogen-boron-doped carbon quantum dots,N,B-CQDs),基于荧光内滤效应对Cr(Ⅵ)进行检测。结果在优化后的最佳检测条件下,N,B-CQDs对Cr(Ⅵ)在0.01~10.00 mg/L内呈现良好的线性关系,检出限低至3.81μg/L,表现出选择性好、灵敏度高等特点。将此方法应用于饮用水、白醋和虾皮中Cr(Ⅵ)含量的测定,加标回收率在85.8%~112.3%之间,相对标准偏差低于5%。结论本研究制备的N,B-CQDs在Cr(Ⅵ)检测方面具有检出限低、灵敏度高、选择性好等优点,可以为Cr(Ⅵ)快速检测提供一定的理论和技术参考。

Competitive role of nitrogen functionalities of N doped GO and sensitizing effect of Bi_(2)O_(3)QDs on TiO_(2)for water remediation

The promising solar irradiated photocatalyst by pairing of bismuth oxide quantum dots(BQDs)doped TiO_(2)with nitrogen doped graphene oxide(NGO)nanocomposite(NGO/BQDs-TiO_(2))was fabricated.It was used for degradation of organic pollutants like 2,4-dichlorophenol(2,4-DCP)and stable dyes,i.e.Rhodamine B and Congo Red.X-ray diffraction(XRD)profile of NGO showed reduction in oxygenic functional groups and restoring of graphitic crystal structure.The characteristic diffraction peaks of TiO_(2)and its composites showed crystalline anatase TiO_(2).Morphological images represent spherical shaped TiO_(2)evenly covered with BQDs spread on NGO sheet.The surface linkages of NO-O-Ti,C-O-Ti,Bi-O-Ti and vibrational modes are observed by Fourier transform infrared spectroscopy(FTIR)and Raman studies.BQDs and NGO modified TiO_(2)results into red shifting in visible region as studied in diffused reflectance spectroscopy(DRS).NGO and BQDs in TiO_(2)are linked with defect centers which reduced the recombination of free charge carriers by quenching of photoluminescence(PL)intensities.X-ray photoelectron spectroscopy(XPS)shows that no peak related to C-O in NGO/BQDs-TiO_(2)is observed.This indicated that doping of nitrogen into GO has reduced some oxygen functional groups.Nitrogen functionalities in NGO and photosensitizing effect of BQDs in ternary composite have improved photocatalytic activity against organic pollutants.Intermediate byproducts during photo degradation process of 2,4-DCP were studied through high performance liquid chromatography(HPLC).Study of radical scavengers indicated that O_(2)^(·-) has significant role for degradation of 2,4-DCP.Our investigations propose that fabricated nanohybrid architecture has potential for degradation of environmental pollutions.