Sulfur and Nitrogen Co‐Doped Graphene for Metal‐Free Catalytic Oxidation Reactions

Sulfur and nitrogen co‐doped reduced graphene oxide (rGO) is synthesized by a facile method and demonstrated remarkably enhanced activities in metal‐free activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol. Based on first‐order kinetic model, S–N co‐doped rGO (SNG) presents an apparent reaction rate constant of 0.043 ± 0.002 min^?1, which is 86.6, 22.8, 19.7, and 4.5‐fold as high as that over graphene oxide (GO), rGO, S‐doped rGO (S‐rGO), and N‐doped rGO (N‐rGO), respectively. A variety of characterization techniques and density functional theory calculations are employed to investigate the synergistic effect of sulfur and nitrogen co‐doping. Co‐doping of rGO at an optimal sulfur loading can effectively break the inertness of carbon systems, activate the sp²‐hybridized carbon lattice and facilitate the electron transfer from covalent graphene sheets for PMS activation. Moreover, both electron paramagnetic resonance (EPR) spectroscopy and classical quenching tests are employed to investigate the generation and evolution of reactive radicals on the SNG sample for phenol catalytic oxidation. This study presents a novel metal‐free catalyst for green remediation of organic pollutants in water.     

N‐Doped Graphene Field‐Effect Transistors with Enhanced Electron Mobility and Air‐Stability

Although graphene can be easily p‐doped by various adsorbates, developing stable n‐doped graphene that is very useful for practical device applications is a difficult challenge. We investigated the doping effect of solution‐processed (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine (N‐DMBI) on chemical‐vapor‐deposited (CVD) graphene. Strong n‐type doping is confirmed by Raman spectroscopy and the electrical transport characteristics of graphene field‐effect transistors. The strong n‐type doping effect shifts the Dirac point to around ‐140 V. Appropriate annealing at a low temperature of 80 ºC enables an enhanced electron mobility of 1150 cm² V^?1 s^?1. The work function and its uniformity on a large scale (1.2 mm × 1.2 mm) of the doped surface are evaluated using ultraviolet photoelectron spectroscopy and Kelvin probe mapping. Stable electrical properties are observed in a device aged in air for more than one month.     

Controllable Synthesis of Doped Graphene and Its Applications

Graphene is a wonder material with the ultimate smallest thickness that is readily accessible to various approaches for engineering its excellent properties. Graphene doping is an efficient way to tailor its electric properties and expand its applications. This topic covers wide research fields and has been developing rapidly. This article presents a broad and comprehensive overview of the developments in the preparation and applications of doped graphene including doping methods, doping levels, doping effect and types of heteroatoms. Very recent advances are also presented. In addition, existing problems in terms of achieving greater control over and further developments of doped graphene are also discussed.     

Controllable Bipolar Doping of Graphene with 2D Molecular Dopants

The fine control of graphene doping levels over a wide energy range remains a challenging issue for the electronic applications of graphene. Here, the controllable doping of chemical vapor deposited graphene, which provides a wide range of energy levels (shifts up to ± 0.5 eV), is demonstrated through physical contact with chemically versatile graphene oxide (GO) sheets, a 2D dopant that can be solution‐processed. GO sheets are a p‐type dopant due to their abundance of electron‐withdrawing functional groups. To expand the energy window of GO‐doped graphene, the GO surface is chemically modified with electron‐donating ethylene diamine molecules. The amine‐functionalized GO sheets exhibit strong n‐type doping behaviors. In addition, the particular physicochemical characteristics of the GO sheets, namely their sheet sizes, number of layers, and degree of oxidation and amine functionality, are systematically varied to finely tune their energy levels. Finally, the tailor‐made GO sheet dopants are applied into graphene‐based electronic devices, which are found to exhibit improved device performances. These results demonstrate the potential of GO sheet dopants in many graphene‐based electronics applications.     

In Operando Probing of Lithium‐Ion Storage on Single‐Layer Graphene

Despite high‐surface area carbons, e.g., graphene‐based materials, being investigated as anodes for lithium (Li)‐ion batteries, the fundamental mechanism of Li‐ion storage on such carbons is insufficiently understood. In this work, the evolution of the electrode/electrolyte interface is probed on a single‐layer graphene (SLG) film by performing Raman spectroscopy and Fourier transform infrared spectroscopy when the SLG film is electrochemically cycled as the anode in a half cell. The utilization of SLG eliminates the inevitable intercalation of Li ions in graphite or few‐layer graphene, which may have complicated the discussion in previous work. Combining the in situ studies with ex situ observations and ab initio simulations, the formation of solid electrolyte interphase and the structural evolution of SLG are discussed when the SLG is biased in an electrolyte. This study provides new insights into the understanding of Li‐ion storage on SLG and suggests how high‐surface‐area carbons could play proper roles in anodes for Li‐ion batteries.     

Chemically Derived Graphene Oxide: Towards Large‐Area Thin‐Film Electronics and Optoelectronics

Chemically derived graphene oxide (GO) possesses a unique set of properties arising from oxygen functional groups that are introduced during chemical exfoliation of graphite. Large‐area thin‐film deposition of GO, enabled by its solubility in a variety of solvents, offers a route towards GO‐based thin‐film electronics and optoelectronics. The electrical and optical properties of GO are strongly dependent on its chemical and atomic structure and are tunable over a wide range via chemical engineering. In this Review, the fundamental structure and properties of GO‐based thin films are discussed in relation to their potential applications in electronics and optoelectronics.     

Ball‐Mill‐Exfoliated Graphene: Tunable Electrochemistry and Phenol Sensing

A simple wet ball‐milling method for exfoliating pristine graphite to graphene nanosheets is proposed. The surfactant of cetyltrimethyl ammonium bromide is utilized to greatly improve the exfoliation efficiency of graphene nanosheets. Variation of the ball‐milling time is an efficient way to control the size and thickness of graphene nanosheets, as well as the level of edge defects. With an increase of ball‐milling time, superior electrochemical reactivity is imparted owing to enlarged active area and increased catalytic ability. The obtained graphene nanosheets are sensitive for electrochemical oxidation of phenols (e.g., hydroquinone, p‐chlorophenol, and p‐nitrophenol), and thus qualified for the simultaneous sensing of trace level of phenols. The detection limits of simultaneous monitoring of hydroquinone, p‐chlorophenol, and p‐nitrophenol are as low as 0.017, 0.024, and 0.42 mg L^?1, respectively. The proposed strategy thus opens up a new way to tune electrochemistry of graphene materials as well as to design their new applications.     

Harnessing the Influence of Reactive Edges and Defects of Graphene Substrates for Achieving Complete Cycle of Room‐Temperature Molecular Sensing

Molecular doping and detection are at the forefront of graphene research, a topic of great interest in physical and materials science. Molecules adsorb strongly on graphene, leading to a change in electrical conductivity at room temperature. However, a common impediment for practical applications reported by all studies to date is the excessively slow rate of desorption of important reactive gases such as ammonia and nitrogen dioxide. Annealing at high temperatures, or exposure to strong ultraviolet light under vacuum, is employed to facilitate desorption of these gases. In this article, the molecules adsorbed on graphene nanoflakes and on chemically derived graphene‐nanomesh flakes are displaced rapidly at room temperature in air by the use of gaseous polar molecules such as water and ethanol. The mechanism for desorption is proposed to arise from the electrostatic forces exerted by the polar molecules, which decouples the overlap between substrate defect states, molecule states, and graphene states near the Fermi level. Using chemiresistors prepared from water‐based dispersions of single‐layer graphene on mesoporous alumina membranes, the study further shows that the edges of the graphene flakes (showing p‐type responses to NO₂ and NH₃) and the edges of graphene nanomesh structures (showing n‐type responses to NO₂ and NH₃) have enhanced sensitivity. The measured responses towards gases are comparable to or better than those which have been obtained using devices that are more sophisticated. The higher sensitivity and rapid regeneration of the sensor at room temperature provides a clear advancement towards practical molecule detection using graphene‐based materials.     

High Detectivity and Transparent Few‐Layer MoS2/Glassy‐Graphene Heterostructure Photodetectors

Layered van der Waals heterostructures have attracted considerable attention recently, due to their unique properties both inherited from individual two‐dimensional (2D) components and imparted from their interactions. Here, a novel few‐layer MoS₂/glassy‐graphene heterostructure, synthesized by a layer‐by‐layer transfer technique, and its application as transparent photodetectors are reported for the first time. Instead of a traditional Schottky junction, coherent ohmic contact is formed at the interface between the MoS₂ and the glassy‐graphene nanosheets. The device exhibits pronounced wavelength selectivity as illuminated by monochromatic lights. A responsivity of 12.3 mA W^?1 and detectivity of 1.8 × 10¹⁰ Jones are obtained from the photodetector under 532 nm light illumination. Density functional theory calculations reveal the impact of specific carbon atomic arrangement in the glassy‐graphene on the electronic band structure. It is demonstrated that the band alignment of the layered heterostructures can be manipulated by lattice engineering of 2D nanosheets to enhance optoelectronic performance.     

Wetting‐Induced Climbing for Transferring Interfacially Assembled Large‐Area Ultrathin Pristine Graphene Film

Owing to inherent 2D structure, marvelous mechanical, electrical, and thermal properties, graphene has great potential as a macroscopic thin film for surface coating, composite, flexible electrode, and sensor. Nevertheless, the production of large‐area graphene‐based thin film from pristine graphene dispersion is severely impeded by its poor solution processability. In this study, a robust wetting‐induced climbing strategy is reported for transferring the interfacially assembled large‐area ultrathin pristine graphene film. This strategy can quickly convert solvent‐exfoliated pristine graphene dispersion into ultrathin graphene film on various substrates with different materials (glass, metal, plastics, and cloth), shapes (film, fiber, and bulk), and hydrophobic/hydrophilic patterns. It is also applicable to nanoparticles, nanofibers, and other exfoliated 2D nanomaterials for fabricating large‐area ultrathin films. Alternate climbing of different ultrathin nanomaterial films allows a layer‐by‐layer transfer, forming a well‐ordered layered composite film with the integration of multiple pristine nanomaterials at nanometer scale. This powerful strategy would greatly promote the development of solvent‐exfoliated pristine nanomaterials from dispersions to macroscopic thin film materials.     

掺杂和修饰的石墨烯对半胱氨酸吸附性能的密度泛函理论研究

使用密度泛函理论计算了掺杂或修饰Al或Mn原子的石墨烯对半胱氨酸的吸附性能。计算结果表明,掺杂或修饰Al或Mn原子后,Graphene与半胱氨酸之间结合稳定,具有较大的结合能。其中掺杂或修饰Mn原子的体系的吸附能整体高于掺杂或修饰Al原子的体系。石墨烯上修饰或掺杂Al或Mn原子,增加了石墨烯基底与半胱氨酸之间的电荷转移,特别是修饰方式显著改变了费米能级附近的性质,同时改变了Graphene的电导性质。Al或Mn原子修饰或者掺杂的Graphene除了增加对半胱氨酸吸附能力外,也是一种潜在的检测半胱氨酸的传感器材料,进而在生物领域得到更广泛的应用,比如用来检测富含半胱氨酸的金属硫蛋白。