Tuning the Electronic Structure of Graphene by Molecular Charge Transfer: A Computational Study

Observation of reversible and irreversible charge transfer processes in dye-monolayer graphene systems using Raman spectroscopy as a tool

Herein, we report the Raman spectroscopy of crystal violet (CV) and IR-780 Iodide molecules dispersed on the monolayer graphene film (MGF). In the CV-MGF system, the enhancement in the Raman scattering of CV molecules is observed irrespective of the location probed during the spectral measurements. This enhancement is due to the charge transfer from the MGF to CV molecules. However, in the case of the IR-780 Iodide - MGF system, the enhancement of Raman scattering of dye molecules or MGF is observed strongly depending upon the probed location. These observations indicate that the charge transfer is irreversible and reversible in the CV-MGF and IR-780 Iodide-MGF systems, respectively. Importantly, for the first time, this experimental study revealed that enhancing the Raman scattering of MGF is possible through the "chemical mechanism" with suitable dye molecules apart from the "electromagnetic mechanism" with plasmonic hot spots of the metal nanoparticles and photonic nanojets of single dielectric microparticles.

Optimizing graphene content in scaffolds for evenly distributed crumpled MoS2paper wads as anodes for high-performance Li-ion batteries

Lithium-ion batteries (LIBs) have revolutionized portable electronics, yet their conventional graphite anodes face capacity limitations. Integrating graphene and 3D molybdenum disulfide (MoS2) offers a promising solution. Ensuring a uniform distribution of 3D MoS2nanostructures within a graphene matrix is crucial for optimizing battery performance and preventing issues like agglomeration and capacity degradation. This study focuses on synthesizing a uniformly distributed paper wad structure by optimizing a composite of reduced graphene oxide RGO@MoS2through structural and morphological analyses. Three composites with varying graphene content were synthesized, revealing that the optimized sample containing 30 mg RGO demonstrates beneficial synergy between MoS2and RGO. The interconnected RGO network enhances reactivity and conductivity, addressing MoS2aggregation. Experimental results exhibit an initially superior capacity of 911 mAh g-1, retained at 851 mAh g-1even after 100 cycles at 0.1 A g-1current density, showcasing improved rate efficiency and long-term stability. This research underscores the pivotal role of graphene content in customizing RGO@MoS2composites for enhanced LIB performance.

Electronic Transport Properties of Molecular Clusters Sb4O6, P4Se3, and P4O6

Inorganic molecular crystal (IMC) is a trending class of materials in which structural units comprise molecular cages or clusters bonded via van der Waal forces. The structure-property relationship in IMCs is less known due to the unusual assembly of molecular clusters in these materials. In this paper, the density functional theory-calculated electronic transport properties of the molecular clusters of antimony oxide (Sb4O6), phosphorus triselenide (P4Se3), and phosphorus trioxide (P4O6) are described in detail. The calculated values of highest occupied molecular orbital-lowest unoccupied molecular orbital gaps appeared as 5.487, 2.296, and 4.425 eV for Sb4O6, P4Se3, and P4O6, respectively. The work was carried out to explore the charge transport mechanism in IMCs in order to disclose their potential in practical applications. The calculations involved charge-transfer integral based on Marcus theory to compute the electronic coupling (V), reorganization energies (λ), and hopping rate (k) in the structures. The hopping rate for Sb4O6, P4Se3, and P4O6 is found as 8.49 × 10-12, 1.28 × 10-14, and 2.51 × 10-20 s-1, respectively. The transport properties of Sb4O6 are found better, which predicts the application of the relevant IMC for device grade applications. The findings of this study are important for future application of the IMCs in electronic and optoelectronic applications.

Effect of terephthalic acid functionalized graphene oxide on the molecular interaction, and mechanical and thermal properties of Hytrel polymer

We report the effect of incorporating functionalized graphene oxide (terephthalic acid functionalized GO; GO-g-TPA) on the thermal and mechanical properties of Hytrel (HTL; a thermoplastic elastomeric polymer). Initially, the synthesis of GO-g-TPA was performed via chemical methods and subsequently characterized using various spectroscopic and imaging techniques. The melt mixing technique was executed in preparing the nanocomposites of HTL/GO and HTL/GO-g-TPA. An excellent GO dispersion was observed in the HTL polymeric matrix, which could be attributed to the significant effect of hydrogen bonding and π-π interaction between the HTL and GO-g-TPA. As a result of incorporating GO and GO-g-TPA into the HTL matrix, the overall mechanical and thermal properties of the nanocomposites were significantly improved. For the HTL/5 wt% GO-g-TPA nanocomposite, the tensile strength and storage modulus significantly increased by 61% and 224%, respectively. In addition, the melting temperature and crystalline temperature are increased by a notable 20 °C and 21 °C, respectively. Thus, the current study found that by improving the dispersion ability of the GO sheets, the properties of the HTL can be significantly enhanced and the prepared composite materials can be relevant for a wide range of applications including sports goods, hose jackets, wire and cable jackets, electronics, fluid power, sheeting belting seals, and footwear, etc.

Modeling the Adsorption of Polycyclic Aromatic Hydrocarbons on Graphynes: An Improved Lennard-Jones Formulation

Research on the development of theoretical methodologies for modeling noncovalent interactions governing the adsorption of polycyclic aromatic hydrocarbons (PAHs) on graphene and other two-dimensional materials is being intensely pursued in recent times. Highly accurate empirical potentials have emerged as a viable alternative to first-principles calculations for performing large-scale simulations. Herein, we report exploration of the potential energy surfaces for the adsorption of cata-condensed and peri-condensed PAHs on graphynes (GYs) using the improved Lennard-Jones (ILJ) potential. Initially, the ILJ potential is parametrized against benchmark electronic structure calculations performed on a selected set of PAH-GY complexes using dispersion-corrected density functional theory. The accuracy of the parametrization scheme is then assessed by a comparison of the adsorption features predicted from the ILJ potential with those computed using electronic structure calculations. The potential energy profiles as well as the single point energy calculations and geometry reoptimizations performed on the minimum-energy configurations predicted by the ILJ potential for a broader range of PAH-GY complexes provided a validation of the parametrization scheme. Finally, by an extrapolation of the PAH adsorption energies on various GYs, we estimated the interlayer cohesion energies for the van der Waals bilayer heterostructures of GYs with graphene to be in the range of 25-50 meV/atom.

Biomolecular control over local gating in bilayer graphene induced by ferritin

Electrical field-induced charge modulation in graphene-based devices at the nanoscale with ultrahigh density carrier accumulation is important for various practical applications. In bilayer graphene (BLG), inversion symmetry can simply be broken by an external electric field. However, control over charge carrier density at the nanometer scale is a challenging task. We demonstrate local gating of BLG in the nanometer range by adsorption of AfFtnAA (which is a bioengineered ferritin, an iron-storing globular protein with ∅ = 12 nm). Low-temperature electrical transport measurements with field-effect transistors with these AfFtnAA/BLG surfaces show hysteresis with two Dirac peaks. One peak at a gate voltage V_BG = 35 V is associated with pristine BLG, while the second peak at V_BG = 5 V results from local doping by ferritin. This charge trapping at the biomolecular length scale offers a straightforward and non-destructive method to alter the local electronic structure of BLG.

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Local gating with 12 nm resolution by charge trapping in ferritin.

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Adsorption of ferritin on graphene via non-invasive self-assembly.

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Charging controlled via iron oxide loading of ferritin.

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Visualization of individual ferritins on graphene by atomic force microscopy.

A Linear Relationship between the Charge Transfer Amount and Level Alignment in Molecule/Two-Dimensional Adsorption Systems

We systematically study the adsorption of tetrathiafulvalene (TTF), tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) on a variety of two-dimensional (2D) monolayers with weak van der Waals (vdW) interactions based on density functional theory. We confirm that TTF can act as an effective donor when its highest occupied molecular orbital (HOMO) level is higher than the conduction band minimum (CBM) state of 2D materials, while TCNQ and TCNE can act as effective acceptors when their lowest unoccupied molecular orbital (LUMO) levels are lower than the valence band maximum (VBM) state of 2D materials. Moreover, our calculations reveal a linear relationship between the charge transfer amount and level alignment between the molecule and 2D monolayer. In other words, the charge transfer is linearly dependent on the energy difference between the HOMO level and 2D CBM state for the donor molecule or the energy difference between the LUMO level and 2D VBM state for the acceptor molecule. The linear relationship indicates that the charge transfer is insensitive to the local binding environments due to the weak vdW interaction. However, the linear relationship cannot be applied to atoms or molecules that are chemisorbed on 2D materials.

Absorption properties of a BODIPY-curved graphene nanoflake system: A theoretical investigation

Modifications in the electronic transitions of a popular 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (boron dipyrromethene, BODIPY) dye caused by quasi-parallel stacking with corannulene (C) were studied by means of time-dependent density functional theory (TD-DFT) with the CAM-B3LYP functional. The effects of the electron-withdrawing (CN) and electron-donating (NH₂) substituents at the meso (8) position in the BODIPY core and the corannulene rim position on the character, location, and oscillator strengths (f) of some transitions of complexes were also discussed. To understand better the nature of the transitions, their occupied and virtual orbitals involved into the first electronic transitions as well as the electron density difference plots between excited and ground states of the complexes were investigated. The S₀ → S₁ transitions of 8H-B/C and 8NH₂-B/C complexes have a small admixture of the charge transfer (CT) character in direction from BODIPY to corannulene (B → C). They located at 2.80 and 3.11 eV, respectively, and have f of ∼0.15. The 8CN-B/C complex with a stronger acceptor BODIPY part has the S₀ → S₁ transition with a higher degree of CT (B → C) at 2.32 eV with f = 0.08. The 8H-B/2NH₂-C complex with a stronger donor corannulene part has the S₀ → S₁ transition with an expressed CT(B → C)-character at 2.58 eV with f = 0.003, whereas the S₀ → S₂ transition acquires in a some extent the features of the LE(B → B) character. A much interesting situation exists in the case of the 8NH₂-B/2CN-C complex. Here we can find both CT (B → C) and CT (C → B) among the first five states. Besides this, different, higher in energy CT states and states delocalized on both molecules were observed.

Two-Dimensional WSe2/Organic Acceptor Hybrid Nonvolatile Memory Devices Based on Interface Charge Trapping

Two-dimensional (2D) materials, with atomic thickness and unique electronic structure, hold great potentials in electronic device applications. Charge transfer at the interface of 2D materials further provides a versatile platform for applications in electronics. Here, we report nonvolatile memory devices based on interface charge trapping between 2D WSe₂ and organic electron acceptors. The 2D WSe₂-organic acceptor hybrid structure exhibits a high storage performance, such as large gate memory windows, high on/off ratios (>10³), and long retention time (>1000 s). Further analysis revealed that organic acceptors with a stronger electron affinity (i.e., higher redox potential) have a larger electron-trapping ability and hence a better memory performance.

Organic charge transfer complexes on graphene with ultrahigh near infrared photogain

Photodetectors have widespread applications in fields including telecommunications, thermal imaging and bio-medical imaging. The photogating effect, arising from charge trapping at defects and/or interfaces, can have extremely high photoelectric gain which can be a benefit to high-sensitivity room temperature photodetection. Here, we introduce thin layered organic charge transfer complexes (CPXs) integrated on graphene transistors for the development of hybrid phototransistors with ultra-high photoresponsivity of ∼10⁶ A W^-1 in the near infrared (NIR) region at room temperature. Our study has demonstrated a graphene-organic CPX with a broadband photoresponse ranging from the visible to the NIR region. The high photoelectric gain was from the photogating effect at the graphene/CPX interface. In addition, the photoresponse properties of the graphene-organic CPX can be regulated by electrical gating of graphene.

Understanding the non-covalent interaction mediated modulations on the electronic structure of quasi-zero-dimensional graphene nanoflakes

In recent years, magnetic or electric field induced modulations on the electronic environment of single molecular systems are common practice. In this particular study, we have instigated the possibility of controlling the electronic and spin-dependent properties of hydrogen-terminated graphene fragments, so-called graphene nanoflakes (GNF), using weak non-covalent interactions as the external stimuli. The topological frustration in the graphene fragment appreciated the compelling electronic behavior of the system. This leads to some unorthodox spin-distribution in the system and it is possible to synchronize this electronic perturbation switching through a non-covalent interaction. These findings institute a new avenue for sculpting such donor-acceptor composites as self-regulated spintronic devices in next generation electronics.

Functionalized graphene oxides for drug loading, release and delivery of poorly water soluble anticancer drug: A comparative study

In this work, the modification of graphene oxides (GOs) have been done with hydrophilic and biodegradable polymer, polyvinylpyrrolidone (PVP) and other excipient β -cyclodextrin (β-CD) through covalent functionalization for efficient loading and compatible release of sparingly water soluble aromatic anticancer drug SN-38 (7-ethyl-10-hydroxy camptothecin). The drug was loaded onto both GO-PVP and GO-β-CD through the π-π interactions.The release of drug from both the nanocarriers were analyzed in different pH medium of pH 7 (water, neutral medium), pH 5 (acidic buffer) and pH 12 (basic buffer). The loading capacity and the cell killing activity of SN-38 loaded on functionalized GO were investigated comprehensively in human breast cancer cells MCF-7.Our findings shown that the cytotoxicity of SN-38 loaded to the polymer modified GO was comparatively higher than free SN-38. In particular, SN-38 loaded GO-PVP nanocarrier has more cytotoxic effect than GO-β-CD nanocarrier against MCF-7 cells, indicating that SN-38 loaded GO-PVP nanocarrier can be used as promising material for drug delivery and biological applications.

In-Situ Synthesis of Hydrogen Titanate Nanotube/Graphene Composites with a Chemically Bonded Interface and Enhanced Visible Photocatalytic Activity

Hydrogen titanate nanotube (HTT)/graphene nanocomposites are synthesized by hydrothermal reduction of graphene oxide (GO) and simultaneous preparation of nanotubular HTT via an alkaline hydrothermal process. By using this facile in-situ compositing strategy, HTT are densely supported upon the surface of graphene sheets with close interface contacts. The as-prepared HTT/graphene nanocomposites possess significantly enhanced visible light catalytic activity for the partial oxidation of benzylic alcohols. The amount of graphene has significant influence on catalytic activity and the optimal content of graphene is 1.0 wt %, giving a normalized rate constant k of 1.71 × 10⁻³ g/m²·h, which exceeds that of pure HTT and HTT/graphene-1.0% mixed by a factor of 7.1 or 5.2. Other than the general role of graphene as a high-performance electron acceptor or transporter, the observed enhancement in photocatalytic activity over HTT/graphene can be ascribed to the improved interfacial charge migration from enhanced chemical bonding (Ti–C bonds) during the in-situ compositing process. The formation of Ti–C bonds is confirmed by XPS analysis and the resulting enhanced separation of photoinduced charge carriers is demonstrated by electrochemical impedance spectra and transient photocurrent response.

Combined molecular and periodic DFT analysis of the adsorption of co macrocycles on graphene

The molecular doping of graphene with π-stacked conjugated molecules has been widely studied during the last 10 years, both experimentally or using first-principle calculations, mainly with strongly acceptor or donor molecules. Macrocyclic metal complexes have been far less studied and their behavior on graphene is less clear-cut. The present density functional theory study of cobalt porphyrin and phthalocyanine adsorbed on monolayer or bilayer graphene allows to compare the outcomes of two models, either a finite-sized flake of graphene or an infinite 2D material using periodic calculations. The electronic structures yielded by both models are compared, with a focus on the density of states around the Fermi level. Apart from the crucial choice of calculation conditions, this investigation also shows that unlike strongly donating or accepting organic dopants, these macrocycles do not induce a significant doping of the graphene sheet and that a finite size model of graphene flake may be confidently used for most modeling purposes. © 2017 Wiley Periodicals, Inc.

Spotting the differences in two-dimensional materials – the Raman scattering perspective

This review discusses the Raman spectroscopic characterization of 2D materials with a focus on the “differences” from primitive 2D materials.

Enhancement of charge transfer between graphene and donor-π-acceptor molecule for ultrahigh sensing performance

In this work, we report the formation of a supramolecular assembly of graphene with a donor-π-acceptor (D-π-A) molecule to detect low concentration NO₂. 5-Aminonaphthalene-1-sulfonic acid (ANS) was used herein to π-π stack with reduced graphene oxide (rGO), the resulting π-conjugated bridge being linked by a donor unit (-NH₂) and an acceptor unit (-SO₃H). The prepared ANS-rGO shows the highest response (R_a/R_g = 13.2 to 10 ppm NO₂) so far among the reported organic molecule modified graphene materials, and excellent selectivity and reliable reversibility at room temperature. Furthermore, as revealed through the charge density difference calculation, it is the effective enhancement of charge transfer between ANS and graphene that should be responsible for the sharp improvement of NO₂ gas response of the material. Thus, for the first time, we demonstrate that supramolecular assembly of a D-π-A molecule and graphene provides a facile and effective approach to fabrication of high performance graphene-based gas sensors.

Real-Time Monitoring of Insulin Using a Graphene Field-Effect Transistor Aptameric Nanosensor

This paper presents an approach to the real-time, label-free, specific, and sensitive monitoring of insulin using a graphene aptameric nanosensor. The nanosensor is configured as a field-effect transistor, whose graphene-based conducting channel is functionalized with a guanine-rich IGA3 aptamer. The negatively charged aptamer folds into a compact and stable antiparallel or parallel G-quadruplex conformation upon binding with insulin, resulting in a change in the carrier density, and hence the electrical conductance, of the graphene. The change in the electrical conductance is then measured to enable the real-time monitoring of insulin levels. Testing has shown that the nanosensor offers an estimated limit of detection down to 35 pM and is functional in Krebs-Ringer bicarbonate buffer, a standard pancreatic islet perfusion medium. These results demonstrate the potential utility of this approach in label-free monitoring of insulin and in timely prediction of accurate insulin dosage in clinical diagnostics.

Molecular assembly on two-dimensional materials

Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule-substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging from flexible electronics and OLEDs to novel electronic devices and spintronics.

Lighting up the Raman signal of molecules in the vicinity of graphene related materials

Surface enhanced Raman scattering (SERS) is a popular technique to detect the molecules with high selectivity and sensitivity. It has been developed for 40 years, and many reviews have been published to summarize the progress in SERS. Nevertheless, how to make the SERS signals repeatable and quantitative and how to have deeper understanding of the chemical enhancement mechanism are two big challenges. A strategy to target these issues is to develop a Raman enhancement substrate that is flat and nonmetal to replace the conventional rough and metal SERS substrate. At the same time, the newly developed substrate should have a strong interaction with the adsorbate molecules to guarantee strong chemical enhancement. The flatness of the surface allows better control of the molecular distribution and configuration, while the nonmetal surface avoids disturbance of the electromagnetic mechanism. Recently, graphene and other two-dimensional (2D) materials, which have an ideal flat surface and strong chemical interaction with plenty of organic molecules, were developed to be used as Raman enhancement substrates, which can light up the Raman signals of the molecules, and these substrates were demonstrated to be a promising for microspecies or trace species detection. This effect was named "graphene enhanced Raman scattering (GERS)". The GERS technique offers significant advantages for studying molecular vibrations due to the ultraflat and chemically inert 2D surfaces, which are newly available, especially in developing a quantitative and repeatable signal enhancement technique, complementary to SERS. Moreover, GERS is a chemical mechanism dominated effect, which offers a valuable model to study the details of the chemical mechanism. In this Account, we summarize the systematic studies exploring the character of GERS. In addition, as a practical technique, the combination of GERS with a metal substrate incorporates the advantages from both conventional SERS and GERS. The introduction of graphene to the Raman enhancement substrate extended SERS applications in a more controllable and quantitative way. Looking to the future, we expect the combination of the SERS concept with the GERS technology to lead to the solution of some important issues in chemical dynamics and in biological processes monitoring.

Computational chemistry for graphene-based energy applications: progress and challenges

Research in graphene-based energy materials is a rapidly growing area. Many graphene-based energy applications involve interfacial processes. To enable advances in the design of these energy materials, such that their operation, economy, efficiency and durability is at least comparable with fossil-fuel based alternatives, connections between the molecular-scale structure and function of these interfaces are needed. While it is experimentally challenging to resolve this interfacial structure, molecular simulation and computational chemistry can help bridge these gaps. In this Review, we summarise recent progress in the application of computational chemistry to graphene-based materials for fuel cells, batteries, photovoltaics and supercapacitors. We also outline both the bright prospects and emerging challenges these techniques face for application to graphene-based energy materials in future.

Density functional studies of small silicon clusters adsorbed on graphene

The structural and electronic properties of small Si_n clusters (n = 1–6, 10) adsorbed on graphene are studied by use of density functional theory within periodic boundary conditions.

Revealing the interactions between pentagon–octagon–pentagon defect graphene and organic donor/acceptor molecules: a theoretical study

The cyano group interacts strongly with 5–8–5 defect graphene, changes the bands near the Fermi level and enhances the infrared light absorption.

Molecular charge transfer via π–π interaction: an effective approach to realize the half-metallicity and spin-gapless-semiconductor in zigzag graphene nanoribbon

Molecular charge transfer via simple π–π interaction is an effective strategy to modulate the electronic and magnetic behaviors of zGNRs.

Molecular adsorption on graphene

Current studies addressing the engineering of charge carrier concentration and the electronic band gap in epitaxial graphene using molecular adsorbates are reviewed. The focus here is on interactions between the graphene surface and the adsorbed molecules, including small gas molecules (H(2)O, H(2), O(2), CO, NO(2), NO, and NH(3)), aromatic, and non-aromatic molecules (F4-TCNQ, PTCDA, TPA, Na-NH(2), An-CH(3), An-Br, Poly (ethylene imine) (PEI), and diazonium salts), and various biomolecules such as peptides, DNA fragments, and other derivatives. This is followed by a discussion on graphene-based gas sensor concepts. In reviewing the studies of the effects of molecular adsorption on graphene, it is evident that the strong manipulation of graphene's electronic structure, including p- and n-doping, is not only possible with molecular adsorbates, but that this approach appears to be superior compared to these exploiting edge effects, local defects, or strain. However, graphene-based gas sensors, albeit feasible because huge adsorbate-induced variations in the relative conductivity are possible, generally suffer from the lack of chemical selectivity.

Hydrothermal synthesis of CaIn2S4-reduced graphene oxide nanocomposites with increased photocatalytic performance

A series of CaIn2S4-reduced graphene oxide (RGO) nanocomposites with different RGO contents were fabricated using a facile hydrothermal approach. During the hydrothermal process, the reduction of graphene oxide to RGO, in situ deposition of synthesized CaIn2S4 nanoparticles on RGO nanosheets and formation of chemical-bonding CaIn2S4-RGO nanocomposites were performed simultaneously. Under visible light irradiation, the as-prepared CaIn2S4-RGO nanocomposites showed enhanced photocatalytic performance for rhodamine B degradation and phenol oxidation. The sample with 5 wt % RGO hybridized CaIn2S4 exhibited the highest photocatalytic activity. The enhancement of photocatalytic performance may be related to the increased adsorption/reaction sites, positive shift of the valence band potential, and high separation efficiency of photogenerated charge carriers due to the electronic interaction between CaIn2S4 and RGO. We hope that this work can not only provide an in-depth study on the photocatalytic mechanism of RGO-enhanced activity, but also provide some insights for fabricating efficient and stable RGO-based photocatalysts in the potential applications of purifying polluted water resources.

An electronic structure perspective of graphene interfaces

The unusual electronic structure of graphene characterized by linear energy dispersion of bands adjacent to the Fermi level underpins its remarkable transport properties. However, for practical device integration, graphene will need to be interfaced with other materials: 2D layered structures, metals (as ad-atoms, nanoparticles, extended surfaces, and patterned metamaterial geometries), dielectrics, organics, or hybrid structures that in turn are constituted from various inorganic or organic components. The structural complexity at these nanoscale interfaces holds much promise for manifestation of novel emergent phenomena and provides a means to modulate the electronic structure of graphene. In this feature article, we review the modifications to the electronic structure of graphene induced upon interfacing with disparate types of materials with an emphasis on iterative learnings from theoretical calculations and electronic spectroscopy (X-ray absorption fine structure (XAFS) spectroscopy, scanning transmission X-ray microscopy (STXM), angle-resolved photoemission spectroscopy (ARPES), and X-ray magnetic circular dichroism (XMCD)). We discuss approaches for engineering and modulating a bandgap in graphene through interfacial hybridization, outline experimental methods for examining electronic structure at interfaces, and overview device implications of engineered interfaces. A unified view of how geometric and electronic structure are correlated at interfaces will provide a rational means for designing heterostructures exhibiting emergent physical phenomena with implications for plasmonics, photonics, spintronics, and engineered polymer and metal matrix composites.

Graphene oxide/α-Bi(2)O(3) composites for visible-light photocatalysis, chemical catalysis, and solar energy conversion

The growing challenges of environmental purification by solar photocatalysis, precious-metal-free catalysis, and photocurrent generation in photovoltaic cells receive the utmost global attention. Here we demonstrate a one-pot, green chemical synthesis of a new stable heterostructured, ecofriendly, multifunctional microcomposite that consists of α-Bi2 O3 microneedles intercalated with anchored graphene oxide (GO) microsheets (1.0 wt %) for the above-mentioned applications on a large economical scale. The bare α-Bi2 O3 microneedles display two times better photocatalytic activities than commercial TiO2 (Degussa-P25), whereas the GO-hybridized composite exhibits approximately four to six times enhanced photocatalytic activities than the neat TiO2 photocatalyst in the degradation of colored aromatic organic dyes (crystal violet and rhodamine 6G) under visible-light irradiation (300 W tungsten lamp). The highly efficient activity is associated with the strong surface adsorption ability of GO for aromatic dye molecules, the high carrier acceptability, and the efficient electron-hole pair separation in Bi2 O3 by individual adjoining GO sheets. The introduction of Ag nanoparticles (2.0 wt %) further enhances the photocatalytic performance of the composite over eightfold because of a plasmon-induced electron-transfer process from Ag nanoparticles through the GO sheets into the conduction band of Bi2 O3 . The new composites are also catalytically active and catalyze the reduction of 4-nitrophenol to 4-aminophenol in the presence of borohydride ions. Photoanodes assembled from GO/α-Bi2 O3 and Ag/GO/α-Bi2 O3 composites display an improved photocurrent response (power conversion efficiency ∼20 % higher) over those prepared without GO in dye-sensitized solar cells.

A high-performance Bi2WO6-graphene photocatalyst for visible light-induced H2 and O2 generation

We developed a highly efficient photocatalyst for both H2 and O2 generation under visible-light irradiation by attaching Bi2WO6 (BWO) nanocrystals on graphene nanosheets to produce a graphene-Bi2WO6 composite (Gr-BWO-T). The composite was prepared by a sonochemical method where graphene oxide (GO) served as the support on which BWO formed in situ. Bi2WO6 nanoparticles with the size of 30-40 nm were homogeneously dispersed on the surface of graphene sheets, due to their bonding with graphene. When used as a photocatalyst under visible-light irradiation, O2 production rate reached a value up to 20.60 μmol h(-1), 4.18 times higher than that of bare BWO, resulting from the strong covalent bonding between graphene and BWO nanoparticles. The chemical bonding facilitated the electron collection and transportation and inhibited the recombination of photo-generated charge carriers, even in this system with a large amount of graphene inside (40 wt%). More interestingly, H2-production by Gr-BWO-T was also observed to be as high as 159.20 μmol h(-1). This could be ascribed to the existence of the graphene that led to decrease in conduction band potential and resulted in a more negative reduction potential than H(+)/H2. This facile sonochemical approach provides a new strategy for engineering ternary compound nanoparticles on graphene sheets, with great potential application in energy conversion.

Highly efficient photocatalytic hydrogen evolution of graphene/YInO3 nanocomposites under visible light irradiation

Visible-light-driven hydrogen evolution with high efficiency is important in the current photocatalysis research. Here we report for the first time the design and synthesis of a new graphene-semiconductor nanocomposite consisting of YInO3 nanoparticles and two-dimensional graphene sheets as efficient photocatalysts for hydrogen evolution under visible light irradiation. The graphene/YInO3 nanocomposites were synthesized using a facile solvothermal method in which the formation of graphene and the deposition of YInO3 nanoparticles on the graphene sheets can be achieved simultaneously. The addition of graphene as a cocatalyst can narrow the band gap of YInO3 to visible photon energy and prolong the separation and lifetime of electron-hole pairs by the chemical bonding between YInO3 and graphene. The photocatalytic reaction with this nanocomposite reaches a high H2 evolution rate of 400.4 μmol h(-1) g(-1) when the content of graphene is 0.5 wt%, over 127 and 3.7 times higher than that of pure YInO3 and Pt/YInO3, respectively. This work can provide an effective approach to the fabrication of graphene-based photocatalysts with high performance in the field of energy conversion.

High photocatalytic performance by engineering Bi2WO6 nanoneedles onto graphene sheets

A sonochemical method was described to engineer Bi₂WO₆ nanoneedles on graphene sheets, which showed improved performances both in H₂ and O₂ creation.

Role of graphene on the surface chemical reactions of BiPO4-rGO with low OH-related defects

Graphene has been widely introduced into photocatalysis to enhance photocatalytic performance due to its unique physical and chemical properties. However, the effect of graphene on the surface chemical reactions of photocatalysis has not been clearly researched, which is important for photocatalysis because photocatalytic reactions ultimately occur on the catalyst surface. Herein, a two-step solution-phase reaction has been designed to synthesize quasi-core-shell structured BiPO4-rGO cuboids and the role of graphene on the surface chemical reactions was investigated in detail. It was found that the introduced graphene modified the process and the mechanism of the surface chemical reactions. The change mainly originates from the interaction between graphene and the adsorbed O2 molecule. Due to the electron transfer from graphene to adsorbed O2, graphene could tune the interfacial charge transport and efficiently activate molecular oxygen to form O2˙(-) anions as the major oxidation species instead of ˙OH. In addition, the two-step synthesis approach could efficiently suppress the formation of OH-related defects in the lattice. As a result, the BiPO4-rGO composite exhibited superior photocatalytic activity to BiPO4 and P25, about 4.3 times that of BiPO4 and 6.9 times that of P25.

Electrical graphene aptasensor for ultra-sensitive detection of anthrax toxin with amplified signal transduction

Detection of the anthrax toxin, the protective antigen (PA), at the attomolar (aM) level is demonstrated by an electrical aptamer sensor based on a chemically derived graphene field-effect transistor (FET) platform. Higher affinity of the aptamer probes to PA in the aptamer-immobilized FET enables significant improvements in the limit of detection (LOD), dynamic range, and sensitivity compared to the antibody-immobilized FET. Transduction signal enhancement in the aptamer FET due to an increase in captured PA molecules results in a larger 30 mV/decade shift in the charge neutrality point (Vg,min ) as a sensitivity parameter, with the dynamic range of the PA concentration between 12 aM (LOD) and 120 fM. An additional signal enhancement is obtained by the secondary aptamer-conjugated gold nanoparticles (AuNPs-aptamer), which have a sandwich structure of aptamer/PA/aptamer-AuNPs, induce an increase in charge-doping in the graphene channel, resulting in a reduction of the LOD to 1.2 aM with a three-fold increase in the Vg,min shift.

Noncovalent binding of xanthene and phthalocyanine dyes with graphene sheets: the effect of the molecular structure revealed by a photophysical study

The fluorescence and absorption properties of several xanthene and phthalocyanine dyes were measured in the presence and absence of chemically derived graphene (CDG) sheets. The interaction of pyronine Y (PYY) with graphene sheets was compared with that of rhodamine 6G (R6G) to reveal the effect of the molecular structure. Although the presence of the perpendicular benzene moiety in a R6G or phthalocyanine molecule does cause the difficulty for forming dye-CDG complex and make CDG less efficient in quenching the fluorescence intensity and shortening the fluorescence lifetime, it does not affect the band position of charge transfer absorption, suggesting that no molecular shape change occurred in a dye molecule caused by the interaction with CDG sheets. The spectroscopic and thermodynamic data indicated that the dye-CDG binding is of charge transfer nature, while the dynamic fluorescence quenching is due to photoinduced energy and electron transfer.