Interest in graphene centres on its excellent mechanical, electrical, thermal and optical properties, its very high specific surface area, and our ability to influence these properties through chemical functionalization. There are a number of methods for generating graphene and chemically modified graphene from graphite and derivatives of graphite, each with different advantages and disadvantages. Here we review the use of colloidal suspensions to produce new materials composed of graphene and chemically modified graphene. This approach is both versatile and scalable, and is adaptable to a wide variety of applications.

Chemical methods for the production of graphenes.

The reduction of graphene oxide

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Graphene: The New Two-Dimensional Nanomaterial

Approaches, Derivatives and Applications Vasilios Georgakilas,† Michal Otyepka,‡ Athanasios B. Bourlinos,‡ Vimlesh Chandra, Namdong Kim, K. Christian Kemp, Pavel Hobza,‡,§,⊥ Radek Zboril,*,‡ and Kwang S. Kim* †Institute of Materials Science, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo naḿ. 2, 166 10 Prague 6, Czech Republic

Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications

Graphene oxide suspended in ethanol undergoes reduction as it accepts electrons from UV-irradiated TiO2 suspensions. The reduction is accompanied by changes in the absorption of the graphene oxide, as the color of the suspension shifts from brown to black. The direct interaction between TiO2 particles and graphene sheets hinders the collapse of exfoliated sheets of graphene. Solid films cast on a borosilicate glass gap separated by gold-sputtered terminations show an order of magnitude decrease in lateral resistance following reduction with the TiO2 photocatalyst. The photocatalytic methodology not only provides an on-demand UV-assisted reduction technique but also opens up new ways to obtain photoactive graphene-semiconductor composites.

http://www.dstuns.iitm.ac.in/grouppresentations/2008/TiO2-Graphene_Nanocomposites_UV-Assisted_Photocatalytic_Reduction_of_Graphene_Oxide.pdf

TiO2-Graphene Nanocomposites. UV-Assisted Photocatalytic Reduction of Graphene Oxide

Graphene oxide sheets suspended in ethanol interact with excited ZnO nanoparticles and undergo photocatalytic reduction. The luminescence quenching of the green emission of ZnO serves as a probe to monitor the electron transfer from excited ZnO to graphene oxide. Anchoring of ZnO nanoparticles on 2-D carbon nanostructures provides a new way to design semiconductor−carbon nanocomposites for catalytic applications.

Graphene-semiconductor nanocomposites: excited-state interactions between ZnO nanoparticles and graphene oxide.

The organic/electrode interfaces in organic solar cells are systematically studied for their light, heat, and electrical stability in an inert atmosphere. Various extraction layers are examined for their effect on device stability, including poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and MoO3 for hole extraction layers, as well as LiF, Cs2CO3, and lithium acetylacetonate (Liacac) for electron extraction layers. The organic/metal interface is shown to be inherently photo-unstable, resulting in significant losses in device efficiency with irradiation. X-ray photoelectron spectroscopy measurements of the organic/aluminum interface suggest that the photo-induced changes are chemical in nature. In general, interfacial layers are shown to substantially reduce photo-degradation of the active layer/electrode interface. In spite of their photo-stability, several interfacial layers present at the active layer/cathode interface suffer from thermal degradation effects due to temperature increases under exposure to light. Electrical aging effects are proven to be negligible in comparison to other major modes of degradation.

The Photo‐Stability of Polymer Solar Cells: Contact Photo‐Degradation and the Benefits of Interfacial Layers

The rapid development of microfluidics and lab-on-a-chip (LoC) technologies have allowed for the efficient separation and manipulation of various biomaterials, including many diagnostically relevant species. Organic electronics have similarly enjoyed a great deal of research, resulting in tiny, highly efficient, wavelength-selective organic light-emitting diodes (OLEDs) and organic photodetectors (OPDs). We consider the blend of these technologies for rapid detection and diagnosis of biological species. In the ideal system, optically active or fluorescently labelled biological species can be probed via light emission from OLEDs, and their subsequent light emission can be detected with OPDs. The relatively low cost and simple fabrication of the organic electronic devices suggests the possibility of disposable test arrays. Further, with full integration, the finalized system can be miniaturized and made simple to use. In this review, we consider the design constraints of OLEDs and OPDs required to achieve fully organic electronic optical bio-detection systems. Current approaches to integrated LoC optical sensing are first discussed. Fully realized OLED- and OPD-specific photoluminescence detection systems from literature are then examined, with a specific focus on their ultimate limits of detection. The review highlights the enormous potential in OLEDs and OPDs for integrated optical sensing, and notes the key avenues of research for cheap and powerful LoC bio-detection systems.

https://www.mdpi.com/2079-9292/3/1/43/pdf

Graeme Williams

Papers

TiO2-Graphene Nanocomposites. UV-Assisted Photocatalytic Reduction of Graphene Oxide

Graphene-semiconductor nanocomposites: excited-state interactions between ZnO nanoparticles and graphene oxide.

The Photo‐Stability of Polymer Solar Cells: Contact Photo‐Degradation and the Benefits of Interfacial Layers

Integration of Organic Light Emitting Diodes and Organic Photodetectors for Lab-on-a-Chip Bio-Detection Systems

Renewed interest in metal phthalocyanine donors for small molecule organic solar cells