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Human exposure to nanoparticles is inevitable as nanoparticles become more widely used and, as a result, nanotoxicology research is now gaining attention. However, while the number of nanoparticle types and applications continues to increase, studies to characterize their effects after exposure and to address their potential toxicity are few in comparison. In the medical field in particular, nanoparticles are being utilized in diagnostic and therapeutic tools to better understand, detect, and treat human diseases. Exposure to nanoparticles for medical purposes involves intentional contact or administration; therefore, understanding the properties of nanoparticles and their effect on the body is crucial before clinical use can occur. This Review presents a summary of the in vitro cytotoxicity data currently available on three classes of nanoparticles. With each of these nanoparticles, different data has been published about their cytotoxicity due to varying experimental conditions as well as differing nanoparticle physiochemical properties. For nanoparticles to move into the clinical arena, it is important that nanotoxicology research uncovers and understands how these multiple factors influence the toxicity of nanoparticles so that their undesirable properties can be avoided.

Isolated graphene, a nanometer‐thick two‐dimensional analog of fullerenes and carbon nanotubes, has recently sparked great excitement in the scientific community given its excellent mechanical and electronic properties. Particularly attractive is the availability of bulk quantities of graphene as both colloidal dispersions and powders, which enables the facile fabrication of many carbon‐based materials. The fact that such large amounts of graphene are most easily produced via the reduction of graphene oxide—oxygenated graphene sheets covered with epoxy, hydroxyl, and carboxyl groups—offers tremendous opportunities for access to functionalized graphene‐based materials. Both graphene oxide and graphene can be processed into a wide variety of novel materials with distinctly different morphological features, where the carbonaceous nanosheets can serve as either the sole component, as in papers and thin films, or as fillers in polymer and/or inorganic nanocomposites. This Review summarizes techniques for preparing such advanced materials via stable graphene oxide, highly reduced graphene oxide, and graphene dispersions in aqueous and organic media. The excellent mechanical and electronic properties of the resulting materials are highlighted with a forward outlook on their applications.

Graphene, a two‐dimensional, single‐layer sheet of sp² hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene‐related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene‐based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene‐based materials are discussed.

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor‐phase versus solution‐phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry–Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time‐resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second‐harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size‐/surface‐dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy‐conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high‐performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.

Perovskite solar cells based on organometal halide light absorbers have been considered a promising photovoltaic technology due to their superb power conversion efficiency (PCE) along with very low material costs. Since the first report on a long‐term durable solid‐state perovskite solar cell with a PCE of 9.7% in 2012, a PCE as high as 19.3% was demonstrated in 2014, and a certified PCE of 17.9% was shown in 2014. Such a high photovoltaic performance is attributed to optically high absorption characteristics and balanced charge transport properties with long diffusion lengths. Nevertheless, there are lots of puzzles to unravel the basis for such high photovoltaic performances. The working principle of perovskite solar cells has not been well established by far, which is the most important thing for understanding perovksite solar cells. In this review, basic fundamentals of perovskite materials including opto‐electronic and dielectric properties are described to give a better understanding and insight into high‐performing perovskite solar cells. In addition, various fabrication techniques and device structures are described toward the further improvement of perovskite solar cells.

Due to their unique 2D structure and outstanding intrinsic physical properties, such as extraordinarily high electrical conductivity and large surface area, graphene‐based materials exhibit great potential for application in supercapacitors. In this review, the progress made so far for their applications in supercapacitors is reviewed, including electrochemical double‐layer capacitors, pseudo‐capacitors, and asymmetric supercapacitors. Compared with traditional electrode materials, graphene‐based materials show some novel characteristics and mechanisms in the process of energy storage and release. Several key issues for improving the structure of graphene‐based materials and for achieving better capacitor performance, along with the current outlook for the field, are also discussed.

A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported. Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene‐based nonstoichiometric derivatives. Fluorographene is a high‐quality insulator (resistivity >10¹² Ω) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting a Young’s modulus of 100 N m⁻¹ and sustaining strains of 15%. Fluorographene is inert and stable up to 400 °C even in air, similar to Teflon.