We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

Single-Atom Catalysts across the Periodic Table.

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters. Over the last decade, different nanomaterials have been exploited to design highly efficient biosensors for the detection of analyte biomolecules. The discovery of graphene has spectacularly accelerated research on fabricating low-cost electrode materials because of its unique physical properties, including high specific surface area, high carrier mobility, high electrical conductivity, flexibility, and optical transparency. Graphene and its oxygenated derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the field of biosensors. The presence of oxygenated functional groups makes GO nanosheets strongly hydrophilic, facilitating chemical functionalization. Graphene, GO and rGO nanosheets can be easily combined with various types of inorganic nanoparticles, including metals, metal oxides, semiconducting nanoparticles, quantum dots, organic polymers and biomolecules, to create a diverse range of graphene-based nanocomposites with enhanced sensitivity for biosensor applications. This review summarizes the advances in two-dimensional (2D) and three-dimensional (3D) graphene-based nanocomposites as emerging electrochemical and fluorescent biosensing platforms for the detection of a wide range of biomolecules with enhanced sensitivity, selectivity and a low limit of detection. The biofunctionalization and nanocomposite formation processes of graphene-based materials and their unique properties, surface functionalization, enzyme immobilization strategies, covalent immobilization, physical adsorption, biointeractions and direct electron transfer (DET) processes are discussed in connection with the design and fabrication of biosensors. The enzymatic and nonenzymatic reactions on graphene-based nanocomposite surfaces for glucose- and cholesterol-related electrochemical biosensors are analyzed. This review covers a very broad range of graphene-based electrochemical and fluorescent biosensors for the detection of glucose, cholesterol, hydrogen peroxide (H2O2), nucleic acids (DNA/RNA), genes, enzymes, cofactors nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP), dopamine (DA), ascorbic acid (AA), uric acid (UA), cancer biomarkers, pathogenic microorganisms, food toxins, toxic heavy metal ions, mycotoxins, and pesticides. The sensitivity and selectivity of graphene-based electrochemical and fluorescent biosensors are also examined with respect to interfering analytes present in biological systems. Finally, the future outlook for the development of graphene based biosensing technology is outlined.

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A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Renewable energy technology has been considered as a "MUST" option to lower the use of fossil fuels for industry and daily life. Designing critical and sophisticated materials is of great importance in order to realize high-performance energy technology. Typically, efficient synthesis and soft surface modification of nanomaterials are important for energy technology. Therefore, there are increasing demands on the rational design of efficient electrocatalysts or electrode materials, which are the key for scalable and practical electrochemical energy devices. Nevertheless, the development of versatile and cheap strategies is one of the main challenges to achieve the aforementioned goals. Accordingly, plasma technology has recently appeared as an extremely promising alternative for the synthesis and surface modification of nanomaterials for electrochemical devices. Here, the recent progress on the development of nonthermal plasma technology is highlighted for the synthesis and surface modification of advanced electrode materials for renewable energy technology including electrocatalysts for fuel cells, water splitting, metal-air batteries, and electrode materials for batteries and supercapacitors, etc.

Plasma-Assisted Synthesis and Surface Modification of Electrode Materials for Renewable Energy

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

http://pubs.acs.org/doi/pdf/10.1021/acsnano.5b05690

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

The nitrogen reduction reaction (NRR) is a pivotal step in electrochemical N2 fixation to NH3. VS2 holds great promise as a NRR electrocatalyst, but its high activity requires the sufficient activation of inert basal planes. Herein, we demonstrate the first successful activation of VS2 basal planes toward the NRR by introducing S-vacancies (Vs) and B-dopants. The theoretical calculations unravel that the synergistic role of VS and B-dopants enables the most effective activation of VS2 basal planes by creating unique B-adjacent-unsaturated-V active sites that can significantly promote the NRR while suppressing hydrogen evolution. The synthesized B-doped VS2 nanoflowers with enriched surface Vs delivered an NH3 yield of 55.7 μg h−1 mg−1 (−0.4 V) and a faradaic efficiency (FE) of 16.4% (−0.2 V) and represent the best V-based catalysts to date. Our theoretical and experimental findings may facilitate the exploration and understanding of advanced transition-metal disulfide catalysts for the NRR.

Activating VS2 basal planes for enhanced NRR electrocatalysis: the synergistic role of S-vacancies and B dopants

CuO nanoparticles on sulfur-doped graphene for nonenzymatic glucose sensing

Green synthesis of silver nanoparticles on nitrogen-doped graphene for hydrogen peroxide detection

Electrochemical N2 fixation through nitrogen reduction reaction (NRR) is a promising way for sustainable NH3 synthesis, while exploring high-performing NRR catalysts lies at the heart of attaining high-efficiency NRR electrocatalysis....

Amorphization engineered VSe2-x nanosheets with abundant Se-vacancies for enhanced N2 electroreduction

Electrochemical conversion of N2–NH3 provides a green and sustainable alternative for artificial NH3 synthesis but requires effective electrocatalysts to promote N2 reduction reaction (NRR). This work reported the first application of N, S co-doped graphene (NSG) as an efficient metal-free NRR catalyst. It was found that the NSG exhibited a high NH3 yield of 7.7 μg h−1 mg−1 and Faradaic efficiency of 5.8% at − 0.6 V versus reversible hydrogen electrode under ambient conditions, which largely outperformed undoped and single-doped counterparts, and compared favorably to most reported metal-based NRR catalysts. The combination of density functional theory calculations and experiments revealed that the N, S co-doping could effectively improve the NRR of graphene by promoting the N2 adsorption and N≡N bond elongation, boosting the electron transfer and creating more defective/active sites. Furthermore, the NSG showed an excellent selectivity and stability, suggesting its great potential for efficient electrochemical synthesis of NH3.

Ye Tian

Papers

Activating VS2 basal planes for enhanced NRR electrocatalysis: the synergistic role of S-vacancies and B dopants

CuO nanoparticles on sulfur-doped graphene for nonenzymatic glucose sensing

Green synthesis of silver nanoparticles on nitrogen-doped graphene for hydrogen peroxide detection

Amorphization engineered VSe2-x nanosheets with abundant Se-vacancies for enhanced N2 electroreduction

Metal-free N, S co-doped graphene for efficient and durable nitrogen reduction reaction