Low-cost and resourceful transition metal phosphides (TMPs) have gradually received wide acceptance in the energy industry through exhibiting comparable catalytic activity and long-term stability to traditional catalysts (e.g., Pt/C, LiCoO₂, LiFePO₄, etc.). With the emergence of the research hotspot of TMPs, probing their mechanism of catalytic energy conversion and storage inspired by the superb structure of metal-phosphorus chelate is of great significance. To this end, recent developments in TMPs with various crystal structures and morphologies have attracted much attention. The design of TMPs ranging from the choice of different transition metals to phosphorus sources has been intensively explored. This research has indicated that multidimensional morphologies of TMPs prominently enrich the patterns of charge storage and electron transportation, and ultra-nanoscaled TMPs obtained by multiple tools and techniques might challenge the threshold of electrocatalytic reactions. Here, recent developments in synthetic strategies of TMPs from different precursors are classified. The underlying mechanism between the structural and crystallographic characteristics and the tuned properties of TMPs in energy applications is also presented. Additionally, the key trends in structure and morphology characterization of TMPs are highlighted. Future perspectives on the challenges and opportunities facing TMPs catalysts are thereby proposed.

In order to improve the photoactivity, many attempts have focused on increasing the exposure of highly reactive surfaces on crystals. However, the connection between the reactive surfaces and enhancement is still elusive. Herein, Bi₂WO₆ nanostructured bipyramids with a large fraction of {100} facets are fabricated by the solvothermal method. The formation of “Bi–O” dimer vacancy pairs on the {100} high-energy facets is responsible for the reduction in band gap and the decrease in the recombination of photo-excited charge carriers, which is unambiguously confirmed by the positron annihilation spectra (PAS), X-ray photoelectron spectrum (XPS), and theoretical calculations. The effective separation of electron–hole pairs and the narrowing bandgap significantly improve the photoactivity of Bi₂WO₆ nanobipyramids, especially under solar light irradiation. These findings can be applied broadly to the design and fabrication of energy efficient and robust catalysts.

Cell signaling consists of diverse events that occur at various temporal and spatial scales, ranging from milliseconds to hours and from single biomolecules to cell populations. The pathway complexities require the development of new techniques that detect the overall signaling activities and are not limited to quantifying a single event. A plasmonic-based electrochemical impedance microscope (P-EIM) that can provide such data with excellent temporal and spatial resolution and does not require the addition of any labels for detection has now been developed. The highly dynamic and transient calcium signaling activities at the early stage of G-protein-coupled receptor (GPCR) stimulation were thus studied. It could be shown that a subpopulation of cells is more responsive towards agonist stimulation, and the heterogeneity of the local distributions and the transient activities of the ion channels during agonist-activated calcium flux in single HeLa cells were investigated.

Cell signaling consists of diverse events that occur at various temporal and spatial scales, ranging from milliseconds to hours and from single biomolecules to cell populations. The pathway complexities require the development of new techniques that detect the overall signaling activities and are not limited to quantifying a single event. A plasmonic-based electrochemical impedance microscope (P-EIM) that can provide such data with excellent temporal and spatial resolution and does not require the addition of any labels for detection has now been developed. The highly dynamic and transient calcium signaling activities at the early stage of G-protein-coupled receptor (GPCR) stimulation were thus studied. It could be shown that a subpopulation of cells is more responsive towards agonist stimulation, and the heterogeneity of the local distributions and the transient activities of the ion channels during agonist-activated calcium flux in single HeLa cells were investigated.

The ability to quantitate and visualize microRNAs (miRNAs) in situ in single cells would greatly facilitate the elucidation of miRNA-mediated regulatory circuits and their disease associations. A toehold-initiated strand-displacement process was used to initiate rolling circle amplification of specific miRNAs, an approach that achieves both stringent recognition and in situ amplification of the target miRNA. This assay, termed toehold-initiated rolling circle amplification (TIRCA), can be utilized to identify miRNAs at physiological temperature with high specificity and to visualize individual miRNAs in situ in single cells within 3 h. TIRCA is a competitive candidate technique for in situ miRNA imaging and may help us to understand the role of miRNAs in cellular processes and human diseases in more detail.

The ability to quantitate and visualize microRNAs (miRNAs) in situ in single cells would greatly facilitate the elucidation of miRNA-mediated regulatory circuits and their disease associations. A toehold-initiated strand-displacement process was used to initiate rolling circle amplification of specific miRNAs, an approach that achieves both stringent recognition and in situ amplification of the target miRNA. This assay, termed toehold-initiated rolling circle amplification (TIRCA), can be utilized to identify miRNAs at physiological temperature with high specificity and to visualize individual miRNAs in situ in single cells within 3 h. TIRCA is a competitive candidate technique for in situ miRNA imaging and may help us to understand the role of miRNAs in cellular processes and human diseases in more detail.

Certain DNA polymerases, such as ϕ29 DNA polymerase, can isothermally copy the sequence of a circular template round by round in a process known as rolling circle amplification (RCA), which results in super-long single-stranded (ss) DNA molecules made of tandem repeats. The power of RCA reflects the high processivity and the strand-displacement ability of these polymerases. In this work, the ability of ϕ29DNAP to carry out RCA over circular templates containing a protein-binding DNA aptamer sequence was investigated. It was found that protein–aptamer interactions can prevent this DNA polymerase from reading through the aptameric domain. This finding indicates that protein-binding DNA aptamers can form highly stable complexes with their targets in solution. This novel observation was exploited by translating RCA arrest into a simple and convenient colorimetric assay for the detection of specific protein targets, which continues to showcase the versatility of aptamers as molecular recognition elements for biosensing applications.

A simple approach for loading LiFePO₄ (LFP) nanoparticles on graphene (G) that could assemble amorphous LiFePO₄ nanoparticles into a stable, crystalline, graphene-modified layered materials (G-S-LFP, S=sucrose) by using graphene as building block and sucrose as a linker has yet to be developed. On the basis of differential scanning calorimetric and transmission electron microscopy analysis of the samples from controlled experiment, a possible mechanism was proposed to explain the “linker” process of LFP and graphene with sucrose as the linker. The electrochemical properties of the samples as cathode material for lithium-ion batteries were studied by cyclic voltammogrametry and galvanostatic methods. Results showed that G-S-LFP displayed superior lithium-storage capability with current density changes randomly form 0.5 to 10 C. The significant improvement for rate and cycle performance could be attributed to the high conductivity of the graphene host, the high crystallinity, and the layered structure.

The high price of platinum (Pt)-based cathode catalysts for the oxygen reduction reaction (ORR) have slowed down the practical application of fuel cells. Thanks to their low cost, and outstanding, stable catalytic properties, titanium nitrides (TiN) are among the most promising non-precious metal electrocatalysts for replacing Pt. However, the shape–activity relationships of TiN electrocatalysts have not been well-studied or understood up to now. In this work, by simply adjusting the shape of TiO₂ precursor, we are able to tailor the morphology of the TiN catalysts from nanoparticles to nanotubes. We have synthetized uniform carbon-coated titanium nitride nanotubes (carbon-coated TiN NTs) through a nitridation reaction in NH₃ flow using a TiO₂ nanotubes/melamine mixture as precursor. The carbon-coated TiN NTs hybrids exhibit excellent electrocatalytic activity for the ORR, coupled with superior methanol tolerance and long-term stability in comparison to commercial Pt/C, through an efficient four-electron-dominant ORR process. Compared with nanoparticles, the one-dimensional and hollow structure of the nanotubes result in greater diffusion of electrolyte and superior electrical conductivity, and contribute to the greatly improved electrocatalytic performance of the carbon-coated TiN NTs nanocomposites.

AgBr nanocrystals, evolving from plates through truncated cubes and finally to regular cubes, corresponding to a progressive shrinkage of exposed {1 1 1} facets and enlargement of exposed {1 0 0} facets, were successfully prepared by facile ion-exchange reactions under the synergistic effects of polyvinylpyrrolidone and NH₃⋅ H₂O. An investigation of the growth mechanism revealed that polyvinylpyrrolidone can selectively adsorb on the {1 1 1} facets of AgBr nanocrystals, whereas NH₃⋅H₂O not only forms a [Ag(NH₃)₂]⁺ complex that slows the rates of ion-exchange reactions, but may also prefer to adsorb on {1 0 0} facets. Studies of their photocatalytic properties showed that the as-prepared AgBr nanocrystals exhibited facet-dependent photocatalytic properties. The {1 1 1}-dominated AgBr nanoplates exhibited the highest photocatalytic activities, and the photodegradation rate of methyl orange dyes over them was 3 times faster than over AgBr nanocubes that expose {1 0 0} facets. Surface atomic models and DFT calculations indicate that the {1 1 1} facets have more dangling bonds and a higher surface energy than the {1 0 0} facets, which substantiate the facet-dependent photocatalytic properties. Therefore, our work not only provides a novel method to prepare regular AgBr nanocrystals, but also demonstrates that the shape and exposed facets have important influence on their photocatalytic activities.

The exploration and fabrication of nano-biointerfaces have fundamental significance and practical importance in many fields including chemistry, biology, and materials science. Recently, the integration of DNA with graphene has been substantially advanced. It is well known that single-stranded (ss) DNA can interact with graphene (or graphene oxide) via π–π stacking. However, for the case of DNA duplex/graphene, the studies are still not conclusive. Most work does not address the question of whether or how dsDNA is attracted to graphene oxide (GO). Here the interaction of DNA/GO is systematically investigated and its nanobiological effects, molecular recognition, and biosensing are explored. It is demonstrated that GO can adsorb DNA duplexes, which is possibly facilitated by partial deformation of the double helix on GO. Additionally dsDNA on GO shows specific effects on enzymatic degradation, which could be effectively cleaved by DNA enzyme I and restriction endonucleases as EcoR I, whereas it is highly resistant to degradation by Exo III. An improved understanding of the behavior of these GO/DNA entities will facilitate the development of applications in biomedicine, biosensing, and bionanotechnology.

A temperature-sensitive polymer/carbon nanotube interface with switchable bioelectrocatalytic capability was fabricated by self-assembly of poly(N-isopropylacrylamide)-grafted multiwalled carbon nanotubes (MWNT-g-PNIPAm) onto the PNIPAm-modified substrate. Electron microscopy and electrochemical measurements revealed that these fairly thick (>6 μm) and highly porous nanocomposite films exhibited high conductivity and electrocatalytic activity. The morphological transitions in both the tethered PNIPAm chains on a substrate and those polymers wrapping around the MWNT surface resulted in the opening, closing, or tuning of its permeability, and simultaneously an electron-transfer process took place through the channels formed in the nanostructure in response to temperature change. By combining the good electron-transfer and electrochemical catalysis capabilities, the large surface area, and good biocompatibility of MWNTs with the responsive features of PNIPAm, reversible temperature-controlled bioelectrocatalysis of 1,4-dihydro-β-nicotinamide adenine dinucleotide with improved sensitivity has been demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The mechanism behind this approach was studied by Raman spectroscopy, in situ attenuated total reflection FTIR spectroscopy, and contact angle measurements. The results also suggested that the synergetic or cooperative interactions of PNIPAm with MWNTs gave rise not only to an increase in surface wettability, but also to the enhancement of the interfacial thermoresponsive behavior. This bioelectrocatalytic “smart” system has potential applications in the design of biosensors and biofuel cells with externally controlled activity. Furthermore, this concept might be proposed for biomimetics, interfacial engineering, bioelectronic devices, and so forth.

Synthesis of inorganic single crystals with exposed high-reactivity facets is a desirable target in the catalytic chemistry field. Polyhedral AgBr microcrystals with an increased percentage of exposed high-reactivity {111} facets have been successfully prepared for the first time, and the photocatalytic performance of these microcrystals when used as an AgBr/Ag plasmonic photocatalyst was investigated. The results indicate that the as-prepared sample has high photocatalytic activity and, under the same measurement conditions, the photodegradation rate of methyl orange dye over these microcrystals is at least four times faster than with other shapes of AgBr/Ag microstructure, as well as 20 times faster than with the highly efficient Ag₃PO₄ photocatalyst. DFT calculations suggest that the AgBr (111) surface is mainly composed of unsaturated Ag atoms and has a relatively high surface energy, both of which are favorable for enhancing the photocatalytic activity of the AgBr/Ag polyhedron photocatalyst. This work not only provides a highly efficient plasmonic photocatalyst of polyhedral AgBr/Ag microcrystals with an increased percentage of exposed high-reactivity AgBr {111} facets, but also demonstrates that the shape and crystalline quality of the exposed facets have an important influence on the photocatalytic activities.

Herein, a chemically bonded BiOBr–graphene composite (BiOBr–RG) was prepared through a facile in situ solvothermal method in the presence of graphene oxide. Graphene oxide could be easily reduced to graphene under solvothermal conditions, and simultaneously BiOBr nanoplates with pure tetragonal phase were grown uniformly on the graphene surface. The structure and photoelectrochemical properties of the resulting materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and impedance and photocurrent action measurements. The combination of BiOBr and graphene introduces some properties of graphene into the photocatalysis reaction, such as excellent conductivity, adsorptivity, and controllability. A remarkable threefold enhancement in the degradation of rhodamine B (RhB) was observed with as-prepared BiOBr–RG as compared with pure BiOBr under visible light (λ>420 nm). The enhanced photocatalytic activity could be attributed to the great adsorptivity of dyes, the extended photoresponse range, the negative shift in the Fermi level of BiOBr–RG, and the high migration efficiency of photoinduced electrons, which may effectively suppress the charge recombination.

The bandgap opening of graphene is extremely important for the expansion of the applications of graphene-based materials into optoelectronics and photonics. Current methods to open the bandgap of graphene have intrinsic drawbacks including small bandgap openings, the use hazardous/harsh chemical oxidations, and the requirement of expensive chemical-vapor deposition technologies. Herein, an eco-friendly, highly effective, low-cost, and highly scalable synthetic approach is reported for synthesizing wide-bandgap fluorinated graphene (F-graphene or or fluorographene) semiconductors under ambient conditions. In this synthesis, ionic liquids are used as the only chemical to exfoliate commercially available fluorinated graphite into single and few-layer F-graphene. Experimental and theoretical results show that the bandgap of F-graphene is largely dependent on the F coverage and configuration, and thereby can be tuned over a very wide range.

The self-assembly of sodium dodecyl benzene sulphonate (SDBS) functionalized graphene sheets (GSs) and horseradish peroxidase (HRP) by electrostatic attraction into novel hierarchical nanostructures in aqueous solution is reported. Data from scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction demonstrate that the HRP–GSs bionanocomposites feature ordered hierarchical nanostructures with well-dispersed HRP intercalated between the GSs. UV-vis and infrared spectra indicate the native structure of HRP is maintained after the assembly, implying good biocompatibility of SDBS-functionalized GSs. Furthermore, the HRP–GSs composites are utilized for the fabrication of enzyme electrodes (HRP–GSs electrodes). Electrochemical measurements reveal that the resulting HRP–GSs electrodes display high electrocatalytic activity to H₂O₂ with high sensitivity, wide linear range, low detection limit, and fast amperometric response. These desirable electrochemical performances are attributed to excellent biocompatibility and superb electron transport efficiency of GSs as well as high HRP loading and synergistic catalytic effect of the HRP–GSs bionanocomposites toward H₂O₂. As graphene can be readily non-covalently functionalized by “designer” aromatic molecules with different electrostatic properties, the proposed self-assembly strategy affords a facile and effective platform for the assembly of various biomolecules into hierarchically ordered bionanocomposites in biosensing and biocatalytic applications.

A novel electrochemical platform was designed by combining the biocompatibility of single-stranded DNA (ss-DNA) and the excellent conductivity of graphene (GP). This nanocomposite (denoted as ss-DNA/GP) was first used as an electrode material for the immobilization and biosensing of redox enzymes. On the basis of electrostatic interactions, horseradish peroxidase (HRP) self-assembled with ss-DNA/GP on the surface of a glassy carbon (GC) electrode to form an HRP/ss-DNA/GP/GC electrode. UV/Vis and FTIR spectra were used to monitor the assembly process and indicated that the immobilized HRP on the ss-DNA/GP matrix retained its native structure well. A pair of stable and well-defined redox peaks of HRP with a formal potential of about −0.26 V (vs. Ag/AgCl) in a pH 7.0 phosphate buffer solution were obtained at the HRP/ss-DNA/GP/GC electrode; this demonstrates direct electron transfer between the immobilized HRP and the electrode. In addition, the modified electrode showed good electrocatalytic performance towards H₂O₂ with high sensitivity, wide linear range, and good stability. Accordingly, the ss-DNA/GP nanocomposite provides a novel and efficient platform for the immobilized redox enzyme to realize direct electrochemistry and has a promising application in the fabrication of third-generation electrochemical biosensors.

In this study, we describe the use of the combination of eletrografting poly(N-mercaptoethyl acrylamide) and Au nanoparticles in the construction of high-performance biosensors. The poly(N-mercaptoethyl acrylamide) was electrografted onto the glassy carbon electrode surface, which provided a strongly adhering primer film for the stable attachment of Au nanoparticles and horseradish peroxidase (HRP) enzymes. The performances of the biosensors based on the HRP immobilized in the Au/poly(N-mercaptoethyl acrylamide) composite film were investigated. A couple of redox peaks were obtained, indicating that the Au nanoparticles could facilitate the direct-electron transfer between HRP and the underlying electrode. The biosensor showed an excellent electrocatalytic activity toward the reduction of hydrogen oxide and long-term stability, owing to the stable electrografted film and biocompatible Au nanoparticles. Our results demonstrate that the combination of electrografting and Au nanoparticles provides a promising platform for the immobilization of biomolecules and analysis of redox enzymes for their sensing applications.

This paper describes the preparation, characterization, and electrochemical properties of reduced graphene sheet films (rGSFs), investigating especially their electrochemical behavior for several redox systems and electrocatalytic properties towards oxygen and some small molecules. The reduced graphene sheets (rGSs) are produced in high yield by a soft chemistry route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. Transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy clearly demonstrate that graphene was successfully synthesized and modified at the surface of a glassy carbon electrode. Several redox species, such as Ru(NH₃)₆^3+/2+, Fe(CN)₆^3−/4−, Fe^3+/2+ and dopamine, are used to probe the electrochemical properties of these graphene films by using the cyclic voltammetry method. The rGSFs demonstrate fast electron-transfer (ET) kinetics and possess excellent electrocatalytic activity toward oxygen reduction and certain biomolecules. In our opinion, this microstructural and electrochemical information can serve as an important benchmark for graphene-based electrode performances.

A facile method is developed to synthesize aligned arrays of open-ended carbon nanotubes (CNTs) via in situ glucose polymerization in the inner pores of anodic aluminum oxide templates under hydrothermal conditions, followed by carbonization at high temperature. Pt nanoparticles are decorated on the surfaces of the as-prepared CNTs using the incipient wet method based on the use of NaBH₄ as a reductant. Characterization of the resulting structures by transmission electron microscopy and field-emission scanning electron microscopy demonstrates that the Pt nanoparticles are anchored on both the inner and outer walls of CNTs, thus giving rise to a shell–core–shell-like nanotube composite. The electrocatalytic properties of the Pt–CNT–Pt electrodes are investigated for methanol oxidation by cyclic voltammetry and chronoamperometric measurements. It is found that the hybrid electrodes show superior catalytic performance compared to commercial carbon-black-supported Pt. The increased catalytic efficiency of Pt might be a result of the unique morphology of these structures.