Composites of graphene quantum dots (GQDs) and reduced graphene oxide (rGO) with unique three-dimensional (3D) structure are prepared and their catalytic activities for reduction of nitroarenes are explored. We demonstrate that the 3D GQDs/rGO composites are more active in nitroarene reduction than GQDs and rGO. Some of them are even more active than the Ag-embedded calcium alginate (Ag/CA) or Au-embedded calcium alginate (Au/CA) catalysts. Interestingly, their catalytic property is closely related to the ratio of GQDs to rGO in the 3D GQDs/rGO composites and GQDs-to-rGO mass ratio of 1/4 exhibits the highest catalytic activity. Raman spectra of the composites show that GQDs-to-rGO ratio is related to the number of the surface/edge defects, indicating that the sites of defect and edges are active sites. In addition, the catalytic performance of the 3D GQDs/rGO composites is also contributed by their unique 3D network structures that are beneficial for the reactant adsorption and product diffusion. Given also the long cycling duration and the easy recovery from the reaction system, 3D GQDs/rGO composites are potential applicable metal-free catalytic system for nitorarene reduction.

Metastable intermolecular composites (MICs) have attracted great attention during the last two decades owing to their potential applications for both civilian and military purposes. In this work, a novel category of MICs are assembled using Al and CuO nanoparticles (NPs), and graphene quantum dots (GQDs) as building blocks. It has been demonstrated that the as-assembled Al/GQDs/CuO MICs show unique energetic performance in contrast to the physical mixture of Al and CuO NPs. More specifically, the MICs assembled at relatively higher temperature and with proper Al : GQDs : CuO ratio of 20 : 1 : 90 (in weight) exhibit overall better energetic performances, including a higher heat releasing rate and larger specific heat. It was also illustrated that the specific heat amount released during the reaction can be lifted by whittling the oxide layer of the Al NPs surface, revealing that the inactive oxide layer on Al NPs should be one of the main reasons influencing the energetic performances of the MICs. Nevertheless, this work shows that the GQDs should be a useful media for MICs assembling.

AbstractMultidrug resistance (MDR) is the major factor in the failure of many forms of chemotherapy, mostly due to the increased efflux of anticancer drugs that mediated by ATP-binding cassette (ABC) transporters. Therefore, inhibiting ABC transporters is one of effective methods of overcoming MDR. However, high enrichment of ABC transporters in cells and their broad substrate spectra made to circumvent MDR are almost insurmountable by a single specific ABC transporter inhibitor. Here, this study demonstrates that graphene quantum dots (GQDs) could downregulate the expressions of P-glycoprotein, multidrug resistance protein MRP1, and breast cancer resistance protein genes via interacting with C-rich regions of their promoters. This is the first example that a single reagent could suppress multiple MDR genes, suggesting that it will be possible to target multiple ABC transporters simultaneously with a single reagent. The inhibitory ability of the GQDs to these drug-resistant genes is validated further by reversing the doxorubicin resistance of MCF-7/ADR cells. Notably, GQDs have superb chemical and physical properties, unique structure, low toxicity, and high biocompatibility; hence, their capability of inhibiting multiple drug-resistant genes holds great potential in cancer therapy.

It is still challenging to improve the electrochemical properties of lithium iron (II) phosphate used as cathode for lithium ion batteries (LIBs). In the work, we describe the composites of lithium iron (II) phosphate/polypyrrole/chemically reduced graphene oxide (LFP/PPy/CRGO) prepared simply through a “one-pot” chemical procedure. We demonstrated that using pyrrole as monomer and graphene oxide as oxidant, PPy and CRGO sheets can be deposited simultaneously on the surface of LiFePO4 nanoparticles forming a uniform coating layer. As cathode for LIBs, the as-prepared composites show improved electrochemical properties and the rate capability and cycling stability of the LIBs can be increased dramatically. Electrochemical impedance spectroscopy and cyclic voltammetry measurements illustrated that the as-coated PPy and CRGO can decrease the charge transfer resistance and increase the Li+ diffusivity of the LiFePO4 particles. The elaboration of the underneath mechanism on the pronounced electrochemical properties of the composites was also attempted and discussed.

Well-defined graphene quantum dots (GQDs) are crucial for their biological applications and the construction of nanoscaled optoelectronic and electronic devices. However, as-synthesized GQDs reported in many works assume a very wide lateral size distribution; thus, their apparent properties cannot truthfully reflect intrinsic properties of the well-defined GQDs, and more importantly, the applications of GQDs will be affected and limited as well. In this work, we demonstrated that different sized GQDs with a narrow size distribution could be obtained via gel electrophoresis of the crude GQDs prepared through a photo-Fenton reaction of graphene oxide (GO). It is illustrated that the photoluminesce (PL) emissions of the well-defined GQDs originated mainly from the peripheral carboxylic groups and conjugated carbon backbone planes through fluorescence and UV–vis spectroscopies. More importantly, our findings challenge the notion that the excitation wavelength dependent PL property of the as-synthesized GQDs is the intrinsic property of the size-defined GQDs. Preliminary data at the cellular level indicated that the small sized GQDs exhibit weaker quenching DNA dye ability but higher toxicity to the cells compared to that of the as-synthesized GQDs. This discovery is essential to explore applications of the GQDs in pharmaceutics and to understand the origin of the optoelectronic properties of GQDs.Keywords: gel electrophoresis; graphene quantum dot; lateral size; photoluminescence

•Hydrous alumina was coated on P.R. 170 particle surface by hydrolysis of Al2(SO4)3.•P.R. 170 was coated with three types of structure; dots, floccules and films.•The relationship between the coating structures and the properties of P.R. 170 are discussed.•The film coating most significantly improves the properties of P.R. 170.C.I. Pigment Red 170 (P.R. 170) is one of the widely used organic pigments, and surface modification is essential to improve its thermal stability, and solvent resistance. In this work, hydrous alumina was coated onto P.R. 170 particles by hydrolysis of Al2(SO4)3, and different coating structures/morphologies were obtained including dots, floccules and films with different thickness. The influence of pH, temperature and Al2(SO4)3 content on the hydrous alumina coating structures were investigated by transmission electron microscopy (TEM), ζ-potential analysis, and several spectroscopic techniques. Thermogravimetric analysis (TGA) and pigment bleeding tests indicated that the thermal stability and solvent resistance of the pigments can be remarkably improved by a film coating, and this reveals that the consecutiveness and density of the coating layers should be the key factors for improvement of the organic pigments.

Monodispersed and size-controlled carbon spherules have great potential in many different applications. We report here the effects of organic and inorganic acids as catalysts on the formation of carbon spherules through the hydrothermal carbonization of glucose. The as-generated carbon spherules had better monodispersity, a narrower size distribution and easier graphitization when organic dicarboxylic acids were used as catalysts. The carbon spherules produced using organic dicarboxylic acids as catalysts and their corresponding composites with chemically reduced graphene oxide had unique electrochemical properties when used as active materials for anodes in lithium ion batteries. Possible mechanisms of formation of carbon spherules with different inorganic and organic acids are proposed and their structure–property relationships are discussed.

•AZONs have been successfully implanted in RGO by a simple annealing process.•The AZONs/RGO composites show unique layered structure.•The composites exhibit remarkably enhanced capacity and cycling stability.Al-doped ZnO nanoparticles (AZONs) have been successfully implanted in reduced graphene oxide (RGO) by a simple annealing process. The unique layered structure of composites is obtained, which is mainly ascribed to the well-anchored AZONs on the surface of RGO sheets. As anode materials for lithium ion batteries, the AZONs/RGO composites deliver an initial charge capacity of 624 mA h g−1 and a 100th charge capacity of 391 mA h g−1. Compared to pure AZONs, the remarkably enhanced reversible capacity and cycling stability of the composites could be attributed to the unique structure and the synergistic effect between the AZONs and RGO.

•Au/GQDs composites were uniformly immobilized on Fe3O4 nanoparticles.•Au/GQDs/Fe3O4 efficiently catalyze the solvent-free oxidation of veratryl alcohol.•Fe3O4 made the recovery of Au/GQDs conveniently and enhance their catalytic activity.•The oxidation of veratryl alcohol to veratraldehyde show superb selectivity.Nanocomposites of graphene quantum dots and Au nanoparticles (GQDs/Au) are immobilized on the Fe3O4 nanoparticles, forming GQDs/Au/Fe3O4 ternary composites. The as-prepared ternary composites exhibit superparamagnetic property rendering them easy to be isolated from the reaction mixture. More importantly, they show superb catalytic activity for solvent-free oxidation of VA and other alcohols that contain an aromatic benzyl group, to the corresponding aldehydes exclusively with air as oxidant. The great stability and selectivity of the GQDs/Au/Fe3O4 indicate that they might be applicable catalysts for the oxidation of aromatic alcohols.

Veratryl alcohol can be oxidized to veratryl aldehyde or veratric acid with excellent selectivity and efficient conversion under acidic and alkaline conditions using Au nanoparticles and graphene quantum dot composites (Au/GQDs) as catalysts.

Nanoporous graphene sheets were generated through a simple thermal annealing procedure using composites of ferrocene nanoparticles and graphene oxide sheets as precursors in a large scale. The morphology, composition, and formation mechanism of the as-obtained nanoporous graphene sheets were studied complementarily with scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and other spectroscopy techniques. We found that the density of nanopores on the graphene sheet was determined by the surface distribution of oxygen-containing groups on the original graphene oxide sheets. The coin cells using nanoporous graphene sheets as anode materials showed higher specific lithium ion storage capacity, better discharge/charge rate capability and higher cycling stability when compared to the coin cells with graphene or chemically reduced graphene sheets as anodes.

It was reported that graphene oxide (GO), a novel carbon material with unique structural and chemical/physical properties, could improve the performance of polymerase chain reaction (PCR), similar to many nanomaterials. However, GO, with a large lateral size, exhibits poor biocompatibility, and the mechanism of its effect on PCR remains unclear. Using graphene quantum dots (GQDs) that inherit the basic properties of GO, but with nanometer lateral sizes and much better biocompatibility, we systematically investigated their functional roles in PCR enhancement. The overall performance of PCR in terms of its yield, sensitivity, and specificity can be improved with much less GQDs than of GO. It is found that the stacking of the primers on GQDs improves the sensitivity and specificity of PCR through improving efficiency of base-pairing between the primer and the template. The yield of PCR is improved primarily by GQDs via increasing the activity of polymerase, which is tuned by GQDs through chelating magnesium ions with their peripheral carboxylic groups. The adsorption of the polymerase on GQDs affects marginally the activity of polymerase that is different from the proposed function of GO to PCR. The superb performance of GQDs in PCR exhibits their practical potential in PCR, and thus they can be used in biology and medical applications.

Use of lithium ion batteries (LIBs) has seen rapid growth in recent years, which requires abundant and low-cost electrode materials. Sweet potato is a worldwide dicotyledonous plant and has usually a high yield. In this work, using sweet potatoes as raw materials, carbon nanoparticles were prepared through a hydrothermal carbonization approach followed by high temperature annealing. We demonstrate that with the as-prepared carbon nanoparticles as anode, the lithium ion battery shows a first discharge capacity as high as 965 mA h g−1 at a current rate of 100 mA g−1. Considering the bio-renewable advantage and facile fabrication procedure, carbon nanoparticles derived from sweet potatoes could sustainably satisfy the increasing need for anode materials for LIBs.

A deep understanding of the interaction of a graphene oxide (GO) sheet with cells at the molecular level may expedite its biomedical application and predict its new functions and adverse effects. Herein we inspect the interaction between micrometer-sized GO (mGO), commonly used in biomedical research, and cells at the molecular level through a variety of techniques. A major finding is that, instead of direct cellular penetration, the mGO sheets can stimulate the cellular response by interacting with the membrane protein and the membrane. Specifically, it is illustrated that even within a short exposure time the mGO sheets can induce the formation of vacuoles in the cytosolic compartment and enhance the cell permeability. The vacuolization is only observed in the cells that strongly express aquaporin (AQP1), indicating the specific interaction of the mGO with AQP1. Moreover, inhibition of the AQP1 activity prevents the formation of vacuoles, revealing that the interaction of the mGO with AQP1 occurs most probably at the vestibule of AQP1 at the extracellular side. Additionally, though the cell permeability was enhanced, it only improves the penetration of small molecules, not for macromolecules such as proteins. These findings are potentially valuable in cancer therapy because AQPs are strongly expressed in tumor cells of different origins, particularly aggressive tumors, and it will also be beneficial for drug transport across barrier membranes.Keywords: AQPs; aquaporins; cell membrane; mGO; micrometer-sized graphene oxide;

Novel boron-doped carbon nanosheets were prepared through a facile hydrothermal method using glucose and sodium borohydride as precursors. Taking structural advantage of the as-prepared boron-doped carbon nanosheets, high density Fe3O4 nanoneedle arrays were generated on them, resulting in the composites of boron-doped carbon nanosheets/Fe3O4 nanoneedles. The nanoneedle-like morphology and the unique perpendicular orientation of the Fe3O4 nanoneedles largely suppressed the aggregation of the boron-doped carbon nanosheets in the composites. Therefore, as lithium ion battery anodes, the composites exhibited an excellent lithium ion storage capacity, high rate capability, and decent discharge/charge cycling stability. It was demonstrated that the reversible specific capacity can reach 1132 mA h g−1 at the charge/discharge current density of 0.1 A g−1, and it can be maintained at 980 mA h g−1 after 400 cycles. Even at a high current density of 10 A g−1, the reversible capacity was still retained above 350 mA h g−1, which is much higher than that of other carbon and Fe3O4 composites reported so far. These results render the as-prepared composite as an ideal anode material for high performance lithium ion batteries.

This mini-review highlights selectively the recent research progress in the composites of LiFePO4 and graphene. In particularly, the different fabrication protocols, and the electrochemical performance of the composites are summarized in detail. The structural and morphology characters of graphene sheets that may affect the property of the composites are discussed briefly. The possible ongoing researches in area are speculated upon.

We previously reported that graphene oxide could enhance nuclease activity of copper complex containing aromatic ligands, thus exhibit the potential for applications in anticancer therapy. However, the functional mechanism of graphene oxide is not well understood. In this work, using graphene quantum dots (GQDs), which have smaller lateral size, better biocompatibility, and a conjugate state higher than that of graphene oxide, we investigated systematically the mechanism of GQDs in enhancing nuclease activity of copper complexes. Through a variety of spectroscopic methods, we found that GQDs promote the reduction of copper ions and accelerate their reaction with O2, forming superoxide anions and copper-centered radicals. These active species then oxidize DNA molecules. The improvement in the reduction of copper complexes can be attributed to the coordination of the GQDs to the copper center of the complex, leading to an efficient electron-transfer from the electron-rich GQDs to the copper complexes. The fundamental understanding of the role of the GQDs in DNA cleavage by the transition complexes is promising for the discovery of anticancer therapeutics. More importantly, unique and rich three-dimensional structures of metal complexes also make it possible to prepare highly active DNA cleavage reagents with a high selectivity for DNA sequences and structures.

Mesocrystals usually assume properties differing from that of nanocrystals with the same compositions due to their unique morphologies and size region. In the work, a simple wet chemical procedure was developed for the preparation of mesocrystals consisting of ZnO nanoparticles. By simply mixing the aqueous solutions of zinc acetate [Zn(Ac)2], sodium hydroxide (NaOH), and tartaric acid (TA) at certain temperatures, composites of zinc hydroxide nanoparticles and tartaric acid, Zn(OH)2–TA, with rod-like morphology were obtained. After being annealed in air at certain temperatures, the mesocrystals composed of ZnO nanoparticles were generated, which inherited the rod-like morphology of the Zn(OH)2–TA composites. The chemical composition, crystalline structure and morphology of as-prepared ZnO mesocrystals were characterized using scanning electron microscopy, X-ray powder diffraction, FT-IR, and thermogravimetric analysis. Their photocatalytic properties were also investigated. It was illustrated that, in comparison with the individual ZnO nanoparticles, the ZnO mesocrystals show decent photocatalytic performance to the photodegradation of methyl orange and the photoreduction of Cr6+.

Graphene sheets coated with a thin layer of nitrogen-enriched carbon possess excellent rate capability and cycle performance at various current rates as anodes for LIBs, as the nitrogen-enriched carbon not only incorporates the nitrogen atoms, but also reduces the aggregation of graphene sheets, which can facilitate the storage and transportation of the lithium within the anode.

DNA i-motif structures have been found in telomeric, centromeric DNA and many in the promoter region of oncogenes; thus they might be attractive targets for gene-regulation processes and anticancer therapeutics. We demonstrate in this work that i-motif structures can be stabilized by graphene quantum dots (GQDs) under acidic conditions, and more importantly GQDs can promote the formation of the i-motif structure under alkaline or physiological conditions. We illustrate that the GQDs stabilize the i-motif structure through end-stacking of the bases at its loop regions, thus reducing its solvent-accessible area. Under physiological or alkaline conditions, the end-stacking of GQDs on the unfolded structure shifts the equilibrium between the i-motif and unfolded structure toward the i-motif structure, thus promoting its formation. The possibility of fine-tuning the stability of the i-motif and inducing its formation would make GQDs useful in gene regulation and oligonucleotide-based therapeutics.Keywords: end-stacking; graphene quantum dots; i-motif; induction; stabilization

It is challenging to develop lithium ion batteries (LIBs) possessing simultaneously large reversible capacity, high rate capability, and good cycling stability, which are in turn determined mainly by the component materials of batteries. We designed and synthesized a series of composites of chemically-reduced graphene oxide (CRG) sheets and carbon nanospheres (CNS). It was illustrated that within the as-obtained composites the CNSs were fully cladded and bridged with CRG sheets forming a three-dimensional (3D) network with cavities and pores. Coin cells using the anodes made of the as-obtained composites with appropriate composition exhibit large reversible capacity, high rate capability, and good cycling stability. The highest reversible specific capacity could reach up to 925 mA h g−1 and 604 mA h g−1 at charge–discharge current densities of 5 A g−1 and 10 A g−1, respectively, and faint capacity and rate capability fades were detected even after 200 charge–discharge cycles. The excellent electrochemical performance of the anodes made of the as-obtained composites in the LIBs originates from the unique 3D network structure and the intrinsic properties of CRG and CNS that provide plenty of transportation pathways for electron and Li+, and sufficient tolerant sites for Li/Li+.

A novel coating process of hydrous alumina on organic pigment particles through direct precipitation in aqueous solution was developed in this work. The aqueous suspensions of organic pigment particles were prepared using cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzene sulfonate (SDBS) as additives before the coating. The organic pigment particles were then coated with hydrous alumina using Al2(SO4)3 as precursor. The morphology and surface states of as-coated organic pigment particles were analyzed by high-resolution transmission electron microscopy (HRTEM) and zeta-potential. TEM images showed that a uniform hydrous alumina film could be formed on the organic pigment particle surface with anion surfactant SDBS. However, with cation surfactant CTAB, no alumina coating film was generated on the organic pigment particle surface.Highlights► Organic pigments coating process was highly depended on the surfactants. ► The content of the organic pigment particles reached 200 g/L ► The solvent is deionized water, temperature = 20 °C, and pH = 6. ► The coating condition is moderate. ► The processes can be scaled up easily and economically.

Fe3O4 nanoparticles were generated on chemically reduced graphene oxide (CRG) surfaces through a controlled hydrothermal procedure. The as-synthesised nanoscaled Fe3O4/CRG composites were characterized complementarily using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, and Raman spectroscopy. It was illustrated that the initial ratio of Fe2+/GO, the pH of reaction solution, and the hydrothermal reaction time all affect the morphology of the nanoscaled Fe3O4 in the composites. The electrical and magnetic characteristics of Fe3O4/CRG composite were studied systematically. The results indicate that the GO sheets were reduced by Fe(OH)2 and their electronic conjugation states were restored readily during the hydrothermal process. This might be developed as a scalable route to prepare magnetic Fe3O4/CRG nanocomposites.

A glass carbon (GC) electrode has been modified with horseradish peroxidase (HRP) molecules, which are immobilized on the partially reduced graphene oxide (PCRG). The surface properties of the as-modified electrode are characterized with scanning electron microscopy (SEM), the electrochemical characteristics of the as-modified electrode are studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). We demonstrated that the PCRG can promote the electron transfer between HRP and GC electrode, and the immobilized HRP maintained its catalytic activity of the decomposition of phenol and p-chlorophenol. The GC electrode modified with PCRG immobilized HRP exhibits better electrochemical property over CRG, the modified electrode may find practical application as enzyme-based amperometric sensors used for detections of phenolic molecules or other permanent organic pollutants in water. The method provides a strategy for preparation of a sensitive amperometric sensor for the detection of phenolic compounds and other permanent organic pollutants.Graphical abstractThe modification of glass carbon electrode with horseradish peroxidase immobilized on partially reduced graphene oxide can promote the electron transfer between HRP and GC electrode, and the catalytic activity of HRP for the decomposition of H2O2, phenol and p-chlorophenol in water.Highlights► PCRG can be used to modify electrode. ► PCRG can promote the electron transfer between enzyme and GC electrode. ► Modified electrode maintained highly catalytic activity. ► These amperometric sensors can be used to detect H2O2 and phenolic compounds.

Graphene quantum dots (GQDs) are great promising in various applications owing to the quantum confinement and edge effects in addition to their intrinsic properties of graphene, but the preparation of the GQDs in bulk scale is challenging. We demonstrated in this work that the micrometer sized graphene oxide (GO) sheets could react with Fenton reagent (Fe2+/Fe3+/H2O2) efficiently under an UV irradiation, and, as a result, the GQDs with periphery carboxylic groups could be generated with mass scale production. Through a variety of techniques including atomic force microscopy, X-ray photoelectron spectroscopy, gas chromatography, ultraperformance liquid chromatography–mass spectrometry, and total organic carbon measurement, the mechanism of the photo-Fenton reaction of GO was elucidated. The photo-Fenton reaction of GO was initiated at the carbon atoms connected with the oxygen containing groups, and C–C bonds were broken subsequently, therefore, the reaction rate depends strongly on the oxidization extent of the GO. Given the simple and efficient nature of the photo-Fenton reaction of GO, this method should provide a new strategy to prepare GQDs in mass scale. As a proof-of-concept experiment, the novel DNA cleavage system using as-generated GQDs was constructed.Keywords: DNA cleavage; graphene quantum dot; photo-Fenton reaction

The enhancement of DNA affinity of small molecules usually ensures their high nuclease activities, and may also open a new scope of their applications in biology and medicine. In this work, we demonstrate that the nuclease activity and cytotoxicity of the small DNA intercalators can be dramatically enhanced by single atomic-layered graphene oxide (GO) sheets. Through π–π stacking interaction mainly between GO and the aromatic ligands of intercalators, the conjugates of GO and a small intercalator could be formed. Because of the large planar structure of the GO sheets, the coupling of GO with the small intercalators increased their affinity to DNA. Owing to the formation of conjugates with GO, the binding site of small intercalators to DNA was also changed from a minor groove to a major groove. Notably, GO and small intercalator conjugates exhibited higher cytotoxicity than that of the small intercalator alone. The results open up potential applications of GO for new chemotherapeutic agents that work through DNA intercalation.

Investigation into the interactions between graphene oxide (GO) and biomolecules is very important for broad applications of GO in bioassay and bioanalysis. In this work, we describe the interactions between double-stranded DNA (dsDNA) and GO. We demonstrated that dsDNA can bind to GO forming complexes (dsDNA/GO) in the presence of certain salts, which protects dsDNA from being enzymatically digested. On the other hand, we found that a nonionic surfactant, such as triton X-100, can block the formation of dsDNA/GO complexes, so that the enzymatic digestion of dsDNA is restored. These results lead us to believe that the reason for GO protecting dsDNA from enzymatic digestion is the formation of dsDNA/GO complexes hindering the access of DNA enzymes to dsDNA, rather than direct inactivation of the DNA enzymes.

Bulk-scale production of individual graphene sheets is still challenging although several methodologies have been developed. We report here a rapid and cost-effective approach to reduction of graphene oxide (GO) using hydroxylamine as a reductant. We demonstrated that the reduction of GO with hydroxylamine could take place quickly under a mild condition, and the as-produced graphene sheet showed high electrical conductivity, fair crystalline state, and admirable aqueous dispersibility without using any stabilizing reagents. A mechanism for removal of epoxide and hydroxyl groups from GO by hydroxylamine has been proposed. Comparing with other reported methods, the reduction of GO with hydroxylamine should be a preferable route to bulk-scale production of the graphene because it is simple, efficient, and cost-effective.

Individual nanocomposite sheets of chemically reduced graphene oxide (CRG) and poly(N-vinyl pyrrolidone) (PVP), namely CRG/PVP, have been fabricated through a simple one-pot procedure. The structure and composition of the as-prepared CRG/PVP sheets were complementarily characterized using solid-state 13C NMR, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and other spectroscopic measurements, demonstrating that the PVP molecules were chemically grafted on the CRG surfaces. The electrical conductivity of the individual CRG/PVP sheets was measured at different levels of relative humidity (RH) using a conductive atomic force microscopy (CAFM) system, revealing that the electrical conductivity of a CRG/PVP sheet is sensitive to RH variation with a response time of a few seconds. Given the easy mass scale production and improved electrical conductivity, we envisage that the CRG/PVP nanocomposite sheets should have a broad spectrum of applications in electrical conductivity based sensors.

This review describes recent progress in creation of nanojunctions between individual nanoobjects. The accomplishments of various strategies used for nanojunction creation are highlighted and the corresponding challenges are discussed. The possible ongoing development for the creation of device-oriented nanojunctions is speculated upon.

We demonstrated that the individual graphene oxide sheets can be readily reduced under a mild condition using L-ascorbic acid (L-AA). This simple approach should find practical applications in large scale production of water soluble graphene.

We reported a composite electrolyte prepared by incorporating layered α-titanium phosphate (α-TiP) into a binary ionic liquid of 1-propyl-3-methylimidazolium iodide (PMII) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) (volume ratio, 13:7) electrolyte. The addition of α-TiP markedly improved the photovoltaic properties of dye-sensitized solar cells (DSSCs) compared to that without α-TiP. The enhancement was explained by improved diffusion of tri-iodide (I3-) ions, suppressed electron recombination with I3- in the electrolyte and increased lifetime of electrons in mesoscopic TiO2 film.

Determination of triiodide diffusion coefficient, charge-transfer resistance and photovoltaic performance of the binary ionic liquid electrolyte of 1-methyl-3-propylimidazolium iodide (MPII) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) for dye-sensitized solar cells (DSSCs) were performed at varying volume ratios of MPII/EMIMBF4. Compared to pure MPII ionic liquid, the addition of EMIMBF4 not only increased triiodide diffusion coefficient, but also decreased charge-transfer resistance at Pt/electrolyte interface, leading to the notably improved photovoltaic performance of DSSC. The highest photoelectric conversion efficiency of 4.99% was obtained under light intensity of 100 mW/cm2 for the DSSC with the binary MPII/EMIMBF4 ionic liquid electrolyte when the volume ratio of MPII/EMIMBF4 was 50/50, which was much higher than that of pure MPII ionic liquid electrolyte (2.6%).

Graphene oxide (GO), having a large specific surface area and abundant functional groups, provides an ideal substrate for study enzyme immobilization. We demonstrated that the enzyme immobilization on the GO sheets could take place readily without using any cross-linking reagents and additional surface modification. The atomically flat surface enabled us to observe the immobilized enzyme in the native state directly using atomic force microscopy (AFM). Combining the AFM imaging results of the immobilized enzyme molecules and their catalytic activity, we illustrated that the conformation of the immobilized enzyme is mainly determined by interactions of enzyme molecules with the functional groups of GO.

The exploration of efficient DNA intercalative agents (intercalators) is essential for understanding DNA scission, repair, and signal transduction. In this work, we explored systematically the graphene oxide (GO) interaction with DNA molecules using fluorescence spectroscopic (FL) and circular dichroism (CD) studies, gel electrophoresis, and DNA thermal denaturation. We demonstrated that the GO nanosheets could intercalate efficiently into DNA molecules. Significantly, we illustrated that the scission of DNA by GO sheets combining with copper ions could take place pronouncedly. The scission of DNA by the GO/Cu2+ system is critically dependent on the concentrations of GO and Cu2+ and their ratio. DNA cleavage ability exhibited by the GO with several other metal ions and the fact that GO/Cu2+-cleaved DNA fragments can be partially relegated suggest that the mechanism of DNA cleavage by the GO/metal ion system is oxidative and hydrolytic. The result reveals that the GO/Cu2+ could be used as a DNA cleaving system that should find many practical applications in biotechnology and as therapeutic agents.Keywords: copper ion; DNA cleavage; DNA intercalation; graphene oxide; metal ions

Composition, morphology, and surface characteristics of solid substrates play critical roles in regulating immobilized enzyme activity. Grapheme oxide (GO), a novel nanostructured material, has been illustrated as an ideal enzyme immobilization substrate due to its unique chemical and structural properties. Physical properties and catalytic activity of GO immobilized horseradish peroxidase (HRP) and its application in phenolic compound removal are described in the present study. HRP loading on GO was found to be much higher than that on reported substrates. The GO immobilized HRP showed improved thermal stability and a wide active pH range, attractive for practical applications. The removal of phenolic compounds from aqueous solution using the GO immobilized HRP was explored with seven phenolic compounds as model substrates. The GO immobilized HRP exhibited overall a high removal efficiency to several phenolic compounds in comparison to soluble HRP, especially for 2,4-dimetheoxyphenol and 2-chlorphenol, the latter a major component of industrial wastewater.

Creating micropatterns of electrically conductive polymers on solid substrates is important for the low-cost construction of organic microelectronic devices. This work develops a novel strategy for the preparation of large-area polypyrrole (Ppy) micropatterns through area-selected in situ electropolymerization of pyrrole within microchannels. The effects on micropattern formation of electropolymerization procedures such as dynamic potential polymerization (DPP), static potential polymerization (SPP), and constant current polymerization (CCP), the solvent, and the polymerization time were studied systematically. The electrical conductivities of the Ppy micropatterns were measured and compared with a homogeneous Ppy thin film synthesized under the same conditions. Given the straightforward and versatile nature of this method, it is expected to contribute greatly to the convenient fabrication of low-cost organic microelectronic devices.

Control on the morphology, including the size and shape of individual legs, of tetrapod ZnO nanocrystals is of importance for tuning their properties. We studied systematically the influences of the Zn vapor oxidization time and temperature, the ZnO condensation time and temperature on the morphologies of tetrapod ZnO nanocrystals fabricated through zinc vapor oxidization followed by ZnO condensation. We found that the variation of ZnO condensation temperature and time can change the tetrapod ZnO nanocrystal growing behavior dramatically. The increase of the condensation time leads to the morphology transition of the tetrapod legs from hierarchical hexagonal (HH) to uniform hexagonal (UH) prism. The tetrapod ZnO nanocrystal with uniform UH prism legs can only be obtained at relatively higher condensation temperature and longer condensation time. While the Zn vapor oxidization time and temperature do not affect the morphology of the tetrapod ZnO nanocrystals noticeably.

We report herein a facile method for the preparation of sodium tungsten bronzes hollow nanospheres using hydrogen gas bubbles as reactant for chemical reduction of tungstate to tungsten and as template for the formation of hollow nanospheres at the same time. The chemical composition and the crystalline state of the as-prepared hollow Na0.15WO3nanospheres were characterized complementarily, and the hollow structure formation mechanism was proposed. The hollow Na0.15WO3nanospheres showed large Brunauer–Emment–Teller specific area (33.8 m2 g−1), strong resistance to acids, and excellent ability to remove organic molecules such as dye and proteins from aqueous solutions. These illustrate that the hollow nanospheres of Na0.15WO3should be a useful adsorbent.

We reported a composite electrolyte prepared by incorporating layered α-titanium phosphate (α-TiP) into a binary ionic liquid of 1-propyl-3-methylimidazolium iodide (PMII) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) (volume ratio, 13:7) electrolyte. The addition of α-TiP markedly improved the photovoltaic properties of dye-sensitized solar cells (DSSCs) compared to that without α-TiP. The enhancement was explained by improved diffusion of tri-iodide (I3-) ions, suppressed electron recombination with I3- in the electrolyte and increased lifetime of electrons in mesoscopic TiO2 film.

Individual nanocomposite sheets of chemically reduced graphene oxide (CRG) and poly(N-vinyl pyrrolidone) (PVP), namely CRG/PVP, have been fabricated through a simple one-pot procedure. The structure and composition of the as-prepared CRG/PVP sheets were complementarily characterized using solid-state 13C NMR, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and other spectroscopic measurements, demonstrating that the PVP molecules were chemically grafted on the CRG surfaces. The electrical conductivity of the individual CRG/PVP sheets was measured at different levels of relative humidity (RH) using a conductive atomic force microscopy (CAFM) system, revealing that the electrical conductivity of a CRG/PVP sheet is sensitive to RH variation with a response time of a few seconds. Given the easy mass scale production and improved electrical conductivity, we envisage that the CRG/PVP nanocomposite sheets should have a broad spectrum of applications in electrical conductivity based sensors.

We demonstrated that the individual graphene oxide sheets can be readily reduced under a mild condition using L-ascorbic acid (L-AA). This simple approach should find practical applications in large scale production of water soluble graphene.

Veratryl alcohol can be oxidized to veratryl aldehyde or veratric acid with excellent selectivity and efficient conversion under acidic and alkaline conditions using Au nanoparticles and graphene quantum dot composites (Au/GQDs) as catalysts.

Novel boron-doped carbon nanosheets were prepared through a facile hydrothermal method using glucose and sodium borohydride as precursors. Taking structural advantage of the as-prepared boron-doped carbon nanosheets, high density Fe3O4 nanoneedle arrays were generated on them, resulting in the composites of boron-doped carbon nanosheets/Fe3O4 nanoneedles. The nanoneedle-like morphology and the unique perpendicular orientation of the Fe3O4 nanoneedles largely suppressed the aggregation of the boron-doped carbon nanosheets in the composites. Therefore, as lithium ion battery anodes, the composites exhibited an excellent lithium ion storage capacity, high rate capability, and decent discharge/charge cycling stability. It was demonstrated that the reversible specific capacity can reach 1132 mA h g−1 at the charge/discharge current density of 0.1 A g−1, and it can be maintained at 980 mA h g−1 after 400 cycles. Even at a high current density of 10 A g−1, the reversible capacity was still retained above 350 mA h g−1, which is much higher than that of other carbon and Fe3O4 composites reported so far. These results render the as-prepared composite as an ideal anode material for high performance lithium ion batteries.

It is challenging to develop lithium ion batteries (LIBs) possessing simultaneously large reversible capacity, high rate capability, and good cycling stability, which are in turn determined mainly by the component materials of batteries. We designed and synthesized a series of composites of chemically-reduced graphene oxide (CRG) sheets and carbon nanospheres (CNS). It was illustrated that within the as-obtained composites the CNSs were fully cladded and bridged with CRG sheets forming a three-dimensional (3D) network with cavities and pores. Coin cells using the anodes made of the as-obtained composites with appropriate composition exhibit large reversible capacity, high rate capability, and good cycling stability. The highest reversible specific capacity could reach up to 925 mA h g−1 and 604 mA h g−1 at charge–discharge current densities of 5 A g−1 and 10 A g−1, respectively, and faint capacity and rate capability fades were detected even after 200 charge–discharge cycles. The excellent electrochemical performance of the anodes made of the as-obtained composites in the LIBs originates from the unique 3D network structure and the intrinsic properties of CRG and CNS that provide plenty of transportation pathways for electron and Li+, and sufficient tolerant sites for Li/Li+.