High quality graphene sheets have been considered as a promising candidate in several industrial applications due to their excellent electronic and thermal conductivity. However, the mass production of high quality graphene sheets from graphite bulk is still facing great challenges. Here we demonstrated a new approach to prepare high quality graphene by mixing a solution of oxalic acid and hydrogen peroxide as the electrolyte. The reaction did not involve the oxidation of graphite and thus exfoliated graphene possesses a uniform lateral size (2–6 μm, 78.1%), low oxygen content (2.41 at. %), few structure defects, and high conductivity of 26 692 S m–1. The optimized mixed electrolyte is environmental friendly, cheap and safe, and most importantly it is easy to be removed through low temperature heating, which facilitates graphene purification. An electrothermal heater, made from highly concentrated graphene ink (8.5 mg mL–1) on A4-size paper or polyester, exhibits excellent performance: a rapid rise of temperature (up to 75.2 °C) in a short time (30 s) under a low voltage of 10 V. The as-made graphene is considered as a promising material for future application of printable electronics and wearable devices.

Aided by Oxone, water-dispersible graphene of 2–5 atomic layers was electrochemically fabricated from graphite in one step without any extra stabilizers or additives. Oxone as a novel electrolyte and the electrochemically enhanced oxidation were responsible for the excellent aqueous dispersibility, effective exfoliation and the reasonably high yield (up to 60.1%).

Graphene has initiated intensive research efforts on 2D crystalline materials due to its extraordinary set of properties and the resulting host of possible applications. Here the authors report on the controllable large-scale synthesis of C3N, a 2D crystalline, hole-free extension of graphene, its structural characterization, and some of its unique properties. C3N is fabricated by polymerization of 2,3-diaminophenazine. It consists of a 2D honeycomb lattice with a homogeneous distribution of nitrogen atoms, where both N and C atoms show a D6h-symmetry. C3N is a semiconductor with an indirect bandgap of 0.39 eV that can be tuned to cover the entire visible range by fabrication of quantum dots with different diameters. Back-gated field-effect transistors made of single-layer C3N display an on–off current ratio reaching 5.5 × 1010. Surprisingly, C3N exhibits a ferromagnetic order at low temperatures (<96 K) when doped with hydrogen. This new member of the graphene family opens the door for both fundamental basic research and possible future applications.

Scalable fabrication of water-dispersible graphene (W-Gr) is highly desirable yet technically challenging for most practical applications of graphene. Herein, a green and mild oxidation strategy to prepare bulk W-Gr (dispersion, slurry, and powder) with high yield was proposed by fully exploiting structure defects of thermally reduced graphene oxide (TRGO) and oxidizing radicals generated from hydrogen peroxide (H2O2). Owing to the increased carboxyl group from the mild oxidation process, the obtained W-Gr can be redispersed in low-boiling solvents with a reasonable concentration. Benefiting from the modified surface chemistry, macroscopic samples processed from the W-Gr show good hydrophilicity (water contact angle of 55.7°) and excellent biocompatibility, which is expected to be an alternative biomaterial for bone, vessel, and skin regeneration. In addition, the green and mild oxidation strategy is also proven to be effective for dispersing other carbon nanomaterials in a water system.Keywords: biomaterial; dispersibility; graphene; hydroxyl radical; reduced graphene oxide;

A thorough investigation of the oxidation mechanism of sp2–sp3 hybrid carbon materials is helpful for the morphological trimming of graphene. Here, porous graphene (PGN) was obtained via a free radical oxidation process. We further demonstrated the difference between traditional and free radical oxidation processes in sp2–sp3 hybrid carbon materials. The sp3 part of graphene oxide was oxidized first, and well-crystallized sp2 domains were reserved, which is different from the oxidation mechanism in a traditional approach. The obtained PGN shows excellent performance in the design of PGN-based detectable molecule separation or other biomedical applications.

Correction for ‘Photoinduced electron transfer of poly(o-phenylenediamine)–rhodamine B copolymer dots: application in ultrasensitive detection of nitrite in vivo’ by Fang Liao et al., J. Mater. Chem. A, 2015, 3, 7568–7574.

A homologous, metal-free electrolyzer in both acidic and alkaline media was developed, consisting of self-supported carbon nitride/carbon nanotube/carbon fiber (C3N4–CNT–CF) and sulfur-doped carbon nitride/carbon nanotube/carbon fiber (S-C3N4–CNT–CF) as oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, respectively. The self-supported C3N4–CNT–CF electrode was proven to be an effective catalyst for the OER, due to the high N content of carbon nitride sheets and enhanced charge transport ability by the synergistic effect between the well-designed three-dimensional hierarchical carbon network and layered carbon nitride. In the meantime, the S-C3N4–CNT–CF was also proven to be an efficient, stable metal-free electrode for the HER. The homologous C3N4–CNT–CF||S-C3N4–CNT–CF water splitting system presents low onset potential and good stability in both acidic and alkaline media, indicating a potential carbon-based, metal-free full water splitting electrolyzer with low cost.

Graphene derivatives (such as graphene oxide and hydrogenated graphene) have been widely investigated because of their excellent properties. Here, we report large-scale (kilogram scale) synthesis of a new unique graphene derivative: hydroxylated graphene (G-OH). The exclusive existence form of oxygen-containing groups in G-OH is hydroxyl, which was verified by spectral characterization and quantitative halogenating reaction. It is very interesting that both the wettability and electrical conductivity show reversible change in halogenating and hydrolysis reaction cycles, which demonstrates the versatility of G-OH. Most importantly, the hydrophilicity and weak inductive nature of G-OH provides a well microenvironment for the cells adhesion and proliferation. On G-OH paper, rat adipose tissue-derived stromal cells exhibited a typical fibroblast-like shape with high rate of increase and survival after 3 day of incubation. This G-OH paper with good mechanical property is expected to be a new biomaterial for bone, vessel and skin regeneration.Keywords: biomaterial; graphene derivative; hydroxylated graphene; regeneration; reversible

We developed a universal method to prepare hydrophilic carbon nitrogen (C3N4) nanosheets. By treating C3N4 nanosheets with oxygen plasma, hydroxylamine groups (N–OH) with intense protonation could be introduced on the surface; moreover, the content of N–OH groups increased linearly with the oxygen-plasma treatment time. Thanks to the excellent hydrophilicity, uniformly dispersed C3N4 solution were prepared, which was further translated into C3N4 paper by simple vacuum filtration. Pure C3N4 paper with good stability, excellent hydrophilicity, and biocompatibility were proved to have excellent performance in tissue repair. Further research demonstrated that the oxygen-plasma treatment method can also introduce N–OH groups into other nitrogen-containing carbon materials (NCMs) such as N-doped graphene, N-doped carbon nanotube, and C2N, which offers a new perspective on the surface modification and functionalization of these carbon nanomaterials.Keywords: C3N4; excellent hydrophilicity; nitrogen-containing carbon materials; oxygen-plasma treatment; tissue repair

The graphene quantum dot based fluorescent probe community needs unambiguous evidence about the control on the ion selectivity. In this paper, polyethylene glycol modified N-doped graphene quantum dots (PN-GQDs) were synthesized by alkylation reaction between graphene quantum dots and organic halides. We demonstrate the tunable selectivity and sensitivity by controlling the supramolecular recognition through the length and the end group size of the polyether chain on PN-GQDs. The relationship formulae between the selectivity/detection limit and polyether chains are experimentally deduced. The polyether chain length determines the interaction between the PN-GQDs and ions with different ratios of charge to radius, which in turn leads to a good selectivity control. Meanwhile the detection limit shows an exponential growth with the size of end groups of the polyether chain. The PN-GQDs can be used as ultrasensitive and selective fluorescent probes for Li+, Na+, K+, Mg2+, Ca2+ and Sr2+, respectively.

Dispersing graphene in various solvents is one of the key technologies toward the practical applications of graphene. Herein, using graphene quantum dots (GQDs) as stabilizer, aqueous dispersions of graphene with good stability were demonstrated by directly dispersing commercialized graphene powder into water. Amazingly, 100 mg of graphene powder could be stabilized by an average of merely 7.8 mg GQDs to form aqueous dispersions with a maximum concentration of up to 0.4 mg/mL and stability at least 3 months. The introduction of a small amount of GQDs also allowed for the fabrication of water-redispersible graphene slurry and powder, which would largely facilitate the transportation and applications of graphene. The mechanism of the GQDs stabilized graphene in water was proposed and experimentally verified through UV–visible spectroscopy and zeta potential measurements. Moreover, flexible graphene papers directly assembled from the water-dispersible graphene exhibited controllable thickness, good conductivity, and acceptable strength. With properties not compromised by GQDs, water-dispersible graphene is expected to be widely applicable in electrical and electrochemical device fields.

A new reversible fluorescent switch for the detection of oxidative hydroxyl radical (•OH) and reductive glutathione (GSH) was designed based on the use of selenium doped graphene quantum dots (Se-GQDs). The Se-GQDs have a thickness of 1–3 atomic layers, a lateral size of 1–5 nm, a quantum yield of 0.29, and a photoluminescence lifetime of 3.44 ns, which ensured a high selectivity and stability for the fluorescent switch. The fluorescence of Se-GQDs was reversibly quenched and recovered by •OH and GSH, respectively, because of the reversible oxidation of C–Se groups and reduction of Se–Se groups. This brand-new GQD-based fluorescent switch gave a rapid response when tested in both aqueous solutions and living HeLa cells. In particular, the detection limit for •OH was only 0.3 nM, which was much lower than that in switches made from organic dyes.

We demonstrate a new semiconducting polymer dot: the poly(o-phenylenediamine)–Rhodamine B copolymer dot (Pp–RhB dot), which emits in the red wavelength range. The Pp–RhB dots can be used as an ultrasensitive fluorescence probe for NO2−in vivo and show high selectivity and ultrasensitivity (detection limit: 2.0 × 10−11 M) for NO2−. The fluorescence of Pp–RhB dots is decreased (φ = 0.014) as a result of fast photoinduced electron transfer (PET) between the modulator (poly(o-phenylenediamine)) and the transducer (RhB), but the N–NO2 bonding mode prevents PET, causing the fluorescence emission to be enhanced (φ = 0.92). This probe effectively avoids the influence of auto-fluorescence in biological systems and gave positive results when tested in both aqueous solution and living cells.

We synthesized nitrogen-doped graphene quantum dots (N-GQDs) under a high temperature range of 800–1200 °C and high pressure of 4.0 GPa through a solid-to-solid process. The graphite N in N-GQDs has a strong negative induction effect on the band gap. Without the interference of surface groups, the direct band gap of these N-GQDs increased with increased nitrogen doping, resulting in tunable photoluminescence (PL) with a high PL efficiency. Based on the recognized PL rules, we synthesised N-GQDs with a higher doping concentration and near ultraviolet light-emittance.

We demonstrated that graphene oxide (GO) can be oxidized and cut into graphene quantum dots (GQDs) by hydroxyl radicals (˙OH), which is obtained by the catalytic decomposition of hydrogen peroxide (H2O2) with a tungsten oxide nanowire (W18O49) catalyst. The clean oxidizing agent (H2O2) and the solid catalyst lead to a simple GQD preparing method without any by-products. The obtained GQD aqueous solution can be directly applied to fluorescence imaging in vitro without any further purification. The effect of the W18O49 catalyst on the ˙OH formation is discussed, and the size of GQDs can be controlled via changing the concentration of hydroxyl radicals.

Urea-assisted aqueous exfoliation of graphite was found to be more efficient than exfoliation in N,N-dimethylformamide (DMF), and high-quality graphene was obtained with a yield up to 2.4%. The mechanism in which a primary amine facilitates aqueous exfoliation was proposed and experimentally validated, which may inspire new strategies for efficient liquid exfoliation.

We report triphenylphosphine (P(Ph)3) modified graphene quantum dots (P-GQDs) with high quantum yield (c) and excellent stability. The light energy absorbed by P(Ph)3 groups can quickly and efficiently transfer to the GQDs through the C–P-(Ph)3 bonds, resulting in a high φ. The obtained P-GQDs have a tunable photoluminescence wavelength from blue to red, and at the same time maintain a high φ, over 58%, with increase of permittivity of the solvents. The main mechanism of full-visible-light-spectrum modulation could be due to the energy loss and electron-donating decrease caused by P(Ph)3 group–solvent interaction or relaxation.

Rapid thermal exfoliation/reduction of graphite oxide is a fast and easy method among the oxidation–reduction approaches for graphene synthesis. In this research, we firstly demonstrated that graphene can be obtained with a surface area of 550 to 700 m2 g−1 and a yield of approximately 50% through one-step rapid thermal treatment in air from 450 to 550 °C, without vacuum or protective gas through a self-protection process. Then, we further demonstrated the effective two-step thermal annealing to significantly improve the C/O ratio from ca. 7.3 to 25.9 in air at the relatively low temperature of 600 °C. The smart self-protecting and enhanced-oxygen-removal mechanisms were discussed.

•We reported the shortest emission wavelength GQDs for solution-based inorganic and organic quantum dots.•The fluorescent quantum yield is high (φ = 0.63).•The strong negative inductive effect of Fe is confirmed by experiments.•These GQDs have good stability.•These GQDs have low in vitro cytotoxicity.It is necessary to broaden the finite band gap of the graphene quantum dots (GQDs) and prepare deep ultraviolet emission GQDs with high luminescence efficiency. In this study, the deep ultraviolet emission ferric passivated GQDs (Fe-GQDs) are successfully prepared. Due to the strong negative inductive effect of Fe, the band gap of the Fe-GQDs was broadened, and the photoluminescence emission wavelength is 275 nm for an excitation at 224 nm with a very high fluorescent quantum yield (φ = 0.63). This is the shortest emission wavelength reported for solution-based inorganic and organic quantum dots. The high efficient ultraviolet emission, as well as the good stability and low in vitro cytotoxicity, may facilitate their applications to carbon-based light-emitting devices and lasers.

Carbon quantum dots (CQDs) have been intensively investigated due to their interesting electrochemical and photoluminescent properties. Here, we report a novel method for large-scale preparation of heavy doped CQDs with tunable photoluminescence. In the present synthetic process, the carbon nanoparticles from Chinese ink were oxidized and cut simultaneously using a mature process to obtain oxidized-CQDs as precursors, and then the heteroatom (N, S or Se) doped CQDs were obtained by a one-step hydrothermal reduction and in situ doping treatment. The heavy doped CQDs are just 1–6 nm size, and have improved photoluminescence with different emission wavelengths, higher quantum yield, longer lifetime and good photostability. Further experiments suggested that these N and S doped CQDs were very sensitive for the detection of Cu2+ and Hg2+, respectively.

A light, 3-D, porous aerogel was fabricated by way of a simple approach from 1-D tungsten oxide nanowires and 2-D reduced graphene oxide sheets. The as-prepared graphene oxide, tungsten oxide nanowires, and tungsten oxide-reduced graphene oxide (W18O49-RGO) aerogel were characterised. The photocatalytic activities of as-prepared aerogel under visible light irradiation were investigated through the degradation of six different organic dyes including Rhodamine B, reactive black 39, reactive yellow 145, weak acid black BR, methyl orange, and weak acid yellow G. In comparison with the pure W18O49 nanowires, the prepared W18O49-RGO aerogel had significantly improved photocatalytic efficiency. Also, the photocatalysis of W18O49-RGO aerogel maintained its efficiency after 30 cycles for each of the six dyes. The photocatalytic mechanism was studied by adding hole and radical scavengers: the results confirmed that the holes generated in W18O49-RGO aerogel played a key role in the visible light photocatalytic process.

•Co3O4 nanocube/RGO composite paper has been firstly synthesized by a simple process.•The average edge length of the Co3O4 nanocubes onto RGO is about 200 nm.•The maximum RL of Co3O4/RGO composite is −32.3 dB at 12.4 GHz with a thickness of 2.5 mm.•The absorption bandwidth of Co3O4/RGO composite with the RL below −10 dB is 10.5 GHz.The Co3O4 nanocube/reduced graphene oxide (Co3O4/RGO) composite paper has been firstly fabricated via a simple process. Several analytical techniques including X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been employed to characterize the Co3O4/RGO composite. The results indicated that the Co3O4 nanocubes attached to the RGO sheets, and that the average edge length of Co3O4 nanocubes is about 200 nm. The obtained composite exhibited a maximum reflection loss of −32.3 dB at 12.4 GHz with a coating layer thickness of 2.5 mm, and the effective absorption bandwidth with reflection loss less than −10 dB is up to 10.5 GHz (from 5.5 to 16.0 GHz) when an appropriate absorber thickness between 2 and 5 mm is chosen. Such high microwave absorption composite can be used as promising candidate for the new type of electromagnetic wave absorptive material.

Several molten metals and their alloys were used for graphene growth by atmosphere pressure chemical vapor deposition. It was found that liquid gallium (Ga) has very effective catalytic ability for graphene formation. Graphene with a controllable thickness and quality can be synthesized on a molten Ga surface only in a few minutes. Compared to solid catalysts, several new and unexpected results have been observed on Ga surface including graphene formation on a liquid surface at high temperature and keeping on a liquid surface at room temperature, time-dependent thickness control and a decrease in quality with increasing hydrogen flow. These growth characteristics can be attributed to the distinct differences in physical/chemical properties of liquid catalysts versus solids, and consequently distinct catalytic behaviors with the precursor gas. Other molten metals and alloys, including indium, tin, tin–nickle and tin–copper etc., were also explored for graphene synthesis. Use of liquid catalysts opens a new window for graphene synthesis.

In this paper, we present evidences of nanoparticle deposition on porous anodic alumina (PAA) surface under different anodizing conditions, and discuss the formation mechanism of precipitations. Low-temperature anodization, vigorous stirring and ultrasound-assisted anodization are proposed to reduce the hydrolysis product or hinder its deposition on the surface as well as inside nanopores of PAA. It is discovered that the ultrasound is very efficient to prevent the deposition of Al3+ hydrolysis product on PAA. This study is of great value for realizing ordered PAAs with clean surface.Highlights► Nanoparticle deposition during anodizing aluminum is revealed. ► The Al3+ ions come out continuously, and some hydrolyze to be solid deposition. ► Low temperature, stirring and ultrasound are used to reduce the deposition. ► Ultrasound is very effective to reduce nanoparticle deposition.

Urea-assisted aqueous exfoliation of graphite was found to be more efficient than exfoliation in N,N-dimethylformamide (DMF), and high-quality graphene was obtained with a yield up to 2.4%. The mechanism in which a primary amine facilitates aqueous exfoliation was proposed and experimentally validated, which may inspire new strategies for efficient liquid exfoliation.

We synthesized nitrogen-doped graphene quantum dots (N-GQDs) under a high temperature range of 800–1200 °C and high pressure of 4.0 GPa through a solid-to-solid process. The graphite N in N-GQDs has a strong negative induction effect on the band gap. Without the interference of surface groups, the direct band gap of these N-GQDs increased with increased nitrogen doping, resulting in tunable photoluminescence (PL) with a high PL efficiency. Based on the recognized PL rules, we synthesised N-GQDs with a higher doping concentration and near ultraviolet light-emittance.

Carbon quantum dots (CQDs) have been intensively investigated due to their interesting electrochemical and photoluminescent properties. Here, we report a novel method for large-scale preparation of heavy doped CQDs with tunable photoluminescence. In the present synthetic process, the carbon nanoparticles from Chinese ink were oxidized and cut simultaneously using a mature process to obtain oxidized-CQDs as precursors, and then the heteroatom (N, S or Se) doped CQDs were obtained by a one-step hydrothermal reduction and in situ doping treatment. The heavy doped CQDs are just 1–6 nm size, and have improved photoluminescence with different emission wavelengths, higher quantum yield, longer lifetime and good photostability. Further experiments suggested that these N and S doped CQDs were very sensitive for the detection of Cu2+ and Hg2+, respectively.

We demonstrate a new semiconducting polymer dot: the poly(o-phenylenediamine)–Rhodamine B copolymer dot (Pp–RhB dot), which emits in the red wavelength range. The Pp–RhB dots can be used as an ultrasensitive fluorescence probe for NO2−in vivo and show high selectivity and ultrasensitivity (detection limit: 2.0 × 10−11 M) for NO2−. The fluorescence of Pp–RhB dots is decreased (φ = 0.014) as a result of fast photoinduced electron transfer (PET) between the modulator (poly(o-phenylenediamine)) and the transducer (RhB), but the N–NO2 bonding mode prevents PET, causing the fluorescence emission to be enhanced (φ = 0.92). This probe effectively avoids the influence of auto-fluorescence in biological systems and gave positive results when tested in both aqueous solution and living cells.

We demonstrated that graphene oxide (GO) can be oxidized and cut into graphene quantum dots (GQDs) by hydroxyl radicals (˙OH), which is obtained by the catalytic decomposition of hydrogen peroxide (H2O2) with a tungsten oxide nanowire (W18O49) catalyst. The clean oxidizing agent (H2O2) and the solid catalyst lead to a simple GQD preparing method without any by-products. The obtained GQD aqueous solution can be directly applied to fluorescence imaging in vitro without any further purification. The effect of the W18O49 catalyst on the ˙OH formation is discussed, and the size of GQDs can be controlled via changing the concentration of hydroxyl radicals.

Correction for ‘Photoinduced electron transfer of poly(o-phenylenediamine)–rhodamine B copolymer dots: application in ultrasensitive detection of nitrite in vivo’ by Fang Liao et al., J. Mater. Chem. A, 2015, 3, 7568–7574.

A homologous, metal-free electrolyzer in both acidic and alkaline media was developed, consisting of self-supported carbon nitride/carbon nanotube/carbon fiber (C3N4–CNT–CF) and sulfur-doped carbon nitride/carbon nanotube/carbon fiber (S-C3N4–CNT–CF) as oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, respectively. The self-supported C3N4–CNT–CF electrode was proven to be an effective catalyst for the OER, due to the high N content of carbon nitride sheets and enhanced charge transport ability by the synergistic effect between the well-designed three-dimensional hierarchical carbon network and layered carbon nitride. In the meantime, the S-C3N4–CNT–CF was also proven to be an efficient, stable metal-free electrode for the HER. The homologous C3N4–CNT–CF||S-C3N4–CNT–CF water splitting system presents low onset potential and good stability in both acidic and alkaline media, indicating a potential carbon-based, metal-free full water splitting electrolyzer with low cost.