The increasing use of fluorescent carbon nanodots (CNDs) demonstrates their advantages for sensing applications; these include superior photostability, absence of toxicity, and rapid analytical capability. However, CNDs usually have multiple types of functional groups covering their surfaces, which decrease their sensitivity and selectivity. In this study, the required structure of β-lactoglobulin (LG)-derived carbon nanodots was achieved by adding ethylenediamine (EDA) to the synthesis process. Due to the consumption of protein carboxyl groups during the preparation process, a homogeneous coverage of amino groups on the surfaces of the CNDs was achieved, resulting in high sensitivity of the CNDs to copper ions. Furthermore, owing to effective passivation of trap states and a high content of N doping, the as-prepared CNDs showed a high quantum yield and an excitation-independent emission property. We believe that this type of preparation method is useful for the design of protein-derived CNDs, which may have promising applications for detecting various metal ions in a biological environment.

A novel three-dimensional (3D) nanoarchitecture consisting of hybrid graphene nanosheets (GNs)/graphene foam (GF) was fabricated on the FTO conducting substrate as a high efficient counter electrode (CE) for dye sensitized solar cells (DSSCs). The GNs with various sized such as large-sized heat-reduced graphene nanosheets (H-GNs) and small-sized laser-reduced graphene quantum dots (L-GQDs) were synthesized and used as catalytic materials incorporated into a 3D GF network, respectively. In this design, the aggregations and restacking of GNs were efficiently reduced, which is beneficial for increasing the amount of the active defective sites at the edges of graphene to the electrolyte solution. Especially, L-GQDs with smaller dimension less than 100 nm have more active defective sites at edges, providing superiority over the large-sized H-GNs in terms of electrocatalytic activity. Meanwhile, the GF network with high conductivity provides fast electron transport channels for charge injection between the GNs and FTO. The DSSC with this hybrid CE exhibited energy conversion efficiency (η) of 7.70% with an open circuit voltage (VOC), short circuit photocurrent density (JSC) and fill factor (FF) of 760 mV, 15.21 mA cm−2, and 72.0%, respectively, which is comparable to that of the conventional Pt CE (7.68%).

Graphene nanosheets@ZnO nanorods as a three-dimensional high efficient counter electrode for dye sensitized solar cells is described, highlighting the ZnO nanorods as a 3D framework nanostructure for preventing the aggregations of GNs. It is demonstrated that, when the nanohybrids are used as CE materials for DSSCs, compared to their pristine GNs, the GNs@ZnO nanorod hybrids without aggregations of GNs have a significant improvement in catalytic performance toward the reduction of triiodide, which were reflected in their electrochemical properties such as high current density, narrow peak-to-peak separation (EPP) and low charge transfer resistance (RCT). The enhancement of electrochemical performance can be attributed to more active defective sites at the edges of GNs and the reduction of the restacking of GNs due to the 3D ZnO nanorod nanostructure. The DSSC with this hybrid CE exhibited energy conversion efficiency (η) of 8.12% with an open circuit voltage (VOC), short circuit photocurrent density (JSC) and fill factor (FF) of 765 mV, 21.7 mA cm−2, and 67.1%, respectively, which is comparable to that of the conventional Pt CE (8.82%).

•Hybrid CNTs/graphene on FTO is synthesized by in-situ Cu-vapor-assisted chemical vapor deposition.•The hybrid CNTs/graphene is thought as the platform for accelerating the ballistic transport.•Bifacial DSSC with the transparent CNTs/graphene electrode improves light utilization efficiency.Herein, a facile in-situ grown nanocarbon composite including one dimensional (1D) carbon nanotubes (CNTs) and two dimensional (2D) graphene nanosheets on FTO conductive glass substrates is used directly as a transparent counter electrode (CE) for dye sensitized solar cells (DSSCs) without any post-treatments. In the novel nano-composite, the CNTs without aggregations are not woven into each other, which is beneficial for the transport of carriers. Additionally, the 2D graphene between CNTs and the FTO conductive glass substrates is thought as the platform for accelerating the ballistic transport. It is found that the hybrid CNTs/graphene nano-composite exhibits relative high electrocatalytic activity for the reduction of triiodide. Besides, the design of bifacial DSSC with the hybrid transparent CNTs/graphene CE improves the utilization ratio of incident light. As a consequence, the bifacial DSSC with the optimized hybrid CNTs/graphene exhibits energy conversion efficiency (η) of 5.16% and 4.30%, corresponding to front- and rear-side illumination, respectively.

Three-dimensional Ag nanoparticle/GNs (Ag/GNs) hybrids as highly efficient counter electrode (CE) materials for dye sensitized solar cells (DSSCs) is described, highlighting the Ag nanoparticles as zero-dimensional nanospacers inserting into GNs to lift the interspacing layer between individual GNs. It is demonstrated that, when the hybrids are used as CE materials for DSSCs, compared to their pure GNs, Ag/GNs hybrids without agglomerates have a significant improvement in their electrochemical properties such as high current density, narrow peak-to-peak separation (Epp) and low charge transfer resistance (RCT). The enhancement of electrochemical performance can be attributed to the increased electrode conductivity, an extended interlayer distance and the reduction of the restacking of graphene sheets due to the insertion of metallic Ag nanoparticles into GNs. The DSSC with this hybrid CE exhibited an energy conversion efficiency (η) of 7.72% with an open circuit voltage (VOC), short circuit photocurrent density (JSC), and fill factor (FF) of 732 mV, 14.67 mA cm−2, and 71.8%, respectively.

Reduced graphene oxide (RGO) has proven to be effective in trace gas detection at room temperature ambient conditions. However, the slow response–recovery characteristic is a major hurdle for the RGO-based gas sensors. Herein, we report a gravure-printed chemoresistor-type NO2 sensor based on sulfonated RGO (S-RGO) decorated with Ag nanoparticles (Ag–S-RGO). Large amounts of silver nanoparticles with an average particle size of 10–20 nm were uniformly assembled on flat S-RGO surfaces. The printed Ag–S-RGO sensor possesses a high sensitivity and fast response–recovery characteristic over NO2 concentrations ranging from 0.5 to 50 ppm. Upon exposure to 50 ppm NO2 at room temperature, the Ag–S-RGO sensor shows a sensitivity of 74.6%, a response time of 12 s and a recovery time of 20 s. In addition, the Ag–S-RGO sensors exhibit satisfactory flexibility with an almost constant resistance after 1000 bending cycles. The printed and high-performance Ag–S-RGO sensors described here will be a good prospect in environmental monitoring of NO2.Keywords: Ag nanoparticles; nanocomposite structure; printed sensor; reduced graphene oxide;

Herein we report a double layer structured transparent, flexible hybrid electrode from a subpercolating network of silver nanowires (Ag NWs) with CVD graphene coating on a PET substrate. The resistance of the obtained hybrid graphene/Ag NW film, with T = 81.5% (at 550 nm) and Rs = 32.5 Ω sq−1, is comparable to that of the resistance of ITO. In comparison with the Ag NW film, the resulting hybrid film has a lower surface roughness and a high DC to optical conductivity ratios. In such an electrode structure, graphene and Ag NWs can serve as the short-range and long-range conductors respectively, which should be more efficient in collecting and transporting the carriers to the external circuits. In addition, the graphene/Ag NW film possesses a desirable mechanical property. It is expected that the graphene/Ag NW double layered electrode might serve as a flexible transparent electrode.

We report the synthesis of high-quality graphene films on Ni foils using a cold-wall reactor by rapid thermal chemical vapor deposition (CVD). The graphene films were produced by shortening the growth time to 10 s, suggesting that a direct growth mechanism may play a larger role rather than a precipitation mechanism. A lower H2 flow rate is favorable for the growth of high-quality graphene films. The graphene film prepared without the presence of H2 has a sheet resistance as low as ∼367 ohm/sq coupled with 97.3% optical transmittance at 550 nm wavelength, which is much better than for those grown by hot-wall CVD systems. These data suggest that the structural and electrical characteristics of these graphene films are comparable to those prepared by CVD on Cu.

We report a simple approach to reduce graphene oxide (GO) solution by pulsed laser irradiation. The reduction was rapidly carried out at room temperature in only 5 min. The reduced graphene oxide (r-GO) was characterized with UV–visible spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, thermo-gravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. Based on this reducing method, an r-GO conductive film with a sheet resistance of 53.8 kΩ/sq was obtained. The pulsed laser reduction of GO in solution creates a new way to produce graphene composites for a variety of applications.

Zinc oxide/indium/zinc oxide multilayer structures have been obtained on glass substrates by magnetron sputtering. The effects of indium thickness on optical and electrical properties of the multilayer structures are investigated. Compared to a single zinc oxide layer, the carrier concentration increases from 8 × 1018 cm−3 to 1.8 × 1020 cm−3 and Hall mobility decreases from 10 cm2/v s to 2 cm2/v s for the multilayer structure at 8 nm of indium thickness. With the increase of indium thickness, the transmittance decreases and optical band gap shifts to lower energy in multilayer structures. Results are understood based on Schottky theory, interface scattering mechanism and the absorption of indium layer.

•We developed a paper-based SERS substrate by gravure and inkjet printing methods.•The S-RGO/AgNPs comoposite structure had higher SERS activity than the pure AgNPs.•The Raman enhancement factor of S-RGO/AgNPs substrate was calculated to be 109.•The paper-based substrate exhibited good reproducibility and long-term stability.Paper-based surface-enhanced Raman scattering (SERS) substrates receive a great deal of attention due to low cost and high flexibility. Herein, we developed an efficient SERS substrate by gravure printing of sulfonated reduced graphene-oxide (S-RGO) thin film and inkjet printing of silver nanoparticles (AgNPs) on weighing paper successively. Malachite green (MG) and rhodamine 6G (R6G) were chosen as probe molecules to evaluate the enhanced performance of the fabricated SERS-active substrates. It was found that the S-RGO/AgNPs composite structure possessed higher enhancement ability than the pure AgNPs. The Raman enhancement factor of S-RGO/AgNPs was calculated to be as large as 109. The minimum detection limit for MG and R6G was down to 10−7 M with good linear responses (R2 = 0.9996, 0.9983) range from 10−4 M to 10−7 M. In addition, the S-RGO/AgNPs exhibited good uniformity with a relative standard deviation (RSD) of 7.90% measured by 572 points, excellent reproducibility with RSD smaller than 3.36%, and long-term stability with RSD less than 7.19%.

Herein we report a double layer structured transparent, flexible hybrid electrode from a subpercolating network of silver nanowires (Ag NWs) with CVD graphene coating on a PET substrate. The resistance of the obtained hybrid graphene/Ag NW film, with T = 81.5% (at 550 nm) and Rs = 32.5 Ω sq−1, is comparable to that of the resistance of ITO. In comparison with the Ag NW film, the resulting hybrid film has a lower surface roughness and a high DC to optical conductivity ratios. In such an electrode structure, graphene and Ag NWs can serve as the short-range and long-range conductors respectively, which should be more efficient in collecting and transporting the carriers to the external circuits. In addition, the graphene/Ag NW film possesses a desirable mechanical property. It is expected that the graphene/Ag NW double layered electrode might serve as a flexible transparent electrode.