Publisher Correction: Graphene Oxide Quantum Dots Derived from Coal for Bioimaging: Facile and Green Approach.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Graphene Oxide Quantum Dots Derived from Coal for Bioimaging: Facile and Green Approach.

Graphene oxide quantum dots (GOQDs) are usually prepared using expensive carbon precursors such as carbon nanotubes (CNT) or graphene under the strong acidic condition, which requires an additional purifying process. Here, we first develop a facile pulsed laser ablation in liquid (PLAL) technique for preparing GOQDs using earth-abundant and low-cost coal as a precursor. Only ethanol and coal are used to produce GOQDs with excellent optical properties. The prepared GOQDs exhibit excellent optoelectronic properties which can be successfully utilized in bioimaging applications.

Laser wavelength modulated pulsed laser ablation for selective and efficient production of graphene quantum dots.

Graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs) can be used in different applications such as optoelectronic and biomedical applications, respectively. Hence, the selective synthesis of GQDs and GOQDs is highly desirable but challenging. Here, we present GQDs and GOQDs selectively prepared by an easy and simple pulsed laser ablation in liquid (PLAL) method by controlling the laser wavelength. The obtained GQDs and GOQDs showed a significantly different optoelectronic nature mainly due to the existence of surface oxygen-rich functional groups (e.g. carboxyl or hydroxy groups). Also, we described a possible mechanism for the formation of oxygen functional groups during the PLAL process based on the Coulomb explosion model, which can give further insight for designing functional carbon materials.

Ultrafast Method for Selective Design of Graphene Quantum Dots with Highly Efficient Blue Emission.

Graphene quantum dots (GQDs) have attractive properties and potential applications. However, their various applications are limited by a current synthetic method which requires long processing time. Here, we report a facile and remarkably rapid method for production of GQDs exhibiting excellent optoelectronic properties. We employed the pulsed laser ablation (PLA) technique to exfoliate GQDs from multi-wall carbon nanotube (MWCNTs), which can be referred to as a pulsed laser exfoliation (PLE) process. Strikingly, it takes only 6 min to transform all MWCNTs precursors to GQDs by using PLE process. Furthermore, we could selectively produce either GQDs or graphene oxide quantum dots (GOQDs) by simply changing the organic solvents utilized in the PLE processing. The synthesized GQDs show distinct blue photoluminescence (PL) with excellent quantum yield (QY) up to 12% as well as sufficient brightness and resolution to be suitable for optoelectronic applications. We believe that the PLE process proposed in this work will further open up new routes for the preparation of different optoelectronic nanomaterials.

High-rate performance of Ti(3+) self-doped TiO2 prepared by imidazole reduction for Li-ion batteries.

Ti(3+) self-doped TiO2 nanoparticles were prepared via a simple imidazole reduction process and developed as an anode material for Li-ion batteries. Introducing the Ti(3+)-state on TiO2 nanoparticles resulted in superior rate performances that the capacity retention of 88% at 50 C. The enhanced electrochemical performances were attributed to the resulting lower internal resistance and improved electronic conductivity, based on galvanostatic intermittent titration technique and electrochemical impedance spectroscopy analyses.

Growth of Er3+/Yb3+ co-doped CaMoO4 thin film by a spray coating and its upconverting luminescence.

Polycrystalline Er3+/Yb3+ co-doped CaMoO4 (CaMoO4:Er3+/Yb3+) film was successfully fabricated by a spray coating method. Crystal structure, surface morphology and upconversion (UC) luminescent properties were investigated. Under 980-nm excitation, CaMoO4:Er3+/Yb3+ film exhibited strong green UC emissions at 530 and 550 nm (2H,11/2 --> 4S3/2 - 4I15/2) visible to the naked eye with a weak red emission near 660 nm (4F9/2 --> 4I15/2) corresponding to the intra 4f transitions of Er3+. A possible UC mechanism related to the pump-power dependence is discussed in detail.

Green lighting upconversion luminescence of Yb3+, Er3+ co-doped BaMoO4.

A green lighting upconversion (UC) system was successfully achieved from Er3+/Yb3+ co-doped BaMoO4 synthesized by the complex citrate-gel method. Under 980 nm laser excitation, the Er3+/Yb3+ co-doped BaMoO4 emitted strong green luminescence around 530 and 550 nm and weak red luminescence near 660 nm, which corresponded to the intra 4f-4f transitions in Er3+. Optimal doping concentrations of Er3+/Yb3+ into the BaMoO4 matrix were investigated. Moreover, based on excitation power dependence, the UC luminescent mechanism in the Er3+/Yb3+ co-doped BaMoO4 was presented in detail.

Catalyst-free fabrication of graphene nanosheets without substrates using multiwalled carbon nanotubes and a spark plasma sintering process.

Catalyst-free graphene nanosheets without substrates were synthesized using pure solid carbon sources of multiwalled carbon nanotubes (MWCNTs) and a spark plasma sintering (SPS) process. Single and few-hundred-nanometer graphene nanosheets were formed from gas-phase carbon atoms which were directly evaporated from MWCNTs at a local high temperature.

Spirally oriented Au microelectrode array sensor for detection of Hg (II).

A simple and reproducible carbon microelectrode array (CMA), designed to eliminate diffusive interference among the microelectrodes, has been fabricated and used as a frame to build a gold (Au) microelectrode array (GMA) sensor. To prepare the CMA initially, rather than use an uncontrollable large number of carbon fibers, only 60 carbon fibers of regular size were used to ensure manageable and reproducible arrangement for array construction. In addition, for efficient spatial arrangement of the microelectrode and easy sensor preparation, carbon fibers were oriented in a spiral fashion by rolling around a Cu wire. The distance between carbon fibers was carefully determined to avoid overlap among individual diffusion layers, one of the important factors governing steady-state current response and sensor-to-sensor reproducibility. After the preparation of a spirally arranged CMA, Au was electrochemically deposited on the surface of individual carbon electrodes to build a final GMA sensor. Then, the GMA sensor was used to measure Hg(2+) in a low concentration range. Simultaneously, multiple GMA sensors were independently prepared to examine reproducibility in sensor fabrication as well as electrochemical measurement (sensor-to-sensor reproducibility). Overall, highly sensitive detection of Hg(2+) was possible using the proposed GMA sensor due to efficient arrangement of microelectrodes and the sensor-to-sensor reproducibility was superior owing to simplicity in sensor fabrication.

Fabrication of single-phase titanium carbide layers from MWCNTs using high DC pulse.

Single-phase layered titanium carbide (TiC) was successfully synthesized by reacting carbon nanotubes (CNTs) and titanium dioxide (TiO2) under a high direct current (DC) pulse. Single-phase TiC layer fabrication is confirmed as the transformation of multi-layered graphene from MWCNTs. Therefore its thickness and width is almost identical to those of transformed graphene layers. This is the first report on the formation of single-phase layered nano-TiC. Scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR-TEM) were used for the characteristic analysis of single-phase layered TiC structures.

Pulsed-Laser-Induced Simple Synthetic Route for Tb(3)Al(5)O(12):Ce Colloidal Nanocrystals and Their Luminescent Properties.

Cerium-doped Tb(3)Al(5)O(12) (TAG:Ce(3+)) colloidal nanocrystals were synthesized by pulsed laser ablation (PLA) in de-ionized water and lauryl dimethylaminoacetic acid betain (LDA) aqueous solution for luminescent bio-labeling application. The influence of LDA molecules on the crystallinity, crystal morphology, crystallite size, and luminescent properties of the prepared TAG:Ce(3+) colloidal nanocrystals was investigated in detail. When the LDA solution was used, smaller average crystallite size, narrower size distribution, and enhanced luminescence were observed. These characteristics were explained by the effective role of occupying the oxygen defects on the surface of TAG:Ce(3+) colloidal nanocrystal because the amphoteric LDA molecules were attached by positively charged TAG:Ce(3+) colloidal nanocrystals. The blue-shifted phenomena found in luminescent spectra of the TAG:Ce(3+) colloidal nanocrystals could not be explained by previous crystal field theory. We discuss the 5d energy level of Ce(3+) with decreased crystal size with a phenomenological model that explains the relationship between bond distance with 5d energy level of Ce(3+) based on the concept of crystal field theory modified by covalency contribution.

Sinterability, mechanical, and electrical properties of Al2O3/8YSZ nanocomposites prepared by ultrasonic spray pyrolysis.

Al2O3 nanoparticles added the YSZ for improving the mechanical property and the ionic conductivity. Al2O3/YSZ nanocomposites were prepared by ultrasonic spray pyrolysis and PECS process. The relative density of the Al2O3/YSZ nanocomposites was fully densified at a sintering temperature of 1100 degrees C. The grain size for 5 vol.% Al2O3/YSZ was less than 100 nm. The fracture toughness and total ionic conductivity of Al2O3/YSZ nanocomposites were improved compared with Al2O3/YSZ nanocomposites by conventional process, due to homogeneous dispersion and uniform particle size of added Al2O3.