Cobalt Incorporated Graphitic Carbon Nitride as a Bifunctional Catalyst for Electrochemical Water-Splitting Reactions in Acidic Media.

Non-noble metal-based bifunctional electrocatalysts may be a promising new resource for electrocatalytic water-splitting devices. In this work, transition metal (cobalt)-incorporated graphitic carbon nitride was synthesized and fabricated in electrodes for use as bifunctional catalysts. The optimum catalytic activity of this bifunctional material for the hydrogen evolution reaction (HER), which benefitted at a cobalt content of 10.6 wt%, was promoted by the highest surface area and conductivity. The activity achieved a minimum overpotential of ~85 mV at 10 mA/cm2 and a Tafel slope of 44.2 mV/dec in an acidic electrolyte. These values of the HER were close to those of a benchmark catalyst (platinum on carbon paper electrode). Moreover, the kinetics evaluation at the optimum catalyst ensured the catalyst flows (Volmer-Heyrovsky mechanism), indicating that the adsorption step is rate-determining for the HER. The activity for the oxygen evolution reaction (OER) indicated an overpotential of ~530 mV at 10 mAcm-2 and a Tafel slope of 193.3 mV/dec, which were slightly less or nearly the same as those of the benchmark catalyst. Stability tests using long-term potential cycles confirmed the high durability of the catalyst for both HER and OER. Moreover, the optimal bifunctional catalyst achieved a current density of 10 mAcm-2 at a cell voltage of 1.84 V, which was slightly less than that of the benchmark catalyst (1.98 V). Thus, this research reveals that the present bifunctional, non-noble metallic electrocatalyst is adequate for use as a water-splitting technology in acidic media.

Surface-Enhanced Resonance Raman Scattering of Rhodamine 6G in Dispersions and on Films of Confeito-Like Au Nanoparticles.

Surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G was measured on confeito-like Au nanoparticles (CAuNPs). The large CAuNPs (100 nm in diameter) in aqueous dispersion systems showed stronger enhancing effect (analytical enhancement factor: over 105) of SERRS than the small CAuNPs (50 nm in diameter), while the spherical Au nanoparticles (20 nm in diameter) displayed rather weak intensities. Especially, minor bands in 1400-1600 cm-1 were uniquely enhanced by the resonance effect of CAuNPs. The enhancement factors revealed a concentration dependence of the enhancing effect at low concentration of rhodamine 6G. This dependency was due to a large capacity of hot-spots on CAuNPs, which were formed without agglomeration. The surface-enhancing behaviour in the film systems was similar to that in the dispersions, although the large CAuNPs had lower enhancing effect in the films, and the small CAuNPs and the spherical Au nanoparticles were more effective in their films. These results suggest that the CAuNPs have an advantage in ultrasensitive devices both in dispersions and films, compared to the agglomerate of spherical Au nanoparticles.

Selective Gas Capture Ability of Gas-Adsorbent-Incorporated Cellulose Nanofiber Films.

The 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized cellulose nanofibers (TOCNF) were hybridized with cation and anion-exchange organoclays, where poly(amido amine) dendrimers were loaded to enhance the functionality of gas adsorption, since dendrimers have the high adsorbability and the enough selectivity on the gas adsorption. The thin films were prepared from the organoclay-TOCNF hybrids and supplied to the gas adsorption. The adsorption of CO2 and NH3 gases increased with an increasing amount of organoclays in TOCNF films, but the behavior of the increase depended on gases, clays, and dendrimers. The hydrotalcite organoclay-TOCNF films displayed the highest adsorption of both gases, but the desorption of CO2 gas from hydrotalcite organoclay-TOCNF films was drastically high in comparison with the other systems. While the CO2 gas is adsorbed and remained on cationic dendrimer sites in cation-exchange organoclay-TOCNF films, the CO2 gas is adsorbed on cationic clay sites in anion exchange organoclay-TOCNF films, and it is easily desorbed from the films. The NH3 adsorption is inversive to the CO2 adsorption. Then the CO2 molecules adsorbed on the cationic dendrimers and the NH3 molecules adsorbed on the anionic dendrimers are preferably captured in these adsorbents. The present research incorporated dendrimers will be contributing to the development of gas-specialized adsorbents, which are selectively storable only in particular gases.

Electrochemical properties of a thermally expanded magnetic graphene composite with a conductive polymer.

A magnetic graphene composite derived from stage-1 FeCl3-graphite intercalation compounds was thermally treated for up to 75 min at 400 °C or for 2 min at high temperatures up to 900 °C. These heat-treatments of the magnetic graphene composite gave rise to the cubical expansion of graphene with the enlargement of inter-graphene distances. The specific capacitance of the magnetic graphene composite increased upon heating and reached 42 F g(-1) at a scan rate of 5 mV s(-1) in 1.0 M NaCl, after being treated for 2 min at 900 °C. This value corresponds to 840% increase in the capacitance activity superior to that (5 F g(-1)) of the pristine magnetic graphene composite before heat-treatment. This capacitance enhancement can play a significant role in the increase of the surface area that reached 17.2 m(2) g(-1) during the non-defective inter-graphene exfoliation. Moreover, the magnetic graphene composite heated at 900 °C was hybridized with polyaniline by in situ polymerization of aniline to reach a specific capacitance of 253 F g(-1) at 5 mV s(-1). The current procedure of heat-treatment and hybridization with a conductive polymer can be an effective method for attaining a well-expanded magnetic graphene composite possessing an enhanced electrochemical activity with a relatively high energy density (141 W h kg(-1) in 1.0 M NaCl) and an excellent stability (99% after 9000 cycles of 20 A g(-1)).

Efficient surface enhanced Raman scattering on confeito-like gold nanoparticle-adsorbed self-assembled monolayers.

Confeito-like gold nanoparticles (AuNPs; average diameter = 80 nm) exhibiting a plasmon absorption band at 590 nm were adsorbed through immersion-adsorption on two self-assembled monolayers (SAMs) of 3-aminopropyltriethoxysilane (APTES-SAM) and polystyrene spheres coated with amine-terminated poly(amido amine) dendrimers (DEN/PS-SAM). The surface enhanced Raman scattering (SERS) effect on the SAM substrates was examined using the molecules of a probe dye, rhodamine 6G (R6G). The Raman scattering was strongly intensified on both substrates, but the enhancement factor (>10,000) of the AuNP/DEN/PS-SAM hierarchy substrate was 5-10 times higher than that of the AuNP/APTES-SAM substrate. This strong enhancement is attributed to the large surface area of the substrate and the presence of hot spots. Furthermore, analyzing the R6G concentration dependence of SERS suggested that the enhancement mechanism effectively excited the R6G molecules in the first layer on the hot spots and invoked the strong SERS effect. These results indicate that the SERS activity of confeito-like AuNPs on SAM substrates has high potential in molecular electronic devices and ultrasensitive analyses.

Fluorescence quenching of uranine on confeito-like Au nanoparticles.

Effect of structure and size of Au nanoparticles (AuNPs) on fluorescence behavior of uranine was examined. Confeito-like AuNPs with different sizes (30 nm, 60 nm and 100 nm, respectively) had plasmon absorption bands at 555, 600 and 660 nm, while the band of spherical AuNP (20 nm in size) was at 525 nm. Fluorescence of uranine was significantly quenched by the small and medium confeito-like AuNPs, and the quenching effect by the large particle was less. In comparison, the spherical AuNP quenched more remarkable than the confeito-like AuNPs. A mechanism of resonance energy transfer from uranine to AuNPs via the surface plasmon was suggested, and the strong quenching effect of the small AuNPs could be explained by the energy transfer from adsorbed uranine molecules to AuNPs. These behaviors indicate that the large confeito-like AuNPs can be a preferable nano-probe and useful for plasmonic devices, which can tune or maintain the fluorescence properties of other markers.

Electrochemical nonenzymatic glucose sensors catalyzed by Au nanoclusters on metallic nanotube arrays and polypyrrole nanowires.

Monitoring blood glucose level is critical, since its abnormality leads to diabetes and causes death, even though glucose is essential for human living. Herein, the sensing study was performed on electrochemical nonenzymatic glucose sensors, which are composed of an Au nanocluster (AuNC) catalyst deposited on a metallic nanotube array (MeNTA) and polypyrrole nanowire (PPyNW). The AuNC was produced by irradiating a femtosecond pulse laser to the Au precursor solution, and it is a simple and facile method. The successful deposition of AuNC on both MeNTA and PPyNW was confirmed by means of the surface morphology and the Au content increase. On the exploration by cyclic voltammetry in alkaline condition, AuNC/MeNTA electrodes showed better performance than AuNC/PPyNW electrodes: The former was a remarkable electrocatalytic detector towards glucose oxidation with better sensitivity, lower detection limit, wider linear range, and longer-term stability without interference from potential interfering agents such as ascorbic acid, urea, NaCl, KCl, etc. Moreover, nonenzymatic AuNC/MeNTA electrodes exhibited high precision and accuracy in real human blood samples and, thus, can be a promising candidate in glucose sensing applications.

Protector-free, non-plasmonic silver quantum clusters by femtosecond pulse laser irradiation: in situ binding on nanocellulose filaments for improved catalytic activity and cycling performance.

This study introduces a new, facile method to synthesize silver clusters from aqueous silver ion solution by using high intensity femtosecond pulse laser irradiation. The particles obtained in the absence of reducing or capping agents are 1-17 nm in size and presented quantum properties, as characterized by fluorescence, but did not exhibit plasmon signals, which is not a common characteristic of conventional silver nanoparticles. In a further development, small silver quantum clusters (∼1 nm) were bound in situ to wet-spun filaments of cellulose nanofibrils by pulsed laser irradiation. The obtained hybrid filaments as well as free silver quantum clusters revealed a catalytic activity remarkably higher than that of free gold quantum clusters; moreover, the hybrid filaments were found to show improved stability and cycling performance for silver-based catalysis. The present results indicate the potential of femtosecond laser irradiation to generate clusters as well as hybrid systems with excellent performance and reactivity.

Effect of a three-dimensional nanotube array substrate on photocatalytic conversion performance of CO2 gas to methanol by amine-loaded CuO/ZnO catalysts.

The photocatalytic conversion of CO2 gas into energy-dense hydrocarbons holds the potential to address both environmental and energy problems. Catalysts consisting of CuO clusters/nanoparticles and ZnO nanorods on a metallic nanotube array (MeNTA) silicon substrate were utilized for CO2 reduction. The surface of the catalysts was modified with 3-amino-propyltriethoxysilane (APTES), the amine terminal of which can selectively bind CO2 gas. When photocatalytic CO2 reduction was performed with varying APTES and CuO contents, the highest methanol production of 4.5 mmol/g(catalyst) was obtained at 10 wt% APTES and 7.5 mM CuO contents. The high yield in the present work in comparison with previous reports is due to some advantages of the present catalytic system such as its enhanced activity, significant selectivity, and easy production: Nanometer-sized CuO produced by femtosecond pulse laser irradiation provides a larger active surface per volume and a free surface without a protector, which is favorable for advancing the catalytic activity. The formation of a heterojunction interface in a nanocomposite of p-type CuO and n-type ZnO increases holes at the valence band level of CuO, resulting in advantageous photovoltaic efficiency. The introduction of APTES on the catalyst surface enhances CO2 adsorption and brings about CO2 gas near the catalyst to accelerate the reaction rate. Finally, a three-dimensional tube array on the substrate enlarges the surface per volume for catalyst-loading compared to the two-dimensional substrate. Thus, the proposed catalytic system consisting of amine-loaded CuO/ZnO constructed on a three-dimensional nanotube array substrate is preferable for the photocatalytic conversion of CO2 gas to methanol.

Nanoarchitectonics of Nanocellulose Filament Electrodes by Femtosecond Pulse Laser Deposition of ZnO and In Situ Conjugation of Conductive Polymers.

Electroactive filament electrodes were synthesized by wet-spinning of cellulose nanofibrils (CNF) followed by femtosecond pulse laser deposition of ZnO (CNF@ZnO). A layer of conducting conjugated polymers was further adsorbed by in situ polymerization of either pyrrole or aniline, yielding systems optimized for electron conduction. The resultant hybrid filaments were thoroughly characterized by imaging, spectroscopy, electrochemical impedance, and small- and wide-angle X-ray scattering. For the filaments using polyaniline, the measured conductivity was a result of the synergy between the inorganic and organic layers, while the contribution was additive in the case of the systems containing polypyrrole. This observation is rationalized by the occurrence of charge transfer between ZnO and polyaniline but not that with polypyrrole. The introduced conductive hybrid filaments displayed a performance that competes with that of metallic counterparts, offering great promise for next-generation filament electrodes based on renewable nanocellulose.

Electrochemical biosensors for biocontaminant detection consisting of carbon nanotubes, platinum nanoparticles, dendrimers, and enzymes.

The presented approach provides the advanced development of effective, rapid, and versatile electrochemical sensors for a small amount of analytes on potential, cheap, and disposable printed chips. The electrocatalytic activity of this biosensor revealed the feasible detection of hydrogen peroxide at low potential (~0.09 V) and the detection of a biocontaminant inhibitor (organophosphorus pesticide) in a wide range of concentrations. This efficiency comes from the chemical immobilization of catalysts (Pt nanoparticles) and electron transfer-enlarging materials (carbon nanotubes) on an electrode. Especially, dendrimers raise the stable conjugation of enzymes (acetylcholinesterase/choline oxidase/peroxidase) as well as nanoparticles and carbon nanotubes on an electrode.

Advantages of electrodes with dendrimer-protected platinum nanoparticles and carbon nanotubes for electrochemical methanol oxidation.

Electrochemical sensors consisting of electrodes loaded with carbon nanotubes and Pt nanoparticles (PtNPs) protected by dendrimers have been developed using a facile method to fabricate them on two types of disposable electrochemical printed chips with a screen-printed circular gold or a screen-printed circular glassy carbon working electrode. The electrochemical performance of these sensors in the oxidation of methanol was investigated by cyclic voltammetry. It was revealed that such sensors possess stable durability and high electrocatalytic activity: the potential and the current density of an anodic peak in the oxidation of methanol increased with increasing content of PtNPs on the electrodes, indicating the promotion of electrocatalytic activity in relation to the amount of catalyst. The low anodic potential suggests the easy electrochemical reaction, and the high catalyst tolerance supports the almost complete oxidation of methanol to carbon dioxide. The significant performance of these sensors in the detection of methanol oxidation comes from the high electrocatalytic ability of PtNPs, excellent energy transfer of carbon nanotubes and the remarkable ability of dendrimers to act as binders. Thus these systems are effective for a wide range of applications as chemical, biomedical, energy and environmental sensors and as units of direct methanol fuel cells.

Surface immobilization of carbon nanotubes by beta-cyclodextrins and their inclusion ability.

The surface immobilization of beta-cyclodextrins on the surface of multiwalled carbon nanotubes (MWNTs) in an aqueous medium was achieved by covalent-binding of diamino-functionalized beta-cyclodextrin with carboxylic acid-functionalized MWNTs via amide linkages using a water-soluble condensation agent at room temperature. The obtained product denoted as beta-cyclodextrin-modified MWNTs was highly dispersible in an aqueous medium. The covalent surface functionalization of MWNTs by beta-cyclodextrin was characterized by FTIR, TGA, EDS and TEM. The thermogravimetric analyses indicated that -70 wt% beta-cyclodextrin was attached on the surface of MWNTs. Furthermore, the fluorometric analysis for adsorption of rhodamine 6G dye suggested that the formation of beta-cyclodextrin-dye inclusion conjugate takes place prior to the adsorption of dyes on MWNTs and uniform dispersion of MWNTs after surface immobilization allows superior fluorescence quenching than the pristine and oxidized MWNTs.

Movements of Magnetite-Encapsulated Graphene Particles at Air-Water Interface and Their Cell Growths under Dynamic Magnetic Field.

The motion of magnetic particles under magnetic fields is an object to be solved in association with basic and practical phenomena. Movement phenomena of magnetite-encapsulated graphene particles at air-water interfaces were evaluated by manufacturing a feedback control system of the magnetic field to cause the motion of particles due to magnetic torque. A homogeneous magnetic field was generated using two pairs of electromagnets located perpendicular to each other, which were connected to an electronic switch. The system influenced the translational movement and the self-rotational speed of magnetic particles located at a center on the surface of fluid media in a continuous duty cycle. Operating the particle at a remote control in the same duty cycle at the air-water surface, the short and elongated magnetic particles successfully rotated. In addition, the rotational speed of the curved particle was slower than that of the elongated particle. The results indicate that the translational and self-rotational movements of magnetite-encapsulated graphene particles at the air-water interface under the external magnetic field are size- and shape-dependent for the speed and the direction. A short magnetic particle was used as a target particle to rotate on cancer cell lines, aiming to study the advantage of this method to induce the growth of HeLa cells. It was monitored for up to 4 days with and without magnetic particles by checking the viability and morphology of cells before and after the electromagnetic treatment. As an outcome, the movement of magnetic particles reduced the number of biological cells, at least on HeLa cells, but it was inactive on the viability of HeLa cells.

Electrochemical immunosensing by carbon ink/carbon dot/ZnO-labeled-Ag@polypyrrole composite biomarker for CA-125 ovarian cancer detection.

In this work, we demonstrated a novel cancer antigen 125 (CA125) biomarker detection based on electrochemical immunosensor. The biomarker on conductive composite materials of carbon ink/carbon dot/zine oxide (C-ink/CD/ZnO) was employed as an electrode platform by using ITO substrate to enhance the interaction of antibodies (Ab) with supporting catalytic performance of ZnO as a labeling signal molecule. They were a scientist attention for biosensor with chemical stability, strong biocompatibility, high conductive signal, and accuracy. Moreover, the nanocomposite of silver@polypyrrole (Ag@PPy) was used as a potential redox mediator. The labeled construction with Ag@PPy was more accuracy than that of a free-labeled. The created immunosensor was a wide linear range as 1 ag·mL-1 - 100 ng·mL-1 and a low limitation of detection as 0.1 fg·mL-1 under the optimal condition. This suggested that the immunosensor is considered to be an accurate and efficient diagnostic tool for CA125 and other biomarkers detection in actual sample analysis for clinic.

Role of HIKESHI on Hyperthermia for Castration-Resistant Prostate Cancer and Application of a Novel Magnetic Nanoparticle with Carbon Nanohorn for Magnetic Hyperthermia.

The prognosis of castration-resistant prostate cancer (CRPC) is technically scarce; therefore, a novel treatment for CRPC remains warranted. To this end, hyperthermia (HT) was investigated as an alternative therapy. In this study, the analysis focused on the association between CRPC and heat shock protein nuclear import factor "hikeshi (HIKESHI)", a factor of heat tolerance. Silencing the HIKESHI expression of 22Rv1 cells (human CRPC cell line) treated with siRNAs inhibited the translocation of heat shock protein 70 from the cytoplasm to the nucleus under heat shock and enhanced the effect of hyperthermia. Moreover, a novel magnetic nanoparticle was developed via binding carbon nanohorn (CNH) and iron oxide nanoparticle (IONP) with 3-aminopropylsilyl (APS). Tumor-bearing model mice implanted with 22 Rv1 cells were examined to determine the effect of magnetic HT (mHT). We locally injected CNH-APS-IONP into the tumor, which was set under an alternative magnetic field and showed that tumor growth in the treatment group was significantly suppressed compared with other groups. This study suggests that HIKESHI silencing enhances the sensitivity of 22Rv1 cells to HT, and CNH-APTES-IONP deserves consideration for mHT.

Preparation of Functional Nanoparticles-Loaded Magnetic Carbon Nanohorn Nanocomposites towards Composite Treatment.

Combination therapy for cancer is expected for the synergetic effect of different treatments, and the development of promising carrier materials is demanded for new therapeutics. In this study, nanocomposites including functional nanoparticles (NPs) such as samarium oxide NP for radiotherapy and gadolinium oxide NP as a magnetic resonance imaging agent were synthesized and chemically combined with iron oxide NP-embedded or carbon dot-coating iron oxide NP-embedded carbon nanohorn carriers, where iron oxide NP is a hyperthermia reagent and carbon dot exerts effects on photodynamic/photothermal treatments. These nanocomposites exerted potential for delivery of anticancer drugs (doxorubicin, gemcitabine, and camptothecin) even after being coated with poly(ethylene glycol). The co-delivery of these anticancer drugs played better drug-release efficacy than the independent drug delivery, and the thermal and photothermal procedures enlarged the drug release. Thus, the prepared nanocomposites can be expected as materials to develop advanced medication for combination treatment.

Fabrication and characterization of dendrimer-functionalized mesoporous hydroxyapatite.

A successful synthesis of mesostructured hydroxyapatite (HAp) using cetyltrimethylammonium bromide and poly(amido amine) dendrimer porogens has been reported. A comparative study of physicochemical properties has also been performed. The formation of a single-phase hydroxyapatite crystal in synthesized HAp particles with an aspect ratio of 2.3 was revealed. The formation of the mesostructural nature of HAp was proven with a specific surface area (56-63 m(2)/g) and a certain pore size (4.7-5.5 nm), although there were significant differences between particles from surfactant micelle and dendrimer porogens. In addition, the surface modification of mesoporous HAp particles was carried out using poly(amido amine) dendrimer. The content and thickness of the dendrimer coating on particle surfaces were highly dependent on the pH. At pH 9 or greater, the coating thickness corresponded to at least a double layer of dendrimer, but it decreased sharply with decreasing pH from 9 to 6, in agreement with the protonation of amine groups in the dendrimer, indicating the strong interaction of nonionic dendrimer with HAp. The developed dendrimer-functionalized mesoporous hydroxyapatite materials may be applicable in biocomposite material and/or bone tissue engineering.

A solution-based nano-plasmonic sensing technique by using gold nanorods.

We have successfully demonstrated a novel sensing technique for monitoring the variation of solution concentrations and measuring the effective dielectric constant in a medium by means of an ultra-small and label-free nanosensor, the mechanism of which is based on the localized surface plasmon resonance (LSPR) of gold nanorods. The nanorods are fabricated in a narrow size distribution, which is characterized by transmission electron microscopy and optical absorption spectroscopy. In addition, we employ a simple analytical calculation to examine the LSPR band of the absorption spectrum, which provides excellent consistency with aspect ratio. The plasmonic sensing is performed by detecting the diffusion process and saturation concentration of hexadecyltrimethylammonium bromide in water, and tracing the effective dielectric constants of the medium simultaneously. This promising sensing and analytical technique can be easily used for investigating the nano-scale variations of mixing or reaction process in a micro/nanofluidic channel or the biological interaction in the cytoplasm of the cell.

Advantages of immobilization of Pt nanoparticles protected by dendrimers on multiwalled carbon nanotubes.

Pt nanoparticles (PtNPs) were synthesized in the presence of a NH(2)-terminated fourth generation poly(amido amine) (PAMAM) dendrimer as a stabilizer at different molar ratios (M:D) of metal precursor to amine terminal group of dendrimer. Subsequently, PtNPs protected by dendrimers (DENPtNPs) were covalently immobilized on multiwalled carbon nanotubes (MWCNTs) by using a condensing agent for amide bond formation between acid-treated MWCNTs and DENPtNPs and the product CNT/DENPtNPs were characterized. PtNPs on MWCNTs increased quantitatively in content with M:D and dispersed with same aspect as the dispersion of DENPtNPs in water: PtNPs homogeneously dispersed at low M:D ratio and slightly aggregated at high ratio. The decomposition of CNT/DENPtNPs occurred at the lower temperature owing to the catalytic effect of PtNPs. A near-infrared absorption band around 2083 nm, which is extremely weak for MWCNTs, was intensified and D, D' and G Raman bands were slightly downshifted when DENPtNPs were attached. These phenomena can be attributed to the electron transfer from DENPtNPs to MWCNTs. Remarkable advantage is apparent from the enhanced electrochemical behavior of CNT/DENPtNPs loaded on gold electrode. PtNPs promoted the electron transfer of MWCNTs and dendrimers contributed to uptake of redox materials.