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Z-scheme transfer is an ideal photocatalytic system with stronger redox ability, but its design and construction still lack understanding. Herein, the work function difference and the band bending are found to be the determining factors for the construction of the Z-scheme transfer mechanism of photoexcited charges in TiO2/WO3. The control of work function and band bending achieved by carbon insertion results from the hybridization of orbitals and redistribution of electron density, as demonstrated by ultraviolet photoelectron spectroscopy and photocatalytic analysis. The heterojunction system, TiO2/WO3, with controlled work function and band bending, shows 2 times faster •OH radical formation rate (0.011 μmol min-1) compared to the undisturbed system. First-principles calculation reveals that the changes in work function and band bending result in an interfacial electric field, which shifts the charge transfer mechanism from type II to Z-scheme. This work proves that the design of work function and band bending allows reconstructing charge transfer mechanism by forming the interfacial electric field in heterojunction systems.

Bimodal porous nitrogen (N) doped carbon supported Pt composite was prepared as a catalyst for oxygen reduction reaction (ORR). The N-doped carbon (NCF) support was obtained via one-pot pyrolysis of the used cigarette filters. Physical characterizations and electrochemical tests proved that the presence of N dopant on the surface of the NCF not only provided highly dispersive active sites for the growth of the Pt nanoparticles but also the active centers for ORR itself. It was demonstrated that these combinative effects contributed on higher ORR activity and durability than those for the commercial carbon (Vulcan XC) supported Pt composites.

Despite the significant advances in nanostructured supporting materials used for metal-based catalysts, intractable problems including poor dispersion and the agglomeration of metal nanoparticles (NPs) within their complicated structure limit the practical applications. We report herein on a facile polyethyleneimine (PEI)-assisted strategy for the high dispersion and controllable coverage of Pt catalysts onto a 3-dimensional mesoporous carbon material, referred to as a “bio-inspired carbon nanosphere (BCN)”. The PEI adsorbed on the carbon surface serves as anchoring sites for metal ions and as templates for metal nanoparticle growth. The resulting spherical Pt NPs are highly dispersed on the surface to the center of the BCN without any agglomeration even after a thermal annealing. The amount of loaded Pt can be adjusted from 7.3 to 27.7 wt% independently, which can be easily controlled by adjusting the precursor concentrations. Given their open pore structures and large surface area, Pt/BCN composites exhibit promising properties for use as electrocatalysts with high electrochemical active surface areas (84.9 m 2 g −1 ) and oxygen reduction reaction activity. The results suggest that this strategy can be widely applied to the deposition of metal NPs on highly controlled 3-D nanostructures.

Although recent development of lithium ion batteries with high energy and power density enables one to actuate electrical vehicles, many challenges concerning the operational sensitivity in extreme climate conditions still exist. In this work, we investigate the effect of three independent parameters on the performance of a lithium ion battery under low temperatures via computational modeling: (1) the diffusion coefficients of lithium ion, (2) the lithiation rate constants at the surface of active material, and (3) the particle radius of active material. From the computational approach, the regions associated with maximum capacity and voltage value are identified in the parameter space. To simulate the operation of battery at low temperature, the particle radius which is independent of temperature is chosen as the control parameter, and the temperature dependence of diffusion coefficient and reaction rate constant is also calculated. By correlating the three parameters with the temperature, the optimized particle radius which can exert high capacity and voltage under low temperature was found.

We report on an on-chip colorimetric method for the detection and analysis of Cu(2+) ions via the targeted assembly of plasmonic silver nanoparticles (2.6 nm satellites) on density-controlled plasmonic gold nanoparticles (50 nm cores) on a glass substrate. Without any ligand modification of the nanoparticles, by directly using an intrinsic moiety (carboxylate ion, COO(-)) surrounded with nanoparticles, the method showed a high selectivity for Cu(2+), resulting in a nearly 2 times greater optical response compared to those of other metal ions via the targeted core-satellites assembly. By modulating the surface chemistry, it was possible to control the density of core gold nanoparticles on the surface, thus permitting easy tuning of the optical responses induced by plasmon coupling generated between each core-satellites nanostructure. Using chips with a controlled optimal core density, we observed the remarkable scattering color changes of the chips from green to yellow and finally to orange with the increase of Cu(2+) concentration. The detection limits of the fabricated chips with controlled core densities (ca. 1821 and 3636 particles/100 μm(2)) are 10 nM and 10 pM, respectively, which are quite tunable and below the level of 20 μM (or 1.3 ppm) defined by the United States Environmental Protection Agency. The findings suggest that the method is a potentially promising protocol for detecting small molecules with target selectivity and the tunability of the detection limits by replacing with ligands and adjusting core densities.

Although little is known about the behavior of engineered nanomaterials after exposure to terrestrial areas, recent studies indicate that silver nanoparticles (AgNPs) can perturb the soil environment due to their biocidal and catalytic properties. The fundamental evaluation of the environmental fate of AgNPs would be a significant step toward a comprehensive understanding of the harmful effects of such particles on ecosystems. Therefore, from an eco-toxicological perspective, the estimation of AgNP behavior in soil should be investigated. Among the various environmental characteristics, the deposition of nanoparticles in the soil constitute is a critical step in their migration into surface or groundwater and interaction with organisms, which is determined by the stability of aqueous dispersions in a soil micro-environment. In the present study, we observed the aggregation and deposition of AgNPs to natural soil surfaces by comparing the partitioning of AgNPs in a soil/water interface with that of Ag + ion. Both AgNPs and Ag + ion were selectively quantified by means of inductively coupled plasma (ICP) spectrometry and an ion-selective electrode (ISE). We interpreted the partitioning of AgNPs and Ag + ion using the Freundlich isotherm and the findings indicate that AgNPs with reduced dispersion stability in a soil micro-environment were aggregated and deposited on the surface of natural soil. This study provides a fundamental basis for understanding the deposition of AgNPs, which will enable their accumulation and mobility in a soil environment to be predicted.

We report core-satellites (Au-Ag) coupled plasmonic nanoassemblies based on bottom-up, high-density assembly of molecular-scale silver nanoparticles on a single gold nanoparticle surface, and demonstrate direct observation and quantification of enhanced plasmon coupling (i.e., intensity amplification and apparent spectra shift) in a single particle level. We also explore metal ion sensing capability based on our coupled plasmonic core-satellites, which enabled at least 1000 times better detection limit as compared to that of a single plasmonic nanoparticle. Our results demonstrate and suggest substantial promise for the development of coupled plasmonic nanostructures for ultrasensitive detection of various biological and chemical analytes.

In situ monitoring of electrode materials reveals detailed physicochemical transition in electrochemical device. The key challenge is to explore the localized features of electrode surfaces, since the performance of an electrochemical device is determined by the summation of local architecture of the electrode material. Adaptive in situ techniques have been developed for numerous investigations; however, they require restricted measurement environments and provide limited information, which has impeded their widespread application. In this study, we realised an optics-based electrochemical in situ monitoring system by combining a dark-field micro/spectroscopy with an electrochemical workstation to investigate the physicochemical behaviours of Pt catalyst. We found that the localized plasmonic trait of a Pt-decorated Au nanoparticle as a model system varied in terms of its intensity and wavelength during the iterations of a cyclic voltammetry test. Furthermore, we show that morphological and compositional changes of the Pt catalyst can be traced in real time using changes in quantified plasmonic characteristics, which is a distinct advantage over the conventional electrochemistry-based in situ monitoring systems. These results indicate the substantial promise of online operando observation in a wide range of electrical energy conversion systems and electrochemical sensing areas.

Despite the significant advances in solid polymer electrolytes used for supercapacitors, intractable problems including poor ionic conductivity and low electrochemical performance limit the practical applications. Herein, we report a facile approach to synthesize a NaCl-agarose gel electrolyte for use in flexible supercapacitors. The as-prepared agarose hydrogel consists of a three-dimensional chemically interconnected agarose backbone and oriented interparticular submicropores filled with water. The interconnected agarose matrix acts as a framework that provides mechanical stability to the gel electrolyte and hierarchical porous networks for optimized ion transport. The developed pores with the water filler provide an efficient ionic pathway to the storage sites of electrode. With these properties, the gel electrolyte enables the supercapacitor to have a high specific capacitance of 286.9 F g(-1) and a high rate capability that is 80% of specific capacitance obtained in the case of a liquid electrolyte at 100 mV s(-1). In addition, attributed to the simple procedure and its components, the gel electrolyte is highly scalable, cost-effective, safe, and nontoxic. Thus, the developed gel electrolyte has the potential for use in various energy storage and delivery systems.

A demand for lithium-oxygen (Li-O­2) batteries with high storage capacity is increasing due to its application for the energy storage systems and electric vehicles. However, there are still critical bottlenecks for fabrication of a commercial Li-O2 battery. The cyclability of Li-O2 battery is very poor compared to lithium-ion battery. The main reasons for this problem are a variety of side reactions during the battery operation, which inactivate the lithium anode and cathode catalyst. To solve this problem, reversible charge/discharge reactions should be presented. During discharge reaction of Li-O2 battery, various superoxide and peroxide species, such as O2 -, LiO2 and Li2O2 appear. These nucleophilic molecules could react with electrolyte and carbon electrode. A dominant portions of side-reactions originate from this process. Therefore, we adopted a catalyst support with surface oxygen-defects to stabilize the nucleophilic molecules. In this study, we used zirconia as a support and observed that electrocatalyst with zirconia support exhibits better cyclability compared to that without support. Experimental and computational approaches are exploited to understand this phenomenon and we found that the reactivity of superoxide and peroxide species decrease with the oxygen-defective support. Our concept proposed in this study could be the clue for the design of cathode catalyst for reversible charge/discharge reactions.

This work reports a solution-based method for on chip growth of wrinkled gold nanoparticles. During the growth process, time-resolved scattering profiles were measured, which permitted one to collect information regarding the growth kinetics. Finally, using the fabricated substrate, a 30 times stronger SERS enhancement was achieved than a spherical nanoparticle immobilized substrate.

Great strides have been made in enhancing solar energy conversion by utilizing plasmonic nanostructures in semiconductors. However, current generation with plasmonic nanostructures is still somewhat inefficient owing to the ultrafast decay of plasmon-induced hot electrons. It is now shown that the ultrafast decay of hot electrons across Au nanoparticles can be significantly reduced by strong coupling with CdS quantum dots and by a Schottky junction with perovskite SrTiO3 nanoparticles. The designed plasmonic nanostructure with three distinct components enables a hot-electron-assisted energy cascade for electron transfer, CdS→Au→SrTiO3, as demonstrated by steady-state and time-resolved photoluminescence spectroscopy. Consequently, hot-electron transfer enabled the efficient production of H2 from water as well as significant electron harvesting under irradiation with visible light of various wavelengths. These findings provide a new approach for overcoming the low efficiency that is typically associated with plasmonic nanostructures.

The use of single gold nanoparticle plasmon-based spectroscopy for the sensitive, anion-selective detection of arsenate is described. The method is based on the selective formation of electrostatic complexes between arsenate and poly(allylamine hydrochloride) (PAH) and changes in the single particle plasmon in Rayleigh scattering profiles. PAH, when modified with gold nanoparticles, binds arsenate via its amine-functionalities. The scattering properties of the resulting selectively formed complexes are altered, leading to significant changes in the surface plasmon resonance wavelength. The limit of detection of the method was determined to be 10 nM, which is ca. 13 times more sensitive than U.S. EPA regulation levels. The response is essentially linear in the concentration range of 50-300 nM. The method also shows good selectivity for arsenate in the presence of other environmentally relevant anions, including H(2)PO(4)(-), SO(4)(2-), NO(3)(-), and Cl(-).

Cu/Zn-superoxide dismutase (SOD1) is present in the cytosol, nucleus, peroxisomes and mitochondrial intermembrane space of human cells. More than 114 variants of human SOD1 have been linked to familial amyotrophic lateral sclerosis (ALS), which is also known as Lou Gehrig's disease. Although the ultimate mechanisms underlying SOD1-mediated cytotoxicity are largely unknown, SOD1 aggregates have been strongly implicated as a common feature in ALS. This study examined the mechanism for the formation of SOD1 aggregates in vitro as well as the nature of its cytotoxicity. The aggregation propensity of SOD1 species was investigated using techniques ranging from circular dichroism spectroscopy to fluorescence dye binding methods, as well as electron microscopic imaging. The aggregation of SOD1 appears to be related to its structural instability. The demetallated (apo)-SOD1 and aggregated SOD1 species, with structurally disordered regions, readily undergo aggregation in the presence of lipid molecules, whereas metallated (holo)-SOD1 does not. The majority of aggregated SOD1s that are induced by lipid molecules have an amorphous morphology and exhibit significant cytotoxicity. The lipid binding propensity of SOD1 was found to be closely related to the changes in surface hydrophobicity of the proteins, even at very low levels, which induced further binding and assembly with lipid molecules. These findings suggest that lipid molecules induce SOD1 aggregation under physiological conditions and exert cytotoxicity, and might provide a possible mechanism for the pathogenesis of ALS.

Specific interactions between heavy metal ions and biomaterials have advantages in the sensitive and selective detection of the metal ions. In this study, Cu-demetallated form of Cu/Zn-superoxide dismutase (SOD1) protein was applied as a sensing probe in order to detect Cu(II) ions selectively via surface plasmon resonance (SPR) analysis. Because demetallated metalloproteins have vacant specific metal-binding sites in their own structures, Cu-demetallated SOD1 protein can successfully form stable complex with Cu(II) ion. By applying the properties as a sensing principle, we designed the Cu(II)-selective sensor chip with Cu-demetallated SOD1 protein. When Cu(II) ions were exposed to the fabricated sensor chips, their interaction was quantitatively measured via SPR analysis, and it was proportional to the concentrations of Cu(II) ions. This result reveals successful development of biosensor for the label-free selective detection of Cu(II) ions.

We demonstrate a novel biosensor for in vitro observation of cell membrane behaviors associated with proteins, adapting a supported lipid bilayer (SLB) that mimics the cellular membrane and using label-free surface plasmon resonance spectroscopy (SPRS). In this study, we focus on the detection of membrane behaviors by the specific types of Cu/Zn-superoxide dismutase (SOD1) species, which have been implicated in the neurodegenerative disease. The biomimetic sensor chip was fabricated by the fusion of unilamellar lipid vesicles on a hydrophilic Au surface for SPRS. After injection of several protein samples, the degradation signal of lipid membrane for specific type of protein species was real-time monitored by SPRS. This sensor allows one to observe in vitro the membrane damage due to the protein aggregations, and, importantly, to further develop biomarkers for injured cells.

A demand for lithium ion batteries which able to operate under harsh condition (e.g. low temperature) is increasing due to its application for the electric vehicles. However, there are still technical bottlenecks for fabrication of a battery cell operating at low temperature. To solve this problem, various parameters and its effects for the kinetic mechanism during battery charge/discharge should be clarified. Computational approach is exploited to understand the relationship between performance of battery and kinetic parameters. In this study, we choose three independent parameters which affects to capacity and operating potential of the battery: the diffusion coefficient of lithium ion in active material, the lithiation constant at the surface of the active material and the particle radius of the active material. Based on pseudo-2D model, the capacity and the operating potential are calculated by varying diffusion coefficient, rate constant, and particle radius. Because diffusion coefficient and rate constant is dependent on temperature, the performance of battery drastically decline at certain temperature. From this theoretical basis, we calculate the particle radius of active material for maximizing the capacity and the optimal operating voltage at low temperature.

We report on a one-step method for preparing nitrogen doped (N-doped) meso-/microporous hybrid carbon material (NCF) via the heat treatment of used cigarette filters under a nitrogen-containing atmosphere. The used cigarette filter, which is mostly composed of cellulose acetate fibers, can be transformed into a porous carbon material that contains both the mesopores and micropores spontaneously. The unique self-developed pore structure allowed a favorable pathway for electrolyte permeation and contact probability, resulting in the extended rate capability for the supercapacitor. The NCF exhibited a better rate capability and higher specific capacitance (153.8 F g(-1)) compared to that of conventional activated carbon (125.0 F g(-1)) at 1 A g(-1). These findings indicate that the synergistic combination of well-developed meso-/micropores, an enlarged surface area and pseudocapacitive behavior leads to the desired supercapacitive performance. The prepared carbon material is capable of reproducing its electrochemical performance during the 6000 cycles required for charge and discharge measurements.

Rayleigh scattering spectra of high-index {730} elongated tetrahexahedral gold nanoparticles and low-index {100}, {110}, and {111} gold nanorods were collected in real time in the reduction of 4-nitrophenol. The high-index facets are capable of accepting electrons seven times faster and emitting electrons two-and-a-half times faster than low-index facets.

A highly sensitive method for the selective detection and quantification of mercuric ions (Hg(2+)) using single plasmonic gold nanoparticle (GNP)-based dark-field microspectroscopy (DFMS) is demonstrated. The method is based on the scattering property of a single GNP that is functionalized with thiolated molecules, which is altered when analytes bind to the functionalized GNP. The spectral resolution of the system is 0.26 nm and a linear response to Hg(2+) was found in the dynamic range of 100 pM-10 microM. The method permits Hg(2+) to be detected at the picomolar level, which is a remarkable reduction in the detection limit, considering the currently proscribed Environmental Protection Agency regulation level (10 nM, or 2 ppb) and the detection limits of other optical methods for detecting Hg(2+) (recently approx. 1-10 nM). In addition, Hg(2+) can be sensitively detected in the presence of Cd(2+), Pb(2+), Cu(2+), Zn(2+) and Ni(2+), which do not interfere with the analysis. Based on the findings reported herein, it is likely that single-nanoparticle-based metal ion sensing can be extended to the development of other chemo- and biosensors for the direct detection of specific targets in an intracellular environment as well as in environmental monitoring.