Chia-Chun Chen

Highly Active and Stable Hybrid Catalyst of Cobalt-Doped FeS2 Nanosheets–Carbon Nanotubes for Hydrogen Evolution Reaction

Hydrogen evolution reaction (HER) from water through electrocatalysis using cost-effective materials to replace precious Pt catalysts holds great promise for clean energy technologies. In this work we developed a highly active and stable catalyst containing Co doped earth abundant iron pyrite FeS(2) nanosheets hybridized with carbon nanotubes (Fe(1-x)CoxS(2)/CNT hybrid catalysts) for HER in acidic solutions. The pyrite phase of Fe(1-x)CoxS(2)/CNT was characterized by powder X-ray diffraction and absorption spectroscopy. Electrochemical measurements showed a low overpotential of ∼0.12 V at 20 mA/cm(2), small Tafel slope of ∼46 mV/decade, and long-term durability over 40 h of HER operation using bulk quantities of Fe(0.9)Co(0.1)S(2)/CNT hybrid catalysts at high loadings (∼7 mg/cm(2)). Density functional theory calculation revealed that the origin of high catalytic activity stemmed from a large reduction of the kinetic energy barrier of H atom adsorption on FeS(2) surface upon Co doping in the iron pyrite structure. It is also found that the high HER catalytic activity of Fe(0.9)Co(0.1)S(2) hinges on the hybridization with CNTs to impart strong heteroatomic interactions between CNT and Fe(0.9)Co(0.1)S(2). This work produces the most active HER catalyst based on iron pyrite, suggesting a scalable, low cost, and highly efficient catalyst for hydrogen generation.

In Vitro and in Vivo Studies of FePt Nanoparticles for Dual Modal CT/MRI Molecular Imaging

The water-solvable FePt nanoparticles of 3, 6, and 12 nm in diameter (3 nm-, 6 nm-, and 12 nm-FePt) were synthesized and applied as a dual modality contrast agent for CT/MRI molecular imaging. These nanoparticles present excellent biocompatibility and hemocompatibility in all test concentrations for the imaging contrast. The biodistribution analysis revealed the highest serum concentration and circulation half-life for 12 nm-FePt, followed by 6 nm-FePt then 3 nm-FePt. Thus, the 3 nm-FePt showed higher brain concentrations. Anti-Her2 antibody conjugated FePt nanoparticles demonstrated molecular expression dependent CT/MRI dual imaging contrast effect in MBT2 cell line and its Her2/neu gene knock out counterpart. Selective contrast enhancement of Her2/neu overexpression cancer lesions in both CT and MRI was found in tumor bearing animal after tail vein injection of the nanoparticles. The 12 nm-FePt outperformed 3 nm-FePt in both imaging modalities. These results indicate the potential of FePt nanoparticles to serve as novel multimodal molecular imaging contrast agents in clinical settings.

FeS2 Nanocrystal Ink as a Catalytic Electrode for Dye‐Sensitized Solar Cells

In the last decade, dye-sensitized solar cells (DSSCs) have attracted great interest for the fabrication of low-cost largearea photovoltaic devices as an alternative to conventional inorganic counterparts. The counter electrode (CE) is a critical component in DSSCs, where electrons are injected into the electrolyte to catalyze iodine reductions (I3 to I ). The most commonly used CE is based on indium-doped tin oxide (ITO)-coated glass loaded with platinum by sputtering. Platinum has a high catalytic activity for triiodide reduction and presents sufficient corrosion resistance. However, Pt is expensive because of its scarcity, and thus, the development of so-called Pt-free CEs for DSSCs using cheaper and abundant materials becomes technologically desirable. Recently, carbon-based materials, such as graphite, graphene, carbon nanotubes, and conducting polymers, have been used to replace Pt as electrocatalysts for triiodide reduction in DSSCs, although these devices still suffer from poor thermal stability and weak corrosion resistance. Extensive research has been performed on using inorganic compounds such as transitional metal carbides, nitrides, oxides, and sulfides as a new class of alternative catalytic materials for Pt in DSSC systems. Therefore, pursuing low-cost and stable CE materials as alternatives to expensive Pt is crucial to make DSSC systems more competitive for future commercial applications. Pyrite iron disulfide (FeS2, so-called fool s gold) is an interesting next-generation photovoltaic material candidate that is abundant in nature and is nontoxic. It is ranked as having the highest material availability among 23 existing semiconducing photovoltaic systems that could potentially lead to lower costs compared to conventional silicon solar cells. Colloidal pyrite nanocrystals (NCs) were recently synthesized and characterized, providing great potential for developing low-cost fabrications of FeS2-based photovoltaic devices using solution processes. We first demonstrated pyrite NC-based photodiode devices with a spectral response extended to near infrared (NIR) wavelengths because of its large optical absorption coefficient (> 10 cm ) and narrow band gap of 0.95 eV, which provided a crucial step toward success in producing colloidal pyrite NCs thin films as photovoltaic absorption layers. This study demonstrates an important photovoltaic application using FeS2 nanocrystal pyrite ink to fabricate a cost-effective CE in DSSCs, which has the unique advantages of earth abundance and of being solution-processable. The DSSC device with the CE using the FeS2 NC ink exhibits a promising power conversion efficiency of 7.31% comparable to that of the cell using the precious metal of Pt deposited by sputtering (7.52 %), as well as remarkable electrochemical stability of greater than 500 consecutive cycle scans. Solution-processable and semi-transparent FeS2 NC-based CEs also enable the fabrication of flexible and bifacial DSSCs. The results indicate that FeS2 NC ink is an extremely promising candidate for replacing Pt to substantially reduce the cost of DSSCs in future commercial applications and have also shed light on employing the low-cost FeS2 NC catalyst in other electrochemical cells. The FeS2 NCs were prepared using wet solution-phase chemical syntheses with a number of modifications according to our previous reports. 25] Figure 1a shows a highresolution transmission electron microscopy (HR-TEM) image of an FeS2 NC with a diameter of 15 3 nm. The clear lattice fringes of the FeS2 NCs with a lattice spacing of 0.31 nm matched the (111) plane of pyrite. The fast Fourier transform (FFT) patterns shown in Figure 1b exhibited various index facets, including {210}, {211}, and {311} on the NC, showing typical signatures of a pyrite-phased crystal structure.Figure 1 c shows a photograph of the FeS2 NCs ink. For fabricating the FeS2 NC CE, FeS2 NC ink of concentration 30 mg mL 1 was spin-coated onto an ITO glass substrate at 4000 rpm for 20 s, as shown in Figure 1d. Because as[*] Y.-C. Wang, Dr. D.-Y. Wang, H.-A. Chen, Prof. C.-W. Chen Department of Materials Science and Engineering National Taiwan University No. 1, Sec. 4, Roosevelt Rd., Taipei, 10617 (Taiwan) E-mail: chunwei@ntu.edu.tw

A mini review on nickel-based electrocatalysts for alkaline hydrogen evolution reaction

High gravimetric energy density, earth-abundance, and environmental friendliness of hydrogen sources have inspired the utilization of hydrogen fuel as a clean alternative to fossil fuels. Hydrogen evolution reaction (HER), a half reaction of water splitting, is crucial to the low-cost production of pure H2 fuels but necessitates the use of electrocatalysts to expedite reaction kinetics. Owing to the availability of low-cost oxygen evolution reaction (OER) catalysts for the counter electrode in alkaline media and the lack of low-cost OER catalysts in acidic media, researchers have focused on developing HER catalysts in alkaline media with high activity and stability. Nickel is well-known as an HER catalyst and continuous efforts have been undertaken to improve Ni-based catalysts as alkaline electrolyzers. In this review, we summarize earlier studies of HER activity and mechanism on Ni surfaces, along with recent progress in the optimization of the Ni-based catalysts using various modern techniques. Recently developed Ni-based HER catalysts are categorized according to their chemical nature, and the advantages as well as limitations of each category are discussed. Among all Ni-based catalysts, Ni-based alloys and Ni-based hetero-structure exhibit the most promising electrocatalytic activity and stability owing to the fine-tuning of their surface adsorption properties via a synergistic nearby element or domain. Finally, selected applications of the developed Ni-based HER catalysts are highlighted, such as water splitting, the chloralkali process, and microbial electrolysis cell.

Infrared and Raman-scattering studies in single-crystalline GaN nanowires

Abstract Infrared and Raman-scattering studies of high-purity and -quality GaN nanowires are presented. The nanosize dependences of the peak shift and the broadening of the four first-order Raman modes agree with those calculated on the basis of the phonon confinement model. Additionally, the appearance of one Raman mode at ∼ 254 cm −1 is attributed to zone-boundary phonon activated by surface disorders and finite-size effects. Moreover, the Raman-scattering intensities of certain phonons show a different resonantly enhanced behavior, which can be used to verify the information on the electronic structures and the electron–phonon interaction in GaN nanowires.

Electrically controlled surface plasmon resonance frequency of gold nanorods

We have presented the voltage-controlled tuning of plasmonic response of absorption spectra of gold nanorods in liquid crystals. We observe that gold nanorods can be aligned along the rubbed polyimide substrate before applying external voltage. It is found that the transverse mode of gold nanorods shows a blueshift or a redshift when rotating the analyzer parallel or perpendicular to the rubbing direction, respectively, while all longitudinal modes display a redshift behavior. This work offers an easy way to tune the transverse and longitudinal modes of gold nanorods simultaneously, which makes it feasible to establish the color tunable devices.

Carrier transfer induced photoluminescence change in metal-semiconductor core-shell nanostructures

Metal-semiconductor core-shell nanostructures have been synthesized to explore the influence of metal nanostructures on the photoluminescence of semiconductors. Up to 40 times enhancement in the emission intensity was observed in the Au–CdS core-shell nanostructures. The mechanism where the excited electrons on Au surface by surface plasmon wave transfer to the conduction band of the CdS shell and recombine with holes in the valence band was proposed to interpret the enhancement. Our model can also be used to explain the quenched emission in FePt–CdS core-shell nanostructures and Au–CdSe nanodumbbells.

Multiple Release Kinetics of Targeted Drug from Gold Nanorod Embedded Polyelectrolyte Conjugates Induced by Near-Infrared Laser Irradiation

The conjugates of gold nanorods and the model drug, fluorescein isothiocyanate (FITC), embedded inside polyelectrolytes (GNRs/FITC@PLE) were synthesized to study the release kinetics of FITC under femtosecond near-infrared (NIR) laser irradiation. The optical and structural properties of GNRs/FITC@PLE conjugates before and after laser treatments were examined using UV-vis spectroscopy, confocal microscopy, and transmission electron microscopy (TEM). The release of FITC from the conjugates was induced by the heat generated from gold nanorods under laser irradiation. The concentration of released FITC was measured as the time of continuous and periodic laser irradiation was varied. Within 5 min of the laser exposure, the release rates of FITC exhibited zero-order and first-order kinetics under continuous and periodic irradiation, respectively. Furthermore, a drug release system was designed based on the conjugates of gold nanorods and the anticancer drug, paclitaxel (PTX), embedded inside polyelectrolytes (GNRs/PTX@PLE). The conjugates were applied for in vitro studies with breast cancer cells. The release of PTX from the conjugates was triggered by NIR laser irradiation, and the inhibition rates of the cells showed strong dependencies on the irradiation modes and time. The results suggested that the multiple releases of PTX from the conjugates can be controlled by laser irradiation within a long period of time. Our system holds great potential for future therapeutic applications on breast cancers.

Globotriose-Functionalized Gold Nanoparticles as Multivalent Probes for Shiga-like Toxin

Compared to monovalent carbohydrates, multivalent carbohydrate ligands exhibit significantly enhanced binding affinities to their interacting proteins. Here, we report globotriose (Pk ligand)‐functionalized gold nanoparticle (AuNP) probes for the investigation of multivalent interactions with the B5 subunit of Shiga‐like toxin I (B‐Slt). Six Pk‐ligand‐encapsulated AuNPs (Pk‐AuNPs) of varying particle size and linker length were synthesized and evaluated for their potential as multivalent affinity probes by using a surface plasmon resonance competition assay. The affinity of these probes for the interacting proteins was greatly affected by nanoparticle size, linker length, and ligand density on nanoparticle surface. For example, the 20‐nm 20‐Pk‐l‐AuNP, which had a relatively long linker showed a >108‐fold increase in affinity compared with the mono Pk ligand. This intrinsic high‐affinity AuNP probe specifically captured the recombinant B‐Slt from Escherichia coli lysate, and the resulting purity of the B‐Slt was >95 %. We also developed a robust Pk‐AuNP‐based detection method for Slt‐I by combining the technique with silver enhancement.

Solution-Processable Pyrite FeS2 Nanocrystals for the Fabrication of Heterojunction Photodiodes with Visible to NIR Photodetection

A heterojunction photodiode with NIR photoresponse using solution processable pyrite FeS(2) nanocrystal ink is demonstrated which has the advantages of earth-abundance and non-toxicity. The device consists of a FeS(2) nanocrystal (NC) thin film sandwiched with semiconducting metal oxides with a structure of ITO/ZnO/FeS(2) NC/MoO(3) /Au, which exhibits an excellent photoresponse with a spectral response extended to NIR wavelengths of up to 1150 nm and a high photocurrent/dark current ratio of up to 8000 at -1 V under AM1.5 illumination (100 mW cm(-2) ).