Noble Metal Deposition Research Articles

Ag-Modified BiOCl Single-Crystal Nanosheets: Dependence of Photocatalytic Performance on the Region-Selective Deposition of Ag Nanoparticles

For single-crystal photocatalysts, selective deposition of noble metals as electron cocatalysts has been demonstrated to be an effective method to improve their photocatalytic performance. However, the effect of the selective deposition location of noble metals on the photocatalytic performance of single-crystal photocatalysts has not been really revealed, because the noble metals can only be selectively deposited on the electron-enrichment facets and cannot be modified on the hole-enrichment facets due to the absence of effective deposition methods. In this study, a photosensitization-deposition strategy, as a new selective deposition method, has been developed to selectively deposit Ag nanoparticles on the hole-enrichment regions (the lateral surfaces) of BiOCl single-crystal nanosheets (referred to as Ag/BiOCl(Dye)), and the effect of selective-deposition locations of Ag nanoparticles on the photocatalytic performance of BiOCl single-crystal photocatalysts has been investigated. For comparison, Ag nano...

Morphology control of noble metal catalysts from planar to dendritic shapes by galvanic displacement

Noble metal electrocatalysts can simply be prepared via galvanic displacement method on a sacrificial substrate, which is advantageous for preparing a uniform and thin catalyst layer. However, it is difficult to control the morphology of deposited metals via galvanic displacement, therefore, there is a limitation to increase the surface area of electrocatalysts. In this study, we demonstrate galvanic displacement for controlling the morphology of Pd, Pt, and Au from planar to whisker shapes by manipulating the dissolution rate of the sacrificial Cu substrate and the mass transport of noble metal ions. The acceleration of the dissolution of sacrificial substrate increases the reduction rate of noble metal, which develops a steep concentration gradient of noble metal ions near the surface of substrate. This induces the selective deposition of noble metal to form a whisker instead of smooth film. To verify the advantage of whisker-type catalysts, the ethanol oxidation with Pd is investigated. Whisker-type Pd shows 21 times higher electrocatalytic performance than planar Pd due to larger surface area. Therefore, it can be suggested that whisker-type catalysts simply prepared by galvanic displacement is applicable for various electrocatalytic reactions.

Pulse Potential Deposition - an Experimental Protocol for Growth of High Quality Thin Films Via Surface Limited Red-Ox Replacement Reaction

Pulse Current Deposition method for growth of thin films and functional coatings has been in use in academia and industry for quite some time [[1]]. However, with few exemptions [[2]], the application of the pulse potential deposition for growth of metallic coatings was mainly confined to academic studies where the conductivity of the substrate, substrate morphology and size do not present a major challenge. Over the years, different deposition protocols have been developed which leverage the benefit of Underpotentially Deposited Monolayers (UPD ML) as a surfactants, mediators or sacrificial materials in deposition process [[3]]. In these examples, the essential step that results in the desired growth mode is achieved by precise control of the electrode potential at which action of the UPD ML is exploited. One of them is deposition via Surface Limited Redox Replacement (SLRR) reaction [[4],[5]], where the main role of UPD layer is to serve as sacrificial reducing metal for deposition of controlled amount of more noble metal. Both, thermodynamics and kinetics of this deposition process are now reasonably well understood which opens more opportunities for practical applications [[6]]. In this talk we show that the control of deposition process during pulse potential deposition is facile and extendable to large area sample plating. The experimental study focuses on design of simple pulse potential function (on/off) for deposition of noble metal coatings on model substrates such as Au and on industrially relevant substrates such as Cu and Ru. The “on” step of the potential cycle is designed to produce a full UPD ML on the substrate surface. The main growth of the deposit occurs during the “off” step of the potential cycle. In this step, at OCP, the deposition of noble metal occurs via SLRR of UPD ML [5]. We will discuss the important parameters of the potential pulse function such as pulse time, off time, and their relation to the deposit morphology, composition and stress. The terminal effect as well as the effect of solution conductivity and solution design in terms of the mutual ratio of UPD metal and depositing metal ion concentration will be discussed as well. [1] J.C. Puippe and F. Leaman, Theory and Practice of Pulse Plating, AESF, (1986). [2] Modern Electroplating V, editors: M. Paunovic and M. Schlesinger, John Willey and Sons, Inc (2010). [3] Chapter 27- Applications to Magnetic Recording and Microelectronic Technologies, S.R. Brankovic, N. Vasiljevic, N. Dimitrov, Modern Electroplating V, editors: M. Paunovic and M. Schlesinger, John Willey and Sons, Inc (2010). [4] S. R. Brankovic , J. X. Wang and R.R. Adzic, Surface Science , 474, L173, (2001). [5] N. Dimitrov, Electrochimica Acta, 209, 599 (2016). [6] Chapter 3: Electrochemical Surface Professes and Opportunities for Material Synthesis, Stanko R. Brankovic and Giovanni Zangari in Electrochemical Engineering Across Scales: From Molecules to Processes, Editors: R. C. Alkire, P. N. Bartlett, J. Lipkowski, Advances in Electrochemical Science and Engineering, vol. 15, Willey-VCH (2015) p. 59-107.

All Polymeric Electrochemical Biochip Array of Patterned Gold on Silver Inkjet Printed Polyimide

Direct writing of patterned functional electronic materials provides a new path to low cost and high throughput fabrication technology for producing integrated flexible circuits. However, it is equally important to assimilate printing technologies with solution based deposition steps in the same environment to attain a continuous and useful manufacturing process[1]. Direct patterning by inkjet printer have advantages of being low capitalization and equipment cost, high material efficiency (less than 5% of material gets wasted) and elimination of processes like photolithography[2]. Nevertheless, printed materials are characterized today by poor electrochemical performance due to i) residues of the ink binding materials on the surface of the printed circuits; ii) texture and morphologies (i.e. roughness, porosity); iii) surface impurities such as oxides. Therefore, currently, ink-jet printed electrodes have inferior biosensing properties compared to common negative printed electrodes where the metal is deposited by physical, chemical or electrochemical methods. A very realistic and simple approach to solve this issue is solution based deposition of noble catalytic metals on printed seed layer. This two-step process provides a relatively pure noble metallic high quality surface with good electrochemical properties for biosensing application. Moreover, this process is compatible with most solid and flexible substrates and fabrication processes. A simple and efficient method has been developed to fabricate flexible, patterned gold (Au) biochip array. Micro-patterns of silver (Ag) ink were printed and dried on polyimide substrates. These micro patterns served as the activating seed layer for electrochemical Au deposition. Au deposition was carried out on Ag ink printed microchip array for various intervals of time to determine desired thickness. The thickness and conductivity measurements were performed. To investigate bio-electrochemical properties of the Au deposited chips, electrochemical impedance spectroscopy and cyclic voltammetry will be applied. The biosensing capabilities will be studied by the chronoamperometric method for different enzyme concentration. Keywords: Inkjet printing, bio-electrochemical , Biochip array, Direct patterning.

A New Strategy to Design Highly Sustainable Sulfide PhotoCatalyst for Hydrogen Production

AbstractA new strategy has been developed to design sulfides photocatalysts with superior stability without any noble metal deposition. The as‐designed Ag8SnS6 showed capability of steadily evolving hydrogen for at least 400 h without any deactivation and the turnover number is as high as 95.8.

Surface characterization and antibacterial response of silver nanowire arrays supported on laser-treated polyethylene naphthalate

Polymeric biomaterials with antibacterial effects are requisite materials in the fight against hospital-acquired infections. An effective way for constructing a second generation of antibacterials is to exploit the synergic effect of (i) patterning of polymeric materials by a laser, and (ii) deposition of noble metals in their nanostructured forms. With this approach, we prepared highly-ordered periodic structures (ripples) on polyethylene naphthalate (PEN). Subsequent deposition of Ag under the glancing angle of 70° resulted in the formation of self-organized, fully separated Ag nanowire (Ag NW) arrays homogenously distributed on PEN surface. Surface properties of these samples were characterized by AFM and XPS. Vacuum evaporation of Ag at the glancing angle geometry of 70° caused that Ag NWs were formed predominantly from one side of the ripples, near to the top of the ridges. The release of Ag+ ions into physiological solution was studied by ICP-MS. The results of antibacterial tests predetermine these novel structures as promising materials able to fight against a broad spectrum of microorganisms, however, their observed cytotoxicity warns about their applications in the contact with living tissues.

Miniature Fuel Cell with Monolithically Fabricated Si Electrodes -Fabrication of Pd-Pt Catalyst By H-UPD-Slrr-

Miniature fuel cells have attracted attention as an ultimate portable power source, and we have developed monolithically fabricated Si electrodes for the miniature fuel cells[1]. Recent prototypes showed satisfying power density about 500mW/cm2 at 313K though the reaction area was only 1 mm2. Besides, the prototype cells used porous Pt as a catalyst layer, and the amount of Pt was quite large. 3.6mg/cm2of Pt was used and the amount of Pt must be reduced. Then, to reduce the Pt amount, slight deposition of Pt on porous Pd was attempted using UPD-SLRR (Underpotential Deposition, and Surface Limited Redox Replacement), and obtained Pd-Pt catalyst showed quite promising results[2]. Furthermore, preliminary results suggested that the Pd-Pt catalyst had high CO tolerance. We are also interested in the use of biomass derived hydrogen for our miniature fuel cells and the high CO tolerance is strongly needed. Therefore, further study of the Pd-Pt catalyst obtained using the UPD-SLRR technique. However, Cu UPD was used for SLRR and the reproducibility was not good enough, because bath change was needed between UPD and SLRR processes, and Cu oxidation was not negligible. Recently, Nutariya et al. reported that UPD-SLRR reaction is available using hydrogen UPD[3]. If this process could be applied to our porous Pd as shown in figure 1, no bath change is needed and repetitive deposition of Pt or other noble metal would be realized, and optimization of the Pd-Pt catalyst would be possible. In this study, Pt deposition on the porous Pd was attempted by H-UPD-SLRR process, and the power generation by the obtained fuel cells was demonstrated. Experimental The Si substrate used in this study was N-type (Resistivity 0.004-0.006 Ohm-cm), (100) oriented, double side mirror polished and 100 um thick wafer. The porous Pd was formed on a Si substrate using anodize porous Si. H-UPD-SLRR was performed on the porous Pd in a solution of 1mM H2PtCl6 and 0.1 M HClO4. MSE was used as a reference electrode. As a counter electrode, Pt wire was used. The electrolyte solution was deaerated for 30 minutes with N2 gas and the whole vessel for the H-UPD-SLRR was filled with N2 during the experiment. H-UPD process was performed at -600mV vs. MSE for 30 seconds. Subsequently, SLRR process was performed by opening the circuit until the electrode potential reached -280mV vs. MSE. Using the slightly Pt deposited porous Pd layer was used as catalyst layers, prototype fuel cells were built. Power generation tests were performed by the cells whose anode and cathode catalysts were Pd-Pt and Pt, respectively. Prototype cells were set into the aluminum casing at 313K in a temperature controllable chamber. 10 sccm pure hydrogen or hydrogen containing 100ppm CO were supplied to the anode. 5sccm oxygen was supplied to the cathode. Power generation was performed for more than 1 hour, and tolerance of the catalyst to the CO poisoning was observed. Results Figure 2 shows cross sectional SEM image of the porous Pd-Pt catalyst layer. Cross sectional EDS analysis of the porous Pd-Pt catalyst layer showed slight Pt deposition, and it seemed that expected reaction was realized(figure 3). The amount of Pt was estimated to be about 20 μg/cm2from the charge of underpotential H deposition. Figure 4 shows preliminary result of power generation test of Pd-Pt catalyst. Red line shows the polarization curve with pure hydrogen supply, and blue line shows polarization curve with hydrogen containing 100 ppm CO. Though the power density was dropped with 100 ppm CO, the power density kept almost constant more than 1h, though conventional catalyst shows quick power drop with 100ppm CO. With these results, CO tolerance was reconfirmed with Pd-Pt catalyst obtained by novel H-UPD-SLRR process. With the H-UPD-SLRR process, amount of Pt deposition can be finely controlled, and further optimization of the catalyst will be performed.

Quasi-noble-metal graphene quantum dots deposited stannic oxide with oxygen vacancies: Synthesis and enhanced photocatalytic properties

Quasi-noble-metal graphene quantum dots (GQDs) deposited stannic oxide (SnO2) with oxygen vacancies (VOs) were prepared by simply sintering SnO2 and citric acid (CA) together. The redox process between SnO2 and GQDs shows the formation of oxygen vacancy states below the conduction band of stannic oxide. The produced VOs obviously extend the optical absorption region of SnO2 to the visible-light region. Meanwhile, GQDs can effectively improve the charge-separation efficiency via a quasi function like noble metal and promote the visible-light response to some degree. In addition, the samples calcinated at 450°C reveals the best performance because of its relatively high concentrations of VOs. What is more, the possible degradation mechanism has been inferred as extended visible-light response as well as raised charge-separation efficiency has also been put forward. Our work may offer a simple strategy to combine the defect modulation and noble metal deposition simultaneously for efficient photocatalysis.

Photocatalytic Water Splitting-The Untamed Dream: A Review of Recent Advances.

Photocatalytic water splitting using sunlight is a promising technology capable of providing high energy yield without pollutant byproducts. Herein, we review various aspects of this technology including chemical reactions, physiochemical conditions and photocatalyst types such as metal oxides, sulfides, nitrides, nanocomposites, and doped materials followed by recent advances in computational modeling of photoactive materials. As the best-known catalyst for photocatalytic hydrogen and oxygen evolution, TiO2 is discussed in a separate section, along with its challenges such as the wide band gap, large overpotential for hydrogen evolution, and rapid recombination of produced electron-hole pairs. Various approaches are addressed to overcome these shortcomings, such as doping with different elements, heterojunction catalysts, noble metal deposition, and surface modification. Development of a photocatalytic corrosion resistant, visible light absorbing, defect-tuned material with small particle size is the key to complete the sunlight to hydrogen cycle efficiently. Computational studies have opened new avenues to understand and predict the electronic density of states and band structure of advanced materials and could pave the way for the rational design of efficient photocatalysts for water splitting. Future directions are focused on developing innovative junction architectures, novel synthesis methods and optimizing the existing active materials to enhance charge transfer, visible light absorption, reducing the gas evolution overpotential and maintaining chemical and physical stability.

Synthesis of Ultrastable Ag Nanoplates/Polyethylenimine–Reduced Graphene Oxide and Its Application as a Versatile Electrochemical Sensor

Investigations on Ag nanostructures/reduced graphene oxide composites have been frequently reported, yet the morphology control of those loaded Ag nanocrystals is still challenging. We herein develop a facile method to grow triangular Ag nanoplates (AgP) on polyethylenimine-modified reduced graphene oxide (AgP/PEI-rGO). The AgP/PEI-rGO hybrids show unexpected high stability against chloride ions (Cl(-) ) and hydrogen peroxide (H2 O2 ), which is possibly due to the strong interaction between surface Ag atoms with the amine groups of PEI. In the chronoamperometry measurements for detecting H2 O2 , N2 H4 , and NaNO2 , the AgP/PEI-rGO hybrid shows very wide linear ranges (usually 10(-6) -10(-2) mol L(-1) for H2 O2 , N2 H4 , and NaNO2 ) and low detection limits (down to ≈1×10(-7) mol L(-1) ), which demonstrate the promising electrochemical sensor applications of these metal/graphene hybrids with well-defined morphologies and facets. In addition, this strategy could be extended to the deposition of other noble metals on rGO with controlled morphologies.

Synthesis of Photocatalytic Nanocomposite Biomaterials for Enhanced Water Filtration Application

Clean and drinkable water is a critical necessity for all human and economic development; unfortunately, millions of people do not have access to potable water, resulting in the death of over 2 million children every year. Over the past decade, emphasis has been placed on the synthesis and design of photocatalytic nanocomposites to enhance the chemical degradation of organic pollutants as a cost effective vehicle for clean water production. Amongst the many semiconducting nanoparticles explored in literature, TiO2has stood out for its favorable physiochemical properties, low toxicity, easy availability, high stability, and low cost. When TiO2is irradiated by ultraviolet light, there is creation an electron-hole pair which provides sites for effective reduction or oxidization of the pollutant, converting the pollutant to carbon dioxide, water, and mineral acids. One major shortcoming of TiO2 is related to the efficiency of these systems to harness the entire solar spectrum; therefore, a main focus of this work is the modification of the TiO2 nanoparticles to increase the photon capture efficiency in the visible light region. Of the various possible functionalization pathways, this work focuses on dye sensitization, noble metal deposition, and silane functionalization as well as understanding the synergy between all three. When looking at the rate of remediation of a organic dye pollutant in a simulated sunlight environment, the functionalized particles completely remediated an organic dye pollutant. These functionalized nanoparticles were then deposited into a cellulose matrix of highly absorbent beads in order to prepare a nanocomposite. Results show there is a decrease in the chemical degradation of the pollutant when in the nanocomposite, but a significant increase in a physio-absorption capacity, thus maintaining the rate of total remediation. In addition, the binding interaction between the dye and the particle is a major component in chemical degradation; an aminosilane can be covalently added to the surface of the nanoparticle, and increase the ability of various dyes to adhere to the surface of the TiO2. The incorporation of Ag-functionalized nanocomposites resulted in a synergistic antimicrobial effect, which eliminated both E. coli and S. aureus from the water sample, in addition to increasing the photochemical degradation rate. The specific aim of this work was to create functionalized TiO2 particles with silane groups, organic dyes, and Ag, for the incorporation into a photocatalytic biomimetic nanocomposite membrane which utilizes sunlight to degrade pollutants and inhibit the growth of deadly bacteria.

Electrocatalytic Activity of Au Core Au-Pt Alloy Shell Nanoparticles Prepared on Ionic Liquid Surface Via Metal Sputtering Deposition

Pt-based bimetallic nanoparticles (NPs) have been considered to be promising materials as electrocatalysts for improving the performance of fuel cells such as a direct methanol fuel cell because of decreasing CO poisoning on Pt surface and enhancing reactivity of Pt via a ligand effect. The compositional control of electrocatalyst surface is of significant importance to effectively utilize noble metals and to improve the electrocatalytic activities, because electrochemical reactions only occurs on the surface of particle catalysts. In our previous study, we have reported a facile method to synthesize noble metal NPs by metal sputter deposition on room temperature ionic liquids (RTILs) under vacuum condition.(1) This RTIL/metal sputtering technique was also useful to prepare core-shell-structured particles of Au@In2O3 and Pt@In2O3, which were prepared by the successive sputter deposition of noble metals and Indium into RTILs. Recently we have reported that a monolayer of Au nanoparticles was formed on the RTIL surface with single step deposition process when Au sputter deposition was carried out onto the surface of RTILs containing hydroxyl-functionalized cations.(2)In this study, we report the synthesis of Au core-AuPt alloy shell NPs monolayer by the sequential sputter deposition of Au and Pt onto hydroxyl-functionalized RTILs. The surface coverage of Pt atoms on individual Au NPs could be controlled with variation of Pt sputtering time. Original Au NPs monolayer was prepared by the sputter deposition of Au on the surface of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (HyEMI-BF4) used as a RTIL with a discharge current of 10 mA under argon pressure of 20 Pa for 150 s. The subsequent sputter deposition of Pt was carried out on thus-obtained Au NPs monolayer. The sputtering condition used for Pt deposition was the same as that used for Au deposition except for sputtering time. The sputter deposition of Au changed the color of RTIL surface from colorless to reddish blue due to the Au film formation. By subsequent sputter deposition of Pt, the film on the solution surface tuned brownish. Extinction spectra of films showed an LSPR peak at 540 nm, the intensity of which was lessened with an increase in the Pt sputtering time and finally vanished after Pt sputter deposition for 80 min or more. This result suggested that the sputter deposition of Pt onto Au film caused surface modification of individual Au NPs. From TEM measurement, it was found that the films prepared by sputter deposition of Au and Pt were monolayers composed of spherical particles, the size of which increased with elapse of Pt sputtering time from 4.2 to 4.8 nm. Since pure Pt particles were not observed in the film, it was suggested that sputtered Pt species were simply deposited on individual Au particles floated on the RTIL surface without additional nucleation. The XPS measurement revealed that deposited Pt formed the surface layer composed of Au-Pt alloy on Au cores. The cyclic voltammograms of Au-Pt bimetallic NPs monolayers transferred on HOPG electrodes were measured in an N2-saturated 0.5 mol dm-3 H2SO4aqueous solution, in which a cathodic peak assigned to the reduction of Au oxide monolayer appeared at 1.2 V vs. RHE along with a pair of redox peaks attributable to the adsorption/desorption of hydrogen on Pt surface at ca. 0.02-0.04 V vs. RHE. The electrochemical surface areas (ECSA) of Au and Pt were obtained by measuring charges flowed in reduction of Au oxide monolayer and in hydrogen desorption on Pt surface, respectively. The fraction of Pt ECSA was higher than the Pt content in particles, regardless of Pt sputtering time, indicating that Pt atoms were predominantly deposited on the surface of Au particles. The methanol oxidation activity of the Au-Pt NPs monolayers was evaluated by a cyclic voltammetry in a 0.5 mol dm-3 KOH aqueous solution containing 0.5 mol dm-3methanol. The obtained voltammograms exhibited an anode peak at ca. 0.9 V vs. RHE, assignable to methanol oxidation (Fig. 1). The peak current intensity of methanol oxidation for Au-Pt bimetallic films was dependent on the Pt sputtering time but was larger than those of monometallic counterparts, indicating that the electrocatalytic activity for methanol oxidation was enhanced by the modification of Au NPs monolayer with AuPt alloy shell layer. The maximum intensity was obtained for the Au-Pt NPs film prepared with Pt sputtering time for 80 min. References T. Torimoto, et al., Appl. Phys. Lett., 89, 243117 (2006).T. Torimoto, et al., Phys. Chem. Chem. Phys., 17, 13150 (2015). Figure 1

Fabrication of silicon nanorod arrays via a facile metal-assisted chemical etching method

Si nanorod arrays exhibit promising potential applications in many fields compared with the bulk counterpart. Therefore, development of a facile and cost-effective method for the fabrication of this kind of nanostructures is essential to enabling a wide range of advanced technologies in electronics and optics. In this paper, a simple and low cost method is presented and the fabrication process includes a combination of polystyrene sphere lithography and metal-assisted chemical etching. Compared with previously reported polystyrene sphere lithography methods, present fabrication has the advantage of simplicity. In addition, the fabrication involves no reactive ion etching equipment or noble metal deposition facilities. Based on the experimental results, a plausible mechanism is proposed to explain the formation of Si nanorod arrays.

The dependence of photocatalytic activity on the selective and nonselective deposition of noble metal cocatalysts on the facets of rutile TiO2

The spatial loading of redox cocatalysts on the different facets of a semiconductor is a novel and ideal approach to constructing an efficient photocatalytic system. Here, taking the series of rutile TiO2 as the research model, the origin of the preferential deposition of noble metal cocatalysts on the particular facet (110) was carefully studied under various experimental conditions, including the effect of fluoride species on the surface, as well as different noble metal deposition methods. Our results clearly show that the noble metals could be photodeposited exclusively on the (110) facet. This implies that the origin of noble metal preferential deposition on the (110) facet of rutile TiO2 is due to the reduction of the noble metal precursors by the photoexcited electrons enriched on the particular facet of (110). Rutile TiO2 samples with cocatalyst selectively deposited on the (110) facets have much higher photocatalytic H2 production activity than rutile samples with noble metal cocatalysts randomly deposited on the entire surface. This demonstrates that facet charge separation upon photoexcitation may be a unique route for efficient photocatalytic systems.

Facile synthesis of gold nanoparticle-coated polystyrene composite particles templated from Pickering emulsion

Abstract Herein we develop a facile and controllable strategy for the preparation of composite particles composed of polystyrene (PS) microspheres decorated with gold nanoparticles (AuNPs) through Pickering emulsion template. The oil-in-water Pickering emulsion is prepared using unmodified citrate-stabilized AuNPs and toluene solution of unfunctionalized PS as stabilizer and dispersion phase, respectively. After the evaporation of toluene from the Pickering emulsion, the AuNP-coated PS composite particles are obtained. The resultant AuNP-coated PS composite particles have been characterized extensively by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. Significantly, our method enables easy and effective control over the size and surface coverage of AuNPs on the surface of PS microspheres. Furthermore, the proposed method does not only allow the easy deposition of other noble metal (Ag, Pt, and Pd) nanoparticles onto the surface of PS microspheres but also can be directly applicable to the employed PS polymers derived from different approaches. In addition, the AuNP-coated PS composite particles as an example exhibited excellent catalytic activity and recyclability in the reduction of rhodamine B by NaBH4.

Ultrafast photoinduced carrier dynamics at ZnO nanohybrid interfaces for light-harvesting applications

AbstractThe use of nanoscale materials for efficient solar light harvesting has attracted immense attention in the recent time in order to address the energy and environmental issues. Among them, semiconductor materials such as ZnO have been widely used in the field of photocatalysis and dye-sensitized solar cells (DSSC). However, due to limited visible-light activity and low photo-conversion efficiency, ZnO needs to be modified to design heterostructures with efficient charge separation. Several strategies have been made to modify the wide-bandgap semiconductors including narrow-bandgap semiconductor coupling, noble metal deposition, conducting polymer sensitization and organic dye sensitization. However, the activity of such heterogeneous systems critically depends on the charge dynamics across the involved nanostructured interface. The present review is an effort to unravel the ultrafast dynamical processes across the interface of heterostructures to enhance the solar light-harvesting efficiency. Here, we have discussed few of our selected results covering the different modification strategies of the ZnO nanostructures. The special emphasis has been given to the correlation between the ultrafast processes at the interface and their implications in the light-harvesting applications. The detailed spectroscopic investigations revealing electronic pathways for light harvesting will be helpful in designing future solar devices.

Biosensor based on excessively tilted fiber grating in thin-cladding optical fiber for sensitive and selective detection of low glucose concentration.

We report a highly sensitive, high Q-factor, label free and selective glucose sensor by using excessively tilted fiber grating (Ex-TFG) inscribed in the thin-cladding optical fiber (TCOF). Glucose oxidase (GOD) was covalently immobilized on optical fiber surface and the effectiveness of GOD immobilization was investigated by the fluorescence microscopy and highly accurate spectral interrogation method. In contrast to the long period grating (LPG) and optical fiber (OF) surface Plasmon resonance (SPR) based glucose sensors, the Ex-TFG configuration has merits of nearly independent cross sensitivity of the environmental temperature, simple fabrication method (no noble metal deposition or cladding etching) and high detection accuracy (or Q-factor). Our experimental results have shown that Ex-TFG in TCOF based sensor has a reliable and fast detection for the glucose concentration as low as 0.1~2.5mg/ml and a high sensitivity of ~1.514 nm·(mg/ml)⁻¹, which the detection accuracy is ~0.2857 nm⁻¹ at pH 5.2, and the limit of detection (LOD) is 0.013~0.02 mg/ml at the pH range of 5.2~7.4 by using an optical spectrum analyzer with a resolution of 0.02 nm.

Water-dispersible boronate nanoparticles as support materials for noble metals in the hydrogenation of levulinic acid to γ-valerolactone

The sequential dehydration reaction of benzene-1,4-diboronic acid with pentaerythritol in the presence of polyethyleneimine (PEI) led to polymeric 3-benzo-2,4,8,10-tetraoxa- 3,9-diboraspiro[5.5]undecane, resulting in the formation of a PEI-coated boronate nanoparticle (BNP) with a mean diameter of 121 ± 43 nm through the spontaneous self-assembly. Subsequently, noble metal deposition on the boronate particle (M/BNP, M = Ru, Pd and Pt) was successfully achieved by NaBH4 reduction of RuCl3, and in the presence of BNP. Exploration of boronate-based catalytic systems applicable to the conversion of biomass to chemicals revealed that Ru/BNP has excellent catalytic activity for the hydrogenation of levulinic acid to γ-valerolactone (GVL) in H2O under 0.8 MPa of H2 at 100 °C; after 4 h, the reaction afforded GVL in 94.6% yield. The catalytic performance and recyclability of Ru/BNP in the reaction were investigated.

Photocatalytic odor abatement by platinized TiO2 under optically transmitted LED–UV light

Combined use of platinized titania and light emitting diode (LED) ultraviolet (UV) illumination was explored for photocatalytic odor abatement with carbon disulfide (CS2) as model odorant. Noble metal deposition on anatase titanium dioxide (TiO2) surface was achieved by UV assisted photoreduction of platinum (Pt). Solid-state and elemental analyses show that surface platinized (Pt/TiO2) and bare (TiO2) titania, while of comparable bulk structural properties, differ in light absorption and surface characteristics as a result of the photodeposited Pt. The effect of distance and collimation was modeled to predict the impact of position of UV source and collimation on UV radiation intensity and distribution on photocatalyst surface. Increased radiation intensity due to minimized divergence with collimated LED–UV has improved output beam intensity, resulting in enhanced photoreaction rates regardless of photocatalyst used. Fitting of batch experimental data into classical Langmuir–Hinshelwood (L–H) kinetic model yielded higher model parameter values with Pt/TiO2 than TiO2 as well as the calcined counterparts. Lower number of surface OH groups and better charge carrier separation in calcined and/or Pt surface treated titania were proposed as main factors underpinning enhanced reaction rates and photonic efficiencies. Data fitting into a pseudo-steady-state L–H kinetic model has returned higher optimized fit parameter values with Pt/TiO2 than TiO2 while showing a nonlinear power law relationship between irradiation intensity and reaction rate. Results of fluorescence excitation-emission (EEM) spectroscopy and infrared (IR) thermography corroborate the occurrence of localized surface plasmon resonance (LSPR) effects such as subdued fluorescence and localized heating. By employing plasmonic photocatalysts and innovative delivery of photoradiation, this study has presented a case of a straightforward approach to environmental odor abatement based on affordable and widely available UV–LEDs and titania support.

M@MIL-100(Fe) (M = Au, Pd, Pt) nanocomposites fabricated by a facile photodeposition process: Efficient visible-light photocatalysts for redox reactions in water

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed noble-metal nanoparticles (Au, Pd, Pt) were immobilized on MIL-100(Fe) (denoted M@MIL-100(Fe)) using a facile room-temperature photodeposition technique. The resulting M@MIL-100(Fe) (M = Au, Pd, and Pt) nanocomposites exhibited enhanced photoactivities toward photocatalytic degradation of methyl orange (MO) and reduction of heavy-metal Cr(VI) ions under visible-light irradiation (λ ≥ 420 nm) compared with blank-MIL-100(Fe). Combining these results with photoelectrochemical analyses revealed that noble-metal deposition can effectively improve the charge-separation efficiency of MIL-100(Fe) under visible-light irradiation. This phenomenon in turn leads to the enhancement of visible-light-driven photoactivity of M@MIL-100(Fe) toward photocatalytic redox reactions. In particular, the Pt@MIL-100(Fe) with an average Pt particle size of 2 nm exhibited remarkably enhanced photoactivities compared with those of M@MIL-100(Fe) (M = Au and Pd), which can be attributed to the integrative effect of the enhanced light absorption intensity and more efficient separation of the photogenerated charge carrier. In addition, possible photocatalytic reaction mechanisms are also proposed.