Hot electrons generated by intraband and interband transition detected using a plasmonic Cu/TiO2 nanodiode

The use of metal nanoparticles, including Au, Ag, Cu, and Al, can increase the efficiency of photovoltaic devices by electromagnetic field enhancement, which is driven by the excitation of localized surface plasmon resonance. Direct energy conversion from light into electricity via the decay of surface plasmons causing the excitation of hot electron–hole pairs is also a feasible channel. The generation of hot electrons in metal nanostructures can occur through intraband excitation within the conduction band or through interband transition, which is caused by transitions from other bands to the unoccupied conduction band states. Here, we show the distinction between hot electron generation induced by intraband excitation and interband transition on a plasmonic Cu/TiO₂ nanodiode by measuring the current conversion efficiency with a monochromator system. We also show the dependence of the production of photocurrent on the thickness of the Cu layer and the effect of an aluminum oxide protection layer on the hot electron flux versus oxidation of the Cu layer. Our results can provide a better understanding for copper-based hot electron photovoltaics, which could lead to more efficient plasmonic energy conversion.

Better hot electron extraction via intraband and interband excitation was discerned on Cu compared with Au using plasmonic nanodiode.     

The influence of three diphenylpyran isomer co-sensitizers with different sterical structures on N719-based dye sensitized solar cells

Aiming to explore the relationship between the molecular structure and photovoltaic performance, three pyran isomer dyes DO, DM and DP were synthesized and applied as a co-sensitizer with N719 dye in dye-sensitized solar cells (DSCs). These sensitizers were investigated by theoretical calculation, UV-vis absorption spectroscopy and cyclic voltammetry measurement to understand their structure, optical and electrochemical properties. The DSC devices based on N719 and the co-sensitizers were characterized using I–V tests, incident photon-to-current conversion efficiency and electrochemical impedance spectroscopy measurements. As compared to the standard N719-based DSCs, the co-sensitization system of N719 and DM with the most sterical structure exhibited an enhancement of the power conversion efficiency (PCE) by 18% from 7.60% to 8.96%. Both the short-circuit photocurrent density (J_sc) and open-circuit voltage (V_oc) of the co-sensitized systems were increased resulting from the better maintained N719 dye loading amount on TiO₂ as well as the prevention of dye aggregation. Co-sensitization of the DO molecule with less steric hindrance reduced the desorbed N719 dye amount by half leading to a decline of the photo-harvesting ability and photocurrent generation in DSCs.

This work applied three isomers with different spatial geometries as co-sensitizers to enhance N719-based dye sensitized solar cells.     

Au nanoparticle-decorated TiO2 hollow fibers with enhanced visible-light photocatalytic activity toward dye degradation

TiO₂ hollow fibers (THF) were prepared by a template method using kapok as a biotemplate and subsequently decorated by plasmonic Au nanoparticles using a solution plasma process. The THF exhibited an anatase phase and a hollow structure with a mesoporous wall. Au nanoparticles with a diameter of about 5–10 nm were uniformly distributed on the THF surface. Au nanoparticles-decorated TiO₂ hollow fibers (Au/THF) have enhanced photocatalytic activity toward methylene blue degradation under visible light-emitting diode (Vis-LED) as compared to pristine THF and P25. This could be attributed to combined effects including effective light-harvesting by a hollow structure, large surface area due to a mesoporous wall of THF, and visible-light absorption and efficient charge separation induced by Au nanoparticles. The Au/THF also showed good recyclability and separation ability.

Plasmonic Au nanoparticles-decorated TiO₂ hollow fibers with enhanced visible-light photocatalytic activity have been successfully prepared by a two-step process: (i) template method using kapok and (ii) solution plasma process.     

Difference in the deactivation of Au catalysts during ethanol transformation when supported on ZnO and on TiO2

Au nanoparticles of different sizes were supported by the deposition–precipitation method on two metal oxides: ZnO and TiO₂. The resulting catalysts were tested in the ethanol catalytic transformation reaction. Both metal oxide support materials exerted a different influence on the achieved Au particle size as well as on the behavior of the subsequent catalyst, with regard to their initial conversion values, product distribution and stability. While TiO₂ favors the formation of smaller nanoparticles, ZnO offers larger Au particle sizes when prepared under similar conditions. At the same time, TiO₂ produced catalysts which displayed higher initial conversions in comparison with AuZnO catalysts, even when observing catalysts of each series with similar particle sizes. At the same time, catalysts supported on ZnO exhibited higher resistance to deactivation caused by coke formation. These results were evidenced employing different characterization techniques on both used and fresh catalyst samples. The decline in deactivation was generally accompanied by an increase in the carbon content on the catalyst''s surface.

Au NPs of different sizes were supported on two metal oxides: ZnO and TiO₂. Differences in ethanol transformation for Au of similar particle size reveal that TiO₂ support induces condensation products while ZnO only gives place to dehydrogenation.     

Plasmonic-enhanced photocatalysis reactions using gold nanostructured films

This work shows the enhancement of the visible photocatalytic activity of TiO₂ NPs film using the localized surface plasmonic resonance of Au nanostructures. We adopted a simple yet effective surface treatment to tune the size distribution, and plasmonic resonance spectrum of Au nanostructured films on glass substrates, by hot plate annealing in air at low temperatures. A hybrid photocatalytic film of TiO₂:Au is utilized to catalyse a selective photodegradation reaction of Methylene Blue in solution. Irradiation at the plasmonic resonance wavelength of the Au nanostructures provides more effective photodegradation compared to broadband artificial sunlight of significantly higher intensity. This improvement is attributed to the active contribution of the plasmonic hot electrons injected into the TiO₂. The broadband source initiates competing photoreactions in the photocatalyst, so that carrier transfer from the catalyst surface to the solution is less efficient. The proposed hybrid photocatalyst can be integrated with a variety of device architectures and designs, which makes it highly attractive for low-cost photocatalysis applications.

This work shows the enhancement of the visible photocatalytic activity of TiO₂ NPs film using the localized surface plasmonic resonance of Au nanostructures.     

Performance of the dye-sensitized quasi-solid state solar cell with combined anthocyanin-ruthenium photosensitizer

This work contributes to combining 12.2 mM purified anthocyanin of cyanidin-3-glucoside extracted from Indonesian black rice as the natural pigment with a ruthenium photosensitizer (1 : 1) in dye-sensitized solar cells (DSSCs) in liquid and quasi solid-state electrolytes. The findings essentially highlight the spectroscopic and electron transfer mechanism for the future trend of D–π–A natural pigment modification. The complete pigment comparison, dye absorbance, dye adsorption onto the semiconductor, dye electronic properties, electron excitation, and regeneration were investigated using spectroscopic methods. Cells employ TiO₂ mesoporous nanoparticles (19.18 nm grain size, 50.99 m² g⁻¹ surface area, 87.8% anatase 12.2% rutile, 10.58 μm thickness, 3.18 eV band gap) sensitized by anthocyanin-N719 photosensitizer (12.2 mM) with the I⁻/I₃⁻ electrolyte (0.1 M lithium iodide/0.05 M iodine/0.6 M 1-buty-3-methylimidazolium iodide/0.5 M 4-tert-butylpyridine/polyethylene oxide M_w = 1 × 10⁶) – Pt film. As a result, the quasi-solid state with combined anthocyanin-ruthenium dye-sensitized solar cell (3.51%) is achieved and reported for the first time. The work also achieved the highest efficiency of the anthocyanin dye-sensitized quasi-solid state solar cells of 2.65%. The insight on how the combined anthocyanin-N719 and the quasi-solid state electrolytes exhibit better performances will be further discussed.

This work contributes to combining 12.2 mM purified anthocyanin of cyanidin-3-glucoside extracted from Indonesian black rice as the natural pigment with a ruthenium photosensitizer (1 : 1) in dye-sensitized solar cells (DSSCs) in liquid and quasi solid-state electrolytes.     

The effect of co-sensitization methods between N719 and boron dipyrromethene triads on dye-sensitized solar cell performance

A boron dipyrromethene (BODIPY) featuring triphenylamine triad, BD, has been synthesized as a co-sensitizer in dye-sensitized solar cells (DSCs). The optical and electrochemical properties of BD have been characterized using UV-vis spectroscopy and cyclic voltammetry. DSCs containing co-sensitizers, N719 and BD, have been prepared in two procedures using co-deposition and stepwise deposition. The influences of the staining processes, co-deposition and stepwise deposition on dye loading, dye dispersion on a TiO₂ photoanode and DSC performance have been investigated using FTIR, SEM-EDS, I–V test and IPCE measurement, respectively. We found that stepwise co-sensitization provided higher solar cell efficiency, compared to those stained with a co-deposition method. N719/5% BD showed the highest power conversion efficiency of 5.14%. Interestingly, the enhanced device efficiency was 66% higher than that of a device containing the single N719 dye.

BODIPY triad, BD, was prepared as co-sensitizer. The stepwise sensitization method exhibited higher PCE, compared to the co-deposition method.     

Synergism of carbon quantum dots and Au nanoparticles with Bi2MoO6 for activity enhanced photocatalytic oxidative degradation of phenol

Localized surface plasmon resonance (LSPR) offers an opportunity to enhance the efficiency of photocatalysis. However, the photocatalysts''s plasmonic enhancement is still limited, as most metals/semiconductors depend on LSPR contribution of isolated metal nanoparticles. In the present work, carbon quantum dots (CQDs) and Au nanoparticles (NPs) were simultaneously assembled on the surface of a three-dimensional (3D) spherical Bi₂MoO₆ (BMO) nanostructure with surface oxygen vacancies (SOVs). The collective excitation of CQDs and Au NPs demonstrated an effective strategy to improve the utilization of up-conversion emission and plasmonic energy. The contribution of CQDs and Au NPs assembled on the surface of BMO (7 wt% CQDs/Au/BMO) realized a photocatalytic phenol degradation enhancement (apparent rate constants, k_app/min⁻¹) of 56.5, 9.5 and 3.9, and 2.2-fold increase compared to BMO, BMO-SOVs, Au/BMO and CQDs/BMO, respectively. The as-fabricated 7 wt% CQDs/Au/BMO exhibited the highest mineralization rate for phenol degradation with 72.4% TOC removal rate in 120 min. The excellent photocatalytic performance of CQDs/Au/BMO was attributed to the synergistic effect of CQDs, Au NPs and SOVs. The CQD up-conversion emission synergetically boosts Au NPs'' LSPR significantly promoting the separation and migration of photogenerated electron (e⁻)/hole (h⁺) pairs, which could improve the oxygen molecule activation process and thereby their ability to generate reactive oxygen species (ROS). The present work is a step forward to understand and construct similar photocatalysts using an entirely reasonable hypothesis of activity enhancement mechanism according to the active species capture experiments and band structure analysis.

Carbon quantum dot up-conversion emission and Au plasmon resonance effect synergetically promote the separation and migration of photogenerated electron e⁻/h⁺ pairs of Bi₂MoO₆, achieving efficient ROS for phenol photocatalytic mineralization.     

Effect of organic ligand-decorated ZnO nanoparticles as a cathode buffer layer on electricity conversion efficiency of an inverted solar cell

Efficiency improvement of the industrial scale solar cells to capture sunlight as an important renewable energy source is attracting significant attention to prevent the consumption of a finite supply of unsustainable fossil fuels. ZnO nanoparticles decorated with an imine-linked receptor have been used in the fabrication of a photocathode based on dye-sensitized solar cells for the purpose of photovoltaic efficiency enhancement. Various characterization techniques have been employed to investigate the structural, morphological, and optical behaviors of the solar cell having ZnO nanoparticles and ZnO nanoparticles decorated with an organic ligand as a photocathode layer. The decorated nanoparticles have a stable wurtzite structure and an average grain size of ∼45 nm, confirmed by the TEM image and XRD through the Scherrer equation. The ZnO sample emits wide peaks in the visible range, and the emission intensity of the ZnO-DOL sample increases along with a red-shift (0.38 eV) in the band gap. This shift can be explained using deep level transition, surface plasmon energy of a surfactant, and coupling of ZnO with local surface plasmon energy. UV-vis absorption spectra together with photoluminescence spectra confirm the higher absorption rate due to organic ligand decoration on ZnO nanoparticles. The greatest solar power-to-electricity conversion efficiency (η) of 3.48% is achieved for the ZnO-DOL sample. It is enhanced by 3.13% as compared to that of the ZnO-based solar cell. The ZnO-DOL device exhibits a higher external quantum efficiency (EQE), responsivity (R_λ), and photocurrent-to-dark current ratio; this confirms the improvement in the solar cell performance.

Efficiency improvement of the industrial scale solar cells to capture sunlight as an important renewable energy source is attracting significant attention to prevent the consumption of a finite supply of unsustainable fossil fuels.     

Enhanced control of plasmonic properties of silver–gold hollow nanoparticles via a reduction-assisted galvanic replacement approach

Hollow noble metal nanoparticles are of growing interest due to their localized surface plasmon resonance (LSPR) tunability. A popular synthetic approach is galvanic replacement which can be coupled with a co-reducer. Here, we describe the control over morphology, and therefore over plasmonic properties including energy, bandwidth, extinction and scattering intensity, offered by co-reduction galvanic replacement. This study indicates that whereas the variation of atomic stoichiometry using the co-reduction method described in this work offers a rather modest tuning range of LSPR energy when compared to traditional galvanic replacement, it nevertheless has a profound effect on shell thickness, which imparts a degree of control over scattering intensity and sensitivity to changes in the dielectric constant of the surrounding environment. Therefore, in this context particle size and gold content become two design parameters that can be used to independently tune LSPR energy and intensity.

A co-reduction assisted method for the synthesis of Ag–Au hollow nanoparticles with enhanced control over plasmon wavelength and scattering intensity.     

Compact TiO2 films with sandwiched Ag nanoparticles as electron-collecting layer in planar type perovskite solar cells: improvement in efficiency and stability

Fabrication of perovskite solar cells (PSCs) in a simple way with high efficiency and stability remains a challenge. In this study, silver nanoparticles (Ag NPs) were sandwiched between two compact TiO₂ layers through a facile process of spin-coating an ethanolic AgNO₃ solution, followed by thermal annealing. The presence of Ag NPs in the electron-transporting layer of TiO₂ improved the light input to the device, the morphology of the perovskite film prepared on top, and eliminated leakage current. Photoluminescence and electron mobility studies revealed that the incorporation of Ag NPs in the ETL of the planar PSC device facilitated the electron–hole separation and promoted charge extraction and transport from perovskite to ETL. Hysteresis-free devices with incorporated Ag NPs gave a high average short-circuit current density (J_sc) of 22.91 ± 0.39 mA cm⁻² and maximum power conversion efficiency of 17.25%. The devices also showed enhanced stability versus a control device without embedded Ag NPs. The possible reasons for the improvement are analyzed and discussed.

Embedding silver nanoparticles in the compact TiO₂ layer effectively improves the efficiency and stability of a perovskite solar cell.     

TiO2 nanofibres decorated with green-synthesized PAu/Ag@CQDs for the efficient photocatalytic degradation of organic dyes and pharmaceutical drugs

Organic pollutants such as dyes and pharmaceutical drugs have become an environmental menace, particularly in water bodies owing to their unregulated discharge. It is thus required to develop an economically viable and environment-friendly approach for their degradation in water bodies. In this study, for the first time, we report green route-synthesized plasmonic nanostructures (P_M-CQDs (where M: Au and Ag)) decorated onto TiO₂ nanofibers for the treatment of toxic dye- and pharmaceutical drug-based wastewater. P_M-CQDs are efficaciously synthesized using carbon quantum dots (CQDs) as the sole reducing and capping agent, wherein CQDs are derived via a green synthesis approach from Citrus limetta waste. The characteristic electron-donating property of CQDs played a key role in the reduction of Au³⁺ to Au⁰ and Ag⁺ to Ag⁰ under visible light irradiation to obtain P_Au-CQDs and P_Ag-CQDs, respectively. Thus, the obtained CQDs, P_Au-CQDs, and P_Ag-CQDs are loaded onto TiO₂ nanofibers to obtain a P_M-CQD/TiO₂ nanocomposite (NC), and are further probed via transmission electron microscopy, scanning electron microscopy and UV-visible spectrophotometry. The degradation of organic pollutants and pharmaceutical drugs using methylene blue and erythromycin as model pollutants is mapped with UV-vis and NMR spectroscopy. The results demonstrate the complete MB dye degradation in 20 minutes with 1 mg mL⁻¹ of P_Au-CQD/TiO₂ NC, which otherwise is 30 minutes for P_Ag@CQD/TiO₂ dose under visible light irradiation. Similarly, the pharmaceutical drug was found to degrade in 150 minutes with P_Au-CQD/TiO₂ photocatalysts. These findings reveal the enhanced photocatalytic performance of the green-synthesized Au decorated with TiO₂ nanofibers and are attributed to the boosted SPR effect and aqueous-phase stability of Au nanostructures. This study opens a new domain of utilizing waste-derived and green-synthesized plasmonic nanostructures for the degradation of toxic/hazardous dyes and pharmaceutical pollutants in water.

Citrus limetta waste-derived plasmonic nanostructures for photocatalytic degradation of toxic dyes and pharmaceutical pollutants in water.     

Mechanism analysis of Au,Ru noble metal clusters modified on TiO2 (101) to intensify overall photocatalytic water splitting

Accelerating the separation and migration of photo-carriers (electron–hole pairs) to improve the photo-quantum utilization efficiency in photocatalytic overall water splitting is highly desirable. Herein, the photo-deposition of Ru or Au noble metal clusters with superior electronic properties as a co-catalyst on the (101) facet of anatase TiO₂ and the mechanism of intensifying the photocatalysis have been investigated by calculation based density functional theory (DFT). As a result, the as-synthesized Ru/TiO₂ and Au/TiO₂ exhibit high hydrogen evolution reaction (HER) activity. Such a greatly enhanced HER is attributed to the interfacial interactivity of the catalysts due to the existence of robust chemical bonds (Ru–O–Ti, Au–O–Ti) as electron-traps that provide the photogenerated electrons. In addition, the formation of new degenerate energy levels due to the existence of Ru-4d and Au-5d electronic impurity states leads to the narrowing of the band gap of the catalysts. In addition, the as-synthesized Au/TiO₂ exhibits more faster HER rate than Ru/TiO₂, which is attributed to the effects of surface plasmon resonance (SPR) as a synergistic effect of plasmon-induced ‘hot’ electrons that enhance the harvesting of the final built-in electric field and promote the migration and separation of the photo-carriers, which efficiently facilitates hydrogen evolution from the photocatalytic overall water splitting reaction.

Enhancement mechanism of the hydrogen evolution reaction (HER) attributed to the synergistic effect of electron-traps and surface plasmon resonance (SPR).     

Choline chloride-based deep eutectic solvents as effective electrolytes for dye-sensitized solar cells

Electrolytes for dye-sensitized solar cells remain a challenge for large-scale production and commercialization, hindering the wide application of solar cells. We have developed two new electrolyte-based deep eutectic solvents using a mixture of choline chloride with urea and with ethylene glycol for dye-sensitized solar cells. The prominent features of the two deep eutectic solvent electrolytes are simple preparation for large-scale production with inexpensive, available, and nontoxic starting materials and biodegradability. The solar cell devices proceeded in a safe manner as the two deep eutectic solvents afforded low-cost technology and comparative conversion efficiency to a popular ionic liquid, namely 1-ethyl-3-methylimidazolium tetracyanoborate. Results showed that devices with choline chloride and urea electrolyte exhibited improved open circuit voltage values (V_OC), while the ones with choline chloride and ethylene glycol showed an increase in the short circuit current (I_sc). Characterization of the devices by electrochemical impedance spectroscopy helped explain the effects of their molecular structures on the enhancement of either V_OC or I_sc values. These new solvents expand the electrolyte choices for designing dye-sensitized solar cells, especially for the purpose of using low-cost and eco-friendly materials for massive production.

Electrolytes for dye-sensitized solar cells remain a challenge for large-scale production and commercialization, hindering the wide application of solar cells.     

Gold nanoparticle decorated titania for sustainable environmental remediation: green synthesis,enhanced surface adsorption and synergistic photocatalysis

Developing materials for efficient environmental remediation via cheap, nontoxic and environmentally benign routes remains a challenge for the scientific community. Here, a novel, facile, and green synthetic approach to prepare gold nanoparticle decorated TiO₂ (Au/TiO₂) nanocomposites for sustainable environmental remediation is reported. The synthesis involved only TiO₂, metal precursor and green tea, obviating the need for any solvents and/or harsh chemical reducing or stabilizing agents, and was efficiently conducted at 50 °C, indicating the prominent sustainability of the novel synthetic approach. The synthesis indicated notable atom economy, akin to that observed in a typical chemical mediated synthesis while high-resolution transmission electron microscopy (HRTEM) findings suggest the presence of a pertinent decoration of spherical and homogeneous gold nanoparticles on the titania surface. Notably, the Au/TiO₂ nanocomposite demonstrated appreciable stability during preparation, subsequent processing and prolonged storage. Further, the nanocomposite was found to have a superior adsorption capacity of 8185 mg g⁻¹ towards methylene blue (MB) in solution using the Freundlich isotherm model, while the rate constants for the photocatalytic degradation of MB on the nanocomposite under UV irradiation indicated a 4.2-fold improvement compared to that of bare TiO₂. Hence, this novel green synthesized Au/TiO₂ nanocomposite shows promising potential for sustainable environmental remediation via efficient contaminant capture and subsequent synergistic photocatalysis.

Green synthesis of gold nanoparticle decorated titania for enhanced surface adsorption and synergistic photocatalysis.     

Photocurrent generation by a photosystem I-NiO photocathode for a p-type biophotovoltaic tandem cell

Photosynthesis is a process used by algae and plants to convert light energy into chemical energy. Due to their uniquely natural and environmentally friendly nature, photosynthetic proteins have attracted attention for use in a variety of artificial applications. Among the various types, biophotovoltaics based on dye-sensitized solar cells have been demonstrated in many studies. Although most related works have used n-type semiconductors, a p-type semiconductor is also a significant potential component for tandem cells. In this work, we used mesoporous NiO as a p-type semiconductor substrate for Photosystem I (PSI) and demonstrated a p-type PSI-biophotovoltaic and tandem cell based on dye-sensitized solar cells. Under visible light illumination, the PSI-adsorbed NiO electrode generated a cathodic photocurrent. The p-type biophotovoltaic cell using the PSI-adsorbed NiO electrode generated electricity, and the IPCE spectrum was consistent with the absorption spectrum of PSI. These results indicate that the PSI-adsorbed NiO electrode acts as a photocathode. Moreover, a tandem cell consisting of the PSI-NiO photocathode and a PSI-TiO₂ photoanode showed a high open-circuit voltage of over 0.7 V under illumination to the TiO₂ side. Thus, the tandem strategy can be utilized for biophotovoltaics, and the use of other biomaterials that match the solar spectrum will lead to further progress in photovoltaic performance.

Photosystem I-biophotovoltaics based on p-type dye-sensitized solar cells and a tandem cell was demonstrated.     

Understanding the effects of shape,material and location of incorporation of metal nanoparticles on the performance of plasmonic organic solar cells

Truncated octahedral gold (Au) nanoparticles (NPs), Au nanocubes (NCs)-, and silver (Ag) NCs are used to study the effect of NPs shape, material and incorporation location on the performance of poly(3-hexylthiophene):[6,6]-phenyl-C₇₁-butyric acid methyl ester (P3HT:PC₇₁BM) based inverted bulk heterojunction (BHJ) organic solar cells (OSCs). Plasmonic OSCs (POSCs) with NPs incorporated as an interfacial layer between zinc oxide (ZnO) and active layer showed highest power conversion efficiency (PCE) and short circuit current density (J_sc) values for all kind of shapes and material compared to POSCs with NPs blended into the active layer. Near-field enhancement as well as enhanced forward scattering cross section is attributed for POSC performance improvement. Among the NPs with two shapes, POSCs with truncated octahedral Au NPs exceeded the photovoltaic performance compared to those of POSCs with Au and Ag NCs. Large number of antennas in truncated octahedral Au NPs compared to NC is reasoned to be the cause for this improvement. Even though Ag has better localised surface plasmon resoanance (LSPR) properties compared to Au, the POSCs with Ag NCs showed lower J_sc value and is due to reduced number of photons at the blue shifted LSPR wavelength of Ag NCs. The improvement in J_sc values of POSCs is confirmed by enhancement in absorption, external quantum efficiency (EQE), exciton generation and exciton dissociation probability measurements and is due to improved LSPR coupling of the NPs with the active layer. The surface enhanced Raman scattering (SERS) and photoluminescence (PL) studies confirm the absorption enhancement in the active layer by NP LSPR coupling and further confirm the enhancement in the photovoltaic performance of POSCs.

Enhanced performance in organic solar cells by incorporating non-spherical metal nanoparticles.     

Au-based bimetallic catalysts: how the synergy between two metals affects their catalytic activity

Supported bimetallic nanoparticles are particularly attractive catalysts due to increased activity and stability compared to their monometallic counterparts. In this work, gold-based catalysts have been studied as catalysts for the selective base-free oxidation of glucose. TiO₂-supported Au–Pd and Au–Cu series prepared by the sol-immobilization and precipitation-reduction methods, respectively, showed a significant synergistic effect, particularly when the theoretical weight ratio of the two metals was close to 1 : 1 (with an actual experimental bulk Au/Pd molar ratio of ca. 0.8 and ca. 0.4 for Au/Cu) in both cases. XPS analysis showed that the presence of Au^δ+, Pd²⁺ and CuOH species played an important role in the base-free glucose oxidation.

Supported bimetallic nanoparticles are particularly attractive catalysts due to increased activity and stability compared to their monometallic counterparts.     

Modeling of the surface plasmon resonance tunability of silver/gold core–shell nanostructures

Tunable plasmonic noble metal nanoparticles are indispensable for chemical sensors and optical near field enhancement applications. Laser wavelengths within the absorption spectrum of the nanoparticle and Localized Surface Plasmon Resonances (LSPR) in the visible and near infrared range are the key points to be met for the successful utilization in the field of aforementioned high sensitivity sensors. This way, Surface Enhanced Raman Spectroscopy (SERS) has been pushed to the sensitivity level of single molecule. The tunability, i.e. the modulation of the surface plasmon resonance wavelength as a function of the ambient refractive index is one of the important criteria to be understood clearly. Among various noble metals, gold and silver nanoparticles have the strongest surface enhancement factors for the Raman signal and their tunability for many practical applications has been experimentally demonstrated. We present a comprehensive numerical investigation by means of a finite element analysis on Ag/Au core–shell nanospheres including agglomerated and non-agglomerated dimers. Tunability as a function of shell thickness, total nanosphere radius and fraction of overlap between the dimer is discussed. Our studies show that tunability is considerably affected by the nanosphere radius rather than the shell thickness. These findings may be helpful in the synthesis of nanoplasmonic structures, especially related to an optimized use of gold as the shell material for the targeted application.

Tunable plasmonic noble metal nanoparticles are indispensable for chemical sensors and optical near field enhancement applications.     

Laser-driven structural transformations in dextran-graft-PNIPAM copolymer/Au nanoparticles hybrid nanosystem: the role of plasmon heating and attractive optical forces

Laser induced structural transformations in a dextran grafted-poly(N-isopropylacrylamide) copolymer/Au nanoparticles (D-g-PNIPAM/AuNPs) hybrid nanosystem in water have been observed. The laser induced local plasmonic heating of Au NPs leads to Lower Critical Solution Temperature (LCST) phase transition in D-g-PNIPAM/AuNPs macromolecules accompanied by their shrinking and aggregation. The hysteresis non-reversible character of the structural transformation in D-g-PNIPAM/AuNPs system has been observed at the decrease of laser intensity, i.e. the aggregates remains in solution after the turn-off the laser illumination. This is an essential difference comparing to the case of usual heating–cooling cycles when there is no formation of aggregates and structural transformations are reversible. Such a fundamental difference has been rationalized as the result of action of attractive optical forces arising due to the excitation of surface plasmons in Au NPs. The attractive plasmonic forces facilitate the formation of the aggregates and counteract their destruction. The laser induced structural transformations have been found to be very sensitive to matching conditions of the resonance of the laser light with surface plasmon resonance proving the plasmonic nature of observed phenomena.

Structural transformations in D-g-PNIPAM/AuNPs hybrid nanosystem arise from the synergetic action of plasmonic heating and attractive optical plasmonic forces.