LSPR Effect Research Articles

Synthesis of a Pt/reduced graphene oxide/polydopamine composite material for localized surface plasmon resonance and methanol electrocatalysis

Pt NPs are synthesized and loaded with rGO onto ITO using polydopamine. The strongest LSPR effect corresponds to the optimal catalyst. The catalyst has a good anti-poison property against CO and shows good cycle stability.

Sandwiched ZnO@Au@CdS nanorod arrays with enhanced visible-light-driven photocatalytical performance

The development of high-performance photocatalysts is central to efforts focused on taking advantage of solar energy to overcome environmental and energy crises. Integrating different functional materials artfully into nanostructures can deliver more efficient photocatalytic activity. Here, sandwiched ZnO@Au@CdS nanorod films were synthesized via successive ZnO nanorod electrodeposition, Au sputtering and CdS electrodeposition. The as-synthesized composites were characterized by UV–vis spectrophotometer, x-ray diffractometer, scanning and transmission electron microscopy. Their photocatalytic activity was assessed by degrading Rhodamine B solution under visible light irradiation. ZnO@Au@CdS exhibited better photocatalytic performance than ZnO@CdS throughout the visible light region, and the corresponding enhancement factor of Au nanoparticles was measured as a function of CdS loading amount, and it could reach 190% with CdS deposition for 1 min. The normalized rate constant could reach 0.387 h−1 for ZnO@Au@CdS-1min, which was equivalent to or better than results in reference photocatalysts. The enhancement mechanism of Au nanoparticles was estimated by comparing the monochromatic photocatalytic action spectra with the absorption spectrum of ZnO@Au@CdS, and it was mainly determined by incident photon energy. With selective excitation of Au nanoparticles by incident photons, the excited hot electrons in Au NPs are transferred to the conduction band of ZnO to boost photocatalytic reaction. With selective excitation of CdS, the enhanced interband absorption of CdS and relay station effect of Au nanoparticles should be responsible for the enhanced photocatalytic performance. Our work not only opens the door to the design of efficient supported photocatalysts, but also helps to understand the enhancement mechanism of LSPR effect on the photoelectric conversion of semiconductors.

Synergistic effect in MMT-dispersed Au/TiO2 monolithic nanocatalyst for plasmon-absorption and metallic interband transitions dynamic CO2 photo-reduction to CO

Structured montmorillonite (MMT) dispersed Au/TiO2 nanocomposite has been designed and synthesized through a facile sol-gel method. Cordierite monolithic support was employed in order to load the catalyst for improved photo-activity and reusability in CO2 utilization process. The samples were characterized by XRD, Raman, SEM, TEM, FTIR, XPS, N2 adsorption-desorption, UV–vis and PL spectroscopy. The synergistic effect of MMT-dispersed Au/TiO2 nanocatalyst was evaluated in a gas-phase dynamic monolith photoreactor system using UV and visible light irradiations. The maximum CO yield over 0.5wt.% Au–10wt.% MMT-loaded TiO2 catalyst reached to 1223μmole g-catal.−1h−1, a 24 fold higher than the amount of CO produced over the 10wt.% MMT/TiO2 and 68 times the amount of CO produced over the bare TiO2 catalyst. The other products observed with considerable amounts were CH4 and C2H6. This enactment under UV-light was due to interband transition of Au in catalyst composite. Enhanced photo-activity under simulated solar energy for CO2-to-CO reduction was due to LSPR effect of Au in the MMT/TiO2 sample. More importantly, the performance of Au-MM/TiO2 catalyst for CO evolution under UV-light was 6 folds higher than using visible light. The synergistic effect between MMT transition metals and Au ions and faster adsorption-desorption process contributed to remarkably enhance dynamic CO2 reduction to CO. The present design of catalyst provides prolonged stability to catalyst while CO evolution sustained even after 44h of operation time. The reaction mechanism developed to understand the role of Au/MMT and monolithic support on the photo-activity and reusability of catalyst for CO2 photo-reduction to fuels.

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting.

Surficial defects in semiconductor can induce high density of carriers and cause localized surface plasmon resonance which is prone to light harvesting and energy conversion, while internal defects may cause serious recombination of electrons and holes. Thus, it is significant to precisely control the distribution of defects, although there are few successful examples. Herein, an effective strategy to confine abundant defects within the surface layer of Cu1.94 S nanoflake arrays (NFAs) is reported, leaving a perfect internal structure. The Cu1.94 S NFAs are then applied in photoelectrochemical (PEC) water splitting. As expected, the surficial defects give rise to strong LSPR effect and quick charge separation near the surface; meanwhile, they provide active sites for catalyzing hydrogen evolution. As a result, the NFAs achieve the top PEC properties ever reported for Cux S-based photocathodes.

Size-dependent plasmonic effects of M and M@SiO2 (M = Au or Ag) deposited on TiO2 in photocatalytic oxidation reactions

Monodispersed Au nanoparticles (NPs) with sizes of 18, 26 and 34nm and Ag NPs with sizes of 17, 25 and 33nm, as well as their corresponding M@SiO2 core-shell NPs (M=Au or Ag), were selectively synthesized. The prepared individual plasmonic NPs were then loaded onto TiO2 and their size-dependent plasmonic effects in photocatalytic oxidation reactions were systematically analyzed. In the removal reactions of the organic compounds, aqueous salicylic acid (SA) and aniline, under UV–vis light irradiation, both the Au and Ag NPs significantly enhanced the catalytic activity of TiO2, while the smaller NPs were more effective. Although the Ag NPs show stronger LSPR effect than the Au NPs, the overall catalytic activity of the Ag/TiO2 systems was not higher than Au/TiO2, and their catalytic activity variation according to the size of plasmonic NPs was more sensitive for Ag/TiO2. The observed results seem to be due to the LSPR sensitization effect. It was also found that the M@SiO2 NPs were significantly more effective than the bare M NPs in enhancing the photocatalytic activity of TiO2 and the size-dependent plasmonic effects of the M@SiO2 NPs were quite different from those of the bare M NPs. In regrading to catalytic activity enhancement, the optimum sizes of the Au and Ag NPs for the Au@SiO2 and Ag@SiO2 NPs were determined to be 26 and 25nm, respectively. Moreover, the Ag@SiO2 NPs, which generate stronger LSPR, were more effective than the Au@SiO2 NPs. Consequently, Ag25@SiO2/TiO2 demonstrates the highest activity in decomposing SA and aniline, which is 3.8 and 2.5 times, respectively, that of the bare TiO2.

Investigating the size effect of Au nanospheres on the photocatalytic activity of Au-modified ZnO nanorods

Plasmonic nanostructures of semiconductors and noble metal nanospheres (NSs) hold great promise in the applications of solar energy conversion. Although it is known that the size of NSs plays a critical role in determining the photocatalytic performance of the resultant nanohybrids, the actual effects depend on multiple variables and needs to be elucidated for each specific scenario. Herein, ZnO nanorods (NRs) modified with AuNSs of diameters varying from 20 to 80nm have been prepared to investigate the size effect of AuNSs on the photocatalytic activity of Au-ZnO hybrids. Interestingly, the Au-ZnONRs with 40-nm AuNSs demonstrate higher photocatalytic activity than the nanohybrids with AuNSs of either smaller or larger sizes. A possible “trade-off” mechanism between efficient charge transfer for smaller NSs and stronger LSPR effect for larger ones is proposed.

Ag/diatomite for highly efficient solar vapor generation under one-sun irradiation

Ag/diatomite exhibited excellent vapor generation performance, owing to the LSPR and confinement effect.

LSPR Biosensor Based on Nanostructured Gold Films: Detection of Mycotoxins

This work focuses on the development of optical sensors based on the LSPR phenomenon in nano-structured gold films suitable for detection of mycotoxins. A simple technology of annealing thin gold films was utilized for the formation of gold nano-islands exhibiting the LSPR effect. The morphology of gold nano-structures produced was studied with SEM and AFM while their optical properties were analysed with UV-vis absorption spectroscopy and spectroscopic ellipsometry (SE). A blue spectral shift of LSPR band caused by changes in the refractive index of medium constitutes the main principle of LSPR sensing. Bio-sensing tests were attempted using SE in total internal reflection mode (TIRE); a noticeable spectral shift was recorded on course of immune binding of aflatoxin B1 to specific antibodies immobilized on the surface of gold.

Enhanced fluorescence properties of terbium complex/poly-l-lactic acid superfine fibers sensitized by the LSPR effect of silver nanoparticles

Due to the LSPR effect of Ag-NPs, the fluorescence intensity, quantum efficiency of Tb-complex in the composite fibers were improved.

Copper particles decorated boron carbon nitride, an efficient catalyst for methyl orange oxidation under sonication and sunlight irradiation

A simple and efficient method has been developed for synthesis of zerovalent copper decorated boron-carbon-nitrogen hybrid layers (Cu-BCN) and its application as a highly effective and reusable catalyst for wet oxidation of methyl orange (MO) under sonication and direct sunlight irradiation. Structural, chemical and morphological properties of as-prepared hybrid structures were thoroughly investigated. The catalytic performance of Cu-BCN studied with MO dye showed enhanced degradation efficiency with ultrasound as compared to direct sunlight irradiation. The effects of various experimental parameters like pH, catalyst loading, dye concentration, scavenger and enhancer on the efficiency of Cu-BCN in degrading MO dye solution under ultrasound irradiation were systematically studied. Experimental results suggested that the degradation efficiency enhances with increase of Cu-BCN dosage, whereas it decreases with increasing dye concentration, solution pH and radical scavenger. The role of Cu in the catalytic performance of Cu-BCN was studied with Cu particles (without BCN support) and BCN (without Cu particles). This proved that degradation of dye is only due to the synergistic effect of Cu and BCN in the hybrid material. The mechanism of MO degradation by Cu-BCN has been elucidated through kinetics of degradation process by calculating the rate constant. It is proposed that the radical formation and LSPR effect are responsible for the photo and sonocatalytic activity of Cu-BCN.

Spectroscopic ellipsometry study of gold nanostructures for LSPR bio-sensing applications

This main aim of this work is the development of optical biosensors based on the LSPR phenomenon in nano-structured gold films suitable for detection of low molecular weight analytes such as mycotoxins. A simple technology of annealing thin gold films was utilized for the formation of gold nano-islands exhibiting the LSPR effect. The morphology of gold nano-structures produced was studied with SEM and AFM, and their optical properties were analysed with UV-visible absorption spectroscopy and spectroscopic ellipsometry (SE). The position of LSPR band appeared to depend on the dimensions of gold nano-islands. The dependence of the LSPR band spectral shift on the refractive index of a medium was studied with both UV-vis absorption and SE, and the refractive index sensitivity (RIS) was evaluated. The method of SE gave from two to three times higher values of RIS as compared to those obtained by absorption spectroscopy. LSPR bio-sensing tests were attempted using total internal reflection ellipsometry (TIRE); a noticeable spectral shift was recorded on course of immune binding of Aflatoxin B1 to specific antibodies immobilized on the surface of gold.

Nanoporous gold films prepared by sputtering-dealloying combination for total internal reflection SERS measurement

Nanoporous gold (NPG) is an advanced functional material with both propagating and localized surface plasmon resonance (PSPR and LSPR) effects. In this work, uniform NPG films with controlled thickness and small pore size were easily prepared by sputtering deposition followed by low-temperature dealloying. Using slab waveguide spectroscopy, the LSPR absorption peak of the NPG film was measured to shift from 566 nm to 586 nm by changing the surrounding refractive index from 1.333 to 1.368. Total internal reflection (TIR) SERS spectra for Rhodamine 6G (R6G) and Nile blue (NB) molecules adsorbed in the NPG film were investigated with a prism coupler. Upon increasing the incident angle (θ) from the critical value, the intensity of the SERS signal excited with the s-polarized laser beam of 532 nm wavelength gradually decreases but with the p-polarized laser beam exhibits a peak at θ ≈53°. The peak intensity is 2 times stronger than that excited with normal incidence of the same laser beam. The PSPR mode of the NPG film can be excited at 785 nm wavelength, which leads to a strong SERS signal of NB. In contrast, the LSPR effect at 785 nm wavelength is too weak to make the SERS signal undetectable with normal incidence. The findings indicate that the TIR geometry can bring about at least a twofold enhancement of SERS sensitivity of NPG film relative to the conventional normal incidence and that the contributions of LSPR and PSPR effects to the SERS sensitivity of NPG film are different at different incident wavelengths.

Fabrication of plasmonic Au/TiO2 nanotube arrays with enhanced photoelectrocatalytic activities

Uniformly dispersed Au nanoparticles (NPs) deposited on the surface of highly ordered TiO2 nanotube arrays (Au/TiO2 NTs) were synthesized through a two-step process including anodization method and microwave-assisted chemical reduction route. The investigation indicated that Au NPs grew uniformly on the walls of TiO2 NTs. Au/TiO2 NTs exhibited excellent visible light absorption due to the LSPR effect of Au NPs. Au/TiO2 NTs exhibited much higher photocurrent density and the photoconversion efficiency of Au decorated TiO2 NTs was about 2.05 times greater than that of bare TiO2 NTs. Besides, the PL intensity of Au/TiO2 NTs was much lower than that of TiO2 NTs, revealing a decrease in charge carrier recombination. The prepared Au/TiO2 NTs exhibited superior photoelectrocatalytic activity and stability in the degradation of MB under simulated solar light irradiation. The synergy effect between nanotubular structures of TiO2 and uniformly dispersed Au nanoparticles, as well as the small bias potential and strong interaction between Au and TiO2, facilitated the Au plasmon-induced charge separation and transfer, which lead to highly efficient and stable photoelectrocatalytic activity.

The Ag shell thickness effect of Au@Ag@SiO2 core-shell nanoparticles on the optoelectronic performance of dye sensitized solar cells.

To tailor the Au@Ag@SiO2 LSPR effect by varying the Ag shell thickness, the Au@Ag@SiO2 core-ultra-thin shell nanoparticles are fabricated and introduced into DSSC for improving light harvesting and decreasing the recombination of photo-carriers. The Au@Ag@SiO2 electrode exhibits a photo-conversion efficiency of 23.42% (486.7 nm, 10 mW cm(-2)).

Au/BiOCl heterojunction within mesoporous silica shell as stable plasmonic photocatalyst for efficient organic pollutants decomposition under visible light

A new mesoporous silica protected plasmonic photocatalyst, Au/BiOCl@mSiO2, was prepared by a modified AcHE method and a subsequent UV light induced photodeposition process. The surfactant-free heterojunction allows the electrons spontaneously flow from Au to nearby BiOCl surface, leading to the accumulation of positive charges on Au surface, and negative charges on Bi species under visible light. Au/BiOCl@mSiO2 exhibits high visible light photocatalytic efficiency in complete oxidation of aqueous formaldehyde and Rhodamin B. We showed that a positive relationship exists between the LSPR effect and rate enhancements, and leads to a hypothesis that the metallic Au LSPR enhances the photocatalytic rates on nearby semiconductors by transferring energetic electrons to BiOCl and increasing the steady-state concentration of active OH species by a multi-electron reduction of molecular oxygen. The OH species is the main oxidant in photocatalytic transformations, whose intensity is greatly enhanced in the dye-involving systems due to the synergetic effect between LSPR and dye sensitization processes. In addition, the mesoporous SiO2 shell not only inhibits the over growth of BiOCl nanocrystals within the silica frameworks, but also protects the dissolution of chloride or Au species into aqueous solution, which ultimately makes the Au/BiOCl@mSiO2 catalysts rather stable during photocatalysis.

Silver nanoparticles on GaSb nanodots: a LSPR-boosted binary platform for broadband light harvesting and SERS

We report the LSPR-augmented optical response of silver nanoparticle-topped GaSb nanodots produced by low-energy ion beam irradiation. Nanostructure ordering and interdot gap play crucial roles for inducing the LSPR effect, enhancing the absorbing capacity of the structure as validated by reflection measurements. The measured size of silver-capped GaSb nanodot varies from 28 to 48 nm. Enhanced plasmon coupling for the 600 eV configuration initiates the presence of giant electromagnetic fields as confirmed by LSPR and SERS measurements. Anisotropic Bruggeman effective medium approximation was performed to match the experimentally observed optical response of the nanostructure. Calculated screening factor values of 0.29 and 0.23 for 600 and 800 eV ion energy produced nanodot configurations were obtained, respectively, which are in tune with the measured reflected and SERS signal. The calculated dielectric constants confirm the directional anisotropy along the length of the silver-capped GaSb nanodots. The proposed model successfully matches the void fraction and nanostructure height in accordance with SEM and reported TEM measurements. Thus, the model developed can be used to optimize the maximum plasmonic coupling efficiency among the dots. We propose two key applications for this nanostructure, first as an absorptive substrate for deep space photovoltaics and second to act as an effective SERS substrate.

Excellent graphitic carbon nitride nanosheets-based photoelectrochemical platform motivated by Schottky barrier and LSPR effect and its sensing application.

A visible light responsive photocatalytic hybrid with excellent photoelectrochemical activity was first fabricated via the self-assembly of Au nanorods onto poly(l-cysteine) modified graphitic carbon nitride nanosheets. Herein, layered structural graphitic carbon nitride nanosheets with a proper band gap, high stability, and nontoxicity, as a photoactive material, demonstrate a high photocatalytic activity. Furthermore, the incorporation of multifunctional Au nanorods gave the hybrid a Schottky barrier and localized surface plasmonic resonance, which considerably enhanced the separation of the photo-excited electrons and holes, resulting in increased photoelectrochemical performance. As a proof of concept, mercapto-beta-cyclodextrin as a bionic recognition device was introduced into the hybrid to selectively detect naringin on the basis of the dramatic decreasing of photocurrent. The visible-light driven photoelectrochemical sensor exhibited excellent analytical performance, including high sensitivity, good selectivity and wide linear range from 1 × 10(-4) to 1 × 10(-10) M.

Vibrational study of adsorption of Congo red onto TiO2and the LSPR effect on its photocatalytic degradation process

Chemisorption of Congo red on a P25 yielded hydrazone tautomer caused distinctions on the photodegradation preference in comparison to another TiO2catalyst based on anatase. Photocatalytic degradation in the presence of Ag NPs demonstrated considerable improvement on kinetic parameters due to the near field enhancement.