Showing papers on "Surface plasmon resonance published in 2014"

Aluminum for Plasmonics

Abstract: Unlike silver and gold, aluminum has material properties that enable strong plasmon resonances spanning much of the visible region of the spectrum and into the ultraviolet. This extended response, combined with its natural abundance, low cost, and amenability to manufacturing processes, makes aluminum a highly promising material for commercial applications. Fabricating Al-based nanostructures whose optical properties correspond with theoretical predictions, however, can be a challenge. In this work, the Al plasmon resonance is observed to be remarkably sensitive to the presence of oxide within the metal. For Al nanodisks, we observe that the energy of the plasmon resonance is determined by, and serves as an optical reporter of, the percentage of oxide present within the Al. This understanding paves the way toward the use of aluminum as a low-cost plasmonic material with properties and potential applications similar to those of the coinage metals.

Nanomaterials enhanced surface plasmon resonance for biological and chemical sensing applications

Abstract: The main challenge for all electrical, mechanical and optical sensors is to detect low molecular weight (less than 400 Da) chemical and biological analytes under extremely dilute conditions. Surface plasmon resonance sensors are the most commonly used optical sensors due to their unique ability for real-time monitoring the molecular binding events. However, their sensitivities are insufficient to detect trace amounts of small molecular weight molecules such as cancer biomarkers, hormones, antibiotics, insecticides, and explosive materials which are respectively important for early-stage disease diagnosis, food quality control, environmental monitoring, and homeland security protection. With the rapid development of nanotechnology in the past few years, nanomaterials-enhanced surface plasmon resonance sensors have been developed and used as effective tools to sense hard-to-detect molecules within the concentration range between pmol and amol. In this review article, we reviewed and discussed the latest trend and challenges in engineering and applications of nanomaterials-enhanced surface plasmon resonance sensors (e.g., metallic nanoparticles, magnetic nanoparticles, carbon-based nanomaterials, latex nanoparticles and liposome nanoparticles) for detecting “hard-to-identify” biological and chemical analytes. Such information will be viable in terms of providing a useful platform for designing future ultrasensitive plasmonic nanosensors.

Metal/Semiconductor Hybrid Nanostructures for Plasmon-Enhanced Applications

Abstract: Hybrid nanostructures composed of semiconductor and plasmonic metal components are receiving extensive attention. They display extraordinary optical characteristics that are derived from the simultaneous existence and close conjunction of localized surface plasmon resonance and semiconduction, as well as the synergistic interactions between the two components. They have been widely studied for photocatalysis, plasmon-enhanced spectroscopy, biotechnology, and solar cells. In this review, the developments in the field of (plasmonic metal)/semiconductor hybrid nanostructures are comprehensively described. The preparation of the hybrid nanostructures is first presented according to the semiconductor type, as well as the nanostructure morphology. The plasmonic properties and the enabled applications of the hybrid nanostructures are then elucidated. Lastly, possible future research in this burgeoning field is discussed.

Direct Photocatalysis by Plasmonic Nanostructures

Abstract: Recent reports have shown that plasmonic nanostructures can be used to drive direct photocatalysis with visible photons, where nanostructures act as the light absorber and the catalytic active site. These reports have showcased direct plasmon driven photocatalysis as a route to concentrate and channel the energy of low intensity visible light into adsorbed molecules, enhancing the rates of chemical transformations, and offering pathways to control reaction selectivity. In this perspective, we will discuss the fundamental photophysics of localized surface plasmon resonance (LSPR) excitation in the context of driving chemical transformations. The various demonstrated chemical conversions executed using direct plasmonic photocatalysis will be reviewed. Experimental observations, such as the dependence of photocatalytic rate on illumination intensity and photon energy, will be related to microscopic mechanisms of photocatalysis. In addition, theoretical treatments of various mechanisms within the process of d...

Au/TiO2 Superstructure-Based Plasmonic Photocatalysts Exhibiting Efficient Charge Separation and Unprecedented Activity

Abstract: Plasmonic photocatalysts were successfully synthesized by the modification of TiO2 mesocrystals with Au nanoparticles (NPs) by a simple impregnation method. The Au NP sensitizers show a strong photoelectrochemical response in the visible-light region (400–800 nm) due to their surface plasmon resonance (SPR). The diffuse reflectance spectroscopy measurements on a wide range of time scales (from picoseconds to minutes) demonstrate that a substantial part of electrons, injected from the Au NPs to the TiO2 mesocrystals through the SPR excitation, directionally migrate from the basal surfaces to the edges of the plate-like mesocrystals through the TiO2 nanocrystal networks and are temporally stored there for further reactions. This anisotropic electron flow significantly retarded the charge recombination of these electrons with the holes in the Au NPs, thereby improving the visible-light-photocatalytic activity (for organic-pollutant degradation) by more than an order of magnitude, as compared to that of conve...

Surface plasmon resonance enhanced light absorption and photothermal therapy in the second near-infrared window.

Abstract: Enhanced near-field at noble metal nanoparticle surfaces due to localized surface plasmon resonance (LSPR) has been researched in fields ranging from biomedical to photoelectrical applications. However, it is rarely explored on nonmetallic nanomaterials discovered in recent years, which can also support LSPR by doping-induced free charge carriers, let alone the investigation of an intricate system involving both. Here we construct a dual plasmonic hybrid nanosystem Au–Cu9S5 with well controlled interfaces to study the coupling effect of LSPR originating from the collective electron and hole oscillations. Cu9S5 LSPR is enhanced by 50% in the presence of Au, and the simulation results confirm the coupling effect and the enhanced local field as well as the optical power absorption on Cu9S5 surface. This enhanced optical absorption cross section, high photothermal transduction efficiency (37%), large light penetration depth at 1064 nm, excellent X-ray attenuation ability, and low cytotoxicity enable Au–Cu9S5 ...

Nanogold plasmonic photocatalysis for organic synthesis and clean energy conversion.

Abstract: This review provides the basic concepts, an overall survey and the state-of-the art of plasmon-based nanogold photocatalysis using visible light including fundamental understanding and major applications to organic reactions and clean energy-conversion systems. First, the basic concepts of localized surface plasmon resonance (LSPR) are recalled, then the major preparation methods of AuNP-based plasmonic photocatalysts are reviewed. The major part of the review is dedicated to the latest progress in the application of nanogold plasmonic photocatalysis to organic transformations and energy conversions, and the proposed mechanisms are discussed. In conclusion, new challenges and perspectives are proposed and analyzed.

Single-molecule nucleic acid interactions monitored on a label-free microcavity biosensor platform

Abstract: Biosensing relies on the detection of molecules and their specific interactions. It is therefore highly desirable to develop transducers exhibiting ultimate detection limits. Microcavities are an exemplary candidate technology for demonstrating such a capability in the optical domain and in a label-free fashion. Additional sensitivity gains, achievable by exploiting plasmon resonances, promise biosensing down to the single-molecule level. Here, we introduce a biosensing platform using optical microcavity-based sensors that exhibits single-molecule sensitivity and is selective to specific single binding events. Whispering gallery modes in glass microspheres are used to leverage plasmonic enhancements in gold nanorods for the specific detection of nucleic acid hybridization, down to single 8-mer oligonucleotides. Detection of single intercalating small molecules confirms the observation of single-molecule hybridization. Matched and mismatched strands are discriminated by their interaction kinetics. Our platform allows us to monitor specific molecular interactions transiently, hence mitigating the need for high binding affinity and avoiding permanent binding of target molecules to the receptors. Sensor lifetime is therefore increased, allowing interaction kinetics to be statistically analysed.

Noble metal-like behavior of plasmonic Bi particles as a cocatalyst deposited on (BiO)2CO3 microspheres for efficient visible light photocatalysis

Abstract: Novel plasmonic Bi nanoparticles deposited in situ in (BiO)2CO3 microspheres (Bi/BOC) were fabricated via a one-pot hydrothermal treatment of bismuth citrate, sodium carbonate, and thiourea. Different characterization techniques, including XRD, SEM, TEM, XPS, UV–vis DRS, PL, time-resolved fluorescence spectra, and photocurrent generation, were performed to investigate the structural and optical properties of the as-prepared samples. The results indicated that the Bi nanoparticles were generated on the surface of (BiO)2CO3 microspheres via the in situ reduction of Bi3+ by thiourea. The Bi nanoparticle deposited (BiO)2CO3 microspheres were employed for the photocatalytic removal of NO in air under visible light irradiation, and the sample exhibited a drastically enhanced photocatalytic activity and oxidation ability. The highly enhanced activity was attributed to the cooperative contribution of the surface plasmon resonance (SPR) effect, the efficient separation of electron–hole pairs, and the prolonged lif...

Plasmon-Enhanced Fluorescence Biosensors: a Review

Abstract: Surfaces of metallic films and metallic nanoparticles can strongly confine electromagnetic field through its coupling to propagating or localized surface plasmons. This interaction is associated with large enhancement of the field intensity and local optical density of states which provides means to increase excitation rate, raise quantum yield, and control far field angular distribution of fluorescence light emitted by organic dyes and quantum dots. Such emitters are commonly used as labels in assays for detection of chemical and biological species. Their interaction with surface plasmons allows amplifying fluorescence signal (brightness) that accompanies molecular binding events by several orders of magnitude. In conjunction with interfacial architectures for the specific capture of target analyte on a metallic surface, plasmon-enhanced fluorescence (PEF) that is also referred to as metal-enhanced fluorescence (MEF) represents an attractive method for shortening detection times and increasing sensitivity of various fluorescence-based analytical technologies. This review provides an introduction to fundamentals of PEF, illustrates current developments in design of metallic nanostructures for efficient fluorescence signal amplification that utilizes propagating and localized surface plasmons, and summarizes current implementations to biosensors for detection of trace amounts of biomarkers, toxins, and pathogens that are relevant to medical diagnostics and food control.

Activation of oxygen on gold and silver nanoparticles assisted by surface plasmon resonances

Abstract: Surface plasmon resonances (SPRs) have been found to promote chemical reactions. In most oxidative chemical reactions oxygen molecules participate and understanding of the activation mechanism of oxygen molecules is highly important. For this purpose, we applied surface-enhanced Raman spectroscopy (SERS) to find out the mechanism of SPR-assisted activation of oxygen, by using p-aminothiophenol (PATP), which undergoes a SPR-assisted selective oxidation, as a probe molecule. In this way, SPR has the dual function of activating the chemical reaction and enhancing the Raman signal of surface species. Both experiments and DFT calculations reveal that oxygen molecules were activated by accepting an electron from a metal nanoparticle under the excitation of SPR to form a strongly adsorbed oxygen molecule anion. The anion was then transformed to Au or Ag oxides or hydroxides on the surface to oxidize the surface species, which was also supported by the heating effect of the SPR. This work points to a promising new era of SPR-assisted catalytic reactions.

Surfactant‐Free Nonaqueous Synthesis of Plasmonic Molybdenum Oxide Nanosheets with Enhanced Catalytic Activity for Hydrogen Generation from Ammonia Borane under Visible Light

Abstract: Plasmonic materials have drawn emerging interest, especially in nontraditional semiconductor nanostructures with earth-abundant elements and low resistive loss. However, the actualization of highly efficient catalysis in plasmonic semiconductor nanostructures is still a challenge, owing to the presence of surface-capping agents in their synthetic procedures. To fulfill this, a facile non-aqueous procedure was employed to prepare well-defined molybdenum oxide nanosheets in the absence of surfactants. The obtained MoO(3-x) nanosheets display intense absorption in a wide range attributed to the localized surface plasmon resonances, which can be tuned from the visible to the near-infrared region. Herein, we demonstrate that such plasmonic semiconductor nanostructures could be used as highly efficient catalysts that dramatically enhance the hydrogen-generation activity of ammonia borane under visible light irradiation.

Ultra-wideband polarization conversion metasurfaces based on multiple plasmon resonances

Abstract: We propose to realize ultra-wideband polarization conversion metasurfaces in microwave regime through multiple plasmon resonances. An ultra-wideband polarization conversion metasurface is designed using a double-head arrow structure and is further demonstrated both numerically and experimentally. Four plasmon resonances are generated by electric and magnetic resonances, which lead to bandwidth expansion of cross-polarization reflection. The simulated results show that the maximum conversion efficiency is nearly 100% at the four plasmon resonance frequencies and a 1:4 3 dB bandwidth can be achieved for both normally incident x- and y-polarized waves. Experimental results agree well with simulation ones.

Nanoscale conducting oxide PlasMOStor.

Abstract: We experimentally demonstrate an ultracompact PlasMOStor, a plasmon slot waveguide field-effect modulator based on a transparent conducting oxide active region. By electrically modulating the conducting oxide material deposited into the gaps of highly confined plasmonic slot waveguides, we demonstrate field-effect dynamics giving rise to modulation with high dynamic range (2.71 dB/μm) and low waveguide loss (∼0.45 dB/μm). The large modulation strength is due to the large change in complex dielectric function when the signal wavelength approaches the surface plasmon resonance in the voltage-tuned conducting oxide accumulation layer. The results provide insight about the design of ultracompact, nanoscale modulators for future integrated nanophotonic circuits.

Coupling surface plasmon resonance of gold nanoparticles with slow-photon-effect of TiO2 photonic crystals for synergistically enhanced photoelectrochemical water splitting

Abstract: The slow photon effect of a photonic crystal (PC) is a promising characteristic for tuning light–matter interactions through material structure designing. A TiO2 bi-layer structure photoanode was constructed by fabricating a TiO2 PC layer through a template-assisted sol–gel process on a TiO2 nanorod array (NR) layer. Gold nanoparticles (Au NPs) with an average size of about 10 nm were deposited in situ into the TiO2 bi-layer structure. The extended photoelectrochemical (PEC) water splitting activity in visible light was ascribed to the energetic hot electrons and holes that were generated in the Au NPs through the excitation and decay of surface plasmons. By alternating the characteristic pore size of the TiO2 PC layer, the slow photon region at the red edge of the photonic band gap could be purposely tuned to overlap with the strong localized surface plasmon resonance (SPR) region of Au NPs. The matching slow photon effect of TiO2 PC (with a characteristic pore size of 250 nm) intensified the SPR responses (central at 536 nm) of Au NPs. Consequently, more hot electrons were generated in the Au NPs and injected into the conduction band of TiO2, resulting in improved PEC water splitting efficiency in the visible light region. Under simulated sunlight illumination, the photoconversion efficiency of the well matching Au/TiO2 photoanode approached 0.71%, which is one of the highest values ever reported in Au/TiO2 PEC systems. The work reported here provides support for designing coupling plasmonic nanostructures with PC-based materials to synergistically enhance PEC water splitting efficiency.

Copper Nanoparticles on Graphene Support: An Efficient Photocatalyst for Coupling of Nitroaromatics in Visible Light

Abstract: Copper is a low-cost plasmonic metal. Efficient photocatalysts of copper nanoparticles on graphene support are successfully developed for controllably catalyzing the coupling reactions of aromatic nitro compounds to the corresponding azoxy or azo compounds under visible-light irradiation. The coupling of nitrobenzene produces azoxybenzene with a yield of 90 % at 60 °C, but azobenzene with a yield of 96 % at 90 °C. When irradiated with natural sunlight (mean light intensity of 0.044 W cm−2) at about 35 °C, 70 % of the nitrobenzene is converted and 57 % of the product is azobenzene. The electrons of the copper nanoparticles gain the energy of the incident light through a localized surface plasmon resonance effect and photoexcitation of the bound electrons. The excited energetic electrons at the surface of the copper nanoparticles facilitate the cleavage of the NO bonds in the aromatic nitro compounds. Hence, the catalyzed coupling reaction can proceed under light irradiation and moderate conditions. This study provides a green photocatalytic route for the production of azo compounds and highlights a potential application for graphene.

Vivid, full-color aluminum plasmonic pixels

Abstract: Aluminum is abundant, low in cost, compatible with complementary metal-oxide semiconductor manufacturing methods, and capable of supporting tunable plasmon resonance structures that span the entire visible spectrum. However, the use of Al for color displays has been limited by its intrinsically broad spectral features. Here we show that vivid, highly polarized, and broadly tunable color pixels can be produced from periodic patterns of oriented Al nanorods. Whereas the nanorod longitudinal plasmon resonance is largely responsible for pixel color, far-field diffractive coupling is used to narrow the plasmon linewidth, enabling monochromatic coloration and significantly enhancing the far-field scattering intensity of the individual nanorod elements. The bright coloration can be observed with p-polarized white light excitation, consistent with the use of this approach in display devices. The resulting color pixels are constructed with a simple design, are compatible with scalable fabrication methods, and provide contrast ratios exceeding 100:1.

Visible-light-induced hydrogen and oxygen formation over Pt/Au/WO₃ photocatalyst utilizing two types of photoabsorption due to surface plasmon resonance and band-gap excitation.

Abstract: Photocatalytic H2 and O2 formations under visible light irradiation (λ > 400 nm) are demonstrated using Pt–Au nanopaticles for the reduction site and WO3 for the oxidation site in solid-state Pt/Au/WO3.

LSPR Chip for Parallel, Rapid, and Sensitive Detection of Cancer Markers in Serum

Abstract: Label-free biosensing based on metallic nanoparticles supporting localized surface plasmon resonances (LSPR) has recently received growing interest (Anker, J. N., et al. Nat. Mater. 2008, 7, 442–453). Besides its competitive sensitivity (Yonzon, C. R., et al. J. Am. Chem. Soc. 2004, 126, 12669–12676; Svendendahl, M., et al. Nano Lett. 2009, 9, 4428–4433) when compared to the surface plasmon resonance (SPR) approach based on extended metal films, LSPR biosensing features a high-end miniaturization potential and a significant reduction of the interrogation device bulkiness, positioning itself as a promising candidate for point-of-care diagnostic and field applications. Here, we present the first, paralleled LSPR lab-on-a-chip realization that goes well beyond the state-of-the-art, by uniting the latest advances in plasmonics, nanofabrication, microfluidics, and surface chemistry. Our system offers parallel, real-time inspection of 32 sensing sites distributed across 8 independent microfluidic channels with ...

Au nanoparticle-modified MoS2 nanosheet-based photoelectrochemical cells for water splitting

Abstract: The surface plasmon resonance of Au nanoparticle on MoS2 nanosheet is successfully measured by the electron energy-loss spectroscopy. Furthermore, Au-MoS2 composite is developed as the photoanode material in the photo-electronchemical cell (PEC) for water splitting. Compared to the pure MoS2 -based PEC, Au-MoS2 based PEC shows the enhanced performance in the photocatalytic water splitting.

Resonant plasmonic enhancement of single-molecule fluorescence by individual gold nanorods

Abstract: Enhancing the fluorescence of a weak emitter is important to further extend the reach of single-molecule fluorescence imaging to many unexplored systems. Here we study fluorescence enhancement by isolated gold nanorods and explore the role of the surface plasmon resonance (SPR) on the observed enhancements. Gold nanorods can be cheaply synthesized in large volumes, yet we find similar fluorescence enhancements as literature reports on lithographically fabricated nanoparticle assemblies. The fluorescence of a weak emitter, crystal violet, can be enhanced more than 1000-fold by a single nanorod with its SPR at 629 nm excited at 633 nm. This strong enhancement results from both an excitation rate enhancement of ∼130 and an effective emission enhancement of ∼9. The fluorescence enhancement, however, decreases sharply when the SPR wavelength moves away from the excitation laser wavelength or when the SPR has only a partial overlap with the emission spectrum of the fluorophore. The reported measurements of fluo...

Graphene-Based Birefringent Photonic Crystal Fiber Sensor Using Surface Plasmon Resonance

Abstract: We propose a graphene-based photonic crystal fiber (PCF) sensor based on surface plasmon resonance. Graphene helps in prevention of oxidation of the silver layer used as a plasmonic active metal. The birefringent nature of the structure allows one component of the core guided mode to be more sensitive. Further, this structure does not need filling of the voids. The structural parameter of PCF and metal thickness has been optimized. The proposed sensor shows high amplitude sensitivity of 860 RIU-1 and has a resolution as high as 4×10-5 RIU. This reported performance is higher than bimetallic (gold on silver) configuration.

(Gold Core)@(Ceria Shell) Nanostructures for Plasmon-Enhanced Catalytic Reactions under Visible Light

Abstract: Driving catalytic reactions with sunlight is an excellent example of sustainable chemistry. A prerequisite of solar-driven catalytic reactions is the development of photocatalysts with high solar-harvesting efficiencies and catalytic activities. Herein, we describe a general approach for uniformly coating ceria on monometallic and bimetallic nanocrystals through heterogeneous nucleation and growth. The method allows for control of the shape, size, and type of the metal core as well as the thickness of the ceria shell. The plasmon shifts of the Au@CeO2 nanostructures resulting from the switching between Ce(IV) and Ce(III) are observed. The selective oxidation of benzyl alcohol to benzaldehyde, one of the fundamental reactions for organic synthesis, performed under both broad-band and monochromatic light, demonstrates the visible-light-driven catalytic activity and reveals the synergistic effect on the enhanced catalysis of the Au@CeO2 nanostructures.

Surface enhanced Raman scattering with gold nanoparticles: effect of particle shape

Abstract: The dependence of the Surface Enhanced Raman Scattering (SERS) by gold nanoparticles on their shape is examined using the organic dye, rhodamine 6G (R6G) as probe molecule. SERS has been explored extensively for applications in sensing and imaging, but the design and optimisation of efficient substrates is still challenging. In order to understand and optimise the SERS process in nanoparticles, gold nanospheres and their aggregates, nanotriangles, and nanostars of similar dimensions were synthesised and characterised according to their average size, zeta potential and UV/visible absorption. SERS from R6G was negligible for unaggregated nanospheres at 532 nm, close to the maximum of the surface plasmon resonance (SPR) at 560 nm. Upon aggregation of the nanospheres, the SPR shifts to ∼660 nm, attributable to local surface plasmon “hotspots” between the spheres, and the SERS signal of R6G is significantly increased, at 785 nm. In monodisperse gold nanotriangles, the SPR is located at ∼800 nm, and significant SERS of R6G is observed using 785 nm as source, as is the case for gold nanostars, which exhibit a double SPR with maxima at ∼600 nm and ∼785 nm, attributable to the core sphere and vertices of the structures, respectively. In suspensions of equal nanoparticle and dye concentration, the SERS effect increases as nanospheres < nanosphere aggregates < nanotriangles < nanostars, clearly indicating that control over the number of local field hotspots can optimise the SERS efficiency. Notably, it is demonstrated that the SERS intensity per nanoparticle scales with the magnitude of the SPR absorbance at the excitation wavelength (785 nm), providing a clear guide to optimisation of the process experimentally.

Plasmoelectric potentials in metal nanostructures

Abstract: The conversion of optical power to an electric potential is of general interest for energy applications and is typically obtained via optical excitation of semiconductor materials. We developed a method for achieving electric potential that uses an all-metal geometry based on the plasmon resonance in metal nanostructures. In arrays of gold nanoparticles on an indium tin oxide substrate and arrays of 100-nanometer-diameter holes in 20-nanometer-thick gold films on a glass substrate, we detected negative and positive surface potentials during monochromatic irradiation at wavelengths below or above the plasmon resonance, respectively. We observed plasmoelectric surface potentials as large as 100 millivolts under illumination of 100 milliwatts per square centimeter. Plasmoelectric devices may enable the development of all-metal optoelectronic devices that can convert light into electrical energy.

Surface Plasmon Resonance Imaging Sensors: A Review

Abstract: Surface plasmon resonance (SPR) imaging sensors realize label-free, real-time, highly sensitive, quantitative, high-throughput biological interaction monitoring and the binding profiles from multi-analytes further provide the binding kinetic parameters between different biomolecules. In the past two decades, SPR imaging sensors found rapid increasing applications in fundamental biological studies, medical diagnostics, drug discovery, food safety, precision measurement, and environmental monitoring. In this paper, we review the recent advances of SPR imaging sensor technology towards high-throughput multi-analyte screening. Finally, we describe our multiplex spectral-phase SPR imaging biosensor for high-throughput biosensing applications.

Size-Dependent Shifts of Plasmon Resonance in Silver Nanoparticle Films Using Controlled Dissolution: Monitoring the Onset of Surface Screening Effects

Abstract: A study of the size dependent blue- and red-shift of the plasmon band of silver nanoparticle films in aqueous solution is reported. A detection scheme, where the particle size is continuously decreased by means of controlled dissolution, while measuring the plasmon band position by UV–vis absorption spectroscopy is used. Both blue- and red-shifts of the peak position are observed, depending on the presence of electron donors and/or acceptors in the solution, respectively. A great increase in plasmon shifts for smaller particle sizes (R 10 nm) is demonstrated, which we ascribe to a transition from an extrinsic regime for the larger particles, where shifts of the plasmon frequency are related to changes in the dielectric environment, while the dielectric function of the metal is constant, to an intrinsic regime for the smaller particles. For this intrinsic regime, operative for small particles, nonlocality of the dielectric constant has to be considered. The experimental data are fitted with a...

Understanding the superior photocatalytic activity of noble metals modified titania under UV and visible light irradiation

Abstract: Although TiO2 is one of the most efficient photocatalysts, with the highest stability and the lowest cost, there are drawbacks that hinder its practical applications like its wide band gap and high recombination rate of the charge carriers. Consequently, many efforts were directed toward enhancing the photocatalytic activity of TiO2 and extending its response to the visible region. To head off these attempts, modification of TiO2 with noble metal nanoparticles (NMNPs) received considerable attention due to their role in accelerating the transfer of photoexcited electrons from TiO2 and also due to the surface plasmon resonance which induces the photocatalytic activity of TiO2 under visible light irradiation. This insightful perspective is devoted to the vital role of TiO2 photocatalysis and its drawbacks that urged researchers to find solutions such as modification with NMNPs. In a coherent context, we discussed here the characteristics which qualify NMNPs to possess a great enhancement effect for TiO2 photocatalysis. Also we tried to understand the reasons behind this effect by means of photoluminescence (PL) and electron paramagnetic resonance (EPR) spectra, and Density Functional Theory (DFT) calculations. Then the mechanism of action of NMNPs upon deposition on TiO2 is presented. Finally we introduced a survey of the behaviour of these noble metal NPs on TiO2 based on the particle size and the loading amount.