Plasmon-enhanced Photocatalytic Activity Research Articles

Synthesis of Ag-OMS Catalyst for Sunlight-Assisted Photodegradation of Crystal Violet Dye

The contamination of water with organic pollutants, such as dyes, has become a serious threat to the environment. Therefore, the development of a cost-effective, eco-friendly, proficient, and visible-light-driven catalyst for the treatment of organic dye-contaminated wastewater has been a burning issue recently. Photocatalysis is suggested as a potential treatment technique for the eradication of organic pollutants. The 1D tunnel-structured manganese oxide octahedral molecular sieve (OMS) is a suitable substance to be tested as a visible-light-driven photocatalyst for the degradation of organic contaminants. However, the fast recombination of photoinduced charges (h+/e−) limits its photocatalytic application. The development of heterojunctions between OMS and other metals, such as Ag, is a suitable technique for improving the photocatalytic performance of OMS. In this study, Ag-OMS with plasmon-enhanced photocatalytic activity is reported for the photodegradation of crystal violet dye. Manganese oxide OMS was prepared by an acidic precipitation method using potassium permanganate, manganese acetate, and nitric acid as precursor materials. Ag nanoparticles were deposited on OMS using leaf extracts of Calotropis gigantea. The deposition of Ag enhanced the photocatalytic performance of OMS from 68 to 95%. The effects of Ag contents, catalyst dosage, and concentration of crystal violet dye on catalytic performance were explored as well. Approximately 100, 95, and 75% photodegradation of 50, 100, and 150 mg/L crystal violet dye was observed in 90, 120, and 120 min in the presence of 10% Ag-OMS, respectively. Excellent photocatalytic performance, low dose utilization, and reusability proved that Ag-OMS might have practical environmental applications.

Hot Electron-Driven Photocatalysis Using Sub-5 nm Gap Plasmonic Nanofinger Arrays.

Semiconductor photocatalysis has received increasing attention because of its potential to address problems related to the energy crisis and environmental issues. However, conventional semiconductor photocatalysts, such as TiO2 and ZnO, can only be activated by ultraviolet light due to their wide band gap. To extend the light absorption into the visible range, the localized surface plasmon resonance (LSPR) effect of noble metal nanoparticles (NPs) has been widely used. Noble metal NPs can couple incident visible light energy to strong LSPR, and the nonradiative decay of LSPR generates nonthermal hot carriers that can be injected into adjacent semiconductor material to enhance its photocatalytic activity. Here we demonstrate that nanoimprint-defined gap plasmonic nanofinger arrays can function as visible light-driven plasmonic photocatalysts. The sub-5 nm gaps between pairs of collapsed nanofingers can support ultra-strong plasmon resonance and thus boost the population of hot carriers. The semiconductor material is exactly placed at the hot spots, providing an efficient pathway for hot carrier injection from plasmonic metal to catalytic materials. This nanostructure thus exhibits high plasmon-enhanced photocatalytic activity under visible light. The hot carrier injection mechanism of this platform was systematically investigated. The plasmonic enhancement factor was calculated using the finite-difference time-domain (FDTD) method and was consistent with the measured improvement of the photocatalytic activity. This platform, benefiting from the precise controllable geometry, provides a deeper understanding of the mechanism of plasmonic photocatalysis.

Plasmonic Metal/Semiconductor Heterostructure for Visible Light-Enhanced H2 Production

A plasmonic Ag/Bi2WO6 heterostructure, having Ag NPs deposited on Bi2WO6, is obtained by a hydrothermal and photodeposition method. The synthesized Ag/Bi2WO6 composite exhibits strong visible light absorption with a localized surface plasmon resonance (LSPR) and shows an enhanced photoabsorption property. It is demonstrated that such a Ag/Bi2WO6 heterostructure shows excellent plasmon-enhanced photocatalytic activity in the dehydrogenation of ammonia borane (NH3BH3) solution under visible light irradiation, which is due to the results from the synergetic effect between Ag NPs and emerging W5+ ions. More importantly, the performance of a Ag/Bi2WO6 hybrid is almost eight times higher than that of sole Bi2WO6 nanosheets. The introduction of LSPR of Ag in Bi2WO6 improves the electrical conductivity of the composite and lowers the recombination rate of charge carriers. This study opens up the opportunity of rationally fabricating plasmonic metal/semiconductor heterostructures for highly efficient photocatalysis.

Plasmon-enhanced photocatalytic activity in the visible range using AgNPs/polydopamine/graphitic carbon nitride nanocomposite

Developing an efficient visible-light-driven photocatalyst is believed to be a practical solution for clean energy and environmental remediation. The present study aimed to broaden current knowledge of the graphitic carbon nitride (g-C3N4)-based plasmonic photocatalysts by decorating polydopamine-grafted g-C3N4 (PDA/g-C3N4) with silver nanoparticles (AgNPs). The nanocomposite was prepared using a facile synthesis method, while XPS and microscopy measurements confirmed the homogenous dispersion of AgNPs on PDA/g-C3N4. AgNPs successfully reduced the recombination rate of photoinduced electron-hole pairs. The calculated bandgap energy was decreased from 2.7 eV for pure g-C3N4 to 2.1 eV for AgNPs/PDA/g-C3N4. The developed AgNPs/PDA/g-C3N4 nanocomposite showed superior performance in degrading methylene blue (MB) up to 96% in less than two hours which is 6 and 3 times faster than g-C3N4 and PDA/g-C3N4, respectively. The developed photocatalyst maintained this performance after four successive runs, which proves its excellent chemical stability. The radical scavenger experiment was used to assess the role of active species in the degradation reaction using the AgNPs/PDA/g-C3N4. The kinetics of the degradation reaction was modeled using pseudo-first-order kinetics with a high-rate constant of 0.022 min−1. The plasmon-enhanced photocatalyst showed promising performance for the degradation of organic pollutants using a low-power lamp with potential application in environmental remediation.

Hydrogenation and plasmon-enhanced photocatalytic activity of rhenium oxide nanosheets

In this study, we synthesized spherical mixed-valence rhenium oxide (MVReO) nanoparticles with localized surface plasmon resonances (LSPRs) covering visible and NIR region. The spherical MVReO nanoparticles were converted into hydrogen rhenium bronze (HxReO3) nanosheets when dispersed in aqueous solution due to the hydrogen insertion into lattice. More importantly, the HxReO3 nanosheets exhibit enhanced LSPR strength and red-shifted LSPR wavelength. The dispersion of HxReO3 in aqueous solution provides a fascinating way for the light-harvesting enhancement as well as a compatible way for the subsequent growth of CdS to form HxReO3-CdS. The photocatalysis experiments of the HxReO3-CdS hetero-nanocrystals have been performed for the first time. Photocatalytic hydrogen production rate of the HxReO3-CdS is about 92.6 times that of the pure CdS, which is attributed to the HxReO3 for both increasing the light absorption and promoting the electron transfer. These results provide a new strategy to prepare plasmon-exciton hybrids with non-metal plasmonic nanomaterials for photocatalysis applications.

Plasmon-enhanced photocatalytic activity of Pt@Au and Pt@Cu nanoparticles in quantum size regime

We have synthesized Pt@Au and Pt@Cu bimetallic nanoparticles and investigated their surface plasmon resonance (SPR) and plasmon-enhanced photocatalytic activity in the quantum size regime. The SPR wavelength of Pt@Au bimetallic nanoparticles monotonously blue-shifts as the thickness of Pt shell increases comparing with the quantum-sized Au core nanoparticles with diameter dAu = 3.6 ± 0.4 nm. On the other hand, the SPR of Pt@Cu bimetallic nanoparticles blue-shifts at first and then red-shifts as the Pt shell thickness increases comparing to the quantum-sized Cu core nanoparticles with diameter dCu = 3.7 ± 0.5 nm. Then, we comparatively investigated the photocatalytic activities of the Pt@Au nanoparticles with quantum and classical sizes. The photocatalytic rate for 4-NP:NaBH4 is enhanced 2 times by the strong plasmon resonance and the large surface area/volume ratio of quantum-sized Pt@Au nanoparticles. Additionally, the increasing photocatalytic activity of the quantum-sized Pt@Cu with the increase of Pt shell thickness is also observed. These findings reveal the significance of the quantum plasmon resonance on the enhancement of photocatalytic activity.

Plasmon-enhanced photocatalytic activity of Na0.9Mg0.45Ti3.55O8 loaded with noble metals directly observed with scanning Kelvin probe microscopy

The noble metals Au, Ag and Pt were loaded onto Na0.9Mg0.45Ti3.55O8 (NMTO) using a chemical bath deposition method devised in our recent work for the first time. The composite photocatalysts exhibit more effective photodegradation of methylene blue, due to the Schottky barrier built between NMTO and noble metal. Hot electrons generated during localized surface plasmon processes in metal nanoparticles transfer to the semiconductor, manifesting as a depression of surface potential directly detectable by scanning Kelvin probe microscopy. The key factor responsible for the improved ability of semiconductor-based photocatalysts is charge separation. The most effective weight concentrations of Au, Ag and Pt loaded onto NMTO were found to be 5.00%, 12.6% and 5.55% respectively. NMTO loaded with noble metals shows good photostability and recyclability for the degradation of methylene blue. A possible mechanism for the photodegradation of methylene blue over NMTO loaded with noble metals is proposed. This work highlights the potential application of NMTO-based photocatalysts, and provides an effective method to detect localized surface plasmons.

The nonmonotonous shift of quantum plasmon resonance and plasmon-enhanced photocatalytic activity of gold nanoparticles.

The surface plasmon resonance (SPR) of metal nanoparticles exhibits quantum behaviors as the size decreases owing to the transitions of quantized conduction electrons, but most studies are limited to the monotonous SPR blue-shift caused by off-resonant transitions. Here, we demonstrate the nonmonotonous SPR red-shift caused by resonant electron transitions and photocatalytic activity enhanced by the quantum plasmon resonance of colloidal gold nanoparticles. A maximal SPR wavelength and the largest photocatalytic activity are observed in the quantum regime for the first time for the gold nanoparticles with a diameter of 3.6 nm. Theoretical analysis based on a quantum-corrected model reveals the evolution of SPR with quantized electron transitions and well explains the nonmonotonous size-dependencies of the SPR wavelength and absorption efficiency. These findings have profound implications for the understanding of the quantum nature of the SPR of metal nanoparticles and their applications in areas ranging from photophysics to photochemistry.

Novel Au/CaIn2S4 nanocomposites with plasmon-enhanced photocatalytic performance under visible light irradiation

A series of Au/CaIn2S4 nanocomposites with different Au contents were prepared by a simple photoreduction process. Under visible light irradiation, the as-prepared Au/CaIn2S4 nanocomposites exhibited plasmon-enhanced photocatalytic activity for the degradation of methylene blue (MB) compared to that of bare CaIn2S4. The sample with 4wt% Au hybridized CaIn2S4 exhibited the highest photocatalytic efficiency for MB degradation compared with those of the other nanocomposites. The mechanism for improving the photocatalytic performance of the Au/CaIn2S4 nanocomposites was proposed by using the photoluminescence measurement and electrochemical analyses. The enhanced photocatalytic performance could be attributed to the high separation efficiency of the photogenerated electron-hole pairs. This work could provide a new insight into the fabrication of CaIn2S4-based plasmonic photocatalysts with enhanced performance.

Morphology-controlled preparation and plasmon-enhanced photocatalytic activity of Pt–BiOBr heterostructures

Pt–BiOBr nanosheets, microflowers, microspheres and sphere-like microflowers are controllably fabricated via a hydro(solvo)thermal treatment-photodeposition route and adjusting Br sources and solvents in the preparation systems. The simulated sunlight and visible-light photocatalytic properties of various morphological Pt–BiOBr heterostructures are evaluated by the degradation of two aqueous light insensitive organic pollutants, p-nitrophenol (PNP) and tetrabromobisphenol-A (TBBPA), and the relationship between the morphological characteristics and photocatalytic properties of the Pt–BiOBr is revealed accordingly. The sphere-like Pt–BiOBr microflowers and microspheres show considerably higher photocatalytic activity with respect to their microflowers and nanosheets counterparts, and their activity outperforms P25 TiO2. This excellent photoactivity is explained in terms of unique performance of BiOBr and plasmonic metal nanoparticles as well as fascinating morphological characteristics. The Pt–BiOBr heterostructures can be reused four times without obvious activity loss.

Synthesis of Au@UiO-66(NH2) structures by small molecule-assisted nucleation for plasmon-enhanced photocatalytic activity.

We have provided a small molecule-assisted heterogeneous nucleation of MOF route to successfully synthesize Au@UiO-66(NH2) heterostructures. UiO-66(NH2) with a localized electronic state that was characterized by C-AFM exhibited higher photocatalytic activity in the heterostructures via a plasmonic sensitization process.

Comprehensive Study on the Controlled Plasmon-Enhanced Photocatalytic Activity of Hybrid Au/ZnO Systems Mediated by Thermoresponsive Polymer Linkers.

Hybrid semiconductor/noble metal nanostructures coupled with responsive polymers were used to probe unique plasmon-mediated photocatalytic properties associated with swelling-shrinking transitions in polymer chains triggered by specific external stimuli. Poly(N-isopropylacrylamide) (PNIPAM) brushes were anchored on Au films by atom transfer radical polymerization and ZnO nanoparticles were immobilized on the PNIPAM layer to explore controlled photocatalytic activity. The plasmon-enhanced photocatalytic activity was dictated by two critical parameters, that is, grafting density and molecular weight of PNIPAM involved in Au film-PNIPAM-ZnO. The effect of the areal density of PNIPAM chains on the temperature-responsive UV light photocatalytic activities showed mutually antagonistic trends at two different temperatures. The performance at high density was higher above a lower critical solution temperature (LCST), that is, under contracted configuration, while the sample with low density showed higher activity below LCST, that is, extended configuration. Among all the cases explored, the UV light activity was highest for the sample with thin PNIPAM layer and high density above LCST. The visible light activity was induced only for thin PNIPAM layer and high density, and it was higher above LCST. The efficiency of photocatalytic decomposition of phenol pollutant was dramatically enhanced from 10% to 55% upon the increase in temperature under visible light illumination.

Facile Photochemical Synthesis of Au/Pt/g-C3N4 with Plasmon-Enhanced Photocatalytic Activity for Antibiotic Degradation.

A novel plasmonic photocatalyst, Au/Pt/g-C3N4, was prepared by a facile calcination-photodeposition technique. The samples were characterized by X-ray diffraction, energy-dispersive spectroscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectroscopy, and the results demonstrated that the Au and Pt nanoparticles (7-15 nm) were well-dispersed on the surfaces of g-C3N4. The Au/Pt codecorated g-C3N4 heterostructure displayed enhanced photocatalytic activity for antibiotic tetracycline hydrochloride (TC-HCl) degradation, and the degradation rate was 3.4 times higher than that of pure g-C3N4 under visible light irradiation. The enhancement of photocatalytic activity could be attributed to the surface plasmon resonance effect of Au and electron-sink function of Pt nanoparticles, which improve the optical absorption property and photogenerated charge carriers separation of g-C3N4, synergistically facilitating the photocatalysis process. Finally, a possible photocatalytic mechanism for degrading TC-HCl by Au/Pt/g-C3N4 heterostructure was tentatively proposed.

A general method to diverse silver/mesoporous–metal–oxide nanocomposites with plasmon-enhanced photocatalytic activity

Incorporating plasmonic Ag nanoparticles into mesoporous metal–oxide (MMO) semiconductors will achieve collective effect to greatly increase the photocatalysis. This work demonstrated a general two-step method to obtain diverse Ag/MMO composite photocatalysts with plasmon-enhanced photocatalytic activity. Several typical MMO (TiO2, ZnO, and CeO2) semiconductors were synthesized by integrating evaporation-induced self-assembly and in situ pyrolysis of metal precursors. Different amounts of Ag nanoparticles were then loaded in these MMO semiconductors through a facile photodeposition process. The Ag nanocrystals with sizes of 50–100nm were embedded in MMO semiconductors, endowing the Ag/MMO composites notable visible light absorption. The photocatalytic activities of the as-prepared diverse photocatalysts were studied systematically. The influencing factors including MMO species, mesoporous structure, and Ag loading amount on the photocatalytic activity were discussed in detail. The Ag/MMO composites exhibited much improved photocatalytic activity than their pure MMO semiconductors. The mesoporous TiO2 with the Ag-loading amount of 5wt.% exhibited the best photocatalytic performance for photodegrading both methylene blue and phenol under a simulated sunlight. The enhancement in photocatalysis is attributed to the synergistic effect of the mesoporous structures for efficient mass transfer as well as the Ag nanoparticles providing plasmonic enhanced light absorption.

Plasmon-Enhanced Photocatalytic Activity of Iron Oxide on Gold Nanopillars

Photocatalytic water splitting represents a promising way to produce renewable hydrogen fuel from solar energy. Ultrathin semiconductor electrodes for water splitting are of particular interest because the optical absorption occurs in the region where photogenerated charge carriers can effectively contribute to the chemical reactions on the surface. It is therefore important to manipulate and concentrate the incident light so that more photons can be absorbed within the thin film. Here we show an enhanced photocurrent in a thin-film iron oxide photoanode coated on arrays of Au nanopillars. The enhancement can be attributed primarily to the increased optical absorption originating from both surface plasmon resonances and photonic-mode light trapping in the nanostructured topography. The resonances can be tuned to a desirable wavelength by varying the thickness of the iron oxide layer. A net enhancement as high as 50% was observed over the solar spectrum.

Plasmon-Enhanced Photocatalytic Activity of Cadmium Sulfide Nanoparticle Immobilized on Silica-Coated Gold Particles

Nanocomposite photocatalysts of CdS nanoparticles immobilized on Au core–SiO2 shell particles, in which the SiO2 layer acts as an insulator layer to prevent direct electron transfer from photoexcited CdS to Au particles, were prepared. The photocatalytic activity of CdS particles for H2 evolution was greatly dependent on the distance between CdS and Au particles, due to the locally enhanced electric field produced by photoexcitation of the localized surface plasmon resonance (LSPR) peak of Au particles. Increase in Au core size enlarged the optimal distance between Au and CdS for the enhancement of photocatalysis. This behavior was theoretically reproduced by solving a self-consistent equation system, in which the range of energy dissipation became wider for larger diameter of the Au sphere, and then the balance with the enhancement of photoexcitation of CdS particles by the LSPR-induced electric field was changed.