Plasmonic Nanocatalysts Research Articles

TiO2-supported Au-Ag plasmonic nanocatalysts achieved by plasma restructuring and activation

Plasmonic Au-Ag/TiO2 bimetallic nanocatalyst is regarded as a promising visible-light (VL) photocatalyst due to its wide light absorption and potentially enhanced activity. For its preparation, Au precursors usually contain Cl and co-impregnation/co-deposition suffers from AgCl precipitation, and consequently Au and Ag have to be sequentially supported. However, Au and Ag species of the sequential preparation are individually isolated and difficult to be homogeneously mixed. Here we report an Au-Ag plasmonic nanocatalyst achieved by plasma restructuring and activation from the sequential preparation. The isolated cationic Au and Ag species on the sequentially-prepared Au-Ag/TiO2 sample are restructured to be homogeneously mixed and highly activated by O2 plasma, which can be partially auto-reduced to Au-Ag bimetallic nanoparticles within the induction period of a few minutes in VL photocatalytic oxidation of CO. The Au-Ag plasmonic nanocatalyst exhibits a strongly enhanced activity in the VL photocatalytic reaction. The contribution of O2 plasma treatment and the enhancement mechanism for the Au-Ag plasmonic nanocatalyst are disclosed.

Clay-supported anisotropic Au-modified N,S-doped TiO2 nanoparticles for enhanced photocatalytic dye degradation and esterification reactions

Kaolinite clay supported doped TiO2 and anisotropic gold deposited visible light induced plasmonic nanocatalysts for dye degradation and esterification reactions.

Plasmonic nanocatalysis for solar energy harvesting and sustainable chemistry

This review discusses the role of plasmonic nanocatalysts in organic transformations and their potential for developing sustainable catalytic processes.

Controlling Reaction Selectivity over Hybrid Plasmonic Nanocatalysts.

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles has been used to accelerate several catalytic transformations under visible-light irradiation. In order to fully harness the potential of plasmonic catalysis, multimetallic nanoparticles containing a plasmonic and a catalytic component, where LSPR-excited energetic charge carriers and the intrinsic catalytic active sites work synergistically, have raised increased attention. Despite several exciting studies observing rate enhancements, controlling reaction selectivity remains very challenging. Here, by employing multimetallic nanoparticles combining Au, Ag, and Pt in an Au@Ag@Pt core–shell and an Au@AgPt nanorattle architectures, we demonstrate that reaction selectivity of a sequential reaction can be controlled under visible light illumination. The control of the reaction selectivity in plasmonic catalysis was demonstrated for the hydrogenation of phenylacetylene as a model transformation. We have found that the localized interaction between the triple bond in phenylacetylene and the Pt nanoparticle surface enables selective hydrogenation of the triple bond (relative to the double bond in styrene) under visible light illumination. Atomistic calculations show that the enhanced selectivity toward the partial hydrogenation product is driven by distinct adsorption configurations and charge delocalization of the reactant and the reaction intermediate at the catalyst surface. We believe these results will contribute to the use of plasmonic catalysis to drive and control a wealth of selective molecular transformations under ecofriendly conditions and visible light illumination.

Design of Silver-Based Controlled Nanostructures for Plasmonic Catalysis under Visible Light Irradiation

Abstract Recent years have marked substantial research interest in the design and development of photocatalyst materials for the conversion of solar to chemical energy. In this brief account, we present some of the recent research on silver-based plasmonic nanocatalysts supported on silica for their preparative techniques, characterization and efficient catalysis under visible light irradiation conditions. Ag nanoparticles (NPs) which can be prepared with different color and morphology, are explored for possible enhancement effects in catalytic performance activities under visible light irradiation. A number of combinations of Ag with other catalytically active metal NPs is studied for exploring the plasmonic enhancement activities. Ag NPs combined with single site Ti-oxide moiety is studied for the enhanced hydrogen production activity attributing to the Ag plasmonic effect under UV-vis light irradiation. The account is further elaborated by citing some recently reported works, plausible mechanism of enhancements, conclusions and outlook. We expect that the present account will provide insights into the design and investigation of catalytic performances in the visible light driven plasmon-mediated chemical reactions.

Electrochemical Synthesis of Ammonia from N2 and H2O under Ambient Conditions Using Pore-Size-Controlled Hollow Gold Nanocatalysts with Tunable Plasmonic Properties.

An electrochemical nitrogen reduction reaction (NRR) could provide an alternative pathway to the Haber-Bosch process for clean, sustainable, and decentralized NH3 production when it is coupled with renewably derived electricity sources. Developing an electrocatalyst that overcomes sluggish kinetics due to the challenges associated with N2 adsorption and cleavage and that also produces NH3 with a reasonable yield and efficiency is an urgent need. Here, we engineer the size and density of pores in the walls of hollow Au nanocages (AuHNCs) by tuning their peak localized surface plasmon resonance (LSPR); in this way, we aim to enhance the rate of electroreduction of N2 to NH3. The interdependency between the pore size/density, the peak LSPR position, the silver content in the cavity, and the total surface area of the nanoparticle should be realized for further optimization of hollow plasmonic nanocatalysts in electrochemical NRRs.

Ultrasmall Plasmonic Nanoparticles Decorated Hierarchical Mesoporous TiO2 as an Efficient Photocatalyst for Photocatalytic Degradation of Textile Dyes.

Hierarchical mesoporous TiO2 was synthesized via a solvothermal technique. The sonochemical method was adopted to decorate plasmonic nanoparticles (NPs) (Ag, Au) on the pores of mesoporous TiO2. The crystallinity, structure, and morphology were determined to understand the physicochemical nature of the nanocomposites. The catalytic efficiency of the plasmonic nanocatalysts was tested for the azo dyes (congo red, methyl orange, acid orange 10, and remazol red) under solar and visible light irradiations. The generation of hydroxyl radicals was also studied using terephthalic acid as a probe molecule. An attempt was made to understand the influence of size, work function and Fermi level of the metal NPs toward the efficiency of the photocatalyst. The efficiency of the nanocomposites was found to be in the order of P25 < mesoporous TiO2 < mesoporous Ag–TiO2 < mesoporous Au–TiO2 nanospheres under both direct solar light and visible light irradiation. The results indicated that the adsorption of dye, anatase phase, and surface plasmon resonance of NPs favored the effective degradation of dyes in aqueous solution. Further, the efficiency of the catalyst was also tested for xanthene (rose bengal), rhodamine (rhodamine B, rhodamine 6G), and thiazine (methylene blue) dyes. Both TiO2 and NPs (Ag & Au) possess a huge potential as an eco-friendly photocatalyst for wastewater treatment.

Reaction Pathway Dependence in Plasmonic Catalysis: Hydrogenation as a Model Molecular Transformation.

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can enhance or mediate chemical transformations. Increased reaction rates for several reactions have been reported due to this phenomenon; however, the fundamental understanding of mechanisms and factors that affect activities remains limited. Here, by investigating hydrogenation reactions as a model transformation and employing different reducing agents, H2 and NaBH4 , which led to different hydrogenation reaction pathways, we observed that plasmonic excitation of Au nanoparticle catalysts can lead to negative effects over the activities. The underlying physical reason was explored using density functional theory calculations. We observed that positive versus negative effects on the plasmonic catalytic activity is reaction-pathway dependent. These results shed important insights on our current understanding of plasmonic catalysis, demonstrating reaction pathways must be taken into account for the design of plasmonic nanocatalysts.

Synthesis of mesoporous silica-supported Ag nanorod-based bimetallic catalysts and investigation of their plasmonic activity under visible light irradiation

Bimetallic Ag nanorod-based heterogeneous plasmonic nanocatalysts were synthesized for obtaining excellent catalytic performances under visible light irradiation.

Tracking the Fate of Surface Plasmon Resonance-Generated Hot Electrons by In Situ SERS Surveying of Catalyzed Reaction.

Plasmonic catalysis is an emerging process that utilizes surface plasmon resonance (SPR) process to harnesses solar energy for the promotion of catalyzed reactions. In most cases, SPR generated hot electrons (HEs) play an indispensable role in this solar-chemical energy shift process. Therefore, understanding the effectiveness of the HEs in promoting chemical reactions, and identifying the key factors that contribute to this utilization efficiency is of profound importance. Herein, the authors outline an in situ surface enhanced Raman spectroscopy protocol to track the fate of HEs. This is based on the unheeded HEs-acceleration nature of the p-nitirothiophenol hydrogenation reaction. By this way, the authors discover that unlike Au@Pd nanostructures which experience a 20-fold increase in rate constant, HEs primary leak to surrounding H+ /O species through Ag pinholes in Ag@Pd. This work sheds light on why Ag is seldom employed as a plasmonic cocatalyst, and provides a new viewpoint to design plasmonic nanocatalysts with efficient light utilization.

Wavelength-Selective Photocatalysis Using Gold–Platinum Nanorattles

The selectivity of a thermal catalyzed reaction with multiple products, catalyzed on the surface of a catalyst exhibiting different surface facets and surface energy, is controlled by the temperature. Manipulating the temperature makes one product more dominant than the other. The selectivity of the photochemical reaction on the surface of plasmonic nanocatalyst of multiple plasmon modes is controlled by changing the wavelength of the exciting light. Gold nanospheres (AuNSs) located inside gold–platinum double-shell nanoparticles in a rattle structure were prepared with different sizes and showed two plasmon spectral modes. The high-energy plasmon mode corresponds to the photoexcitation of the small nanosphere, whereas the low-energy plasmonic mode is related to both the gold–platinum double-shell plasmon and the inside nanosphere, as assigned by calculation using the discrete dipole approximation (DDA) simulation technique. Photodimerization of 4-nitrothiophenol (4NTP) adsorbed on the surface of gold–pla...

Designed plasmonic nanocatalysts for the reduction of eosin Y: absorption and fluorescence study

Abstract In this work, we report a one-step green synthesis of gold nanoparticles (AuNPs) by microwave irradiation using nontoxic and biodegradable polysaccharide chitosan as a reducing and stabilizing agent. The interaction between gold nanoparticles with the amine group of chitosan was confirmed by Fourier transform infrared spectroscopy analysis, and the stability of the nanoparticle is ascertained by zeta potential measurements. Transmission electron microscopy photograph and dynamic light scattering measurements confirmed the average size of gold nanoparticles as 25 nm. The ability of the synthesised gold nanoparticles as a catalyst for the reduction of eosin dye in the presence of NaBH4 was monitored by means of spectrofluorometry and spectrophotometry. It is found that the NaBH4-induced reduction of eosin is enhanced in the presence of AuNPs even without a catalyst. Time-resolved fluorescence decay studies also confirmed the reduction of eosin in the presence of AuNPs.

In situ capture of active species and oxidation mechanism of RhB and MB dyes over sunlight-driven Ag/Ag3PO4 plasmonic nanocatalyst

Sunlight-driven Ag/Ag3PO4 plasmonic nanocatalysts have been successfully prepared using an in situ ethylene glycol reduction method. The photocatalysts showed strong photocatalytic activity for decomposition of RhB and MB dyes under visible light irradiation (λ>420nm). The excellent photocatalytic performance of Ag/Ag3PO4 came from the sensitivity of Ag3PO4 and the high separation efficiency of electron–hole pairs, which resulted in a large number of holes participating in the photocatalytic oxidation process. The results of density function theory calculation revealed that the visible-light absorption band in the Ag3PO4 catalyst is attributed to the band transition from the hybrid orbital of O 2p and Ag 4d to the Ag 5s and 5p orbital. The generation of active species in the photocatalytic system was evaluated using the fluorescence (FL) and electron spin resonance (ESR) techniques as well as in situ capture of active species by t-butanol and EDTA. The results indicated that the free hydroxyl radicals were not the major active oxidizing species in the photocatalytic process. The photocatalytic reaction process of the pollutants was mainly governed by the direct oxidation by the holes.