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Influence of Semiconductor Morphology on Photocatalytic Activity of Plasmonic Photocatalysts: Titanate Nanowires and Octahedral Anatase Nanoparticles
摘要： Octahedral anatase particles (OAP) with eight exposed and thermodynamically most stable (101) facets were prepared by an ultrasonication-hydrothermal (US-HT) reaction from potassium titanate nanowires (TNW). The precursor (TNW) and the product (OAP) of US-HT reaction were modi?ed with nanoparticles of noble metals (Au, Ag or Pt) by photodeposition. Samples were characterized by X-ray di?raction (XRD), X-ray photoelectron spectroscopy (XPS), di?use re?ectance spectroscopy (DRS), scanning transmission electron microscopy (STEM) and time-resolved microwave conductivity (TRMC). The photocatalytic activity was investigated in three reaction systems, i.e., anaerobic dehydrogenation of methanol and oxidative decomposition of acetic acid under UV/vis irradiation, and oxidation of 2-propanol under vis irradiation. It was found that hydrogen liberation correlated with work function of metals, and thus the most active were platinum-modi?ed samples. Photocatalytic activities of bare and modi?ed OAP samples were much higher than those of TNW samples, probably due to anatase presence, higher crystallinity and electron mobility in faceted NPs. Interestingly, noble metals showed di?erent in?uence on the activity depending on the semiconductor support, i.e., gold-modi?ed TNW and platinum-modi?ed OAP exhibited the highest activity for acetic acid decomposition, whereas silver- and gold-modi?ed samples were the most active under vis irradiation, respectively. It is proposed that the form of noble metal (metallic vs. oxidized) as well as the morphology (well-organized vs. uncontrolled) have a critical e?ect on the overall photocatalytic performance. TRMC analysis con?rmed that fast electron transfer to noble metal is a key factor for UV activity. It is proposed that the e?ciency of plasmonic photocatalysis (under vis irradiation) depends on the oxidation form of metal (zero-valent preferable), photoabsorption properties (broad localized surface plasmon resonance (LSPR)), kind of metal (silver) and counteraction of “hot” electrons back transfer to noble metal NPs (by controlled morphology and high crystallinity).
关键词： silver,platinum,gold,photocatalyst morphology,faceted titania,morphology-governed activity,plasmonic photocatalysis,octahedral particle,titanate nanowire,noble metal
更新于2025-09-11 14:15:04
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Comparison and convergence of optical absorption spectra of noble metal nanoparticles computed using linear-response and real-time time-dependent density functional theories
摘要： The real-time time-dependent density functional theory (RT-TDDFT) is rapidly gaining prominence as an alternative approach to capture optical properties of molecular systems, which warrants the necessity to benchmark the traditional linear response (LR) method and the RT approach. We calculate the absorption spectra of noble metal nanoparticles with a variety of sizes and shapes to demonstrate the consistency of the two methods over a broad range of energy. The RT spectrum obtained using a grid-based basis set with pseudopotentials achieves results in good agreement with the LR spectrum obtained with large QZ4P atom-centered basis sets. Factors that lead to convergence of the spectra are considered. In addition, the real-time variation of the electron density is visualized to show the collective oscillation of electron density for the plasmon modes of noble metal nanoparticles. The RT approach is most useful when calculating wide absorption spectra of larger gold or silver nanoparticles.
关键词： optical absorption spectra,noble metal nanoparticles,RT-TDDFT,LR-TDDFT,plasmon modes
更新于2025-09-10 09:29:36
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Electronic and Geometric Structure, Optical Properties, and Excited State Behavior in Atomically Precise Thiolate-Stabilized Noble Metal Nanoclusters
摘要： Ligand-protected noble metal nanoclusters are of interest for their potential applications in areas such as bioimaging, catalysis, photocatalysis, and solar energy harvesting. These nanoclusters can be prepared with atomic precision, which means that the properties of these nanoclusters can vary significantly depending on the exact stoichiometry and geometric structure of the system. This leads to important questions such as: What are the general principles that underlie the physical properties of these nanoclusters? Do these principles hold for all systems? What properties can be “tuned” by varying the size and composition of the system? In this Account, we describe research that has been performed to analyze the electronic structure, linear optical absorption, and excited state dynamics of thiolate-stabilized noble metal nanoclusters. We focus primarily on two systems, Au25(SR)18? and Au38(SR)24, as models for understanding the principles underlying the electronic structure, optical properties, luminescence, and transient absorption in these systems. In these nanoclusters, the orbitals near the HOMO?LUMO gap primarily arise from atomic 6sp orbitals located on Au atoms in the gold core. The resulting nanocluster orbitals are delocalized throughout the core of these systems. Below the core-based orbitals lies a set of orbitals that are primarily composed of Au 5d and S 3p atomic orbitals from atoms located around the exterior gold?thiolate oligomer motifs. This set of orbitals has a higher density of states than the set arising from the core 6sp orbitals. Optical absorption peaks in the near-infrared and visible regions of the absorption spectrum arise from excitations between core orbitals (lowest energy peaks) and excitations from oligomer-based orbitals to core-based orbitals (higher energy peaks). Nanoclusters with different stoichiometries have varying gaps between the core orbitals themselves as well as between the band of oligomer-based orbitals and the band of core orbitals. These gaps can slow down nonradiative electron transfer between excited states that have different character; the excited state electron and hole dynamics depend on these gaps. Nanoclusters with different stoichiometries also exhibit different luminescence properties. Depending on factors that may include the symmetry of the system and the rigidity of the core, the nanocluster can undergo large or small nuclear changes upon photoexcitation, which affects the observed Stokes shift in these systems. This dependence on stoichiometry and composition suggests that the size and the corresponding geometry of the nanocluster is an important variable that can be used to tune the properties of interest. How does doping affect these principles? Replacement of gold atoms with silver atoms changes the energetics of the sp and d atomic orbitals that make up the nanocluster orbitals. Silver atoms have higher energy sp orbitals, and the resulting nanocluster orbitals are shifted in energy as well. This affects the HOMO?LUMO gap, the oscillator strength for transitions, the spacings between the different bands of orbitals, and, as a consequence, the Stokes shift and excited state dynamics of these systems. This suggests that nanocluster doping is one way to control and tune properties for use in potential applications.
关键词： ligand-protected noble metal nanoclusters,doping,electronic structure,optical properties,transient absorption,luminescence,atomic precision
更新于2025-09-10 09:29:36
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Theoretical Calculation of the Optical Properties of Dielectric Material @ Noble Metal Core-Shell Composite Nanoparticles
摘要： Objectives: Methods: Surface plasmon exhibited in nano-sized particles such as gold, silver, copper has recently attracted a great deal of attention due to the enhancement and tunable optical properties in the visible to near-infrared region of the electromagnetic spectrum. In this work, the optical properties of dielectric material at noble metal core-shell nanoparticles Mie theory is the analytical method is used to study via parameters of extinction, scattering and absorption efficiencies. The samples for studying were the composites of a dielectric material core coated by a thin noble metal (Ag, Au, and Cu). The core size was fixed at 50 nm, while the metal shell thicknesses were varied from 3 nm to 40 nm. The calculated optical properties were found that the surface plasmon resonance can be enhanced and tuned the wavelength from the near ultraviolet to near infrared regions by varying the shell thickness. The dielectric core coated with a thin noble metal to promote the properties of the core can be applied in the field of plasmonic nanolaser, nonlinear plasmonic antenna, light trapping in thin-film organic solar cells, and biomedical research.
关键词： Dielectric Material @ Noble Metal Core-Shell,Surface Plasmon
更新于2025-09-10 09:29:36
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Atomic-Level Doping of Metal Clusters
摘要： Atomically precise noble metal (mainly silver and gold) nanoclusters are an emerging category of promising functional materials for future applications in energy, sensing, catalysis, and nanoelectronics. These nanoclusters are protected by ligands such as thiols, phosphines, and hydride and have sizes between those of atoms and plasmonic nanoparticles. In metallurgy, the properties of a pure metal are modified by the addition of other metals, which often offers augmented characteristics, making them more utilizable for real-life applications. In this Account, we discuss how the incorporation of various metal atoms into existing protected nanoclusters tunes their structure and properties. The process of incorporating metals into an existing cluster is known as doping; the product is known as a doped cluster, and the incorporated metal atom is called a dopant/foreign atom. We first present a brief historical overview of protected clusters and the need for doping and explain (with examples) the difference between an “alloy” and a “doped” cluster, which are two frequently confused terms. We then discuss several commonly observed challenges in the synthesis of doped clusters: (i) doping produces a mixture of compositions that prevents the growth of single crystals; (ii) doping with foreign atoms sometimes changes the overall composition and structure of the parent cluster; and (iii) doping beyond a certain number of foreign atoms decomposes the doped cluster. After delineating the challenges, we review a few potential synthetic methods for doped clusters: (i) the co-reduction method, (ii) the galvanic exchange method, (iii) ligand-induced conversion of bimetallic clusters to doped clusters, and (iv) intercluster reactions. As a foreign atom is able to occupy different positions within the structure of the parent cluster, we examine the structural relationship between the parent clusters and their different foreign-atom-doped clusters. We then show how doping enhances the stability, luminescence, and catalytic properties of clusters. The enhancement factor highly depends on the number and nature of the foreign atoms, which can also alter the charge state of the parent cluster. Atomic-level doping of foreign atoms in the parent cluster is confirmed by high-resolution electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry techniques and single-crystal X-ray diffraction methods. The photophysical properties of the doped clusters are investigated using both time-dependent and steady-state luminescence and optical absorption spectroscopies. After presenting an overview of atomic-level doping in metal clusters and demonstrating its importance for enriching the chemistry and photophysics of clusters and extending their applications, we conclude this Account with a brief perspective on the field’s future.
关键词： applications,doping,properties,atomically precise,noble metal nanoclusters,alloy,synthesis,structure
更新于2025-09-09 09:28:46
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Aluminum and Nitrogen Codoped Graphene: Highly Active and Durable Electrocatalyst for Oxygen Reduction Reaction
摘要： The development of highly active and exceedingly durable electrocatalyst at low cost for oxygen reduction reaction (ORR) is extremely desirable, but remains to be a grand challenge. Over the past decade, the transitional-metal (e.g., Fe, Co, Ni) and N codoped graphene materials have attracted most attention as the state-of-the-art non-precious-metal-based effective electrocatalyst for ORR, but still entail unsatisfactory issues such as moderate activity and life. Herein, the main-group-metal Al and N codoped graphene (ANG) is successfully fabricated via thermal annealing treatment of N-doped graphene with aluminum tri-(8-hydroxyquinoline). As a highly effective electrocatalyst for ORR, the as-prepared ANG exhibits not only high electrocatalytic activity that even outperforms the commercial Pt/C, but also good durability in both three-electrode cell and Zn-air battery. Theory calculations show that the inhomogeneous charge density distribution and the interaction between Al and N are mainly responsible for the marked enhancement of ORR activity. The designed ANG electrocatalysts will provide a perspective application in energy storage and promote further exploration of main-group-element-based inexpensive, active and durable electrocatalysts.
关键词： N-doped graphene,noble-metal free,Al-doped graphene,oxygen reduction reaction,electrocatalyst
更新于2025-09-09 09:28:46
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Anomalous K-Point Phonons in Noble Metal/Graphene Heterostructure Activated by Localized Surface Plasmon Resonance
摘要： Metal/graphene interface has been one of the most important research topics with regard to charge screening, charge transfer, contact resistance, and solar cells. Chemical bond formation of metal/graphene can be deduced from the defect induced D-band and its second-order mode, 2D band, measured by Raman spectroscopy, as a simple and non-destructive method. However, a phonon mode located at ~ 1350 cm-1, which is normally known as the defect-induced D-band, is intriguing for graphene deposited with noble metals (Ag, Au, and Cu). We observe anomalous K-point phonons in non-reactive noble metal/graphene heterostructure. The intensity ratio of the mid-frequency mode at ~ 1350 cm-1 over G-band (~1590 cm-1) exhibits non-linear but resonant behavior with the excitation laser wavelength and more importantly, the phonon frequency–laser energy dispersion is ~ 10-17 cm-1/eV, which is much less than the conventional range. These phonon modes of graphene at non-zero phonon wave vector (q ≠ 0) around K points are activated by localized surface plasmon resonance, and not by the defects due to chemical bond formation of metal/graphene. This hypothesis is supported by density function theory (DFT) calculations for noble metals and Cr along with the measured contact resistances.
关键词： K-point phonon,Raman,graphene,localized surface plasmon,noble metal
更新于2025-09-09 09:28:46
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Outstanding hydrogen evolution performance of supported Pt nanoparticles: Incorporation of preformed colloids into mesoporous carbon films
摘要： Platinum is the best catalyst known so far for the hydrogen evolution reaction (HER) in acidic environments, but it is also a scarce and expensive resource. Maximizing its performance per metal atom is essential in order to reduce costs. The deposition of small Pt nanoparticles (2–3 nm) onto electrically conductive, highly accessible and stable carbon supports leads to active catalysts. However, blocking of pores and active sites by Na?on, which acts as a binding species, reduces the catalytic activity. Moreover, inaccessible Pt located in micropores diminishes an ef?cient exploitation of the noble metal. We report a new synthesis approach to ordered mesoporous carbon (OMC) coatings with preformed Pt nanoparticles. The particles are exclusively located inside the mesopores. Furthermore, no Na?on binder is needed. As a consequence, the PtNP/OMC catalyst ?lm outperforms Pt/C catalysts reported in literature particularly at high current densities. PtNP/OMC catalyst ?lms with a geometric Pt loading of 1.6 mgPt/cm2 achieve a current density of (cid:1)100 mA/cm2 at an overpotential of ca. (cid:1)70 mV.
关键词： Ordered mesoporous carbon,Noble metal colloids,Electrocatalysis,Mesoporous ?lms,Hydrogen evolution reaction
更新于2025-09-04 15:30:14
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Synthesis of Fluorescent Core-Shell Metal Nanohybrids: A Versatile Approach
摘要： A ?exible way of fabricating core-shell noble metal-organic nanohybrids with tailored chemical and spectroscopic properties is proposed here. The synthetic protocol consists of a multi-step procedure able to guarantee acceptable reproducibility of core size and shape as well as control of the organic outer layer. The proposed method highlights limitations in obtaining highly controllable products, although the heterogeneity degree of the nanostructures is in line with that expected from bottom-up approaches in solution. Selective functionalization of the nanohybrids with properly-substituted ?uorescent dyes under variable experimental conditions allowed the preparation of composite systems of tunable spectroscopic properties to be employed as nanoprobes in sensing or photonic applications. To this end, preliminary investigation on embedding the nanohybrids in compatible polymeric matrices is also reported.
关键词： polymeric matrix,spectroscopic properties,core-shell architecture,noble metal nanoparticles,self-assembly
更新于2025-09-04 15:30:14
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Preparation and Use of Chemically Modified Noble Metal Nanoparticles
摘要： Papers dealing with chemical modi? cation of the surface of noble metal nanoparticles and their use in analytical and bioanalytical chemistry, pharmacology, etc., are analyzed. Grafting of a layer of preset chemical composition on the nanoparticle surface allows preparation of functional materials combining the properties of the metal core (surface plasmon resonance, enhancement of ? uorescence and nonelastic scattering) and shell (selective interaction with components of the surrounding medium). Combination of these properties opens wide prospects for using the modi? ed nanoparticles in various branches of science and engineering, primary in chemical and biochemical analysis, and also in pharmacology.
关键词： functional materials,biochemical analysis,noble metal nanoparticles,chemical analysis,chemical modi? cation of the surface
更新于2025-09-04 15:30:14