Quenching of TiO2 photo catalysis by silver nanoparticles

The plasmon resonance of metal nanostructures affects neighboring semiconductors, quenching or enhancing optical transitions depending on various parameters. These plasmonic properties are currently investigated with respect to topics such as photovoltaics and optical detection and could also have important consequences for photocatalysis. Here the effect of silver nanoparticles of a size up to 30 nm and at maximum 0.50 monolayers on the photocatalytic oxidation of ethylene on TiO₂ is studied. Since the plasmon resonance energy of silver nanoparticles is comparable with the TiO₂ band gap, dipole-dipole interaction converts excitons into heat at the silver nanoparticle. This indicates that plasmonic interaction with TiO₂ semiconductor catalysts can reduce the photo catalytic activity considerably.     

Nanostructured materials with localized surface plasmon resonance for photocatalysis

Localized surface plasmon resonance（LSPR） enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts.In the past decades,noble metal nanoparticles（Au and Ag） with LSPR feature have found wide applications in solar energy conversion.Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures.However,high cost and...     

Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO2 Surfaces with Surface OH Groups and Surface Oxygen Vacancies

Three catalytic oxidation reactions have been studied: The ultraviolet (UV) light induced photocatalytic decomposition of the synthetic dye sulforhodamine B (SRB) in the presence of TiO₂ nanostructures in water, together with two reactions employing Au/TiO₂ nanostructure catalysts, namely, CO oxidation in air and the decomposition of formaldehyde under visible light irradiation. Four kinds of TiO₂ nanotubes and nanorods with different phases and compositions were prepared for this study, and gold nanoparticle (Au‐NP) catalysts were supported on some of these TiO₂ nanostructures (to form Au/TiO₂ catalysts). FTIR emission spectroscopy (IES) measurements provided evidence that the order of the surface OH regeneration ability of the four types of TiO₂ nanostructures studied gave the same trend as the catalytic activities of the TiO₂ nanostructures or their respective Au/TiO₂ catalysts for the three oxidation reactions. Both IES and X‐ray photoelectron spectroscopy (XPS) proved that anatase TiO₂ had the strongest OH regeneration ability among the four types of TiO₂ phases or compositions. Based on these results, a model for the surface OH group generation, absorption, and activation of molecular oxygen has been proposed: The oxygen vacancies at the bridging O^2? sites on TiO₂ surfaces dissociatively absorb water molecules to form OH groups that facilitate adsorption and activation of O₂ molecules in nearby oxygen vacancies by lowering the absorption energy of molecular O₂. A new mechanism for the photocatalytic formaldehyde decomposition with the Au/TiO₂ catalysts is also proposed, based on the photocatalytic activity of the Au‐NPs under visible light. The Au‐NPs absorb the light owing to the surface plasmon resonance effect and mediate the electron transfers that the reaction needs.     

Converting Ag2SCdS and Ag2SZnS into AgCdS and AgZnS Nanoheterostructures by Selective Extraction of Sulfur

A mild three‐step solution strategy is developed to prepare Ag? MS (M=Zn, Cd) nanoheterostructures composed of MS nanorods with silver tips. First, Ag₂S? MS heterostructures are synthesized by following a solution–liquid–solid mechanism with Ag₂S nanoparticles as catalysts, then the Ag₂S sections of the heterostructures are converted into silver nanoparticles by selective extraction of sulfur. Notably, for the prepared Ag? CdS heterostructures, the localized surface plasmon resonance of silver remarkably intensifies the photoluminescence of CdS by enhancing the excitation light absorption, which is beneficial for potential applications of CdS nanoparticles in the fields of biolabeling, light‐emitting diodes, and so forth. The strategy reported herein would be useful for designing and fabricating other metal–semiconductor hybrid nanostructures with desirable performances.     

The Polarization Effect in Surface‐Plasmon‐Induced Photocatalysis on Au/TiO2 Nanoparticles

Controlling the interaction of polarization light with an asymmetric nanostructure such as a metal/semiconductor heterostructure provides opportunities for tuning surface plasmon excitation and near‐field spatial distribution. However, light polarization effects on interfacial charge transport and the photocatalysis of plasmonic metal/semiconductor photocatalysts are unclear. Herein, we reveal the polarization dependence of plasmonic charge separation and spatial distribution in Au/TiO₂ nanoparticles under 45° incident light illumination at the single‐particle level using a combination of photon‐irradiated Kelvin probe force microscopy (KPFM) and electromagnetic field simulation. We quantitatively uncover the relationship between the local charge density and polarization angle by investigating the polarization‐dependent surface photovoltage (SPV). The plasmon‐induced photocatalytic activity is enhanced when the polarization direction is perpendicular to the Au/TiO₂ interface.     

Plasmonic Titanium Nitride Tubes Decorated with Ru Nanoparticles as Photo-Thermal Catalyst for CO2 Methanation

Photo-thermal catalysis has recently emerged as a viable strategy to produce solar fuels or chemicals using sunlight. In particular, nanostructures featuring localized surface plasmon resonance (LSPR) hold great promise as photo-thermal catalysts given their ability to convert light into heat. In this regard, traditional plasmonic materials include gold (Au) or silver (Ag), but in the last years, transition metal nitrides have been proposed as a cost-efficient alternative. Herein, we demonstrate that titanium nitride (TiN) tubes derived from the nitridation of TiO₂ precursor display excellent light absorption properties thanks to their intense LSPR band in the visible–IR regions. Upon deposition of Ru nanoparticles (NPs), Ru-TiN tubes exhibit high activity towards the photo-thermal CO₂ reduction reaction, achieving remarkable methane (CH₄) production rates up to 1200 mmol g⁻¹ h⁻¹. Mechanistic studies suggest that the reaction pathway is dominated by thermal effects thanks to the effective light-to-heat conversion of Ru-TiN tubes. This work will serve as a basis for future research on new plasmonic structures for photo-thermal applications in catalysis.     

Plasmon Coupling-Induced Hot Electrons for Photocatalytic Hydrogen Generation

We present the fabrication of core-shell-satellite Au@SiO₂-Pt nanostructures and demonstrate that LSPR excitation of the core Au nanoparticle can induce plasmon coupling effect to initiate photocatalytic hydrogen generation from decomposition of formic acid. Further studies suggest that the plasmon coupling effect induces a strong local electric field between the Au core and Pt nanoparticles on the SiO₂ shell, which enables creation of hot electrons on the non-plasmonic-active Pt nanoparticles to participate hydrogen evolution reaction on the Pt surface. In addition, small SiO₂ shell thickness is required in order to obtain a strong plamon coupling effect and achieve efficient photocatalytic activities for hydrogen generation.     

Photoanodic and photocathodic behaviour of La5Ti2CuS5O7 electrodes in the water splitting reaction

The particulate semiconductor La₅Ti₂CuS₅O₇ (LTC) with a band gap energy of 1.9 eV functioned as either a photocathode or a photoanode when embedded onto Au or Ti metal layers, respectively. By applying an LTC/Au photocathode and LTC/Ti photoanode to, respectively, photoelectrochemical (PEC) water reduction and oxidation concurrently, zero-bias overall water splitting was accomplished under visible light irradiation. The band structures of LTC/Au and LTC/Ti calculated using a semiconductor device simulator (AFORS-HET) confirmed the critical role of the solid/solid junction of the metal back contact in the charge separation and PEC properties of LTC photoelectrodes. The prominently long lifetime of photoexcited charge carriers in LTC, confirmed by transient absorption spectroscopy, allowed the utilization of both photoexcited electrons and holes depending on the band structure at the solid/solid junction.     

贵金属负载TiO2对光催化还原CO2选择性的影响

利用光沉积方法在TiO₂表面分别负载1%(质量分数) Pt、Pd、Au和Ag助催化剂.用TEM、XRD、UV-vis等技术对催化剂进行了表征,并利用连续瞬态电流时间响应和线性扫描伏安法等电化学方法,对贵金属负载的TiO₂光催化剂在光照条件下的电流响应强度及电催化析氢电位等特性加以测试.分析了贵金属助催化剂对光催化还原CO₂性能的差异.结果表明,负载贵金属助催化剂能显著加速光生电子空穴的分离,降低复合率;另外,助催化剂对还原CO₂选择性的顺序为Ag>Au>Pd>Pt.贵金属助催化剂还原CO₂的加氢选择性和析氢过电位存在相关性,即越不利于析氢过程的助催化剂,其催化CO₂加氢还原产物的选择性越高.     

Effect of Cl− anions on photocatalytic decomposition of gaseous ozone over Au @ Ag/TiO2 catalyst

Au core Ag shell composite structure nanoparticles were prepared using a sol method. The Au core Ag shell composite nanoparticles were loaded on TiO₂ nanoparticles as support using a modified powder–sol method, enabling the generation of Au @ Ag/TiO₂ photocatalysts for photocatalytic decomposition and elimination of ozone. The sols were characterized by means of ultraviolet–visible light (UV–Vis) reflection spectrometry, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The activity of the Au @ Ag/TiO₂ photocatalysts for photocatalytic decomposition and elimination of ozone was evaluated and the effect of Cl^? anions on the photocatalytic activity of the catalysts was highlighted. Results showed that Au @ Ag/TiO₂ prepared via the modified powder–sol route in the presence of an appropriate amount of NaCl solid as demulsifier had better activity in the photocatalytic decomposition and elimination of ozone. At the same time, Au @ Ag/TiO₂ catalysts had better ability to resist poisonous Cl^? anions than conventional Au/TiO₂ catalyst. The reasons could be, first, that NaCl was capable of reducing the concentration of free Ag⁺ by adsorption on the surface of Ag particles forming AgCl and enhancing the formation of Au core Ag shell particles, leading to a better resistance to Cl^? anions of the catalysts, and, second, AgCl took part in the photocatalytic decomposition of ozone together with Au @ Ag/TiO₂ catalysts and had a synergistic effect on the latter, resulting in better photocatalytic activity of Au @ Ag/TiO₂ catalysts.     

The Polarization Effect in Surface-Plasmon-Induced Photocatalysis on Au/TiO2 Nanoparticles

Controlling the interaction of polarization light with an asymmetric nanostructure such as a metal/semiconductor heterostructure provides opportunities for tuning surface plasmon excitation and near-field spatial distribution. However, light polarization effects on interfacial charge transport and the photocatalysis of plasmonic metal/semiconductor photocatalysts are unclear. Herein, we reveal the polarization dependence of plasmonic charge separation and spatial distribution in Au/TiO₂ nanoparticles under 45° incident light illumination at the single-particle level using a combination of photon-irradiated Kelvin probe force microscopy (KPFM) and electromagnetic field simulation. We quantitatively uncover the relationship between the local charge density and polarization angle by investigating the polarization-dependent surface photovoltage (SPV). The plasmon-induced photocatalytic activity is enhanced when the polarization direction is perpendicular to the Au/TiO₂ interface.     

Plasmon‐Mediated Syntheses of Metallic Nanostructures

The ability to prepare noble metal nanostructures of a desired composition, size, and shape enables their resulting properties to be exquisitely tailored, which has led to the use of these structures in numerous applications, ranging from medicine to electronics. The prospect of using light to guide nanoparticle reactions is extremely attractive since one can, in principle, regulate particle growth based on the ability of the nanostructures to absorb a specific excitation wavelength. Therefore, using the nature of light, one can generate a homogenous population of product nanoparticles from a heterogeneous starting population. The best example of this is afforded by plasmon‐mediated syntheses of metal nanoparticles, which use visible light irradiation and plasmon excitation to drive the chemical reduction of Ag⁺ by citrate. Since the initial discovery that Ag triangular prisms could be prepared by the photo‐induced conversion of Ag spherical nanoparticles, plasmon‐mediated synthesis has become a highly controllable technique for preparing a number of different Ag particles with tight control over shape, as well as a wide variety of Au‐Ag bimetallic nanostructures. We discuss the underlying physical and chemical factors that drive structural selection and conclude by outlining some of the important design considerations for controlling particle shape as learned through studies of plasmon‐mediated reactions, but applicable to all methods of noble metal nanocrystal synthesis.     

Theoretical insights into the mechanism of photocatalytic reduction of CO2 over semiconductor catalysts

Photocatalytic reduction of CO₂ is one important approach to alleviate greenhouse gas emission and energy crisis, which has gained huge attention in the past decades. However, the lack of understanding complex reaction mechanism impedes new catalysts design. It is also very difficult to understand the mechanism by using only experimental approaches. For this concern, theoretical calculations can effectively supplement the experimental deficiency and thus play an important role. Recently theoretical calculations have been performed on adsorption, migration and reduction of CO₂ molecule on the photocatalyst surface, leading to useful information that have contributed greatly to this field. This review summarizes recent advances in first-principles calculations about CO₂ photoreduction over various semiconductor photocatalysts like metal oxides, sulfides and g-C₃N₄. The methods, models, adsorption and reaction pathways have been discussed in detail. The perspective about future investigation on the photocatalytic reduction of CO₂ using first principles calculations is also presented.     

Insights into Charge Transfer at an Atomically Precise Nanocluster/Semiconductor Interface

The deposition of an atomically precise nanocluster, for example, Ag₄₄(SR)₃₀, onto a large‐band‐gap semiconductor such as TiO₂ allows a clear interface to be obtained to study charge transfer at the interface. Changing the light source from visible light to simulated sunlight led to a three orders of magnitude enhancement in the photocatalytic H₂ generation, with the H₂ production rate reaching 7.4 mmol h^?1 g_catalyst^?1. This is five times higher than that of TiO₂ modified with Ag nanoparticles and even comparable to that of TiO₂ modified with Pt nanoparticles under similar conditions. Energy band alignment and transient absorption spectroscopy reveal that the role of the metal clusters is different from that of both organometallic complexes and plasmonic nanoparticles: A type II heterojunction charge‐transfer route is achieved under UV/Vis irradiation, with the cluster serving as a small‐band‐gap semiconductor. This results in the clusters acting as co‐catalysts rather than merely photosensitizers.     

石墨相氮化碳的化学合成及应用

石墨相氮化碳(g-C₃N₄)具有独特的电子结构和优异的化学稳定性, 近年来不仅被作为不含金属组分的催化剂和催化剂载体, 广泛地应用于有机官能团的选择性转换、光催化分解水、氧还原和Au、Pd、Ag、Pt等贵金属的负载, 还被作为绿色储能材料和硬模板剂用于H₂、CO₂的存储和纳米金属氮(氧)化物的制备等, 在能源和材料相关领域逐渐引起人们的关注. 本文将从材料的制备和应用角度,综述国内外同行近年来在g-C₃N₄研究中所取得的一些重要进展, 并对其未来发展趋势,特别是在能源和环境领域中的应用进行了展望.     

Constructing Ordered Three‐Dimensional TiO2 Channels for Enhanced Visible‐Light Photocatalytic Performance in CO2 Conversion Induced by Au Nanoparticles

As a typical photocatalyst for CO₂ reduction, practical applications of TiO₂ still suffer from low photocatalytic efficiency and limited visible‐light absorption. Herein, a novel Au‐nanoparticle (NP)‐decorated ordered mesoporous TiO₂ (OMT) composite (OMT‐Au) was successfully fabricated, in which Au NPs were uniformly dispersed on the OMT. Due to the surface plasmon resonance (SPR) effect derived from the excited Au NPs, the TiO₂ shows high photocatalytic performance for CO₂ reduction under visible light. The ordered mesoporous TiO₂ exhibits superior material and structure, with a high surface area that offers more catalytically active sites. More importantly, the three‐dimensional transport channels ensure the smooth flow of gas molecules, highly efficient CO₂ adsorption, and the fast and steady transmission of hot electrons excited from the Au NPs, which lead to a further improvement in the photocatalytic performance. These results highlight the possibility of improving the photocatalysis for CO₂ reduction under visible light by constructing OMT‐based Au‐SPR‐induced photocatalysts.     

Photocatalytic Au–Bi2S3 Heteronanostructures

Au–Bi₂S₃ heteronanostructure photocatalysts were designed in which the coupling of a metal plasmon and a semiconductor exciton aids the absorption of solar light, enhances charge separation, and results in improved catalytic activity. Furthermore, these nanostructures show a unique pattern of structural combination, with Au nanoparticles positioned at the center of Bi₂S₃ nanorods. The chemistry of formation of these nanostructures, their epitaxy at the junction, and their photoconductance were studied, as well as their photoresponse properties.     

LaOCl-Coupled Polymeric Carbon Nitride for Overall Water Splitting through a One-Photon Excitation Pathway

It is a challenge to explore photocatalytic materials for sunlight-driven water splitting owing to the limited choice of a single semiconductor with suitable band energy levels but with a minimized band gap for light harvesting. Here, we report a one-photon excitation pathway by coupling polymeric carbon nitride (PCN) semiconductor with LaOCl to achieve overall water splitting. This artificial photosynthesis composite catalyzes the decomposition of H₂O into H₂ and O₂, with evolution rates of 22.3 and 10.7 μmol h⁻¹, respectively. The high photocatalytic performance of PCN/LaOCl can be ascribed to the simultaneously accomplished reduction and oxidation of water on LaOCl and PCN domains, respectively, as well as the fast charge separation and migration induced by the interfacial electric field related to LaOCl modification. This study provides new insights on the development of composite photocatalysts for pure water splitting based on polymer-based materials via charge modulation.     

Enhanced Photocatalytic Activity of MIL‐125 by Post‐Synthetic Modification with CrIII and Ag Nanoparticles

NH₂‐MIL‐125, [Ti₈O₈(OH)₄(bdc‐NH₂)₆] (bdc^2?=1,4‐benzene dicarboxylate) is a highly porous metal–organic framework (MOF) that has a band gap lying within the ultraviolet region at about 2.6 eV. The band gap may be reduced by a suitable post‐synthetic modification of the nanochannels using conventional organic chemistry methods. Here, it is shown that the photocatalytic activity of NH₂‐MIL‐125 in the degradation of methylene blue under visible light is remarkably augmented by post‐synthetic modification with acetylacetone followed by Cr^III complexation. The latter metal ion extends the absorption from the ultraviolet to the visible light region (band gap 2.21 eV). The photogenerated holes migrate from the MOF’s valence band to the Cr^III valence band, promoting the separation of holes and electrons and increasing the recombination time. Moreover, it is shown that the MOF’s photocatalytic activity is also much improved by doping with Ag nanoparticles, formed in situ by the reduction of Ag⁺ with the acetylacetonate pendant groups (the resulting MOF band gap is 2.09 eV). Presumably, the Ag nanoparticles are able to accept the MOF’s photogenerated electrons, thus avoiding electron–hole recombination. Both, the Cr‐ and Ag‐bearing materials are stable under photocatalytic conditions. These findings open new avenues for improving the photocatalytic activity of MOFs.     

Nanoplasmonic zirconium nitride photocatalyst for direct overall water splitting

The ability of plasmonic nanostructures to efficiently harvest light energy and generate energetic hot carriers makes them promising materials for utilization in photocatalytic water spitting.Apart from the traditional Au and Ag based plasmonic photocatalysts,more recently the noble-metal-free alternative plasmonic materials have attracted ever-increasing interest.Here we report the first use of plasmonic zirconium nitride（ZrN） nanoparticles as a promising photocatalyst for water splitting.Highl...