Plasmonic photocatalysts: harvesting visible light with noble metal nanoparticles

The efforts to produce photocatalysts operating efficiently under visible light have led to a number of plasmonic photocatalysts, in which noble metal nanoparticles are deposited on the surface of polar semiconductor or insulator particles. In the metal-semiconductor composite photocatalysts, the noble metal nanoparticles act as a major component for harvesting visible light due to their surface plasmon resonance while the metal-semiconductor interface efficiently separates the photogenerated electrons and holes. In this article, we survey various plasmonic photocatalysts that have been prepared and characterized in recent years.     

Photocatalytic activity enhanced by plasmonic resonant energy transfer from metal to semiconductor

Plasmonic metal nanostructures have been incorporated into semiconductors to enhance the solar-light harvesting and the energy-conversion efficiency. So far the mechanism of energy transfer from the plasmonic metal to semiconductors remains unclear. Herein the underlying plasmonic energy-transfer mechanism is unambiguously determined in Au@SiO(2)@Cu(2)O sandwich nanostructures by transient-absorption and photocatalysis action spectrum measurement. The gold core converts the energy of incident photons into localized surface plasmon resonance oscillations and transfers the plasmonic energy to the Cu(2)O semiconductor shell via resonant energy transfer (RET). RET generates electron-hole pairs in the semiconductor by the dipole-dipole interaction between the plasmonic metal (donor) and semiconductor (acceptor), which greatly enhances the visible-light photocatalytic activity as compared to the semiconductor alone. RET from a plasmonic metal to a semiconductor is a viable and efficient mechanism that can be used to guide the design of photocatalysts, photovoltaics, and other optoelectronic devices.     

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...     

Stable Isolated Metal Atoms as Active Sites for Photocatalytic Hydrogen Evolution

The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co‐catalysts. Generally, the noble metals have been widely applied as co‐catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co‐catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO₂, a model photocatalystic system, by a facile one‐step method. The isolated metal atom based photocatalysts show excellent stability for H₂ evolution and can lead to a 6–13‐fold increase in photocatalytic activity over the metal clusters loaded on TiO₂ by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.     

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...     

轻元素调控的贵金属催化剂在能源相关领域的应用

贵金属广泛用于多相催化研究,对于诸多具有重要科学意义和工业应用价值的化学反应展现出优异的催化活性和选择性.引入轻合金元素(如C,H,B和N),可以调控贵金属的晶体结构和电子性质,是进一步提高贵金属催化性能的重要策略.与传统的金属合金催化剂相比,这种轻元素合金化的催化剂具有一些独特性:(1)轻元素由于原子尺寸很小,容易溶于金属晶格的间隙位点;(2)一些轻元素(如C,N和S)的电负性与金属的差别很大,能够在相邻原子间引起较大的电荷转移;(3)轻元素-金属合金中的电子相互作用主要由金属的d轨道和轻元素的sp轨道杂化主导,这与金属合金中的d-d轨道杂化显著不同.这些独特性为贵金属原子结构和电子结构的调控以及催化性能的优化带来了更多的可能性.轻合金元素研究的主要瓶颈在于其原子尺寸小、分布不均匀、难以直接观察和精准控制,从而限制了对活性提升机制和构效关系的研究.近几十年来,纳米合成技术和材料表征技术的长足发展使得轻合金元素改性的催化剂研究渐入佳境.此外,计算化学在结构分析和催化应用中的日趋成熟为揭示轻合金元素对贵金属晶体结构、电子结构和催化性质的调控作用提供了有力工具.本文综述了引入轻合金元素改性的贵金属催化剂在不同催化应用中的主要研究进展,总结了贵金属催化性能的主要影响因素(包括轻合金元素的种类、位置、浓度和有序度等),阐述了轻合金原子如何影响催化反应性能,介绍了轻元素的实验引入策略以及揭示轻元素合金效应的实验表征和理论研究方法.重点讨论了不同轻合金原子改性的贵金属基催化剂在催化反应中的广泛应用,并试图建立其结构特征与催化性能之间的密切联系.总的来说,轻合金原子的活性调控作用主要表现在以下几个方面:(1)晶相转变:轻元素的引入能够改变金属原子的堆积模式,产生有利于催化反应的晶相结构;(2)电荷转移:轻元素和母体金属的电负性差异能够导致电荷重新分布,影响金属的电子结构;(3)应力效应:轻元素的引入会导致金属晶格膨胀,产生拉伸应力,引起电子结构变化;(4)配体效应:轻元素的sp轨道和金属的d轨道杂化,引起d带中心下移,降低表面吸附性质;(5)集团效应:轻元素的引入能够孤立金属原子,产生特定的表面金属位点,有利于促进催化反应;(6)次表面化学:在氢相关的催化反应中,次表面的间隙轻元素能够阻止氢的渗入,抑制活性衰减或不利的副反应发生.最后,本文对于当前该领域存在的挑战和未来的发展前景进行了分析,以期促进该合金体系的合成、理解和催化应用,内容包括:(1)开发更精确可控的轻元素掺入策略;(2)合理阐明轻合金元素与宏观催化性能之间的关系;(3)发展新型的轻元素改性催化剂;(4)扩展轻元素改性催化剂的催化应用范围.     

Emerging materials for plasmon-assisted photoelectrochemical water splitting

Energy production and environmental pollution are the two major problems the world is facing today. The depletion of fossil fuels and the emission of harmful gases into the atmosphere leads to the research on clean and renewable energy sources. In this context, hydrogen is considered an ideal fuel to meet global energy needs. Presently, hydrogen is produced from fossil fuels. However, the most desirable way is from clean and renewable energy sources, like water and sunlight. Sunlight is an abundant energy source for energy harvesting and utilization. Recent studies reveal that photoelectrochemical (PEC) water splitting has promise for solar to hydrogen (STH) conversion over the widely tested photocatalytic approach since hydrogen and oxygen gases can be quantified easily in PEC. For designing light-absorbing materials, semiconductors are the primary choice that undergoes excitation upon solar light irradiation to produce excitons (electron-hole pairs) to drive the electrolysis. Visible light active semiconductors are attractive to achieve high solar to chemical fuel conversion. However, pure semiconductor materials are far from practical applications because of charge carrier recombination, poor light-harvesting, and electrode degradation. Various heteronanostructures by the integration of metal plasmons overcome these issues. The incorporation of metal plasmons gained significance for improving the PEC water splitting performance. This review summarizes the possible main mechanisms such as plasmon-induced resonance energy transfer (PIRET), hot electron injection (HEI), and light scatting/trapping. It also deliberates the rational design of plasmonic structures for PEC water splitting. Furthermore, this review highlights the advantages of plasmonic metal-supported photoelectrodes for PEC water splitting.     

Evaluation of the plasmonic effect of Au and Ag on Ti-based photocatalysts in the reduction of CO_2 to CH_4

Crystalline TiO_2(P25) and isolated titanate species in a ZSM-5 structure(TS-1) were modified with Au and Ag, respectively, and tested in the gas-phase photocatalytic CO_2 reduction under high purity conditions. The noble metal modification was performed by photodeposition. Light absorbance properties of the catalysts are examined with UV–Vis spectroscopy before and after the activity test. In the gas-phase photocatalytic CO_2 reduction, it was observed that the catalysts with Ag nanostructures are more active than those with Au nanostructures. It is thus found that the energetic difference between the band gap energy of the semiconductor and the position of the plasmon is influencing the photocatalytic activity.Potentially, plasmon excitation due to visible light absorption results in plasmon resonance energy, which affects the excitation of the semiconductor positively. Therefore, an overlap between band gap energy of the semiconductor and metal plasmon is needed.     

基于等离激元热电子调控的全谱光催化产氢增强（英文）

等离激元效应在光催化体系中的集成为实现广谱光吸收提供了一个新的途径,然而等离激元热电子的较低迁移率和不确定扩散方向使得其光催化效率仍较低.等离激元金属与n型半导体接触后,其界面间会形成肖特基结.在特定波长太阳光照射下,等离激元金属将其表面等离子体能量聚集在表面自由电子上,进而产生热电子.当这些热电子具有的能量高于肖特基势垒时,热电子便可注入到半导体导带上.与此同时,半导体上的电子可以通过肖特基接触发生回流,与金属上的空穴复合,进而降低半导体-等离激元金属复合材料的光催化性能.因此,为了提高光催化效率,如何调控等离激元热电子迁移和充分利用等离激元效应是一个重要挑战.本文尝试将"表面异质结"与肖特基结相结合的复合结构,得以有效地调控等离激元热电子的迁移.在该复合结构中,金纳米颗粒和铂纳米颗粒分别作为等离激元吸光单元和助催化剂,集成在TiO_2纳米片表面.其中"表面异质结"是由TiO_2纳米片的两种不同表面晶面所构成,我们选择由{001}和{101}两组晶面组成的TiO_2纳米片作为半导体衬底.该结构中的{001}晶面导带能级高于{101}导带能级,因而电子由高能级的{001}流向低能级的{101}晶面,可以用来引导等离激元热电子从可见光响应的金纳米颗粒向TiO_2进行高效转移.通过巯基丙酸的桥联作用,将等离激元Au纳米颗粒锚定在TiO_2纳米片的{001}晶面上,获得Au-TiO_2{001}样品.另一方面,利用TiO_2纳米片自身光生电荷导向性光沉积,得到与{101}晶面结合形成的Au-TiO_2{101}样品.我们对两组样品进行光电流和光催化产氢实验对比,确认在"表面异质结"诱导下Au-TiO_2{001}样品中Au产生的光生热电子可以更好地注入到TiO_2纳米片导带上.我们进一步通过光沉积Pt纳米颗粒来判定光生电子所能到达的区域,验证了以上结论.与此同时,肖特基结由铂纳米颗粒与TiO_2纳米片所形成,可以促使电子由TiO_2向铂纳米颗粒进行转移,而避免发生向金纳米颗粒的反向迁移,从而在Au-TiO_2体系中实现高效的单向载流子转移.基于该设计,等离激元光催化剂实现了明显改善的全谱光催化产氢性能.本文为全谱光催化的复合结构理性设计提供了一个新的思路.     

Plasmonic biosensing based on non-noble-metal materials

This review focuses on the research progress of non-noble-metal materials with nanostructures for plasmonic biosensing. Firstly, the physical and sensing principles of localized surface plasmon resonance (LSPR) sensors are briefly introduced; then non-noble-metal materials, such as copper, aluminum, semiconductor, graphene and other materials, for plasmonic sensing are categorized and presented. Finally, a rational discussion about the future prospective of novel materials for plasmonic sensing is given.     

帽状铝纳米粒子的制备及表面等离子共振特性

金属纳米材料具有许多独特的物理和化学性质,其中一个重要的光学性质就是表面等离子共振,然而在大多数情况下,金属纳米粒子表面等离子共振所产生的吸收峰被限制在相对狭小的范围内,很难进行调谐。近年来,以电介质为核金属为壳的核壳结构复合纳米材料成功的解决了这一问题,通过设计和剪裁内核的直径与外壳层厚度的比值,可以实现光学性质可调的特性[1～5]。此类复合材料可被广泛应用于光催化、传感器、光信息存储、生物光子学、生物医学等领域[6～11]。美国莱斯大学及德州的研究人员利用这类核壳结构纳米材料成功地实现了对体外乳腺肿瘤的杀灭实验[12]。在这种类型的材料中,对称性降低的即不完全包裹的纳米粒子如杯状[13]、帽状[13,14]、半球壳状[15]、月牙状[16]等核壳结构复合粒子由     

Utilizing photocurrent transients for dithiolene-based photodetection: stepwise improvements at communications relevant wavelengths

Photodetection based on bis-(4-dimethylaminodithiobenzil)-Ni(II) (BDN), a representative and well-studied metal dithiolene that shows strong absorption in the near-infrared region of the electromagnetic spectrum, has been investigated. By adopting a metal/insulator/semiconductor/metal (MISM) structure, the peak photocurrent response to an oscillating light chain is increased by up to 50 times, compared to devices without an insulating layer. The transient form of the MISM photoresponse, while unsuitable for steady-state photodetection, can be used to detect periodic light signals of frequencies up to 1 MHz, and is thus applicable for optical communication. Further improvements have been realized by nanostructuring carbon black into the dithiolene layer, improving charge collection, and yielding detectivity of up to 1.6 × 10(11) Jones at wavelengths beyond the scope of silicon photodiodes. Such an architecture may allow the favorable absorption properties of other such metal dithiolenes to be harnessed, where their low charge carrier mobilities and short excitation lifetimes have previously limited their applicability to this field.     

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

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.     

Light‐Gated Synthetic Protocells for Plasmon‐Enhanced Chemiosmotic Gradient Generation and ATP Synthesis

Herein, we present a light‐gated protocell model made of plasmonic colloidal capsules (CCs) assembled with bacteriorhodopsin for converting solar energy into electrochemical gradients to drive the synthesis of energy‐storage molecules. This synthetic protocell incorporated an important intrinsic property of noble metal colloidal particles, namely, plasmonic resonance. In particular, the near‐field coupling between adjacent metal nanoparticles gave rise to strongly localized electric fields and resulted in a broad absorption in the whole visible spectra, which in turn promoted the flux of photons to bacteriorhodopsin and accelerated the proton pumping kinetics. The cell‐like potential of this design was further demonstrated by leveraging the outward pumped protons as “chemical signals” for triggering ATP biosynthesis in a coexistent synthetic protocell population. Hereby, we lay the ground work for the engineering of colloidal supraparticle‐based synthetic protocells with higher‐order functionalities.     

Surface-enhanced Raman spectroscopy toward application in plasmonic photocatalysis on metal nanostructures

Among photothermal, photovoltaic and photochemical techniques, photochemistry is superior in energy storage and transportation by converting photons into chemical fuels. Recently plasmonic photocatalysis, based on localized surface plasmon resonance (LSPR) generated from noble metal nanostructures, has attracted much attention. It promotes photochemical reaction efficiency by optimizing the solar spectrum absorption and the surface reaction kinetics. The deeper understanding is in urgent need for the development of novel plasmonic photocatalysts. Surface-enhanced Raman spectroscopy (SERS), which is also originated from the LSPR effect, provides an excellent opportunity to probe and monitor plasmonic photoreactions in situ and in real-time, with a very high surface sensitivity and energy resolution. Here, fundamentals of plasmonic photocatalysis and SERS are first presented based on their connections to the LSPR effect. Following by a validity analysis, latest studies of SERS applied for the plasmon mediated photochemical reaction are reviewed, focusing on the reaction kinetics and mechanism exploration. Finally, limitations of the present study, as well as the future research directions, are briefly analyzed and discussed.     

Plasmoelectronics: coupling plasmonic excitation with electron flow

Explorations of the coupling of light and charge via localized surface plasmons have led to the discovery that plasmonic excitation can influence macroscopic flows of charge and, conversely, that charging events can change the plasmonic excitation. We discuss recent theory and experiments in the emerging field of plasmoelectronics, with particular emphasis on the application of these materials to challenges in nanotechnology, energy use, and sensing.     

New insight into daylight photocatalysis of AgBr@Ag: synergistic effect between semiconductor photocatalysis and plasmonic photocatalysis

Noble metal nanoparticles (NPs) are often used as electron scavengers in conventional semiconductor photocatalysis to suppress electron-hole (e(-)-h(+) ) recombination and promote interfacial charge transfer, and thus enhance photocatalytic activity of semiconductors. In this contribution, it is demonstrated that noble metal NPs such as Ag NPs function as visible-light harvesting and electron-generating centers during the daylight photocatalysis of AgBr@Ag. Novel Ag plasmonic photocatalysis could cooperate with the conventional AgBr semiconductor photocatalysis to enhance the overall daylight activity of AgBr@Ag greatly because of an interesting synergistic effect. After a systematic investigation of the daylight photocatalysis mechanism of AgBr@Ag, the synergistic effect was attributed to surface plasmon resonance induced local electric field enhancement on Ag, which can accelerate the generation of e(-)-h(+) pairs in AgBr, so that more electrons are produced in the conduction band of AgBr under daylight irradiation. This study provides new insight into the photocatalytic mechanism of noble metal/semiconductor systems as well as the design and fabrication of novel plasmonic photocatalysts.     

应用于有机加氢反应的等离激元催化材料设计

金属纳米晶体具有独特的表面等离激元特性,为太阳能转换成化学能提供了新的机遇。本文以课题组近期的研究工作为例,阐述在催化有机加氢反应中表面等离激元效应所产生的多种物理过程的作用机制。该系列工作实现了太阳能向化学能的有效转换,为太阳能替代传统有机化工中的热催化提供了可能性,对等离激元催化材料的设计具有一定的指导意义。     

具有异质结的铋系光催化剂研究进展

由于人类面临的能源危机与环境污染问题日益严重,光催化技术作为最有可能解决这两大问题的技术而备受关注。其中,光催化剂是光催化技术的核心。开发具有宽光谱响应、高载流子分离效率的光催化剂既是研究热点也是难点。铋系光催化剂具有较强的可见光吸收能力。但是,提高铋系光催化剂对入射光的吸收效率、降低光生载流子复合效率仍是提高其光催化活性的关键。目前主要通过以下策略来解决这些问题：(1)贵金属负载,(2)半导体复合,(3)金属/非金属掺杂,(4)碳材料修饰,(5)铋金属负载等。最后还简要探讨了具有异质结的铋系光催化剂的发展趋势及其潜在应用。
　　采用贵金属负载于铋系光催化剂(构建肖特基结),可以通过等离子体共振效应拓宽铋系光催化剂的光吸收范围,同时贵金属还能有效转移半导体上的光生电子,促进光生载流子的有效分离。但是,采用贵金属负载存在昂贵、容易发生团聚等不足。通过半导体之间构建紧密异质结,不仅可以调节所制备复合催化剂的能带结构,满足不同光催化反应的要求,而且由于内电场的存在可以促进光生载流子定向转移,从而提高光生载流子的分离效率。除此之外,通过杂原子掺杂可以在原子层面上构建异质结结构,也能有效抑制光生载流子的复合。近年来,通过与具有较好导电性能的碳材料复合,可以快速转移铋系半导体上产生的光子,提高光催化剂的活性和量子效率。铋纳米颗粒具有与贵金属类似的性能,通过采用铋金属对铋系半导体进行负载也可以发生等离子体共振效应,从而可以提高铋系半导体的活性。最后,作者展望了铋系半导体复合光催化剂发展的三个重要方向：(1)创制非化学计量比的铋系半导体复合光催化材料;(2)通过与还原能力更强的半导体构建复合光催化材料,实现光催化 CO2还原制备有机物和光催化全解水的应用中去;(3)充分利用铋系半导体化合物具有较强氧化能力的优点,将其应用于光催化有机物合成中,比如光催化甲苯类有机物选择性氧化等。     

Photo-responsive metal/semiconductor hybrid nanostructure:A promising electrocatalyst for solar light enhanced fuel cell reaction

Direct alcohol fuel cells(DAFCs) have received wide attention as a new type of clean energy device because of their high energy conversion efficiency,portability,non-toxicity and pollution-free.Anode catalysts are the key factors affecting the performance of DAFCs.Recently studies show that using the optical activity of semiconductor materials as the carriers of traditional precious metal electrocatalysts,under the illumination of light sources,can greatly improve the electrocatalytic activity and stability of electrodes.In this review,the research progress of photo-responsive metal/semiconductor hybrids as the electrocatalysts for DAFCs in recent years is summarized,including:(1) Mechanism and advantages of photo-assistant electrochemical alcohol oxidation reaction,(2) me tal/semiconductor electrocatalyst for the different type of fuel cell reactions,(3) different kind of metals in photo-responsive metal/semiconductor hybrid nanostructure,(4) the personal prospects of the photo-responsive metal/semiconductor electrode for future application in DAFCs.