Strategies for Designing Nanoparticles for Electro‐ and Photocatalytic CO2 Reduction

Conversion of carbon dioxide (CO₂) into value‐added chemicals has attracted much attention because it can not only resolve global warming issues by reducing CO₂ accumulation in the atmosphere, but also produce renewable hydrocarbon fuels that are important feedstocks for the chemical industry. Among the diverse approaches reported, CO₂ reduction via electro‐ and photocatalytic methods is at the center of topics due to potential engineering of reaction performance through rational design of catalyst features. In this Minireview, we highlight recent strategies for designing nanoparticles to maximize the reaction efficiency and selectivity; from a materials viewpoint, these strategies can provide critical information to guide future research directions.     

Au/Ag核一壳结构复合纳米粒子形成机制的研究

在已制备好的Au纳米粒子表面,通过化学还原的方法沉积生长Ag包覆层,通过 控制Au, Ag的比列,制备了粒度均匀且粒径可控的Au/Ag核-壳结构纳米粒子。利用 UV-vis吸收光谱和透射电子显微镜（TEM）对SAu, Ag摩尔比为1：10的复合纳米粒 子的光学性质和形态进行随时监测,直接观察了核-壳结构纳米粒子的生长过程： 一部分Ag+在Au核表面还原生长,溶液中其余Ag+还原形成银的纳米团簇向粒子表面 的继续沉积生长,壳层增厚。     

Thiol‐Assisted Synthesis of Carbon‐Supported Metal Nanoparticles for Efficient Electrocatalytic CO2 Reduction

The typical preparation route of carbon‐supported metallic catalyst is complex and uneconomical. Herein, we reported a thiol‐assisted one‐pot method by using 3‐mercaptopropionic acid (MPA) to synthesize carbon‐supported metal nanoparticles catalysts for efficient electrocatalytic reduction of carbon dioxide (CO₂RR). We found that the synthesized Au?MPA/C catalyst achieves a maximum CO faradaic efficiency (FE) of 96.2% with its partial current density of ?11.4 mA/cm², which is much higher than that over Au foil or MPA‐free carbon‐supported Au (Au/C). The performance improvement in CO₂RR over the catalyst is probably derived from the good dispersion of Au nanoparticles and the surface modification of the catalyst caused by the specific interaction between Au nanoparticles and MPA. This thiol‐assisted method can be also extended to synthesize Ag?MPA/C with enhanced CO₂RR performance.     

Ultrasonic‐assisted Synthesis of Fe Nanoparticles in the Presence of Poly(N‐vinyl‐2‐pyrrolidone)

Zero‐valent iron particles were prepared by wet reduction chemistry assisted with ultrasonic treatment. Such prepared particles have uniform size, exhibit crystalline structure and show strong paramagnetic property. Their surface modification by coating poly(N‐vinyl‐2‐pyrrolidone) (PVP) was investigated. The resulting Fe(0)‐PVP particles were monodispersed and possessed enhancing magnetization saturation. Those synthesis conditions to control the particle size and distribution were exploited.     

Crystal Engineering of MOF-Derived Bimetallic Oxide Solid Solution Anchored with Au Nanoparticles for Photocatalytic CO2 Reduction to Syngas and C2 Hydrocarbons

Considering that CO₂ reduction is mostly a multielectron reaction, it is necessary for the photocatalysts to integrate multiple catalytic sites and cooperate synergistically to achieve efficient photocatalytic CO₂ reduction to various products, such as C₂ hydrocarbons. Herein, through crystal engineering, we designed and constructed a metal–organic framework-derived Zr/Ti bimetallic oxide solid solution support, which was confirmed by X-ray diffraction, electron microscopy and X-ray absorption spectroscopy. After anchoring Au nanoparticles, the composite photocatalyst exhibited excellent performances toward photocatalytic CO₂ reduction to syngas (H₂ and CO production rates of 271.6 and 260.6 μmol g⁻¹ h⁻¹) and even C₂ hydrocarbons (C₂H₄ and C₂H₆ production rates of 6.80 and 4.05 μmol g⁻¹ h⁻¹). According to the control experiments and theoretical calculations, the strong interaction between bimetallic oxide solid solution support and Au nanoparticles was found to be beneficial for binding intermediates and reducing CO₂ reduction, highlighting the synergy effect of the catalytic system with multiple active sites.     

高载量PtNi金属间化合物的氧还原电催化性能

采用改进的多元醇法制备了PtNi(原子比1∶1)质量分数为60%的高金属载量碳载PtNi合金(PtNi/C), 通过在450 ℃下退火处理获得了碳载PtNi金属间化合物氧还原电催化剂. 该催化剂对氧还原的质量比活性和面积比活性分别是商业化Pt/C(JM Pt/C)催化剂的1.66和2.3倍; 并且加速耐久性测试后PtNi金属间化合物催化剂的质量比活性仍与Pt/C的初始性能相当, 耐久性得到了大幅提升. PtNi/C金属间化合物催化剂氧还原活性和稳定性的提高归因于PtNi的有序原子排布结构及催化剂表面零价金属含量的提高.     

Confined‐Space Alloying of Nanoparticles for the Synthesis of Efficient PtNi Fuel‐Cell Catalysts

The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nanostructured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 A mg_Pt^?1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined‐space alloying of the nanoparticles in a controlled manner in the pores of the support.     

Space-Selective Precipitation of Au Nanoparticles Inside Silica Gel

Au colloids were prepared by irradiation with a Nd:YAG laser. Au nanoparticles were characterized by absorption spectra, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. It is found that the wavelength of the laser has no effect on the size but the number of the Au nanoparticles. By irradiating a transparent silica gel doped with gold ions with the focused laser in the gel and subsequent exposing in air, a space-selective pattern of letter “P” consisting of Au nanoparticles was observed inside the silica gel.     

二维金纳米粒子结构的制备及影响因素

用电泳沉积方法制备了金纳米粒子的二维排列结构。研究了电场强度、沉积时间、溶胶浓度、温度和方波脉冲等对沉积结构的影响。提高外加电场强度和旋加方波脉冲可以提高金粒子结构的有序性。粒子浓度减小,温度升高不利于粒子的电泳沉积。     

Resonance Light Scattering Method for Microdetermination of Proteins Based on Aggregation of Au Nanoparticles

By using a resonance light scattering (RLS) technique, a highly sensitive method for protein determination based on the aggregation of Au nanoparticles on protein template is described. For the Au nanoparticles of 15 nm, the detection limit of bovine serum albumin was 5.0 ng/mL and the linear range was 10–300 ng/mL. The experimental results indicated that various metal ions do not interfere with this assay. The proposed RLS assay exhibited lower variation in response signals for the same weight of different proteins and showed satisfactory results when it was used for determination of proteins in human serum.     

Au/Ag核-壳结构纳米粒子的制备及其SERS效应

随着大量有关表面增强拉曼散射 (SERS)的实验和理论研究的开展 ,金属纳米粒子作为一类重要的 SERS增强介质 ,已引起了人们浓厚的研究兴趣 [1] .而 Au和 Ag作为最常用的活性基底物质 ,更是研究的热点 [2 ,3 ] .最近 ,美国印第安那大学的 Nie等 [4 ] 在单个银纳米粒子上 ,观察到高达 1 0 14 ～ 1 0 15的SERS因子 .同时 ,他们的另外一项工作表明银纳米粒子的形状和大小对 SERS活性有很大影响 [5] .但是 ,由于 Ag溶胶制备的重复性较差 ,且粒度分布不均匀 ,通过控制银颗粒大小而调控 SERS活性是相当困难的[6] .与 Ag相比 ,Au在可见光…     

纳米金胶增强葡萄糖生物传感器的构建

将纳米金胶(AuNPs)和羟基磷灰石(HAp)按一定比例混合制备了新型复合膜用于葡萄糖氧化酶(GOD)的固定,构建了高灵敏的葡萄糖传感器。由于纳米金胶的存在,葡萄糖氧化酶的直接电化学性质得以增强,在去除氧气的PBS(pH 7.0)介质中,固定在复合膜内的GOD表现出一对良好的氧化还原峰。在饱和氧气条件下,当加入一定量的葡萄糖时,由于GOD催化葡萄糖氧化消耗溶液中的溶解氧,-0.8 V处溶解氧的还原峰电流降低,且峰电流降低的量与葡萄糖浓度在0.02～1.62 mmol/L范围内呈线性相关,检出限为5.0μmol/L,检测灵敏度达9.91 mA.mol-1.L,可实现对葡萄糖的快速检测。     

2‐Aminobenzenethiol‐Functionalized Silver‐Decorated Nanoporous Silicon Photoelectrodes for Selective CO2 Reduction

A molecularly thin layer of 2‐aminobenzenethiol (2‐ABT) was adsorbed onto nanoporous p‐type silicon (b‐Si) photocathodes decorated with Ag nanoparticles (Ag NPs). The addition of 2‐ABT alters the balance of the CO₂ reduction and hydrogen evolution reactions, resulting in more selective and efficient reduction of CO₂ to CO. The 2‐ABT adsorbate layer was characterized by Fourier transform infrared (FTIR) spectroscopy and modeled by density functional theory calculations. Ex situ X‐ray photoelectron spectroscopy (XPS) of the 2‐ABT modified electrodes suggests that surface Ag atoms are in the +1 oxidation state and coordinated to 2‐ABT via Ag?S bonds. Under visible light illumination, the onset potential for CO₂ reduction was ?50 mV vs. RHE, an anodic shift of about 150 mV relative to a sample without 2‐ABT. The adsorption of 2‐ABT lowers the overpotentials for both CO₂ reduction and hydrogen evolution. A comparison of electrodes functionalized with different aromatic thiols and amines suggests that the primary role of the thiol group in 2‐ABT is to anchor the NH₂ group near the Ag surface, where it serves to bind CO₂ and also to assist in proton transfer.     

Au与Fe_3O_4纳米微粒共嵌TiO_2纳米纤维的制备及可见光催化性能

通过静电纺丝法制备出含有Fe3O4纳米微粒的TiO2纳米纤维,再采用浸渍还原法将Au纳米微粒嵌入到TiO2纳米纤维上,制备出一种具有较强磁性和良好可见光响应能力的复合光催化材料.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和紫外-可见固体漫反射光谱仪(UV-VisDRS)等对样品的结构和形貌进行表征,并以降解罗丹明B(RhB)为模型反应,考察了样品在可见光照射下的光催化性能.结果表明,嵌入Au纳米微粒可使复合纳米纤维在可见光下降解RhB时表现出非常好的降解速率和降解率;同时,将Fe3O4纳米微粒嵌入TiO2纳米纤维内部可以赋予材料较强的磁性,使材料便于分离和重复利用.     

Synthesis of Highly Stable,Water‐Dispersible Copper Nanoparticles as Catalysts for Nitrobenzene Reduction

We report an aqueous‐phase synthetic route to copper nanoparticles (CuNPs) using a copper–surfactant complex and tests of their catalytic efficiency for a simple nitrophenol reduction reaction under atmospheric conditions. Highly stable, water‐dispersed CuNPs were obtained with the aid of polyacrylic acid (PAA), but not with other dispersants like surfactants or polymethacrylic acid (PMAA). The diameter of the CuNPs could be controlled in the range of approximately 30–85 nm by modifying the ratio of the metal precursor to PAA. The catalytic reduction of p‐nitrophenol to p‐aminophenol takes place at the surface of CuNPs at room temperature and was accurately monitored by UV/Vis spectroscopy. The catalytic efficiency was found to be remarkably high for these PAA‐capped CuNPs, given the fact that at the same time PAA is efficiently preventing their oxidation as well. The activity was found to increase as the size of the CuNPs decreased. It can therefore be concluded that the synthesized CuNPs are catalytically highly efficient in spite of the presence of a protective PAA coating, which provides them with a long shelf life and thereby enhances the application potential of these CuNPs.     

Solid Phase Extraction of Neutral Analytes through Silica Gel Coated with Layers of Au Nanoparticles Self‐Assembled with Alkanethiols

In this study, we used Au nanoparticle (NP)‐coated silica gel as a solid phase extraction sorbent for the preconcentration of neutral analytes (steroid drugs). The sorbent was fabricated using two alkanethiol self‐assembly processes: one to deposit the Au NPs onto a 3‐aminopropyltrimethoxysilane‐modified silica gel and the other to functionalize the surfaces of the Au NPs. A large volume of the steroid solution was passed through the silica gel to facilitate adsorption mediated by hydrophobic interactions between the steroids and the hydrophobic moieties on the silica gel surface. Extraction of the steroids was accomplished by flushing the silica gel with a low‐polarity solvent. In this preliminary study, we found that the particle size of the silica gel and the number of layers of Au NPs coated on the silica gel both affected the preconcentration performance for the steroids. When using six layers of Au NPs coated on 5–20‐μm silica gel, the detection limits for steroids were below 80 ng L^?1; the preconcentration efficiency was over 170‐fold higher than that of the original steroid solution. Our findings provide further evidence that nanotechnology has much to benefit analytical science.     

Efficient CO2 Removal for Ultra‐Pure CO Production by Two Hybrid Ultramicroporous Materials

Removal of CO₂ from CO gas mixtures is a necessary but challenging step during production of ultra‐pure CO as processed from either steam reforming of hydrocarbons or CO₂ reduction. Herein, two hybrid ultramicroporous materials (HUMs), SIFSIX‐3‐Ni and TIFSIX‐2‐Cu‐i , which are known to exhibit strong affinity for CO₂, were examined with respect to their performance for this separation. The single‐gas CO sorption isotherms of these HUMs were measured for the first time and are indicative of weak affinity for CO and benchmark CO₂/CO selectivity (>4000 for SIFSIX‐3‐Ni ). This prompted us to conduct dynamic breakthrough experiments and compare performance with other porous materials. Ultra‐pure CO (99.99 %) was thereby obtained from CO gas mixtures containing both trace (1 %) and bulk (50 %) levels of CO₂ in a one‐step physisorption‐based separation process.     

Self-Assembly of Nanoparticles into Two-Dimensional Arrays for Catalytic Applications

Self-assembly of nanoparticles (NPs) is at the heart of nanotechnology, and has shown many potential applications in fabricating nanodevices with highly controlled functionality. Two-dimensional (2D) arrays of NPs can provide a thin and uniform NP array with each NP being exposed on the surface to maximize NP catalysis. This minireview summarizes the recent progress on the fabrication and application of 2D NP arrays. It conveys the important message to readers that creation of libraries of NP arrays with varying catalytic strengths is an exciting direction in catalysis. This approach can be used to solve complicated catalytic problems in which multiple chemical reactions need to be catalyzed in a single reaction vessel.     

Light-Driven Syngas Production over Defective ZnIn2S4 Nanosheets

Photocatalytic syngas (CO and H₂) production with CO₂ as gas source not only ameliorates greenhouse effect, but also produces valuable chemical feedstocks. However, traditional photocatalytic systems require noble metal or suffers from low yield. Here, we demonstrate that S vacancies ZnIn₂S₄ (V_S-ZnIn₂S₄) nanosheets are an ideal photocatalyst to drive CO₂ reduction into syngas. It is found that building S vacancies can endow ZnIn₂S₄ with stronger photoabsorption, efficient electron–hole separation, and larger CO₂ adsorption, finally promoting both hydrogen evolution reaction (HER) and CO₂ reduction reaction (CO₂RR). The syngas yield of CO and H₂ is therefore significantly increased. In contrast to pristine ZnIn₂S₄, the syngas yield over V_S-ZnIn₂S₄ can be improved by roughly ≈4.73 times and the CO/H₂ ratio is modified from 1:4.18 to 1:1. Total amount of syngas after 12 h photocatalysis is as high as 63.20 mmol g⁻¹ without use of any noble metals, which is even higher than those of traditional noble metal-based catalysts in the reported literatures. This work demonstrates the critical role of S vacancies in mediating catalytic activity and selectivity, and highlights the attractive ability of defective ZnIn₂S₄ for light-driven syngas production.