Oxidation Ability of Plasmon‐Induced Charge Separation Evaluated on the Basis of Surface Hydroxylation of Gold Nanoparticles

The oxidation ability of plasmonic photocatalysts, which has its origins in plasmon‐induced charge separation and has not yet been studied quantitatively and systematically, is important for designing practical photocatalytic systems. Oxidation ability was investigated on the basis of surface hydroxylation of Au nanoparticles on TiO₂ at various irradiation wavelengths and electrolyte pH values. The reaction proceeds only when the sum of the flat band potential of TiO₂ and the irradiated photon energy is close to, or more positive than, the theoretical potential for the reaction.     

Correlating the Surface Basicity of Metal Oxides with Photocatalytic Hydroxylation of Boronic Acids to Alcohols

Photoredox catalysis provides opportunities in harnessing clean and green resources such as sunlight and O₂, while the acid and base surface sites of metal oxides are critical for industrial catalysis such as oil cracking. The contribution of metal oxide surfaces towards photocatalytic aerobic reactions was elucidated, as demonstrated through the hydroxylation of boronic acids to alcohols. The strength and proximity of the surface base sites appeared to be two key factors in driving the reaction; basic and amphoteric oxides such as MgO, TiO₂, ZnO, and Al₂O₃ enabled high alcohol yields, while acidic oxides such as SiO₂ and B₂O₃ gave only low yields. The reaction is tunable to different irradiation sources by merely selecting photosensitizers of compatible excitation wavelengths. Such surface complexation mechanisms between reactants and earth abundant materials can be effectively utilized to achieve a wider range of photoredox reactions.     

表面富锡MCM-41分子筛的表面金属有机化学制备及其对苯酚羟基化催化反应性能研究

采用SnBu₄在MCM-41表面的接枝反应和后续处理制备出了一种只在表面含锡的MCM-41型介孔分子筛。通过与采用纳米SnO₂和MCM-41机械混合法、SnCl₄浸渍法、水热合成法等制备的具有相当硅锡比(Si/Sn≈100)的SnMCM-41分子筛进行结构和对苯酚羟基化反应催化性能的比较发现， 由该法所得分子筛的水热稳定性明显提高，并在苯酚羟基化反应中表现出优良的催化活性、选择性和过氧化氢利用率。本文还详细考察了该催化剂对苯酚羟基化反应的最佳反应条件。     

Liquid-Repellent Metal Oxide Photocatalysts

Metal oxide photocatalysts (MOPCs) decompose organic molecules under illumination. However, the application of MOPCs in industry and research is currently limited by their intrinsic hydrophilicity because MOPCs can be wetted by most liquids. To achieve liquid repellency, the surface needs to possess a low surface energy, but most organic molecules with low surface energy are degraded by photocatalytic activity. Herein, current methods to achieve liquid repellency on MOPCs, while preventing degradation of hydrophobic coatings, are reviewed. Classically, composite materials containing MOPCs and hydrophobic organic compounds possess good liquid repellency. However, composites normally form irregular coatings and are hard to prepare on surfaces such as those that are mesoporous or nanostructured. In addition, the adhesion of composites to substrates is often weak, resulting in delamination. Recent studies have shown that the direct grafting reaction of polydimethylsiloxane (PDMS) from silicone oil (methyl-terminated PDMS) under illumination results in a stable polymer brush. This easy and simple grafting method allows us to create stable liquid-repellent surfaces on MOPCs of various types, structures, and sizes. In particular, super-liquid-repellent drops with an underlying air layer can be created on PDMS-grafted nano-/microstructured MOPCs. Potential applications of surfaces combining liquid repellency and photocatalytic activity are also discussed; thus offering new ways of using MOPCs in a wider range of applications.     

Carboxylic‐Acid‐Passivated Metal Oxide Nanocrystals: Ligand Exchange Characteristics of a New Binding Motif

Ligand exchange is central in the processing of inorganic nanocrystals (NCs) and requires understanding of surface chemistry. Studying sterically stabilized HfO₂ and ZrO₂ NCs using ¹H solution NMR and IR spectroscopy as well as elemental analysis, this paper demonstrates the reversible exchange of initial oleic acid ligands for octylamine and self‐adsorption of oleic acid at NC surfaces. Both processes are incompatible with an X‐type binding motif of carboxylic acids as reported for sulfide and selenide NCs. We argue that this behavior stems from the dissociative adsorption of carboxylic acids at the oxide surface. Both proton and carboxylate moieties must be regarded as X‐type ligands yielding a combined X₂ binding motif that allows for self‐adsorption and exchange for L‐type ligands.     

Thermally Induced Growth of ZnO Nanocrystals on Mixed Metal Oxide Surfaces

An in situ method for the growth of ZnO nanocrystals on Zn/Al mixed metal oxide (MMO) surfaces is presented. The key to this method is the thermal treatment of Zn/Al layered double hydroxides (Zn/Al LDHs) in the presence of nitrate anions, which results in partial demixing of the LDH/MMO structure and the subsequent crystallization of ZnO crystals on the surface of the forming MMO layers. In a first experimental series, thermal treatment of Zn/Al LDHs with different fractions of nitrate and carbonate in the interlayer space was examined by thermogravimetry coupled with mass spectrometry (TG‐MS) and in situ XRD. In a second experimental series, Zn/Al LDHs with only carbonate in the interlayer space were thermally treated in the presence of different amounts of an external nitrate source (NH₄NO₃). All obtained Zn/Al MMO samples were analysed by electron microscopy, nitrogen physisorption and powder X‐ray diffraction. The gas phase formed during nitrate decomposition turned out to be responsible for the formation of crystalline ZnO nanoparticles. Accordingly, both interlayer nitrate and the presence of ammonium nitrate led to the formation of supported ZnO nanocrystals with mean diameters between 100 and 400 nm, and both methods offer the possibility to tailor the amount and size of the ZnO crystals by means of the amount of nitrate.     

含铜过渡金属水滑石类化合物对苯酚过氧化氢羟化的催化作用

合成了一系列二元、三元过渡金属水滑石类化合物, 并经XRD、IR进行了表征.苯酚过氧化氢羟化结果表明, 含铜水滑石类化合物对该反应有较高的催化活性, 并初步提出了反应机理.     

Highly Reactive Nonheme Iron(III) Iodosylarene Complexes in Alkane Hydroxylation and Sulfoxidation Reactions

High‐spin iron(III) iodosylarene complexes bearing an N‐methylated cyclam ligand are synthesized and characterized using various spectroscopic methods. The nonheme high‐spin iron(III) iodosylarene intermediates are highly reactive oxidants capable of activating strong C? H bonds of alkanes; the reactivity of the iron(III) iodosylarene intermediates is much greater than that of the corresponding iron(IV) oxo complex. The electrophilic character of the iron(III) iodosylarene complexes is demonstrated in sulfoxidation reactions.     

Nanoscale Effects on Thermodynamics and Phase Equilibria in Oxide Systems

Because different solid materials (phases) have different surface energies, equilibria among them will be significantly affected by particle size. This Minireview summarizes experimental (calorimetric) data for the surface energies of oxides and discusses shifts in the stability of polymorphs, the thermodynamics of hydration, and oxidation–reduction reactions in nanoscale oxide systems.     

Catalytic Activation of a Solid Oxide in Electronic Contact With Gold Nanoparticles

Although inert in its bulk form, nanostructured gold supported on oxides has been found to be catalytically active. In many cases, the oxide promotes the activity of Au. It is now shown that in turn, nanoscale Au particles can chemically activate the solid oxide. Specifically, it was discovered that 4 nm Au nanoparticles deposited on zinc oxide catalyze the transformation of the oxide into the sulfide in the presence of an organosulfur species. Contact of the oxide with Au nanoparticles lowers the activation barrier for the solid‐state reaction by approximately 20 kJ mol^?1, allowing the reaction to be achieved closer to ambient temperatures. Electron transfer from oxygen vacancies to Au nanoparticles is proposed to generate acidic sites on the surface of the zinc oxide, resulting in the enhanced reactivity of the oxide. Knowledge of such electronic interactions between the noble metal and oxide can be exploited for engineering reactive heterostructures for low‐temperature pollutant sorption and hydrocarbon processing.     

Reduction Mechanism of Transition Metal Oxide Particles in Thermally Induced Nanobubbles during Pulsed Laser Melting in Ethanol

Pulsed laser melting in liquid (PLML) is a technique to fabricate spherical submicrometer particles (SMPs) wherein nanosecond pulsed laser (several tens to several hundreds of mJ pulse⁻¹ cm⁻²) irradiates raw particles dispersed in liquid. Raw particles are transiently heated above the melting point to form spherical particles, which enables pulsed heating of surrounding liquid to form thermally induced bubbles by liquid vaporization. These transient bubbles play an important role as a thermal barrier to rapidly heat the particle. Reduced SMPs are generated from raw metal-oxide nanoparticles by PLML process in ethanol. This reduction cannot be explained by high-temperature thermal decomposition, but by mediation of molecules decomposed from ethanol. Computational simulations of ethanol decomposition by pulsed heating for 100 ns at the temperature 1000–4000 K revealed that ethylene is generated as the main product. Gibbs free energies of oxide reduction reactions mediated by ethylene greatly decreased compared to those without ethylene mediation. This explanation can be applied to reductive SMP formation from various transition metal oxides by PLML.     

Hydroxylation of 3-nitrotyrosine by hydroxyl radical

Hydroxylation of 3-nitrotyrosine (3-NT) and 3-NT containing peptide Gly-nitroTyr-Gly in aqueous solution by hydroxyl radical were investigated with gamma irradiation. The structures of the hydroxylated products were confirmed by electrospray ionization mass spectrometry and 1H NMR spectrometry. The reactivity of 3-nitrotyrosine has been investigated using density functional theory (DFT) calculation.     

Salt‐Driven Deposition of Thermoresponsive Polymer‐Coated Metal Nanoparticles on Solid Substrates

Here we report on a simple, generally applicable method for depositing metal nanoparticles on a wide variety of solid surfaces under all aqueous conditions. Noble‐metal nanoparticles obtained by citrate reduction followed by coating with thermoresponsive polymers spontaneously form a monolayer‐like structure on a wide variety of substrates in presence of sodium chloride whereas this phenomenon does not occur in salt‐free medium. Interestingly, this phenomenon occurs below the cloud point temperature of the polymers and we hypothesize that salt ion‐induced screening of electrostatic charges on the nanoparticle surface entropically favors hydrophobic association between the polymer‐coated nanoparticles and a hydrophobic substrate.     

Reconstruction of Supported Metal Nanoparticles in Reaction Conditions

Metal nanoparticles (NPs) dispersed on a high‐surface‐area support are normally used as heterogeneous catalysts. Recent in situ experiments have shown that structure reconstruction of the NP occurs in real catalysis. However, the role played by supports in these processes is still unclear. Supports can be very important in real catalysis because of the new active sites at the perimeter interface between nanoparticles and supports. Herein, using a developed multiscale model coupled with in situ spherical aberration‐corrected (Cs‐corrected) TEM experiments, we show that the interaction between the support and the gas environment greatly changes the contact surface area between the metal and support, which further leads to the critical change in the perimeter interface. The dynamic changes of the interface in reactive environments can thus be predicted and be included in the rational design of supported metal nanocatalysts. In particular, our multiscale model shows quantitative consistency with experimental observations. This work offers possibilities for obtaining atomic‐scale structures and insights beyond the experimental limits.     

纳米磷钼钒杂多酸盐催化苯羟基化合成苯酚

纳米磷钼钒杂多酸盐催化苯羟基化合成苯酚;苯; 羟基化; 苯酚; 纳米杂多化合物     

介孔铁铝/蒙脱土复合材料：解离柱撑制备、结构及催化羟基化性能

利用极稀悬浮液中蒙脱土的解离作用并结合柱化技术过程，制备了介孔结构的铝铁/蒙脱土复合材料(Fe-Al/mmt)；并采用粉末X射线衍射、氮等温吸脱附、傅立叶红外光谱、紫外可见光漫反射光谱及苯酚催化羟基化反应表征了其结构和性能。结果显示，铁铝聚合前驱液中铁/铝比影响复合材料中蒙脱土的解离程度，且仅当低铁/铝比时(即Fe/(Fe+Al)物质的量的比介于0.05～0.3)，嵌入解离的蒙脱土片层间的混合铁铝物种呈现能耐温350 ℃的热稳定性；氮等温吸脱附分析反映出这种解离的蒙脱土堆积结构呈现介孔特征，孔径分布窄，介于2.0～2.3 nm；红外分析表明材料表面具有L酸和B酸位，并且L酸位量与嵌入解离的蒙脱土结构中的混合铁铝物种相关；由于结构中混合铁铝物种的存在及相应的Si-O → Fe、Al-O → Fe间的电子跃迁，Fe-Al/mmt材料在紫外区呈现宽泛的能量吸收特征。这些结果说明，由于混合铁铝物种嵌入于解离的蒙脱土片层堆积结构中，形成了“卡片屋”式介孔结构。实验条件下，Fe/(Fe+Al)物质的量的比为0.3的Fe-Al/mmt呈现较佳的催化羟基化性能，苯酚转化率为36.7%，二酚产物选择性32.3%；并且初步表明铝掺杂后，通过铁铝比和表面酸性的调整，材料的部分选择氧化性能可以得到改善。     

纳米金属氧化物的制备及应用研究的若干进展

综述了氧化物及复合氧化物纳米晶的各种制备方法及特点 ,重点介绍了有机配合物前驱体法 聚乙二醇法、明胶法和硬脂酸法制备氧化物纳米晶的原理、特点以及在磁性材料、电磁波吸收材料、催化剂和塑料改性方面的若干应用     

醌类化合物在苯酚羟化反应中的电子传递作用

Fenton试剂是某些烃类化合物的有效氧化剂^[1],该体系对芳香化合物具有羟化作用。我们^[2]曾报道了含Cu类钙钛石型复合氧化物在苯酚烃化反应中的催化活性,并提出了相应的反应机理。高价态的过渡金属离子如C^3 [2]和Fe^3 [3]通常被认为是中间自由基的氧化剂。实际上,醌类化合物及其还原形式半醌、氢醌与生物体内许多电子转移过程密切相关^[4],如泛醌或辅酶Q在生物体呼吸链电子传递过程中起重要作用^[5]。在实验中我们观察到苯酚羟化反应中不仅有苯醌生成,而且生成的苯醌还能促进羟化反应。本文报道了醌类化合物在苯酚羟化循环中的传递电子作用。     

Ti-MCM-41催化剂的表面性质及介质极性对

用不同的铝源改性Ti MCM 41催化剂 ,得到了具有长程有序结构、n(Si) /n(Ti) =2 5的不同Si/Al比的改性Ti MCM 41.通过研究芳烃羟化反应随催化剂表面性质的变化规律发现 ,调变催化剂的表面性质 ,可控制反应物苯及目的产物苯酚与Al Ti MCM 41催化活性中心接近的程度 ,从而可实现对芳烃羟化反应化学选择性的控制 .介质极性对芳烃的化学亲和选择性也有影响 ,只有富含供电子氧原子且其极性大于苯的介质才有利于芳烃的羟化反应