Supercritical fluid synthesis of metal and semiconductor nanomaterials

In the near future physical and economic constraints are expected to limit the continued miniaturisation of electronic and optical devices using current "top-down" lithography-based methods. Consequently, nonlithographic methods for synthesising and organising materials on the nanometre scale are required. In response to these technological needs a number of research groups are developing new supercritical fluids methodologies to synthesise and self-assemble "building blocks" of nanomaterials, from the "bottom-up", into structurally complex device architectures. This concept paper highlights some of the recent advances in the synthesis of metal and semiconductor nanoparticles and nanowires by using supercritical fluids. In addition, we describe an efficient supercritical fluid approach for constructing ordered arrays of metal and semiconductor nanowires within mesoporous silica templates.     

Delving noble metal and semiconductor nanomaterials into enantioselective analysis

With growing interests paid to the enantioselective analysis of chiral molecules, roles played by noble metal and semiconductor nanomaterials surface gradually. Given the unique physicochemical properties of noble metal and semiconductor nanomaterials, the enantioselective analyses are classified into three categories: ?uorescence-based, colorimetry-based, and circular dichroism-based ones. In this paper, we review the existing progresses on enantioselective analysis, thanks to noble metal and semiconductor nanomaterials. Finally, the prospect of enantioselective analysis based on noble metal and semiconductor are discussed.     

Delving noble metal and semiconductor nanomaterials into enantioselective analysis

The chiroplasmonic and chiroexcitonic platform constructed from noble metal and semiconductor nanomaterials have significantly advanced enantioselective analysis. In this paper, we summarized the exciting progresses and contributions by the peers in the field.     

Time-resolved photoluminescence spectra of Si species encapsulated in zeolite supercages

Photoluminescence (PL) spectra of Si species encapsulated in zeolite supercages are studied. It is reported that the chained Si species terminated partially with phenyl groups and with some unsaturated bonds are formed in zeolite supercages by the reaction with phenylsilane and they show PL around 4 eV (J. Phys. Chem. 2004, 108, 2501-2508). In the present paper they are reduced with hydrogen to prepare Si chained species terminated and saturated with hydrogen atoms. The PL spectra are deconvoluted to be four components at 1.9, 2.2, 2.6, and 3.7 eV, which can tentatively be assigned to Si nanocrystals and Si quantum wires in addition to defects in SiO2 and uncontrolled organic impurities in zeolite, respectively. At elevated temperatures the Si quantum wires in zeolite pores seem to change the Si nanocrystals with the size larger than that of the zeolite pore diameter. It is the first case in which the PL decay lifetime of oxygen vacancies in zeolite can be detected to be quite short to be about 16 ns. The detected lifetimes of Si quantum wires are significantly very short, about 12 ns. The Si species encapsulated zeolite is solvated with hydrofluoric acid solution to separate the Si quantum wires by dissolving zeolite lattice. The Si quantum wires in the HF solution show intense PL spectra peaked at 2.33 eV and broad UV spectra around 2.8-3.5 eV. They will have different shapes and lengths. The HF solvated zeolite shows still PL spectra characteristic of oxygen vacancies and the absorption edge at 3.6 eV. The result means that zeolite lattice is solvated in HF solution as clusters with a band gap of 3.6 eV and they can still have some oxygen vacancies. Oxygen vacancies situate about 1.0 eV below the zeolite conduction band minimum, and the absorbed energy can be dissipated as PL between the valence band maximum and the oxygen vacancies. It is concluded that the excitation photon energy can be absorbed in zeolite and the Si quantum wires and then the absorbed energies are competitively relaxed in zeolite and the Si quantum wires.     

CE characterization of semiconductor nanocrystals encapsulated with amorphous silicium dioxide

The electrophoretic mobility of silica-encapsulated semiconductor nanocrystals (quantum dots) dependent on the pH and the ionic strength of the separation electrolyte has been determined by CE. Having shown the viability of the approach, the electrophoretic mobility mu of the nanoparticles investigated is calculated for varied zeta potential zeta, particle radius r, and ionic strength I employing an approximate analytical expression presented by Ohshima (J. Colloid Interface Sci. 2001, 239, 587-590). The comparison of calculated with measured data shows that the experimental observations exactly follow what would be expected from theory. Within the parameter range investigated at fixed zeta and I there is an increase in mu with r which is a nonlinear function. This dependence of mu on size parameters can be used for the size-dependent separation of particles. Modeling of mu as function of I and zeta makes it possible to calculate the size distribution of nanoparticles from electrophoretic data (using the peak shape of the particle zone in the electropherogram) without the need for calibration provided that zeta is known with adequate accuracy. Comparison of size distributions calculated via the presented method with size histograms determined from transmission electron microscopy (TEM) micrographs reveals that there is an excellent matching of the size distribution curves obtained with the two independent methods. A comparison of calculated with measured distributions of the electrophoretic mobility showed that the observed broad bands in CE studies of colloidal nanoparticles are mainly due to electrophoretic heterogeneity resulting from the particle size distribution.     

Photovoltaic effects of CdS and PbS quantum dots encapsulated in zeolite Y

Zeolite Y films (0.35-2.5 μm), into which CdS and PbS quantum dots (QDs) were loaded, were grown on ITO glass. The CdS QD-loaded zeolite Y films showed a photovoltaic effect in the electrolyte solution consisting of Na(2)S (1 M) and NaOH (0.1 M) with Pt-coated F-doped tin oxide glass as the counter electrode. In contrast, the PbS QD-loaded zeolite Y films exhibited a negligible PV effect. This contrasting behavior was proposed to arise from the large difference in driving force for the electron transfer from S(2-) in the solution to the hole in the valence band of QDs, with the former being much larger (~2 eV) than the latter (~1 eV). In the case of CdS QD-loaded zeolite Y with a loaded amount of CdS of 6.3 per unit cell, the short circuit current, open circuit voltage, fill factor, and efficiency were 0.3 mA cm(-2), 423 V, 28, and 0.1%, respectively, under the AM 1.5, 100 mW cm(-2) condition. This cell was stable for more than 18 days of continuous measurements. A large (3-fold) increase in overall efficiency was observed when PbS QD-loaded zeolite Y on ITO glass was used as the counter electrode. This phenomenon suggests that the uphill electron transfer from ITO glass to S in the solution is facilitated by the photoassisted pumping of the potential energy of the electron in ITO glass to the level that is higher than the reduction potential of S by PbS QDs. Under this condition, the incident-photon-to-current conversion efficiency (IPCE) value at 398 nm was 42% and the absorbed-photon-to-current conversion efficiency (APCE) value at 405 nm was 82%. The electrolyte-mediated interdot charge transport within zeolite films is concluded to be responsible for the overall current flow.     

Plasmonic metal/semiconductor hybrid nanomaterials for solar to chemical energy conversion

Plasmonic nanomaterials are sources of light,heat and electrons at nanometer scale.Given the outstand-ing performance in harvesting and converting solar energy ...     

Tight confinement of semiconductor quantum dots within zeolite by surface silylation

Various MX (M = Cd, Zn, and Mn, X = S and Se) semiconductor quantum dots (QDs) were prepared in zeolite Y. While the QDs are readily expelled from zeolite interior upon exposure of the MX QD-incorporating zeolite Y ([MX]-Y) to the ambient atmosphere due to moisture adsorption, they remain tightly confined within zeolites even after exposure to the moist atmosphere for several weeks when the surfaces were silylated with various silylating agents. This methodology will facilitate the characterization of the zeolite-encapsulated QDs and the application of QD-incorporating zeolites.     

Biomimetical catalytic activity of iron(III) porphyrins encapsulated in the zeolite X

The approach adopted for the obtention of zeolite-encapsulated FeP led to clean syntheses of biomimetical catalyst. The catalysts were obtained through the zeolite synthesis method, where NaX zeolite was synthesised around one of the cationic FePs: iron(III) 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (FeP1) or iron(III) 5-mono(2,6-dichloro-phenyl)10,15,20-tris(4-N-methylpyridyl)porphyrin (FeP2). The syntheses yielded pure FeP1NaX and FeP2NaX catalysts without any by-products blocking the zeolite nanopores. FeP1NaX and FeP2NaX efficiently catalysed the epoxidation of (Z)-cyclooctene by iodosylbenzene (PhIO) in DCE, giving rise to cis-epoxycyclooctane yields of 85% and 95%, respectively. Hydroxylation of adamantane shows a preferable alkane oxidation at the tertiary C---H bond, indicating a hydrogen abstraction through the Fe^IV(O)P^·+species in the initial step. The total adamantanol yields were 52% and 45% for FeP1NaX and FeP2NaX, respectively. Concerning selectivity, FeP1NaX and FeP2NaX gave an 1-adamantanol (Ad-1-ol)/2-adamantanol (Ad-2-ol) ratio of 20:1 and 11:1, respectively (after statistical correction). Therefore, these results indicate a free radical activation of the C---H bonds of adamantane as expected for P-450 models. In the cyclohexane oxidation catalysed by FeP1NaX in DCE, a cyclohexanol (C₆-ol) yield of 50% and an alcohol/ketone ratio of 10 was obtained. The hydroxylation occurs according to the so-called oxygen rebound mechanism, as expected for a P-450 model system. FeP2NaX is less selective (C₆-ol yield=25% and alcohol/ketone=1.2). One possible explanation is that a Russell-type mechanism involving O₂ imprisoned within the zeolite cages may be operating parallelly, generating both C₆-ol and cyclohexanone.     

沸石分子筛孔道中聚苯胺的选择性掺杂研究

用电化学方法聚合分子筛孔道内的苯胺, 根据聚苯胺在无机质子酸中的掺杂反应研究了ZSM-5,Y型分子筛对磷钼杂多酸的形状选择作用     

Formaldehyde encapsulated in zeolite: a long-lived, highly activated one-carbon electrophile to carbonyl-ene reactions

Gaseous formaldehyde is extremely unstable and readily undergoes self-polymerization to a solid paraformaldehyde or disproportionation to methanol and formic acid in the presence of moisture. We disclose a simple method to stably store such a labile formaldehyde as a monomer in a nanoporous faujasite zeolite at 5 degrees C for at least 50 days without self-polymerization or disproportionation. The greater stability of formaldehyde encapsulated in zeolite was confirmed by 13C MAS NMR spectroscopy. Formaldehyde was not only stabilized within the zeolite cages but functioned as a powerful electrophile toward various olefins. Zeolite-encapsulated formaldehyde was proved to be a stable but highly reactive C1 reagent.     

Enhanced photocatalytic activities of ZnO thin films: a comparative study of hybrid semiconductor nanomaterials

Nanostructure single ZnO, SnO₂, In₂O₃ and composite ZnO/SnO₂, ZnO/In₂O₃ and ZnO/SnO₂/In₂O₃ films were prepared using sol?Cgel method. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV?CVis spectroscopy. The photocatalytic activities of composite films were investigated using phenol (P), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 4-aminophenol (4-AP) as a model organic compounds under UV light irradiation. Hybrid semiconductor thin films showed a higher photocatalytic activity than single component ZnO, SnO₂ and In₂O₃ films. The substituted phenols degrade faster than phenol. The ease of degradation of phenols is different for each catalyst and the order of catalytic efficiency is also different for each phenol. The use of multiple components offered a higher control of their properties by varying the composition of the materials and related parameters such as morphology and interface. It was also found that the photocatalytic degradation of phenolic compounds on the composite films and single films followed pseudo-first order kinetics.     

Chiral II-VI semiconductor nanostructure superlattices based on an amino acid ligand

Reaction of L-cysteine with M(NO3)2 x xH2O (M = Cd, Zn) generates M(L-cysteinate), which feature one-dimensional substructures that can be viewed as fragments of bulk structures of CdS (rock salt high pressure phase) and ZnS (wurtzite) because of the bridging modes accessible to the sulfur atom of L-cysteine. The MS substructures are arranged in a regular and periodic fashion within the crystal via the carboxylate function of L-cysteine. Considering the structural similarities with bulk materials, the optical properties of M(L-cysteinate) were studied and indicate blue shifts of the band gap of 2.59 eV (M = Cd, compared to CdS rock salt) and 1.37 eV (M = Zn, compared to ZnS wurtzite) with respect to the bulk MS structures, due to the low dimensionality of the metal-sulfur arrangement. The chelating nature of the cysteine ligand imposes an unusual mer arrangement of three binding S moieties at Cd with a correspondingly high Cd coordination number in a chalcogenide-based material. Density of states calculations show strong electronic structure similarities with the bulk phases and rationalize the band gap changes.     

The chemistry of organic nanomaterials

The development of nanotechnology using organic materials is one of the most intellectually and commercially exciting stories of our times. Advances in synthetic chemistry and in methods for the investigation and manipulation of individual molecules and small ensembles of molecules have produced major advances in the field of organic nanomaterials. The new insights into the optical and electronic properties of molecules obtained by means of single-molecule spectroscopy and scanning probe microscopy have spurred chemists to conceive and make novel molecular and supramolecular designs. Methods have also been sought to exploit the properties of these materials in optoelectronic devices, and prototypes and models for new nanoscale devices have been demonstrated. This Review aims to show how the interaction between synthetic chemistry and spectroscopy has driven the field of organic nanomaterials forward towards the ultimate goal of new technology.     

国际互联网与沸石相关的化学化工信息资源

介绍了Internet上与沸石和天然沸石有关的化学化工信息资源,并初步讨论国际互联网和国内互联网上沸石信息量。     

Visible light-induced highly selective transformation of olefin to ketone by 2,4,6-triphenylpyrylium cation encapsulated within zeolite Y

2,4,6-Triphenylpyrylium cation encapsulated within zeolite Y promotes highly selective transformation of olefins to ketones with molecular oxygen, under visible light (lambda > 400 nm) irradiation at room temperature.     

Finned Zn-MFI zeolite encapsulated noble metal nanoparticle catalysts for the oxidative dehydrogenation of propane with carbon dioxide

Oxidative dehydrogenation of propane with carbon dioxide(CO₂-ODP) characterizes the tandem dehydrogenation of propane to propylene with the reduction of the greenhouse gas of CO₂ to valuable CO.However, the existing catalyst is limited due to the poor activity and stability, which hinders its industrialization. Herein, we design the finned Zn-MFI zeolite encapsulated noble metal nanoparticles(NPs)as bifunctional catalysts(NPs@Zn-MFI) for CO₂-ODP. Characterization...     

The art of two-dimensional soft nanomaterials

The discovery of graphene has triggered the explosive development of two-dimensional(2D) nanomaterials, including both inorganic and organic species. Benefiting from the simple elemental composition, inorganic 2D nanomaterials were the center research in the past decade, which has long shadowed the research of 2D organic(or soft) nanomaterials. Although many kinds of2D soft nanomaterials have been successfully prepared, a unified definition for them is still impossible due to the complicate and quite different chemical structures between each other and even relying on totally different techniques to distinguish them. Since our first review on 2D soft nanomaterials in 2015, this field has moved forward with big success. In this review, we will focus on the development of 2D soft nanomaterials after 2015. In order to deliver better overview of this field, new and comprehensive classification is used in this review: 2D aromatic molecules, graphene and graphene nanoribbons, graphyne and graphdiyne,BxCyNznanosheets, 2D polymers, 2D supramolecules, crystalline 2D assemblies, 2D covalent organic frameworks, 2D metalorganic frameworks, sandwich-like 2D porous polymers, 2D polymer nanosheets, etc. The focus of this review lies on synthetic strategies and the challenges of characterization, definition and fundamental understanding.     

Ultra-small PtNi bimetallic encapsulated in silicalite-1 zeolite with fine-tuned surface acidity for selective conversion of levulinic acid

Exploration of levulinic acid (LA) hydrogenation to γ-valerolactone (GVL) contributes to the conversion from carbohydrates to valuable fuels and chemicals. Here, we obtained a series of ultra-small PtNix bimetallic composite catalysts encapsulated in silicalite-1 zeolite (S-1) via a one-pot synthesis strategy protected by tetra(p-carboxyphenyl)porphyrin (TCPP) ligands. The catalytic results showed that PtNi₃@S-1 (TCPP) exhibited the most active catalytic performance (95.7% LA conversion and 93.8% GVL selectivity) under optimized conditions. The characterization results indicate that ligand modification and bimetallic synergy play an important role in enhancing the catalytic activity. The introduction of TCPP provides a guarantee for the homogeneous encapsulation of PtNi₃ in S-1 zeolite at sub-nanometer size. The electronic interaction of PtNi bimetallic, high dispersibility of active components, improved surface acidity and excellent stability co-contribute to the satisfactory hydrogenation activity.