Self-Assembly of Nanosized 0D Clusters: CdS Quantum Dot-Polyoxotungstate Nanohybrids with Strongly Coupled Electronic Structures and Visible-Light-Active Photofunctions

Visible-Light-Driven Oxidation of Amines to Imines in Air Catalyzed by Polyoxometalate-Tris(bipyridine)ruthenium Hybrid Compounds

The development of visible-light photocatalysts for the selective oxidative coupling of amines to imines is an area of great interest. Herein, four hybrid compounds based on polyoxometalate anions and tris(bipyridine)ruthenium cations, Ru(bpy)₃[M₆O₁₉] (M = Mo, W) 1-2, [Ru(bpy)₃]₂[Mo₈O₂₆] 3, [Ru(bpy)₃]₂[W₁₀O₃₂] 4, are prepared and characterized by X-ray diffraction (single-crystal and powder), elemental analysis, energy-dispersive X-ray spectroscopy (EDS) analysis, infrared (IR) spectroscopy, and solid diffuse reflective spectroscopy. Single-crystal structural analysis indicates that polyoxometalate anions and tris(bipyridine)ruthenium cations interact with each other through extensive hydrogen bonds in these compounds. These hybrid species with strong visible-light-harvesting abilities and suitable photocatalytic energy potentials show excellent photocatalytic activity and selectivity for the oxidation of amines to imines at room temperature in air as an oxidant. Among them, compound 1 with the [Mo₆O₁₉]^2- anion has the highest catalytic activity, which can swiftly convert >99.0% of benzylamine into N-benzylidenebenzylamine with a selectivity of 98.0% in 25 min illumination by a 10 W 445 nm light-emitting diode (LED). Its turnover frequency reaches 392 h^-1, which is not only better than the homogeneous catalyst [Ru(bpy)₃]Cl₂ but also much superior to those achieved over most of reported heterogeneous catalysts. Moreover, it shows a wide generality for various aromatic amines, accompanied by the advantages of good recyclability and stability. The photocatalytic oxidation mechanism of amines to the corresponding imines over polyoxometalate-based hybrid compounds was fully investigated.

Biomolecule-mediated hydrothermal synthesis of polyoxoniobate-CdS nanohybrids with enhanced photocatalytic performance for hydrogen production and RhB degradation

Using a biomolecule of l-cystine as the sulfur source and coordinating agent, polyoxoniobate-CdS nanohybrids were successfully synthesized under mild hydrothermal conditions. The adsorption of ammonium group (-NH₂) in l-cystine molecular structure on the surface of CdS renders the amine-anchored CdS positively charged, which readily combines with the negatively charged polyoxoniobate clusters in terms of the electrostatic interaction. The as-obtained polyoxoniobate-CdS nanohybrids exhibit much superior activity for H₂ evolution and RhB degradation under visible light as compared to the unhybridized CdS and polyoxoniobate. After co-loading Nb₆ and NiS as cocatalyst, the H₂-evolution activity of the nanohybrids is further increased up to 39 times as high as that of naked CdS, which can be attributed to an enhanced electron-transfer by adopting polyoxoniobate as electron-acceptor to retard the electron-hole recombination. The work may open an avenue for the green synthesis of cost-effective POMs-CdS nanohybrid photocatalysts for solar energy applications.

Highly Stable Nanocontainer of APTES-Anchored Layered Titanate Nanosheet for Reliable Protection/Recovery of Nucleic Acid

A universal technology for the encapsulative protection of unstable anionic species by highly stable layered metal oxide has been developed via the surface modification of a metal oxide nanosheet. The surface anchoring of (3-aminopropyl)triethoxysilane (APTES) on exfoliated titanate nanosheet yields a novel cationic metal oxide nanosheet, which can be universally used for the hybridization with various biological and inorganic anions. The encapsulation of deoxyribonucleic acid (DNA) in the cationic APTES-anchored titanate lattice makes possible the reliable long-term protection of DNA against enzymatic, chemical, and UV-vis light corrosions. The encapsulated DNA can be easily released from the titanate lattice via sonication, underscoring the functionality of the cationic APTES-anchored titanate nanosheet as a stable nanocontainer for DNA. The APTES-anchored titanate nanosheet can be also used as an efficient CO2 adsorbent and a versatile host material for various inorganic anions like polyoxometalates, leading to the synthesis of novel intercalative nanohybrids with unexplored properties and useful functionalities.

A new organo-ruthenium substituted tungstotellurate: synthesis, structural characterization and catalytic properties

A novel organo-Ru supported tungstotellurate(iv) has been synthesized and its catalytic activity was assessed towards the oxidation of n-tetradecane using air without any additives or solvents.

Microwave assisted synthesis of high-surface area WO3 particles decorated with mosaic patterns via hydrochloric acid treatment of Bi2W2O9

High surface area WO₃ particles with mosaic patterned-structures were obtained under microwave irradiation.

Facile ion-exchange synthesis of urchin-shaped CdS/Bi2S3 heterostructures with enhanced photostability and visible light photocatalytic activity

Core/shell CdS/Bi₂S₃ heterostructures have been synthesized through in situ cation-exchange method. These heterostructures exhibit enhanced photostability and visible light photocatalytic activity.

Graphene–CdS quantum dots–polyoxometalate composite films for efficient photoelectrochemical water splitting and pollutant degradation

rGO–CdS–H2W12 nanocomposite film was successfully fabricated by a layer-by-layer self-assembly method. The film showed good photo-electrical response under irradiation of solar light.

Preparation of NiS/ZnIn2S4 as a superior photocatalyst for hydrogen evolution under visible light irradiation

In this study, NiS/ZnIn2S4 nanocomposites were successfully prepared via a facile two-step hydrothermal process. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). Their photocatalytic performance for hydrogen evolution under visible light irradiation was also investigated. It was found that the photocatalytic hydrogen evolution activity over hexagonal ZnIn2S4 can be significantly increased by loading NiS as a co-catalyst. The formation of a good junction between ZnIn2S4 and NiS via the two step hydrothermal processes is beneficial for the directional migration of the photo-excited electrons from ZnIn2S4 to NiS. The highest photocatalytic hydrogen evolution rate (104.7 μmol/h), which is even higher than that over Pt/ZnIn2S4 nanocomposite (77.8 μmol/h), was observed over an optimum NiS loading amount of 0.5 wt %. This work demonstrates a high potential of the developing of environmental friendly, cheap noble-metal-free co-catalyst for semiconductor-based photocatalytic hydrogen evolution.

Highly efficient visible light-induced O₂ generation by self-assembled nanohybrids of inorganic nanosheets and polyoxometalate nanoclusters

Unusually high photocatalytic activity of visible light-induced O₂ generation can be achieved by electrostatically-derived self-assembly between exfoliated Zn-Cr-LDH 2D nanosheets and POM 0D nanoclusters (W₇O₂₄⁶⁻ and V₁₀O₂₈⁶⁻) acting as an electron acceptor. This self-assembly can provide a high flexibility in the control of the chemical composition and pore structure of the resulting LDH-based nanohybrids. The hybridization with POM nanoclusters remarkably enhances the photocatalytic activity of the pristine Zn-Cr-LDH, which is attributable to the formation of porous structure and depression of charge recombination. Of prime interest is that the excellent photocatalytic activity of the as-prepared Zn-Cr-LDH-POM nanohybrid for visible light-induced O₂ generation can be further enhanced by calcination at 200 °C, leading to the very high apparent quantum yield of ∼75.2% at 420 nm. The present findings clearly demonstrate that the self-assembly of LDH–POM is fairly powerful in synthesizing novel LDH-based porous nanohybrid photocatalyst for visible light-induced O₂ generation.