Aerobic Oxidation of Formaldehyde Catalyzed by Polyvanadotungstates

Three tetra-<i>n</i>-butylammonium (TBA) salts of polyvanadotungstates, [<i>n</i>-Bu₄N]₆[PW₉V₃O₄₀] (<b>PW</b>_<b>9</b><b>V</b>_<b>3</b>), [<i>n</i>-Bu₄N]₅H₂PW₈V₄O₄₀ (<b>PW</b>_<b>8</b><b>V</b>_<b>4</b>), and [<i>n</i>-Bu₄N]₄H₅PW₆V₆O₄₀·20H₂O (<b>PW</b>_<b>6</b><b>V</b>_<b>6</b>), have been synthesized and shown to be effective catalysts for the aerobic oxidation of formaldehyde to formic acid under ambient conditions. These complexes, characterized by elemental analysis, Fourier transform infrared spectroscopy, UV–vis spectroscopy, and thermogravimetric analysis, exhibit a catalytic activity for this reaction comparable to those of other polyoxometalates. Importantly, they are more effective in the presence of water than the metal oxide-supported Pt and/or Au nanoparticles traditionally used as catalysts for formaldehyde oxidation in the gas phase. The polyvanadotungstate-catalyzed oxidation reactions are first-order in formaldehyde, parabolic-order (slow, fast, and slow again) in catalyst, and zero-order in O₂. Under optimized conditions, a turnover number of ∼57 has been obtained. These catalysts can be recycled and reused without a significant loss of catalytic activity

Near Unity Quantum Yield of Light-Driven Redox Mediator Reduction and Efficient H₂ Generation Using Colloidal Nanorod Heterostructures

The advancement of direct solar-to-fuel conversion technologies requires the development of efficient catalysts as well as efficient materials and novel approaches for light harvesting and charge separation. We report a novel system for unprecedentedly efficient (with near-unity quantum yield) light-driven reduction of methylviologen (MV²⁺), a common redox mediator, using colloidal quasi-type II CdSe/CdS dot-in-rod nanorods as a light absorber and charge separator and mercaptopropionic acid as a sacrificial electron donor. In the presence of Pt nanoparticles, this system can efficiently convert sunlight into H₂, providing a versatile redox mediator-based approach for solar-to-fuel conversion. Compared to related CdSe seed and CdSe/CdS core/shell quantum dots and CdS nanorods, the quantum yields are significantly higher in the CdSe/CdS dot-in-rod structures. Comparison of charge separation, recombination and hole filling rates in these complexes showed that the dot-in-rod structure enables ultrafast electron transfer to methylviologen, fast hole removal by sacrificial electron donor and slow charge recombination, leading to the high quantum yield for MV²⁺ photoreduction. Our finding demonstrates that by controlling the composition, size and shape of quantum-confined nanoheterostructures, the electron and hole wave functions can be tailored to produce efficient light harvesting and charge separation materials

Syntheses, Structural Characterization, and Catalytic Properties of Di- and Trinickel Polyoxometalates

The syntheses, structural characterization, and catalytic properties of two different nickel-containing polyoxometalates (POMs) are presented. The dinickel-containing sandwich-type POM [Ni₂(P₂W₁₅O₅₆)₂]^20– (<b>Ni</b>_<b>2</b>) exhibits an unusual αααα geometry. The trinickel-containing Wells–Dawson POM [Ni₃(OH)₃(H₂O)₃P₂W₁₆O₅₉]^9– (<b>Ni</b>_<b>3</b>) shows a unique structure where the [α-P₂W₁₅O₅₆]^12– ligand is capped by a triangular Ni₃O₁₃ unit and a WO₆ octahedron. <b>Ni</b>_<b>3</b> shows a high catalytic activity for visible-light-driven hydrogen evolution, while the activity for <b>Ni</b>_<b>2</b> is minimal. An analysis of the structures of multinickel-containing POMs and their hydrogen evolution activity is given

All-Inorganic Bis-Sb₃O₃‑Functionalized A‑Type Anderson–Evans Polyoxometalate for Visible-Light-Driven Hydrogen Production

An all-inorganic, novel bis-Sb3O3-functionalized A-type Anderson–Evans polyoxometalate, [Ni­(H2O)6]­KH­[NiMo6O24(Sb3O3)2]·5H2O (1), has been synthesized under hydrothermal conditions. The chemical composition, molecular structure, and elemental oxidation states of the resulting compound have been systematically characterized by various techniques, including single-crystal X-ray diffraction, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy. The title complex 1 has been investigated for the first time as a catalyst for visible-light-driven hydrogen production by coupling with a [Ir­(coumarin)2(dtbbpy)]­[PF6] photosensitizer and a triethanolamine (TEOA) sacrificial electron donor. Under minimally optimized conditions, a H2 generation rate of as high as 10 358 μmol g–1 h–1 is achieved during a 6 h photocatalysis. Additional control experiments and spectroscopic analyses have demonstrated that complex 1 will undergo the in situ photoreduction during photocatalysis and its specific geometric structure is essential to efficient photocatalysis for H2 production

CsPbBr₃/Polyoxometalate Composites for Selective Photocatalytic Oxidation of Benzyl Alcohol

Selective oxidation of benzyl alcohols to the corresponding carbonyl compounds is of great importance for providing versatile intermediates for the synthesis of pharmaceuticals and fine chemicals. In this work, we constructed a CsPbBr3/[Ni4(H2O)2(PW9O34)2]10– (CsPbBr3/Ni4P2) composite by integrating the visible light-responsive ability of CsPbBr3 and the multielectron-transfer ability of polyoxometalates. The resulting CsPbBr3/Ni4P2 composite exhibited good photocatalytic activity toward the selective conversion of benzyl alcohol to benzaldehyde with ∼100% selectivity. Mechanistic studies revealed that the tetra-nickel-substituted polyoxotungstate, Ni4P2, played crucial roles in the separation/migration and utilization of photogenerated charge carries due to its well-matched energy level with that of CsPbBr3 and the distinctive electron/proton-transferring ability as a redox shuttle. Multiple scavenging experiments confirmed that the photogenerated electrons (e–), holes (h+), •O2–, and 1O2 were key reactive species for efficient photocatalysis

40Ni-Added Poly(polyoxometalate) Assembled by {Ni₆GeW₉} and {Ni₈(GeW₉)₂} Units: Structure, Magnetic, and Heterogeneous Catalysis Properties

A novel 40Ni-added germanotungstate, Cs8K14Na3H3{[Ni6(OH)3(H2O)6(B-α-GeW9O34)]2[Ni8(μ6–O)(μ2–OH)2 (μ3–OH)2(H2O)B2O3(OH)2(B-α-GeW9O34)2]}2·84H2O (1), was made by the reaction of the trivacant [A-α-GeW9O34]10– ({GeW9}) precursor with Ni2+ cations and B5O8–, and systematically investigated by Fourier-transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and powder X-ray diffraction. Single crystal X-ray analysis indicates that the polyoxoanion of 1 is a novel octamer constructed by {Ni6GeW9} and {Ni8(GeW9)2} structural building units via Ni–OW linkages. The magnetic behavior shows the existence of overall ferromagnetic interactions among the Ni2+ centers in compound 1. Photocatalytic H2 production studies have implied that 1 can work as a heterogeneous catalyst for hydrogen production with decent robustness and recyclability

Hole Removal Rate Limits Photodriven H₂ Generation Efficiency in CdS-Pt and CdSe/CdS-Pt Semiconductor Nanorod–Metal Tip Heterostructures

Semiconductor–metal nanoheterostructures, such as CdSe/CdS dot-in-rod nanorods with a Pt tip at one end (or CdSe/CdS-Pt), are promising materials for solar-to-fuel conversion because they allow rational integration of a light absorber, hole acceptor, and electron acceptor or catalyst in an all-inorganic triadic heterostructure as well as systematic control of relative energetics and spatial arrangement of the functional components. To provide design principles of such triadic nanorods, we examined the photocatalytic H₂ generation quantum efficiency and the rates of elementary charge separation and recombination steps of CdSe/CdS-Pt and CdS-Pt nanorods. We showed that the steady-state H₂ generation quantum efficiencies (QEs) depended sensitively on the electron donors and the nanorods. Using ultrafast transient absorption spectroscopy, we determined that the electron transfer efficiencies to the Pt tip were near unity for both CdS and CdSe/CdS nanorods. Hole transfer rates to the electron donor, measured by time-resolved fluorescence decay, were positively correlated with the steady-state H₂ generation QEs. These results suggest that hole transfer is a key efficiency-limiting step. These insights provide possible ways for optimizing the hole transfer step to achieve efficient solar-to-fuel conversion in semiconductor–metal nanostructures

Syntheses, Structural Characterization, and Catalytic Properties of Di- and Trinickel Polyoxometalates

The syntheses, structural characterization, and catalytic properties of two different nickel-containing polyoxometalates (POMs) are presented. The dinickel-containing sandwich-type POM [Ni₂(P₂W₁₅O₅₆)₂]^20– (<b>Ni</b>_<b>2</b>) exhibits an unusual αααα geometry. The trinickel-containing Wells–Dawson POM [Ni₃(OH)₃(H₂O)₃P₂W₁₆O₅₉]^9– (<b>Ni</b>_<b>3</b>) shows a unique structure where the [α-P₂W₁₅O₅₆]^12– ligand is capped by a triangular Ni₃O₁₃ unit and a WO₆ octahedron. <b>Ni</b>_<b>3</b> shows a high catalytic activity for visible-light-driven hydrogen evolution, while the activity for <b>Ni</b>_<b>2</b> is minimal. An analysis of the structures of multinickel-containing POMs and their hydrogen evolution activity is given

Chiral {Ni₆PW₉} Cluster–Organic Framework: Synthesis, Structure, and Properties

A chiral three-dimensional polyoxometalate cluster–organic framework (POMCOF) H3[(btc)­Ni6(μ3-OH)3(H2O)5(B-α-PW9O34)]·17H2O (1, btc = 1,2,4-benzenetricarboxylate) has been made under hydrothermal conditions in the absence of amine or chiral starting reagents. 1 shows high stability in CH3CN/DMF (1:3), acidic, and basic solutions with the pH ranging from 2 to 12 for 5 days. The UV–vis reflectance spectra and Mott–Schottky measurements reveal that 1 could be a suitable catalyst for photocatalysis. Visible-light-driven H2 evolution studies have demonstrated that 1 is an ecofriendly, efficient, and recyclable catalyst with a H2 evolution rate of 1058.24 μmol h–1g–1. Nonlinear optical (NLO) measurement reveals that 1 exhibits a second-harmonic generation (SHG) response of about 1.4 times that of KH2PO4 (KDP), indicating that 1 is a potential NLO material as well

Catalytic Light-Driven Generation of Hydrogen from Water by Iron Dithiolene Complexes

The development of active, robust systems for light-driven hydrogen production from aqueous protons based on catalysts and light absorbers composed solely of earth abundant elements remains a challenge in the development of an artificial photosynthetic system for water splitting. Herein, we report the synthesis and characterization of four closely related Fe bis­(benzenedithiolate) complexes that exhibit catalytic activity for hydrogen evolution when employed in systems with water-soluble CdSe QDs as photosensitizer and ascorbic acid as a sacrificial electron source under visible light irradiation (520 nm). The complex with the most electron-donating dithiolene ligand exhibits the highest activity, the overall order of activity correlating with the reduction potential of the formally Fe­(III) dimeric dianions. Detailed studies of the effect of different capping agents and the extent of surface coverage of these capping agents on the CdSe QD surfaces reveal that they affect system activity and provide insight into the continued development of such systems containing QD light absorbers and molecular catalysts for H₂ formation