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Polyampholytic Graft Copolymers as Matrix for TiO₂ /Eosin Y/[Mo₃ S₁₃ ]^2- Hybrid Materials and Light-Driven Catalysis.

ABSTRACT: An effective strategy to enhance the performance of inorganic semiconductors is moving towards organic-inorganic hybrid materials. Here, we report the design of core-shell hybrid materials based on a TiO₂ core functionalized with a polyampholytic (poly(dehydroalanine)-graft-(n-propyl phosphonic acid acrylamide) shell (PDha-g-PAA@TiO₂ ). The PDha-g-PAA shell facilitates the efficient immobilization of the photosensitizer Eosin Y (EY) and enables electronic interactions between EY and the TiO₂ core. This resulted in high visible-light-driven H₂ generation. The enhanced light-driven catalytic activity is attributed to the unique core-shell design with the graft copolymer acting as bridge and facilitating electron and proton transfer, thereby also preventing the degradation of EY. Further catalytic enhancement of PDha-g-PAA@TiO₂ was possible by introducing [Mo₃ S₁₃ ]^2- cluster anions as hydrogen-evolution cocatalyst. This novel design approach is an example for a multi-component system in which reactivity can in future be independently tuned by selection of the desired molecular or polymeric species.

SUBMITTER: Nabiyan A

PROVIDER: S-EPMC9290844 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Structural Properties of Gas-Phase Molybdenum Oxide Clusters [Mo4O13]2-, [HMo4O13]-, and [CH3Mo4O13]- Studied by Collision-Induced Dissociation.

Project description:Molybdenum oxide-based catalysts are widely used for the ammoxidation of toluene, methanation of CO, or hydrodeoxygenation. As a first step towards a gas-phase model system, we investigate here structural properties of mass-selected [Mo4O13]2-, [HMo4O13]-, and [CH3Mo4O13]- by a combination of collision-induced dissociation (CID) experiments and quantum chemical calculations. According to calculations, the common structural motif is an eight-membered ring composed of four MoO2 units and four O atoms. The 13th O atom is located above the center of the ring and connects two to four Mo centers. For [Mo4O13]2- and [HMo4O13]-, dissociation requires opening or rearrangement of the ring structure, which is quite facile for the doubly charged [Mo4O13]2-, but energetically more demanding for [HMo4O13]-. In the latter case, the hydrogen atom is found to stay preferentially with the negatively charged fragments [HMo2O7]- or [HMoO4]-. The doubly charged species [Mo4O13]2- loses one MoO3 unit at low energies while Coulomb explosion into the complementary fragments [Mo2O6]- and [Mo2O7]- dominates at elevated collision energies. [CH3Mo4O13]- affords rearrangements of the methyl group with low barriers, preferentially eliminating formaldehyde, while the ring structure remains intact. [CH3Mo4O13]- also reacts efficiently with water, leading to methanol or formaldehyde elimination.

| S-EPMC6805806 | biostudies-literature

Structural Properties of Gas Phase Molybdenum Sulfide Clusters [Mo3S13]2-, [HMo3S13]-, and [H3Mo3S13]+ as Model Systems of a Promising Hydrogen Evolution Catalyst.

Project description:Amorphous molybdenum sulfide (MoS x ) is a potent catalyst for the hydrogen evolution reaction (HER). Since mechanistic investigations on amorphous solids are particularly difficult, we use a bottom-up approach and study the [Mo3S13]2- nanocluster and its protonated forms. The mass selected pure [Mo3S13]2- as well as singly and triply protonated [HMo3S13]- and [H3Mo3S13]+ ions, respectively, were investigated by a combination of collision induced dissociation (CID) experiments and quantum chemical calculations. A rich variety of H x S y elimination channels was observed, giving insight into the structural flexibility of the clusters. In particular, it was calculated that the observed clusters tend to keep the Mo3 ring structure found in the bulk and that protons adsorb primarily on terminal disulfide units of the cluster. Mo-H bonds are formed only for quasi-linear species with Mo centers featuring empty coordination sites. Protonation leads to increased cluster stability against CID. The rich variety of CID dissociation products for the triply protonated [H3Mo3S13]+ ion, however, suggests that it has a large degree of structural flexibility, with roaming H/SH moieties, which could be a key feature of MoS x to facilitate HER catalysis via a Volmer-Heyrovsky mechanism.

| S-EPMC6453024 | biostudies-literature

[Mo3 S13 ]2- as a Model System for Hydrogen Evolution Catalysis by MoSx : Probing Protonation Sites in the Gas Phase by Infrared Multiple Photon Dissociation Spectroscopy.

Project description:Materials based on molybdenum sulfide are known as efficient hydrogen evolution reaction (HER) catalysts. As the binding site for H atoms on molybdenum sulfides for the catalytic process is under debate, [HMo3 S13 ]- is an interesting molecular model system to address this question. Herein, we probe the [HMo3 S13 ]- cluster in the gas phase by coupling Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS) with infrared multiple photon dissociation (IRMPD) spectroscopy. Our investigations show one distinct S-H stretching vibration at 2450 cm-1 . Thermochemical arguments based on DFT calculations strongly suggest a terminal disulfide unit as the H adsorption site.

| S-EPMC7986116 | biostudies-literature

Total synthesis of [13 C]2 -, [13 C]3 -, and [13 C]5 -isotopomers of xanthohumol, the principal prenylflavonoid from hops.

Project description:Xanthohumol [(E)-6'-methoxy-3'-(3-methylbuten-2-yl)-2',4',4″-trihydroxychalcone], he principal prenylated flavonoid from hops, has a complex bioactivity profile, and 13 C-labeled isotopomers of this compound are of potential use as molecular probes and as analytical standards to study metabolism and mode of action. 1,3-[13 C]2 -Xanthohumol was prepared by an adaptation of the total synthesis of Khupse and Erhardt in 7 steps and 5.7% overall yield from phloroglucinol by a route incorporating a cascade Claisen-Cope rearrangement to install the 3'-prenyl moiety from a 5'-prenyl aryl ether and an aldol condensation between 1-[13 C]-2',4'-bis(benzyloxymethyloxy)-6'-methoxy-3'-(3-methylbuten-2-yl)acetophenone and 1'-[13 C]-4-(methoxymethyloxy)benzaldehyde. The 13 C-atom in the methyl ketone was derived from 1-[13 C]-acetyl chloride while that in the aryl aldehyde was derived from [13 C]-iodomethane. Tri- and penta-13 C-labeled xanthohumols were similarly prepared by applying minor modifications to the route.

| S-EPMC5832448 | biostudies-literature

Substitutions of Zr4+/V5+ for Y3+/Mo6+ in Y2Mo3O12 for Less Hygroscopicity and Low Thermal Expansion Properties.

Project description:In this investigation, ZrxY2-xVxMo3-xO12 (0 ≤ x ≤ 1.4) is developed and the effects of the substitutions of Zr4+/V5+ for Y3+/Mo6+ in Y2Mo3O12 on the hygroscopicity and thermal expansion property are investigated. For the smaller substitution content (x ≤ 0.5), their crystal structures remain orthorhombic, while there is crystal water still in the lattice. The linear coefficients of thermal expansions (CTEs), for x = 0.1, 0.3, 0.5, and 0.7, are about -4.30 × 10-6, -0.97 × 10-6, 0.85 × 10-6, and 0.77 × 10-6 K-1, respectively, from 476 to 773 K, which means that the linear CTE could be changed linearly with the substitution content of Zr4+/V5+ for Y3+/Mo6+ in Y2Mo3O12. As long as the substitution content reaches x = 1.3/1.4, almost no hygroscopicity and low thermal expansion from room temperature are obtained and are discussed in relation to the crystal structure and microstructure.

| S-EPMC6926913 | biostudies-literature

Steric Switching From Photochemical to Thermal N2 Splitting: A Computational Analysis of the Isomerization Reaction {(Cp*)(Am)Mo}2(?-?1:?1-N2) ? {(Cp*)(Am)Mo}2(?-N)2.

Project description:A ?-?1:?1-N2-bridged Mo dimer, {(?5-C5Me5)[N(Et)C(Ph)N(Et)]Mo}2(?-N2), cleaves dinitrogen thermally resulting in a crystallographically characterized bis-?-N-bridged dimer, {(?5-C5Me5)[N(Et)C(Ph)N(Et)]Mo}2(?-N)2. A structurally related Mo dimer with a bulkier amidinate ligand, ([N(iPr)C(Me)N(iPr)]), is only capable of photochemical dinitrogen activation. These opposing reactivities were rationalized as steric switching between the thermally and photochemically active species. A computational analysis of the geometric and electronic structures of intermediates along the isomerization pathway from Mo2(?-?1:?1-N2) to Mo2(?-?2:?1-N2) and Mo2(?-?2:?2-N2), and finally Mo2(?-N)2, is presented here. The extent to which dispersion affects the thermodynamics of the isomers is evaluated, and it is found that dispersion interactions play a significant role in stabilizing the product and making the reaction exergonic. The concept of steric switching is further explored with theoretical models with sterically even less demanding ligands, indicating that systematic ligand modifications could be used to rationally design the N2 activation energy landscape. An analysis of electronic excitations in the computed UV-vis spectra of the two complexes shows that a particular type of asymmetric excitations is only present in the photoactive complex.

| S-EPMC6535493 | biostudies-literature

Selective growth of Ti3+/TiO2/CNT and Ti3+/TiO2/C nanocomposite for enhanced visible-light utilization to degrade organic pollutants by lowering TiO2-bandgap.

Project description:A convenient route was developed for the selective preparation of two stable nanocomposites, Ti3+/TiO2/CNT (labeled as TTOC-1 and TTOC-3) and Ti3+/TiO2/carbon layer (labeled as TTOC-2), from the same precursor by varying the amount of single-walled carbon nanotubes used in the synthesis. TiO2 is an effective photocatalyst; however, its wide bandgap limits its usefulness to the UV region. As a solution to this problem, our prepared nanocomposites exhibit a small bandgap and wide visible-light (VL) absorption because of the introduction of carbonaceous species and Ti3+ vacancies. The photocatalytic efficiency of the nanocomposites was examined via the degradation of methylene blue dye under VL. Excellent photocatalytic activity of 83%, 98%, and 93% was observed for TTOC-1, TTOC-2, and TTOC-3 nanocomposites within 25 min. In addition, the photocatalytic degradation efficiency of TTOC-2 toward methyl orange, phenol, rhodamine B, and congo red was 28%, 69%, 71%, and 91%, respectively, under similar experimental conditions after 25 min. Higher reusability and structural integrity of the as-synthesized photocatalyst were confirmed within five consecutive runs by photocatalytic test and X-ray diffraction analysis, respectively. The resulting nanocomposites provide new insights into the development of VL-active and stable photocatalysts with high efficiencies.

| S-EPMC8096813 | biostudies-literature

Enhanced Solar Photothermal Catalysis over Solution Plasma Activated TiO2.

Project description:Colored wide-bandgap semiconductor oxides with abundant mid-gap states have long been regarded as promising visible light responsive photocatalysts. However, their catalytic activities are hampered by charge recombination at deep level defects, which constitutes the critical challenge to practical applications of these oxide photocatalysts. To address the challenge, a strategy is proposed here that includes creating shallow-level defects above the deep-level defects and thermal activating the migration of trapped electrons out of the deep-level defects via these shallow defects. A simple and scalable solution plasma processing (SPP) technique is developed to process the presynthesized yellow TiO2 with numerous oxygen vacancies (Ov), which incorporates hydrogen dopants into the TiO2 lattice and creates shallow-level defects above deep level of Ov, meanwhile retaining the original visible absorption of the colored TiO2. At elevated temperature, the SPP-treated TiO2 exhibits a 300 times higher conversion rate for CO2 reduction under solar light irradiation and a 7.5 times higher removal rate of acetaldehyde under UV light irradiation, suggesting the effectiveness of the proposed strategy to enhance the photoactivity of colored wide-bandgap oxides for energy and environmental applications.

| S-EPMC7435248 | biostudies-literature

Convergent synthesis of 13N-labelled Peptidic structures using aqueous [13N]NH3.

Project description:BackgroundNitrogen-13 has a 10-min half-life which places time constraints on the complexity of viable synthetic methods for its incorporation into PET imaging agents. In exploring ways to overcome this limitation, we have used the Ugi reaction to develop a rapid one-pot method for radiolabelling peptidic molecules using [13N]NH3 as a synthetic precursor.MethodsCarrier-added [13N]NH3 (50 μL) was added to a solution of carboxylic acid, aldehyde, and isocyanide in 2,2,2-TFE (200 μL). The mixture was heated in a microwave synthesiser at 120 °C for 10 min. Reactions were analysed by radio-HPLC and radio-LCMS. Isolation of the target 13N-labelled peptidic Ugi compound was achieved via semi-preparative radio-HPLC as demonstrated for Ugi1.ResultsRadio-HPLC analysis of each reaction confirmed the formation of radioactive products co-eluting with their respective reference standards with radiochemical yields of the crude products ranging from 11% to 23%. Two cyclic γ-lactam structures were also achieved via intra-molecular reactions. Additional radioactive by-products observed in the radio-chromatogram were identified as 13N-labelled di-imines formed from the reaction of [13N]NH3 with two isocyanide molecules. The desired 13N-labelled Ugi product was isolated using semi-preparative HPLC.ConclusionWe have developed a one-pot method that opens up new routes to radiolabel complex, peptidic molecules with 13N using aqueous [13N]NH3 as a synthetic precursor.

| S-EPMC5824707 | biostudies-literature

Ag2Mo2O7: an oxide solid-state Ag+ electrolyte.

Project description:Ag2Mo2O7 powders and micro-crystals were prepared at 400 °C for 24 h and 500 °C for 6 h using solid-state reactions. The Ag2Mo2O7 samples crystalized in a triclinic P1̄ space group with the cell parameters a = 6.0972(1) Å, b = 7.5073(1) Å, c = 7.6779(2) Å, α = 110.43(1)°, β = 93.17(1)°, γ = 113.51(1)°, and V = 294.17(1) Å3 from Rietveld refinements. Ag2Mo2O7 powder is homogeneous with size of 2-8 μm and the ceramic pellets are in good sintering conditions with a relative density ∼93%. The indirect band gaps E g(i) of Ag2Mo2O7 from reflectance measurements and DFT calculations are 2.63(1) and 1.80 eV. The vibrational modes of Ag2Mo2O7 were investigated by first-principles (DFT) calculations and Raman spectrum measurements with 24 of 33 predicted Raman modes recorded. According to DOS analyses, the valence bands (VB) of Ag2Mo2O7 are mainly constituted of O-2p and Ag-4d orbitals, while the conduction bands (CB) are mainly composed of Mo-4d and the O-2p orbitals. Regarding the impedance analysis, Ag2Mo2O7 is a silver oxide ion electrolyte with a conductivity of ∼5 × 10-4 S cm-1 at 450 °C. The carrier activation energy of Ag2Mo2O7 is 0.88(3) eV from the temperature dependent conductivity measurements.

| S-EPMC8979251 | biostudies-literature