Reducing the computational cost of NMR crystallography of organic powders at natural isotopic abundance with the help of 13C-13C dipolar couplings

Structure determination of functional organic compounds remains a formidable challenge when the sample exists as a powder. Nuclear magnetic resonance crystallography approaches based on the comparison of experimental and Density Functional Theory (DFT)-computed ¹H chemical shifts have already demonstrated great potential for structure determination of organic powders, but limitations still persist. In this study, we discuss the possibility of using ¹³C-¹³C dipolar couplings quantified on powdered theophylline at natural isotopic abundance with the help of dynamic nuclear polarization, to realize a DFT-free, rapid screening of a pool of structures predicted by ab initio random structure search. We show that although ¹³C-¹³C dipolar couplings can identify structures possessing long range structural motifs and unit cell parameters close to those of the true structure, it must be complemented with other data to recover information about the presence and the chemical nature of the supramolecular interactions.     

Activation of α-Fe2O3 for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Photoelectrochemical (PEC) water splitting is a promising method for the conversion of solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α-Fe₂O₃) is one of the most attractive materials for a highly efficient charge carrier generation and collection due to its large specific surface area and the short minority carrier diffusion length. In the present work, the PEC water splitting performance of nanostructured α-Fe₂O₃ is investigated which was prepared by anodization followed by annealing in a low oxygen ambient (0.03 % O₂ in Ar). It was found that low oxygen annealing can activate a significant PEC response of α-Fe₂O₃ even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The photocurrent of the α-Fe₂O₃ annealed in the low oxygen at 1.5 V vs. RHE results as 0.5 mA cm⁻², being 20 times higher than that of annealing in air. The obtained results show that the α-Fe₂O₃ annealed in low oxygen contains beneficial defects and promotes the transport of holes; it can be attributed to the improvement of conductivity due to the introduction of suitable oxygen vacancies in the α-Fe₂O₃. Additionally, we demonstrate the photocurrent of α-Fe₂O₃ annealed in low oxygen ambient can be further enhanced by Zn-Co LDH, which is a co-catalyst of oxygen evolution reaction. This indicates low oxygen annealing generates a promising method to obtain an excellent PEC water splitting performance from α-Fe₂O₃ photoanodes.     

Multimetallic Oxynitrides Nanoparticles for a New Generation of Photocatalysts

A versatile synthetic strategy for the preparation of multimetallic oxynitrides has been designed and here exemplarily discussed considering the preparation of nanoscaled zinc–gallium oxynitrides and zinc–gallium–indium oxynitrides, two important photocatalysts of new generation, which proved to be active in key energy related processes from pollutant decomposition to overall water splitting. The synthesis presented here allows the preparation of small nanoparticles (less than 20 nm in average diameter), well-defined in size and shape, yet highly crystalline and with the highest surface area reported so far (up to 80 m² g⁻¹). X-ray diffraction studies show that the final material is not a mixture of single oxides but a distinctive compound. The photocatalytic properties of the oxynitrides have been tested towards the decomposition of an organic dye (as a model reaction for the decomposition of air pollutants), showing better photocatalytic performances than the corresponding pure phases (reaction constant 0.22 h⁻¹), whereas almost no reaction was observed in absence of catalyst or in the dark. The photocatalysts have been also tested for H₂ evolution (semi-reaction of the water splitting process) with results comparable to the best literature values but leaving room for further improvement.     

Synergism of Interface and Electronic Effects: Bifunctional N-Doped Ni3S2/N-Doped MoS2 Hetero-Nanowires for Efficient Electrocatalytic Overall Water Splitting

The realization of water electrolysis on the basis of highly active, cost-effective electrocatalysts is significant yet challenging for achieving sustainable hydrogen production from water. Herein, N-doped Ni₃S₂/N-doped MoS₂ 1D hetero-nanowires supported by Ni foam (N-Ni₃S₂/N-MoS₂/NF) are readily synthesized through a chemical transformation strategy by using NiMoO₄ nanowire array growth on Ni foam (NiMoO₄/NF) as the starting material. With the in situ generation of Ni₃S₂/MoS₂ heterointerfaces within nanowires and the incorporation of N⁻ anions, an extraordinary hydrophilic nature with abundant, well-exposed active sites and optimal reaction dynamics for both oxidation and reduction of water are obtained. Attributed to these properties, as-converted N-Ni₃S₂/N-MoS₂/NF exhibits highly efficient electrocatalytic activities for both hydrogen and oxygen evolution reactions under alkaline conditions. The superior bifunctional properties of N-Ni₃S₂/N-MoS₂/NF enable it to effectively catalyze the overall water-splitting reaction.     

Colloidally Stable CdS Quantum Dots in Water with Electrostatically Stabilized Weak-Binding,Sulfur-Free Ligands

Colloidal quantum dot (QD) photocatalysts have the electrochemical and optical properties to be highly effective for a range of redox reactions. QDs are proven photo-redox catalysts for a variety of reactions in organic solvents but are less prominent for aqueous reactions. Aqueous QD photocatalysts require hydrophilic ligand shells that provide long-term colloidal stability but are not so tight-binding as to prevent catalytic substrates from accessing the QD surface. Common thiolate ligands, which also poison many co-catalysts and undergo photo-oxidative desorption, are therefore often not an option. This paper describes a framework for the design of water-solubilizing ligands that are in dynamic exchange on and off the QD surface, but still provide long-term colloidal stability to CdS QDs. The binding affinity and inter-ligand electrostatic interactions of a bifunctional ligand, aminoethyl phosphonic acid (AEP), are tuned with the pH of the dispersion. The key to colloidal stability is electrostatic stabilization of the monolayer. This work demonstrates a means of mimicking the stabilizing power of a thiolate-bound ligand with a zwitterionic tail group, but without the thiolate binding group.     

Advantageous Interfacial Effects of AgPd/g-C3N4 for Photocatalytic Hydrogen Evolution: Electronic Structure and H2O Dissociation

Bimetallic AgPd nanoparticles have been synthesized before, but the interfacial electronic effects of AgPd on the photocatalytic performance have been investigated less. In this work, the results of hydrogen evolution suggest that the bimetallic AgPd/g-C₃N₄ sample has superior activity to Ag/g-C₃N₄ and Pd/g-C₃N₄ photocatalysts. The UV/Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, CO adsorption diffuse reflectance FTIR spectroscopy, and FTIR results demonstrate that in the AgPd/g-C₃N₄, the surface electronic structures of Pd and Ag are changed, which is beneficial for faster photogenerated electron transfer and greater H₂O molecule adsorption. In situ ESR spectra suggest that, under visible light irradiation, there is more H₂O dissociation to radical species on the AgPd/g-C₃N₄ photocatalyst. Furthermore, DFT calculations confirm the interfacial electronic effects of AgPd/g-C₃N₄, that is, Pd^δ−⋅⋅⋅Ag^δ+, and the activation energy of H₂O molecule dissociation on AgPd/g-C₃N₄ is the lowest, which is the main contributor to the enhanced photocatalytic H₂ evolution.     

Transition-metal,organic solvent and base free α-hydroxylation of β-keto esters and β-keto amides with peroxides in water

Without employing any transition metal, organic solvent and base, a facile, economical and environmentally friendly strategy has been developed for the α-hydroxylation of β-keto esters and β-keto amides with peroxides via radical cross-coupling reaction in water under open-air conditions. This protocol allows a convenient access to various α-hydroxy-β-keto esters and α-hydroxy-β-keto amides with up to 92% yield (34 examples). Moreover, the reaction was successfully scaled up to gram quantity and mechanistic studies showed the radical pathway was involved in this hydroxylation.     

Nitrogen Doping and Carbon Coating Affects Substrate Selectivity of TiO2 Photocatalytic Organic Pollutant Degradation

A series of carbon-coated, nitrogen-doped titanium dioxide photocatalysts was produced and characterized. N-doped TiO₂ powder samples were prepared using a sol-gel method and subsequently used for making doped-TiO₂ thin films on glass substrates. Carbon layers were coated on the films by a thermal decomposition method using catechol. Diffuse reflectance spectra and Mott-Schottky analyses of the samples proved that nitrogen doping and carbon coating can slightly lower the band gap of TiO₂, broaden its absorption to visible light and enhance its n-type character. According to photocatalytic tests against model contaminants, carbon-coated nitrogen-doped TiO₂ films have better performance than simple TiO₂ on the degradation of Rhodamine B dye molecules, but are poorly effective for degrading 4-chlorophenol molecules. Several possible explanations are proposed for this result, supported by scavenging experiments. This reveals the importance of a broad substrate scope when assessing new photocatalytic materials for water treatment, something which is often overlooked in many literature studies.     

A detailed chemical kinetic model for the supercritical water oxidation of methylamine: The importance of imine formation

A detailed chemical kinetic model has been developed for supercritical water oxidation (SCWO) of methylamine, CH₃NH₂, providing insight into the intermediates and final products formed in this process as well as the dominant reaction pathways. The model was adapted from previous mechanisms, with a revision of the peroxyl radical chemistry to include imine formation, which has recently been identified as the dominant gas-phase pathway in amine oxidation. The developed model can reproduce previous experimental data on methylamine consumption and major product formation to reasonable accuracy, although with deficiencies in describing the induction time. Our simulations indicate that oxidation of the ^•CH₂NH₂ radical to methanimine, CH₂NH, is the major channel in methylamine SCWO, with subsequent hydrolysis of CH₂NH providing the experimentally observed reaction products ammonia and formaldehyde. Integral-averaged reaction rates were used to identify major reaction pathways, and a first-order sensitivity analysis indicated that the concentration of CH₃NH₂ is most sensitive to OH radical kinetics. Overall, this work clarifies the importance of imine chemistry in the oxidation of nitrogen-containing compounds and indicates that they are necessary to model these compounds in SCWO processes.     

A novel nano‐size lanthanum metal–organic framework based on 5‐amino‐isophthalic acid and phenylenediamine: Photoluminescence study and sensing applications

In this paper, a novel lanthanum metal–organic framework La‐MOF was prepared via hydrothermal and reflux methods. The La‐MOF was achieved through the reaction of a 5‐amino‐isophthalic acid with 1, 2‐phenylenediamine and lanthanum chloride. The prepared La‐MOF structure was confirmed by XRD, mass spectrometry, IR, UV–Vis and elemental analysis, whereas the size, and morphology was examined by FE‐SEM/EDX and HR‐TEM. The results indicated that the La‐MOF prepared via both methods have the same structure and composition. Meanwhile, the MOF yield, reaction time, morphology, physiochemical and sensing properties were highly depended on the used preparation method. The photoluminescence (PL) study was carried out for the La‐MOF, and the results showed that La‐MOF exhibits strong emission at 558 nm after excitation at 369 nm. Moreover, the PL data indicating that the La‐MOF has highly selective sensing properties for iron (III) competing with different metal ions. The Stern‐Völmer graph shows a linear calibration curve which achieved over a concentration range 1.0–500 μM of Fe³⁺ with a correlation coefficient, detection, and quantitation limits 0.998, 1.35 μM and 4.08 μM, respectively. According to the remarkable quenching of the PL intensity of La‐MOF using various concentrations of Fe³⁺, it was successfully used as a sensor for Fe³⁺detecting in different water resources (pure and waste) samples. The quenching mechanism was studied and it has a dynamic type and due to efficient energy transfer between the La‐MOF and Fe³⁺.