Metal heteroanionic compounds such as oxynitrides, oxysulfides, and oxyhalides have emerged as promising photocatalysts for water splitting, owing to their reduced band gaps compared to conventional oxides. Nonetheless, many of these compounds undergo self-oxidation of the non-oxide anions by photogenerated holes. Herein, we present new metal oxychloride intergrowths based on Bi4TaO8Cl–Bi2GdO4Cl as stable visible light photocatalysts. These intergrowths were prepared using a halide flux method, with their crystal structures analyzed by Rietveld refinement of powder X-ray diffraction data and high-resolution scanning transmission electron microscopy. These analyses support intergrowth formation. The Ta/Gd molar ratio was systematically varied in the intergrowths to rationalize the effect of charge separation and changes in band structure toward photocatalytic water-splitting activity. Furthermore, these intergrowths are capable of sustained overall water splitting in a Z-scheme with Ru/SrTiO3/Rh as a hydrogen evolution catalyst. The high stability of these intergrowth materials is attributed to O 2p orbitals at the valance band edge rather than Cl 3p orbitals, as discerned from electronic structure calculations. These results provide new strategies for designing durable artificial photosynthetic systems by rational modulation of crystal and electronic structure.

To improve their synthesis and ultimately realize the technical promise of two-dimensional covalent organic frameworks (2D COFs), it is imperative that a robust understanding of their structure be developed. However, high-resolution transmission electron microscopy (HR-TEM) imaging of such beam-sensitive materials is an outstanding characterization challenge. Here, we overcome this challenge by leveraging low electron flux imaging conditions and high-speed direct electron counting detectors to acquire high-resolution images of 2D COF films. We developed a Fourier mapping technique to rapidly extract nanoscale structural information from these TEM images. This postprocessing script analyzes the evolution of 2D Fourier transforms across a TEM image, which yields information about polycrystalline domain orientations and enables quantification of average domain sizes. Moreover, this approach provides information about several types of defects present in a film, such as overlapping grains and various types of grain boundaries. We also find that the pre-eminent origin of defects in COF-5 films, a prototypical boronate ester-linked COF, arises as a consequence of broken B−O bonds formed during polymerization. These results suggest that the nanoscale features observed are a direct consequence of chemical phenomena. Taken together, this mapping approach provides information about the fundamental microstructure and crystallographic underpinnings of 2D COF films, which will guide the development of future 2D polymerization strategies and help realize the goal of using 2D COFs in a host of thin-film device architectures.

Molybdenum nitrides have been employed in a variety of applications. For use in catalysis, the cubic γ phase with the nominal stoichiometry Mo 2 N and the space group Fm3̅ m is typically prepared by high-temperature reaction of MoO 3 with NH 3 . The literature presents conflicting reports of the possible presence of residual oxygen from typical ammonolysis reactions and whether such species influence the crystal structure and morphology. With the aim of resolving these open questions, a comprehensive study of the chemistry, crystal structure, and electronic structure of molybdenum nitride materials prepared by ammonolysis has been undertaken here, with particular focus on the role of reaction temperature. Ammonolysis of MoO 3 was carried out at 973 and 1073 K and yielded single-phase cubic products. Using electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, prompt gamma-ray neutron activation analysis, and combustion analysis, significant concentrations of oxygen and, to a lesser extent, hydrogen were found in both materials. The crystal structure of each phase was refined by Rietveld analysis using combined synchrotron X-ray diffraction and neutron diffraction data. The structures were found to be derivatives of the B1 rock salt (halite) structure, as is often reported for "γ-Mo 2 N." However, both materials adopt the space group Pm3̅ m, as opposed to the typically presumed space group of Fm3̅ m, and both have much higher anion content than implied by the stoichiometry Mo 2 N. Ordering of cation vacancies and of anion species is responsible for the loss of the translational symmetry expected for the space group Fm3̅ m. X-ray absorption spectroscopy studies, along with the EELS and XPS results, showed the Mo oxidation state to be diminished with higher temperature synthesis, consistent with the retention of a lower concentration of anions and in particular oxygen. The difficulty in differentiating oxygen and nitrogen and the impossibility of detecting hydrogen by X-ray and electron diffraction methods, especially in the presence of the heavy element Mo, have likely inhibited accurate identification of Mo 1−x (N 1−y O y )H z as the product of MoO 3 ammonolysis. The findings reported here offer a critical assessment for understanding the properties of molybdenum "nitrides" in electronic and catalytic applications.

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We report a reactive flux technique using the common reagent P 2 S 5 and metal precursors developed to circumvent the synthetic bottleneck for producing high-quality single-and mixed-metal two-dimensional (2D) thiophosphate materials. For the monometallic compound, M 2 P 2 S 6 (M = Ni, Fe, and Mn), phase-pure materials were quickly synthesized and annealed at 650 °C for 1 h. Crystals of dimensions of several millimeters were grown for some of the metal thiophosphates using optimized heating profiles. The homogeneity of the bimetallic thiophosphates MM′P 2 S 6 (M, M′ = Ni, Fe, and Mn) was elucidated using energy-dispersive X-ray spectroscopy and Rietveld refinement. The quality of the selected materials was characterized by transmission electron microscopy and atomic force microscopy measurements. We report two novel bimetallic thiophosphates, MnCoP 2 S 6 and FeCoP 2 S 6 . The Ni 2 P 2 S 6 and MnNiP 2 S 6 flux reactions were monitored in situ using variable-temperature powder X-ray diffraction to understand the formation reaction pathways. The phases were directly formed in a single step at approximately 375 °C. The work functions of the semiconducting materials were determined and ranged from 5.28 to 5.72 eV.