CrystEngComm最新文献

Expression of Concern for ‘The behavior of Ni nanotubes under the influence of environments with different acidities’ by Maksim D. Kutuzau et al., CrystEngComm, 2018, 20, 3258–3266, https://doi.org/10.1039/C8CE00362A.

The performance of NiFe-layered double hydroxides (LDHs) as electrocatalysts for the oxygen evolution reaction (OER) can be significantly enhanced through precise structural and compositional modifications. In this study, ammonium fluoride (NH₄F) was introduced as an effective reagent to tune the microstructure and cation distribution of NiFe-LDHs, which in turn influenced their OER activity. Through a one-step hydrothermal synthesis method, NiFe-LDHs were fabricated with varying amounts of NH₄F. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis revealed a shift in the oxidation states of Ni and Fe, with an increase in the proportion of high-valent cations in the NFL-7F sample. This shift was closely correlated with enhanced OER performance. Detailed characterization through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical tests demonstrated that the NFL-7F sample exhibited the best OER performance, including superior stability and activity, compared to other samples. The results indicate that NH₄F plays a crucial role in optimizing the electronic structure and morphology of NiFe-LDHs, thereby facilitating enhanced OER kinetics. This study provides valuable insights into the structure–performance relationship of NiFe-LDH catalysts and highlights the importance of tuning the oxidation states of metal cations for the development of efficient electrocatalysts.

The crystalline sponge (CS) method has become an important technique for structural elucidation of compounds that are challenging to crystallise. The impact of the CS environment on guest molecule conformations has not been systematically studied. We present a computational investigation of the conformations of organic molecules of varying flexibility in a set of experimentally determined CS structures, comparing them to gas phase conformers and, where available, pure and co-crystal structures. Via solid state and molecular density functional theory calculations, we quantify the total relative energy, conformational energy, and intramolecular strain of guest molecules, as well as framework strain. Our results show that while CS structures induce distortion in guest geometries (total relative energies up to 41 kJ mol⁻¹), they generally adopt low-energy conformations, often within 2 kJ mol⁻¹ of the global energy minimum. Intramolecular strain in CS structures is often lower than in conventional crystal structures, suggesting a more neutral packing environment where molecules are closer to their favoured isolated-molecule geometries. We also observe that multiple guests can influence each other's geometries, even in the absence of direct guest–guest interactions. These findings provide a quantification of conformational distortion that can form the basis for interpreting molecular geometries obtained from CS structures.

Developing new, high-efficiency and low-cost adsorbents is of significant importance for efficient removal of contaminants from wastewater. Herein, hierarchical nanowire-assembled Zn₃(OH)₂V₂O₇·2H₂O microspheres (ZVO Ms) are prepared by a facile L-threonine (L-Thr) assisted hydrothermal method and explored as nano-adsorbents for the removal of Pb²⁺ from simulated wastewater. A formation mechanism is proposed based on the morphological evolution. The optimal ZVO Ms demonstrate satisfactory adsorption performance for Pb²⁺ with a maximum adsorption capacity of 461.6 mg g⁻¹, and the removal efficiency is approximately three times higher than that of nanosheet-assembled ZVO Ms obtained in the absence of L-Thr. The adsorption isotherms and kinetics were well described by the Langmuir isotherm model and the pseudo-second-order model, respectively. The thermodynamic data indicate that Pb²⁺ adsorption is an endothermic and spontaneous chemical adsorption process. The adsorption mechanism is uncovered based on electrostatic attraction and ion exchange. The excellent adsorption performance may be attributed to unique hierarchical structures and higher surface areas, which accelerate the transport of reactant molecules and provide abundant active sites for adsorption of Pb²⁺. This work provides a reasonable strategy to prepare novel hierarchical micro/nanoarchitectures and the as-prepared ZVO adsorbent may be used as a candidate for the removal of Pb²⁺ contaminants in wastewater.

Correction for ‘The Sc₂W_xMo_3−xO₁₂ series as electrodes in alkali-ion batteries' by Junnan Liu et al., CrystEngComm, 2021, 23, 3880–3891, https://doi.org/10.1039/D1CE00318F.

As a representative p-type semiconductor, two-dimensional GaTe has recently attracted considerable attention due to its promising applications in future integrated electronic and optoelectronic devices. Here, h-GaTe thin films were grown on highly oriented pyrolytic graphite substrates using molecular beam epitaxy. By adjusting the growth temperature and source flux, h-GaTe thin films with various morphologies were obtained. Particularly, h-GaTe with screw dislocations can be achieved. The morphology, surface structure, and composition of the h-GaTe films were characterized using atomic force microscopy, scanning tunneling microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. This work provides new opportunities for h-GaTe as a candidate material in electronic and optoelectronic devices.

In high-pressure carbon science, the sp²-to-sp³ type phase transition (e.g., graphite-to-diamond) is considerably known, however, the sp³-to-sp² type phase transition remains inadequately understood. Due to the high bulk modulus, manipulating the crystal structure is challenging. Herein, we report the phase transition of tetrahedral amorphous carbon into graphite under transient pressure-dependent acoustic shocked conditions with the values of 2.0 MPa and 15.6 MPa and exposed to different shock pulses such as 0, 250 and 500 such that a shock-wave-induced superheating mechanism is put forth for the observed graphitization process. For clarity of the discussion, we represent case-1 for 2.0 MPa and case-2 for 16.5 MPa which refers to the two shock transient pressures. In the case-1 experiment, the values of the intensity ratio of the D-band and G-band (I_D/I_G ratio) are found to be 0.70, 0.83, and 0.82 for 0, 250 and 500 shocks, respectively. In the case-2 experiment, the I_D/I_G ratio values are found to be 0.70, 0.32, and 0.16 for 0, 250 and 500 shocks, respectively. In case 2, at the 500-shocked condition, the observed I_D/I_G value is nearly equal to the pure graphite single crystal. According to the XPS results, normalized intensity ratio values of the control and case-2 samples sp²/sp³ bands are found to be 1.0 and 7.14 which provides convincing evidence for the occurrence of sp³-to-sp² phase transition and HR-TEM results support the XPS and Raman results. As a result of a high degree of graphite formation, the proposed technique offers a new platform to manipulate the crystal structure of hard sp³ hybridized components, thereby a large-scale synthesis of graphite can be a reality.

The structural flexibility of fluorophores and their ability to display different conformations provides an opportunity to develop fluorescent polymorphs that exhibit tunable solid-state fluorescence. In this study, a conformationally flexible organic fluorophore (4-(diphenylamino)benzaldehyde (TPA-CHO)) was crystallized from polar to non-polar solvents, and the solid-state fluorescence and structural assembly were explored. TPA-CHO, a typical donor–acceptor fluorophore, showed solvent polarity-dependent locally excited (LE) state blue fluorescence in toluene and charge transfer (CT) state greenish-yellow fluorescence in polar DMF. In contrast, crystals obtained from polar DMF exhibited strong blue fluorescence (LE state, λ_max = 453 nm, ϕ_f = 2.54%), whereas crystals grown from hexane displayed greenish-yellow fluorescence (CT state) at 532 nm (ϕ_f = 7.68%) along with a weak emission at shorter wavelengths. Depending upon the solvent polarity, the crystals displayed dual fluorescence with varied LE and CT state fluorescence intensity between greenish-yellow (longer) and blue (shorter) wavelength emission. CIE chromaticity displayed fluorescence tuning from blue–greenish-yellow. Single-crystal structural analysis did not show any drastic change in the conformation or packing (polymorphism), and the same molecular packing was exhibited. However, a closer examination of the structure revealed subtle conformational differences dependent upon the solvent polarity. Although highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) calculations showed a similar intramolecular charge transfer (ICT) from the diphenylamine donor to the benzaldehyde acceptor in all crystals, the optical band gap comparison revealed a clear difference between the crystals and supported subtle conformation-controlled tunable fluorescence. Thus, the present work provides insight into the solvent–solute interactions of conformationally flexible molecules for designing tunable fluorescent functional materials.

Two new coordination polymers (compounds 1 and 2) based on the use of a V-shaped ligand L (9,9-bis(4-carboxyphenyl)fluorene) combined with Cu(NO₃)₂ or Zn(NO₃)₂ were synthesized and structurally characterized by single-crystal X-ray diffraction. These compounds add to the list of very few examples of reported CPs derived from ligands with a fluorene core. X-ray diffraction analysis revealed the structures of the compounds; 2D (1) and robust 3D (2) structures were reported, and their sorption and emission properties were analysed. Additionally, it was possible to isolate the following compounds as side products: compound 4, a 2D compound that is isomorphous to 1, and compound 3, a polymorph of 1.

Expanding the diameter and reducing the defect density of 4H silicon carbide (4H-SiC) single crystals are key development trends and primary challenges in the preparation of 4H-SiC single-crystal substrates. During the physical vapor transport (PVT) process, the thermal field is regulated by the furnace configuration and temperatures of the monitoring points, while crystal diameter enlargement is facilitated by the bevel of the crucible. In this study, experiments on enlarging the diameter of 200 mm 4H-SiC crystals have been conducted, with the radial and axial temperature gradient controlled by adjusting the shape of the graphite insulation and the temperatures of the monitoring points. The increase in radial temperature gradient successfully eliminated marginal polycrystals and polytype inclusions. Besides, increasing the radial or axial temperature gradient led to larger expanding angles, greater thickness, and increased diameters of the SiC ingots. We also proposed a growth mechanism to explain the elimination and generation of foreign polytypes. Furthermore, the densities of micropipes (MPs) and the electrical resistivities indicated good qualities of the wafers at the latest growth stage. Our work offers valuable insights into growing high-quality large-diameter SiC single crystals using the PVT method.