Martin Charles Wilding

Neutron scattering with isotopic substitution and high-energy X-ray scattering have been used to evaluate the ordering of the polar solvent, dimethylformamide (DMF), around the surface of dispersed graphene oxide (GO) nanosheets. Empirical potential structural refinement (EPSR) has been used to model the interaction of this technically important material with the solvent. In reciprocal space, both neutron and X-ray scattering patterns show significant differences between the GO solution and the solvent. In real space, these differences in structure persist to at least 5 Å from the GO surface, and some changes to the solvent structure are discernible to 10 Å. EPSR modelling of the solvent interaction was undertaken using a supercell generated from the GO surface, extended in the z-direction and filled with DMF molecules. Two different GO surfaces were used: one with a random distribution of epoxide and hydroxide functional groups and one in which the arrangement was semi-ordered. There is no apparent influence of the arrangement of the functional groups on the modelled structure. The z-dependent distribution functions indicate that the oxygen atoms within the DMF molecule are closest to the nanosheet surface, implying that the solvent ordering reflects a small positive charge to the GO surface. This article is part of the theme issue ‘Surfaces, interfaces and heterogeneous catalysis’.

Photocatalytic synthesis of hydrogen peroxide (H₂O₂) from oxygen (O₂) is a challenging process. Metal-organic framework (MOF) materials are emerging photocatalysts with potential tunable light absorption properties. Herein, we report a rhenium (Re) modified Zr-based MOF, Re10-MFM-67, in which active Re sites are incorporated into MFM-67 by partial replacement of 9,9'-bianthracene-10,10'-dicarboxylic acid (H₂L¹) with a [(H₂L²)Re^I(CO)₃Cl] (H₂L² = 2,2'-bipyridine-5,5'-dicarboxylic acid) moiety. Re10-MFM-67 (10 refers to the molar percentage content of Re complex within the material) exhibits broadband light absorption with an exceptional rate of formation of H₂O₂ from O₂ of 8.50 mmol g_cat^-1 h^-1 and a record turnover frequency (TOF) of 28.7 h^-1 under visible light irradiation (λ > 400 nm). Synchrotron powder X-ray diffraction (SPXRD) and neutron powder diffraction (NPD) confirm the structure of Re10-MFM-67, and together with extended X-ray absorption fine structure (EXAFS) analysis establish the coordination environment and binding of the [Re^I(CO)₃Cl] moiety within the framework structure. In situ electron paramagnetic resonance (EPR) spectroscopy suggests that photocatalytic H₂O₂ generation on Re10-MFM-67 occurs via a two-step oxygen reduction reaction (ORR) pathway with the superoxide anion formed as an intermediate. This study promotes the design of MOF-based photocatalysts with conjugated ligands for efficient photosynthesis.

Publishing supporting data significantly impacts researchers' productivity, especially in experiments requiring extensive tracking of data, processing steps, parameters, and outputs. A managed workflow environment, combined with RO‐Crates, addresses these data management challenges. Workflows provide an alternative for handling complex data analyses by orchestrating various processing tools. The RO‐Crate format, a community‐driven proposal for packaging data, provenance, and workflows, facilitates publishing and reproducibility. The Galaxy workflow management system integrates workflows and RO‐Crates, enabling the export of analyses, which can be shared and restored by other users. Using Galaxy, we demonstrate how to improve support for reproducibility. We tested our approach by designing an experiment using diverse supporting data from selected papers. In the experiment, we identified specific FAIRness and completeness issues hindering result reproduction, even when authors made significant efforts to document and publish their supporting data. In comparison, the proposed approach supports reproducibility by packaging datasets in RO‐Crate format, streamlining the process. The Galaxy RO‐Crates, published as supporting materials, enhance data sharing, transparency, and reproducibility, thus supporting the advancement of FAIR research practices in catalysis research.

Amorphous carbonates, in their liquid and solid (glassy) forms, have been identified to play important roles in biomineralization, volcanism, and deep element cycling. Anhydrous amorphous calcium and calcium-magnesium carbonate (ACC and ACMC05, respectively) are structural glasses that exhibit a glass transition upon being heated. We report a significant effect of the water content on glass formation. The results yield a parametrization enabling prediction of the stability of their liquid and solid amorphous phases as a function of temperature and water content. These results, obtained through novel fast differential scanning calorimetry, demonstrate that hydrous ACC and ACMC05 do indeed exhibit the behavior of structural glasses and that dehydration of these materials by lyophilization is a route that can be used to isothermally cross the glass transition. This work presents a viable process for a significantly wider range of geo- and biomaterials. Dehydration-controlled formation of glassy ACC therefore constitutes the missing link in the transformation from supersaturated aqueous solutions through an intermediate amorphous glassy state to crystalline CaCO₃ polymorphs. These results yield direct implications for the mechanistic interpretation of geological processes and biomineralization.

The diffusion of sodium and carbonate ions in molten sodium carbonate is investigated by quasi-elastic neutron scattering (QENS) at T = 1143 K. The quasi-elastic scattering at small wave vectors is dominated by diffusing sodium ions, and the derived self-diffusion coefficient of D_Na = 4.5 × 10^-5 cm²/s agrees well with previous tracer diffusion measurements. The quasi-elastic scattering from the carbonate anion is coherent, and the coherent scattering dominates the QENS signal at scattering vectors with a modulus greater than 1 Å^-1. The line width of the coherent scattering function is used to obtain the diffusion coefficient of the carbonate anion at this temperature of DCO₃^2- = 2.4 × 10^-5 cm²/s, again in agreement with values from tracer diffusion studies. The results from this QENS measurement are larger compared with molecular dynamics simulations using a recently developed model, which introduces flexibility to the carbonate anion and allows charge to fluctuate across the anion. The model was improved concerning the melting point of the simulated liquid. Scaling the temperature in terms of this melting point is shown to bring the simulated and experimental diffusion coefficients into good agreement. The self-diffusion coefficients are consistent with those expected for a fragile liquid, and the changes in viscosity expected as the carbonate liquid is cooled are explained by the development of chains and complex structures that directly result from the flexibility of the anion introduced in this modeling approach. This simulation methodology can therefore be applied to further studies of complex molten salts.

The design and preparation of efficient catalysts for ammonia production under mild conditions is a desirable but highly challenging target. Here, we report a series of single-atom catalysts [M-SACs, M = Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Mo(II)] derived from UiO-66 containing structural defects and their application to electrochemical reduction of nitrate (NO₃^-) to ammonia (NH₃). Cu-SAC and Fe-SAC exhibit remarkable yield rates for NH₃ production of 30.0 and 29.0 mg h⁻¹ cm⁻², respectively, with a high Faradaic efficiency (FE_NH3) of over 96% at −1.0 V versus the reversible hydrogen electrode. Importantly, their catalytic performance can be retained in various simulated wastewaters. Complementary experiments confirmed the nature of single-atom sites within these catalysts and the binding domains of NO₃^- in UiO-66-Cu. In situ spectroscopic techniques, coupled with density functional theory calculations confirm the strong binding of NO₃^- and the formation of reaction intermediates, thus facilitating the catalytic conversion to NH₃.

Electrochemical hydrogen peroxide (H₂O₂) production (EHPP) via a two-electron oxygen reduction reaction (2e^- ORR) provides a promising alternative to replace the energy-intensive anthraquinone process. M-N-C electrocatalysts, which consist of atomically dispersed transition metals and nitrogen-doped carbon, have demonstrated considerable EHPP efficiency. However, their full potential, particularly regarding the correlation between structural configurations and performances in neutral media, remains underexplored. Herein, a series of ultralow metal-loading M-N-C electrocatalysts are synthesized and investigated for the EHPP process in the neutral electrolyte. CoNCB material with the asymmetric Co-C/N/O configuration exhibits the highest EHPP activity and selectivity among various as-prepared M-N-C electrocatalyst, with an outstanding mass activity (6.1 × 10⁵A g_Co⁻¹ at 0.5 V vs. RHE), and a high practical H₂O₂ production rate (4.72 mol g_catalyst⁻¹ h⁻¹ cm⁻²). Compared with the popularly recognized square-planar symmetric Co-N₄ configuration, the superiority of asymmetric Co-C/N/O configurations is elucidated by X-ray absorption fine structure spectroscopy analysis and computational studies.

The ordering of solvent molecules around nanostructures is of broad scientific importance from understanding biological processes to the manipulation of nanomaterials in liquids, to optimiz-ing the performance of electrochemical devices. However, experimental measurements of this solvent ordering are scarce. Herein, the structures of concentrated solutions of anionic carbon nanotubes in two amidic solvents are measured via total neutron scattering leading to a previ-ously unattainable picture of nanoparticle solvation, revealing a far richer structure than hitherto assumed. The solvent molecules form densely-packed, concentric shells around the charged carbon nanotubes, ordered according to two distinct orientations due to competing effects. Firstly, a surface monolayer that maximizes attractive interactions between anionic surface and solvent molecular dipole moment. The second orientation extends ~40 Å into the bulk solvent, with molecules preferentially oriented perpendicularly to the first layer due to dipole interac-tions with the charged nanoparticle. This complex, long-ranged order drastically differs from the simplistic treatment of the solvent in classical models commonly employed to understand these systems. Moreover, our analysis indicates that a fraction of counterions condense on the sur-face as a Stern layer which are desolvated due to the solvent preferentially interacting with the charged surface. Ions at further distances are fully solvated, and their distribution is strongly in-fluenced by the dense solvation shells around the nanotube. Our results thus underscore the critical importance of multi-body interactions in solvated nanoscale systems, highlighting new competing ion/surface solvation effects crucial for understanding electrolyte-surface interfaces in supercapacitors, batteries, and electrolytically-gated devices.

This themed issue explores the different length and timescales that determine the physics and chemistry of a variety of key of materials, explored from the perspective of a wide range of disciplines, including physics, chemistry materials science, Earth science and biochemistry. The topics discussed include catalysis, chemistry under extreme conditions, energy materials, amorphous and liquid structure, hybrid organic materials and biological materials. The issue is in two parts, with this second set of contributions exploring hybrid organic materials, catalysis low-dimensional and graphitic materials, biological materials and naturally occurring, super-hard material as well as dynamic high pressure and new developments in imaging techniques pressure.This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

The crystalline graphitic carbon nitride, poly-triazine imide (PTI) is highly unusual among layered materials since it is spontaneously soluble in aprotic, polar solvents including dimethylformamide (DMF). The PTI material consists of layers of carbon nitride intercalated with LiBr. When dissolved, the resulting solutions consist of dissolved, luminescent single to multilayer nanosheets of around 60–125 nm in diameter and Li+ and Br− ions originating from the intercalating salt. To understand this unique solubility, the structure of these solutions has been investigated by high-energy X-ray and neutron diffraction. Although the diffraction patterns are dominated by inter-solvent correlations there are clear differences between the X-ray diffraction data of the PTI solution and the solvent in the 4–6 Å ⁻¹ range, with real space differences persisting to at least 10 Å. Structural modelling using both neutron and X-ray datasets as a constraint reveal the formation of distinct, dense solvation shells surrounding the nanoparticles with a layer of Br ⁻ close to the PTI-solvent interface. This solvent ordering provides a configuration that is energetically favourable underpinning thermodynamically driven PTI dissolution. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.