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Abstract The buried interface tens of nanometers beneath the solid-liquid junction is crucial for photocarrier extraction, influencing the overall efficiency of photoelectrochemical devices. Precise characterization of the interfacial properties is essential for device optimization but remains challenging. Here, we directly probe the in situ transformation of a Cu x O interlayer at the NiO/n-Si interface by hard X-ray photoelectron spectroscopy. It is found that Cu(I) in the Cu x O interlayer gradually transforms to Cu(II) with air exposure, forming an energetically more favorable interface and improving photoanode’s efficiency. Based on this finding, a reactive e-beam evaporation process is developed for the direct deposition of a CuO interlayer, achieving a half-cell solar-to-hydrogen efficiency of 4.56% for the optimized NiO/CuO/n-Si heterojunction photoanode. Our results highlight the importance of precision characterization of interfacial properties with advanced hard X-ray photoelectron spectroscopy in guiding the design of efficient solar water-splitting devices.

Abstract Electrochemical chlorine evolution reaction is of central importance in the chlor-alkali industry, but the chlorine evolution anode is largely limited by water oxidation side reaction and corrosion-induced performance decay in strong acids. Here we present an amorphous CoOxCly catalyst that has been deposited in situ in an acidic saline electrolyte containing Co2+ and Cl- ions to adapt to the given electrochemical condition and exhibits ~100% chlorine evolution selectivity with an overpotential of ~0.1 V at 10 mA cm−2 and high stability over 500 h. In situ spectroscopic studies and theoretical calculations reveal that the electrochemical introduction of Cl- prevents the Co sites from charging to a higher oxidation state thus suppressing the O-O bond formation for oxygen evolution. Consequently, the chlorine evolution selectivity has been enhanced on the Cl-constrained Co-O* sites via the Volmer-Heyrovsky pathway. This study provides fundamental insights into how the reactant Cl- itself can work as a promoter toward enhancing chlorine evolution in acidic brine.

If and how non-bonding ligands mediate the electronic states of metal sites is interesting yet remains to be explored. Here the authors show that a non-covalent phenanthroline can promote the population of Co4+ and induce polaron-like Co sites for improved water oxidation.

Abstract Barium hexaferrite nanoplatelets (BHF NPLs) are permanent nanomagnets with the magnetic easy axis aligned perpendicular to their basal plane. By combining this specific property with optimised surface chemistry, novel functional materials were developed, e.g., ferromagnetic ferrofluids and porous nanomagnets. We compared the interaction of chemically different phosphonic acids, hydrophobic and hydrophilic with 1–4 phosphonic groups, with BHF NPLs. A decrease in the saturation magnetisation after functionalising the BHF NPLs was correlated with the mass fraction of the nonmagnetic coating, whereas the saturation magnetisation of the NPLs coated with a tetraphosphonic acid at 80 °C was significantly lower than expected. We showed that such a substantial decrease in the saturation magnetisation originates from the disintegration of BHF NPLs, which was observed with atomic-resolution scanning transmission electron microscopy and confirmed by a computational study based on state-of-the-art first-principles calculations. Fe K-edge XANES (X-ray absorption near-edge structure) and EXAFS (Extended X-ray absorption fine structure) combined with Fourier-transformed infrared (FTIR) spectroscopy confirmed the formation of an Fe–phosphonate complex on the partly decomposed NPLs. Comparing our results with other functionalised magnetic nanoparticles confirmed that saturation magnetisation can be exploited to identify the disintegration of magnetic nanoparticles when insoluble disintegration products are formed.

Wide-bandgap gallium oxide (Ga2O3) is one of the most promising semiconductor materials for solar-blind (200 ​nm–280 ​nm) photodetection. In its amorphous form, a-Ga2O3 maintains its intrinsic optoelectronic properties while can be prepared at a low growth temperature, thus it is compatible with Si integrated circuits (ICs) technology. Herein, the a-Ga2O3 film is directly deposited on pre-fabricated Au interdigital electrodes by plasma enhanced atomic layer deposition (PE-ALD) at a growth temperature of 250 ​°C. The stoichiometric a-Ga2O3 thin film with a low defect density is achieved owing to the mild PE-ALD condition. As a result, the fabricated Au/a-Ga2O3/Au photodetector shows a fast time response, high responsivity, and excellent wavelength selectivity for solar-blind photodetection. Furthermore, an ultra-thin MgO layer is deposited by PE-ALD to passivate the Au/a-Ga2O3/Au interface, resulting in the responsivity of 788 A/W (under 254 ​nm at 10 ​V), a 250-nm-to-400-nm rejection ratio of 9.2 ​× ​103, and the rise time and the decay time of 32 ​ms and 6 ​ms, respectively. These results demonstrate that the a-Ga2O3 film grown by PE-ALD is a promising candidate for high-performance solar-blind photodetection and potentially can be integrated with Si ICs for commercial production.

Numerous nanobiotechnologies include manipulations of short polypeptide chains. The conformational properties of these polypeptides are studied in vitro by circular dichroism and time-resolved infrared spectroscopy. To find out the interaction parameters, the measured temperature dependence of normalized helicity degree needs to be further processed by fitting to a model. Using recent advances in the Hamiltonian formulation of the classical Zimm and Bragg model, we explicitly include chain length and solvent effects in the theoretical description. The expression for the helicity degree we suggest successfully fits the experimental data and provides hydrogen bonding energies and nucleation parameter values within the standards in the field.

In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reaction of the GLPC with molecular oxygen. Such investigations suggested the stability of the dioxagermirane (DIOG) bulk defect, and its back conversion into GLPC with a local release of O2 under irradiation. Furthermore, it is also inferred that a remarkable portion of the O2 passivated GLPC may form Ge tetrahedra connected to peroxy bridges. Such structures may have a larger resistance to the irradiation and not be back converted into GLPC.

Electrocatalysis using low-cost materials is a promising, economical strategy for remediation of water contaminated with organic chemicals and microorganisms. Here, we report the use of iron phosphide (Fe2P) precatalyst for electrocatalytic water oxidation; degradation of a representative aromatic hydrocarbon, the dye rhodamine B (RhB); and inactivation of Escherichia coli (E. coli) bacteria. It was found that during anodic oxidation, the Fe2P phase was converted to iron phosphate phase (Fe2P-iron phosphate). This is the first report that Fe2P precatalyst can efficiently catalyze electrooxidation of an organic molecule and inactivate microorganisms in aqueous media. Using a thin film of Fe2P precatalyst, we achieved 98% RhB degradation efficiency and 100% E. coli inactivation under an applied bias of 2.0 V vs. reversible hydrogen electrode in the presence of in situ generated reactive chlorine species. Recycling test revealed that Fe2P precatalyst exhibits excellent activity and reproducibility during degradation of RhB. High-performance liquid chromatography with UV-Vis detection further confirmed the electrocatalytic (EC) degradation of the dye. Finally, in tests using Lepidium sativum L., EC-treated RhB solutions showed significantly diminished phytotoxicity when compared to untreated RhB. These findings suggest that Fe2P-iron phosphate electrocatalyst could be an effective water remediation agent.

A sustainable nexus between renewable energy production and plastic abatement is imperative for overall sustainable development. In this regard, this study aims to develop a cheaper and environmentally friendly nexus between plastic waste management, wastewater treatment, and renewable hydrogen production. Fluorescent carbon (FCs) were synthesized from commonly used LDPE (low-density polyethylene) by a facile hydrothermal approach. Optical absorption study revealed an absorption edge around 300 nm and two emission bands at 430 and 470 nm. The morphological analysis showed two different patterns of FCs, a thin sheet with 2D morphology and elongated particles. The sheet-shaped particles are 0.5 μm in size, while as for elongated structures, the size varies from 0.5 to 1 μm. The as-synthesized FCs were used for the detection of metal ions (reference as Cu2+ ions) in water. The fluorescence intensity of FCs versus Cu2+ ions depicts its upright analytical ability with a limit of detection (LOD) reaching 86.5 nM, which is considerably lesser than earlier reported fluorescence probes derived from waste. After the sensing of Cu2+, the as-obtained FCs@Cu2+ was mixed with TiO2 to form a ternary FCs@CuO@TiO2 composite. This ternary composite was utilized for photocatalytic hydrogen production from water under 1.5 AM solar light irradiation. The H2 evolution rate was found to be ~1800 μmolg−1, which is many folds compared to the bare FCs. Moreover, the optimized FCs@CuO@TiO2 ternary composite showed a photocurrent density of ~2.40 mA/cm2 at 1 V vs. Ag/AgCl, in 1 M Na2SO4 solution under the illumination of simulated solar light. The achieved photocurrent density corresponds to the solar-to-hydrogen (STH) efficiency of ~0.95%. The efficiency is due to the fluorescence nature of FCs and the synergistic effect of CuO embedded in TiO2, which enhances the optical absorption of the composite by reaching the bandgap of 2.44 eV, apparently reducing the recombination rate, which was confirmed by optoelectronic, structural, and spectroscopic characterizations.

Technologies for mass production require cheap and abundant materials such as ferrous chloride (FeCl2). The literature survey shows the lack of experimental studies to validate theoretical conclusions related to the population of ionic Fe-species in the aqueous FeCl2 solution. Here, we present an in situ X-ray absorption study of the structure of the ionic species in the FeCl2 aqueous solution at different concentrations (1–4 molL−1) and temperatures (25–80 °C). We found that at low temperature and low FeCl2 concentration, the octahedral first coordination sphere around Fe is occupied by one Cl ion at a distance of 2.33 (±0.02) Å and five water molecules at a distance of 2.095 (±0.005) Å. The structure of the ionic complex gradually changes with an increase in temperature and/or concentration. The apical water molecule is substituted by a chlorine ion to yield a neutral Fe[Cl2(H2O)4]0. The observed substitutional mechanism is facilitated by the presence of the intramolecular hydrogen bonds as well as entropic reasons. The transition from the single charged Fe[Cl(H2O)5]+ to the neutral Fe[Cl2(H2O)4]0 causes a significant drop in the solution conductivity, which well correlates with the existing conductivity models.

In this work the interface between a Pt film and a Bi2Se3 (0001) surface is investigated using electron microscopy and microanalysis, in order to characterize the structure of the interface and verify if it is chemically stable or an interaction occurs. At room temperature, the Pt film is composed of small clusters (∼10 nm) and the interface is stable. However, already upon mild annealing (200 °C) the interface displays instability and forms an interfacial phase. The interfacial phase, not previously reported in literature, is a long-range ordered ternary Pt:Bi:Se phase aligned with the Bi2Se3 crystal, most probably an intermetallic compound. The presence of a new phase at Pt/Bi2Se3 interface, together with the possible effects on the topological surface states, has to be considered in all the applied studies where this interface is present, as well as in the models for theoretical studies.

Functional layered double hydroxide (LDH) usually contains different cationic substitutes to increase the activity of the oxygen evolution reaction (OER). The intrinsic OER activity of LDH materials is connected with the chemical composition and dispersion of metal cations substitutions in the matrix phase. The potential induced phase transitions, in particular hydroxide-to-oxyhydroxide transitions, are a predisposition for the high OER activity of LDH materials and can be followed by coupling the electrochemical experiments with spectroscopic techniques. The understanding of LDH catalysts under electrochemical conditions also allows an understanding of the behavior of OER catalysts based on transition metals, metal-chalcogenides, -pnictides, -carbides, and metal–organic frameworks. The surfaces of those materials are intrinsically poor OER catalysts. However, they act as precursors to catalysts, which are oxidized into a metal (oxy)hydroxide. This review summarizes the use of in situ techniques for the characterization of LDH-based OER electrocatalysts and presents the influence of these techniques on the understanding of potential induced phase transitions, identification of active sites, and reaction mechanisms.

Localized surface plasmon resonance (LSPR) is the cause of the photo-thermal effect observed in topological insulator (TI) bismuth selenide (Bi2Se3) nanoparticles. These plasmonic properties, which are thought to be caused by its particular topological surface state (TSS), make the material interesting for application in the field of medical diagnosis and therapy. However, to be applied, the nanoparticles have to be coated with a protective surface layer, which prevents agglomeration and dissolution in the physiological medium. In this work, we investigated the possibility of using silica as a biocompatible coating for Bi2Se3 nanoparticles, instead of the commonly used ethylene-glycol, which, as is presented in this work, is not biocompatible and alters/masks the optical properties of TI. We successfully prepared Bi2Se3 nanoparticles coated with different silica layer thicknesses. Such nanoparticles, except those with a thick, ≈200 nm silica layer, retained their optical properties. Compared to ethylene-glycol coated nanoparticles, these silica coated nanoparticles displayed an improved photo-thermal conversion, which increased with the increasing thickness of the silica layer. To reach the desired temperatures, a 10–100 times lower concentration of photo-thermal nanoparticles was needed. In vitro experiments on erythrocytes and HeLa cells showed that, unlike ethylene glycol coated nanoparticles, silica coated nanoparticles are biocompatible.