1,2,4-Triazole-Based Approach to Noble-Metal-Free Visible-Light Driven Water Splitting over Carbon Nitrides

MoS₂/Co₂O₃/poly­(heptazine imide) composite photocatalysts which are active in both noble-metal-free water reduction and water oxidation half reactions upon irradiation with visible light were synthesized by a one-step procedure. Here, the LiCl/KCl eutectic melt was used as a high-temperature solvent; 3-amino-1,2,4-triazole-5-thiol simultaneously acts as a carbon nitride precursor, sulfur source, and reducing agent for Mo⁵⁺, while MoCl₅ was added as a metal source for MoS₂ nanoparticles being active centers for the water reduction reaction. Water oxidation centers could be created using the rich complexation chemistry of 1,2,4-triazoles. Namely, cobalt species were introduced into carbon nitride network using Co₃[3,5-diamino-1,2,4-triazole]₆ complex as a dopant, prepared in a separate step. The developed method enables one to control the cocatalysts’ loading and tune the dimensions of MoS₂ NPs. The materials reported here show 10% of the efficiency of a reference Pt/mesoporous graphitic carbon nitride composite in hydrogen evolution, and half of the performance of the reference Co₃O₄/S-doped carbon nitride material, prepared by multistep synthesis, in oxygen evolution, however, in one and the same system

Synchrotron Radiation X‑ray Photoelectron Spectroscopy as a Tool To Resolve the Dimensions of Spherical Core/Shell Nanoparticles

In this work we demonstrate the potential of synchrotron X-ray photoelectron spectroscopy (XPS) to provide quantitative information on the intrinsic dimensions of core–shell nanoparticles. The methodology is based on the simulation of depth profiling curves, using simplified quantitative models earlier proposed in the literature. Three model systems consisting of X@Fe₂O₃ (with X = Au, Pt, and Rh) metal–iron oxide core–shell nanoparticles, formed via oxidation of size-selected 5 nm bimetallic FeX nanoparticles inside the spectrometer, were measured in situ by near ambient pressure XPS. We show that when the shell layer is composed of a unique component, the experimental depth profiling curve can be simulated by the quantitative calculations and reveal the core and the shell thickness of the nanoparticles. On the contrary, a significant offset between the experimental and the theoretical depth profiling curves implies intermixing between the core and the shell layers. In this case the theoretical model has been modified to represent the more complex particle morphology. Transmission electron microscopy results are in good agreement with the XPS findings, confirming the validity of the model to predict the nanoparticle dimensions

Synchrotron Radiation X‑ray Photoelectron Spectroscopy as a Tool To Resolve the Dimensions of Spherical Core/Shell Nanoparticles

In this work we demonstrate the potential of synchrotron X-ray photoelectron spectroscopy (XPS) to provide quantitative information on the intrinsic dimensions of core–shell nanoparticles. The methodology is based on the simulation of depth profiling curves, using simplified quantitative models earlier proposed in the literature. Three model systems consisting of X@Fe₂O₃ (with X = Au, Pt, and Rh) metal–iron oxide core–shell nanoparticles, formed via oxidation of size-selected 5 nm bimetallic FeX nanoparticles inside the spectrometer, were measured in situ by near ambient pressure XPS. We show that when the shell layer is composed of a unique component, the experimental depth profiling curve can be simulated by the quantitative calculations and reveal the core and the shell thickness of the nanoparticles. On the contrary, a significant offset between the experimental and the theoretical depth profiling curves implies intermixing between the core and the shell layers. In this case the theoretical model has been modified to represent the more complex particle morphology. Transmission electron microscopy results are in good agreement with the XPS findings, confirming the validity of the model to predict the nanoparticle dimensions

Layer-by-Layer Photocatalytic Assembly for Solar Light-Activated Self-Decontaminating Textiles

Novel photocatalytic nanomaterials that can be used to functionalize textiles, conferring to them efficient solar-light-activated properties for the decontamination of toxic and lethal agents, are described. Textiles functionalized with one-dimensional (1D) SnS₂-based nanomaterials were used for photocatalytic applications for the first time. We showed that 1D SnS₂/TiO₂ nanocomposites can be easily and strongly affixed onto textiles using the layer-by-layer deposition method. Ultrathin SnS₂ nanosheets were associated with anatase TiO₂ nanofibers to form nano-heterojunctions with a tight interface, considerably increasing the photo-oxidative activity of anatase TiO₂ due to the beneficial interfacial transfer of photogenerated charges and increased oxidizing power. Moreover, it is easy to process the material on a larger scale and to regenerate these functionalized textiles. Our findings may aid the development of functionalized clothing with solar light-activated photocatalytic properties that provide a high level of protection against chemical warfare agents

Mixing Patterns and Redox Properties of Iron-Based Alloy Nanoparticles under Oxidation and Reduction Conditions

The redox behavior of 5 nm Fe-Me alloyed nanoparticles (where Me = Pt, Au, and Rh) was investigated <i>in situ</i> under H₂ and O₂ atmospheres by near ambient pressure X-ray photoelectron and absorption spectroscopies (NAP-XPS, XAS), together with <i>ex situ</i> transmission electron microscopy (TEM) and XAS spectra simulations. The preparation of well-defined Fe-Me nanoalloys with an initial size of 5 nm was achieved by using the mass-selected low energy cluster beam deposition (LECBD) technique. The spectroscopic methods permit the direct observation of the surface segregation and composition under different gas atmospheres and annealing temperatures. The ambient conditions were found to have a significant influence on the mixing pattern and oxidation state of the nanoparticles. In an oxidative atmosphere, iron oxidizes and segregates to the surface, leading to the formation of core–shell nanoparticles. This structure persists upon mild reduction conditions, while phase separation and formation of heterostructured bimetallic particles is observed upon H₂ annealing at a higher temperature (400 °C). Depending on the noble metal core, the iron oxide shell might be partially distorted from its bulk structure, while the reduction in H₂ is also significantly influenced. These insights can be of a great importance in understanding the activity and stability of Fe-based bimetallic nanoparticles under reactive environments

<i>Operando</i> Near Ambient Pressure XPS (NAP-XPS) Study of the Pt Electrochemical Oxidation in H₂O and H₂O/O₂ Ambients

Oxides on the surface of Pt electrodes are largely responsible for the loss of their electrocatalytic activity in the oxygen reduction and oxygen evolution reactions. In this work we apply near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study <i>in operando</i> the electrooxidation of a nanoparticulated Pt electrode integrated in a membrane-electrode assembly of a high temperature proton-exchange membrane under water and water/oxygen ambient. Three types of surface oxides/hydroxides gradually develop on the Pt surface depending on the applied potential at +0.9, + 2.5, and +3.7 eV relative to the 4f peak of metal Pt and were attributed to the formation of adsorbed O/OH, PtO, and PtO₂, respectively. The presence of O₂ in the gas-phase results in the increase of the extent of surface oxidation, and in the growth of the contribution of the PtO₂ oxide. Depth profiling studies, in conjunction with quantitative simulations, allowed us to propose a tentative mechanism of the Pt oxidation at high anodic polarization, consisting of adsorption of O/OH followed by nucleation of PtO/PtO₂ oxides and their subsequent three-dimensional growth

When a Metastable Oxide Stabilizes at the Nanoscale: Wurtzite CoO Formation upon Dealloying of PtCo Nanoparticles

Ambient pressure photoelectron and absorption spectroscopies were applied under 0.2 mbar of O₂ and H₂ to establish an unequivocal correlation between the surface oxidation state of extended and nanosized PtCo alloys and the gas-phase environment. Fundamental differences in the electronic structure and reactivity of segregated cobalt oxides were associated with surface stabilization of metastable wurtzite-CoO. In addition, the promotion effect of Pt in the reduction of cobalt oxides was pronounced at the nanosized particles but not at the extended foil

Methanol Steam Reforming over Indium-Promoted Pt/Al₂O₃ Catalyst: Nature of the Active Surface

The surface state of the Pt/In₂O₃/Al₂O₃ catalyst coated onto a microchannel stainless steel reactor was investigated under working conditions using synchrotron-based ambient pressure photoelectron (APPES) and X-ray absorption near-edge structure (XANES) spectroscopies, combined with online mass spectrometry. The surface of the fresh catalyst consists of metallic Pt, In₂O₃, and Al₂O₃. Reduction under 0.2 mbar of H₂ at 250 °C leads to surface enhancement of Pt and partial reduction of In₂O₃, while Al₂O₃ remains unchanged. Reoxidation in O₂ atmosphere stimulates surface segregation of In₂O₃ over Pt, accompanied by partial oxidation of Pt to PtO_<i>x</i>. Based on these results a dynamic, gas-phase-dependent surface state is demonstrated. Under methanol steam reforming conditions, the surface state rapidly adapts under the reaction stream regardless of the pretreatment. However, correlation of gas phase with spectroscopic results under working conditions pointed out the beneficial effect of surface indium to reduce the CO selectivity. Finally, evidence of a distorted symmetry of Al sites on Pt/In₂O₃/Al₂O₃ catalyst compared to that of γ-Al₂O₃ is given. The findings obtained in the present study are of fundamental significance in understanding the relation between the surface state and the catalytic performance of a functional methanol reforming catalyst