IR and X-ray time-resolved simultaneous experiments: an opportunity to investigate the dynamics of complex systems and non-equilibrium phenomena using third-generation synchrotron radiation sources

Chemical and Structural In-Situ Characterization of Model Electrocatalysts by Combined Infrared Spectroscopy and Surface X-ray Diffraction

New diagnostic approaches are needed to drive progress in the field of electrocatalysis and address the challenges of developing electrocatalytic materials with superior activity, selectivity, and stability. To this end, we developed a versatile experimental setup that combines two complementary in-situ techniques for the simultaneous chemical and structural analysis of planar electrodes under electrochemical conditions: high-energy surface X-ray diffraction (HE-SXRD) and infrared reflection absorption spectroscopy (IRRAS). We tested the potential of the experimental setup by performing a model study in which we investigated the oxidation of preadsorbed CO on a Pt(111) surface as well as the oxidation of the Pt(111) electrode itself. In a single experiment, we were able to identify the adsorbates, their potential dependent adsorption geometries, the effect of the adsorbates on the surface morphology, and the structural evolution of Pt(111) during surface electro-oxidation. In a broader perspective, the combined setup has a high application potential in the field of energy conversion and storage.

A novel in situ sample environment setup for combined small angle x-ray scattering (SAXS), wide-angle x-ray scattering (WAXS), and Fourier transform infrared spectrometer (FTIR) simultaneous measurement

Developing the synchrotron radiation experiment method based on combined technology offers more information on the formation mechanism of new materials and their physical and chemical properties. In this study, a new small-angle x-ray scattering/ wide-angle x-ray scattering/ Fourier-transform infrared spectroscopy (SAXS/WAXS/FTIR) combined setup was established. Using this combined SAXS/WAXS/FTIR setup, x-ray and FTIR signals can be obtained simultaneously from the same sample. The in situ sample cell was designed to couple two FTIR optical paths for the attenuated total reflection and transmission modes, which greatly saved the time of adjusting and aligning the external infrared light path when switching between the two modes with good accuracy. A transistor-transistor logic circuit was used to trigger the synchronous acquisition from the IR and x-ray detectors. A special sample stage is designed, allowing access by the IR and x-ray with temperature and pressure control. The newly developed, combined setup can be used to observe the evolution of the microstructure during the synthesis of composite materials in real-time at both the atomic and molecular levels. The crystallization of polyvinylidene fluoride (PVDF) at different temperatures was observed. The time-dependent experimental data demonstrated the success of the in situ SAXS, WAXS, and FTIR study of the structural evolution, which is feasible to track the dynamic processes.

Iron oxidation dynamics vs. temperature of synthetic potassic-ferro-richterite: a XANES investigation

We investigated the oxidation behaviour of a synthetic potassic-ferro-richterite up to 750 °C by using simultaneous X-ray absorption spectroscopy and X-ray diffraction experiments with synchrotron radiation. From the X-ray diffraction results, we observed an abrupt decrease of cell dimensions at ∼335 °C accompanied by an anomalous increase in the monoclinic cell angle β. From the analysis of the XANES spectra at the iron K-edge, we observed that the structural shrinkage is due to the iron oxidation process, coupled to hydrogen loss, occurring at ∼315 °C, slightly before the cell contraction. Combining these results with previous studies performed on similar samples by single-crystal structure refinement, Mössbauer, high temperature-Fourier transform IR and Raman spectroscopies, we show that the temperature evolution in Fe-amphiboles is a multi-step process. Following the iron oxidation driven by temperature, the structural dynamics in this double-chain silicate is ruled by local strains in the ribbon of iron-filled octahedra, mainly due to the contraction of the M(1) site.

Time-resolved infrared spectroscopy in the study of photosynthetic systems

Time-resolved (TR) infrared (IR) spectroscopy in the nanosecond to second timescale has been extensively used, in the last 30 years, in the study of photosynthetic systems. Interesting results have also been obtained at lower time resolution (minutes or even hours). In this review, we first describe the used techniques-dispersive IR, laser diode IR, rapid-scan Fourier transform (FT)IR, step-scan FTIR-underlying the advantages and disadvantages of each of them. Then, the main TR-IR results obtained so far in the investigation of photosynthetic reactions (in reaction centers, in light-harvesting systems, but also in entire membranes or even in living organisms) are presented. Finally, after the general conclusions, the perspectives in the field of TR-IR applied to photosynthesis are described.

New advances in the use of infrared absorption spectroscopy for the characterization of heterogeneous catalytic reactions

Infrared absorption spectroscopy has proven to be one of the most powerful spectroscopic techniques available for the characterization of catalytic systems. Although the history of IR absorption spectroscopy in catalysis is long, the technique continues to provide key fundamental information about a variety of catalysts and catalytic reactions, and to also offer novel options for the acquisition of new information on both reaction mechanisms and the nature of the solids used as catalysts. In this review, an overview is provided of the main contributions that have been derived from IR absorption spectroscopy studies of catalytic systems, and a discussion is included on new trends and new potential directions of research involving IR in catalysis. We start by briefly describing the power of Fourier-transform IR (FTIR) instruments and the main experimental IR setups available, namely, transmission (TIR), diffuse reflectance (DRIFTS), attenuated total reflection (ATR-IR), and reflection-absorption (RAIRS), for advancing research in catalysis. We then discuss the different environments under which IR characterization of catalysts is carried out, including in situ and operando studies of typical catalytic processes in gas-phase, research with model catalysts in ultrahigh vacuum (UHV) and so-called high-pressure cell instruments, and work involving liquid/solid interfaces. A presentation of the type of information extracted from IR data follows in terms of the identification of adsorbed intermediates, the characterization of the surfaces of the catalysts themselves, the quantitation of IR intensities to extract surface coverages, and the use of probe molecules to identify and titrate specific catalytic sites. Finally, the different options for carrying out kinetic studies with temporal resolution such as rapid-scan FTIR, step-scan FTIR, and the use of tunable lasers or synchrotron sources, and to obtain spatially resolved spectra, by sample rastering or by 2D imaging, are introduced.

Simultaneous nanocalorimetry and fast XRD measurements to study the silicide formation in Pd/a-Si bilayers

The use of a membrane-based chip nanocalorimeter in a powder diffraction beamline is described. Simultaneous wide-angle X-ray scattering and scanning nanocalorimetric measurements are performed on a thin-film stack of palladium/amorphous silicon (Pd/a-Si) at heating rates from 0.1 to 10 K s(-1). The nanocalorimeter works under a power-compensation scheme previously developed by the authors. Kinetic and structural information of the consumed and created phases can be obtained from the combined techniques. The formation of Pd2Si produces a broad calorimetric peak that contains overlapping individual processes. It is shown that Pd consumption precedes the formation of the crystalline Pd2Si phase and that the crystallite size depends on the heating rate of the experiment.

Applications of synchrotron-based spectroscopic techniques in studying nucleic acids and nucleic acid-functionalized nanomaterials

In this review, we summarize recent progress in the application of synchrotron-based spectroscopic techniques for nucleic acid research that takes advantage of high-flux and high-brilliance electromagnetic radiation from synchrotron sources. The first section of the review focuses on the characterization of the structure and folding processes of nucleic acids using different types of synchrotron-based spectroscopies, such as X-ray absorption spectroscopy, X-ray emission spectroscopy, X-ray photoelectron spectroscopy, synchrotron radiation circular dichroism, X-ray footprinting and small-angle X-ray scattering. In the second section, the characterization of nucleic acid-based nanostructures, nucleic acid-functionalized nanomaterials and nucleic acid-lipid interactions using these spectroscopic techniques is summarized. Insights gained from these studies are described and future directions of this field are also discussed.

Adding diffuse reflectance infrared Fourier transform spectroscopy capability to extended x-ray-absorption fine structure in a new cell to study solid catalysts in combination with a modulation approach

We describe a novel cell used to combine in situ transmission X-ray absorption spectroscopy (XAS) with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in a single experiment. The novelty of the cell design compared to current examples is that both radiations are passed through an X-ray and IR transparent window in direct contact with the sample. This innovative geometry also offers a wide surface for IR collection. In order to avoid interference from the crystalline IR transparent materials (e.g., CaF2, MgF2, diamond) a 500 μm carbon filled hole is laser drilled in the center of a CaF2 window. The cell is designed to represent a plug flow reactor, has reduced dead volume in order to allow for fast exchange of gases and is therefore suitable for experiments under fast transients, e.g., according to the concentration modulation approach. High quality time-resolved XAS and DRIFTS data of a 2 wt.% Pt/Al2O3 catalyst are obtained in concentration modulation experiments where CO (or H2) pulses are alternated to O2 pulses at 150 °C. We show that additional information can be obtained on the Pt redox dynamic under working conditions thanks to the improved sensitivity given by the modulation approach followed by Phase Sensitive Detection (PSD) analysis. It is anticipated that the design of the novel cell is likely suitable for a number of other in situ spectroscopic and diffraction methods.