An Algebraic Blueprint for Predicting Turnover Numbers and Endpoints in Photocatalysis.

The front cover artwork is provided by the Institute of Analytical and Bioanalytical Chemistry and the Institute of Inorganic Chemistry I at Ulm University within the Collaborative Research Center TRR 234 CataLight. The image shows an algebraic approach to generically calculate and predict the turnover number (TON) and the endpoint of photocatalytic hydrogen gas evolution experiments. Read the full text of the Research Article at 10.1002/cphc.202300767.

An Algebraic Blueprint for Predicting Turnover Numbers and Endpoints in Photocatalysis.

Photocatalysis is a contemporary research field given that the world's fossil energy resources including coal, mineral oil and natural gas are finite. The vast variety of photocatalytic systems demands for standardized protocols facilitating an objective comparison. While there are commonly accepted performance indicators such as the turnover number (TON) that are usually reported, to date there is no unified concept for the determination of TONs and the endpoint of the reaction during continuous measurements. Herein, we propose an algebraic approach using defined parameters and boundary conditions based on partial-least squares regression for generically calculating and predicting the turnover number and the endpoint of a photocatalytic experiment. Furthermore, the impact of the analysis period was evaluated with respect to the fidelity of the obtained TON, and the influence of the data point density along critical segments of the obtained fitting function is demonstrated.

Sensing Liquid- and Gas-Phase Hydrocarbons via Mid-Infrared Broadband Femtosecond Laser Source Spectroscopy.

In this study, we demonstrate the combination of a tunable broadband mid-infrared (MIR) femtosecond laser source separately coupled to a ZnSe crystal horizontal attenuated total reflection (ATR) sensor cell for liquid phase samples and to a substrate-integrated hollow waveguide (iHWG) for gas phase samples. Utilizing this emerging light source technology as an alternative MIR radiation source for Fourier transform infrared (FTIR) spectroscopy opens interesting opportunities for analytical applications. In a first approach, we demonstrate the quantitative analysis of three individual samples, ethanol (liquid), methane (gas), and 2-methyl-1-propene (gas), with limits of detection of 0.3% (ethanol) and 22 ppmv and 74 ppmv (methane and isobutylene), respectively, determined at selected emission wavelengths of the MIR laser source (i.e., 890 cm-1, 1046 and 1305 cm-1). Hence, the applicability of a broadband MIR femtosecond laser source as a bright alternative light source for quantitative analysis via FTIR spectroscopy in various sensing configurations has been demonstrated.

A Portable Infrared Attenuated Total Reflection Spectrometer for Food Analysis.

The analytical performance of a compact infrared attenuated total reflection spectrometer using a pyroelectric detector array has been evaluated and compared to a conventional laboratory Fourier transform infrared system for applications in food analysis. Analytical characteristics including sensitivity, repeatability, linearity of the calibration functions, signal-to-noise ratio, and spectral resolution have been derived for both approaches. Representative analytes of relevance in food industries (i.e., organic solvents, fatty acids, and mycotoxins) have been used for the assessment of the performance of the device and to discuss the potential of this technology in food and feed analysis.

Flexible terahertz gas sensing platform based on substrate-integrated hollow waveguides and an opto-electronic light source.

We report on a flexible platform for molecular sensing in the terahertz range. Merging the well-established technologies of near-infrared electro-optic modulation and photomixing realizes a spectrally adaptable terahertz source, which is combined with a new generation of compact gas cells, so-called substrate-integrated hollow waveguides (iHWGs). iHWGs have been developed in the mid-infrared and provide flexibility in the design of the optical absorption path. Here, we demonstrate its suitability for the terahertz domain by presenting its low propagation losses and by measuring rotational transitions of nitrious oxide (N2O). A fast frequency sideband modulation technique results in substantially reduced measurement times and increased accuracy compared to a standard wavelength tuning method.

Advanced mid-infrared lightsources above and beyond lasers and their analytical utility.

In the mid-infrared (MIR) spectral range, a series of applications have successfully been shown in the fields of sensing, security and defense, energy conservation, and communications. In particular, rapid and recent developments in MIR light sources have significantly increased the interest in developing MIR optical systems, sensors, and diagnostics especially for chem/bio detection schemes and molecular analytical application scenarios. In addition to the advancements in optoelectronic light sources, and especially quantum and interband cascade lasers (QCLs, ICLs) largely driving the increasing interest in the MIR regime, also thermal emitters and light emitting diodes (LEDs) offer opportunities to alternatively fill current gaps in spectral coverage specifically with analytical applications and chem/bio sensing/diagnostics in the focus. As MIR laser technology has been broadly covered in a variety of articles, the present review aims at summarizing recent developments in MIR non-laser light sources highlighting their analytical utility in the MIR wavelength range.