Near-field infrared spectroscopy is a vital analysis method that is extensively utilized in materials science, biological sciences as well as optical studies. This article provides a thorough review of the basics of near-field infrared spectroscopy, its principle, and its uses in the identification of traces of sulfur poisoning on the nanometer scale.
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What is Near-Field Infrared Spectroscopy?
Near-infrared spectroscopy (NIRS) is an investigative process that utilizes a generator that emits light with a specified frequency and wavelength spectrum (often 800–2500nm), allowing researchers to gain a comprehensive image of the organic composition of the substances under investigation. It capitalizes on the electromagnetic spectrum's near-infrared area.
Over the last two decades or more, NIR spectroscopy has made significant development in many areas, including equipment, spectrum analysis, and implementations, and has been widely employed as a potent tool in various industries.
A Brief History of Near-Field Infrared Spectroscopy
Although NIR spectrometry is considered a recent technique, its origin could be dated back to 1800 when it was determined that the scattering of electromagnetic radiation beyond the visible part of the spectra could be viewed utilizing a succession of thermometers with darkened bulbs. However, significant advances happened around the 1960s, enabling its implementation in numerous parts of livestock farming and other sectors.
Working Principles of Near-Field Infrared Spectroscopy
Broad streaks in the NIR spectra result from strong absorption at adjacent frequencies. NIR spectroscopy absorption bands are largely harmonics and mixtures of phonon modes featuring various chemical bonds. The ionizing waves absorbed from such chemical bonds at NIR wavelengths provide spectra that are distinctive to material and function as a "fingerprint."
The gathered spectrum contains information on the physiochemical characteristics of natural components in the sample, as well as essential information about chemical compositions.
Which Materials are Used in Catalytic Processes?
Catalysis is an essential process serving as the backbone of several industries. Improving catalyst lifespan and endurance is a major area of intersectional analysis. Many catalytic processes involve the use of platinum group metal (PGM) nanoparticles (NPs) and multi-metallic structures with diverse dimensions, morphologies, and topologies, that are disseminated over permeable metal-oxide support substrates.
Sulfur-containing compounds, such as SOx, can attach to platinum group metals as well as the metal-oxide support substrate in a robust and typically permanent way, culminating in catalytic inactivation and decreased catalytic transformation and specificity.
Sulfur Poisoning – A Serious Threat to Catalytic Processes
Catalytic deactivation caused by sulfur toxicity is a crucial challenge in various industrial chemical methods. This includes complex processes such as solid oxide fuel cells (SOFC), catalytic exhaust outflow control framework, the industrial (modified) Claus process, catalytic hydrocarbon pyrolysis structures, photo/ electrocatalytic water electrolysis, and mass sulfuric acid production.
Challenges in the Study of Sulfur Poisoning
The molecular-level scientific knowledge to fully understand and eradicate this massive problem is still incomplete. This is due to the fact that a complete knowledge of sulfur poisoning necessitates advanced experimental methods that allow for nanometer-scale positional precision without compromising details regarding chemical bonds, chemical bonding, sorption locations, and adsorption morphologies.
Limitations of Conventional Spectroscopy Methods
Unfortunately, the majority of available traditional spectroscopic, micrometer, and crystallographic methods used to characterize reactive metal/metal-oxide interface lack a trade-off between high resolution and chemical structure/bonding specificity.
Scanning tunneling/atomic force/transmission electron microscopy (STM/AFM/TEM) cannot often offer relevant information regarding biochemical organic compounds, structural properties, and sorption morphologies of catalytic adsorption sites at the same moment. For cellular data gathering, such approaches are usually constrained to unreasonably low concentrations (10-12 atm) and freezing conditions (less temperature than 20 K).
Some of these procedures may also cause specimen damage due to the use of high-energy electrons or radiation.
Advantage of NFIR over Conventional Techniques
Infrared (IR) photons used in optical far-field spectroscopy/microscopy offer comprehensive chemical/bonding/adsorption morphology data without causing specimen deterioration. They are, however, restricted to a potential pixel size of >1.2 μm owing to the diffraction limits.
As a result, typical far-field IR spectroscopic/microscopic investigations on metal/metal-oxide catalytic integrations produce complicated results emanating from many regions, making the unique accurate identification of specific adsorbates on various domains impossible.
Ozensoy et al. have published an article in the Journal of the American Chemical Society displaying scanning NFIR for identification and analysis of sulfur poisoning. The result data suggested that the kinds of adsorbent surfaces and their sorption patterns on the catalyst surface might vary significantly not only on a particular PGM nanoparticle but also between several PGM nanoparticles due to surface morphological differences.
The near-field signal intensity varied with tip surface contact, peak interface proximity, tip/disk configuration, and near-field linkage between nearby discs. The recent DFT theoretical results suggest that by varying the amount of sulfate toxicity through variation of the H2SO4(aq) contact period, not only the sorption patterns but also the adsorption intensities of sulfates on the Pd nanodisk/Al2O3 (thin-film)/Si(100) surface may be altered.
Catalysis has been a significant industrial motivator, with an international economy worth up to $34 billion by 2025, growing at a 4.5 percent annual pace. Research is needed to further understand the chemistry of sulfur poisoning to avoid this phenomenon.
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References and Further Reading
Prieto, N. et. al. (2017). A review of the principles and applications of near-infrared spectroscopy to characterize meat, fat, and meat products. Applied spectroscopy, 71(7), 1403-1426. Available at: https://journals.sagepub.com/doi/10.1177/0003702817709299
Say, Z. et. al. (2022). Unraveling Molecular Fingerprints of Catalytic Sulfur Poisoning at the Nanometer Scale with Near-Field Infrared Spectroscopy. Journal of the American Chemical Society. Available at: https://pubs.acs.org/doi/10.1021/jacs.2c03088
Size, C. M. (2020). Share & Trends Analysis Report by Raw Material (Chemical Compounds, Zeolites, Metals), By Product (Heterogeneous, Homogeneous), By Application, By Region, And Segment Forecasts, 2020–2027, Catalysts & Enzymes, Catalyst Market Size & Share, Industry Report 2020–2027. Grand review research.