In Situ Time-Dependent Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy of a Powdered Specimen in a Controlled Atmosphere: Monitoring Sorption and Desorption of Water Vapor

Abstract

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy is a powerful instrumental method of chemical analysis of solids and liquids. The majority of published studies by in-situ ATR-FTIR spectroscopy describe analysis of homogeneous samples, such as liquid solutions under circulation, or films on the ATR crystal that react with the gas of interest. The in-situ ATR-FTIR spectroscopic studies of specimens in physical shape of crystals or powder that react with a gas or vapor are rare. This work describes a modification of in-situ time-dependent ATR-FTIR spectroscopy to allow monitoring heterogeneous reaction “solid-gas” of powder in controlled atmosphere and in the time domain. Also, we describe a new facile gas flow chamber attachment to ATR-FTIR spectrometer which allows creating controlled atmosphere surrounding the specimen on the ATR crystal. Additionally, the capabilities of the described in-situ time-dependent ATR-FTIR spectroscopy experiment in controlled atmosphere are enhanced by the sensor for in-situ time-dependent monitoring the relative humidity (RH) of air surrounding the specimen. The operation of the setup for in-situ time-dependent ATR-FTIR spectroscopy in controlled atmosphere is demonstrated by monitoring reaction of gradual desorption of water vapor from color-indicating molecular sieves under controlled low air humidity. Further, the described spectroscopic method and apparatus is applied to monitor the reverse process, namely sorption of water vapor by color-indicating molecular sieves under controlled elevated air humidity. Water molecules are found to reversibly interact with two distinct sorption sites in the sorbent: the Si-O backbone and the color-indicating Co(II) centers. The reported variant of in-situ time-dependent ATR-FTIR spectroscopy in controlled atmosphere is powerful, yet facile and straightforward. It is promising for mechanistic, in-situ studies of sorption, desorption, chemo-sensing, heterogeneous catalysis and photocatalysis, and analysis of chemical kinetics of various “solid-gas” reactions.

A zinc-containing porphyrin aluminum MOF in sorption of diethyl sulfide vapor: mechanistic experimental and computational study

“…Recently, we reported a new variant of in situ timedependent ATR-FTIR spectroscopy in a controlled gaseous environment, where the sorbent is in the physical form of powder. 29 In studies of the kinetics of sorption, the Langmuir adsorption model is frequently used; see, for example, analytical and numerical solution of kinetics of sorption in the flow of a gas. 41 Fig.…”

“…water vapor, oxygen, and carbon dioxide and protects operators from toxic gases; this finds use in work with hazardous materials. 28 Recently, we reported an in situ time-dependent ATR-FTIR spectroscopic study of the mechanism of sorption and desorption of water vapor on molecular sieves, 29 using a custom-built flow chamber in the shape of a large box (height of 7 inches and width of 9 inches) attached to the ATR-FTIR spectrometer.…”

Sorption and Desorption of Vapor of n-Pentane by Porphyrin Aluminum Metal–Organic Framework: Mechanism of Bonding, Kinetics and Stoichiometry by Complementary In-Situ Time-Dependent and Ex-Situ Methods

“…The flow chamber has a "roof" but no "bottom", and its open bottom side is attached to the top panel of the FTIR spectrometer Nicolet IS10 and over the ATR accessory with a specimen. The process of fabrication of the flow chamber was described recently by us [32]. Outside of the flow chamber, the adapter had quick-disconnect termination for the connection of the gas inlet supply line.…”

Interaction of a Porphyrin Aluminum Metal–Organic Framework with Volatile Organic Sulfur Compound Diethyl Sulfide Studied via In Situ and Ex Situ Experiments and DFT Computations

“…Recently, we reported a new modality of in situ time-dependent ATR-FTIR spectroscopy in the controlled gaseous environment, which allowed facile mechanistic studies of sorption and desorption of vapor by the powder of sorbent on the ATR crystal [25]. There are no studies of kinetics of sorption of any organosulfur compound on any MOF, to our knowledge, using in situ time-dependent ATR-FTIR spectroscopy in a controlled atmosphere.…”

“…Surprisingly, there are only very few publications on in situ time-dependent ATR-FTIR spectroscopic studies of sorption of gases or vapors by powders [24]. Recently, we described the in situ time-dependent ATR-FTIR spectroscopy to investigate the mechanisms of sorption and desorption of vapor of water in air on molecular sieves [25] using a custom-built large flow attachment to the FTIR spectrometer.…”