FTIR techniques in clay mineral studies

Halloysite clay minerals are ubiquitous in soils and weathered rocks where they occur in a variety of particle shapes and hydration states. Diversity also characterizes their chemical composition, cation exchange capacity and potassium selectivity. This review summarizes the extensive but scattered literature on halloysite, from its natural occurrence, through its crystal structure, chemical and morphological diversity, to its reactivity toward organic compounds, ions and salts, involving the various methods of differentiating halloysite from kaolinite. No unique test seems to be ideal to distinguish these 1:1 clay minerals, especially in soils. The occurrence of 2:1 phyllosilicate contaminants appears, so far, to provide the best explanation for the high charge and potassium selectivity of halloysite. Yet, hydration properties of the mineral probably play a major role in ion sorption. Clear trends seem to relate particle morphology and structural Fe. However, future work is required to understand the possible mechanisms linking chemical, morphological, hydration and charge properties of halloysite.

Halloysite clay minerals — a review

Infrared (IR) spectroscopy has a long and successful history as an analytical technique and is used extensively (McKelvy et al., 1996; Stuart, 1996). It is mainly a complementary method to X-ray diffraction (XRD) and other methods used to investigate clays and clay minerals. It is an economical, rapid and common technique because a spectrum can be obtained in a few minutes and the instruments are sufficiently inexpensive as to be available in many laboratories. An IR spectrum can serve as a fingerprint for mineral identification, but it can also give unique information about the mineral structure, including the family of minerals to which the specimen belongs and the degree of regularity within the structure, the nature of isomorphic substituents, the distinction of molecular water from constitutional hydroxyl, and the presence of both crystalline and non-crystalline impurities (Farmer, 1979).

The interpretation of the absorption spectra of the Source Clays in the middle-IR (MIR) region (4000–400 cm−1) given here follows those of Farmer and Russell (1964), Farmer (1974a, 1979) and Russell and Fraser (1994). In addition, reflectance spectra in the near-IR (NIR) region (11,000–4000 cm−1), where overtones and combination vibrations occur, are included. These spectra provide information on structural OH groups and H2O in clay minerals (Bishop et al., 1994; Frost and Johansson, 1998; Petit et al., 1999a) which may not be clearly observed in the MIR spectra. Small changes in stretching and bending band positions are additive in the combination bands, thereby making them more readily differentiated (Post and Noble, 1993).

Dispersive IR spectrometers are slowly being replaced by quicker and more sensitive Fourier transform (FT) instruments (Rintoul et al., 1998). The greater sensitivity of the FTIR spectrometers is related to the continuous detection of the entire transmitted energy …

Baseline Studies of the Clay Minerals Society Source Clays: Infrared Methods

The thermal stability of organically modified layered silicate (OLS) plays a key role in the synthesis and processing of polymer-layered silicate (PLS) nanocomposites. The nonoxidative thermal degradation of montmorillonite and alkyl quaternary ammonium-modified montmorillonite were examined using conventional and high-resolution TGA combined with Fourier transform infrared spectroscopy and mass spectrometry (TG−FTIR−MS) and pyrolysis/GC−MS. The onset temperature of decomposition of these OLSs was approximately 155 °C via TGA and 180 °C via TGA−MS, where TGA−MS enables the differentiation of water desorbtion from true organic decomposition. Analysis of products (GC−MS) indicates that the initial degradation of the surfactant in the OLS follows a Hoffmann elimination reaction and that the architecture (trimethyl or dimethyl), chain length, surfactant mixture, exchanged ratio, or preconditioning (washing) does not alter the initial onset temperatures. Catalytic sites on the aluminosilicate layer reduce ther...

Thermal Degradation Chemistry of Alkyl Quaternary Ammonium Montmorillonite

I INTRO DUCTION . . . . . . ...... . . . . . . ...... . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 455 1.1 Criteria of Lignin Detection . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . 457 1.2 Lignin Distribution in the Plant Kingdom: A Reevaluation . . . . . . . . . . . . . . . . . . . . . . . . . 458 1.3 Lignin Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 2 LIGNIN B IOG ENE SI S AND S TRUCT URE.... .. ... . . .. . . . . . .. . . . . . . . . .. . . . . . . .. . . . ...... . . . 469 2.1 Arogenic Acid . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . """'"'''''''''''''''''''' 470 2.2 p-Coumaric Acid to £and Z-Monolignols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 2.3 Monolignol Transport into the Cell Wall . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . .. . . . . . . . . . . . . . 472 2.4 Lignin Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . .. .. .. . .... . . . . . . . . 473 2.5 Regulation of Lignification . . . . . . . . . . . . . . . . . . . . . . . . .. . " . . "" . . . . . . . . . . . . . . . . . . . . . . ". . . . . . 476 2.6 Lignin Structure . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . .. .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . 477 3 LIGNIN BIO DEGRADATION . . . . . ..... . .... .. . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . .. . 481 3.1 Lignin-like Polymers in White-Rot Fungi .. .. . . . . . . . . . . . . . . . . . . .. .. . . . . . .. ... . .... . . . . . . 481 3.2 Criteria of Lignin Degradation . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 3.3 Lignin Biodegradation by White-Rot Fungi ...... " . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 482 CONCLU SIONS 487

Lignin: Occurrence, Biogenesis and Biodegradation

The infra-red spectra of layer silicates

Heating weakly acidic dilute solutions containing hydroxyaluminium orthosilicate complexes gives a fibrous polymer, each fibre consisting of tubes about 2·2 nm external diameter and 1·0 nm internal diameter, essentially identical with those of the natural mineral, imogolite.

Synthesis of imogolite: a tubular aluminium silicate polymer

Characterization of the chemical structures of natural and synthetic aluminosilicate gels and sols by infrared spectroscopy

Transverse and longitudinal crystal modes associated with OH stretching vibrations in single crystals of kaolinite and dickite

O-Acetyl groups were detected by i.r. spectroscopy in cell-wall preparations from grasses and other higher plants and their presence was confirmed chemically. The amounts present are likely to influence both the physical state of the cell-wall polysaccharides and also their digestion by enzymes.

V.C. Farmer

Papers

The infra-red spectra of layer silicates

Synthesis of imogolite: a tubular aluminium silicate polymer

Characterization of the chemical structures of natural and synthetic aluminosilicate gels and sols by infrared spectroscopy

Transverse and longitudinal crystal modes associated with OH stretching vibrations in single crystals of kaolinite and dickite

Acetyl groups in cell-wall preparations from higher plants.