Infrared Emission Spectroscopic Study of the Dehydroxylation of Some Natural and Synthetic Saponites

The infrared emission spectra of hydrothermally synthesized saponites have been compared to those of naturally occurring saponites. The spectra are very similar and only very minor differences are observed in the band positions and intensities. The OH-stretching region reveals for only the synthetic saponite a small band around 3040-3120cm ascribed to ammonium in the interlayer position. OH-stretching bands associated with adsorbed and interlayer water are observed around 3250 and 3425 cm. The strong band around 3600-3630 cm is ascribed to the Mg(Al, vac)-OH stretching mode whereas the band around 3670 cm is ascribed to the Mg-OH stretching mode. Upon heating the OH-stretching region shows firstly the disappearance of the interlayer water and secondly a decrease in intensity of the Mg(Al, vac)-OH hydroxyl-band. In contrast the Mg-(OH) hydroxyl-band decreases far less in intensity. A silanol band at 3778 cm is observed over the whole temperature range from room temperature to 750 °C in the spectra of all saponites. The MgAl-OH translation mode around 450 cm and deformation mode around 750cm decrease in intensity and are no longer observed in the 700 °C spectrum. Instead, a new band is observed around 730-740 cm ascribed to the restructuring of the octahedral layer and the formation of a new Al-O bond after the dehydroxylation. Because the dehydroxylation is not complete at 700-750 °C no new bands due to the formation of new Mg-O-Mg, Mg-O-Al or Mg-O-Si bonds are observed. Only a minor decrease in the Mg-OH bands is observed

Towards a Single Crystal Raman Spectrum of Kaolinite at 77K

The Raman spectra at 77 K of the hydroxyl stretching of kaolinite were obtained along the three axes perpendicular to the crystal faces. Raman bands were observed at 3616, 3658 and 3677 cm−1 together with a distinct band observed at 3691 cm−1 and a broad profile between 3695 and 3715 cm−1. The band at 3616 cm−1 is assigned to the inner hydroxyl. The bands at 3658 and 3677 cm−1 are attributed to the out-of-phase vibrations of the inner surface hydroxyls. The Raman spectra of the in-phase vibrations of the inner-surface hydroxyl-stretching region are described in terms of transverse and longitudinal optic splitting. The band at 3691 cm−1 is assigned to the transverse optic and the broad profile to the longitudinal optic mode. This splitting remained even at liquid nitrogen temperature. The transverse optic vibration may be curve resolved into two or three bands, which are attributed to different types of hydroxyl groups in the kaolinite

Raman Microscopy Study of Kalinite, Tschermigite and Lonecreekite at 298 and 77K

The Raman spectra of some common naturally occurring alums, kalinite (KSO · Al(SO) · 22HO) and tschermigite ((NH)SO · Al(SO) · 24HO) have been obtained at 298 and 77K. A comparison is made with lonecreekite ((NH)SO · -Fe(SO) · 24HO), the ammonium ferric alum. Two bands are observed at 990 and 972 cm and are assigned to the v(A) SO vibration. Two bands are also observed at 1130 and 1104 cm and are attributed to the antisymmetric stretching vibration V(B) SO. A single band at 454 cm attributed to the V(A,) SO mode splits into three bands at 476, 457 and 442 cm in the 77K spectrum. The band at 618 cm assigned to the V(B) SO mode resolves into three bands at 632, 612 and 596 cm at 77K. The splitting of the v, v and V modes is attributed to the reduction of symmetry of the SO and it is proposed that the sulphate coordinates to water in the hydrated aluminium in bidentate chelation

Clays and the Origin of Life: The Experiments

There are three groups of scientists dominating the search for the origin of life: the organic chemists (the Soup), the molecular biologists (RNA world), and the inorganic chemists (metabolism and transient-state metal ions), all of which have experimental adjuncts. It is time for Clays and the Origin of Life to have its experimental adjunct. The clay data coming from Mars and carbonaceous chondrites have necessitated a review of the role that clays played in the origin of life on Earth. The data from Mars have suggested that Fe-clays such as nontronite, ferrous saponites, and several other clays were formed on early Mars when it had sufficient water. This raised the question of the possible role that these clays may have played in the origin of life on Mars. This has put clays front and center in the studies on the origin of life not only on Mars but also here on Earth. One of the major questions is: What was the catalytic role of Fe-clays in the origin and development of metabolism here on Earth? First, there is the recent finding of a chiral amino acid (isovaline) that formed on the surface of a clay mineral on several carbonaceous chondrites. This points to the formation of amino acids on the surface of clay minerals on carbonaceous chondrites from simpler molecules, e.g., CO2, NH3, and HCN. Additionally, there is the catalytic role of small organic molecules, such as dicarboxylic acids and amino acids found on carbonaceous chondrites, in the formation of Fe-clays themselves. Amino acids and nucleotides adsorb on clay surfaces on Earth and subsequently polymerize. All of these observations and more must be subjected to strict experimental analysis. This review provides an overview of what has happened and is now happening in the experimental clay world related to the origin of life. The emphasis is on smectite-group clay minerals, such as montmorillonite and nontronite

Near-Infrared Spectroscopic Study of Basic Aluminum Sulfate and Nitrate

The tridecameric Al-polymer [AlO4Al12(OH)24(H2O)12]7+ was prepared by forced hydrolysis of Al3+ up to an OH/Al molar ratio of 2.2. Under slow evaporation crystals were formed of Al13-nitrate. Upon addition of sulfate the tridecamer crystallised as the monoclinic Al13-sulfate. These crystals have been studied using near-infrared spectroscopy and compared to Al2(SO4)3.16H2O. Although the near-infrared spectra of the Al13-sulfate and nitrate are very similar indicating similar crystal structures, there are minor differences related to the strength with which the crystal water molecules are bonded to the salt groups. The interaction between crystal water and nitrate is stronger than with the sulfate as reflected by the shift of the crystal water band positions from 6213, 4874 and 4553 cm–1 for the Al13 sulfate towards 5925, 4848 and 4532 cm–1 for the nitrate. A reversed shift from 5079 and 5037 cm–1 for the sulfate towards 5238 and 5040 cm–1 for the nitrate for the water molecules in the Al13 indicate that the nitrate-Al13 bond is weakened due to the influence of the crystal water on the nitrate. The Al-OH bond in the Al13 complex is not influenced by changing the salt group due to the shielding by the water molecules of the Al13 complex

The Behavior of Hydroxyl Units of Synthetic Goethite and its Dehydroxylated Product Hematite

The behavior of the hydroxyl units of synthetic goethite and its dehydroxylated product hematite was characterized using a combination of Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) during the thermal transformation over a temperature range of 180-270 degrees C. Hematite was detected at temperatures above 200 degrees C by XRD while goethite was not observed above 230 degrees C. Five intense OH vibrations at 3212-3194, 1687-1674, 1643-1640, 888-884 and 800-798 cm(-1), and a H2O vibration at 3450-3445 cm(-1) were observed for goethite. The intensity of hydroxyl stretching and bending vibrations decreased with the extent of dehydroxylation of goethite. Infrared absorption bands clearly show the phase transformation between goethite and hematite: in particular. the migration of excess hydroxyl units from goethite to hematite. Two bands at 536-533 and 454-452 cm(-1) are the low wavenumber vibrations of Fe-O in the hematite structure. Band component analysis data of FTIR spectra support the fact that the hydroxyl units mainly affect the a plane in goethite and the equivalent c plane in hematite

Modification of Chrysotile Surface by Organosilanes: An IR-Photoacoustic Spectroscopy Study

Chrysotile and its dimethylsilyl (DMS) and dimethylphenylsilyl (DMPS) derivatives were studied by Fourier transform infrared–photoacoustic spectroscopy. In the Si–O stretching region of chrysotile a new band was revealed at 985 cm−1, besides absorptions at 1083, 1028, and 947 cm−1. The Si–O stretching frequencies did not undergo major changes in the DMS derivative, but the 985- and 1028-cm−1 peaks were undetected in DMPS due to the HCl attack on chrysotile tetrahedral sheets. Similar effects were observed in the region 900–400 cm−1, by a decrease in intensities of the 600- and 642-cm−1 Mg-OH libration modes in the DMPS spectrum, indicating also a HCl attack on the octahedral sheet. The Si–C band at 800 cm−1 in the spectra of both DMS and DMPS was accompanied by minor components. DMPS showed a strong peak at 813 cm−1 assigned to a Si–phenyl vibration. A sharp peak at 1263 cm−1 in the DMS spectrum was ascribed to a diagnostic C–H bending mode of the dimethylsilyl groups in DMS. The complex bands around 1413 cm−1 in DMS were attributed to CH3 deformation vibrations and that at 1466 cm−1 in DMPS to phenyl groups. In DMPS a distinct peak at 1593 cm−1 was attributed to a Si–phenyl vibration. In the region 3700–2500 cm−1 absorptions at 2964, 2931, and 2907 cm−1 in DMS were ascribed to C–H-stretching vibrations of dimethylsilyl groups, while a strong peak at 2919 cm−1 in the DMPS spectrum was attributed to a Si–C6H5 mode

Heating Stage Raman and Infrared Emission Spectroscopic Study of the Dehydroxylation of Synthetic Mg-Hydrotalcite

The thermal behaviour of synthetic hydrotalcite, Mg5.6Al2.4(OH)16(CO3,NO3)·nH2O, has been studied by Infrared Emission Spectroscopy (IES) and heating stage Raman microscopy. Heating stage Raman microscopy reveals that upon heating and subsequent dehydration the bands at 553, 1052, 3503, 3603 and 3689 cm−1 associated with the (Mg,Al)3–OH translation, deformation and stretching vibrations decrease in intensity due to changes in the stacking order of the hydroxide layers. During this rearrangement around 150–175°C the free interlayer nitrate forms a type of bridging nitrato complex with the metals in the hydroxide layers as evidenced by the disappearance of the normal free nitrate vibrations at 716, 1067 and 1386 cm−1 and the formation of a new band at 1039 cm−1. Further heating to 300°C results in the dehydroxylation and decarbonisation of the hydrotalcite, which is only partially reversed upon cooling in air over a period of more than 12 h. The Mg-hydrotalcite IES spectra show major changes around 350–400°C indicating the end of the dehydroxylation. In this temperature range, “Al”–OH bands at 772, 923 and 1029 cm−1 disappear. New bands are observed around 713, 797 and 1075 cm−1. The first and the last bands plus the 545 cm−1 band indicate the formation of spinel (MgAl2O4). The 713 cm−1 band is also close to the νLO position of MgO at 717 cm−1, which is another product formed after dehydroxylation. However, decarbonisation is not complete at this stage as evidenced by both a continuing weight loss in the TGA up to at least 625°C and a decreasing carbonate signal in the IES up to 800°C