J. T. Kloprogge

Porous materials for oil spill cleanup: A review of synthesis and absorbing properties

This paper reviews the synthesis and the absorbing properties of the wide variety of porous sorbent materials that have been studied for application in the removal of organics, particularly in the area of oil spill cleanup. The discussion is especially focused on hydrophobic silica aerogels, zeolites, organoclays and natural sorbents many of which have been demonstrated to exhibit (or show potential to exhibit) excellent oil absorption properties. The areas for further development of some of these materials are identified.

THERMAL DECOMPOSITION OF BAUXITE MINERALS: INFRARED EMISSION SPECTROSCOPY OF GIBBSITE, BOEHMITE AND DIASPORE

Infrared emission spectroscopy has been used to study the dehydroxylation behavior over the temperature range from 200 to 750°C of three major Al-minerals in bauxite: gibbsite (synthetic and natural), boehmite (synthetic and natural) and diaspore. A good agreement is found with the thermal analysis and differential thermal analysis curves of these minerals. Loss in intensity of especially the hydroxyl-stretching modes of gibbsite, boehmite and diaspore as function of temperature correspond well with the observed changes in the TGA/DTA patterns. The DTA pattern of gibbsite clearly indicates the formation of boehmite as an intermediate shown by a endotherm around 500°C. Dehydroxylation of gibbsite is followed by a loss of intensity of the 3620 and 3351 cm−1 OH-stretching bands and the corresponding deformation band around 1024 cm−1. Dehydroxylation starts around 220°C and is complete around 350°C. Similar observations were made for boehmite and diaspore. For boehmite dehydroxylation was observed to commence around 250°C and could be followed by especially the loss in intensity of the bands around 3319 and 3129 cm−1. The DTA pattern of diaspore is more complex with overlapping endotherms around 622 and 650°C. The dehydroxylation can be followed by the decrease in intensity of the OH-stretching bands around 3667, 3215 and 2972 cm−1. Above 550°C only a single band is observed that disappears after heating above 600°C corresponding to the two endotherms around 622 and 650°C in the DTA.

Raman and infrared spectroscopic study of the vivianite-group phosphates vivianite, baricite and bobierrite

Abstract The molecular structure of the three vivianite-structure, compositionally related phosphate minerals vivianite, baricite and bobierrite of formula M32+(PO4)2‧8H2O where M is Fe or Mg, has been assessed using a combination of Raman and infrared (IR) spectroscopy. The Raman spectra of the hydroxyl-stretching region are complex with overlapping broad bands. Hydroxyl stretching vibrations are identified at 3460, 3281, 3104 and 3012 cm-1 for vivianite. The high wavenumber band is attributed to the presence of FeOH groups. This complexity is reflected in the water HOH-bending modes where a strong IR band centred around 1660 cm-1 is found. Such a band reflects the strong hydrogen bonding of the water molecules to the phosphate anions in adjacent layers. Spectra show three distinct OH-bending bands from strongly hydrogen-bonded, weakly hydrogen bonded water and non-hydrogen bonded water. The Raman phosphate PO-stretching region shows strong similarity between the three minerals. In the IR spectra, complexity exists with multiple antisymmetric stretching vibrations observed, due to the reduced tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Strong IR bands around 800 cm-1 are attributed to water librational modes. The spectra of the three minerals display similarities due to their compositions and crystal structures, but sufficient subtle differences exist for the spectra to be useful in distinguishing the species.

Infrared spectroscopy of goethite dehydroxylation: III. FT-IR microscopy of in situ study of the thermal transformation of goethite to hematite

Fourier transform infrared microscopy has been used to investigate in situ dehydroxylation of goethite to form hematite. The characterisation was based on the behaviour of hydroxyl units, which were observed in the hydroxyl stretching and hydroxyl deformation and water bending regions, and the Fe-O vibrations of the newly formed hematite during the thermal dehydroxylation process. Two hydroxyl stretching modes (v1 and v2), and three bending (V(bending-1, 2, 3)) and two deformation (V(deformation-1, 2)) modes were observed for goethite. The characteristic vibration at 916 cm(-1) was observed together with the residuals of the v1 and v2 bands in hematite spectrum. The structural transformation between goethite and hematite through thermal dehydroxylation was interpreted in order to provide criteria that can be used for the characterisation of thermally activated bauxite and their conversion to activated alumina phases.

The effects of various hydrothermal treatments on magnesium-aluminium hydrotalcites

Mg/Al hydrotalcites were synthesised by coprecipitation followed by hydrothermal treatment. The materials were characterised by XRD, infrared and Raman spectroscopy, electron microscopy and thermal analysis. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO32−, with a basal distance of ∼23.5 Å. All possible CO32− modes were observed in the infrared and Raman spectra, at 1068 cm−1, 844 cm−1, ∼1380 cm−1, and ∼680 cm−1. XRD, Infrared and Raman spectroscopy complimented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity and that treatment in water rather than in the mother liquid resulted in a more crystalline material. TEM showed that crystal size increased with aging, such that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. Thermal analysis showed 3 major weight losses corresponding to the loss of interparticle water, interlayer water, and dehydroxylation of the hydroxide layers and decarbonation of the interlayer region.

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.

Low temperature synthesis and characterization of nesquehonite

Nesquehonite, Mg(HCO3)(OH).2H2O or MgCO3.3H2O, was named after its type locality in Nesquehoning, Pennsylvania, USA. The structure of nesquehonite can be envisaged as infinite chains of corner sharing MgO6 octahedra along the b-axis. Within these chains CO32- groups link 3 MgO6 octahedra by two common corners and one edge. This structural arrangement causes strong distortion of the octahedra. Chains are interconnected by hydrogen bonds only, whereby each Mg atom is coordinated to two water ligands and one free water molecule is located in between the chains [1, 2]. Under natural conditions nesquehonite can form in evaporites depending on the availability of Mg2+ ions in solution relative to other cations, such as Ca2+ [3-5]. Additionally, nesquehonite occurs as an alteration product in the form of scales or efflorescences on existing carbonate rocks, serpentine, or volcanic breccias [6-11]. Interestingly it has also been observed on the surface of a limited number of meteorites found in Antarctic regions, where it has formed by reactions of the meteorite minerals with terrestrial water and CO2 at near freezing temperatures [12-16]. Nesquehonite has also been identified on the surfaces of manmade materials, such as bricks and mortar [17, 18]. The synthesis of nesquehonite forms a continuation of our work on the synthesis and study of the vibrational spectroscopy of natural and synthetic minerals in the hydroxide (brucite, gibbsite, boehmite, etc.)[19-23], carbonate (cerussite, azurite, malachite, etc.)[24-26] and hydroxycarbonate (hydrotalcite)[21, 27-32] groups. This work aims at describing a simple method for the synthesis of nesquehonite and the detailed characterization of the structure and morphology by X-ray diffraction (XRD), vibrational spectroscopy and scanning electron microscopy (SEM).

Infrared spectroscopy of goethite dehydroxylation. II. Effect of aluminium substitution on the behaviour of hydroxyl units

Dehydroxylation of goethite as affected by aluminium substitution was investigated using Fourier transform infrared spectroscopy (FT-IR) in conjunction with X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA). The band intensities of hydroxyl vibrations were indicative of the degree of dehydroxylation and the changes in band parameters due to aluminium substitution were observed. The effect of aluminium substitution on band parameters of FT-IR spectra of goethite and its partially and fully dehydroxylated products, the mixture of goethite/hematite and hematite, were interpreted. The results of this study have confirmed that aluminium substituted goethite is thermally more stable than non-substituted goethite and is in harmony with the results of XRD and DTGA. A larger amount of non-stoichiometric hydroxyl units is associated with a higher aluminium substitution. A shift to a higher wavenumber of bending and hydroxyl stretching vibrations is attributed to the effects of aluminium substitution associated with non-stoichiometric hydroxyl units on the a-b plane relative to the b-c plane of goethite. The results provide information for the characterisation of activated bauxite containing hematite and goethite.

Detection of four different OH-groups in ground kaolinite with controlled-rate thermal analysis

The thermal behaviour of mechanochemically treated kaolinite has been investigated under dynamic and controlled rate thermal analysis (CRTA) conditions. Ten hours of grinding of kaolinite results in the loss of the d(001) spacing and the replacement of some 60% of the kaolinite hydroxyls with water. Kaolinite normally dehydroxylates in a single mass loss stage between 400 and 600°C. CRTA technology enables the dehydroxylation of the ground mineral to be observed in four overlapping stages at 385, 404, 420 and 433°C under quasi-isobaric condition in a self-generated atmosphere. It is proposed that mechanochemical treatment of the kaolinite causes the localization of the protons when the long range ordering is lost.

DSC AND HIGH-RESOLUTION TG OF SYNTHESIZED HYDROTALCITES OF Mg AND Zn

A combination of DSC and high resolution DTG coupled to a gas evolution mass spectrometer has been used to study the thermal properties of a series of Mg/Zn hydrotalcites of formulae MgxZn6-xAl2(OH)16(CO3) ·4H2O where x varied from 6 to 0. The effect of increased Zn composition results in the decrease of the endotherms and mass loss steps to lower temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps. The interlayer carbonate anion is lost simultaneously with hydroxyl units.