Christopher Breen

Adsorption of polyamine, polyacrylic acid and polyethylene glycol on montmorillonite: An in situ study using ATR-FTIR

Abstract Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray diffraction (XRD) have been employed to investigate the adsorption of water soluble polymers from aqueous solution onto a clay mineral surface in situ, to gain an understanding of the interactions occurring at the microscopic level in water based muds (WBM). The water soluble polymers studied were; polyethylene glycol (PEG) (molecular weight, M w , 300 and 1000) (neutral), polyamine (FL15) ( M w 5000) (cationic) and polyacrylic acid, PAA, ( M w 2000) (charge dependant on pH) to establish the effect of polymer charge on the nature and extent of adsorption. XRD and ATR-FTIR spectroscopy have shown that water soluble polymers adsorb onto clay dispersions and are stable when deposited as thin solid films. XRD indicates that PEG stacks as either one or two layers whereas PAA and FL15 are restricted to a single layer between the clay lamellae. ATR-FTIR spectroscopy showed that FL15 penetrated the Na–SWy-1 films which contained low loadings of PEG without displacing any of the resident PEG. When a bilayer of PEG was present, FL15 did not penetrate into the film. Both PAA and PEG adsorbed onto FL15 loaded Na–SWy-1 films irrespective of FL15 loading or the molecular weight of the PEG. ATR-FTIR indicated that significant adsorption occurred in under 30 s and the adsorption rate was not influenced by the presence of a second polymer preloaded into the clay.

The characterisation and use of polycation-exchanged bentonites

The interaction of polymers with clays is considered with particular emphasis on the adsorption of polycations of the type [CH2CHOHCH2N(CH3)(2)](n)(n+) onto a low iron Texas bentonite, Westone-L (WL). The influence of clay type, particle size and resident cation on the amount of adsorbed polycation is reported along with variable temperature X-ray diffraction of the resulting complexes. The information obtained from Cs+- and Na+-WL suspensions using Cs-133 and Na-23 solution phase NMR is summarised and used to show that this technique can provide quantitative information regarding the displacement of Cs+-ions from the exchange sites by polycation in suspension and reflect subtle in situ changes intimated from Zeta potential measurements. The use of polycation-exchanged clays as scavengers of p-nitrophenol from water is described as is the significant activity of acid-treated polycation-exchanged clays for the catalytic isomersion of alpha-pinene to camphene and limonene

Characterisation of moderately acid-treated, size-fractionated montmorillonites using IR and MAS NMR spectroscopy and thermal analysis

The < 2 µm fractions of Cheto (Arizona, USA) and Jelsový Potok (Slovakia) montmorillonites have been treated with 1 mol dm–3 H2SO4 for periods up to 6 h at 95 °C. The materials obtained were investigated by X-ray fluorescence (XRF), X-ray diffraction (XRD), infrared (IR) spectroscopy, and 29Si and 27Al magic-angle spinning (MAS) NMR spectroscopy. Both clays were partially decomposed under the conditions utilized, but the Cheto montmorillonite, which contained a higher proportion of octahedral magnesium, was more susceptible to acid attack. XRD was insensitive to this level of acid attack but XRF, IR and 29Si MAS NMR revealed the depopulation of the octahedral sheet. The number of acid sites was determined from the thermal desorption of cyclohexylamine and the catalytic activity was evaluated by reacting 2,3-dihydropyran with methanol to yield the tetrahydropyranyl ether. The test reaction was a more sensitive indicator of changes in clay acidity than the values determined by desorption of cyclohexylamine from acid sites.

Correlation of catalytic activity with infra-red, 29Si MAS NMR and acidity data for HCl-treated fine fractions of montmorillonites

The <2 μm fractions of SAz-1 (Cheto, Arizona, USA) and JP (Jelsový Potok, Slovakia) montmorillonites were treated with 6 M HCl for 30, 300 and 900 minutes at 95°C. The materials obtained were investigated by X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetry (TG), infrared (IR) spectroscopy, and 29Si MAS NMR spectroscopy. The number of acid sites was determined from the thermal desorption of cyclohexylamine and the catalytic activity was evaluated by reacting 2,3-dihydropyran with methanol to yield the tetrahydropyranyl ether. All the investigative methods utilised, which each provided discrete evidence for the depopulation of the octahedral sheet, confirmed that treatment of SAz-1 for 300 and 900 minutes caused complete destruction of the original structure. In contrast JP was more resistant to acid attack and the treatments resulted in materials with different levels of structural decomposition. Samples of JP and SAz-1 treated for 30 minutes exhibited Bronsted acidities commensurate with the exchange capacities of the parent materials and this was reflected in their catalytic activity. A reduction in both acidity and catalytic activity was observed after longer treatment times and this was attributed to the presence of fewer exchange sites due to the depopulation of the octahedral sheet. The Ca back-exchanged samples did not catalyse the ether forming reaction.

Acid-activated organoclays: preparation, characterisation and catalytic activity of polycation-treated bentonites

Samples of SWy-2 and SAz-1 loaded with increasing amounts of the polycation magnafloc 206, [(Me2NCH2CHOHCH2)n]n+Cln, were acid-treated using 6 M HCl at 95°C for 30, 90 and 180 min. The activity of these acid-activated polycation-exchanged clays for the conversion of α-pinene to camphene and limonene was determined and compared with that from clay samples (without polycation) acid-treated in the same manner. Acid treatment of polycation-exchanged bentonites produced hybrid catalysts which enhanced the activity of the clays for the isomerisation of α-pinene to camphene and limonene. The presence of the polycation had a more marked influence on the activity of samples derived from SAz-1 increasing the yield from 25% for acid-activated SAz-1 with no added polycation to 50% camphene for acid-activated polycation-exchanged SAz-1. The increase in yield for corresponding samples derived from SWy-2 was only from 42 to 52%. This enhancement in yield for samples derived from SAz-1 was attributed to the increased hydrophobicity of the polycation loaded clay whilst the comparable yields for SWy-2 in the absence and presence of polycation may suggest that SWy-2 disperses well in the non-polar α-pinene. The total yields (based on α-pinene) for the most active catalysts was between 80 and 90%. These yields are directly comparable with those obtained by others using zeolites and pillared clays although the acid-activated polycation-treated clays were marginally less selective towards camphene.

Acidity and catalytic activity of mildly acid-treated Mg-rich montmorillonite and hectorite

XRD, FTIR spectroscopy, cyclohexylamine desorption, potentiometric titrations and catalytic activity in an ether-forming test reaction have been used to investigate mildly acid-treated montmorillonite (SAz-1) and hectorite. The number of acid sites obtained from the cyclohexylamine desorption agreed with the accepted cation exchange capacity values for all samples. No evidence of any free protons was found in the potentiometric titration curves, which proved that complete autotransformation of the acid-treated samples had occurred over a much shorter period than previously recorded. Acid sites associated with Al3+ (Fe3+) released from the SAz-1 structure during acid treatment and subsequent autotransformation were of sufficient strength to catalyse the test reaction and produce tetrahydropyranyl ether in 80% yield. The complete absence of catalytic activity in the acid-treated hectorite samples confirmed that acid sites associated with interlayer Mg2+ and Li+ were unable to catalyse the test reaction.

A new nano-TiO2 immobilized biodegradable polymer with self-cleaning properties

This study concentrated on the direct immobilization of anatase nano titanium dioxide particles (TiO(2), 10nm particle size) into or onto a biodegradable polymer, polycaprolactone, by solvent-cast processes. The self-cleaning, namely photocatalytic properties of the produced materials were tested by photocatalytic removal of methylene blue as model compound and antimicrobial properties were investigated using Candida albicans as model microorganism. Produced TiO(2) immobilized polymer successfully removed methylene blue (MB, 1 × 10(-5)M) from aqueous solution without additional pH arrangement employing a UV-A light (365 nm) source. Almost 83.2% of dye was removed or decomposed by 5 wt% TiO(2) immobilized into PCL (0.08 g) and removal percentage reached to 94.2% with 5 wt% TiO(2) immobilized onto PCL after a 150 min exposure period. Although removal percentage decrease with increased ionic strength and usage of a visible light source, produced materials were still effective. TiO(2) immobilized onto PCL (5 wt%) was quite effective killing almost 54% of C. albicans (2 × 10(6)CFU/mL) after only 60 min exposure with a near visible light source. Control experiments employing PCL alone in the presence and absence of light were ineffective under the same condition.

Ageing of oilfield cement at high humidity: a combined FEG-ESEM and Raman microscopic investigation

The ageing of oil-well cement, Dyckerhoff class G, under saturated water vapour in the presence of carbon dioxide has been studied using the complementary techniques of Raman microscopy and environmental scanning electron microscopy. This combination of techniques has enabled the key components involved in the surface hydration processes to be identified in situ, their time evolution to be monitored directly (without the need for quenching and sample extraction) and this evolution of chemistry/mineralogy to be related to local structural changes. It has also enabled local chemical changes in this highly heterogeneous material to be related to the original cement grain mineralogy. High aspect ratio structural features, rich in aluminium and sulfur, were formed on the grain surface during the ageing process. These were identified as ettringite, which exhibited a diagnostic band at 988 cm−1 in the Raman spectrum.

In situ Raman analysis of hydrating C3A and C4AF pastes in presence and absence of sulphate

Abstract Raman spectroscopy has been used to follow the hydration of C3A and C4AF, two of the principal components of ordinary Portland cement (OPC), in the absence and presence of calcium sulphate (gypsum). Raman spectroscopy enabled in situ, real time analysis of the hydrating pastes. Analysis of the pastes by X-ray diffraction complemented the Raman data and confirmed sample composition. Subtle changes in the Raman spectra of the different pastes illuminated differences in hydration behaviour between C3A and C4AF. The similarities and differences between the various systems are discussed. The influence of carbon dioxide on the hydration products has also received attention.

In situ determination of Bronsted/Lewis acidity on cation-exchanged clay mineral surfaces by ATR-IR

Abstract Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has been used to determine the nature of acid sites present in Na+-, Ni2+- and Al3+-exchanged montmorillonite using the diagnostic base, pyridine. The pyridine additions were performed in situ at 25℃ in the presence of liquid benzene or deuterated 1,4-dioxan to ascertain whether the acidity profile was influenced by the presence of either the non-polar or oxygenated solvent. Pyridine treated Ni2+-montmorillonite exhibited absorption bands characteristic of Lewis bound base in both benzene and deuterated 1,4-dioxan indicating that the Lewis acid sites were present at low temperature and were accessible in both solvents. The presence of a strong 1537 cm-1 band in pyridine-saturated Al3+-montmorillonite confirmed that this clay acted as a Brønsted acid in benzene. However, this diagnostic band was significantly reduced in the presence of deuterated 1,4-dioxan.