Lorraine Gibson

Large pore diameter MCM-41 and its application for lead removal from aqueous media

A room temperature method to create large pore size and pore volume ordered mesoporous silica (MCM-41) is demonstrated. Template removal was achieved with a microwave digestion procedure using a solution of nitric acid and hydrogen peroxide. The silica product exhibited an ordered hexagonal mesostructure, large pore volume (up to 0.99 cm(3)/g), and large pore size (up to 6.74 nm) indicating its potential as a high capacity adsorbent. Surface modification, to enhance the ability of the material to extract potentially toxic metals (PTMs) from water was performed using different amino- and mercapto-functional groups. This paper reports on the extraction of lead ions from aqueous solution to demonstrate the materials significant improvement in adsorption capacity (up to 1000 μmol g(-1) for lead). Moreover, methods have been developed to regenerate the sorbent allowing 100% recovery of Pb and reuse of the sorbent material in subsequent extractions. The performance of the material was also demonstrated for environmental samples containing relatively high concentrations (ppmv) of mixed metal ions reducing them to lower values (<100 ppbv) indicating that the sorbent may have applicability for environmental remediation of polluted water.

Selective extraction of mercury(II) from water samples using mercapto functionalised-MCM-41 and regeneration of the sorbent using microwave digestion

Silica sorbents, based on mesoporous crystalline material-41 (MCM-41), were functionalised using mercaptopropyl (MP) or diethylenetriamine (DETA) to extract mercury (II) ions from water. MP-MCM-41 is an extremely efficient and selective sorbent for the removal of mercury (II) from samples of distilled water doped with heavy metal ions and additionally from more complex matrices including tap and river water. In contrast DETA-MCM-41 preferentially removes hard metal ions (chromium, manganese, lead and zinc) over soft metal ions such as mercury. During extraction, the influence of pH on adsorption capacity was examined; a maximum adsorption capacity of 1245 μmol g(-1) was achieved for MP-MCM-41 even at pH values as low as 3. Significantly, a method has been developed for the first time to remove Hg (II) from loaded MP-MCM-41 allowing this analyte to be selectively recovered from water contaminated with a wide range of heavy metal ions. The regeneration method does not disrupt the chelating agent which remains on the surface of the silica permitting reuse of the sorbent in further extractions.

A diffusion tube sampler for the determination of acetic acid and formic acid vapours in museum cabinets

A passive, diffusion-tube sampler has been developed for the quantification of acetic acid and formic acid vapours in ambient air. The sampling rates of the diffusion tube and the response times were calculated to be 0.88 ml min−1 and 3.8 min for acetic acid and 1.02 ml min−1 and 3.3 min for formic acid, respectively. The sampler has been deployed unobtrusively in museum environments to collect pollutants over a period of typically 1–2 weeks. Determination of the collected analytes was performed using ion chromatography. Under laboratory test conditions, the results of the sampler for replicate analyses were found to be repeatable and reproducible; typical RSD values were less than 5% for the collection of acetic and formic acid vapours from atmospheres of approximately 187 and 88 mg m−3, respectively. Detection limits of 44 and 13 μg m−3 were calculated for a two week sampling period for acetic acid and formic acid, respectively. The mass of acids collected by the passive sampler increased linearly with atmospheric acid concentrations up to approximately 386 mg m−3 acetic acid and 194 mg m−3 formic acid. In an atmosphere containing approximately 187 and 88 mg m−3 of acetic and formic acid vapours, respectively, the mass of acids collected by passive samplers increased linearly for exposure times between 2 and 75 h. The sampler has been used to investigate the concentration of acetic acid and formic acid vapours in museum cabinets where damage to artefacts by atmospheric pollution has been observed.

A comparative study of selected sorbents for sampling of aromatic VOCs from indoor air

Indoor air can become polluted with VOCs, and understanding the factors which affect adsorption of VOCs from indoor air is important for: (i) the accurate measurement of VOCs, and (ii) to apply mitigation strategies when high analyte concentrations are measured. In this study four VOCs (toluene, ethylbenzene, cumene and dichlorobenzene) were generated as a constant and controlled polluted air stream of VOCs from a dynamic atmospheric chamber. The effects of relative humidity, and sampling flow rate, on adsorption onto Tenax TA and the relatively new silica adsorbents SBA-15 or MCM-41 were studied. Air samples were collected and analyzed by thermal desorption followed by GC/MS. All sorbents were shown to be affected by changing the RH conditions from 25 to 80% RH, and sampling flow rates from 25 to 200 cm3 min−1, even when pollutant concentrations and sampled air volumes remained consistent. Although further work is required to examine the effect of the full RH range on scavenging potential, in this study Tenax TA was shown to provide best performance in high RH conditions whereas silica sorbents were more effective at low RH. Moreover it was shown that to provide accurate measurements in the field (e.g., when humidity conditions are fixed) it is suggested that Tenax TA is the preferred sorbent of choice as the masses of VOCs collected were less affected by changing the sampling flow rates.

Characterisation of an unusual crystalline efflorescence on an Egyptian limestone relief

Fibrous crystals, up to 2 cm long and 3 μm in diameter, have been observed on an Egyptian limestone relief, stored in a wooden cabinet at the Burrell Collection, Glasgow. X-ray diffraction and infrared spectroscopy have shown that the crystals are identical to an uncharacterised efflorescence first reported in 1971. Ion chromatography was used in conjunction with scanning electron microscopy, x-ray spectrometry, and thermogravimetry to determine the composition of the salt efflorescence. The salt comprises, primarily, calcium, acetate, chloride and nitrate ions. Proton nuclear magnetic resonance spectrometry at 400 MHz was used to establish the degree of hydration. The stoichiometric formula derived from the analyses is Ca3(CH3COO)3Cl(NO3)2· 7H2O. This is a new crystalline salt not previously characterised.

Preconcentration and selective extraction of chromium species in water samples using amino modified mesoporous silica

Speciation and separation of chromium (VI) and chromium (III) from aqueous solutions were investigated using amino-propyl functionalised mesoporous silica (AP-MCM-41) as an adsorbent. The as-synthesised adsorbent was produced following a simple synthesis method at room temperature prior to template removal using microwave digestion. The maximum adsorption capacity at 111.1 mg/g was calculated according to the Langmuir isotherm model, suggesting a 1:1 monolayer adsorption mechanism. Moreover, AP is a simple chelate, yet it can extract Cr (VI) exclusively from solutions containing other mixed metal ions simply by tuning the solution pH. Recovery of Cr (VI) from loaded sorbents is equally easy to perform with 100% extraction efficiencies allowing reuse of the sorbent and recovery of Cr (VI) from aqueous solutions containing a complex mixture of ions. The material would find use in environmental remediation applications, as a selective adsorbent of Cr (VI) or even as a solid-phase extraction stationary phase to remove and pre-concentrate Cr (VI) from aqueous solutions; this study demonstrates enrichment factors of 100 although higher levels are also possible.

On-site determination of formaldehyde: a low cost measurement device for museum environments.

A trapping reagent for formaldehyde, based on the pararosaniline reaction, was evaluated as a method of determination of formaldehyde in the aqueous or vapour phase. Collection of formaldehyde vapour relied upon passive diffusion of formaldehyde into the trapping media and quantitative results were obtained without the need for liquid impingers, bubblers or active sampling pumps. Moreover, a novel, hand-held absorption spectrophotometric measurement device was designed to provide on-site, quantitative measurements. It is proposed that the full measurement system devised would be ideally suited to specific sampling applications such as those found in museum enclosures.

Assessment of historical polymers using attenuated total reflectance-Fourier transform infra-red spectroscopy with principal component analysis

IntroductionAttenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy with a diamond ATR crystal was used to examine 41 historical polymer fragments and a selection of polyurethane fragments subjected to accelerated ageing. The advantages and limitations of FTIR data for polymer assessment is discussed. Moreover the efficacy of the data interpretation tool principal component analysis (PCA) is debated for potential applications in polymer characterisation and polymer degradation.ResultsAnalysis of polymer fragments by ATR-FTIR spectra was shown, as expected, to be an ideal method for polymer classification. Curved surfaces could be tolerated when spectral data were carefully collected, similarly opaque samples could be analysed due to the reflective nature of the FTIR technique used. More importantly perhaps, these results reaffirm the necessity to examine individual spectra as further information can be obtained which allow a better understanding of the material’s stability. It was possible to identify potential degradation of cellulose nitrate and rubber, discriminate between the ether and ester-form of polyurethane, and discriminate between high and low density polyethylene. It was also shown that PCA could be used to unambiguously identify samples which contained cellulose acetate, cellulose nitrate, polycarbonate or polyurethane with a selection of known samples, but without the use of a spectral library.ConclusionsThis study supports previous publication results indicating that ATR-FTIR is a useful tool for the examination of objects containing polymers. Here it was shown that polymers could be characterised in object fragments that were not specially prepared and without the use of a spectral library. PCA was shown to be a useful tool for the unambiguous identification of cellulose acetate, cellulose nitrate, polycarbonate or polyurethane polymers in historical plastics with different additives, plasticisers or age. More excitingly, even though spectral features were similar for new and aged samples of polyurethane, PCA was able to discriminate between samples of foam that had been treated by heat (50°C for 24 h or 144 h) or by exposure to light, although more results for other polymeric materials are required to support this proof of concept study.

Investigation of the composition of a unique efflorescence on calcareous museum artifacts

Fibrous crystals, consisting principally of calcium, acetate, chloride and nitrate ions on a number of calcareous museum artifacts worldwide, have been examined. Ion chromatography (IC) was used to determine the exact composition of the efflorescence and nuclear magnetic resonance spectrometry (NMR) was used to determine the degree of hydration associated with the salt. Of the twelve samples analysed, eleven salts had the same stoichiometry as Efflorescence X, a novel salt identified from an Egyptian limestone relief sculpture in the Burrell Collection, Glasgow, that has the composition Ca3(CH3,COO)3 Cl(NO3)2 · 7H2O.

Determination of experimental diffusion coefficients of acetic acid and formic acid vapours in air using a passive sampler

Abstract A passive sampling method has been developed for acetic acid and formic acid vapours in ambient air. The procedure involves collection of the vapours in a Palmes diffusion tube (7.1 cm long and 1.1 cm i.d.) and analysis by ion chromatography. Application of Ficks first law of diffusion allows calculation of the acid vapour concentrations. To validate the procedure, the tubes have been exposed to calculated or known concentrations of acetic acid and formic acid vapours, so that the diffusion coefficients of each acid can be calculated for comparison with theoretical values. Two procedures were used to generate acid vapour concentrations in the range 6–26 mg m −3 . Solutions containing calcium chloride and acetic acid or formic acid were placed in desiccators in which replicate diffusion tubes were exposed. The derived diffusion coefficients of acetic acid and formic acid were 0.110 ± 0.003 and 0.127 ± 0.005 cm 2 s −1 , respectively. An alternative procedure used a 43 dm 3 exposure chamber and acid permeation devices to produce the acid vapour concentrations. The experimentally derived diffusion coefficients obtained with this system were 0.133 ± 0.007 and 0.120 ± 0.008 cm 2 s −1 for acetic acid and formic acid vapours, respectively. The theoretical diffusion coefficients for acetic acid and formic acid vapours are 0.105 and 0.129 cm 2 s −1 , respectively.