3 results
Heats of Adsorption of N-Hexane by Thermal Gravimetry with Differential Scanning Calorimetry (Tg-DSC): A Tool for Textural Characterization of Pillared Clays
- J. Pires, M. Brotas de Cavalho, A. P. Carvalho, J. M. Guil, J. A. Perdigón-Melón
-
- Journal:
- Clays and Clay Minerals / Volume 48 / Issue 3 / June 2000
- Published online by Cambridge University Press:
- 28 February 2024, pp. 385-391
-
- Article
- Export citation
-
Microporous materials, (materials with pore sizes with widths <2 nm) were prepared by pillaring of smectites obtained from different soil deposits. The materials were prepared by intercalation with oligomeric cations of aluminum, which were transformed to aluminum-oxide pillars by calcination. The adsorption of n-hexane in the pillared clays was studied by the determination of heats of adsorption. Heats of adsorption were measured using either a static microcalorimeter or differential scanning calorim-etry coupled with thermogravimetry (TG-DSC). In this latter case, two different procedures were used that differ on the introduction of the (n-hexane) molecules that are to be adsorbed. The results obtained by the (standard) static microcalorimeter method and the TG-DSC method were compared. This comparison showed the heats of adsorption obtained by TG-DSC are differential heats of adsorption, and it showed the range of adsorption. Characterizing the texture of pillared clays, especially microporosity, is important for monitoring the intercalation process and for determining potential applications of these materials. Correlations between the obtained heats of adsorption and the dimensions of micropores suggest that TG-DSC is a semi-quantitative method for characterizing micropores in aluminum-pillared clays.
Characterization of the Acidity of Al- and Zr-Pillared Clays
- Ana P. Carvalho, Angela Martins, João M. Silva, João Pires, Helena Vasques, M. Brotas de Carvalho
-
- Journal:
- Clays and Clay Minerals / Volume 51 / Issue 3 / June 2003
- Published online by Cambridge University Press:
- 01 January 2024, pp. 340-349
-
- Article
- Export citation
-
The surface acidic properties of pillared clays (PILCs) with Al or Zr oxide pillars (prepared from a natural Portuguese smectite and a synthetic Laponite), and of a protonic NaHY zeolite, were studied by two methods: pyridine adsorption followed by infrared (IR) spectroscopy, and the catalytic transformation of 1-butene. The results of the pyridine adsorption revealed that all the pillared clays studied have mainly Lewis-type acidity, the exception being the clay pillared with Zr oxide, obtained from natural smectite, which also presents a significant number of Brönsted acid sites. The results of 1-butene transformation showed that the pillared clays exhibit catalytic properties similar to those of the protonic Y zeolite. The acid character of the solids was confirmed by the values of the cis/trans 2-butene isomers ratio. At short reaction times, product distribution showed that the main reaction is oligomerization, followed by cracking. After 15 min the products are mainly the linear isomers, cis and trans-2-butene, showing that the majority of the catalytic active sites, are already poisoned after 15 min of reaction. The particular behaviour of Laponite intercalated with Al oxide pillars is discussed. The IR spectra of the pyridine adsorbed on the fresh samples and after the catalytic assays, revealed that Lewis acid sites behave as active sites for 1-butene catalytic transformation. The consistency between the results of the two complementary techniques used for the characterization of the acidity of the solids was proved.
Effect of Cadmium exposure in the ubiquitous coccolithophore Emiliania huxleyi
- A. Amorim, F. Africano, V. Brotas, M.L. Dâmaso-Rodrigues, V. Veloso, A.P. Alves de Matos, M.F. Caeiro, R. Costa, P.A. Carvalho, M. Cachão
-
- Journal:
- Microscopy and Microanalysis / Volume 19 / Issue S4 / August 2013
- Published online by Cambridge University Press:
- 06 August 2013, pp. 5-6
- Print publication:
- August 2013
-
- Article
-
- You have access Access
- Export citation
-
The coccolithophores are a marine phytoplankton group that can play an important role in selective uptake of Cadmium (Cd) in neritic environments. Under project Cd-ToxCoN (PTDC/MAR/102800/2008) studies were conducted to investigate the in vitro reaction of Emiliania huxleyi to Cd exposure, namely changes in the crystal lattice of (cocco)liths, the calcite elements of the exoskeleton (coccosphere).
Uni-algal cultures of E. huxleyi were obtained by multiple cell isolation from the same water sample collected from Portuguese offshore waters, during opportunity cruises (Portuguese Marine Navy). Several morphotypes of E. huxleyi are currently recognized. The identification of the morphotype of E. huxleyi from Portuguese coastal waters was done by morphological analysis of the exoskeleton using scanning electron microcopy (JEOL JSM-5200LV and FEG-SEM JEOL 7001F) and by DNA sequencing of tufA gene following.
Experiments were conducted in batch cultures grown in enriched sea-water medium (K/10) under constant environmental conditions (14h L: 10h D, 15ºC, 40 µmol photons m-2 s-1). At the exponential growth phase, 3 replicate E. huxleyi cultures were subject for 48h to Cd concentrations of 10 µgL-1 and 100 µgL-1, two and three orders of magnitude above average marine concentration values respectively. In each case three additional replicate cultures with no Cd added were used as control.
The effect of Cd was evaluated by measuring in vivo fluorescence (ratio of variable (Fv) to maximum (Fm) fluorescence) (Water PAM fluorometer – Walz) and by detailed morphometric analysis of coccospheres and liths performed on SEM micrographs. The parameters measured are those presented in Figure 1. Malformed, damaged or tilted liths were not measured.
Morphological observations of the coccosphere and liths and DNA sequencing allowed the identification of the isolated strains of E. huxleyi as morphotype A. Results on the Cd exposure experiments indicate that E. huxleyi type A seems to tolerate high concentrations of Cd. Despite the very high concentration of Cd tested no lethal limit was reached and Fv/Fm values recorded after 48h at 10 µgL-1 Cd (0.607±0.008) and 100 µgL-1 Cd (0.603±0.008), very similar to the values recorded in the control cultures (0.642±0.016 and 0.636±0.018, respectively) and before Cd addition (0.642±0.012 and 0.636±0.007, respectively).
Regarding the different morphometric parameters analysed on coccospheres and liths, no significant measurable effects were observed. However, we observed, in response to increasing Cd concentration, an increasing number of liths with fused or partially fused elements (Fig. 2) suggesting a higher calcification of liths. This interpretation is supported by the results of the analysis of coccosphere calcium content. Cultures exposed to Cd presented a higher Ca content compared to control cultures. The highest values were recorded in coccospheres submitted to 100 µg.L-1 of Cd representing a 65% increase in Ca content in comparison to control coccospheres.
E. huxleyi is ubiquitous in present day oceans and usually very tolerant to culture conditions and is thus frequently used as a model species in the study of coccolithophores. These same characteristics may also justify the observed high tolerance to Cd. Studies with other species are needed to clarify if the surprising resistance to Cd is unique to E. huxleyi or characteristic of other unicellular algae with calcium carbonate shells.
This work was funded by projects PEst-OE/Mar/UI0199/2011, Pest/OE/CTE/UI/0263 and PTDC/MAR/102800/2008
2