J. Pires

Designing Novel Hybrid Materials by One-Pot Co-condensation: From Hydrophobic Mesoporous Silica Nanoparticles to Superamphiphobic Cotton Textiles

This work reports the synthesis and characterization of mesoporous silica nanoparticles (MSNs) functionalized with tridecafluorooctyltriethoxysilane (F13) and their in situ incorporation onto cotton textiles. The hybrid MSNs and the functional textiles were prepared by a one-pot co-condensation methodology between tetraethylorthosilicate (TEOS) and F13, with hexadecyltrimethylammonium chloride (CTAC) as the template and triethanolamine as the base. The influence of the F13 to TEOS molar ratio (1:10, 1:5 and 1:3) on the nanoparticle morphology, porosity, degree of functionalization, and hydro/oleophobic properties is discussed. The hybrid nanosilicas presented high colloidal stability and were spherical and monodispersed with average particle size of ∼45 nm. They also showed high surface areas, large pore volumes, and a wormhole-type mesoporous structure. The increase in the organosilane proportion during the co-condensation process led to a more radially branched wormhole-like mesoporosity, a decrease in the surface area, pore volume, and amount of surface silanol groups, and an enrichment of the surface with fluorocarbon moieties. These changes imparted hydrophobic and oleophobic properties to the materials, especially to that containing the highest F13 loading. Cotton textiles were coated with the F13-MSNs through an efficient and less time-consuming route. The combination between surface roughness and mesoporosity imparted by the MSNs, and the low surface energy provided by the organosilane resulted in superhydrophobic functional textiles. Moreover, the textile with the highest loading of fluorocarbon groups was superamphiphobic.

Characterisation of clays and aluminium pillared clays by adsorption of probe molecules

Abstract Aluminium pillared clays (PILCs) from three different starting materials namely two Portuguese clays from Benavila (Alentejo) and Porto Santo (Madeira archipelago) and a Wyoming SPV-200 clay were obtained. A characterisation of the textural and some surface chemistry properties of the starting materials and PILCs was made using the adsorption of different probe molecules (water, ethylene glycol, nitrogen, n-hexane, cyclohexane, triethylamine) and also by other routine techniques. The adsorption of probe molecules was also employed to characterise the microporosity of the obtained PILCs. The effect of freeze-drying on PILCs texture was also discussed and related with the size of the clay particles.

Preparation of activated carbons from cork waste by chemical activation with KOH

In the western Mediterranean region, and specially in the final temperature attained values in the range 500–900 8C south of Portugal, cultivation of cork oak, Quercus suber, and was maintained for a time, t (h), from 0 to 16 h. After is an important economic activity, with Portugal being the carbonisation the samples were cooled to room temperaworld’s major producer. Besides the production of stopture under nitrogen flow, washed up to pH 7 and dried at pers, an economically important product, the industry 100 8C. The samples will be designated according to the creates enormous volumes of waste formed by particles expression: ratio KOH:cork /T (8C)/t (h). Adsorption isowith very small dimensions, generally designated cork therms of N at 2196 8C were determined in a convention2 powder. This industrial waste was the raw material used in al volumetric apparatus. Hydrocarbon (n-hexane and this work since it has the essential features of an activated cyclohexane) vapour adsorption was studied at 25 8C by carbon precursor and, according to the results of previous the gravimetric method. The samples were studied in the studies [1,2], allows one to obtain materials with textural form of small wafers made by pressing (without binder) characteristics, e.g. apparent surface areas, comparable the as-obtained form, i.e. finely divided powders. From N2 with those of commercially available carbons. This work adsorption data, the apparent surface area, A , was BET 0 reports the first systematic evaluation of the influence of determined through BET equation (0.05,p /p ,0.15). several experimental parameters (activating agent content Using the Dubinin-Radushkevich (DR) equation, the miand temperature and duration of calcination) on the textural cropore volume, V , the characteristic adsorption energy, DR characteristics of the activated carbons prepared from E , and the mean micropore half width, L , were esti0 0 industrial cork waste using KOH as activating agent. mated. To calculate L , the empirical equation: L 5 0 0 25 3.5 The raw material was a sample of industrial waste, (13.028–1.53310 E ) /E [3] was used. The micropor0 0 previously treated with H SO (10%) at room temperature, osity was also assessed by applying the a method, taking 2 4 S washed up to pH 7, dried at 80 8C and finally sieved to as reference the isotherm reported in Ref. [4]. Hydrocarbon obtain the fraction of cork particles smaller than 0.297 adsorption data were analysed by the DR equation. mm. Cork powder was physically mixed with different The N adsorption isotherms displayed in Fig. 1 are 2 volumes of KOH solution (25%), to obtain mixtures with representative of the curves obtained in this study and weight ratios of KOH:cork between 0:1 and 4:1. After reveal the essential microporous nature of the materials. drying at 80 8C, the mixtures were heated in a horizontal The values of apparent A (Table 1) show that the BET 3 21 furnace under a nitrogen flow (2 cm s ). The temperaexperimental parameters have different effects on the ture was increase in two steps: from room temperature up development of the microporous structure of the samples. 21 to 300 8C (5 8C min ), maintained for 3 h, and afterwards In fact, the increase in the calcination time and in the 21 raised (10 8C min ) up to a higher value, T (8C). The calcination temperature promote a continuous increase in the A values, which is considerably more accentuated BET in the case of the temperature. The increase of the KOH:cork weight ratio, although initially (until * KOH:cork51:1), also has a positive effect on the apparent Corresponding author. Fax: 1351-217-500-088. E-mail address: ana.carvalho@fc.ul.pt (A.P. Carvalho). surface area of the samples, for high contents of KOH, the

Aluminum-pillared clays : Decomposition of the intercalating species and textural properties

Pillared clays (PILCs) are microporous solids obtained by the intercalation of suitable clays with large polyoxicationic species which, in the process of preparation, are thermally decomposed into oxide species forming the pillars. In this work the thermal decomposition of the intercalating species—aluminum polyoxications—is studied by t.g.-d.s.c. and the results are compared with the chemical analysis. Textural properties of PILCs obtained by two methods are studied by nitrogen adsorption and the use of different reference materials, in order to analyze adsorption data, is discussed.

Slow release of NO by microporous titanosilicate ETS-4.

A novel approach to designing nitric oxide (NO) storage and releasing microporous agents based on very stable, zeolite-type silicates possessing framework unsaturated transition-metal centers has been proposed. This idea has been illustrated with ETS-4 [Na(9)Si(12)Ti(5)O(38)(OH)·xH(2)O], a titanosilicate that displays excellent NO adsorption capacity and a slow releasing kinetics. The performance of these materials has been compared to the performance of titanosilicate ETS-10, [(Na,K)(2)Si(5)TiO(13)·xH(2)O], of benchmark zeolites mordenite and CaA, and of natural and pillared clays. DFT periodic calculations have shown that the presence of water in the pores of ETS-4 promotes the NO adsorption at the unsaturated (pentacoordinated) Ti(4+) framework ions.

Characterization of the acidity of Al- and Zr-pillared clays

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.

Textural characteristics of Y and ZSM-20 zeolites determined by nitrogen adsorptions

The adsorption of nitrogen at 77 K on Y and ZSM-20 zeolites has been studied. The isotherms have been analyzed by use of the α s method and the Dublinin-Radushkevich equation, and the microporous capacities, sizes of pores, and the external areas were evaluated. The mechanisms involved in the microporous filling of these solids, which have pores of uniform size and shape, are discussed.

Degree of crystallinity of dealuminated offretites determined by X-ray diffraction and by a new method based on nitrogen adsorption

Samples obtained from thermal dealumination (in the presence and absence of water vapour) of three offretite zeolites with, respectively, 4.4, 3.4, and 2.9 aluminium atoms per unit cell, were investigated by i.r. spectroscopy. X-ray diffraction, and nitrogen adsorption. The percentage of crystallinity was then evaluated by two different methods: the standard XRD technique and a new method based on nitrogen adsorption data analysed through the αs-method. In this case the volume of the ultramicropores (width less than 0.7 nm) was considered. Differences between the two estimates, as well as the loss of crystallinity during dealumination, which is expressed by the representation of both crystallinity evaluations, CXRD or CADS, versus ν1 (the frequency of the stretching asymmetric T-O band), were analysed for self-steamed and steamed samples. The results obtained agree within 20%, and often better. For self-steamed samples the crystallinity evaluated from XRD patterns is always smaller than that estimated from adsorption data, whereas for steamed samples the opposite situation is generally observed.

Adsorption of Fe(CO)5 in Y and ZSM-20 zeolites: textural properties of thermally decomposed products

Abstract Adsorption of Fe(CO) 5 from the vapour phase, as a way of preparing iron-loaded zeolites, was performed in sodic and protonic forms of Y and ZSM-20 zeolites. The solids with iron were obtained from thermal decomposition, under vacuum, of the adsorbed Fe(CO) 5 . Decomposition temperatures between room temperature and 493 K were used. Textural properties of the products obtained from the different decomposition temperatures were studied. For this, nitrogen and n -hexane adsorption at 77 and 298 K, respectively, as well as transmission electron microscopy (TEM) were used. The effects of metal aggregates in the textural properties of Y and ZSM-20 zeolites are discussed in terms of the different supercages of these structurally related materials.

Toluene methylation over pillared clays with Al, Zr and Al/Zr oxides

Pillared clays (PILCs), with Al, Zr and Al/Zr oxides, obtained from a natural montmorillonite from Benavila (Portugal), were investigated in terms of their structure (XRD), texture (N 2 and toluene adsorption), acidity (pyridine chemisorption) and catalytic performances on methylation of toluene. Zr content reflects on the d 001 values and on the acidity of PILCs, that present, besides Lewis sites, also Bronsted acid sites. All the solids showed activity to toluene alkylation revealing that, even the Bronsted acidic properties that proceed only from the clay sheets are enough to promote alkylation. A mixture of xylenes (XY) was obtained as the main reaction products, and the isomers distribution followed generally the order m ≥ o > p . Trimethylbenzenes (TMB) and ethyltoluenes (EtT) were also found, and on all the samples the selectivities were S xy >> S TMB > S EtT .