Manuela B. de Carvalho

Adsorption of volatile organic compounds in Y zeolites and pillared clays

Abstract The adsorption of four common volatile organic compounds (VOCs), namely 1,1,1-trichloroethane, trichloroethylene, methanol and propanone, was studied by the gravimetric method in different cationic forms of Y zeolite and in pillared interlayered clays (PILCs). The latter were pillared with aluminium or zirconium oxide pillars using as starting materials two types of clays: a natural smectite and a synthetic laponite. In this way the adsorption of VOCs was studied in solids with different types of porosity, since zeolites and pillared smectites were mainly microporous materials, but the pillared laponites had a high proportion of mesoporous volume. Therefore, the adsorption isotherms of the VOCs in the zeolites and PILCs were mainly of type I, according to the IUPAC classification, but in the case of the pillared laponites type II isotherms were found. The absolute values of the amounts of VOCs adsorbed in the zeolites were about three times higher than for the pillared smectites. In the case of the pillared laponites the amounts adsorbed approached those of the pillared smectites in the region of the low relative pressures and, at the higher relative pressures, approached or in some cases exceeded the amounts adsorbed in Y zeolites. The adsorption isotherms were analysed by the Langmuir and the Dubinin–Astakhov equations. The latter was able to reproduce the experimental data and made possible the partial definition of a characteristic curve of adsorption. For the microporous solids the results showed that the adsorption of VOCs is favoured in those materials where the unspecific interactions can be expected to predominate, but the results obtained with the pillared laponites indicated that mesoporous materials also have a potential in the adsorption of VOCs.

Epoxidation of styrene by a manganese(III) salen complex encapsulated in an aluminium pillared clay

The manganese(III) complex—carboxylate-[N,N′-bis(salicylaldehyde)cyclohexanediaminate]manganese(III), [Mn(salhd)CH3COO]—was encapsulated into an aluminium pillared clay (denoted as Al-WYO) using a two-step liquid phase methodology: (i) adsorption of manganese(II) acetate in ethanolic solution within Al-WYO, followed by (ii) diffusion of N,N′-bis(salicylaldehyde)cyclohexanediamine in ethanolic solution. The new material was characterised by several techniques (ICP-AES, XPS, FTIR, UV–Vis and low temperature nitrogen adsorption) which showed that in situ synthesis of the manganese(III) complex took place within the aluminium pillared clay porous structure. The catalytic activity of the heterogenised [Mn(salhd)CH3COO] in the epoxidation of styrene was studied in acetonitrile, at room temperature, using iodosylbenzene or sodium hypochlorite as oxygen source. With PhIO the new heterogeneous catalyst showed high styrene epoxide chemoselectivity and could be reused at least 3 times without significant loss in styrene epoxide yield, suggesting that no complex leaching took place under the reaction conditions used. When sodium hypochlorite was used as oxidant, high selectivity in by-products was observed, as well as extensive leaching of the catalyst into solution. XPS spectra of the catalyst after the catalytic reaction confirm manganese complex leaching and also show a significant decrease in aluminium content, thus suggesting that partial damage of aluminium pillars took place in this reaction media, inducing complex leaching.

Encapsulation of Copper(II) Complexes with Pentadentate N3O2 Schiff Base Ligands in a Pillared Layered Clay

Two copper(II) complexes with five-coordinate Schiff-base ligands derived from acetylacetone and with a N3O2 coordination sphere, namely bis(acetylacetonate)-3-amino-bis(propyldiimine) and bis(acetylacetonate)-3-methylamino-bis(propyldiimine), were entrapped in the interlayers of a pillared layered clay (PILC). A two-step process in the liquid phase was used: (i) adsorption of copper(II) acetylacetonate in the porous structure of the PILC, and (ii) in situ Schiff condensation of the copper(II) precursor complex with the corresponding triamine. The new materials were characterised by chemical analysis, surface techniques (SEM and XPS), X-ray powder diffraction, nitrogen adsorption isotherms and spectroscopic methods (FTIR, UV/Vis). These data indicate conclusively that the CuII complexes are encapsulated in the PILC, and that the entrapped complexes exhibit structural and electronic properties that are different from those of the free complexes. These differences can arise from distortions caused either by steric effects imposed by the structure of pillared clay, or by strong interactions with the matrix.

Open Cell Polyurethane Foams for New Filters with Supported Adsorbents

A flexible foam was developed based on polymeric diphenylmethane diisocyanate (MDI) to be used as support for pre-synthesized adsorbent additives (activated carbon) for air-conditioning filters that provide air purification and improve indoor air quality. Foam for air purification filters must be an open cell foam with low density, air permeability and the adsorbents must retain indoor air pollutants, such as volatile organic compounds (VOCs). To achieve the right structural characteristics different polyether polyols, catalysts and surfactants were used and several tests of pressure drop, apparent volume, real volume and densities were performed. Another aspect that was studied in this work was the adsorption capacity of several activated carbons and the foam matrix influence in the adsorption. For that purpose room temperature adsorption isotherms of toluene, which is a probe of noxious aromatic VOCs, were determined and compared. For scale up purpose, rise time curves of the foams were measured. This study was made at different starting temperatures and with different types and quantities of catalyst. The relationships rise time/starting temperature and rise time/quantity of catalyst were obtained and expressed in equations.

Preparation of New Materials Containing Diazoalcene Molybdenum Complexes in Pillared Clays

The complex, trans-[FMo(NNCHCHCHCH2CH3)(Ph2PCH2CH2PPh2)2][BPh4], was encapsulated in a PILC (Pillared Clay) and the obtained material was characterized using different physicochemical techniques. The data gathered indicate that the diazoalcene molybdenum complex was effectively encapsulated in the host matrix, and this process does not modify the morphology and structure of the PILC upon metal complex loading.