Templated mesoporous materials: expectations, facts and challenges

This presentation included an overview of the main types of the mesoporous structures that can be generated via template processes, addressing the role of surface chemistry on their formation and implications in their properties and applications. Some aspects considered involved the introduction of catalytic functionalities, the important contributions that these model porous solids brought to the testing of fundamentals underlying gas adsorption, previously developed with common mesoporous materials having broad pore size distributions, and also their potential as molecular sieves for big molecules in the liquid phase. Together with the beautiful aspects, some challenges still to overcome, were also mentioned

Carbon aerogels used in carbon dioxide capture

In this work the maximum carbon dioxide adsorption capacity of carbon aerogels, obtained by a sol-gel process using 2,4-dihydroxybenzoic acid/formaldehyde (DHBAF) and resorcinol/formaldehyde (RF) as precursors, was studied. The effect of increasing the temperature of carbonization and physical activation of the samples DHBAF was also studied. The results showed that the maximum adsorption capacity is favoured at lower temperatures, adsorption and desorption are rapid and the performance is maintained over several cycles of CO2 adsorption/desorption. A comparison with samples of commercial carbons was also made and it was concluded that carbon aerogels exhibit a behaviour comparable or superior to that obtained for the commercial carbons studied

Amine-modified Carbon Aerogels for CO2 Capture

Ten different amines of different molar mass and structure were deposited from aqueous and methanolic solutions of different concentrations onto two types of carbon aerogel. Thermogravimetric analysis (TGA) was used to quantify the loading, thermal stability and CO2 capture capacity of the materials. Our results show that the amount of amine deposited did not depend on the solvent used, but was generally greater from more concentrated solutions, and increased with increasing molar mass. Deposition of amines was principally achieved by adsorption onto the mesopore walls, but without complete pore filling, and also, in some cases, by adsorption in the aerogel micropores. It was also concluded that the thermal stability of the amines deposited on the walls of the mesopores was independent of the solvent used, concentration or aerogel type. Preliminary studies of CO2 adsorption-desorption were carried out and a good correlation between ln(Cn) and 1/T, where Cn is the capacity at temperature T, was found. This enabled direct comparison to be made with published results obtained at different temperatures, and it was found that those obtained in this work were highly comparable with others found for amine-impregnated porous materials with similar amine loadings

Using Different Co-Adjuvant Activating Agents to Improve Activated Carbon Adsorption Capacities

Activated carbon (AC) has proved to be an effective adsorbent for the removal of an assortment of organic and inorganic pollutants from aqueous or gaseous media. However, the pursuit for more effective and cheaper AC is still very active and a diversity of textural and chemical treatments are described as a way to expand their applications. It is well known that the surface area and surface chemistry of AC strongly affect their adsorption capacity [1-3]. In particular, an increase in the nitrogen content has been related to an increase of the basic character and also to the development of the porous structure. In most published work this was achieved through an AC post treatment, including either a reaction with nitrogen containing reagents, such as ammonia, nitric acid, or a diversity of amines. However, the AC prepared directly from a nitrogen rich precursor through a physical or chemical activation is referred to as presenting the best characteristics, namely high nitrogen content, high basic character, low nitrogen leaching and also a good thermal stability [4]. To improve the AC adsorption capacities for acidic pesticide removal from the aqueous phase, we intend to improve the porous structure and introduce nitrogenated groups directly into the AC matrix, using different co-adjuvant activating agents as a nitrogen source, by chemical activation, with potassium hydroxide, of cork or poly(ethyleneterephthalate) (PET) precursors

Hydrothermal stability of ordered mesoporous titanosilicate materials prepared at room temperature

A study of hydrothermal stability, performed in boiling water under static conditions, of MCM-41 materials containing different titanium content, prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium ethoxide and octadecyltrimethylammonium bromide is presented. The behaviour is compared with pure silica grades prepared by a similar procedure. The samples were characterised by X-ray diffraction, adsorption of nitrogen at 77K and diffuse reflectance UV–Vis spectroscopy. It was found that the stability improves as the amount of titanium increases and that Ti-MCM-41 samples prepared with Si/Ti≤50 are significantly stable. After 12h in boiling water the pore size uniformity was practically maintained and only a small decrease in pore volume (5-9%), total surface area (2-7%) and mesopore width (3%) and a slight increase in pore wall thickness (3-6%) occurred. In contrast, some degradation of the MCM- 41 structure for the pure silica and the lower Ti content (Si/Ti=100) samples was observed with the effect being less pronounced for the latter. The higher hydrothermal stability of titanium substituted samples is probably correlated with a higher degree of polymerisation of the pore walls and with the presence of extra framework titanium

Activated Carbons Prepared from Natural and Synthetic Raw Materials with Potential Applications in Gas Separations

A carbon molecular sieve for the purification of a gas mixtures containing O2, N2 and CO2, CH4 was produced from a waste granulated PET by means of a single carbonisation step at 973 K. Activated carbon materials presenting good adsorption capacity and some selectivity for O2/N2 and CO2/CH4 were prepared from granulated PET and cork oak with pore mouth narrowing using CVD from benzene. The diffusion coefficients of O2, N2, CO2 and CH4 in these materials were calculated and are comparable to published values determined on Takeda 3A and on a carbon molecular sieve prepared from PET textile fibres by means of carbonisation and subsequent CVD with benzene. However, the selectivities were not quite as good as those given by Takeda 3A. However, taking into account that this is a first attempt at producing CMS from PET, the results are encouraging, and it is to be expected that further development of the experimental procedure will result in new materials with improved performanc

Designing activated carbons from natural and synthetic raw materials for pollutants adsorption

Over the last decades the literature has shown the possibility of producing activated carbons (AC) from a wide variety of raw materials, and to use them as one of the most environmentfriendly solutions for waste disposal [1]. Simultaneously, it has been shown that the adsorption of pollutants from different sources by activated carbons is one of the most efficient techniques for remediating or solving this kind of problem [2]. In this context, phenolic compounds represent one of the most important classes of pollutant present in the environment [3]. In this perspective, we present a study involving the production of AC from cork (Quercus suber L.), PEEK (polyetheretherketone) wastes or granulated recycled PET (polyethyleneterephthalate) and their applicability for the adsorption of phenolic compounds from the liquid phase. All samples were characterised in relation to their structural properties and chemical composition, by different techniques, including nitrogen adsorption at 77 K, elemental analysis (C, H, N, O and S) and point of zero charge (PZC). The activated carbons produced demonstrated high adsorption capacities both in the gas and liquid phase as exemplified by N2 and phenolic compounds adsorption experiments. Based on the structural and chemical properties, and on the kinetic and equilibrium studies of liquid phase adsorption, it is possible to conclude that it is the porous volume of the ACs that predominantly controls the process of phenolic compounds adsorption

Ordered mesoporous silica materials for protein adsorption

Lysozyme and BSA were used, as model proteins of considerably different dimensions, in order to evaluate the influence of the distinct pore structural characteristics of three types of ordered mesoporous silica materials (MCF, SBA-15 and MCM-41) on protein adsorption. Characterisation by X ray diffraction and nitrogen adsorption at 77K revealed the typical pore structural features of each type of material. The maximum of the pore size distributions indicated that the width of the windows of MCF (2) (mesitylene/P123 of 2) was larger than the pore diameter of the unidirectional tubular pores of SBA-15. All the materials presented similar small external surface areas but high pore volumes, with that of MCF (2) being the highest. The adsorption of lysozyme at pH=8 increased in the order MCM-41<< SBA-15< MCF (2), and the uptakes were well above those of BSA at pH=5. Although BSA is not completely excluded from the mesopores of SBA-15 and MCF (2), as happens with MCM-41, the adsorption occurs to a very limited extent. The overall behaviour of these SBA-15 and MCF (2) samples was not significantly different and both revealed potential for the separation of these proteins

Adsorption of MCPA on different activated carbons

Pesticides play an important role in the success of modern farming and food production but their use increases the residue levels in soils and waters and has been a public concern because of the potential risk to human health and the environment. Pesticides are generally applied in larger amounts than those needed for the pest control and they are swept away by transport processes such as leaching. Liquid phase adsorption is one of the mechanisms which decrease solute mobility and thus could be suitable for assessing the capacity of materials to adsorb pollutants. Several treatment processes are available to remove inorganic and organic pollutants (including herbicides) from aqueous or gaseous phase, with adsorption on activated carbons being often considered to be highly efficient, easy to use and one of the most economical [1]. In particular, the concentration of compounds belonging to the phenoxyacid group has increased and a worrying fact is that these compounds are more often detected in both superficial and underground waters. MCPA was selected because it is considered highly carcinogenic, its biological degradation is very slow and it has been detected in natural and drinking waters with contamination levels up to 0.4 µg/L [2]. In Portugal, for example, permitted levels have been decreased to only 0.1 µg/L for any one pesticide or a total of 0.5 µg/L for all [3]

Porosity of clay catalysts for biomass conversion: a comparative study

A detailed description of the porosity, in particular of microporosity, was reported and allowed a clear comparison of the effects on the porosity of chemical treatments on clays from the Source Clays Repository (USA) and SD clay from Porto Santo (Portugal)