Moisés L. Pinto

Activated carbons from sisal waste by chemical activation with K2CO3: Kinetics of paracetamol and ibuprofen removal from aqueous solution

Sisal waste was used as precursor to prepare carbons by chemical activation. The influence of the K(2)CO(3) amount and activation temperature on the materials textural properties were studied through N(2) and CO(2) adsorption assays. As the severity of the treatment increases there is a development of supermicropores, and the micropore size distribution changes from mono to bimodal. A carbon with an apparent surface area of 1,038 m(2)g(-1) and pore volume of 0.49 cm(3)g(-1) was obtained. TPD results showed the incidence in acidic type groups although the pH(PZC) reveals an almost neutral character of the surface. Adsorption kinetic data of ibuprofen and paracetamol show that the processes obey to a pseudo-second order kinetic equation. Regarding the removal efficiency the prepared samples attained values comparable to a commercial carbon (>65%), revealing that chemical activation of sisal wastes with K(2)CO(3) allows obtaining samples suitable for pharmaceutical compounds removal from liquid phase.

Physicochemical characterization of silylated functionalized materials

Silylation of several materials where the surface area arises from the internal pores (MCM-41 and FSM-16) or is essentially external (silica gel, and clays) was performed using three organosilanes: (3-aminopropyl)triethoxysilane (APTES), 4-(triethoxysilyl)aniline (TESA) and (3-mercaptopropyl)trimethoxysilane (MPTS). The materials were characterized by nitrogen adsorption-desorption at -196 degrees C, powder XRD, XPS, bulk chemical analysis, FTIR and (29)Si and (13)C MAS NMR. For MCM-41 and FSM-16 the highest amounts of organosilane are obtained for APTES, while for the remaining materials the highest amounts are for MPTS; TESA always anchored with the lowest percentage. In terms of surface chemical analysis, TESA anchored with the highest contents irrespectively of the material, and the opposite is registered for MPTS. Comparison of bulk vs surface contents indicate that TESA is mainly anchored at the material external surface. Moreover, with N or S (surface and bulk) contents expressed per unit of surface area, MCM-41 and FSM-16 (internal porosity) show the lowest amounts of silane; the highest amounts of silane per unit of surface area are obtained for the clays. Grafting of the organosilanes to the surface hydroxyl groups was corroborated by FTIR and (29)Si and (13)C MAS NMR. Furthermore, NMR data suggested that TESA and APTES grafted mostly through a bidentate approach, whereas MPTS grafted by a monodentate mechanism.

Chars from gasification of coal and pine activated with K2CO3: Acetaminophen and caffeine adsorption from aqueous solutions

The high carbon contents and low toxicity levels of chars from coal and pine gasification provide an incentive to consider their use as precursors of porous carbons obtained by chemical activation with K2CO3. Given the chars characteristics, previous demineralization and thermal treatments were made, but no improvement on the solids properties was observed. The highest porosity development was obtained with the biomass derived char (Pi). This char sample produced porous materials with preparation yields near 50% along with high porosity development (ABET≈1500m(2)g(-1)). For calcinations at 800°C, the control of the experimental conditions allowed the preparation of samples with a micropore system formed almost exclusively by larger micropores. A mesopore network was developed only for samples calcined at 900°C. Kinetic and equilibrium acetaminophen and caffeine adsorption data, showed that the processes obey to a pseudo-second order kinetic equation and to the Langmuir model, respectively. The results of sample Pi/1:3/800/2 outperformed those of the commercial carbons. Acetaminophen adsorption process was ruled by the micropore size distribution of the carbons. The caffeine monolayer capacities suggest a very efficient packing of this molecule in samples presenting monomodal micropore size distribution. The surface chemistry seems to be the determinant factor that controls the affinity of caffeine towards the carbons.

Assessment of Hydrophobic-Hydrophilic Properties of Microporous Materials from Water Adsorption Isotherms

The characterization of the hydrophobic-hydrophilic properties of different types of microporous materials, namely activated carbons, pillared clays and zeolites, was made by the determination of water adsorption isotherms. The data were analysed by the Dubinin and Astakhov (D-A) equation. The use of the E parameter of the D-A equation as a measure of the hydrophobic-hydrophilic character is proposed. When the information obtained from the E parameter is compared with the information that can be obtained from other parameters used in the literature to characterize the hydrophobicity of materials, it is found that the former is more sensitive and is more directly related with the shape of the adsorption isotherms which, ultimately, is the more direct manifestation of the hydrophobic-hydrophilic properties of a given material.

Composite MOF foams: the example of UiO-66/polyurethane.

Composite MOF foams were prepared using a direct synthesis of UiO-66 over a polyurethane foam template. Under optimized conditions, the composite materials maintained the macrostructure and flexibility of the polyurethane foam, and exhibited the microporosity, high surface area, and adsorption properties of the UiO-66. The composite MOF foam has hierarchical porosity and high adsorption capacity for benzene and n-hexane, maintaining more than 70% of the adsorption capacity of the UiO-66.

High performance microspherical activated carbons for methane storage and landfill gas or biogas upgrade

Microspherical activated carbons were successfully prepared via a novel synthetic route that involves hydrothermal carbonization of a renewable material, sucrose, and activation with K2CO3. The use of K2CO3 resulted in better yields (∼50%) and the retention of the spherical shape of the hydrochar, while with the less environmentally desirable and commonly used activating agent, KOH, the process occurs at the expense of the spherical morphology. The superior performance of the K2CO3 activated samples for methane storage and upgrade of landfill gas or biogas results from the combination of several key properties including high packing densities (∼0.9 g cm−3), high surface areas (up to 1400 m2 g−1) and micropore sizes suitable for methane storage and selective CO2–CH4 separation. In fact, the micropore size distributions assessed from CO2 adsorption data through a methodology not imposing a Gaussian distribution gave meaningful values to explain both the selectivity and storage capacity of samples. Sample activated with K2CO3 at 800 °C presenting micropore sizes ∼0.8 nm and high packing density has high volumetric methane uptake (90 (V/V) at 1000 kPa), close to the best activated carbons reported in the literature. Sample activated with K2CO3 at 700 °C has narrower micropores (∼0.5 nm) and presents a remarkable selectivity (4–7) in CO2–CH4 mixtures for the upgrade of methane based fuels, like natural gas, landfill gas, and biogas. Although a superactivated carbon (∼2400 m2 g−1) was obtained with KOH activation, the low packing density and wider micropores rendered it less effective for both methane storage and upgrade.

Ethane Selective IRMOF-8 and Its Significance in Ethane–Ethylene Separation by Adsorption

The separation of ethylene from ethane is one of the most energy-intensive single distillations practiced. This separation could be alternatively made by an adsorption process if the adsorbent would preferentially adsorb ethane over ethylene. Materials that exhibit this feature are scarce. Here, we report the case of a metal-organic framework, the IRMOF-8, for which the adsorption isotherms of ethane and ethylene were measured at 298 and 318 K up to pressures of 1000 kPa. Separation of ethane/ethylene mixtures was achieved in flow experiments using a IRMOF-8 filled column. The interaction of gas molecules with the surface of IRMOF-8 was explored using density functional theory (DFT) methods. We show both experimentally and computationally that, as a result of the difference in the interaction energies of ethane and ethylene in IRMOF-8, this material presents the preferential adsorption of ethane over ethylene. The results obtained in this study suggest that MOFs with ligands exhibiting high aromaticity character are prone to adsorb ethane preferably over ethylene.

Potentialities of polyurethane foams for trace level analysis of triazinic metabolites in water matrices by stir bar sorptive extraction

Polyurethane (PU) foams were applied for stir bar sorptive extraction of five triazinic metabolites (desethyl-2-hydroxyatrazine, desisopropylatrazine, desethylatrazine, 2-hydroxyatrazine and desethylterbuthylazine) in water matrices, followed by liquid desorption and high performance liquid chromatography with diode array detection (SBSE(PU)-LD/HPLC-DAD). The optimum conditions for SBSE(PU)-LD were 5h of extraction (1000 rpm) and 5% (v/v) of methanol for the analysis of desethyl-2-hydroxyatrazine and 2-hydroxyatrazine, 15% (w/v) of sodium chloride for the remaining compounds and acetonitrile as back-extraction solvent (5 mL) under ultrasonic treatment (60 min). The methodology provided recoveries up to 26.3%, remarkable precision (RSD<2.4%), excellent linear dynamic ranges between 5.0 and 122.1 microg/L (r(2)>0.9993) and convenient detection limits (0.4-1.3 microg/L). The proposed method was applied in the analysis of triazinic metabolites in tap, river and ground waters, with remarkable performance and negligible matrix effects. The comparison of the recoveries obtained by PU and commercial stir bars was also performed, where the yields achieved with the former were up to ten times higher proving that PU is appropriate for analysis at trace level of this type of polar compounds in water matrices.

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.

Understanding gas adsorption selectivity in IRMOF‐8 using molecular simulation

Grand canonical Monte Carlo simulations were used to explore the adsorption behavior of methane, ethane, ethylene, and carbon dioxide in isoreticular metal-organic frameworks, IRMOF-1, noninterpenetrated IRMOF-8, and interpenetrated IRMOF-8. The simulated isotherms are compared with experimentally measured isotherms, when available, and a good agreement is observed. In the case of IRMOF-8, the agreement is much better for the interpenetrated model than for the noninterpenetrated model, suggesting that the experimental data was obtained on an essentially interpenetrated structure. Simulations show that carbon dioxide is preferentially adsorbed over methane, and a selective adsorption at low pressures of ethane over ethylene, especially in the case of IRMOF-8, confirm recent experimental results. Analysis of simulation results on both the interpenetrated and the noninterpenetrated structures shows that interpenetration is responsible for the higher adsorbed amounts of ethane at low pressures (<100 kPa) and for the interesting selectivity for ethane in ethane/ethylene binary mixtures. Van der Waals interactions seem to be enhanced in the interpenetrated structure, favoring ethane adsorption. This indicates that interpenetrated MOF structures may be of interest for the separation of small gas molecules.