José B. Parra

Waste-derived activated carbons for removal of ibuprofen from solution: Role of surface chemistry and pore structure

The removal of a widespread used drug (i.e., ibuprofen) from water was investigated using high valuable carbon adsorbents obtained from chemical and physical activation of a bioresource (cork) and a municipal waste (plastic). The waste-derived carbons outperformed the adsorption capacity of commercial carbonaceous adsorbents due to their adequate features for the removal of the targeted compound. Regarding the adsorption mechanism, the results obtained point out that ibuprofen retention is favored in activated carbons with basic surface properties. On the other hand, the textural features also play an important role; the presence of a transport pores network (i.e., mesopores) is crucial to ensure the accessibility to the inner porosity, and the microporosity must be large enough to accommodate the ibuprofen molecule. Specifically, adsorbents with a large fraction of ultramicropores (pore widths <0.7 nm) are not adequate to effectively remove ibuprofen.

Deep eutectic solvents as both precursors and structure directing agents in the synthesis of nitrogen doped hierarchical carbons highly suitable for CO2 capture

Deep eutectic solvents (DESs) have been used in the synthesis of nitrogen-doped carbons exhibiting a hierarchical porous structure. The CO2 sorption capacity of these solid sorbents was extraordinary because of their relatively high nitrogen content and their bimodal porous structure where micropores provide high surface areas (ca. 700 m2 g−1) and macropores provide accessibility to such a surface. DESs were composed of resorcinol, 3-hydroxypyridine and choline chloride in 2 : 2 : 1 and 1 : 1 : 1 molar ratios. Polycondensation of resorcinol and 3-hydroxypyridine (with formaldehyde) promoted DES segregation in a spinodal-like decomposition process by the formation of a polymer rich phase and a depleted polymer phase. Thus, DESs played a multiple role in the synthetic process; the liquid medium that ensured reagents homogenization, the structure-directing agent that is responsible for the achievement of the hierarchical structure, and the source of carbon and nitrogen of the solid sorbent obtained after carbonization. Interestingly, the homogeneous incorporation of nitrogen at the solution stage of the synthetic process (rather than by post-treatment of the preformed carbon) allowed the achievement of significant nitrogen contents even in carbons obtained at relatively high temperatures (e.g. 8–12 at% for 600 °C and ca. 5 at% for 800 °C). It is worth noting that, despite thermal treatments at high temperatures tend to decrease the nitrogen content, the high surface area of the solid sorbents obtained at 800 °C contributed to a significant enhancement of CO2 capture while providing superior selectivity, recyclability and stability.

Understanding Gas-Induced Structural Deformation of ZIF-8.

ZIF-8 is a zeolitic imidazolate framework with very good thermal and chemical stability that opens up many applications that are not feasible by other metal-organic frameowrks (MOFs) and zeolites. Several works report the adsorption properties of ZIF-8 for strategic gases. However, despite the vast experimental corpus of data reported, there seems yet to be a dearth in the understanding of the gas adsorption properties. In this work we provide insights at a molecular level on the mechanisms governing the ZIF-8 structural deformation during molecular adsorption. We demonstrate that the ZIF-8 structural deformation during the adsorption of different molecules at cryogenic temperature goes beyond the gas-induced rotation of the imidazolate linkers. We combine experimental and simulation studies to demonstrate that this deformation is governed by the polarizability and molecular size and shape of the gases, and that the stepped adsorption behavior is defined by the packing arrangement of the guest inside the host.

Adsorption of naphthalene from aqueous solution on activated carbons obtained from bean pods

The preparation of activated carbons from bean pods waste by chemical (K(2)CO(3)) and physical (water vapor) activation was investigated. The carbon prepared by chemical activation presented a more developed porous structure (surface area 1580 m(2) g(-1) and pore volume 0.809 cm(3) g(-1)) than the one obtained by water vapor activation (258 m(2) g(-1) and 0.206 cm(3) g(-1)). These carbons were explored as adsorbents for the adsorption of naphthalene from water solutions at low concentration and room temperature and their properties are compared with those of commercial activated carbons. Naphthalene adsorption on the carbons obtained from agricultural waste was stronger than that of carbon adsorbents reported in the literature. This seems to be due to the presence of large amounts of basic groups on the bean-pod-based carbons. The adsorption capacity evaluated from Freundlich equation was found to depend on both the textural and chemical properties of the carbons. Naphthalene uptake on biomass-derived carbons was 300 and 85 mg g(-1) for the carbon prepared by chemical and physical activation, respectively. Moreover, when the uptake is normalized per unit area of adsorbent, the least porous carbon displays enhanced naphthalene removal. The results suggest an important role of the carbon composition including mineral matter in naphthalene retention. This issue remains under investigation.

Borderline microporous-ultramicroporous palladium(II) coordination polymer networks. Effect of pore functionalisation on gas adsorption properties

PdII coordination polymer networks of the type [Pd(μ-X-pymo-N1,N3)2·(H2O)m]n (X = H, 2HHH; F, 2FFF; Br, 2BrBrBr; I, 2III), containing the X-pymo (X-Hpymo = 5-X-2-hydroxypyrimidine) ligands, have been obtained by refluxing aqueous suspensions of the monomeric trans-[Pd(X-Hpymo-N1)2Cl2] (1HH-1II) precursors with NaOH in a 1 : 1 ratio. While 2BrBrBr and 2III have been recovered as amorphous materials, the microcrystalline species 2HHH and 2FFF, in their hydrated and anhydrous forms, have been structurally characterised by ab initio XRPD methods: square planar PdII ions, symmetrically connected by exobidentate N1,N3-X-pymo bridges, give rise to neutral sodalite zeotypic frameworks (with H2O guest molecules eventually included in the pores). The thermal properties and porosity have been determined for all of the 2XXX systems. The H2, N2 and CO2 adsorption isotherms showed that the 2HHH and 2FFF materials possess permanent porosity, as opposed to the 2BrBrBr and 2III ones. Moreover, the isomorphic incorporation of fluorine in the framework causes important modifications in the gas-adsorption isotherms; stronger interactions at very low pressures (Henrys law region) appear in all of the probes studied (N2, CO2 and H2). Compounds 2HHH and 2FFF possess high H2 adsorption capacities at 77 K with respective values of 1.3 and 1.15 weight percentage, and storage densities of about 0.018 kg H2 L−1, which are combined with large isosteric adsorption heats (8–9 kJ mol−1).

Deep eutectic assisted synthesis of carbon adsorbents highly suitable for low-pressure separation of CO2–CH4 gas mixtures

Ionic liquids and deep eutectic solvents (a new class of ionic liquids obtained by complexation of quaternary ammonium salts with hydrogen bond donors such as acids, amines, and alcohols among others) have been recently used as solvents and even as precursors in the synthesis of carbonaceous materials. The use of long-alkyl-chain derivatives of ionic liquids that, playing the role of structure directing agents, were capable of designing the mesoporous structure of the resulting carbons is of particular interest. Meanwhile, deep eutectic solvents proved efficient in tailoring the structure comprised between large mesopores and small macropores, but the control over the smaller ones (e.g. small mesopores and micropores) is still a challenge as compared to ILs. Herein, we have used deep eutectic solvents composed of resorcinol, 4-hexylresorcinol and tetraethylammonium bromide for the synthesis of carbon monoliths with a tailor-made narrow microporosity. Behaving as molecular sieves, these carbons exhibited not only good capacities for CO2 adsorption (up to 3 mmol g−1) but also an outstanding – especially at low pressures – CO2–CH4 selectivity.

Role of surface adsorption and porosity features in the molecular recognition ability of imprinted sol-gels

Organically modified molecularly imprinted silicas (MIS) for nafcillin recognition were prepared using a simple sol-gel procedure. Molecular recognition of the template was observed by tuning the chemical and structural properties of the MIS. The relative amounts of organically modified alkoxysilane precursors were found to be key in the textural and morphological characteristics of the MIS as well as for developing an imprinting effect in the materials. The recognition properties of the imprinted materials were found to be strongly influenced by the hydrolytic stability of the alkoxysilanes and their inductive effects during sol-gel hydrolysis/condensation stages. The concept was to combine properties of organic groups with those of glass-like materials in order to develop synergetic properties through variations in the composition. Results from batch rebinding experiments as well as from the thorough study of the N(2) adsorption properties and the textural and structural characteristics of the MIS revealed that an imprint effect could be attributed to the presence of the template during the synthesis of MIS.

Influence of char structure on reactivity and nitric oxide emissions

The aim of this study was to investigate the influence of coal rank and operating conditions during coal pyrolysis on the resultant char texture properties, morphology and reactivity. A range of bituminous coals were pyrolysed in a fixed bed reactor at different heating rates. It was found that the higher the heating rate and the lower the coal rank, the more microporous chars were obtained. Isothermal (500 °C) gasification in 20% oxygen in argon of the chars was carried out using a differential thermogravimetric system (DTG). The results of this work indicated that the increase in the availability of char-active surface sites led to an increase in char reactivity, not only for oxygen but also for other reactive gases, in particular NO, diminishing emissions during the combustion process.

Reactivity of alpha-titanium phosphate/n-alkylamine intercalation compounds with mono- and polymeric aluminum species

Abstract The reaction of Al(H2O)63+ and [Al13O4(OH)24(H2O)12]7+ with α-Ti(PO4)2·2RNH3·H2O (R = C3H7, C4H9) has been investigated. The processes can be considered as RNH 3 + Al(H 2 O) 6 3+ or RNH 3 + [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ ion exchange. With Al(H2O)63+, saturation is reached and an α-Ti[Al(H 2 O) 6 ] 2 3 (PO 4 ) 2 ·nH 2 O phase is formed. With [Al13O4(OH)24(H2O)12]7+, materials were obtained with the highest aluminum content, having the formula α-Ti[Al13O4(OH)24(H2O)12]x(PO4)2·(2−7x)RNH3·nH2O (x = 0.20, R = C3H7; x = 0.14, R = C4H9). These compounds maintain ion-exchange properties. The porosity of the materials obtained is discussed.

Phenol Adsorption and Photo-oxidation on Porous Carbon/Titania Composites

Carbon/titania composites with different loadings were prepared and investigated for phenol adsorption and photo-oxidation from dilute aqueous solutions. The rate of phenol adsorption increased when titanium oxide (P25, Degussa) was immobilized on the carbon support due to the porous features of the resulting C/TiO2 composites. The kinetics of phenol adsorption were very fast for samples containing low titanium oxide contents, whereas titania loadings above 20 wt% presented some operational problems that prevented their application in aqueous solutions. Those C/TiO2 composites which exhibited higher adsorption rates in the absence of illumination also showed a more rapid disappearance of phenol from aqueous solution under UV light, together with the formation of lower amounts of intermediates. Removal efficiencies close to 100% were obtained for C/TiO2 composites containing ca. 10–15 wt% titanium oxide, with preferential oxidation of phenol through the formation of catechol.