Conchi O. Ania

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.

Influence of oxygen-containing functional groups on active carbon adsorption of selected organic compounds

Abstract Two commercial activated carbons (AC) were treated with HNO3 and (NH4)2S2O8. The changes in surface area and pore size distribution resulting from the oxidising treatments were studied by means of nitrogen adsorption isotherms. The modifications in the surface chemistry were evaluated by means of the point of zero charge (PZC) and the oxygen content. Selective removal of oxygen complexes by heating under N2 and CO2 flow at 723 and 1123 K was also studied. The treatment with HNO3 was found to broaden the microporosity and mesoporosity of the carbons when low concentrations of the oxidising agent were employed. Severe oxidation conditions resulted in an almost total destruction of the texture of the carbons. The point of zero charge values changed systematically with the extent of the oxidation; the more oxidised the carbon, the lower its point of zero charge. Thermal treatment at high temperatures leads to an enhancement of the carbon basicity and a slight decrease in the textural properties of the original carbons.

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.

Kinetics of naphthalene adsorption on an activated carbon: comparison between aqueous and organic media.

The purpose of this work was to explore the kinetics of naphthalene adsorption on an activated carbon from aqueous and organic solutions. Kinetic curves were fitted to different theoretical models, and the results have been discussed in terms of the nature and properties of the solvents, the affinity of naphthalene to the solutions, and the accessibility to the porosity of the activated carbon. Data was fitted to the pseudo-second order kinetic model with good correlation coefficients for all the solution media. The faster adsorption rate was obtained for the most hydrophobic solvent (heptane). The overall adsorption rate of naphthalene seems to be controlled simultaneously by external (boundary layer) followed by intraparticle diffusion in the porosity of the activated carbon when water, ethanol and cyclohexane are used as solvents. In the case of heptane, only two stages were observed (pore diffusion and equilibrium) suggesting that the limiting stage is the intraparticle diffusion. The low value of the boundary thickness supports this observation.

Effect of texture and surface chemistry on adsorptive capacities of activated carbons for phenolic compounds removal

Three microporous commercial activated carbons (AC) were used for the adsorption of phenol and salicylic acid from aqueous solution. Equilibrium adsorption data were obtained by the bottle-point technique. Long periods of time were needed to reach the equilibrium between the active carbon and the aqueous solution. Adsorptive capacities obtained from the isotherms were calculated following the ASTM 3860 procedure. Carbons with a high oxygen content were found to present lower adsorptive capacities for both phenol and salicylic acid. Column tests were also used for the uptake of phenol and salicylic acid, and adsorptive capacities were calculated from the breakthrough curves. Adsorptive capacities calculated from the breakthrough curves were found to be significantly lower than those evaluated from the equilibrium isotherms.

Competitive adsorption of ibuprofen and amoxicillin mixtures from aqueous solution on activated carbons

This work investigates the competitive adsorption under dynamic and equilibrium conditions of ibuprofen (IBU) and amoxicillin (AMX), two widely consumed pharmaceuticals, on nanoporous carbons of different characteristics. Batch adsorption experiments of pure components in water and their binary mixtures were carried out to measure both adsorption equilibrium and kinetics, and dynamic tests were performed to validate the simultaneous removal of the mixtures in breakthrough experiments. The equilibrium adsorption capacities evaluated from pure component solutions were higher than those measured in dynamic conditions, and were found to depend on the porous features of the adsorbent and the nature of the specific/dispersive interactions that are controlled by the solution pH, density of surface change on the carbon and ionization of the pollutant. A marked roll-up effect was observed for AMX retention on the hydrophobic carbons, not seen for the functionalized adsorbent likely due to the lower affinity of amoxicillin towards the carbon adsorbent. Dynamic adsorption of binary mixtures from wastewater of high salinity and alkalinity showed a slight increase in IBU uptake and a reduced adsorption of AMX, demonstrating the feasibility of the simultaneous removal of both compounds from complex water matrices.

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.