Manuel Pérez-Mendoza

Polymorphic coordination networks responsive to CO2, moisture, and thermal stimuli: porous cobalt(II) and zinc(II) fluoropyrimidinolates.

The novel porous [{M(F-pymo)(2)}(n)]2.5n H(2)O coordination networks (M=Co, Zn; F-pymo=5-fluoropyrimidin-2-olate), possessing sodalitic topology, have been synthesised and structurally characterised by means of powder diffraction methods. Thermodiffractometry demonstrated their plasticity: when heated up to 363 K, they reversibly transform into three-dimensional dehydrated [{M(F-pymo)(2)}(n)] species, with significantly different lattice parameters. Further heating induces irreversible polymorphic transformations into layered phases, in which the original MN(4) coordination sphere changes into an MN(3)O one. A mixed-metal phase, [{Co(x)Zn(1-x)(F-pymo)(2)}(n)]2.5n H(2)O, was also prepared, showing that zinc is preferentially inserted, when starting from a Co/Zn reagent ratio of 1:1. The solid-gas adsorption properties of the anhydrous 3D frameworks have been explored towards N(2), H(2) (77 K) and CH(4), CO(2) (273 K). These results show that these materials permit the diffusion of CO(2) molecules only. Remarkably, the CO(2) adsorption process for the [{Co(F-pymo)(2)}(n)] network proceeds in two steps: the first step takes place at low pressures (<600 kPa) and the second one above a threshold pressure of 600 kPa. By contrast, the [{Zn(F-pymo)(2)}(n)] network only permits CO(2) diffusion by applying pressures above 900 kPa. This type of behaviour is typical of porous networks with gated channels. The high CO(2) selectivity of these systems over the rest of the essayed probe gases is explained in terms of flexibility and polarity of the porous network. Finally, the magnetic studies on the Co(II) systems reveal that the as synthesised [{Co(F-pymo)(2)}(n)]2.5n H(2)O material behaves as an antiferromagnet with a T(N) of about 29 K. At variance, the [{Co(F-pymo)(2)}(n)] layered phase shows an unusually weak ferromagnetic ordering below 17 K, arising from a spin-canting phenomenon.

Modifications produced by O2 plasma treatments on a mesoporous glassy carbon

A glassy carbon, P3, obtained by carbonization of polyfurfuryl alcohol was used to study the changes produced by oxygen plasma treatments which were compared to those obtained by molecular oxygen. The sample was selected for its well defined mesoporosity. The aim was to study the influence of porosity on the reactivity of the sample in oxygen plasma. The results were compared to previously reported data obtained using a glassy carbon with no macro or mesoporosity. It is concluded that the influence of mesoporosity is almost negligible in such a way that only the external surface was affected by plasma treatment.

Modifications produced by O2 and CO2 plasma treatments on a glassy carbon : comparison with molecular gases

Abstract A carbon material obtained by pyrolysis of polyfurfuryl alcohol was submitted to four different treatments. Two of these were carried out using molecular gases (oxygen and carbon dioxide) and two using plasma of the same molecules. The textural and chemical modifications produced by these treatments were studied by N2 and CO2 adsorption at 77 and 273 K, respectively, mercury porosimetry and Fourier Transformed Infrared Spectroscopy (FTIR). In addition, the changes in the external surface produced by the treatments were observed by Scanning Electron Microscopy (SEM). Molecular carbon dioxide treatment opens and creates microporosity. However, plasma treatments mainly produce constrictions at the entrance of the micropores. The effect of the molecular treatments on the external surface is not easily observed, while plasmas treatments produce pits on the surface. The statistical analysis of these have been obtained in order to establish their evolution.

Grafting the surface of carbon nanotubes and carbon black with the chemical properties of hyperbranched polyamines

Abstract Controlling the chemistry on the surface of new carbon materials is a key factor to widen the range of their applicability. In this paper we show a grafting methodology of polyalkylamines to the surface of carbon nanomaterials, in particular, carbon nanotubes and a carbon black. The aim of this work is to reach large degrees of covalent functionalization with hyperbranched polyethyleneimines (HBPEIs) and to efficiently preserve the strong chelating properties of the HBPEIs when they are fixed to the surface of these carbon materials. This functionalization opens new possibilities of using these carbon nanotubes-based hybrids. The results show that the HBPEIs are covalently attached to the carbon materials, forming hybrids. These hybrids emerge from the reaction of amine functions of the HBPEIs with carbonyls and carboxylic anhydrides of the carbon surface which become imine and imide bonds. Thus, due to the nature of these bonds, the pre-oxidized samples with relevant number of C=O groups showed an increase in the degree of functionalization with the HBPEIs. Furthermore, both the acid-base properties and the coordination capacity for metal ions of the hybrids are equivalent to that of the free HBPEIs in solution. This means that the chemical characteristics of the HBPEIs have been efficiently transferred to the hybrids. To reach this conclusion we have developed a novel procedure to assess the acid-base and the coordination properties of the hybrids (solids) by means of potentiometric titration. The good agreement of the values obtained for the hybrids and for the free HBPEIs in aqueous solution supports the reliability of the procedure. Moreover, the high capacity of the hybrids to capture Ni2+ by complexation opens new possibilities of using these hybrids to capture high-value metal ions such as Pd2+ and Pt2+. Hyperbranched polyethylenimines are covalently fixed to the surface of carbon materials, so the chemical characteristics of the amines are transferred to the hybrid materials.

Modulation of pore shape and adsorption selectivity by ligand functionalization in a series of “rob”-like flexible metal–organic frameworks

We report the synthesis of a new family of four new isoreticular metal–organic frameworks (MOFs) based on Cu–Cu paddle-wheel building units. The four MOFs contain 1D microchannels modulated by chemical functionalisation of a dicarboxylate ligand or the use of different bis-4,4′-pyridyl-like connectors behaving as ancillary linkers. A deep analysis of their CO2, H2 and CH4 adsorption properties, combining both experimental and grand canonical Monte Carlo isotherms as well as in situ synchrotron X-ray diffraction, shows variable adsorption behaviour towards the studied gases, with some materials acting as molecular sieves with virtually infinite selectivity.

HBPEI-grafted carbon nanotubes for the effective retention of Pd2+ and Pt2+ through complexation

Hyperbranched poly(ethyleneimine) (HBPEI) molecules in solution present high capacity to form stable complexes with transition metal ions due to the large number of amino groups ready to form chelates. We grafted HBPEI molecules to a multi-walled carbon nanotube (MWCNT) surface through covalent bonding, preparing solid hybrids which retain the chemical properties of the free poly-alkylamine molecules. In this way, we are able to transfer the complexation capacity of such molecules to a solid material adequate to act as a high-capacity sorbent for metal transition ions. We tested the HBPEI/MWCNT hybrids for the retention of Pd2+ and Pt2+ and the retention values obtained are much larger than those previously reported with fast retention kinetics. The kinetics and the XPS analysis of the metal ion/HBPEI/MWCNT ensemble indicate that the retention takes place through the formation of chelates with two or three nitrogen atoms and with Cl− anions as co-ligands. Moreover, the results allow us to tune the metal loading on the hybrids by controlling the solution conditions. This is important because the XPS valence band analysis demonstrates that metal complexation directly modifies the electronic behaviour of the carbon nanotubes, which supports the stable covalent bond between HBPEI molecules and MWCNT and opens the possibility for tuning the electronic properties of the tubes.

2D-cadmium MOF and gismondine-like zinc coordination network based on the N-(2-tetrazolethyl)-4′-glycine linker

This work was supported by the MEC of Spain (Project CTQ2011-24478) and the Junta de Andalucia (FQM-1484). D. F.-J. thanks the Royal Society for a University Research Fellowship.