One-step preparation of nitrogen doped titanium oxide/Au/reduced graphene oxide composite thin films for photocatalytic applications

© The Royal Society of Chemistry 2015. Titanium dioxide (TiO2) and TiO2/Au/reduced graphene oxide (rGO) nanocomposite thin films were grown by ultraviolet matrix assisted pulsed laser evaporation (UV-MAPLE) in controlled O2 or N2 atmospheres. An UV KrF∗ excimer laser (λ = 248 nm, τFWHM ∼ 25 ns, ν = 10 Hz) was used for the irradiation of the MAPLE targets consisting of TiO2 nanoparticles (NPs) or mixtures of TiO2 NPs, Au NPs, and graphene oxide (GO) platelets in aqueous solutions. The effect of Au and GO addition as well as nitrogen doping on the photocatalytic activity of the TiO2 thin films was investigated. The evaluation of the photocatalytic activity was performed by photodegradation of the organic methylene blue model dye pollutant under UV-visible light, >simulated sun> irradiation conditions. Our results show that the photocatalytic properties of TiO2 were significantly improved by the addition of Au NPs and rGO platelets. Nitrogen inclusion into the rGO structure further contributes to the enhancement of the TiO2/Au/rGO nanocomposites photocatalytic activity.The authors thank the financial support of the Executive Unit for Financing Higher Education, Research, Development, and Innovation of the Romanian Ministry of Education and Scientific Research under the contract PN-IIPT-PCCA-2011-3.2-1235 and the Spanish Ministry of Economy and Competitiveness under the contract ENE2014-56109-C3-3-R.Peer reviewedPeer Reviewe

Direct multipulse laser processing of titanium oxide–graphene oxide nanocomposite thin films

Nanocomposite thin films consisting of titanium oxide (TiO2) nanoparticles (NPs) and graphene oxide (GO) platelets were deposited by a spin-coating technique. The obtained films were submitted to direct laser irradiation using a frequency quadrupled Nd:YAG (λ=266 nm, τFWHM≅3 ns, ν=10 Hz) laser source. The effect of the laser processing conditions, as laser fluence value and number of subsequent laser pulses incident onto the same target location, on the surface morphology, crystalline structure, and chemical composition of the TiO2/GO nanocomposite thin films was systematically investigated. The laser fluence values were maintained below the vaporization threshold of the irradiated composite material. With the increase of the laser fluence and number of incident laser pulses melting and coalescence of the TiO2 NPs into inter-connected aggregates as well as rippling of the GO platelets take place. The gradual reduction of GO platelets and the onset of anatase to rutile phase transition were observed at high laser fluence values.The authors acknowledge the financial support from the Romanian Ministry of Education and Scientific Research under the Contract PNII-ID-PCE-2012-4-0292 and the Spanish Ministry of Economy and Competitiveness under the Contracts ENE2014-56109-C3-3-R and SEV-2015-0496.Peer reviewe

UV–vis light induced photocatalytic activity of TiO2/graphene oxide nanocomposite coatings

Peer reviewe

Self-assembly of carboxylic substituted PTM radicals: from weak ferromagnetic interactions to porous magnets

An overview of the work that have been developed over the last six years in our group on the use of polychlorotriphenylmetyl radicals (PTM) functionalized by carboxylic groups to access to purely organic/molecular magnetic materials is reported. From the seminal work on the monocarboxylic PTM (Section 2), of great importance to determine both the ability of these molecules to form intermolecular H-bonds and the nature of the intermolecular interactions mediated through the resulting supramolecular motifs, we will move to the self-assembly of PTM radicals functionalized with two and three carboxylic groups (Section 3). In those cases, the self-assembly of the paramagnetic units yield robust and porous magnetic structures, associating in some cases magnetic ordering to the latest remarkable characteristics. The last part of the review will present the latest results obtained with the idea to increase both the structural and magnetic dimensionality in purely organic PTM-based materials using a PTM radical functionalized by six carboxylic groups (Section 4). New trends and challenges for this research line, concerning the design and synthesis of new PTM radicals, as well as the obtaining of PTM based sensors or multifunctional materials will be presented in the concluding section (Section 5).This work was supported by the Dirección General de Investigación (Spain) under project EMOCIONa (CTQ2006-06333/BQU), Generalitat de Catalunya (2001SGR00362), EU under a Marie Curie Research Training Network (contract “QuEMolNa” number MCRTN-CT-2003-504880), as well as by NoE MAGMANet (contract 515767-2). D.M. is grateful to the Generalitat de Catalunya for both predoctoral and postdoctoral grants. N.R. thanks the MCRTN for its postdoctoral contract. A.D. is grateful to the MCRTN for a predoctoral grant.Peer Reviewe

Titanium oxide – reduced graphene oxide – silver composite layers synthesized by laser technique: Wetting and electrical properties

Electrically conductive and highly hydrophobic surface layers are attractive for many practical applications. In this work the functional, wetting and electrical properties of titanium dioxide (TiO2), TiO2/silver (Ag), and TiO2/reduced graphene oxide (rGO)/Ag nanocomposite coatings layers are reported. The functional properties of the layers were correlated with their chemical composition and bonding states between the constituent elements, determined in turn by the synthesis and immobilization process parameters. The nanocomposite coatings were obtained by matrix assisted pulsed laser evaporation, a laser-based environmental friendly thin film deposition technique. The synthesized ternary TiO2/rGO/Ag coatings has optimum performances, highly hydrophobic character and low electrical resistance, attributed to the presence of Ag nanoparticles and to the reduction of the oxygen containing functional groups of the GO platelets during laser irradiation and transfer processes leading to the formation of graphene-like material.The authors acknowledge the financial support from the Romanian Ministry of Education and Scientific Research under the contract PN-IIPT-PCCA-2011-3.2-1235 and the Spanish Economy and Competitiveness Ministry under the contract ENE2014-56109-C3-3-R. ICMAB acknowledges financial support from the Spanish Economy and Competitiveness Ministry, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496).Peer reviewe

Europium (III) complexes derived from carboxylic-substituted polychlorotriphenylmethyl radicals

Two europium (III) complexes (3 and 4) have been obtained reacting europium (III) nitrate and two polychlorotriphenylmethyl radicals properly functionalized with one (PTMMC−, 1) and six (PTMHC6−, 2) carboxylate groups, respectively. While complex 3 reveals a lamellar polar–apolar separated ion pair structure alternating PTM-based bilayers with nonaaquaeuropium cations ([Eu(H2O)9](PTMMC)3(PTMMCH)3 · 7H2O · 6EtOH), complex 4 shows a one-dimensional chain-like structure with formula [Eu2(PTMHC)(H2O)13] · 16H2O · EtOH. Magnetic properties of both complexes were studied in the 2–300 K range, and show the presence of weak inter-radical antiferromagnetic interactions below 5 K.This work was supported by the Ministerio de Educación y Ciencia of Spain under Consolider (project EMOCIONa, CTQ2006-06333/BQU), by EU under a Marie Curie Research Training Network (contract “QuEMolNa” number MCRTN-CT-2003-504880), as well as by NOE MAGMANET (Contract 515767-2). N.R. thanks the MCRTN for his postdoctoral contract. A.D. is grateful to the MCRTN for a predoctoral grant. D.M. acknowledges the Ministerio de Ciencia y Tecnologia of Spain for a Ramón y Cajal contract, and S.P. thanks the Ministerio de Ciencia y Tecnologia for a postdoctoral fellowship.Peer Reviewe

Three-dimensional open-frameworks based on LnIII ions and open-/closed-shell PTM ligands: synthesis, structure, luminescence, and magnetic properties

A series of isostructural open-framework coordination polymers formulated as [Ln(dmf)3(ptmtc)] (Ln=Sm (1), Eu (2), Gd (3), Tb (4), Dy (5); PTMTC=polychlorotriphenylmethyl tricarboxylate) and [Ln(dmf)2H2O(αH-ptmtc)] (Ln=Sm (1′), Eu (2′), Gd (3′), Tb (4′), Dy (5′)) have been obtained by treating LnIII ions with PTMTC ligands with a radical (PTMTC3−) or a closed-shell character (αH-PTMTC3−). X-ray diffraction analyses reveal that these coordination polymers possess 3D architectures that combine large channels and fairly rare lattice complex T connectivity. In addition, these compounds show selective framework dynamic sorption properties. For both classes of ligands, the ability to act as an antenna in Ln sensitization processes has been investigated. No luminescence was observed for compounds 1-5, and 3′ because of the PTMTC3− ligand and/or GdIII ion characteristics. Conversely, photoluminescence measurements show that 1′, 2′, 4′, and 5′ emit dark orange, red, green, and dark cyan metal-centered luminescence. The magnetic properties of all of these compounds have been investigated. The nature of the {Ln-radical} exchange interaction in these compounds has been assessed by comparing the behavior of the radical-based coordination polymers 1-5 with those of the compounds with the diamagnetic ligand set. While antiferromagnetic {Sm-radical} interactions are found in 1, ferromagnetic {Ln-radical} interactions propagate in the 3D architectures of 3, 4, and 5 (Ln=Gd, Tb, and Dy, respectively). This procedure also provided access to information on the {Ln--Ln} exchange existing in these magnetic systems

Nanosized trigonal prismatic and antiprismatic CuII coordination cages based on tricarboxylate linker

3D coordination cages have been synthesized via the supramolecular 3 + 2 self-assembly of macrocyclic dicopper molecular clips and tricarboxylate linkers, the nature of which allows the introduction of different functionalities to the 3D cages.This research has been supported by Spanish MEC (CTQ2006–05367/BQU, CTQ2006–06333/BQU and CTQ2005–08797-C02–01), and by the Catalan DURSI (2005SGR-00238 and 2005SGR-00591). AC, MG and LG give thanks for a predoctoral FPU grant from MEC-Spain. AD thanks the Marie Curie RTN Quemolna for a doctoral grant, and VM a postdoctoral I3P contract from the CSIC. JV is grateful for the support of the “Instituto de Salud Carlos III” through “Acciona CIBER”.Peer Reviewe

A hexacarboxylic open-shell building block: synthesis, structure and magnetism of a three-dimensional metal-radical framework

An octahedral hexacarboxylic polychlorotriphenylmethyl radical (PTMHC) and its hydrogenated precursor (aH-PTMHC) have been reacted with Cu(II) and 4,4'-bipyridine to prepare two isomorphic three-dimensional (3-D) coordination polymers of formula [Cu6(PTMHC)2(4,4'-bipy)3(H20)12]n(1) and [Cu6(aH-PTMHC)2(4,4'-bipy)3(EtOH)6(H20)6]n (2). Both 3-D structures can be described as two interpenetrating primitive cubic nets connected through bipyridine linkers, which defines an unusual topology with Schläfi symbol of (62·81)·(66·89). Magnetic properties of both metal-organic frameworks have been studied in detail. 2 shows weak antiferromagnetic interactions between Cu(II) ions at low temperature. In contrast, 1 reveals unexpected metal-radical ferromagnetic interactions (θ=2.1 (2) K). Information on the existence of magnetic ordering and the nature of the ordered phase for 1 has been investigated via very low temperature magnetic susceptibility measurements. Surprisingly, the experimental data indicate the occurrence of 3-D antiferromagnetic ordering below 0.5 K. This latter phenomenon has been explained with specific heat measurements. Experimental results reveal the coexistence of relatively strong ferromagnetic interactions with weaker antiferromagnetic ones, mediated through the bipyridine linkers, which finally determine the low temperature magnetic structure. A deeper study of the data allows the analysis of the magnetic behavior of 1 as a 3-D antiferromagnet, with Tc = 0.39 K, with ferromagnetic exchange interactions that do not propagate with equal strength along the three crystallographic directions above this temperature.This work was supported by the Ministerio de Educación y Ciencia of Spain under Consolider-C project EMOCIONa (project CTQ2006-06333/BQU), by the EU under the Marie Curie Research Training Network ‘‘QuEMolNa’’ (contract MCRTN-CT-2003-504880), as well as by NOE MAGMANET (contract NMP3-CT-2005-515767). N. R. thanks the MCRTN for its postdoctoral contract. D. M. acknowledges the Ministerio de Ciencia y Tecnologia for a Ramo´n y Cajal contract. F. L. and A. C. acknowledge the funding from DGA project PIP039 ‘‘NANOMATERIA’’ and project MAT2005/1272.Peer reviewe

MAPLE synthesis of reduced graphene oxide/silver nanocomposite electrodes: Influence of target composition and gas ambience

Graphene oxide (GO) and reduced GO films with different amounts of silver nanoparticles (Ag NPs) have been deposited on quartz and silicon substrates by matrix assisted pulsed laser evaporation (MAPLE). The morphology, structure, chemical composition, and optical and electrochemical properties were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy, ultravioletevisible spectrophotometry, and cyclic voltammetry measurements. The properties of the films obtained with two types of GO precursors have been compared. A reduction of the amount of oxygen containing groups is observed with the increase of the Ag concentration, which leads to a decrease of the optical band gap. Moreover, the deposition in nitrogen gas ambience leads to the N-doping of rGO material. The films obtained with the highest amount of Ag and with nitrogen doping show potential to be used in energy storage electrodes. (C) 2017 Elsevier B.V. All rights reserved