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Colombian metallurgical coke as catalysts support of the direct coal liquefaction

Rico, D; Agamez, Y; Romero, E; Centeno, MA; Odriozola, JA; Diaz, JD
Fuel, 255 (2019) 115748
Química de Superficies y Catálisis


A Colombian metallurgical coke was modified in its surface chemistry and was used as support of iron sulfide catalysts for direct coal liquefaction. The modification was made by treatments with diluted oxygen and HNO3 at different conditions. Changes in surface chemistry were studied by determining the point of zero charge (PZC), the isoelectric point (IEP), thermogravimetric analysis (TGA), temperature programmed decomposition-mass spectrometry (TPD-MS), Diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) and nitrogen adsorption at 77 K. The results show that the materials obtained have a wide range of functional groups incorporated in a different proportion and quantity. The textural parameters indicate that treatment with diluted oxygen increases the surface area and incorporates micropores while the samples treated with HNO3 maintain the textural properties of the original material. The catalysts were also characterized by Raman spectroscopy. It was found that impregnation with the iron sulfide precursor does not significantly affect the Raman characteristics of the support. Additionally, XRD analysis shows smaller pyrite crystallites in the coke enriched with oxygenated groups of phenol and lactone indicating better dispersion of the active phase. The amount of oxygen chemisorbed per gram of catalyst shows that both, oxygen and nitric acid treatments, improve the relative dispersion of the active phase. It was found that the presence of the catalysts increases the conversion and yields towards oils and gases with respect to those of the tests without catalysts. Cokes modified by dilute oxygen gaseous treatment contain surface phenol and lactone groups and present the highest yield to oils.

Noviembre, 2019 | DOI: 10.1016/j.fuel.2019.115748

Ultrastable CoxSiyOz Nanowires by Glancing Angle Deposition with Magnetron Sputtering as Novel Electrocatalyst for Water Oxidation

Cano, M; Garcia-Garcia, FJ; Rodriguez-Padron, D; Gonzalez-Elipe, AR; Giner-Casares, JJ; Luque, R
Nanotecnología en Superficies y Plasma


Cobalt is one of the most promising non-noble metal as electrocatalyst for water oxidation. Herein, a highly stable silicon-cobalt mixed oxide thin film with a porous columnar nanostructure is proposed as electrocatalyst for oxygen evolution reaction (OER). CoOx and CoxSiyOz layers with similar thickness were fabricated at room temperature by magnetron sputtering in a glancing angle configuration (MS-GLAD) on tin-doped indium oxide (ITO) substrates. After characterization, a comparative study of the electrocatalytic performance for OER of both layers was carried out. The excellent long-term stability as electrocatalyst for OER of the porous CoxSiyOz thin film demonstrates that the presence of silicon on the mixed oxide network increases the mechanical stability of the Si/Co layer, whilst maintaining a considerable electrocatalytic response.

Noviembre, 2019 | DOI: 10.1002/cctc.201901730

Design of highly stabilized nanocomposite inks based on biodegradable polymer-matrix and gold nanoparticles for Inkjet Printing

Begines, Belen; Alcudia, Ana; Aguilera-Velazquez, Raul; Martinez, Guillermo; He, Yinfeng; Wildman, Ricky; Sayagues, Maria-Jesus; Jimenez-Ruiz, Aila; Prado-Gotor, Rafael
Scientific Reports, 9 (2019) 16097
Reactividad de Sólidos


Nowadays there is a worldwide growing interest in the Inkjet Printing technology owing to its potentially high levels of geometrical complexity, personalization and resolution. There is also social concern about usage, disposal and accumulation of plastic materials. In this work, it is shown that sugar-based biodegradable polyurethane polymers exhibit outstanding properties as polymer-matrix for gold nanoparticles composites. These materials could reach exceptional stabilization levels, and demonstrated potential as novel robust inks for Inkjet based Printing. Furthermore, a physical comparison among different polymers is discussed based on stability and printability experiments to search for the best ink candidate. The University of Seville logo was printed by employing those inks, and the presence of gold was confirmed by ToF-SIMS. This approach has the potential to open new routes and applications for fabrication of enhanced biomedical nanometallic-sensors using stabilized AuNP.

Noviembre, 2019 | DOI: 10.1038/s41598-019-52314-2

Phyllite clays as raw materials replacing cement in mortars: Properties of new impermeabilizing mortars

Arce, Carolina; Garzon, Eduardo; Sanchez-Soto, Pedro J.
Construction and Building Materials, 224 (2019) 348-358
Materiales Avanzados


The aim of this investigation was to determine the suitability of phyllite clays as a raw construction material. For that purpose, the cement in mortars was replaced by a phyllite clay (0–90 wt%) making this study the first of its kind to be performed. These materials were prepared with different water proportions according to the water content and water/cement and water/binder (cement plus phyllite clay) relationships. A comparative study of the most important properties of the resulting experimental mortars was carried out, such as apparent density, water retentivity, consistency and mechanical strength (flexural and compressive strength), along with an evaluation of the pozzolanic activity and permeability. The results showed that the increase of phyllite decreases the apparent density, the consistency and mechanical properties of the mortar, while water retentivity fluctuates. Good correlations (R2 > 0.84) were obtained between flexural and compressive strength for the mortars after 28 days of curing. Pozzolanic activity was observed at cement replacement of 80 wt% of phyllite. Moreover, new impermeabilizing mortars constituted by phyllite clay and cement have been obtained according to the low coefficients of permeability. Taking into account the findings of this research, phyllite clays can be applied as raw construction materials with savings derived from replacing cement in mortars and the low energy consumption involved in their production. However, the present study concluded that the use of phyllite clays did not improve the mechanical strength of these new mortars but, in contrast, they can be applied for impermeabilization purposes in Construction and Civil Engineering.

Noviembre, 2019 | DOI: 10.1016/j.conbuildmat.2019.07.081

Encapsulation of Upconversion Nanoparticles in Periodic Mesoporous Organosilicas

Rahmani, S; Jimenez, CM; Aggad, D; Gonzalez-Mancebo, D; Ocana, M; Ali, LMA; Nguyen, C; Nieto, AIB; Francolon, N; Oliveiro, E; Boyer, D; Mahiou, R; Raehm, L; Gary-Bobo, M; Durand, JO; Charnay, C
Molecules, 24 (2019) 22
Materiales Coloidales


(1) Background: Nanomedicine has recently emerged as a promising field, particularly for cancer theranostics. In this context, nanoparticles designed for imaging and therapeutic applications are of interest. We, therefore, studied the encapsulation of upconverting nanoparticles in mesoporous organosilica nanoparticles. Indeed, mesoporous organosilica nanoparticles have been shown to be very efficient for drug delivery, and upconverting nanoparticles are interesting for near-infrared and X-ray computed tomography imaging, depending on the matrix used. (2) Methods: Two different upconverting-based nanoparticles were synthesized with Yb3+-Er3+ as the upconverting system and NaYF4 or BaLuF5 as the matrix. The encapsulation of these nanoparticles was studied through the sol-gel procedure with bis(triethoxysilyl)ethylene and bis(triethoxysilyl)ethane in the presence of CTAB. (3) Results: with bis(triethoxysilyl)ethylene, BaLuF5: Yb3+-Er3+, nanoparticles were not encapsulated, but anchored on the surface of the obtained mesoporous nanorods BaLuF5: Yb3+-Er3+@Ethylene. With bis(triethoxysilyl)ethane, BaLuF5: Yb3+-Er3+ and NaYF4: Yb3+-Er(3+)nanoparticles were encapsulated in the mesoporous cubic structure leading to BaLuF5: Yb3+-Er3+@Ethane and NaYF4: Yb3+-Er3+@Ethane, respectively. (4) Conclusions: upconversion nanoparticles were located on the surface of mesoporous nanorods obtained by hydrolysis polycondensation of bis(triethoxysilyl)ethylene, whereas encapsulation occurred with bis(triethoxysilyl)ethane. The later nanoparticles NaYF4: Yb3+-Er3+@Ethane or BaLuF5: Yb3+-Er3+@Ethane were promising for applications with cancer cell imaging or X-ray-computed tomography respectively.

Noviembre, 2019 | DOI: 10.3390/molecules24224054

Graphene nanoplatelets for electrically conductive 3YTZP composites densified by pressureless sintering

Lopez-Pernia, C; Gallardo-Lopez, A; Morales-Rodriguez, A; Poyato, R
Journal of the European Ceramic Society, 39 (2015) 4435-4439
Reactividad de Sólidos


3 mol% yttria tetragonal zirconia polycrystalline (3YTZP) ceramic composites with 2.5, 5 and 10 vol% graphene nanoplatelets (GNP) were pressureless sintered in argon atmosphere between 1350 and 1450 degrees C. The effects of the GNP content and the sintering temperature on the densification, microstructure and electrical properties of the composites were investigated. An isotropic distribution of GNP surrounding ceramic regions was exhibited regardless the GNP content and sintering temperature used. Electrical conductivity values comparable to the ones of fully dense composites prepared by more complex techniques were obtained, even though full densification was not achieved. While the composite with 5 vol% GNP exhibited electrical anisotropy with a semiconductor-type behaviour, the composite with 10 vol% GNP showed an electrically isotropic metallic-type behaviour.

Noviembre, 2019 | DOI: 10.1016/j.jeurceramsoc.2019.05.067

From structure to luminescence investigation of oxyfluoride transparent glasses and glass-ceramics doped with Eu3+/Dy3+ ions

Walas, M; Lisowska, M; Lewandowski, T; Becerro, AI; Lapinski, M; Synak, A; Sadowski, W; Koscielska, B
Journal of Alloys and Compounds, 896 (2019) 1410-1418
Materiales Coloidales


Glasses and glass-ceramics with nominal composition 73 TeO2- 4BaO-3Bi(2)O(3)-18SrF(2)-2RE(2)O(3) (where RE = Eu, Dy) have been synthesized by conventional melt-quenching technique and subsequent heat treatment at 370 degrees C for 24 h in air atmosphere. Various Eu3+ to Dy3+ molar ratio have been applied to investigate luminescence properties in both glass and glass-ceramic matrices. Especially, white light emission through simultaneous excitation of Eu3+ and Dy3+ has been studied in detail. Influence of crystalline SrF2 phase on luminescence kinetics has been determined by luminescence decay time measurements. Presence of crystalline SrF2 phase has been confirmed by X-ray diffraction technique XRD and transmission electron microscopy TEM. X-ray photoelectron spectroscopy XPS and Fourier-transform infrared spectroscopy FTIR have been applied to get further insight into structural properties of glass and glass-ceramic materials. Color tunable white light emission has been obtained using UV excitation. Influence of the SrF2 crystallization on luminescence properties of prepared materials have been described in detail. Moreover, luminescence properties and especially emission color dependence on the Eu3+ to Dy3+ molar ratio have been exhaustively studied. Color-tunable white light emission has been observed as a result of simultaneous radiative transition of both, Eu3+ and Dy3+ ions when applying UV excitation. Judd - Ofelt and other optical parameters have been calculated based on luminescence emission spectra. Achieved results confirm that tellurite glass-ceramics containing SrF2 nanocrystals are good hosts for RE3+ ions and they can be considered as new phosphors for white light emitting diodes WLEDs.

Octubre, 2019 | DOI: 10.1016/j.jallcom.2019.07.017

Casimir-Lifshitz Force Based Optical Resonators

Esteso, V; Carretero-Palacios, S; Miguez, H
Journal of Physical Chemistry Letters, 10 (2019) 5856-5860
Materiales Ópticos Multifuncionales


We theoretically investigate the building of optical resonators based on the levitation properties of thin films subjected to strong repulsive Casimir-Lifshitz forces when immersed in an adequate medium and confronted with a planar substrate. We propose a design in which cavities supporting high Q-factor optical modes at visible frequencies can be achieved by means of combining commonly found materials, such as silicon oxide, polystyrene or gold, with glycerol as a mediating medium. We use the balance between flotation and repulsive Casimir-Lifshitz forces in the system to accurately tune the optical cavity thickness and hence its modes. The effects of other forces, such as electrostatic, that may come into play are also considered. Our results constitute a proof of concept that may open the route to the design of photonic architectures in environments in which dispersion forces play a substantial role and could be of particular relevance for devising novel microfluidic optical resonators.

Octubre, 2019 | DOI: 10.1021/acs.jpclett.9b02030

A QTAIM and DFT study of the dizinc bond in non-symmetric [CpZn2Ln] complexes

Ayala, R; Galindo, A
Journal of Organometallic Chemistry, 898 (2019) UNSP 120878
Reactividad de Sólidos


Several [Zn2L2] and [CpZn2Ln] dizinc compounds have been studied by density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) in order to compare the nature and topology of the Zn-Zn bond in symmetrical and non-symmetrical complexes. The stability of these complexes have been evaluated on the basis of the formation energies. The disproportionation reaction has also been analysed indicating that symmetric complexes are less stable than non-symmetric ones. To certain extent, the properties of the [CpZn2Ln] complexes are between those of the [Zn2L2] and [Zn2Cp2] compounds. The asymmetry of the [CpZn2Ln] compounds is illustrated in terms of the topological properties, especially in the Source Function (SF) and Natural Bond Orbital (NBO) analysis. 

Octubre, 2019 | DOI: 10.1016/j.jorganchem.2019.120878

Influence of pre-deformation on the precipitation hardening in Cu-Ni-Si alloy

Donoso, E; Dianez, MJ; Criado, JM
Revista de Metalurgia, 55 (2019) e157
Reactividad de Sólidos


The effects of pre-deformation on the precipitation processes in a Cu-2.8 Ni-1.4 Si (at.%) alloy were studied using differential scanning calorimetric (DSC), transmission electron microscopy (TEM) and microhardness measurements. The calorimetric curves shows the presence of one exothermic reaction attributed to the formation of delta-Ni2Si precipitates in the copper matrix that was confirmed by TEM. In addition it can be observed that the temperature of the maximum of the DSC peak decreases with the increase of the pre-deformation to the aging treatments. The activation energies calculated for the precipitation of by the Kissinger method, were similar to those calculated by an Arrhenius function, from the maximum hardening of the matrix due to aging treatments (saturation of the hardness during isothermal aging). The analysis of the microhardness measurements together with the calorimetric curves and the TEM micrographs confirm, on the one hand, that the formation of the delta-Ni2Si phase, during the aging treatments, are responsible for the hardening of the copper matrix, and on the other hand that the deformation prior to the aging treatment partially inhibits the formation of the precipitates.

Octubre, 2019 | DOI: 10.3989/revmetalm.157

Spatially Resolved Analysis of Defect Annihilation and Recovery Dynamics in Metal Halide Perovskite Single Crystals

Galisteo-Lopez, JF; Calvo, ME; Miguez, H
ACS Applied Energy Materials, 2 (2019) 6967-6972
Materiales Ópticos Multifuncionales


The spectacular advances in efficiency of optoelectronic devices based on lead-halide perovskites have been accompanied by detailed structural and optical studies regarding the instability presented by these materials, which constitute their main bottleneck for commercialization. Following a pump and probe scheme in a laser scanning confocal microscope, we resolve the photoinduced emission activation/deactivation dynamics in CH3NH3PbBr3 single crystals with millisecond and sub-micrometer resolution. This is complemented with a study of spectral variations and interpreted in the framework of light-induced ion migration and associated defect passivation. Our results point to the presence of photoinduced structural changes accompanying the migration of ions.

Octubre, 2019 | DOI: 10.1021/acsaem.9b01335

Sodium ion storage performance of magnetron sputtered WO3 thin films

Garcia-Garcia, FJ; Mosa, J; Gonzalez-Elipe, AR; Aparicio, M
Electrochimica Acta, 321 (2019) 134669
Nanotecnología en Superficies y Plasma


WO3 thin film electrodes were successfully prepared by magnetron sputtering (MS) deposition under an oblique angle configuration (OAD). Intercalation of Na ions in the tungsten oxide layers has been studied using electrochemical techniques. Sample characterization before and after sodium intercalation has been carried out by Raman, XPS and XRD measurements. ToF-SIMS analysis has been also performed in order to analyze the element depth profiles along the electrode thickness. Electron microscopy evaluation of the cross section confirms the porous structure of the coatings. Batteries integrating these WO3 electrodes have a discharge capacity of 120 mA h g(-1) at the initial cycles and show an adequate capacity retention upon 300 cycles. The WO3-OAD thin-films are proposed as promising electrodes for Na-ion batteries.

Octubre, 2019 | DOI: 10.1016/j.electacta.2019.134669

Synthesis, functionalization and properties of uniform europium-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)(2), X = Mo,W) probes for luminescent and X-ray computed tomography bioimaging

Laguna, M; Nunez, NO; Becerro, AI; Lozano, G; Moros, M; de la Fuente, JM; Corral, A; Balcerzyk, M; Ocana, M
Journal of Colloid and Interface Science, 554 (2019) 520-530
Materiales Coloidales, Materiales Ópticos Multifuncionales


A one-pot simple procedure for the synthesis of uniform, ellipsoidal Eu3+-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)(2), X = W, Mo) nanophosphors, functionalized with carboxylate groups, is described. The method is based on a homogeneous precipitation process at 120 degrees C from appropriate Na+ Ln(3+) and tungstate or molybdate precursors dissolved in ethylene glycol/water mixtures containing poly acrylic acid. A comparative study of the luminescent properties of both luminescent materials as a function of the Eu3+ doping level has been performed to find the optimum nanophosphor, whose efficiency as X-ray computed tomography contrast agent is also evaluated and compared with that of a commercial probe. Finally, the cell viability and colloidal stability in physiological pH medium of the optimum samples have also been studied to assess their suitability for biomedical applications.

Octubre, 2019 | DOI: 10.1016/j.jcis.2019.07.031

The Success Story of Gold-Based Catalysts for Gas- and Liquid-Phase Reactions: A Brief Perspective and Beyond

Price, CAH; Pastor-Perez, L; Ivanova, S; Reina, TR; Liu, J
Frontiers in Chemistry, 7 (2019) 691
Química de Superficies y Catálisis


Gold has long held the fascination of mankind. For millennia it has found use in art, cosmetic metallurgy and architecture; this element is seen as the ultimate statement of prosperity and beauty. This myriad of uses is made possible by the characteristic inertness of bulk gold; allowing it to appear long lasting and above the tarnishing experienced by other metals, in part providing its status as the most noble metal.

Octubre, 2019 | DOI: 10.3389/fchem.2019.00691

The influence of mechanical activation process on the microstructure and mechanical properties of bulk Ti2AlN MAX phase obtained by reactive hot pressing

Salvo, C; Chicardi, E; Garcia-Garrido, C; Jimenez, JA; Aguilar, C; Usuba, J; Mangalaraja, RV
Ceramics International, 45 (2019) 17793-17799
Reactividad de Sólidos


The effect of mechanical activation process on the microstructure and mechanical properties of bulk nanostructured Ti2AlN compound has been investigated in this work. The mixture of Ti and AlN powders was prepared in a 2:1 molar ratio, and a part of this powder was subjected to a high-energy milling process under argon atmosphere for 10 h using agate as grinding media. Finally, the densification and formation of the ternary Ti2AlN MAX phase through solid state reaction of both unmilled and milled powders were carried out by hot pressing under 15 or 30 MPa at 1200 degrees C for 2 h. The microstructure of precursor powder mixtures and the consolidated samples was characterized by using X-ray diffraction (XRD) and a scanning electron microscope equipped with an energy dispersive X-ray spectroscopy (SEM/EDS). The X-ray diffraction patterns were fitted using the Rietveld refinement for phase quantification and to determine their most important microstructural parameters. Microstructure and mechanical properties of the consolidated samples were correlated with the load used for the hot pressing process. The substantial increase of hardness, the higher densification and the lower grain sizes observed in the samples prepared from the activated powders were attributed to the formation of second phases like Ti5Si3 and Al2O3.

Octubre, 2019 | DOI: 10.1016/j.ceramint.2019.05.350

Sintering kinetics, defect chemistry and room-temperature mechanical properties of titanium nitride prepared by spark plasma sintering

Chavez, JMM; Moshtaghioun, BM; Hernandez, FLC; Garcia, DG
Journal of Alloys and Compounds, 807 (2019) 151666
Propiedades Mecánicas de Sólidos


Fully dense titanium nitride polycrystals have been prepared by spark plasma sintering. The kinetics of the sintering process and the optimized conditions for SPS processing have been put forward. Microstructural analyses of the resulting samples have unambiguously shown the coexistence of titanium as Ti2+, Ti3+ and Ti4+, thus driving the presence of cation vacancies. This fact is a new ingredient which is shown to influence the mechanical properties of this strategic ceramic. 

Octubre, 2019 | DOI: 10.1016/j.jallcom.2019.151666

The Calcium-Looping (CaCO3/CaO) process for thermochemical energy storage in Concentrating Solar Power plants

Ortiz, C; Valverde, JM; Chacartegui, R; Perez-Maqueda, LA; Gimenez, P
Renewable & Sustanaible Energy Reviews, 113 (2019) 109252
Reactividad de Sólidos


Energy storage based on thermochemical systems is gaining momentum as a potential alternative to molten salts in Concentrating Solar Power (CSP) plants. This work is a detailed review about the promising integration of a CaCO3/CaO based system, the so-called Calcium-Looping (CaL) process, in CSP plants with tower technology. The CaL process relies on low cost, widely available and non-toxic natural materials (such as limestone or dolomite), which are necessary conditions for the commercial expansion of any energy storage technology at large scale. A comprehensive analysis of the advantages and challenges to be faced for the process to reach a commercial scale is carried out. The review includes a deep overview of reaction mechanisms and process integration schemes proposed in the recent literature. Enhancing the multicycle CaO conversion is a major challenge of the CaL process. Many lab-scale analyses carried out show that residual effective CaO conversion is highly dependent on the process conditions and the CaO precursors used, reaching values in a wide range (0.07–0.82). The selection of the optimal operating conditions must be based on materials performance, process integration, technology and economics aspects. Global plant efficiencies over 45% (without considering solar-side losses) show the interest of the technology. Furthermore, the technological maturity and potential of the process is assessed. The direction towards which future works should be headed is discussed.

Octubre, 2019 | DOI: 10.1016/j.rser.2019.109252

Influence of Titanium Oxide Pillar Array Nanometric Structures and Ultraviolet Irradiation on the Properties of the Surface of Dental Implants-A Pilot Study

Leon-Ramos, JR; Diosdado-Cano, JM; Lopez-Santos, C; Barranco, A; Torres-Lagares, D; Serrera-Figallo, MA
Nanomaterials, 9 (2019) 1458
Nanotecnología en Superficies y Plasma


Aim: Titanium implants are commonly used as replacement therapy for lost teeth and much current research is focusing on the improvement of the chemical and physical properties of their surfaces in order to improve the osseointegration process. TiO2, when it is deposited in the form of pillar array nanometric structures, has photocatalytic properties and wet surface control, which, together with UV irradiation, provide it with superhydrophilic surfaces, which may be of interest for improving cell adhesion on the peri-implant surface. In this article, we address the influence of this type of surface treatment on type IV and type V titanium discs on their surface energy and cell growth on them. Materials and methods: Samples from titanium rods used for making dental implants were used. There were two types of samples: grade IV and grade V. In turn, within each grade, two types of samples were differentiated: untreated and treated with sand blasting and subjected to double acid etching. Synthesis of the film consisting of titanium oxide pillar array structures was carried out using plasma-enhanced chemical vapor deposition equipment. The plasma was generated in a quartz vessel by an external SLAN-1 microwave source with a frequency of 2.45 GHz. Five specimens from each group were used (40 discs in total). On the surfaces to be studied, the following determinations were carried out: (a) X-ray photoelectron spectroscopy, (b) scanning electron microscopy, (c) energy dispersive X-ray spectroscopy, (d) profilometry, (e) contact angle measurement or surface wettability, (f) progression of contact angle on applying ultraviolet irradiation, and (g) a biocompatibility test and cytotoxicity with cell cultures. Results: The application of ultraviolet light decreased the hydrophobicity of all the surfaces studied, although it did so to a greater extent on the surfaces with the studied modification applied, this being more evident in samples manufactured in grade V titanium. In samples made in grade IV titanium, this difference was less evident, and even in the sample manufactured with grade IV and SLA treatment, the application of the nanometric modification of the surface made the surface optically less active. Regarding cell growth, all the surfaces studied, grouped in relation to the presence or not of the nanometric treatment, showed similar growth. Conclusions. Treatment of titanium oxide surfaces with ultraviolet irradiation made them change temporarily into superhydrophilic ones, which confirms that their biocompatibility could be improved in this way, or at least be maintained.

Octubre, 2019 | DOI: 10.3390/nano9101458

Highly selective few-ppm NO gas-sensing based on necklace-like nanofibers of ZnO/CdO n-n type I heterojunction

Naderi, H; Hajati, S; Ghaedi, M; Espinos, JP
Sensors and Actuators B-Chemical, 297 (2019) 126774
Nanotecnología en Superficies y Plasma


Electrospinning method followed by calcination is applied to synthesize ZnO/CdO nanofibers. Characterization is performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and reflection electron energy loss spectroscopy (REELS), which resulted in detailed analysis of the sensing material. For instance, it was found that the ZnO/CdO is n-n type I heterojunction which possesses straddling energy band gap, which could affect the mechanism of gas sensing. An electroless gold-plated interdigitated electrode with spacing 200 mu m is fabricated on alumina substrate to host the designed nanofibers being used as gas sensor. Gas-sensing activity of the heterojunction is investigated against NO, NO2, H2S, CH4, SO2 and CO in addition to VOCs such as ethanol, acetone, ammonia, methanol, and chloroform with high selectivity and response to NO gas by monitoring resistance changes. Detailed discussion on the mechanism of sensing is presented. The ZnO/CdO nanofibers are found to be highly sensitive to very low concentration range of NO gas (1.2-33 ppm) at optimal operating temperature of 215 degrees C. The influence of humidity (20-96%) on the sensor response was found to be ignorable. Additionally, good repeatability and long-term stability (45 days, every 5 days, SD = 0.7) was obtained for this sensor. Typically, short response times of 47 and 35 s are obtained versus 3 and 33 ppm of NO, respectively, making our sensor promisingly applicable for monitoring this toxic gas in polluting industries, metropolises and maybe in exhaled breath.

Octubre, 2019 | DOI: 10.1016/j.snb.2019.126774

Effect of starch as binder in carbon aerogel and carbon xerogel preparation

Rodriguez, N; Agamez-Pertuz, YY; Romero, E; Diaz-Velasquez, JD; Odriozola, JA; Centeno, MA
Journal of Non-Crystalline Solids, 522 (2019) UNSP 119554
Química de Superficies y Catálisis


Carbon aerogels and carbon xerogels were synthesized through resorcinol - formaldehyde polycondensation using Na2CO3 as catalyst. The effect of soluble starch introduction in the organic gel preparation on the porous surface properties of these materials was studied. The role of the drying process of the organic gels on the changes in the surface and structural properties of these materials after the addition of soluble starch is discussed. The presence of starch in the prepared carbon xerogels results in the development of microporosity while maintaining the characteristic mesoporosity of carbon xerogels. The Brunauer - Emmett -Teller (BET) surface area increases from 309 m(2)/g in carbon xerogel without soluble starch until 685 m(2)/g when 10% of soluble starch is added. The R- value and average crystallite lattice parameters, inter-layer spacing, crystallite height, crystallite diameter and the average number of aromatic layers per carbon crystallite are discussed in function of drying step and presence of soluble starch. The surface properties were also studied by Raman and DRIFT spectroscopies.

Octubre, 2019 | DOI: 10.1016/j.jnoncrysol.2019.119554