Sirera-Bejarano, R. (Rafael)
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- Visible light-sensitive photocatalytic aditives to render cement-based materials suitable depolluting agents(Universidad de Navarra, 2015-03-26) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)The presence of NOx in the atmosphere is an environmental challenge that needs to be addressed. Good NOx removal efficiencies have been attained by photocatalytic activity of TiO2 under UV light. TiO2 has been incorporated to cement-based materials to obtain depollutant and self-cleaning building materials. With the aim of broadening the sensitivity of these materials towards the visible light, two doped photocatalytic additives based on TiO2 were synthesized and used. Flame spray pyrolysis (FSP) allowed us to obtain TiO2 doped with either Fe or V, which generated hole-electron pairs with band gaps corresponding to visible light. Fe-TiO2, V-TiO2 and plain TiO2 were added (up to 2.5 wt.%) to different binding matrices: Portland cement (OPC) and air lime. The effect of the three photocatalytic additives on the setting time, consistency and mechanical properties of the cements were assessed.
- Design of repair air lime mortars combining nanosilica and different superplasticizers(Aristotle University of Thessaloniki, 2016-10-12) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
- Treatment of toxic metal aqueous solutions: encapsulation in a phosphate-calcium aluminate matrix(Elsevier, 2014-07-01) Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)Polyphosphate-modified calcium aluminate cement matrices were prepared by using aqueous solutions polluted with toxic metals as mixing water to obtain waste-containing solid blocks with improved management and disposal. Synthetically contaminated waters containing either Pb or Cu or Zn were incorporated into phosphoaluminate cement mortars and the effects of the metal’s presence on setting time and mechanical performance were assessed. Sorption and leaching tests were also executed and both retention and release patterns were investigated. For all three metals, high uptake capacities as well as percentages of retention larger than 99.9% were measured. Both Pb and Cu were seen to be largely compatible with this cementitious matrix, rendering the obtained blocks suitable for landfilling or for building purposes. However, Zn spoilt the compressive strength values because of its reaction with hydrogen phosphate anions, hindering the development of the binding matrix.
- Obtaining of self-cleaning repair air lime mortars with photocatalysts(Aristotle University of Thessaloniki, 2016-10-12) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)
- Solvent-free formation of cyclodextrin-based pseudopolyrotaxanes of polyethylene glycol: kinetic and structural aspects(2022) González-Gaitano, G. (Gustavo); Sirera-Bejarano, R. (Rafael); Duran-Benito, A. (Adrian); Guembe-Michel, N. (Nerea)Pseudopolyrotaxanes (PPRs) are supramolecular structures consisting of macrocycles able to thread on a linear polymer chain in a reversible, non-covalent way, often referred to in the literature as "molecular necklaces". While the synthesis and reaction mechanisms of these structures in solution have been widely described, their solvent-free production has received little attention, despite the advantages that this route may offer. We propose in this work a kinetic mechanism that describes the PPR formation in the solid phase as a process occurring in two consecutive stages. This mechanism has been used to investigate the spontaneous formation of a PPR that occurs when grinding alpha-Cyclodextrin (alpha-CD) with polyethylene glycol (PEG). In the threading stage, the inclusion of the polymer and subsequent release of the water molecules lodged in the cavity of the macrocycle cause vibrational changes that are reflected in the time-dependence of the FTIR-ATR spectra, while the further assembly of PPRs to form crystals produces characteristic reflections in the XRD patterns, due to the channel-like arrangement of CDs, that can be used to track the formation of the adduct in crystalline form. The effects that working variables have on the kinetics of the reaction, such as temperature, feed ratio, molar mass of the polymer and the introduction of an amorphous block in the polymer structure, have been investigated. The rate constants of the threading step increase with the temperature and the activation energy of the process increases at lower proportions of CD to PEG. This is attributed to the lower degree of covering of the polymer chain with CDs that reduces the hydrogen-bonding driven stabilization between adjacent macrocycles. The formation of crystalline PPR, which takes place slowly at room temperature, is markedly promoted at higher temperatures, with lower proportions of CD favoring both the formation and the growth of the crystals. The molar mass of the polymer does not modify the typical channel-like arrangement of packed PPRs but the conversion into crystalline PPR diminishes when using PEG1000 instead of PEG400. At a microscopic level, the crystals arrange into lamellar structures, in the order of hundreds of nm, embedded in an amorphous-like matrix. The introduction of a polypropylene oxide block in the structure of the polymer (Pluronic L62) renders poorer yields and a considerable loss of crystallinity of the product of the reaction. The methodology here proposed can be applied to the general case of inclusion complexes of CDs with drugs in the solid phase, or to multicomponent systems that contain polymers as excipients in pharmaceutical formulations along with CDs.
- Role of different superplasticizers on hydrated lime pastes and mortars(2015-10) Sirera-Bejarano, R. (Rafael); Perez-Nicolas, M. (María); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)The use of plasticizing admixtures in order to improve the handling of cement-based media has been extensively reported. High-range water reducers or superplasticizers (SPs) act reducing the water demand and enhancing the flowability of the fresh mortars, yielding workable materials. So far little attention has been devoted to the study of the performance of superplasticizers in lime-bearing pastes and mortars. The widespread use of hydrated lime and pozzolan-hydrated lime pastes for paints, consolidant products, soil treatments and the obtaining of repair mortars and grouts, especially for architectural monuments of the Cultural Heritage, supports the interest of these materials. In order to design suitable hydrated lime pastes and mortars, the use of compatible and effective SPs seems to be imperative.
- Study of the mechanical behavior of masonry repair lime-based mortars cured and exposed under different conditions(Elsevier, 2006-05) Lanas, J. (Javier); Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio)Specimens of aerial and hydraulic lime-based mortars to be used in restoration works were prepared, hardened and subjected to different environments in order to study their mechanical behavior and durability. Outside exposure, weathering cycles in a climatic chamber, SO2-rich environment, freezing–thawing cycles and indoor exposure were selected to expose (as control group) the mortars. Flexural and compression strength tests were performed at 7, 14, 21 and 28 days. Porosity values and SEM/EDAX analysis were used to evaluate the microstructural changes. Flexural strength has been strongly influenced by the RH of the environments. Outside exposure improves, in general, the compressive strength, whereas SO2 chamber only provides the strength in hydraulic specimens. Porosity reduction has been related with a strength increment. In climatic chamber, the porosity increment matches a gradual higher degree of alteration. A strength reduction has been determined through a fracture mechanism using the cracks of climatic alteration. In SO2 chamber, sulfation appears as a surface phenomenon, giving gypsum in aerial specimens and gypsum and syngenite in hydraulic specimens, as SEM/EDAX confirms. Freezing–thawing cycles showed a high destruction capacity. Hydraulic specimens endured better durability tests than aerial specimens: a discussion on the mortar durability was also introduced.
- Low-temperature sol–gel methods for the integration of crystalline metal oxide thin films in flexible electronics(Springer, 2023) Echániz-Cintora, M. (María); Sirera-Bejarano, R. (Rafael); Jiménez, R. (Ricardo); Bretos, I. (Íñigo); Rivas, A.Y. (Andrea Y.); Calzada, M.L. (María Lourdes); Ricote, J. (Jesús)The development of low-temperature sol–gel (solution) processes for the fabrication of crystalline metal oxide thin films has become a key objective in the emerging Flexible Electronics. To achieve this target, crystalline oxide films need to be deposited on flexible substrates, which have degradation temperatures below 350 °C (e.g., polymers or textile). This achievement would be a step towards improving the performance of the flexible device, making feasible applications now restrained (e.g. smart-skin, flexible-displays or solar-cells) and whose performance is associated to the functional properties of the crystalline oxide (e.g., ferroelectricity, pyroelectricity or piezoelectricity). However, this is a challenge because the crystallization of these oxides usually occurs at high temperatures, over 600 °C. This paper shows an overview to the solution strategies devised in our group for the low-temperature fabrication of crystalline metal oxide thin films, mostly ferroelectric perovskites (e.g., BiFeO3, PbTiO3 or Pb(Zr,Ti)O3). We have made use of UV-light as an alternative energy source to the thermal energy conventionally used to obtain the crystalline oxide. High photosensitive sol–gel solutions have been synthesized and the solution-deposited layers irradiated with UV-excimer lamps. A precise control of the photoreactions occurring during the irradiation of these layers has been carried out with the aim of advancing the formation of a high-densified, defect-free amorphous metal oxide film that easily can be converted into crystalline at temperatures compatible with the use of polymer substrates.
- Influence of nanosilica and a polycarboxylate ether superplasticizer on the performance of lime mortars(Elsevier, 2013-01-01) Lanas, J. (Javier); Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Fernandez-Alvarez, J.M. (José María)The effect of individual and combined addition of both nanosilica (NS) and polycarboxylate-ether plasticizer (PCE) admixtures on aerial lime mortars was studied. The sole incorporation of NS increased the water demand, as proved by the mini-spread flow test. An interaction between NS and hydrated lime particles was observed in fresh mixtures by means of particle size distribution studies, zeta potential measurements and optical microscopy, giving rise to agglomerates. On the other hand, the addition of PCE to a lime mortar increased the flowability and accelerated the setting process. PCE was shown to act in lime media as a deflocculating agent, reducing the particle size of the agglomerates through a steric hindrance mechanism. Mechanical strengths were improved in the presence of either NS or PCE, the optimum being attained in the combined presence of both admixtures that involved relevant microstructural modifications, as proved by pore size distributions and SEM observations.
- Hydrophobized lime grouts prepared with microsilica and superplasticizers(RILEM Publications S.a.r.l., 2019-07-16) Sirera-Bejarano, R. (Rafael); Alvarez-Galindo, J.I. (José Ignacio); Duran-Benito, A. (Adrian); Navarro-Blasco, I. (Iñigo); Gonzalez-Sanchez, J.F. (Jesús Fidel); Fernandez-Alvarez, J.M. (José María)This work reports the obtaining of lime-based grouts as repairing materials. Microsilica was added as pozzolanic additive to enhance the compressive strength of the hardened grouts. Sodium oleate, as water repellent admixture, and different superplasticizers (SPs) were also incorporated to reduce the water absorption and to enhance the injectability of the grouts. Polycarboxylate ether (PCE), polynaphthalene sulfonate (PNS), melamine sulfonate (MMS) and polyacrylic acid (PA) were tested as SPs. Regarding the fluidity of the grouts, PCE was seen to improve the injectability, followed by PNS, MMS and PA. However, PCE addition was also accompanied by a severe delay in the setting time. The other three superplasticizers did not provoke significant delays in the hardening of the samples. The water contact angle underwent an increase pointing to an effective hydrophobization of the surface as a consequence of the water repellent admixture. The combination with PCE was the most effective in keeping the water repellency in comparison with the control sample (lime grout + oleate). MMS yielded high compressive strengths and durability of the mortars, in the face of freezing-thawing cycles, was enhanced.