Anexo: análisis de un vástago metálico del yacimiento prehistórico de Peña Parda (Laguardia - Álava)

Se presenta el estudio metalográfico de un vastago metálico recuperado en el abrigo de Peña Parda (Laguardia, Álava), para determinar su composición química, que resulta mayoritariamente cobre

ZnO on rice husk: a sustainable photocatalyst for urban air purification

A cost-effective and sustainable De-NOx photocatalyst is prepared usingzinc acetate and rice husk. ZnO@SiO2samples are obtained from the calcination of a homogenised precursor mixture at 600 C. ZnO nanoparticles (70 –180 nm) grow aggregated in spheres and well dispersed (40 –53 m2g-1surface area) covering the silicon skeleton. The corresponding band gap for ZnO@SiO2photocatalysts was estimated at3.1 –3.2 eV. When the samples are irradiated by sunlight in anitrogen oxide atmosphere the NO HNO2NO2NO3-photochemical oxidation takes place. In comparison to unsupported ZnO and TiO2-P25, ZnO@SiO2samples exhibit high NOXremoval values (70 %) and outstanding selectivity (> 90%), the latter related to the sensitivity of zinc oxide towards NO2gas. This new photocatalyst is easily recyclable and reusabl

Cr3+ substituted Zn-Al layered double hydroxides as UV–Vis light photocatalysts for NO gas removal from the urban environment

The ZnAl-CO3, ZnAlCr-CO3 and ZnCr-CO3 LDH samples were studied as De-NOx photocatalysts in this work. Samples without Cr and increasing the presence of Cr3+ in the LDH framework in the 0.06, 0.15 and 0.3 Cr/Zn ratio were prepared by co-precipitation method, all of them constituted by pure LDH phase. The increase of chromium content in the LDH framework leads to lower crystallinity and higher specific surface area in the samples. Moreover, the CrO6 octahedron centres expand the photo-activity from UV to Visible light and assist to decrease the recombination rate of the electrons and holes. The favourable textural, optical and electronic properties of Cr-containing LDH samples explain the good NO removal efficiency (55%) and outstanding selectivity (90%) found for the analysed De-NOx process

The Inhibitive Effect of Sebacate-Modified LDH on Concrete Steel Reinforcement Corrosion

In recent decades, layered double hydroxides (LDH) have been proposed as innovative corrosion inhibitors for reinforced concrete. Their protective action is based on the ability to intercalate specific anions in the interlayer and on their ability to exchange the intercalated anion. In the present study, an organically charged LDH, with sebacate anions in the interlayer (LDH-S), is proposed as a water-repellent additive for mortar. The waterproofing efficiency of LDH-S and the associated corrosion inhibition ability has been evaluated in reinforced mortar samples. A 42% decrease in the water capillary absorption coefficient has been estimated when 3% LHD-S is added to a mortar. Both the passivation processes of the steel rebars during the curing period and the initiation of corrosion due to chloride exposure have been studied by electrochemical measurements. Three different mortars have been evaluated: reference mortar (REF), mortar with Mg-Al LDH (LDH), and mortar with LDH-sebacate (LDH-S). The latter has shown an important protective capacity for preventing the initiation of corrosion by chloride penetration, with an inhibitory efficiency of 74%. The presence of LDHs without sebacate in the interlayer also improved the performance of the mortar against rebar corrosion, but with lower efficiency (23% inhibitory efficiency). However, this protection is lost after continued chloride exposure over time, and corrosion initiates similarly to the reference mortar. The low corrosion current density values registered when LDH-S is added to the mortar may be related to the increased electrical resistance recorded in this mortar

Effects of Fe3+ substitution on Zn-Al layered double hydroxides for enhanced NO photochemical abatement

In this work the ability of ZnAlFe-CO3 layered double hydroxides (LDHs) as highly efficient UV-Vis light photocatalysts for the photochemical oxidation of NO gas was studied. LDHs with 3.5 to 4.1 M2+/M3+ and 0.33 to 1.55 Fe/Al ratios were prepared by a coprecipitation method. The samples were characterized by different techniques such as XRD, XPS, FT-IR, ICP-MS, TG, SBET, SEM and Diffuse reflectance (DR). The increased presence of the Fe3+ ions gave rise to changes in the structure, morphology and optical properties of the LDHs. The prepared ZnAlFe-CO3 systems exhibited increased surface area and enhanced visible-light absorbance. The photochemical NO abatement resulted in outstanding conversion efficiency (56 %) and selectivity (93 %) for the iron containing samples, due to a decrease of the e-/h+ recombination, higher generation of ⋅O2- and ⋅OH radicals and their NO2 adsorption ability