Organic-inorganic lead bromide perovskites nanoparticles: synthesis, stability and photophysical properties

Las perovskitas orgánica-inorgánicas de haluro de plomo son materiales semiconductores ampliamente estudiados para aplicaciones fotovoltaicas y optoelectrónicas, debido a sus excepcionales propiedades ópticas y electrónicas. Su preparación en película mesoporosa dio lugar a nanopartículas con nuevas propiedades, como la luminiscencia, que atrajo gran interés debido a su potencial aplicación en dispositivos optoelectrónicos. La falta de un procedimiento sintético adecuado para obtener nanopartículas de perovskita coloidales (materiales 0D), motivó nuestro interés en su preparación. Por lo tanto, esta tesis se centró en la síntesis de nanopartículas de perovskita híbridas orgánica-inorgánicas de bromuro de plomo coloidales altamente luminiscentes mediante un método sin plantilla basado en el uso de sales de alquilamonio como ligando orgánico y el estudio de sus propiedades conductoras. En esta tesis se demostró por primera vez la preparación de nanopartículas coloidales de perovskita híbridas de bromuro de plomo, CH3NH3PbBr3, con un tamaño de 6 nm, luminiscentes y con un rendimiento cuántico de emisión del 20 % mediante el uso de una sal de alquilamonio de tamaño medio y condiciones de reacción suaves. Las nanopartículas demostraron ser dispersables en solventes orgánicos apróticos y altamente estables en estado sólido (hasta tres meses). Además, el coloide en tolueno se usó en la preparación de películas delgadas luminiscentes y en un dispositivo electroluminiscente. En este último se observó una mejora en la electroluminiscencia del dispositivo basado en la película de nanopartículas de perovskita en comparación con un dispositivo preparado con el material volumétrico. Posteriormente, se estudió el efecto de la relación molar entre los componentes, la longitud de la cadena alquílica de la sal de amonio, y el disolvente sobre la síntesis, estabilidad y propiedades ópticas de las nanopartículas coloidales. El rendimiento cuántico de emisión de las nanopartículas aumentó hasta un 83 % como coloide y un 72 % como película delgada mediante el ajuste de la relación molar entre las sales de alquilamonio y bromuro de plomo. Estas nanopartículas conservaron sus propiedades emisivas en estado sólido y mostraron una alta fotoestabilidad bajo irradiación continua con luz ultravioleta del coloide. Además, este método sin plantilla para la síntesis de perovskitas coloidales también permitió la preparación de perovskitas luminiscentes con estructura inorgánico 2D. Estas perovskitas mostraron un rendimiento cuántico de emisión cercano al 21% y demostraron ser fácilmente procesables. Por otra parte, se demostró que la pasivación de la superficie de las nanopartículas de CH3NH3PbBr3 con bromuro de 2-adamantilamonio como único ligando orgánico, permitió alcanzar el máximo de eficiencia en sus propiedades emisivas con un excepcional rendimiento cuántico de emisión del 100 %. Sin embargo, se observó la agregación de las nanopartículas en disolución y tiempos de vida de luminiscencia largos. Con el objetivo de preparar películas sólidas de nanopartículas se estudió la modificación de la superficie de las nanopartículas utilizando 2-adamantilamina y diferentes ácidos carboxílicos como sistema binario de ligandos orgánicos para disminuir la tendencia de agregación de las nanopartículas. Este sistema binario de ligandos permitió la preparación de coloides altamente dispersables y luminiscentes (rendimiento cuántico de emisión de aproximadamente 100 %), redujo la tendencia de agregación de nanopartículas en disolución y permitió el ensamble de las nanopartículas en forma de películas sólidas con un espesor de varios cientos de nanómetros. Las nanopartículas conservaron su morfología en la película, así como sus propiedades ópticas. Además, un estudio de conductividad por microscopía de fuerza atómica demostró la presencia de regiones con una alta conductividad que se atribuyeron a regiones con una efectiva conectividad eléctrica entre las nanopartículas. Finalmente, se demostró la preparación de nanopartículas coloidales de CH3NH3PbBr3 libres de ligandos orgánicos mediante la adición de una sal inorgánica de potasio lipófila a la disolución de los precursores de la perovskita. Los cationes de potasio actuaron como agentes de confinamiento, proporcionaron estabilidad coloidal a las nanopartículas en un disolvente moderadamente polar y además permitieron el ensamble de las nanopartículas en una película sólida con propiedades de transporte comparables a las de una película policristalina de material volumétrico.The organic-inorganic lead halide perovskites have emerged as novel semiconductor materials for photovoltaic and related optoelectronic applications, due to their exceptional optical and electronic properties. Their preparation into mesoporous films gave rise to nanoparticles with new properties, such as photoluminescence, which attracted great interest owing to their potential in optoelectronic applications. The lack of a suitable synthetic procedure to obtain colloidal perovskite nanoparticles (0D materials), with sizes as small as several nanometers, motivated our interest in their preparation. Therefore, this thesis was focused on the synthesis of highly photoluminescent colloidal organic-inorganic lead bromide perovskite nanoparticles by means of a non-template approach based on the use of medium alkyl chain ammonium ligands, and the study of their conductive properties. We reported for the first time the preparation of green photoluminescent colloidal methylammonium lead bromide perovskite nanoparticles with a size of ca. 6 nm, a photoluminescence quantum yield of ca. 20 % and a 3D perovskite inorganic framework, by using medium alkyl ammonium salts and mild reaction conditions. The nanoparticles proved to be dispersible in aprotic and moderate polar organic solvents and highly stable in solid state (up to three months). Moreover, the toluene colloid was used in the preparation of photo- and electro-luminescent thin films. An improvement in the electroluminescence was observed in the device based on the perovskite nanoparticles film compared to the bulk device. Subsequently, the effect of the components molar ratio and the length of the alkyl chain ammonium, as well as of the non-coordinating solvent, on the synthesis, stability and unique optical properties of colloidal nanoparticles was studied. Thus, the photoluminescence quantum yield of methylammonium lead bromide nanoparticles was increased, to up to 83 % as colloid and 72 % as thin film, through the fine tuning of the molar ratio between the alkyl ammonium salts and lead bromide. These nanoparticles preserved their emissive properties in solid state and exhibited high photostability under continuous ultraviolet irradiation of the colloid. In addition, these non-template synthetic approach for the synthesis of colloidal perovskite also enabled the preparation of blue photoluminescent perovskites with a 2D inorganic framework, which showed a photoluminescence quantum yield of ca. 21 % and proved to be easily processed. Later on, we demonstrated the efficient surface passivation of the methylammonium lead bromide perovskite nanoparticles by using 2-adamantylammonium bromide as the capping ligand, as demonstrated by their exceptional photoluminescence quantum yield of 100 %. However, a considerable aggregation in solution and a long-lived photoluminescence were observed. Then, surface engineering by using 2-adamantylamine and different alkyl carboxylic acids was studied to decrease their aggregation tendency in solution with the final aim of prepare conductive nanoparticle solid films. Remarkably, this binary ligand systems enabled the preparation of highly dispersible and photoluminescent methylammonium lead bromide colloids (photoluminescence quantum yield ca. 100 %), reduced the tendency of aggregation of nanoparticles in solution and allowed the assembly of nanoparticles into densely packed solid films with thicknesses up to several hundreds of nanometers. The nanoparticles retained the pre-engineered confined morphologies in the film as well as their optical properties. Moreover, the conductive atomic force microscopy measurements demonstrated the presence of high conductive domains that can be attributed to conductive regions due to an effective electrical connectivity between the nanoparticles. Finally, we demonstrated the possibility of preparing colloidal ligand-free methylammonium lead bromide perovskite nanoparticles. The strategy consisted in the addition of a lipophilic potassium salt to the perovskite precursor solution and an excess of methylammonium bromide. The potassium cations eventually acted as the confinement agent and provided colloidal stability in the moderately polar solvent ethyl acetate. The assembly of methylammonium lead bromide nanoparticles on substrates led to densely packed nanoparticle solid films, which showed transport properties comparable to that of a polycrystalline bulk thin film

Broad-host range expression vectors containing manipulated meta-cleavage pathway regulatory elements of the TOL plasmid

AbstractThe construction of pERD20 and pERD21, two broad-host range expression vectors, is described. The vectors contain the Pm promoter of the meta-cleavage pathway operon of the TOL plasmid pWWO; this promoter is present within a polylinker which provides a number of downstream cloning sites close to the transcription initiation site. Transcription from the Pm promoter in these vectors is controlled not by the natural positive regulator of Pm, the Xy1S protein, but by an Xy1S mutant analogue, Xy1S2tr6, which ??hibits an altered effector specificity and can mediate a 3–8-fold higher level of transcription than can Xy1S in a wide range of temperatures. Controlled expression of cloned genes can be achieved in a broad spectrum of Gram negative bacteria grown at a wide range of temperatures

Herida antebraquial infectada por Aeromonas hydrophila

Se presenta un caso de celulitis por Aeromonas hydrophila, en un paciente de 23 años, tras una herida antebraquial producida en el medio acuático. La celulitis se resolvió mediante desbridamiento agresivo y quimioterapia. En los controles posteriores no se han apreciado déficits funcionales tras la infección.A case of Aeromonas hidrophila cellulitis developped in a 23-year-old patient, after aquatic environment forearm wound is presented. His cellulitis was effectively resolved with aggressive debridement and chemotherapy. Follow-up examinations have shown no residual functional deficits from the infection

Biological activities specified by antibiotic resistance plasmids

Bacteria can display resistance to a wide spectrum of noxious agents and environmental conditions, and these properties are often mediated by genes located on extrachromosomal DNA elements called plasmids. Replication, vertical and horizontal transmission and evolution of these elements are discussed, and examples of the genes responsible for the resistance phenotypes are given. Selective forces that drive the evolution of new combinations of bacterial properties of particular importance in clinical situations are analyse

Biological activities specified by antibiotic resistance plasmids

Bacteria can display resistance to a wide spectrum of noxious agents and environmental conditions, and these properties are often mediated by genes located on extrachromosomal DNA elements called plasmids. Replication, vertical and horizontal transmission and evolution of these elements are discussed, and examples of the genes responsible for the resistance phenotypes are given. Selective forces that drive the evolution of new combinations of bacterial properties of particular importance in clinical situations are analyse

La comprensión lectora en niños sordos en Ed. Primaria. Influencia de variables individuales y textuales.

El objetivo básico de este trabajo es analizar los resultados obtenidos por una muestra de niños sordos en tareas de comprensión de textos. Y contrastar la influencia de diferentes variables audiológicas, lingüísticas y textuales en su rendimiento. La muestra está compuesta por 35 niños con sordera bilateral prelocutiva (70-120 dB), de Educación Primaria, 21 con implante coclear y 14 con audífonos digitales. Se les administró la prueba de Comprensión de Textos del Test de Procesos Lectores Revisado (PROLEC-R) para obtener la medida de comprensión lectora. Se obtuvieron resultados que confirman que los alumnos sordos, en general, no alcanzan el nivel de comprensión lectora adecuado ni siquiera en niveles superiores de Ed. Primaria (5º y 6º). Es interesante anotar que el rendimiento fue superior en los textos narrativos (independientemente de su longitud) y que en los textos expositivos rindieron significativamente mejor en los textos de menor extensión. Que la competencia gramatical influye de forma relevante en los resultados en comprensión de textos. Y que los alumnos sordos con implante coclear no rindieron significativamente mejor que los sordos con audífonos digitales, como sugería la investigación reciente. No hubo diferencias significativas en función de otras variables audiológicas como el grado de pérdida y la edad de implantación de la prótesis auditiva. Los resultados nos animan a profundizar en esta línea de investigación, ampliando la muestra y planteando una explicación contrastada para estos fenómenos.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Clinical study of cervicogenic headache

The cervicogenic headache was studied to get a deeper insight into the pathogenetic mechanisms, and clinical presentation forms. Material and Methods. Eleven female patients, ranging from 34 to 81 years-old, with cervicogenic headaches, were studied and correlated with NMR images of the cervical spine. Results. Intense neck pain irradiated to parietal, occipital, temporal regions, and shoulders were correlated with NMR images of the degenerated cervical spine. Also, lumbar spine pathology, osteoporosis, gallstones, and cholecystitis were found. The following associated neurological, neurobehavioral, and metabolic diseases comorbidities were observed, such as blood hypertension, diabetes, obesity, hypothyroidism, partial epilepsy, tremor, familial stress, memory, sleep disorders, and dizziness. Also, we found mixed cervicogenic headaches and migraines in 50% of cases studied. Conclusion. The headache and the associated images of cervical pathology have been clinically interpreted as cardinal signs of cervicogenic headache. A mixed cervicogenic mixed type was observed

ZnO/BiOI heterojunction photoanodes with enhanced photoelectrochemical water oxidation activity

ZnO/BiOI heterojunction photoanode thin films were prepared by aerosol-assisted chemical vapour deposition, and the impact of growth temperature and film thickness on the water oxidation functionality was systematically investigated. A top ZnO layer with a thickness of 120 nm (deposited at 350 °C) and a 390 nm thick BiOI layer (deposited at 300 °C) were found to achieve the best photoelectrochemical performance of the heterojunction. The ZnO/BiOI heterojunction exhibited a significant increase in photoelectrochemical activity, with a photocurrent of 0.27 mA·cm−2 observed at 1.1 VRHE (350 nm, 2.58 mW·cm−2), which is ~ 2.2 times higher than that of single-layer ZnO and far higher than that of BiOI. Photoluminescence spectroscopy and transient absorption spectroscopy measurements showed that there was effective charge transfer across the heterojunction which spatially separated charge carriers and increased their lifetime and ability to drive photoelectrochemical water oxidation

Mechanochemically synthesized Pb-free halide perovskite-based Cs2AgBiBr6–Cu–RGO nanocomposite for photocatalytic CO2 reduction

Pb-based halide perovskites have recently showed great potential in various applications such as solar cells, optoelectronics and photocatalysis. Despite their high performance, the Pb2+ toxicity along with poor stability hinders long term applications in photocatalysis. Herein, we report mechanochemically prepared Pb-free Cs2AgBiBr6 double perovskite nanoplates and their heterostructure with Cu-loaded reduced graphene oxide (Cu–RGO) for gas-phase photocatalytic CO2 reduction using water vapor as the proton source in the absence of a hole scavenger. The resulting Cs2AgBiBr6–Cu–RGO nanocomposite shows significant photocatalytic activity of 10.7 (±0.6) μmol CH4 g−1 h−1, 1.9 (±0.3) μmol CO g−1 h−1 and 1.0 (±0.2) μmol H2 g−1 h−1, with a CH4 selectivity of 93.0 (±0.5)% on an electron basis with 1 sun and a remarkable apparent quantum efficiency of 0.89 (±0.21)% at 590 nm. A further 32% enhancement in photocatalytic activity on an electron basis is achieved when the light intensity is doubled (2 suns). The high performance was attributed to their improved charge separation and suppressed electron–hole recombination, along with extended visible light absorption, better stability in a humid environment and improved CO2 adsorption. These findings support Cs2AgBiBr6 as a potential Pb-free alternative to conventional halide perovskites for photocatalytic solar-to-fuel conversion and CO2 utilization

Reduced Salivary Lactoferrin Levels in Early-Onset Alzheimer's Disease

Grants from Instituto de Salud Carlos III (PI22CIII/00042), CIBERNED (CB07/502, CB06/05/1111, PI2021/03), the Spanish Ministry of Economy and Competitiveness (PID2020-119978RB-I00) and the Andalucía-FEDER Program (UPO-1380913).S