Photocatalytic and Photoelectrochemical Degradation of Organic Compounds with All-Inorganic Metal Halide Perovskite Quantum Dots.

Inspired by the outstanding optoelectronic properties reported for all-inorganic halide perovskite quantum dots (QDs), we have evaluated the potential of these materials toward the photocatalytic and photoelectrochemical degradation of organic compounds, taking the oxidation of 2-mercaptobenzothiazole (MBT) as a proof-of-concept. First, we determined electrochemically the energy levels of dispersions of perovskite QDs with different band gaps induced by the different ratios between halides (Br and I) and metallic cations (Pb and Sn). Then, we selected CsPbBr3 QDs to demonstrate the photocatalytic and photoelectrochemical oxidation of MBT, confirming that hole injection takes place from CsPbBr3 QDs to MBT, resulting in the total degradation of MBT as evidenced by electrospray mass spectrometry analyses. Although the stability and toxicity of these QDs are major issues to address in the near future, the results obtained in the present study open promising perspectives for the implementation of solar-driven catalytic strategies based on these fascinating materials.

Study of the Partial Substitution of Pb by Sn in Cs-Pb-Sn-Br Nanocrystals Owing to Obtaining Stable Nanoparticles with Excellent Optical Properties.

Halide perovskites are revolutionizing the photovoltaic and optoelectronic fields with outstanding performances obtained in a remarkably short time. However, two major challenges remain: the long-term stability and the Pb content, due to its toxicity. Despite the great effort carried out to substitute the Pb by a less hazardous element, lead-free perovskite still remains more unstable than lead-containing perovskites and presents lower performance as well. In this work, we demonstrate the colloidal preparation of Cs-Pb-Sn-Br nanoparticles (NPs) where Sn is incorporated up to 18.8%. Significantly, we have demonstrated that the partial substitution of Pb by Sn does not produce a deleterious effect in their optical performance in terms of photoluminescence quantum yield (PLQY). We observed for the first time a positive effect in terms of enhancement of PLQY when Sn partially substitutes Pb in a considerable amount (i.e., higher than 5%). PLQYs as high as 73.4% have been obtained with a partial Pb replacement of 7% by Sn. We present a systematic study of the synthesis process in terms of different growth parameters (i.e., precursor concentration, time, and temperature of reaction) and how they influence the Sn incorporation and the PLQY. This high performance and long-term stability is based on a significant stabilization of Sn2+ in the NPs for several months, as determined by XPS analysis, and opens an interesting way to obtain less Pb-containing perovskite NPs with excellent optoelectronic properties.

Tunable light emission by exciplex state formation between hybrid halide perovskite and core/shell quantum dots: Implications in advanced LEDs and photovoltaics.

We report the first observation of exciplex state electroluminescence due to carrier injection between the hybrid lead halide perovskite (MAPbI3-xClx) and quantum dots (core/shell PbS/CdS). Single layers of perovskite (PS) and quantum dots (QDs) have been produced by solution processing methods, and their photoluminescent properties are compared to those of bilayer samples in both PS/QD and QD/PS configurations. Exciplex emission at lower energies than the band gap of both PS and QD has been detected. The exciplex emission wavelength of this mixed system can be simply tuned by controlling the QD size. Light-emitting diodes (LEDs) have been fabricated using those configurations, which provide light emission with considerably low turn-on potential. The "color" of the LED can also be tuned by controlling the applied bias. The presence of the exciplex state PS and QDs opens up a broad range of possibilities with important implications not only in tunable LEDs but also in the preparation of intermediate band gap photovoltaic devices with the potentiality of surpassing the Shockley-Queisser limit.

Recombination reduction on lead halide perovskite solar cells based on low temperature synthesized hierarchical TiO2 nanorods.

Intensive research on the electron transport material (ETM) has been pursued to improve the efficiency of perovskite solar cells (PSCs) and decrease their cost. More importantly, the role of the ETM layer is not yet fully understood, and research on new device architectures is still needed. Here, we report the use of three-dimensional (3D) TiO2 with a hierarchical architecture based on rutile nanorods (NR) as photoanode material for PSCs. The proposed hierarchical nanorod (HNR) films were synthesized by a two-step low temperature (180 °C) hydrothermal method, and consist of TiO2 nanorod trunks with optimal lengths of 540 nm and TiO2 nanobranches with lengths of 45 nm. Different device configurations were fabricated with TiO2 structures (compact layer, NR and HNR) and CH3NH3PbI3, using different synthetic routes, as the active material. PSCs based on HNR-CH3NH3PbI3 achieved the highest power conversion efficiency compared to PSCs with other TiO2 structures. This result can be ascribed mainly to lower charge recombination as determined by impedance spectroscopy. Furthermore, we have observed that the CH3NH3PbI3 perovskite deposited by the two-step route shows higher efficiency, surface coverage and infiltration within the structure of 3D HNR than the one-step CH3NH3PbI(3-x)Cl(x) perovskite.

Effect of Organic and Inorganic Passivation in Quantum-Dot-Sensitized Solar Cells.

The effect of semiconductor passivation on quantum-dot-sensitized solar cells (QDSCs) has been systematically characterized for CdS and CdS/ZnS. We have found that passivation strongly depends on the passivation agent, obtaining an enhancement of the solar cell efficiency for compounds containing amine and thiol groups and, in contrast, a decrease in performance for passivating agents with acid groups. Passivation can induce a change in the position of TiO2 conduction band and also in the recombination rate and nature, reflected in a change in the ß parameter. Especially interesting is the finding that ß, and consequently the fill factor can be increased with the passivation treatment. Applying this strategy, record cells of 4.65% efficiency for PbS-based QDSCs have been produced.

Open versus closed management of the abdomen in the surgical treatment of severe secondary peritonitis: a randomized clinical trial.

BACKGROUND: Despite recent advances in diagnosis, antimicrobial therapy, and intensive care support, operative treatment remains the foundation of the management of patients with severe secondary peritonitis (SSP). This management is based on three fundamental principles: (1) Elimination of the source of infection; (2) reduction of bacterial contamination of the peritoneal cavity; and (3) prevention of persistent or recurrent intra-abdominal infection. Although recent studies have emphasized the role of open management of the abdomen and planned re-laparotomies to fulfill these principles, controversy surrounds the optimal approach because no randomized studies exist. METHODS: Patients with SSP, documented clinically, with calculated Sequential Organ Failure Assessment (SOFA) and Acute Physiology and Chronic Health Evaluation (APACHE II) scores and appropriate ancillary studies, were allocated randomly to two groups for the management of the abdomen after operation for SSP (group A: open; group B: closed). Both surgical strategies were standardized, and patients were followed up until cure or death. RESULTS: During a 24-month period, 40 patients with SSP were admitted for treatment. Patients in group A (n = 20) and group B (n = 20) did not differ in sex, age, site of origin (etiology), APACHE II score (24 vs. 22), SOFA score (15 vs. 15), or previous operative treatment (< or =1: 20 vs. 20). Postoperatively, there were no differences in the likelihood of acute renal failure (25% vs. 40%), duration of mechanical ventilatory support (10 vs. 12 days), need for total parenteral nutrition (80% vs. 75%), or rate of residual infection or need for reoperation because of the latter (15% vs. 10%). Although the difference in the mortality rate (55% vs. 30%) did not reach statistical significance (p < 0.05; chi-square and Fisher exact test), the relative risk and odds ratio for death were 1.83 and 2.85 times higher in group A. This clinical finding, as evidenced by the clear tendency toward a more favorable outcome for patients in group B, led to termination of the study at the first interim analysis. CONCLUSION: This randomized study from a single institution demonstrates that closed management of the abdomen may be a more rational approach after operative treatment of SSP and questions the recent enthusiasm for the open alternative, which has been based on observational studies.

Prevalencia puntual de infecciones intrahospitalarias. Hospital Eugenio Espejo. Enero de 1996

Se realiza un estudio de prevalencia puntual de infecciones intrahospitalarias en el Hospital Eugenio espejo en un día específico del mes de enero de 1996. el objetivo principal fue el de conocer la situación actual de la sinfecciones nosocomiales y su comportamiento según ciertas variables (servicio, localización, procedimiento diagnóstico o terpéutico usado, utilización de cultivo y antibioticoterapia entres las principales). La proporción de prevalencia de infecciones nosocomiales y de pacientes con infección nosocomial fueron de 11.29 por cientos y 8.38 por ciento respectivamente. La frecuencia de infecciones según la localización anatómica, en orden decreciente fueron: vías urinarias, aparato respiratorio, herida post-operatoria y aparato locomotor. La proporción de prevalencia de nosocomiales más importantes según el servicio hospitalario fueron terapia intensiva, neurocirugía, quemados, cirugía y cardiología. Los procedimientos más frecuentemente utilizados en las infecciones hospitalarias fueron; sondaje vesical, venoclisis, sondaje nasogástrico, intubación y cateterismo para presión venosa central. Por otro lado, se realizó un cultivo y antibiograma en el 45.7 por ciento de los casos. Los gérmenes aislados en orden de frecuencia fueron: Pseudomona A., Eschericha coli y estafilococo A. en el 91.2 por ciento de los casos se encontró el antecedente de la utilización de antibióticos. Se enfatiza en la necesidad de instaurar un eficiente y eficaz sistema de vigilancia de infecciones hospitalarias basado en un adecuado funcionamiento del comité de infecciones y en un asesoramiento humano-técnico por parte de la Dirección Provincial de Salud de Pichincha con el objeto de intervenir en los servicios de riesgo identificados, establecer las medidas preventivas adecuadas, así como capacitar al personal involucrado en el conocimiento del Manual de Normás Técnicas y Procedimientos exitente...