The optoelectronic properties of quantum dots are strongly controlled by the chemical nature of their surface-passivating ligands. In this work, we present the synthesis, characterization, and ...surface modification of CdSe quantum dots (QDs) and their application in solar cells. CdSe QDs were capped in oleic acid (OA), 3-mercaptopropionic acid (MPA), and 4-mercaptobenzoic acid (MBA). The QDs were characterized by transmission electron microscopy (TEM), UV-Vis absorption and emission spectrophotometry, thermogravimetric analyses, and 1H and 13C NMR. From TEM analysis, it has been observed that interparticle distance can be effectively controlled by the presence of different molecular size ligands. From the 1H and 13C NMR, specific types of interactions between the Cd2+ and the ligands have been observed. Although CdSe/OA presented larger interparticle distance as compared to CdSe/MPA and CdSe/MBA, the photocatalytic oxidation of the thiol groups on the surface of the MPA- and MBA-based quantum dots resulted in poor surface stabilization, ultimately resulting in poor power conversion efficiencies which were ca. 70% smaller than that of OA-based solar cell.
In this work, we show the effect of the thermal treatment temperature on the photoelectrochemical (PEC) activity of CdSe/TiO
2
nanocomposites. TiO
2
nanotubes (NTs) were synthesized by anodization ...and the nanocomposites were obtained by depositing CdSe clusters
via
magnetron sputtering. A two-step thermal treatment was performed: heating the TiO
2
NTs at different temperatures prior to CdSe deposition and further heating the CdSe/TiO
2
nanocomposites. The nanocomposites were characterized by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV-Vis spectrophotometry, and electrochemical impedance spectroscopy (EIS). To compare the PEC performance of the CdSe/TiO
2
nanocomposites and pristine TiO
2
NTs, linear sweep voltammetry (LSV) curves were obtained under visible light and under 1 sun illumination. It was observed that CdSe incorporation into the TiO
2
template enhances the visible light absorbance thereby improving the PEC performance of the nanocomposites. We have found that the optical, structural and PEC properties of the CdSe/TiO
2
nanocomposites are dependent on the thermal treatment temperature of the TiO
2
nanotubular substrate, prior to CdSe deposition. Moreover, a three-fold improvement in photocurrent was observed upon further thermal treatment of the obtained nanocomposite.
Effect of the thermal treatment temperature on the photoelectrochemical (PEC) activity of CdSe/TiO
2
nanocomposites.
In this work, we show the effect of the thermal treatment temperature on the photoelectrochemical (PEC) activity of CdSe/TiO 2 nanocomposites. TiO 2 nanotubes (NTs) were synthesized by anodization ...and the nanocomposites were obtained by depositing CdSe clusters via magnetron sputtering. A two-step thermal treatment was performed: heating the TiO 2 NTs at different temperatures prior to CdSe deposition and further heating the CdSe/TiO 2 nanocomposites. The nanocomposites were characterized by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV-Vis spectrophotometry, and electrochemical impedance spectroscopy (EIS). To compare the PEC performance of the CdSe/TiO 2 nanocomposites and pristine TiO 2 NTs, linear sweep voltammetry (LSV) curves were obtained under visible light and under 1 sun illumination. It was observed that CdSe incorporation into the TiO 2 template enhances the visible light absorbance thereby improving the PEC performance of the nanocomposites. We have found that the optical, structural and PEC properties of the CdSe/TiO 2 nanocomposites are dependent on the thermal treatment temperature of the TiO 2 nanotubular substrate, prior to CdSe deposition. Moreover, a three-fold improvement in photocurrent was observed upon further thermal treatment of the obtained nanocomposite.
In this work, we show the effect of the thermal treatment temperature on the photoelectrochemical (PEC) activity of CdSe/TiO sub(2) nanocomposites. TiO sub(2) nanotubes (NTs) were synthesized by ...anodization and the nanocomposites were obtained by depositing CdSe clusters viamagnetron sputtering. A two-step thermal treatment was performed: heating the TiO sub(2) NTs at different temperatures prior to CdSe deposition and further heating the CdSe/TiO sub(2) nanocomposites. The nanocomposites were characterized by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV-Vis spectrophotometry, and electrochemical impedance spectroscopy (EIS). To compare the PEC performance of the CdSe/TiO sub(2) nanocomposites and pristine TiO sub(2) NTs, linear sweep voltammetry (LSV) curves were obtained under visible light and under 1 sun illumination. It was observed that CdSe incorporation into the TiO sub(2) template enhances the visible light absorbance thereby improving the PEC performance of the nanocomposites. We have found that the optical, structural and PEC properties of the CdSe/TiO sub(2) nanocomposites are dependent on the thermal treatment temperature of the TiO sub(2) nanotubular substrate, prior to CdSe deposition. Moreover, a three-fold improvement in photocurrent was observed upon further thermal treatment of the obtained nanocomposite.
The essential oil from leaves of Croton grewioides Baill was obtained by hydrodistillation using Clevenger apparatus, and its chemical composition was analyzed by GC-MS, where 18 compounds were ...identified, mostly as monoterpenes (55.56%) and sesquiterpenes (44.44%), in which the major constituent was the α-pinene (47.43%). The essential oil of Croton grewioides (EOCg) and its major compound (α-pinene) were evaluated as modulators of antibiotic resistance in strain SA-1199B and IS-58 of Staphylococcus aureus that overexpresses efflux protein. The minimum inhibitory concentrations (MICs) of the antibiotics were determined by the microdilution assay in the absence and in the presence of sub-inhibitory concentration of EOCg and α-pinene. Although the EOCg and α-pinene did not indicate relevant antibacterial activity in vitro, they acted as antibiotic resistance modulators, i.e., EOCg in combination with norfloxacin, reducted its MIC, by 64× whereas in combination with tetracycline it was observed a reduction of 4×. Additionally, it was observed a MIC reduction of tetracycline by 32×, when combined with α-pinene. The results suggest that EOCg and α-pinene modulate or even reverse bacterial resistance as a putative efflux pump inhibitor.
•The essential oil and α-pinene had a synergistic effect when associated with the antibiotics.•Essential oil exhibited the best result.•Reducing the MIC of norfloxacine and tetracicline, essential oil, α-pinene are consider as a putative efflux pump inhibitor.
Este trabalho foi desenvolvido em duas etapas: i) síntese, caracterização e aplicação de pontos quânticos de CdS, CdSe e CdTe em células solares. ii) modificação da superfície dos pontos quânticos de ...CdSe através de troca de ligante, seguida de caracterização e aplicação em células solares. Os pontos quânticos foram sintetizados utilizando acetatos de cádmio, selênio, telúrio e enxofre como precursores e ácido oleico como agente de estabilização. Na segunda etapa o ácido oleico foi substituído por ligantes com maior afinidade eletrônica pelos sítios de Cd2+: ácido 3-mercaptopropiônico, 4-ácido-mercaptobenzóico e ácido 11-mercaptoundecanóico. As amostras foram caracterizadas por UV-Vis, fluorescência, microscopia eletrônica de transmissão, difratometria de raios-X e voltametria cíclica. Adicionalmente, testes de solubilidade, análises de TGA e de RMN foram realizadas para confirmar a troca de ligante. Através dos resultados, verificou-se que todos os pontos quânticos sintetizados são adequados para sensibilização de TiO2 em dispositivos fotovoltaicos. No entanto, os pontos quânticos de CdSe e CdTe apresentaram fatores que evidenciam maior confinamento quântico, sendo que a maior estabilidade do éxciton foi obtida para o CdSe. Através das análises de RMN foi possível verificar que não existe apenas uma confirguração espacial preferencial para a adsorção do ligante sobre a superfície deste ponto quântico enquanto que curvas de corrente versus potencial e de eficiência de conversão de fóton incidente mostraram que a eficiência do dispositivo é fracamente dependente do ligante. Contudo, a troca de ligantes favorece a solubilidade em solventes com diferentes polaridades, inclusive água, o que amplia as possibilidades de aplicação dos pontos quânticos sintetizados neste trabalho.
This work was developed in two stages: i) synthesis, characterization and application of CdS, CdSe and CdTe quantum dots to assemble solar cells, ii) surface modification, characterization and application of CdSe quantum dots to assemble solar cells. The quantum dots were synthesized by using cadmium acetate, Se, S or Te as precursors and oleic acid as stabilizing agent. In the second stage the oleic acid capping layer was replaced by other ligands with higher electron affinity to Cd2+: 3-mercaptopropionic acid, 4-mercaptobenzoic acid and 11-mercaptoundecanoic acid. The samples were characterized by UV-Vis, fluorescence, transmission electron microscopy, x-ray diffractometry and cyclic voltammetry. Additionally, solubility tests, TGA analysis and NMR were performed to evaluate the CdSe surface modification. The results showed that all quantum dots synthesized are adequate to sensitize TiO2 in photovoltaic devices. However, CdSe and CdTe quantum dots presented better quantum confinement and the exciton generated in CdSe presented the higher stability. NMR analysis provided information about the non-preferential orientation for adsorption of the ligands on the CdSe surface, meanwhile measurements of current vs. potential and incident photon current efficiency showed a weak dependence of photovoltaic device efficiency with the nature of the ligand. On the other side, the surface modification favors the solubility in solvents with different polarizabilities, including water, widening the range for applications of the quantum dots synthesized in this work.
Medical or drug-induced abortion has been proven as an effective means for termination of pregnancy. However, training of providers in the use of misoprostol has been limited. The current article ...aims to identify the degree of knowledge on medical abortion among Brazilian medical residents in Gynecology and Obstetrics. A multicenter cross-sectional study was performed with residents regularly enrolled in residency programs in Gynecology and Obstetrics in 21 teaching hospitals. A self-responded questionnaire was used. Correct responses to each of the alternatives were identified, and a binary response variable (≥ P70, < P70) was defined by the 70th percentile of the number of questions on misoprostol. Four hundred and seven medical residents returned the questionnaire, of which 404 were completed and three were blank. The majority (56.3%) of the residents were 27 years or younger, females (81.1%), and single or not living with a partner (70%). Two-thirds (68.2%) were in the first or second year of residency. Only 40.8% of the participants answered 70% or more of the questions correctly. In the multivariate analysis, enrollment in the third year of residency or greater (OR = 2.18; 95%CI: 1.350-3.535) and having participated in treatment of a woman with induced or probably induced abortion (OR = 4.12; 95%CI: 1.761-9.621) were associated with better knowledge on the subject. Among Brazilian medical residents in Gynecology and Obstetrics, knowledge on medical abortion is very limited and poses an obstacle to proper care in cases of legal termination of pregnancy.
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