The present work describes the comparison of the optical and structural properties between CdTe quantum dots (QD) synthesized in water and in the binary solvent (water + glycerin) via one-pot approach synthesis. The optical properties of the nanocrystals obtained with different synthesis parameters were characterized by UV-visible and photoluminescence spectroscopies. The structural chracterization were performed by Fourier transform infrared spectroscopy (FTIR), zeta potential, size-distribution by dynamic light scattering (DLS), X-ray diffraction (XRD), and also by high-resolution transmission electron microscopy (HRTEM). The optical properties of CdTe QD when synthesized in the binary solvent were better, resulting in the increase of photoluminescence quantum yield (Φƒ). The CdTe QD prepared in 120 min, at pH 10.0, in the Cd:Te molar ratio 20:1, using the molar ratio 1:1.5 of Cd:TGA (thioglycolic acid), exhibited a narrow photoluminescence band and enhanced Φƒ for the samples synthesized in a binary solvent in comparison to water solvent (58.4 and 49.5%, respectively).

RESUMO Neste trabalho são aplicados corantes extraídos de plantas da Floresta Amazônica como sensibilizadores em células solares sensibilizadas por corantes. As plantas selecionadas foram Euterpe oleracea, Arrabidaea chica, Bixa orellana, Genipa americana e Myrcia sylvatica e os corantes foram coletados de frutos, folhas, sementes, polpa e sementes e do caule, respectivamente. Os estudos de caracterização através da espectroscopia UV-vis possibilitaram conhecer os espectros de absorção para cada corante e a técnica de difração de raios X permitiu a caracterização estrutural da camada semicondutora nanoestruturada. As células solares foram caracterizadas quanto a seus parâmetros de eficiência (Voc, Jsc, FF e ? (%)), obtidas das curvas de corrente vs potencial. Tais parâmetros se mostraram modestos, apresentando valores de Voc sobre os 0,334 volts e Jsc de 0,452 mA/cm2 para célula fotossensibilizada com o corante extraído da Genipa americana. Dessa forma foi possível verificar o potencial fotoeletroquímico dos corantes extraídos de plantas da Floresta Amazônica.

ABSTRACT In this work, plant dyes extracted from Amazon Forest are applied as a sensitizer in Dye-Sensitized Solar Cells. The selected plants were Euterpe oleracea, Arrabidaea chica, Bixa orellana, Genipa Americana, and Myrcia sylvatica, and the dyes were collected from fruits, leaves, seeds, pulp and seeds and stalk scrapings respectively. Characterization studies by the UV-vis spectroscopy made it possible to know the absorption spectra of each plant dye, and the X-ray diffraction technique allows the structural characterization of the nanostructured semiconductor layer. The solar cells were characterized according to their efficiency parameters (Voc, Jsc, FF and ? (%)), obtained from the current vs voltage curves. Such parameters proved to be modest, presenting Voc and Jsc values over 0.334 volts and 0.452 mA/cm2 for a photosensitized cell with the dyes extracted from Genipa americana. In this way, it was possible to verify the photoelectrochemical potential of the dyes extracted from plants of the Amazon Forest.

RESUMO Este trabalho relata nanopartículas de prata estabilizadas com citrato (AgNPs) sintetizadas pela redução química do íon nitrato com boro-hidreto de sódio, em diferentes pHs (2-9). As AgNPs sintetizadas por este método apresentaram distribuição de tamanho de 5 a 249 nm dependente do pH, conforme determinado por espalhamento dinâmico de luz, além de morfologia esférica, conforme determinado por microscopia eletrônica de transmissão. Na faixa de pH de 3 a 7 ocorreu a agregação das nanopartículas. A distribuição de tamanho, dependendo do pH, foi determinada por espalhamento dinâmico de luz. O potencial Zeta foi determinado e a estabilidade coloidal foi correlacionada com a agregação de nanopartículas em diferentes pHs. A atividade antimicrobiana dependente do tamanho foi avaliada para duas soluções, em que ambas as amostras exibiram atividade antimicrobiana, embora as menores AgNPs sem aglomeração apresentaram propriedades antimicrobianas melhores.

ABSTRACT This paper reports citrate-stabilized silver nanoparticles (AgNPs) synthesized by nitrate ion chemical reduction with sodium borohydride, at different pHs (2–9). The AgNPs synthesized by this method exhibited size distribution from 5 to 249 nm, depending on pH, as determined by dynamic light scattering, and morphology spherical, as determined by transmission electron microscopy. In pH range 3–7 occurred aggregation of the nanoparticles. The size distribution depending on pH was determined by dynamic light scattering. The zeta potential was determined, and the colloidal stability was correlated with nanoparticles aggregation at different pHs. The size-dependent antimicrobial activity was evaluated for two solutions, wherein both samples exhibited antimicrobial activity, although the smallest AgNPs without agglomeration have enhanced antimicrobial properties.

Solar energy has been considered as an important source of clean and safe energy to overcome the problems associate to the burn of fossil fuels (e.g. climate changes, pollution, health problems, etc.). In the area of photovoltaics, devices that convert solar energy into electricity, perovskites solar cells (PSC) have attracted great attention due to their rapid development, high energy conversion efficiency, diversification of the processing methods and different materials. The fantastic properties of the hybrid perovskite materials, such as high absorption coefficient, direct and tunable bandgap, ambipolar charge carrier, simple preparation, etc., have quoted this technology as one the most important in this century. The rapid development of PSC has provided a significant increase in energy conversion efficiency, which was first reported, in 2009, as 3.8% and now reaches up to 22.10%, according to the National Laboratory of Renewable Energy (NREL). Many studies have been carried out to further increase the efficiency of devices and solve problems as the instability of the material, and the presence of lead, so that the PSC can be applied commercially. This paper presents a review on PSC and the major advances reported in device’s architecture, preparation methods, novel materials and interface engineering.

In this work, we have synthesized CdTe quantum dots (QDs) dispersed in an aqueous medium at ambient temperature, and investigated their optical properties. Synthesis of CdTe QDs in the presence of simple amines removed the need for an additional energy source and inert atmosphere, in a simple and inexpensive experimental setup. The use of ammonia or hydrazine promoted nanoparticle growth by kinetic nanocrystal agglomeration in the initial growth stage. These weak electrolytes acted in the electrical double layer during the growth of the nanocrystals. A comparative study on the concentration of hydrazine in the reaction medium helped to investigate their role in nanocrystal growth. Substitution of hydrazine for ethylenediamine and other electrolytes like sodium chloride and ammonium chloride contributed to a better understanding of the mechanism that underlies the use of primary amines in the synthesis of CdTe. The synthesis conditions afforded the highest photoluminescence quantum yield for CdTe QDs prepared at room temperature (27.5%).

Quantum dot solar cells (QDSC) have been subject of extensive research in recent years. QDSC, as a promising alternative to existing solar cells, are among the candidates for next-generation photovoltaic devices that require low cost, high efficiency, so that quantum dots stand out for their unique features and versatile desirable on photovoltaic systems. The rapid development of QDSC provided a significant increase in energy conversion efficiency, which was certified for the first time in 2010 as 2% then being currently as 11.3%, according to the National Renewable Energy Laboratory (NREL). This paper presents a review of the quantum dot-sensitized solar cells and the major advances reported concerning these cells, besides other types of cell architectures involving quantum dots.

In this work a colloidal approach to synthesize water-soluble CdSe quantum dots (QDs) bearing a surface ligand, such as thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), glutathione (GSH), or thioglycerol (TGH) was applied. The synthesized material was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-Vis), and fluorescence spectroscopy (PL). Additionally, a comparative study of the optical properties of different CdSe QDs was performed, demonstrating how the surface ligand affected crystal growth. The particles sizes were calculated from a polynomial function that correlates the particle size with the maximum fluorescence position. Curve resolution methods (EFA and MCR-ALS) were employed to decompose a series of fluorescence spectra to investigate the CdSe QDs size distribution and determine the number of fraction with different particle size. The results for the MPA-capped CdSe sample showed only two main fraction with different particle sizes with maximum emission at 642 and 686 nm. The calculated diameters from these maximum emission were, respectively, 2.74 and 3.05 nm.

NiO nanoparticles with an average size of 15 nm were prepared by a simple, reproducible and low-cost controlled method, using nickel nitrate hexahydrate (Ni(NO3)2·6H2O). These nanoparticles were added to an agar-based polymer electrolyte formula, resulting, after reflux and solution casting, in a proton conducting membrane. The highest ionic conductivity values of 5.19x10-5 S cm-1 at room temperature and 3.32x10-4 S cm-1 at 80 ºC, were obtained for the sample with 50 wt. % of acetic acid and 0.25 g of NiO. Moreover, the samples showed 75 % of transparency in the visible region, a homogeneous surface and mainly amorphous structure. All the obtained results suggest that agar-based polymer electrolyte with NiO nanoparticles are promising candidates for electrochemical devices application.