Instituto de Física

ZnO nanostructures of different morphologies were grown in a controlled manner using a simple low-temperature hydrothermal technique. Controlling the content of ethylenediamine (soft surfactant) and the pH of the reaction mixture, nanoparticles, nanorods, and flowerlike ZnO structures could be synthesized at temperatures 80-100°C with excellent reproducibility. High-resolution electron microscopy revealed the well crystalline nature of all the nanostructures with preferential growth along the [002] direction for linear structures. Photoluminescence spectra of the as-grown nanostructures revealed oxygen-vacancy-related defects in them, which could be reduced by air annealing at 250°C. Possible mechanisms for the variation of morphology with synthesis parameters are discussed.

We report the synthesis of Fe3O4@mSiO2 nanostructures of different meso-silica (mSiO2) shell thickness, their
biocompatibility and behaviors for loading and release of a model drug ibuprofen. The composite nanostructures
have superparamagnetic magnetite cores of 208 nm average size and meso-silica shells of 15 to 40 nm thickness.
A modified Stöber method was used to grow the meso-silica shells over the hydrothermally grown monodispersed
magnetite particles. The composite nanoparticles show very promising drug holding and releasing behaviors,
which depend on the thickness of meso-silica shell. The biocompatibility of the meso-silica-coated and uncoated
magnetite nanoparticles was tested through cytotoxicity assay on breast cancer (MCF-7), ovarian cancer (SKOV3),
normal human lung fibroblasts MRC-5, and IMR-90 cells. The high drug holding capacity and reasonable biocompatibility
of the nanostructures make them ideal agents for targeted drug delivery applications in human body.

ZnO nanostructures of different morphologies were fabricated through ultrasound-assisted hydrolysis of zinc acetate at room temperature, by controlling the pH of the reaction mixture. It has been observed that the pH of the reaction solution affects both the morphology and defect content of the nanostructures. To study the effects of morphology and other parameters like specific surface area, defect content, and surface contamination on photocatalytic activity, both the as-grown and air annealed nanostructures were tested for methylene blue (MB) degradation under UV light. While all the
above mentioned parameters have been seen to affect the photocatalytic performance of ZnO nanostructures, specific surface area, defect content, and carbon contamination at the surface have been seen to be the most important parameters, and should be controlled for their application in photocatalysis. Therefore, for photocatalytic applications of ZnO nanostructures, not only their morphology or the specific surface area are important, but care should be taken to control their defect contents and surface contaminants.

We report on the synthesis of spherical, well-dispersed colloidal gold nanoparticles of 17.5–23.5 nm average sizes in water using potato extract (PE) both as reducing and stabilizing agent. The effects of PE content and the pH value of the reaction mixture have been studied. Formation and growth
dynamics of the Au nanoparticles in the colloids were
studied using transmission electron microscopy and
UV-Vis optical absorption spectroscopy techniques.
While the reductor content and, hence, the nucleation
and growth rates of the nanoparticles could be controlled by controlling the PE content in the reaction solution, the stability of the nanoparticles depended strongly on the pH of the reaction mixture. The mechanisms of Au ion reduction and stabilization of Au nanoparticles by potato starch have been discussed. The use of common natural solvent like water and
biological reductor like PE in our synthesis process opens up the possibility of synthesizing Au nanoparticles in fully green (environmental friendly) way, and the Au nanoparticles produced in such way should have good biocompatibility.

Production of biogas utilizing agricultural wastes is one of the most demanding technologies for generating energy in sustainable manner considering environmental concerns. However, though the agricultural wastes are available in abundance, the technologies used for the production of biogas such as biological and thermochemical processes are not very efficient. In the present article, we describe a process for the production of biogas from coffee pulp utilizing Cu/TiO2 as an
efficient photocatalyst in its solar photocatalytic pretreatment, producing biogas of high caloric value at enhanced rate. The pretreatment process enhances the coffee pulp–cattle manure codigestion, producing increased amounts of methane,
propane, and other combustible components of biogas. The photocatalytic pretreatment was performed using 10%Cu/TiO2 as photocatalyst, bubbling air as oxidizing agent, and solar radiation as light source. The process enhances the degradation
rate of lignocellulosic components of coffee pulp, consequently increasing the biogas production through anaerobic codigestion. The mechanism of photocatalytic degradation of lignocelluloses has been discussed. The results presented
in this work indicate the photocatalytic pretreatment is a useful process to increase biogas generation from lignocelluloses-rich natural wastes.

Biogas could be produced by the co-digestion of coffee-pulp and cow-dung mixture under solar radiation. Gas chromatography and FTIR spectroscopy were used to analyze the chemical compositions of the generated biogas and its postcombustion emissions. From the first month of co-digestion at mesophylic conditions, methane content in the biogas attains 50% of the yield. This content increased up to 60% and remained almost constant for at least 8 months of further digestion. The FTIR gas spectroscopy analysis
revealed the presence of over 70 chemical compounds in the biogas generated after 4 months of co-digestion along with several compounds hazardous to environment and animal health like isocyanic acid, and bromomethane. Combustion emission of the biogas contained several components like CH4, C3H8, CO, SO2, HI, and probably Br2 which are strongly harmful to human and animal health. Results presented
in this work indicate that if the biogas is to be considered as a fuel, the conventional combustion technology has to be upgraded to prevent these hazardous emissions to the atmosphere.

Hydrothermally grown SnO2 and SnO2:Eu nanoparticles of 4–11 nm size range were analyzed by photoluminescence (PL) and therrmoluminescence (TL) spectroscopy to study the effect of Eudoping on their emission behaviors. It has been observed that most of the incorporated Eu3þ ions remain at the interstitial sites of SnO2 lattice. High Eu-contents in the nanoparticles generate lattice deformation, formation of Eu3þ/Eu0 clusters at interstitial sites, or segregation to their surfaces. Formation of Eu clusters at interstitial sites enhances electronic defect density in the crystal lattice, reorganizes carrier trapping centers, and modifies their activation energies. Room temperature PL emission and beta-irradiated TL dose response of SnO2 nanoparticles enhance significantly when
doped with 0.5 and 1.0 mol. % nominal of Eu3þ, respectively, opening up their possibilities of applications in bio-imaging and radiation therapy. Possible mechanisms of enhanced PL and TL
responses of the samples have been discussed.