Passivated gold nanoparticles were synthesized through a microwave-assisted process in a two-phase system, in the presence of 1-dodecanethiol. An average particle size of 1.8 nm of the gold nanoparticles obtained and 0.35 S.D. was determined through HRTEM and STEM analysis. It was observed that these nanoparticles spontaneously self-assemble into self-supported superstructures of 1 μm in diameter avg and 400 nm thickness, yielding an off-white powder which can be handled as a simple powder. XRD analysis indicates that n-alkanethiol molecules used as a passivating compound, besides protecting against crystal growth, interact to form cubic ordered arrays between the nanoparticles. This interaction leads to the superstructure formation, with an average distance between nanoparticles in the array, of 3.56 nm. Theoretical calculations and molecular dynamics simulations were performed to analyze the resulting structure.

The pKa and the isosbestic point of the universal pH indicator Carlo Ebra 1-11 (catalog number 45712) were determined using UV-Vis spectrophotometry. Aqueous buffer solutions with pHs ranging from 3.83 to 10.85 were mixed. Four methods-two graphical and two mathematicalwere used to estimate the acid dissociation constant (pKa) and isosbestic point using absorbance measurements. The equation for the dependence of the absorbance on pH at λ = 600 nm was obtained using calibration curves. The resulting average pKa of the four methods was 8.277 with a standard deviation of 0.1728. The results obtained using the mathematical methods were very similar, with a deviation of 0.0014; the average pKa determined using these methods was 8.263 ± 0.001. The literature contains no previous reports of the pKa of this indicator. The isosbestic point occurs at a wavelength of 494 nm, with an absorbance of 0.46.

In the present work we show that synthesis of gold nanoparticles ͑NPs͒ could be performed by microwave-assisted technique without the need of adding any reducing agent. Only water and the gold salt precursor are necessary to generate the NPs under the influence of microwaves. The produced NPs have been characterized by state-of-art microscopy techniques, like high resolution transmission electron microscopy, scanning electron microscopy, and energy-dispersive x-ray. Theoretical calculations have been performed to support the experimental findings. It is expected that the present work opens routes for synthesis of NPs using green, fast, and safe methods.

Chemical bath deposition (CBD), a direct low cost technique that involves a cadmium salt solution, a complexing agent and a chalcogen source, was used to prepare CdSe semiconductor films. The most favourable conditions for acceptable quality CdSe films grown on glass were obtained. Commercially available microscope glass slides (with a size of 1 cm × 1 cm × 1 mm) were used as substrates to deposit CdSe films. CdSe films were deposited in a freshly prepared aqueous solution containing CdSO 4 (0.2 -0.4 M), NH 4 OH (3.8 -14 M) as a complexing agent for slow release of Cd 2+ ions, and Na 2 SeSO 3 (0.118 and 0.16) as a source of Se 2-ions. The solutions were prepared in deionized water. The glass slides were immersed in a mixture of CdSO 4 -NH 4 OH for 5 min before the solution of Na 2 SeSO 3 was added. The bath temperature varied from 20 to 60 °C. Structural and morphological quality of the films was analyzed by XRD, SEM, EDS, and XPS. The results show that the crystallinity of the CdSe films as-deposited is improved by increasing temperature. The initial growth stages of CdSe films at 20 and 60 °C start on CdO x and Cd(OH) 2 buffer layers respectively.