2016-11-16T20:15:18

No abstract

Gold nanoparticles of different morphologies have been synthesized on a silica‐based organic‐inorganic hybrid material for catalytic applications. The gold nanoparticles formations proceed through in situ chemical reduction of the AuCl4− anions previously adsorbed on 3‐(1‐imidazolyl)propyl‐silsesquioxane, which plays the role of substrate and stabilizer. Two distinct reducing agents, sodium citrate and sodium borohydride, were employed to generate gold nanoparticles of different sizes. UV‐vis diffuse reflectance as well as transmission electron microscopy were employed to evaluate the particle’s morphology. Modified carbon paste electrodes were prepared from these materials and their electrochemical behavior investigated using potassium ferrocyanide and 4‐nitrophenol as redox model compounds. Both AuNPs‐modified electrodes decreased the overpotential of 4‐nitrophenol reduction by around 90 mV compared to the unmodified electrode as evidenced by cyclic voltammetry experiment. However, the smaller diameter particles (borohydride‐reduced) produced more significant catalytic effect as a consequence of their large surface area. Regarding the sensing parameters, the sensitivity is higher for the borohydride‐reduced AuNPs while the values of limit of detection are of the same order of magnitude. Thus, the detection limit and sensitivity are 70.0±0.6 nM and 187 µA/mM for the citrate‐reduced AuNPs; and 75.0±2.2 nM and 238 µA/mM for the borohydride‐reduced AuNPs.

Since the chemical analysis advancement has required increasingly chemometric applications, teaching materials became important for the infrared spectrometry teaching. In this sense, it is proposed an experimental activity for undergraduate and graduate students, where hierarchical cluster analysis (HCA) and principal component analysis (PCA) are applied in infrared spectra of organic solvents. Four studies were accomplished in a gradual manner, starting with the analysis of the simplest groups to the most complex group. The procedure analysis of the hydrocarbon, alcohols and ketones samples effectively illustrated the concepts of multivariate exploratory analysis, HCA and PCA. In addition, the resulting spectra clearly demonstrated the differences of the organic functions and aromaticity and also the used software proved to be adequate for users with little prior knowledge in this area.