Sergio Gómez-Salazar

Removal of Cu(II) ions from aqueous streams using poly(acrylic acid-co-acrylamide) hydrogels

The adsorption of Cu(II) ions from aqueous solutions onto poly(acrylic acid-co-acrylamide) hydrogels was investigated. The hydrogels were prepared via free-radical solution polymerization using Irgacure 754 as a photoinitiator and ethylene glycol dimethacrylate as a cross-linking agent. Loading of acrylamide/acrylic acid moieties on the surfaces of hydrogels and the amount of cross-linking agent were varied to determine the maximum metal uptake. Polymerization kinetics was investigated by (1)H NMR. The physicochemical properties of hydrogels were investigated by nitrogen sorption measurements, elemental analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The (1)H NMR results demonstrated that the polymerization reaction was carried out almost to completion and confirmed the absence of residual monomers. Swelling results indicated that, by appropriate selection of cross-linking agent amount and monomer ratio, hydrogels can be swollen up to 70,000%. Further characterization of the hydrogels showed rapid adsorption kinetics and equilibrium Cu(II) adsorption capacities of 121 mg g(-1). Cu(II) adsorption kinetic data followed pseudo-first-order kinetics. Adsorption equilibrium data were better fitted by a Langmuir isotherm. FTIR and XPS results indicated the presence of a tetradentate copper complex on the surfaces of hydrogels. The copper uptake achieved suggests the potential use of hydrogels to extract toxic metals from industrial aqueous streams.

Determination of Distributions of Cd, Cu, and Pb Concentrations in Sediments of a Mexican Reservoir to Infer Their Environmental Risk

The José Antonio Alzate Dam in the State of Mexico, Mexico, receives wastewaters from domestic, industrial, and agricultural activities through the Lerma River. Chemical and physicochemical characteristics of the water were determined. Sediment has been studied in order to define the importance of its influence on the reservoir’s state as a whole. The quantification of the metals, Cd, Cu, and Pb in total forms and the geochemical distribution and the chemical mobility of these metals in sediment have been established using a chemical sequential extraction scheme. The three metals showed a common characteristic, being more abundant in fraction F6 (residual), but the other fractions of the geochemical distribution were variable depending on the metal. First, the contamination level was evaluated with the results of the total metals, using the criteria of EPA, Thomas and Murdoch, and the Ontario Ministry of Environment for sediment in water bodies. Subsequently, the risk was assessed using the same criteria but considering the results of sequential extractions, where the geochemical distribution of each metal allowed a better understanding of metal portions with more influence on the risk, in which Cu and Pb presented low risk, but not Cd.

Assessment of Physicochemical Properties of Tequila Brands: Authentication and Quality

Several physicochemical properties were measured in commercial tequila brands: conductivity, density, pH, sound velocity, viscosity, and refractive index. Physicochemical data were analyzed by Principal Component Analysis (PCA), cluster analysis, and the one-way analysis of variance to identify the quality and authenticity of tequila brands. According to the Principal Component Analysis, the existence of 3 main components was identified, explaining the 87.76% of the total variability of physicochemical measurements. In general, all tequila brands appeared together in the plane of the first two principal components. In the cluster analysis, four groups showing similar characteristics were identified. In particular, one of the clusters contains some tequila brands that are not identified by the Regulatory Council of Tequila and do not meet the quality requirements established in the Mexican Official Standard 006. These tequila brands are characterized by having higher conductivity and density and lower viscosity and refractive index, determined by one-way analysis of variance. Therefore, these economical measurements, PCA, and cluster analysis can be used to determinate the authenticity of a tequila brand.

Localized Impedance Measurements in Different Redox Potential Metals and their Galvanic Coupling by Using AC-SECM

In recent years, the use of Scanning Electrochemical Microscopy in its Alternating Current mode (AC-SECM) has increased due to its capability for detecting and interpreting local variations of electrochemical properties on surfaces with high spatial resolution. In this paper, we intend to extend the applications of AC-SECM for identifying local impedance variations on surfaces of materials with different redox potential, immersed in resistive media such as tequila in presence of supporting electrolyte. Preliminary results are promising since it is possible to visualize boundaries of materials with different redox potential by means of localized impedance measurements, which opens a new perspective for studying composite materials such as minerals.