Renato S. Freire

Characterization of self-assembled thiols monolayers on gold surface by electrochemical impedance spectroscopy

Thiols with different alkyl chain length and containing COOH terminal group were self-assembled on gold electrodes. The electron transfer of Fe(CN)63-/4- couple to the electrode was studied at different pH by means cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Changes in solution pH resulted in the charge variation of the self-assembled monolayer (SAM) terminal group and, consequently, the electrostatic interaction of SAM with the electroactive species in the solution.

Ferro zero: uma nova abordagem para o tratamento de águas contaminadas com compostos orgânicos poluentes

Anthropogenic pollution of groundwater and surface water has become a very serious environmental problem around the world. A wide range of toxic pollutants is recalcitrant to the conventional treatment methods, thus there is much interest in the development of more efficient remediation processes. Degradation of organic pollutants by zero-valent iron is one of the most promising approaches for water treatment, mainly because it is of low cost, easy to obtain and effective. After a general introduction to water pollution and current treatments, this work highlights the advances, applications and future trends of water remediation by zero-valent iron. Special attention is given to degradation of organochloride and nitroaromatic compounds, which are commonly found in textile and paper mill effluents.

Azo dye degradation by recycled waste zero-valent iron powder

In this paper an efficient method for azo dye degradation using an environmentally friendly zero-valent iron powder source is presented (iron particles discarded from a manufacturing process). The influence of several experimental parameters (such as pH, iron mass, particle size, substrate concentration, oxidizing and inert atmospheres) on the ability of zero-valent iron to reduce the chromophoric groups and total organic carbon content of the azo dye Remazol Black B was evaluated. Kinetic studies revealed that the azo degradation by Fe0 appeared to be first-order with respect to substrate, with an observed rate constant (kobs) of 0.153 min-1. Under the optimized operational conditions (pH 3, [Fe] = 5 g L-1, iron particle size < 250 µm), the iron-based process produced net a reduction in color and total organic carbon of about 95% and 70%, respectively. The process was also evaluated for the degradation of textile effluent. The studied process showed good characteristics, which can make it an effective alternative for polluted aquatic system remediation.

Métodos emergentes para aumentar a eficiência do ozônio no tratamento de águas contaminadas

Many industrial processes produce effluents with a wide variety of xenobiotic organic pollutants, which cannot be efficiently degraded by conventional biological treatments. Thus, the development of new technologies to eliminate these refractory compounds in water has become very imperative in order to assure the quality of this important resource. Ozonation is a very promising process for the treatment of wastewaters containing non-easily removable organic compounds. The present work aims at highlighting new methods of enhancing the efficiency of ozone towards the removal organic pollutants in aqueous solution. Special attention is given to catalytic ozonation processes contemplating homo- and heterogeneous catalysis, their activity and mechanisms. Recent results and future prospects about the application of these processes to real effluents are also evaluated.

Ag3PO4 sunlight-induced photocatalyst for degradation of phenol

Micrometric particles of Ag3PO4 were prepared by a simple precipitation method, and the as-prepared material was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FEG-SEM), nitrogen sorption isotherms, Raman spectroscopy and UV-visible diffuse reflectance spectrophotometry. Ag3PO4 particles showed excellent catalytic activity for degradation of phenol using simulated sunlight irradiation (Xenon lamp). After one hour of treatment, approximately 75% of phenol was completely mineralized. Additional experiments were conducted in order to evaluate the influence of dissolved oxygen in the photocatalytic process. During photodegradation assisted by Ag3PO4, it was considered that oxygen production and phenol oxidation were competitive processes.

Cério: propriedades catalíticas, aplicações tecnológicas e ambientais

Cerium based-compounds have great importance in a wide range of technological applications, such as: fuel cell devices development; metallurgic processes, petroleum refining; glass and ceramic production. Recently, its catalytic properties have been also explored for environmental applications, especially those to prevent or to control atmospheric and water pollution. Subjects covered in this work include a brief description of the fundaments of cerium catalytic properties and some relevant technological applications. Special attention is given to its photocatalytic activity and its ability to degrade pollutants. Recent results and future prospect about these applications are also evaluated.

One-pot green synthesis of cerium oxide–carbon microspheres and their catalytic ozonation activity

Monodisperse carbon microspheres surrounded by CeO2 nanoparticles were prepared by a one-pot green hydrothermal method. The hybrid microspheres were synthesized using a mixed D(+)-glucose and Ce(NO3)3 aqueous solution with subsequent hydrothermal treatment at 160 °C for 12 h. The as-prepared material was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. The results showed that microsphere growth is catalyzed by Ce3+ ions, for the same hydrothermal treatment period the diameters of hybrid microspheres were 5 μm, 25 times higher than for pure carbon spheres. These hybrid materials exhibited excellent catalytic activity in salicylic acid (SA) degradation by ozone. Ozonation studies showed when the CS20Ce microsphere was used as a catalyst, the mineralization rate of AS reached 80% after 60 minutes of treatment. Cerium oxide–carbon microspheres catalytic activity was attributed to the synergic effect of the carbon and CeO2 interface structures that were capable of enhancing radical species generation in the ozonation process.