Djalma Ribeiro da Silva

Solar photocatalytic application of NbO2OH as alternative photocatalyst for water treatment

Water recycling and industrial effluents remediation are a hot topic of research to reduce the environmental impact of the human activity. Persistent organic pollutants are highly recalcitrant compounds with hazardous effects associated to their fate in water bodies. Several novel technologies have been developed during the last decades to deal with this novel contamination. However, the natural sources and idiosyncrasy of each country lead to the potential application of different technologies. In this context, we have focused on the development of phocotalytic treatment of solutions containing dyes using a novel photocatalytic material, the NbO2OH. The NbO2OH was synthesized and characterized with different techniques. Several assays demonstrated the solar photoactivity of this novel oxyhydroxide catalyst, achieving complete decolorizations after 10min of treatment under optimal conditions of 1.0gL-1 NbO2OH photocatalyst loading, 0.1M of H2O2 as electron scavenger, pH4.0 and methyl orange concentrations up to 15mgL-1. Also, the catalyst recuperation demonstrated the potential reuse of this photocatalyst without losing catalytic response after five cycles. This work is of significant importance because niobium is a natural resource, mainly extracted in Brazil and the annual global sunlight irradiation in the near-equatorial region of northeast Brazil is over the average solar irradiation of the planet. Thus, the solar photocatalytic treatment using NbO2OH in northeast Brazil appears as a highly potential environmental-friendly nanotechnology to mitigate the water pollution.

Large disk electrodes of Ti/TiO2-nanotubes/PbO2 for environmental applications

Large disk electrodes of Ti/TiO2-nanotubes/PbO2 (65 cm2 of geometrical area) were successfully synthesized by anodization and electrodeposition procedures. Characterization of anodes was performed by SEM, EDS, AFM and electrochemical measurements, aiming towards environmental applications. PbO2, an electrocatalytic material, promotes the production of strong oxidising species (hydroxyl radicals) that can be used for decontamination. Electrochemical treatment of synthetic dye effluent (2 L) containing 250 mg L−1 of Acid Blue 113 dye (AB 113) was performed using a disk Ti/TiO2-nanotubes/PbO2 anode and an electrochemical flow cell. More than 85% of organic matter was removed by applying current densities of 20, 40 and 60 mA cm−2. Moreover, colour decay achieved values of 60%, 90% and 100%, depending on the applied current density. Alternatively, this study allows us to understand how nanomaterials have prevented the corrosion phenomena on the anode surface (Pb2+ pollution) due to the homogeneous migration of PbO2 within the TiO2 nanotubes previously formed on the Ti support.

Chlorine determination via MgCl molecule in environmental samples using high resolution continuum source graphite furnace molecular absorption spectrometry

This paper describes a method development for chlorine determination through the formation of MgCl molecule, applied for the first time for Cl quantification, by high resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) in environmental samples. Pyrolysis and vaporization temperatures were optimized as well as the use of chemical modifier. Determinations were carried out at the wavelength of 377.010 and the compromise conditions of the graphite furnace temperature program were 500°C and 2500°C for pyrolysis and vaporization, respectively, using 10µg of chemical modifier Pd. The concentration of reactants for the generation of MgCl molecule was optimized through Box-Behnken experimental design, using MgCl2 solution as source of chlorine. The optimum values according to the surface response were 5gL-1 Mg, 25mgL-1 of chlorine and 2% vv-1 of HNO3, condition in which the amount of Mg is at least 200 times higher than that of chloride. This excess of the forming agent ensures the complete formation of MgCl molecular species, since Cl is the limiting reactant. Certified reference materials, BCR 182 and NIST 8414, and addition and recovery tests were used to evaluate the accuracy of the method and good results were achieved at a 95% confidence level. The method was applied to direct determination of Cl in five produced water samples from offshore oil wellbore, high complex matrix, whose conventional methods require tedious treatment before the analysis.

Treatment of an azo dye effluent by peroxi-coagulation and its comparison to traditional electrochemical advanced processes

Peroxi-coagulation (PC) is an interesting new process that has not been widely studied in the literature. This work presents the application of this technology to treat an azo dye synthetic effluent, studying the effect of different parameters including initial pH, current density (j), initial dye concentration and supporting electrolyte. The two former variables significantly affected the colour removal of the wastewater, followed by the initial dye concentration and the kind of electrolyte, in a lesser extent. The optimum operating conditions achieved were initial pH of 3.0, j = 33.3 mA cm-2, 100 mg L-1 of methyl orange (MO) and Na2SO4 as supporting electrolyte. The performance of PC was also compared to other electrochemical advanced processes, under similar experimental conditions. Results indicate that the kinetic decay of the MO increases in the following order: electrocoagulation (EC) < electrochemical oxidation (EO) with electrogenerated H2O2 << PC < electro-Fenton (EF). This behaviour is given to the high oxidant character of the homogenous OH radicals generated by EF and PC approaches. The EO process with production of H2O2 (EO-H2O2) is limited by mass transport and the EC, as a separation method, takes longer times to achieve similar removal results. Energy requirements about 0.06 kWh gCOD-1, 0.09 kWh gCOD-1, 0.7 kWh gCOD-1 and 0.1 kWh gCOD-1 were achieved for PC, EF, EO-H2O2 and EC, respectively. Degradation intermediates were monitored and carboxylic acids were detected for PC and EF processes, being rapidly removed by the former technology. PC emerges as a promising and competitive alternative for wastewaters depollution, among other oxidative approaches.

Scale-up on Electrokinetic Treatment of Polluted Soil with Petroleum: Effect of Operating Conditions

This study investigates the influence of the scale-up of electrokinetic remediation (EKR) approach in carbonaceus soils. The scale-up study was performed in an electrokinetic lab scale (2.55 dm 3 ) by using two graphite electrodes placed in the cathodic and anodic compartments. The solution used was to humidify the soil were Na2SO4 0.1 M and water. A soil polluted (1.5 Kg) with petroleum (ranging from 500 to 2500 ppm) was treated by applying different currents (ranging from 0.5 A to 0.2 A). The effects such as current, pH, conductivity, z-potential and solution were evaluated to understand the better conditions to remove the organic matter from polluted soil. An increase in scale directly influenced the amount of energy supplied to the soil being treated. As a result, electroosmotic and electromigration flows and electric heating are more intense than in previous study performed where a smaller-scale cell was used.

Comparative Study of Injection Systems in Vapor Phase in the Remediation of Soils Contaminated by Diesel

Gasoline and diesel leaks in underground storage tanks contaminate soils with petroleum hydrocarbons. Various techniques using surfactants have been proposed to remedy this type of contamination. This study presents the application of different systems containing surfactants in vapor phase. It compares the removal efficiencies of diesel contaminated soils using vapor injection systems: surfactant water solutions, micro-emulsions, and nano-emulsions. The surfactant used in the experiments was ethoxylated alcohol UNTL-90 in aqueous solution, in nano-emulsion, and micro-emulsion systems. Among the systems investigated, the nano-emulsion showed the highest removal efficiency (88%), being environmentally friendly and technically feasible with a system that has a lower content of active matter.

Determination of Chlorine in Crude Oil Emulsified via the MgCl Molecule by HR‑CS MAS

A method for chlorine determination in crude oil samples, through the formation of MgCl molecule, by high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) was developed and is described in this paper. The use of this molecule for chlorine determination in crude oil has not been reported up to now. Measures were carried out at the wavelength 377.010 nm and the samples were submitted to a simple treatment as emulsion, whose composition was optimized applying a simplex-centroid experimental design. Magnesium was used as molecule forming agent at the concentration of 10 g L, at least 500 times higher than the concentration of chlorine. This excess is required to ensure the molecule formation of all content of Cl present in the sample. Chemical modifier Pd was used and improved greatly the signal intensities. Optimized pyrolysis and vaporization temperatures, applied for determination, were 800 and 2300 °C, respectively. Accuracy was evaluated through analysis of certified reference materials, NIST 1848 and NIST 1634c, and addition and recovery tests with recoveries between 92 and 117%. Limits of detection and quantification were 3.0 and 9.0 μg g, respectively. The method was applied to eight crude oil samples.

Functional group influences on the reactive azo dye decolorization performance by electrochemical oxidation and electro-Fenton technologies

Electrochemical water treatment technologies are highly promising to achieve complete decolorization of dyebath effluents, as demonstrated by several studies reported in the literature. However, these works are focused on the treatment of one model pollutant and generalize the performances of the processes which are not transposable since they depend on the pollutant treated. Thus, in the present study, we evaluate, for the first time, the influence of different functional groups that modify the dye structure on the electrochemical process decolorization performance. The textile azo dyes Reactive Orange 16, Reactive Violet 4, Reactive Red 228, and Reactive Black 5 have been selected because they present the same molecular basis structure with different functional groups. The results demonstrate that the functional groups that reduce the nucleophilicity of the pollutant hinder the electrophilic attack of electrogenerated hydroxyl radical. Thereby, the overall decolorization efficiency is consequently reduced as well as the decolorization rate. Moreover, the presence of an additional chromophore azo bond in the molecule enhances the recalcitrant character of the azo dyes as pollutants. The formation of a larger and more stable conjugated π system increases the activation energy required for the electrophyilic attack of •OH, affecting the performance of electrochemical technologies on effluent decolorization.

Modified Diamond Electrodes for Electrochemical Systems for Energy Conversion and Storage

The aim of this chapter was to summarize the techniques used for surface modification of BDD materials, improving their catalytic efficiency as supported catalysts for PEM fuel cells (methanol and ethanol oxidation) as well as the studies concerning to the production of electrochemical capacitors using BDD materials. Also, the recent advances on the use of modified BDD materials for fuel cells will be discussed.