Dielectric barrier discharge-assisted determination of methylmercury in particulate matter by atomic absorption spectrometry.

Particulate matter (PM) impregnated with methlymercury (MeHg+) was analyzed using atomic absorption spectrometry coupled to a customized dielectric barrier discharge (DBD) device. Chemical vapor generation (CVG) was applied to generate methylmercury hydride and the DBD device promoted bond cleavage with subsequent release of free Hg atoms to the gas phase. Hydride generation was carried out using a lab-made syringe-based device in batch mode using argon as a carrier gas. Optimized conditions included the use of 1.0 mL of a 0.05% m/v NaBH4 solution and 1.0 mL of a 10% v/v HCl solution. This system was coupled to the DBD device, designed to operate in "plasma jet" configuration. Assessment of the designed device for methylmercury detection was established based on an on-off switch, which promptly demonstrated that Hg signals could only be detected upon activation of the plasma discharge. In parallel, adsorption of MeHg+ to PM-loaded glass fiber filters was investigated. Direct analysis of methylmercury-impregnated PM resulted in significant signal suppression compared to the same mass of analyte from an aqueous standard, which suggests that methylmercury is efficiently adsorbed on PM. This was later confirmed by repeating the same experiment with "blank" (PM-free) glass fiber filters. Hence, extraction of methylmercury to a liquid phase was required for quantification. In order to demonstrate the feasibility of the proposed setup to carry out methylmercury detection in the presence oh Hg2+, recovery tests were conducted by mixing MeHg+ with Hg2+ at three distinct concentration levels (100 : 1, 10 : 1 and 1 : 1 MeHg+ : Hg2+). Recoveries better than 91% were obtained for MeHg+ under these conditions, which demonstrates that the device is efficient for MeHg+ determination by simply modulating the plasma (switching on-off). Limits of detection and quantification were established as 6 ng and 19 ng, respectively.

Comparision of photocatalysis and photolysis processes for arsenic oxidation in water.

The oxidation of As(III) to As(V) in aqueous solution was evaluated using heterogeneous photocatalysis and photolysis. The influence of TiO2 as catalyst in different crystalline (rutile, anatase) and commercial forms was evaluated in a batch reactor and an insignificant difference was observed between them. The process by photocatalysis reached up to 97% As(III) oxidation and no significant difference was observed comparing to results obtained by photolysis. The photolysis experiments (UV radiation only), also carried out in a batch system, showed a high oxidation rate of As(III) (90% in 20min). The influence of different matrices (well water, river water and public water supply) were evaluated. Additionally, the effect of As(V) concentration, generated during the oxidation process, was studied. Continuous photolysis experiments using only UV radiation were performed, resulting in a high As(III) oxidation rate. Using a flow rate of 5mLmin-1 and an initial concentration of As(III) 200µgL-1, gave an oxidation percentage of As(III) of up to 72%, showing a simple and economical alternative to the oxidation step of As(III) to As(V) in the treatment of water contaminated with arsenic.

Textile dye removal from aqueous solutions by malt bagasse: Isotherm, kinetic and thermodynamic studies.

The biosorption of orange solimax TGL 182% (OS-TGL) textile dye onto new and low cost biossorbent (malt bagasse) in aqueous solutions was investigated. The malt bagasse was characterized by Fourier transform infrared spectroscopy and specific surface area (BET method).Batch biosorption experiments were conducted in order to determine the following parameters: particles size, pH, agitation speed, temperature, contact time, biomass dosage, influence of the ionic strength and, finally, the influence of other textile dye on the OS-TGL biosorption. The optimum conditions for OS-TGL removal were obtained at pH 1.5, agitation speed of 150rpm, contact time of 180min and biomass dosage 2, 8gL(-1). The results show that the kinetics of biosorption followed a pseudo-second-order model and by increasing the temperature from 293 up to 313K, the biosorption capacity was improved. The Langmuir model showed better fit and the estimated biosorption capacity was 23.2mgg(-1). The negative values of Gibbs free energy, ΔG°, and positive value of enthalpy, ΔH°, confirm the spontaneous nature and endothermic character of the biosorption process. The results of the ionic strength effect indicated that the biosorption process under study had a strong tolerance in high salt concentrations. The removal capacity (>95%) was not affected with the presence of other textile dyes.