Wilson F. Jardim

Photocatalytic destruction of VOCs in the gas-phase using titanium dioxide

The gas-phase photocatalytic destruction of 17 VOCs over illuminated titanium dioxide was investigated using a plug flow reactor with the following experimental conditions: 200 ml min−1 flow rate, 23% relative humidity, 21% oxygen and an organic compound concentration range of 400–600 ppmv. At steady state, high conversion yields were obtained for trichloroethylene (99.9%), isooctane (98.9%), acetone (98.5%), methanol (97.9%), methyl ethyl ketone (97.1%),t-butyl methyl ether (96.1%), dimethoxymethane (93.9%), methylene chloride (90.4%), methyl isopropyl ketone (88.5%), isopropanol (79.7%), chloroform (69.5%) and tetrachloroethylene (66.6%). However, the photodegradation of isopropylbenzene (30.3%), methyl chloroform (20.5%) and pyridine (15.8%) was not so efficient. Carbon tetrachloride photoreduction was investigated in the presence of methanol as an electron donor. It was observed that the presence of methanol results in higher degradation rates. No reaction byproducts were detected for all VOCs tested under the experimental set-up and conditions described. Also, long-term conversion was obtained for all tested compounds. Catalyst deactivation was detected with toluene only, but the activity was restored by illuminating the catalyst in the presence of hydrogen peroxide. The capacity of the process to destroy different classes of volatile organic compounds present in the atmosphere was demonstrated.

Photocatalytic degradation of aromatic chlorinated compounds using TiO2: Toxicity of intermediates

The photocatalytic degradation of four chlorinated aromatic compounds, namely pentachlorophenol (PCP), 2,4,-dichlorophenol (2,4,-DCP), 3,5,-dichlorophenol (3,5,-DCP), and 2,3,5,-trichlorophenol (2,3,5,-TCP), was investigated in the presence of an aqueous suspension of TiO2 irradiated with near-UV light. The toxicity of the transient species was compared to that observed for the parent compound. The comparison was carried out by monitoring the inhibition in bacterial respiration (Escherichia coli) by measuring the CO2 in the aqueous culture medium using flow injection analysis (FIA). Only in the case of PCP and 2,3,5,-TCP were the intermediates, identified by HPLC and GC/MS, found to be more toxic than the parent compound. The principal intermediates observed during the photocatalytic oxidation process of PCP were 2,3,5,6,-tetrachloro-1,4,-hydroquinone, 2,3,5,6,-tetrachloro-1,4,-benzoquinone and 2,3,5,6,-tetrachlorophenol. In the case of 2,3,5,-TCP and 3,5,-DCP, the identified intermediates were 2,3,5,-trichloro-1,4,-hydroquinone and 2,5,dichloro-1,4,-hydroquinone, respectively. The intermediates of 2,4,-DCP were not identified.

Is the Negro River Basin (Amazon) impacted by naturally occurring mercury

In order to investigate the major sources and cycling of mercury in the Negro River Basin (Amazon), total metal measurements were carried out in soils, in river and lake waters, in the atmosphere, and in bulk precipitation during the period 1995 throughout 1998. Median values of 1.3 ng m(-3) in the atmosphere, 172 microg kg(-1) in soils, 4.6-7.5 ng l(-1) in three different lakes, 4.5 ng l(-1) in 17 different Negro River tributaries and 20.3 microg m(-2) year(-1) in bulk precipitation were found. Mercury concentrations in rivers and lakes waters, as well as in soils and bulk precipitation were high, considering the scarcity of anthropogenic point sources in the region. Mercury leaching from soil, the largest regional reservoir of this metal, was considered to be the major pathway to mercury enrichment in the region.

A fotocatálise heterogênea e sua aplicação ambiental

This article gives some basic principles of heterogeneous photocatalysis using titanium dioxide as photocatalyst and the state of art of its applications to the abatement of aqueous and atmospheric pollutants.

Gas-phase destruction of H2S using TiO2/UV-VIS

Photocatalytic destruction of H2S using TiO2/UV-VIS was conducted in the gas-phase. This process showed high efficiency, reaching degradation yields of 99% at concentration ranges of 33 to 855 ppmv. Oxygen was shown to be necessary for the photodestruction of H2S. Conversion rates were small in experiments conducted under nitrogen atmosphere (17%) compared with experiments in the presence of oxygen (99%). The photocatalytic activity of TiO2 showed that at 217 ppmv, there was no loss of the activity over extended operation periods. Deactivation of the catalyst was observed only when working at higher H2S concentrations (such as 600 ppmv), and is assumed to be caused by the adsorption of the byproducts produced onto the catalyst surface. The main product in the photocatalytic destruction of H2S in gasphase detected by FTIR and for turbidimetric analysis was sulfate ions. A mass balance showed that H2S is oxidized to SO4poststaggered−2 (95% of SO4poststaggered−2 were easily recovered from the catalyst surface), and that only 0.02% of this ion was detected at the reactor effluent. Experiments carried out using the photocatalytic process to minimize noxious emission of H2S stripped from a raw sewage sample showed that this process is viable for the elimination of odor in wastewater treatment plants.

Mercury speciation in contaminated soils by thermal release analysis

Thermal release analysis of mercury species in contaminated soils was performed by temperature controlled continuous heating of the samples in a furnace coupled to an Atomic Absorption Spectrophotometer (AAS). It was shown that this method allows the identification of different redox states of Hg-species through their characteristic releasing temperature ranges. The method was applied to Hg-contaminated samples from an inactive chlor-alkali production plant in former East Germany (GER), and from a gold mining area in Poconé, Mato Grosso, Brazil (BRA), as well as synthetic soil samples obtained by spiking pre-heated soil matrices (GER and BRA) with the following mercury species: Hg0, Hg2Cl2, HgCl2, HgO and HgS.The samples GER, in general, frequently showed the presence of Hg2+ probably bound to humic substances, in the case of samples with higher total carbon content. Only in highly contaminated samples (>3000 ppm of mercury) was Hg0 the predominant species. The samples BRA more frequently showed the presence of mercury species in the lower oxidation states, i.e. Hg1+ in combination with Hg0. The method allows observing changes in Hg-speciation in the samples with time, mainly changes among the oxidation states Hg0, Hg1+ and Hg2+.The treated GER matrix showed a stronger tendency to oxidise Hf-species than the BRA treated matrix, in which only added Hg0 is partially oxidised to Hg2+ and Hg1+. In contrast, the BRA matrix showed a pronounced tendency to reduce spiked Hg2+ to Hg1+. This may be the reason for the presence of Hg1+ in the majority of original BRA samples.The method appears to be very useful to study speciation of mercury and its dynamics. It can be used as a tool for monitoring mercury oxidation states and/or reactions of mercury in soils.

Interferentes endócrinos no ambiente

Although the hypothesis that environmental chemicals may exhibit endocrine disrupting effects is not new, the issue has been a growing level of concern due to reports of increased incidences of endocrine-related disease in humans, including declining male fertility, and more significantly, to adverse physiological effects observed in wildlife where cause and effect relationships are more evident. The list of endocrine disrupting chemicals (EDCs) includes a range of anthropogenic compounds, phytoestrogens, naturally occurring sex steroids and synthetic estrogens. Within the aquatic environment, the presence of EDCs has concerned many scientists and water quality regulators. Discharge of effluents from treatment facilities is likely to be a significant source of input of contaminants to many systems, and the potential for concentration of hydrophilic compounds and transformation products within sludges has implications for their disposal. Then, understanding the processes and the fate of EDCs on the environment, as well as the mechanisms of endocrine disruption, may facilitate controlling or limiting exposure of both humans and the environment to these compounds.

TiO2-fixed-bed reactor for water decontamination using solar light

A photocatalytic reactor using immobilized TiO2 (Degussa P25) on a glass plate was studied on a bench scale using solar light as the source of radiation. The influence of parameters such as the slope of the plate, solar light intensity, flow rate and molar flow rate, as well as the geometry of the reactor, was studied using dichloroacetic acid (DCA) as a model compound. A linear dependence of degradation with solar light intensity, measured at 365 nm, was observed. Experiments with recirculation as well as a single pass of solution suggested no mass transfer limitations in this system. The mineralization of DCA resulted in the production of quantitative amounts of chloride ions. An initial concentration of 5 mmol/L of DCA decayed to 2 mmol/L in about 2 min of irradiation. An exponential decay of degradation was observed with an increase of the molar flow rate, achieving saturation around 1.5 mmol DCA/min.

Spatial and seasonal variations of pharmaceuticals and endocrine disruptors in the Atibaia River, São Paulo State (Brazil)

A single run optimization chromatographic method for the determination of 15 emerging contaminants in surface water was optimized using solid-phase extraction (SPE) and high performance liquid chromatography (HPLC) with detection through ultraviolet-diode array (UV-DAD) or fluorescence (FLD). Selected compounds included acetaminophen, acetylsalicylic acid, diclofenac, ibuprofen, caffeine, 17β-estradiol, estrone, progesterone, 17α-ethynylestradiol, levonorgestrel, diethylphthalate, dibutylphthalate, 4-octylphenol, 4-nonylphenol and bisphenol A. Quality parameters of the proposed method showed a linearity r2 > 0.996, coefficient of variation lower than 5%, recoveries between 80 to 120% for a spike of 10 µg L-1 for each of the 15 compounds. The lowest limit of detection (LOD) was 38 ng L-1 for caffeine, whereas the highest value was 170 ng L-1 for ibuprofen. The method was applied to the spatial and seasonal monitoring of these compounds in the Atibaia River, which is the main drinking water source for Campinas City (Sao Paulo State, Brazil). Among the 15 selected emerging contaminants, 10 were detected at least once. The lowest concentration determined was 0.096 µg L-1 for diclofenac, whereas caffeine showed concentrations as high as 127 µg L-1.

Photocatalytic degradation of phenol and chlorinated phenols using AgTiO2 in a slurry reactor

Abstract Photodegradation of phenol (PhOH), 2,4-dichlorophenol (2,4-DCP), 2,3,5-trichlorophenol (2,3,5-TCP) and pentachlorophenol (PCP) was investigated using an open upflow slurry reactor and TiO 2 (Ag-loaded) as photocatalyst. Light was provided by three 125 W high-pressure mercury lamps. Best degradation rates were obtained using 250 mg l −1 of AgTiO 2 in the presence of H 2 O 2 and a constant supply of air (1.71 min −1 ). Under this optimized condition, destruction rate constants obtained for a 1 × 10 −4 M solution of PhOH, 2,4-DCP, 2,3,5-TCP and PCP were 0.0493, 0.0430, 0.0367 and 0.0356 min −1 , respectively. Each gram of phenol required 1.70 kW for its photodestruction.