RESUMO
The photocatalytic activity of TiO2 nanoparticles (NPs) supported on mesoporous silica SBA-15 (TiO2/SBA-15) was evaluated for the photodegradation of sulfadiazine (SDZ), as target contaminant of emerging concern (CEC), using either pure water solutions (PW) or a real secondary urban wastewater (UWW) spiked with SDZ. For this purpose, TiO2/SBA-15 samples with 10, 20 and 30% TiO2 (w/w) were prepared by the sol-gel post synthetic method on pre-formed SBA-15, using titanium (IV) isopropoxide as a precursor. The TiO2/SBA-15 materials were characterized by HRTEM, SAXS and XRD, nitrogen adsorption isotherms and UV-vis diffuse reflectance spectroscopy. TiO2 NPs were shown to be attached onto the external surface, decorating the SBA-15 particles. The TiO2/SBA-15 catalysts were active in SDZ photodegradation using the annular FluHelik photoreactor, when irradiated with UVA light. The 30% TiO2/SBA-15 sample presented the best performance in optimization tests performed using PW, and it was further used for the tests with UWW. The photocatalytic activity of 30% TiO2/SBA-15 was higher (56% SDZ degradation) than that of standard TiO2-P25 (32% SDZ degradation) in the removal of SDZ spiked in the UWW ([SDZ] = 2 mg L-1). The photodegradation of SDZ with 30% TiO2/SBA-15 eached 90% for UWW spiked with a lower SDZ concentration ([SDZ] = 40 µg L-1). Aside of SDZ, a suit of 65 other CECs were also identified in the UWW sample using LC-MS spectrometry. A fast-screening test showed the heterogeneous photocatalytic system was able to remove most of the detected CECs from UWW, by either adsorption and/or photocatalysis.
Assuntos
Dióxido de Silício , Águas Residuárias , Espalhamento a Baixo Ângulo , Difração de Raios XRESUMO
The degradation of three pesticides, azoxystrobin (AZO), difenoconazole (DFZ), and imidacloprid (IMD), commonly found in the tomato rinse water, was studied through UVC (251-257 nm) and UVC/H2O2 photolysis. The results showed that direct photolysis follows pseudo-first-order kinetics, with total AZO and IMD removals within 15 min, using 21.8 and 28.6 W m-2, respectively, while the highest percentage of DFZ degradation was 51.7% at 28.6 W m-2 UVC. The estimated quantum yields were 0.572, 0.028, and 0.061 mol Einstein-1 for AZO, DFZ, and IMD, respectively. With regard to UVC/H2O2, total pesticide removal was achieved after 10 min, while optimal treatment conditions in relation to the pesticide removal rates, estimated through the sequential Doehlert design, were about [H2O2]0 = 130 mg L-1 and 26 W m-2. Cytotoxicity and genotoxicity assays carried out with Allium cepa, for real industrial tomato rinse water sampled from washing belts did not show abnormalities during cell division, with total pesticides degradation after 15 min, demonstrating the potential application of the UVC/H2O2 process as a viable localized treatment with a focus on the possible reuse of treated water.
Assuntos
Praguicidas , Solanum lycopersicum , Poluentes Químicos da Água , Purificação da Água , Peróxido de Hidrogênio , Oxirredução , Fotólise , Raios Ultravioleta , Água , Poluentes Químicos da Água/análiseRESUMO
Solar-driven photocatalysis is a promising water-cleaning and energy-producing technology that addresses some of the most urgent engineering problems of the twenty-first century: universal access to potable water, use of renewable energy, and mitigation of CO2 emissions. In this work, we aim at improving the efficiency of solar-driven photocatalysis by studying a novel reactor design based on microfluidic principles using 3D-printable geometries. The printed reactors had a dimensional accuracy of 97%, at a cost of less than $1 per piece. They were packed with 1.0-mm glass and steel beads coated with ZnO synthesised by a sol-gel routine, resulting in a bed with 46.6% void fraction (reaction volume of ca. 840 µL and equivalent flow diameter of 580 µm) and a specific surface area of 3200 m2 m-3. Photocatalytic experiments, under sunlight-level UV-A irradiation, showed that reactors packed with steel supports had apparent reaction rates ca. 75% higher than those packed with glass supports for the degradation of an aqueous solution of acetaminophen; however, they were strongly deactivated after the first use suggesting poor fixation. Glass supports showed no measurable deactivation after three consecutive uses. The apparent first-order reaction rate constants were between 1.9 and 9.5 × 10-4 s-1, ca. ten times faster than observed for conventional slurry reactors. The mass transfer was shown to be efficient (Sh > 7.7) despite the catalyst being immobilised onto fixed substrates. Finally, the proposed reactor design has the merit of a straightforward scaling out by sizing the irradiation window according to design specifications, as exemplified in the paper.
Assuntos
Poluentes Químicos da Água , Purificação da Água , Catálise , Luz Solar , TitânioRESUMO
The presence of toxic chlorinated compounds in drinking water, generated during the disinfection step in water treatment plants, is of great concern for public health. In the present study, the performance of the UVC/H2O2 process, preceded by zero-valent-copper reduction, was evaluated for degrading 2,4,6-trichlorophenol (TCP). With this aim, the oxidation performed alone or in combination with the pre-reductive step was evaluated regarding TCP concentration over time, removal rate, mineralization, and toxicity to Vibrio fischeri, as well as oxidant dosage and the effect of water matrix. The UV/H2O2 process achieved fast (kobs = 1.4 min-1) and complete TCP degradation, as well as important mineralization (40.4%), with best results obtained for initial H2O2 concentration of 0.056 mmol L-1. Coupling of reductive and oxidative processes intensified contaminant mineralization, due to the synergistic effect of copper ions leached in the reductive process, particularly Cu(I), providing an additional route of H2O2 activation for generating HO⢠radicals (photo-Fenton-like process). High toxicity removals and increased mineralization could be successfully accomplished by the combined processes even in tap water, which is a clear advantage for practical application.
Assuntos
Poluentes Químicos da Água , Purificação da Água , Clorofenóis , Cobre , Peróxido de Hidrogênio , Oxirredução , Raios Ultravioleta , ÁguaRESUMO
Alarming amounts of organic pollutants are being detected in waterbodies due to their ineffective removal by conventional treatment techniques, which warn of the urgent need of developing new technologies for their remediation. In this context, advanced oxidation processes (AOPs), especially those based on Fenton reactions, have proved to be suitable alternatives, due to their efficacy of removing persistent organic compounds. However, the use of ferrous iron in these processes has several operational constraints; to avoid this, an alternative iron source was here investigated: zero-valent-iron (ZVI). A Fenton-like process based on the activation of a recently explored oxidant-persulfate (PS)-with ZVI was applied to degrade an emerging contaminant: Amicarbazone (AMZ). The influence of ZVI size and source, PS/ZVI ratio, pH, UVA radiation, dissolved O2, and inorganic ions was evaluated in terms of AMZ removal efficiency. So far, this is the first time these parameters are simultaneously investigated, in the same study, to evaluate a ZVI-activated PS process. The radical mechanism was also explored and two radical scavengers were used to determine the identity of major active species taking part in the degradation of AMZ. The degradation efficiency was found to be strongly affected by the ZVI dosage, while positively affected by the PS concentration. The PS/ZVI system enabled AMZ degradation in a wide range of pH, although with a lower efficiency under slightly alkaline conditions. Dissolved O2 revealed to play an important role in reaction kinetics as well as the presence of inorganic ions. UVA radiation seems to improve the degradation kinetics only in the presence of extra O2 content. Radicals quenching experiments indicated that both sulfate (SO4â¢-) and hydroxyl (â¢OH) radicals contributed to the overall oxidation performance, but SO4â¢- was the dominant oxidative species.