Ecotoxicidade de nanocatalisadores de óxidos de ferro, produzidos a partir da drenagem ácida de mina, quando submetidos à ação de ozônio em meio aquoso / Ecotoxicity of iron oxide nanocatalysts, produced from acid mine drainage, when submitted to the action of ozone in aqueous medium

RESUMO Óxidos de ferro recuperados da drenagem ácida de minas representam uma matéria-prima potencial para a produção de baixo custo de nanogoetita ou nanohematita, com grau de pureza adequado para o seu uso como catalisador em processos de tratamento de efluentes líquidos com ozônio. Assim, a toxicidade das nanopartículas de ferro precisa ser determinada para prever seu impacto no meio ambiente, antes e depois de terem sido utilizadas nesses processos. Nesse contexto, o objetivo deste estudo foi avaliar a toxicidade de nanogoetita e nanohematita produzidas a partir da drenagem ácida de minas bem como comparar os resultados com hematita sintética de alta pureza. A nanogoetita foi obtida da drenagem ácida de minas e, após seu tratamento térmico a 450°C, produziu nanopartículas de hematita. Os materiais foram caracterizados por difração de raios X, microscopia eletrônica de transmissão e determinação da área superficial específica e porosidade com base nas isotermas de adsorção/dessorção de N2. Foram realizados os ensaios de ecotoxicidade usando os protocolos padronizados para bioluminescência com Vibrio fischeri, letalidade da Artemia sp., germinação de sementes de Lactuca sativa L. (alface) e crescimento das raízes de Allium cepa L. (cebola). Os resultados de toxicidade indicaram estabilidade das nanopartículas, que não são alteradas significativamente pela ação do ozônio em meio aquoso. Para todas as amostras, os valores indicaram baixa ou nenhuma toxicidade nas condições dos experimentos, para os bioindicadores utilizados. Esses resultados fornecem indicação de que as nanopartículas de ferro recuperadas da indústria de resíduos podem ser usadas como catalisadores sem efeitos adversos ao meio ambiente.

ABSTRACT Iron oxides recovered from acid mine drainage represent a potential raw material for the low-cost production of nanogoethite or nanohematite, with a degree of purity suitable for its use as a catalyst in processes for treating liquid effluents with ozone. Thus, the toxicity of iron nanoparticles needs to be determined to predict their impact on the environment, before and after they have been used in these processes. In this context, the objective of this study was to evaluate the toxicity of nanogoethite and nanohematite produced from acid mine drainage as well as to compare the results with high-purity synthetic hematite. Nanogoethite was obtained from acid mine drainage and, after its heat treatment at 450°C, produced nanoparticles of hematite. The materials were characterized by X-ray diffraction, transmission electron microscopy, and determination of the specific surface area and porosity based on N2 adsorption/desorption isotherms. Ecotoxicity tests were carried out using standardized protocols for bioluminescence with Vibrio fischeri, lethality of Artemia sp, germination of Lactuca sativa L (lettuce) seeds, and growth of Allium cepa L (onion) roots. The toxicity results indicated stability of the nanoparticles, which are not significantly altered by the action of ozone in aqueous medium. For all samples, the values indicated low or no toxicity under the conditions of the experiments. These results provide an indication that the iron nanoparticles recovered from the waste industry can be used as catalysts without adverse effects on the environment.

Tuning the photoactivity of TiO2 nanoarchitectures doped with cerium or neodymium and application to colour removal from wastewaters.

The impact of cerium (Ce) and neodymium (Nd) rare-earth metal doping of TiO2 prepared by the hydrothermal method was investigated to tailor effective photocatalytic degradation of coloured wastewater under UV or visible illumination. The hydrothermal treatment of TiO2 decreased the pHpzc from 6.3 to 3.1-3.8 favouring the affinity for cationic water contaminants. Doping with Ce and Nd modified the crystallinity and the morphology of the photocatalysts and significantly increased the BET surface area and the adsorption capacity of cationic dyes. The photocatalytic activity under UV light irradiation decreased due to shielding of the catalyst active area by excessive amount of dye adsorbed. Conversely, the photocatalytic activity of the Ce and Nd doped TiO2 increased under visible light irradiation by 1.2 times as a result of the dye photosensitization effect. It was demonstrated that two-steps dark adsorption and photocatalytic reaction or one-step simultaneous adsorption and reaction can produce significantly different results for the photocatalytic degradation of dyes in coloured waters, the rate being controlled by the competitive adsorption of the reacting organics and the H2O/OH- species. The reaction is driven by the radical oxygen species (ROS) formed on the catalyst surface the nature of which, differs under UV or visible light irradiation. The Ce-doped TiO2 and Nd-doped TiO2 photocatalysts with 0.5% rare-earth content were found to be efficient in the degradation of MB in aqueous solution, removing the colour and reducing the toxicity of wastewaters.

Peroxidation and photo-peroxidation of pantoprazole in aqueous solution using silver molybdate as catalyst.

In this study, silver molybdate was used as a catalyst in different oxidation processes to degrade pantoprazole (PAN) from aqueous suspension. The catalyst was synthesized using a controlled precipitation method and characterized by XRD, FTIR spectroscopy, BET analysis, Zeta potential, FEG-SEM/EDS, DRS and EPR. The α- and ß-phases of Ag2MoO4 were identified as crystalline structure of the butterfly-shaped particles. The metastable α-phase could be completely converted into ß-Ag2MoO4 by thermal treatment at 300 °C. The band gap energy of ß-Ag2MoO4 (Eg = 3.25 eV) is slightly higher than for as-prepared catalyst (α-Ag2MoO4 + ß-Ag2MoO4) (Eg = 3.09 eV), suggesting that as-prepared catalyst should be active under visible light. PAN is sensible to UV light irradiation, and the addition of H2O2 as electron acceptor enhanced the mineralization rate. In the catalytic UV-based reactions, high PAN oxidation efficiencies were obtained (>85%) but with low mineralization (32-64%). Catalytic peroxidation and photo-catalytic peroxidation under visible light showed the highest PAN oxidation efficiency, leading to its almost complete mineralization (>95%), even under dark conditions (98% in 120 min). Several degradation byproducts were identified and three mechanistic routes of PAN decomposition were proposed. The identified byproducts are less toxic than the parent compound. EPR coupled with the spin trapping method identified •OH radicals as the main ROS species in both photocatalytic and catalytic peroxidation reactions. Ag2MoO4 showed to be a promising catalyst to promote the decomposition of hydrogen peroxide into ROS.1.

1,4-Dioxane removal from water and membrane fouling elimination using CuO-coated ceramic membrane coupled with ozone.

1,4-Dioxane is a synthetic cyclic ether traditionally used as a chlorinated solvent stabilizer. It is a small molecule and recalcitrant compound that is difficult to remove by conventional processes and in this regard, there is a need for the development of new technologies. In this study, an innovative CuO-coated ceramic membrane (CM) reactor system that can be used to oxidize 1,4-dioxane dissolved in surface water by catalytic ozonation was developed. The effect of the thickness of the CuO deposited on the ceramic membrane surface on the permeability, fouling resistance, 1,4-dioxane removal, and toxicity was evaluated. The efficiency of the hybrid ozonation coupled to the use of a CuO-coated CM in 1,4-dioxane removal and the antifouling properties were assessed from TOC and 1,4-dioxane removal kinetics data. Reusability in four cycles was also tested. The performance of the CuO-coated CM remained stable during the four cycles of the reusability test. The ceramic membrane coated with CuO particles coupled with ozonation is appropriate for 1,4-dioxane degradation in the aqueous phase (45% efficiency, rate constant increased by a factor of 2.98 compared with the uncoated-hybrid process) and fouling removal (60 min to recovery the permeate flux).

Structural, optical and photocatalytic properties of erbium (Er3+) and yttrium (Y3+) doped TiO2 thin films with remarkable self-cleaning super-hydrophilic properties.

The self-cleaning and super hydrophilic properties of pristine TiO2 and of TiO2 doped with Er3+ or Y3+ transparent thin films deposited onto glass substrates were investigated. The thin films prepared by multiple dipping and drying cycles of the glass substrate into the pristine TiO2 sol and Er3+ or Y3+-doped TiO2 sol were characterized by X-ray diffraction, UV-vis spectrophotometry, and atomic force microscopy (AFM). The self-cleaning photocatalytic activity of the thin films towards the removal of oleic acid deposited on the surface under UVA irradiation was evaluated. A remarkable enhancement was observed in the hydrophilic nature of the TiO2 thin films under irradiation. The optical properties and wettability of TiO2 were not affected by Er3+ or Y3+ doping. However, the photocatalytic degradation of oleic acid under UVA irradiation improved up to 1.83 or 1.95 fold as the Er3+ or Y3+ content increased, respectively, due to the enhanced separation of the photogenerated carriers and reduced crystallite size. AFM analysis showed that the surface roughness increased by increasing the Er3+ or Y3+ content due to the formation of large aggregates. This in turn contributes to the increase of the active surface area enhancing the photodegradation process. This study demonstrates that TiO2 doped with low amounts of Er3+ or Y3+ down to 0.5 mol% can produce transparent, super-hydrophilic, thin film surfaces with remarkable self-cleaning properties.

Treatment of aqueous solutions of 1,4-dioxane by ozonation and catalytic ozonation with copper oxide (CuO).

In this study, treatment for the removal of 1,4-dioxane by ozone and by catalytic ozonation using CuO as the catalyst was investigated. While the removal of 1,4-dioxane was small (20%) and mineralization negligible after 6 h of ozonation treatment, the removals of 1,4-dioxane and total organic carbon increased by factors of 10.35 and 81.25, respectively, after catalytic ozonation in the presence of CuO. The mineralization during catalytic ozonation was favoured at pH 10 (94.91 min-1), although it proceeded even at pH 3 (54.41 min-1). The CuO catalyst decreased the equilibrium concentration of soluble ozone and favoured its decomposition to reactive oxidative species. Radical scavenging experiments demonstrated that superoxide radicals were the main species responsible for the degradation of 1,4-dioxane. Further scavenging experiments with phosphate confirmed the presence of Lewis active sites on the surface of CuO, which were responsible for the adsorption and decomposition of ozone. The reaction mechanism proceeded through the formation of ethylene glycol diformate, which quickly hydrolyzed to ethylene glycol and formic acid as intermediate products. The stability of CuO indicated weak copper leaching and high catalytic activity for five recycling cycles. The toxicity of the water, assessed by Vibrio fischeri bioluminescence assays, remained the same (low toxicity) after catalytic ozonation while it increased after treatment with ozonation alone.

Residue-based iron oxide catalyst for the degradation of simulated petrochemical wastewater via heterogeneous photo-Fenton process.

Iron oxide with a high degree of purity was recovered from waste and used as an environmentally friendly, low-cost catalyst in the application of the photo-Fenton process to simulated petrochemical wastewater (SPW). Iron oxide nanoparticles were characterized by X-ray powder diffraction, transmission electron microscopy, N2 adsorption/desorption isotherms, zeta potential, toxicity and atomic absorption spectrometry. The experiments were performed in a batch photochemical reactor, at 20 ± 2.0°C and pH 3.0. The SPW was efficiently mineralized and oxidized using a low catalyst dosage. The results showed that the organic compounds present in the wastewater were not adsorbed onto the solid surface. The solid was found to be stable with negligible leaching and low toxicity. The kTOC/kCOD ratios were calculated and varied according to the process: for a homogeneous reaction, the ratio obtained was 0.31 and for the heterogenous photo-Fenton process, it was closer to 1. The chemical oxygen demand and total organic carbon removal values were very close, indicating that the SPW is immediately mineralized, without producing partially oxidized compounds. The residue-based goethite studied represents a good alternative to commercially available catalysts in terms of sources and availability.

Avaliação da eficiência da gestão dos serviços municipais de abastecimento de água e esgotamento sanitário utilizando Data Envelopment Analysis / Evaluation of municipal service management efficiency of water supply and sanitation using Data Envelopment Analysis

O presente estudo teve por objetivo avaliar a eficiência da gestão dos serviços municipais de abastecimento de água e esgotamento sanitário utilizando-se da abordagem Data Envelopment Analysis. Foram avaliados 53 municípios prestadores de serviços de abastecimento de água potável e esgotamento sanitário, conforme definições da Lei 11.445/2007, com população residente entre 50 mil e 100 mil habitantes e constantes da amostra do Sistema Nacional de Informações sobre Saneamento. Utilizaram-se na avaliação 33 indicadores de desempenho cujos resultados foram transformados em medidas adimensionais de intervalo [0, 1]. Da amostra total, nove serviços de abastecimento de água potável e três de esgotamento sanitário obtiveram avaliação com índice igual a 1 e classificação eficiente, sendo que os demais obtiveram avaliação inferior, ou seja, menores que 1 e classificação ineficiente. Na avaliação agregada da gestão do saneamento básico (abastecimento de água potável e esgotamento sanitário), somente um município obteve classificação eficiente.

The present study aimed to evaluate the municipal management efficiency of water supply and sanitation using the approach of Data Envelopment Analysis. We evaluated 53 municipalities' service providers of potable water supply and sanitation, as definitions of Law 11.445/2007, with resident population between 50 thousand and 100 thousand inhabitants and from the sample of the National Information on Sanitation. Were used 33 indicators to evaluate the performance whose the results were transformed into dimensionless measures the interval [0, 1]. Of the total sample, nine services potable water supply and three sanitation obtained evaluation with index equal 1 and efficient classification, and the others had a lower valuation, in other words, lower than 1 and inefficient ranking. In the aggregate evaluation of the management sanitation (water supply and sanitation), only one municipality had efficiency classification.