This study reports a protocol for the treatment of a sanitary landfill leachate through integration between a stage of coagulation-flocculation, a step of filtration of the resulting suspension, and application of the photo-Fenton process using a ferrioxalate complex and solar irradiation. The best results for turbidity removal by coagulation-flocculation were reached using Al3+ as nitrate salt mainly using concentrations up close 4.4 mmol L-1, at the natural pH of the effluent (pH 7.9), when the removal of 66% of the turbidity was achieved. By using a ferrioxalate complex after adjusting the pH of the effluent to 5, it was possible to circumvent the classical limitations of the Fenton process (related to the pH of the medium limited to between 2.5 and 3.0), performing a removal of 68% of the remaining dissolved organic carbon. The global dissolved organic carbon removal in this process was of 86% after a membrane filtration step before the photo-Fenton process.

Kojic acid (KA) is an organic acid widely used in pharmaceutical industry, mainly as a skin lightening agent. Based on the ability of KA to form complexes with ions, we found the most possible kind of complex formed with cation aluminum. KA-Al3+ complex structures were studied using potentiometric and spectrophotometric (UV) titrations, FTIR and 13C NMR. The electronic spectroscopy showed that the KA-Al3+ complexes absorb at higher wavelengths (λmax= 305 nm) than do the non-complexed KA (λmax= 269 nm), confirming complexation. The IR spectra of KA complexed and not complexed allowed us to correlate the changes in the absorption of enol and carbonyl groups in absence and presence of Al3+ in aqueous solutions. The complexation suggested by the potentiometric titration and FTIR spectroscopy are in accordance with the data obtained from NMR results. Calculations based on quantum mechanics were utilized to understand the differences found in the noncomplexed and complexed KAH electronic spectra

In this study the coagulation-flocculation process was evaluated as an alternative for treatment of biodiesel wastewater. The role of two coagulants, Al3+ and Fe3+, as well as its dosage, pH, treatment time, stirring and aeration were evaluated. It was observed that in the treatment using Al3+ the pH of the effluent (9.7) does not need to be adjusted, while for Fe3+ a previous adjustment to pH 5.0 was necessary. On the other hand, a high concentration of Al3+ (243 mg L-1) and a relatively long treatment time (70 min) were required to reach more than 96% of turbidity removal, when compared to the processing using Fe3+ (56 mg L-1 and 53 min), attributed to the formation of different mole fractions of hydrolyzed cationic species. Under the optimized conditions, more than 96% of turbidity, apparent color and suspended solids, and 82% of oil and fats were removed.

In this study it was evaluated the role of the composition of sanitary landfill leachate on the removal of dissolved organic carbon (DOC) by photo-Fenton process. The composition of the matrix (high turbidity and color, as well as presence of inorganic ions sulfate and chloride) does not reduce the efficiency of DOC removal by photo-Fenton reactions, but influences significantly the reaction time and consumption of H2O2. An expressive increase in the efficiency of DOC removal occurred for concentrations of Fe2+ between 50 and 100 mg L-1, remaining constant in the range between 100 and 200 mg L-1. On the other hand, the pre-treatment of this effluent by coagulation-flocculation before the photo-Fenton process is recommended, since a similar efficiency of DOC removal, between 70 and 77%, was achieved using only 17% of the time and 7% of H2O2 necessary for the treatment of raw leachate treatment.

The photocatalytic performance of a composite based on the association of TiO2 and 2.5 wt.% of zinc(II) phthalocyanine (TiO2/ZnPc) was evaluated towards the mineralization of paracetamol and compared to that observed for the bare oxide in different pH and H2O2 concentrations. The results show that the photocatalytic performances were influenced by the pH, with maximum efficiency around the isoelectric point. Mineralization efficiencies between 86-91% was obtained using TiO2/ZnPc in pH 5.5-6.8, with 33 mg L-1 of H2O2, ca. 15% higher than that observed with TiO2. The mineralization efficiencies using bare TiO2 and TiO2/ZnPc were respectively 112 and 18% lower in the absence of H2O2. The better performance of TiO2/ZnPc is related to its extended light absorption and non-uniform coating of the TiO2 surface by ZnPc aggregates. Above pH 6.8, the mineralization efficiencies decrease for both photocatalysts, although the consumption of H2O2 remains above 90%, due to its decomposition in alkaline pH.

This paper aimed to study the mode of inclusion for 7-hydroxyflavone (7HF) in β-cyclodextrin (β-CD) complex in basic (pH 12) and acid (pH 4.5) media. The thermodynamic parameters of the complexation of 7HF with β-CD were evaluated by means of steady-state fluorescence and solubility measurements at several temperatures. The 7HF-β-CD inclusion complex was spontaneously formed at 1:1 stoichiometry in both basic and acid media. The high number of hydrogen bonds formed between the host and the guest molecules favored complexation in the basic medium, with a ground-state equilibrium constant (K) of 990 ± 130 mol-1 L, at 25 ºC. The quantum-mechanics calculations showed that complexation of 7HF (neutral or anionic form) with β-CD occurred mainly via the phenyl group of the flavonoid. This result agreed with the induced circular dichroism signal of 7HF complexed with β-CD.

In this study, we evaluated the combination between an electrochemical process, occurring in the dark, and a heterogeneous photocatalytic process for dye degradation, using the azo dye tartrazine as model of oxidizable substrate. TiO2 P25 and an Ag-doped TiO2 were used as photocatalysts in suspensions containing 50 mg L–1 of tartrazine. The best result, 74% of dye mineralization in 120 min of reaction, was obtained using TiO2 P25 as photocatalyst and a current density of 10 mA cm–2 in the electrochemical cell, a value 30% higher than the sum of the results obtained by heterogeneous photocatalysis (44%) and electrochemical oxidation (13%). The use of Ag-doped TiO2 did not result in significant improvement on tartrazine mineralization, due to the aggregation of these nanoparticles. Our results suggest that this process can be an alternative for a complete treatment (discoloration and mineralization) of tartrazine and most likely other azo dyes.

Crystalline (BiO)2CO3 nanosheets were synthesized by a rapid one-step reaction via microwave-assisted hydrothermal method using urea as a morphology mediator and carbon source. The hydrothermal method combined with microwave heating allowed to obtain sheet-like (BiO)2CO3 particles at shorter reaction times when compared to the conventional heating hydrothermal method. The photocatalytic activity of the as prepared samples was evaluated towards degradation of Ponceau 4R (C.I. 16255) under artificial UV-Vis light irradiation. The results show that good photocatalytic efficiency can be obtained for powders prepared with reaction times as low as 2 minutes.

A fotodegradação de cloranfenicol (CAP) em água ultrapura (UW), água superficial não tratada (USW), e efluente tratado de estação de tratamento de esgoto (TESTP) em escala de laboratório e planta piloto, foi avaliada usando radiação artificial e solar. Os resultados mostram, em todos os casos, que a degradação de CAP ocorre segundo uma cinética de pseudo-primeira ordem, com as constantes de velocidade de degradação aparente (k app) seguindo a ordem UW ≡ USW > TESTP. A k app e o tempo de meia-vida foram influenciados pela fonte de radiação. Produtos de transformação mono e di-hidroxilados foram identificados em UW após 40 min de irradiação solar, enquanto toxicidade aguda para Artemia salina aumentou de 35% para 100%, respectivamente após 180 e 1440 min, sob irradiação artificial e solar (94 e 132 kJ L-1), quando houve 99,2% e 97,7% de degradação de CAP. Os produtos de transformação não apresentaram atividade antimicrobiana.

The photodegradation of cloramphenicol (CAP) in ultrapure water (UW), untreated surface water (USW), and treated effluent from sewage treatment plant (TESTP) in laboratory scale and pilot scale, was evaluated using solar and artificial radiation. The results show, in all cases, that the CAP degradation occurs according to pseudo-first order kinetics, with the apparent degradation rate constants (k app) following the order UW ≡ USW > TESTP. The k app and half-life were strongly influenced by the radiation source. Mono- and di-hydroxyl transformation products were identified in UW after 40 min of solar irradiation, while the acute toxicity to Artemia salina increased from 35% to 100%, respectively after 180 and 1440 min of artificial and solar irradiation (94 and 132 kJ L-1), when 99.2 and 97.7% of CAP degradation occurred. The transformation products did not present antimicrobial activity.

Parâmetros que influenciam a eficiência da degradação do glifosato (adição única de Fe2+, adição simultânea de Fe2+ e Fe3+ numa razão molar de 1:1 (Fe2+/Fe3+), adição de íons oxalato e de H2O2) foram avaliados em escala de laboratório. Efeitos sinérgicos sobre a degradação e formação de fosfato foram observados utilizando a adição simultânea de Fe2+/Fe3+, bem como adicionando oxalato. Por outro lado, aumentos nas concentrações de Fe2+/Fe3+, oxalato e H2O2 não proporcionaram incremento linear da mineralização de glifosato e liberação de fosfato. Utilizando concentrações elevadas dessas espécies, a eficiência de mineralização de glifosato e de liberação de fosfato foi constante ou até mesmo reduzida. Sob condições otimizadas (0,27 mmol L-1 de Fe2+/Fe3+; 1,13 mmol L-1 de oxalato e 10,3 mmol L-1 de H2O2), os resultados obtidos em escala laboratorial e de planta piloto solar foram próximos. Uma relação direta entre a redução da toxicidade e concentração de glifosato também foi observada.

Parameters that influence the efficiency of the degradation of glyphosate (addition of Fe2+, simultaneous addition of Fe2+ and Fe3+ at a 1:1 (Fe2+/Fe3+) molar ratio, addition of oxalate and of H2O2) were evaluated at lab-scale. Synergic effects on its degradation and release of phosphate were observed using Fe2+/Fe3+, as well as adding oxalate. On the other hand, the concentration increase of Fe2+/Fe3+, oxalate and H2O2 did not promote a linear increase of glyphosate mineralization and release of phosphate. Using high concentrations of these species, the efficiency of glyphosate mineralization and release of phosphate was constant or even decreased. Under optimized conditions (0.27 mmol L-1 of Fe2+/Fe3+; 1.13 mmol L-1 of oxalate and 10.3 mmol L-1 of H2O2), close results for mineralization and release of phosphate were obtained in lab-scale and using a solar pilot plant. A direct ratio between reducing the toxicity and glyphosate concentration was also observed.

Este trabalho descreve a influência e otimização dos reagentes de Fenton (concentração de Fe2+ e H2O2) na eficiência da mineralização do herbicida paraquat (PQT, 50 mg L-1) em água, após 60 min (equivalendo a 642 kJ L-1 de radiação UVA acumulada) de tratamento por processo foto-Fenton em escala de laboratório, usando planejamento composto central (CCD). Sob condições otimizadas, experimentos cinéticos foram feitos, avaliando a remoção do PQT, sua mineralização e toxicidade em escala de laboratório, usando irradiação artificial, e em planta piloto sob irradiação solar. A mesma eficiência de remoção e mineralização do PQT foram obtidas em ambos os reatores utilizados. A toxicidade das amostras, estimada em termos de mortalidade de Artemia salina, diminui simultaneamente com o decaimento da concentração de PQT, sugerindo a formação de intermediários de menor toxicidade. Dessa maneira, o processo foto-Fenton/solar pode ser considerado uma alternativa viável para o tratamento de águas residuais contendo PQT.

This study describes the influence and optimization of Fenton's reagent (concentration of Fe2+ and H2O2 ) on the efficiency of mineralization of the herbicide paraquat (PQT, 50 mg L-1) in water, after 60 min (equivalent to 642 kJ L-1 of accumulated UVA radiation) treatment by photo-Fenton process in laboratory scale, using central composite design (CCD). Under optimized conditions, kinetic experiments were done, evaluating the PQT removal, its mineralization and toxicity in laboratory scale, using artificial irradiation, and in a pilot plant under solar irradiation. The same removal efficiency and mineralization of PQT were obtained in both reactors. The toxicity of the samples, estimated in terms of mortality of Artemia salina, decreases simultaneously with the decay of concentration of PQT, suggesting the formation of intermediates of lower toxicity. In this way, the solar photo-Fenton process can be considered as a viable alternative for the treatment of wastewater containing PQT.

Este estudo fornece uma avaliação teórica do comportamento fotofísico da ftalocianina de zinco (FtZn) usando teoria do funcional da densidade (DFT) e a sua abordagem dependente do tempo (TD-DFT), baseado na combinação do funcional híbrido B3LYP e o conjunto de base 6-311+G(d,p). A influência da solvatação foi estimada utilizando o método IEFPCM (modelo do contínuo polarizável) e considerando DMSO (dimetilsulfóxido) como solvente. Os espectros de absorção simulados foram baseados no cálculo dos primeiros 40 estados excitados sendo que os oito picos mais intensos podem ser atribuídos às bandas Q e Soret (B). Comprimento de onda de emissão de fluorescência e tempo de vida radiativo foram calculados utilizando a abordagem TD-DFT e comparados com dados experimentais. O fenômeno de cruzamento intersistema (CIS) da FtZn foi atribuído ao acoplamento spin-órbita induzida pelo Zn2+ pelo fato dos estados singlete e triplete adjacentes possuirem a mesma simetria orbital. Os dados de fosforescência em fase gasosa também foram comparados.

This study provides a theoretical evaluation of the photophysical behavior of zinc phthalocyanine (ZnPc) using density functional theory (DFT) and its time-dependent (TD-DFT) approach, based on the combination of the B3LYP hybrid functional and the 6-311+G(d,p) basis set. The influence of solvation was estimated using IEFPCM (integral equation formalism approach of polarizable continuum model) considering DMSO (dimethyl sulfoxide) as solvent. The simulated absorption spectra were based in the calculation of the first 40 excited states being that the eight most intense peaks could be assigned to the Q and Soret (B) bands. Fluorescence emission wavelength and radiative lifetime were calculated using the TD-DFT approach and compared to experimental data. The ZnPc intersystem crossing (ISC) phenomena was attributed to spin-orbit coupling induced by Zn2+ since the adjacent singlet and triplet states have the same orbital symmetry. The phosphorescence data in gas phase were also compared.