Synthesis, characterization, and photocatalytic activity of pure and N-, B-, or Ag- Doped TiO2

This article reports the synthesis and characterization of pure and N-, B-, and Ag-doped TiO2 and the ability of these oxides to photodegrade methylene blue (MB) under sunlight or UV-ABC radiation. The compounds were synthesized using the sol-gel method and characterized by scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Photocatalytic efficiency was significantly increased by N-doping, resulting in 98% MB decomposition under UV-ABC irradiation for 180 min. Ag- and B-doped TiO2 lowered MB degradation rates to 52 and 73%, respectively, compared with pure TiO2. The same behavior was observed with exposure to UV-Vis, with 88, 65, 60, and 42% MB removal with N-doped, pure, B-doped, and Ag-doped TiO2, respectively. Under visible light alone, N-doped TiO2 exhibited higher photocatalytic efficiency than commercial P25-type TiO2. Photocatalysis with N-doped TiO2 proved to be a promising alternative for MB degradation, given the potential of employing solar energy, thus minimizing operating costs

Monitoramento de esporos de Phakopsora pachyrhizi em unidade de referência no município da Lapa-PR, como ferramenta para manejo da doença em soja – safra 2022/2023

Orientadora: Profª Drª Louise Larissa May De MioTrabalho de Conclusão de Curso (Especialização) - Universidade Federal do Paraná, Setor de Ciências Agrárias, Curso de Especialização em Fitossanidade.Resumo: A cultura da soja possui a maior relevância econômica no Brasil, porém há muitos fatores limitantes que podem interferir nas produtividades das lavouras. A Ferrugem Asiática (Phakopsora pachyrhizi) é considerada a principal doença fúngica que pode acometer a cultura, uma vez que os danos causados por essa doença representam até 90% de perdas, tendo em vista a agressividade da doença e sua disseminação. O Instituto de Desenvolvimento Rural do Paraná – IAPAR – EMATER (IDR-Paraná) em conjunto com e Empresa Brasileira de Pesquisa Agropecuária – Soja (EMBRAPA Soja), desenvolve o programa de Manejo Integrado de Doenças da Soja com ênfase em Ferrugem Asiática, utilizando como ferramenta o Coletor de Esporos que possibilita detectar os uredosporos do fungo disseminados pelo vento. Essa detecção antes do estabelecimento da doença na lavoura permite que o controle químico seja mais assertivo e evitando apenas aplicações calendarizadas. O presente estudo teve por objetivo apresentar os resultados do monitoramento de Phakopsora pachyrhizi em uma unidade de referência no município da LapaPR, na safra 2022/2023 e discutir manejo específico para esta área a partir da detecção com base nas premissas do manejo integrado de doenças. A variedade utilizada foi a BMX Zeus IPRO, semeada em 15 de novembro de 2022, em duas áreas sob mesmo manejo pré-plantio, porém uma área adotando-se o monitoramento de Phakopsora pachyrhizi por meio do coletor de esporos e a outra adotando-se o manejo convencional do agricultor. Na área do coletor de esporos foram realizadas apenas duas aplicações, sendo nos dias 08 e 29 de janeiro e 2023, utilizando os produtos comerciais Sphere Max (ciproconazol e trifloxistrobina) e Cronnos (picoxistrobina, tebuconazol e mancozebe), obtendo uma produtividade de 70,66 sacas/ha. Na área de manejo convencional, onde foram adotados os mesmos manejos pré-plantio de adubação, mesma cultivar utilizada, mesma data de plantio e em área na mesma localidade, foram realizadas quatro aplicações, sendo nos dias 20 de dezembro, 03 e 19 de janeiro e 05 de fevereiro alternado-se os produtos comerciais Sphere Max e Cronnos, obtendo uma produtividade de 61,98 sacas/ha

Influence of chelation on the Fenton-based electrochemical degradation of herbicide tebuthiuron

This study describes the performance of electro-Fenton (EF) and photoelectro-Fenton (PEF) processes to degrade the herbicide tebuthiuron (TBH) in 0.050 M Na2SO4 at pH = 3.0. Experiments were performed in an undivided cell equipped with a boron-doped diamond (BDD) or Pt anode and an air-diffusion cathode that produces H2O2. Physisorbed hydroxyl radicals (M(●OH)) generated from water oxidation at the anode and/or free ●OH formed from Fenton's reaction acted as main oxidants. All processes became much more effective using a BDD anode because of the higher oxidation power of BDD(●OH). Sulfate and nitrate were the predominant ions released during TBH destruction. In both, EF and PEF treatments, two distinct kinetic regimes were observed, the first one corresponding to the oxidation of free TBH by ●OH and the second one to that of the Fe(III)-TBH complex by M(●OH). The effect of Fe2+ and TBH concentrations on the kinetics of both regions has been examined. Moreover, a poor mineralization was reached with Pt anode, whereas almost total mineralization was attained by EF and PEF with BDD. Both processes showed analogous mineralization rates because the intermediates produced could not be photodegraded by UVA light. Gas chromatography-mass spectrometry analysis of electrolyzed solutions revealed the generation of eight heteroaromatics along with 1,3-dimethylurea, which have been included in a reaction pathway proposed for the initial degradation of TBH

Treatment of single and mixed pesticide formulations by solar photoelectro-Fenton using a flow plant

Solutions of single real formulations of herbicides tebuthiuron and ametryn have been degraded by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and solar photoelectro-Fenton (SPEF). The assays were made in a flow plant of 2.5 L equipped with a boron-doped diamond (BDD)/air-diffusion cell and a solar planar photoreactor. Main oxidants were hydroxyl radicals formed from water discharge at the BDD anode and in the bulk from Fenton's reaction between added Fe2+ and cathodically generated H2O2. Partial mineralization was achieved for all the treatments, with the relative oxidation ability growing in the sequence: AO-H2O2 < EF < SPEF. The superiority of SPEF over EF was related to the contribution of photo-oxidation of intermediates and/or their Fe(III) complexes upon sunlight irradiation. No short-linear carboxylic acids were identified, whereas heteroatoms were mainly released as NO3- and SO42- ions. For herbicide contents < 0.18 mM in EF and SPEF, a very rapid pseudo-first-order decay kinetics was related to the oxidation of the Fe(II) complexes of each herbicide at short time, whereupon a much slower pseudo-first-order kinetics associated with the decay of their Fe(III) complexes was observed. Ametryn disappeared more quickly than tebuthiuron, but its solutions were more poorly mineralized. The effect of j and substrate concentration on the performance of SPEF was examined. Mixtures of both formulations were efficiently treated by SPEF, showing similar but slower decays than single solutions. Four primary heteroaromatic products were detected by GC-MS upon prolonged electrolysis of an equimolar mixture. Our results indicate that SPEF is viable for the treatment of water contaminated with tebuthiuron and ametryn herbicides, either single or mixed

Influence of electrolysis conditions on the treatment of herbicide bentazon using artificial UVA radiation and sunlight. Identification of oxidation products

The main objective of this work is to demonstrate the viability of solar photoelectro-Fenton (SPEF) process to degrade pesticides in urban wastewater matrix, selecting the herbicide bentazon as a model molecule. In order to provide a correct assessment of the role of the different oxidants and catalysts involved, bentazon was comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and UVA-assisted EF (i.e., PEF) processes as well, either in sulfate or chloride media. Trials were made in a stirred tank reactor with an air-diffusion cathode and a boron-doped diamond (BDD), RuO2-based or Pt anode. In chlorinated matrices, the herbicide disappeared more rapidly using a RuO2-based anode because of the generated active chlorine. The best mineralization performance was always obtained using BDD due to its higher oxidation power, which allowed the complete destruction of refractory chloroderivatives. A concentration of 0.50 mM Fe2+ was found optimal to catalyze Fenton's reaction, largely enhancing the mineralization process under the action of OH. Among photo-assisted treatments, sunlight was proven superior to a UVA lamp to promote the photolysis of intermediates, owing to its greater UV irradiance and contribution of visible photons, although PEF also allowed achieving a large mineralization. In all cases, bentazon decay obeyed a pseudo-first-order kinetics. SPEF treatment in urban wastewater using BDD at only 16.6 mA cm−2 yielded 63.2% mineralization. A thorough, original reaction pathway for bentazon degradation is proposed, including seven non-chlorinated aromatics, sixteen chloroaromatics and two chloroaliphatics identified by GC-MS, most of them not previously reported in literature. Ion-exclusion HPLC allowed the detection of seven short-chain linear carboxylic acids

Degradation of the insecticide propoxur by electrochemical advanced oxidation processes using a boron-doped diamond/air-diffusion cell

A solution with 0.38 mM of the pesticide propoxur (PX) at pH 3.0 has been comparatively treated by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). The trials were carried out with a 100 mL boron-doped diamond (BDD)/air-diffusion cell. The EO-H2O2 process had the lowest oxidation ability due to the slow reaction of intermediates with ¿OH produced from water discharge at the BDD anode. The EF treatment yielded quicker mineralization due to the additional ¿OH formed between added Fe2+ and electrogenerated H2O2. The PEF process was the most powerful since it led to total mineralization by the combined oxidative action of hydroxyl radicals and UVA irradiation. The PX decay agreed with a pseudo-first-order kinetics in EO-H2O2, whereas in EF and PEF it obeyed a much faster pseudo-first-order kinetics followed by a much slower one, which are related to the oxidation of its Fe(II) and Fe(III) complexes, respectively. EO-H2O2 showed similar oxidation ability within the pH range 3.0-9.0. The effect of current density and Fe2+ and substrate contents on the performance of the EF process was examined. Two primary aromatic products were identified by LC-MS during PX degradation

Antituberculosis drug isoniazid degraded by electro-Fenton and photoelectro-Fenton processes using a boron-doped diamond anode and a carbon-PTFE air-diffusion cathode

Solutions with 0.65 mM of the antituberculosis drug isoniazid (INH) in 0.050 M Na2SO4 at pH 3.0 were treated by electro-Fenton (EF) and UVA photoelectro-Fenton (PEF) processes using a cell with a BDD anode and a carbon-PTFE air-diffusion cathode. The influence of current density on degradation, mineralization rate, and current efficiency has been thoroughly evaluated in EF. The effect of the metallic catalyst (Fe2+ or Fe3+) and the formation of products like short-chain linear aliphatic carboxylic acids were assessed in PEF. Two consecutive pseudo-first-order kinetic regions were found using Fe2+ as catalyst. In the first region, at short time, the drug was rapidly oxidized by ●OH, whereas in the second region, at longer time, a resulting Fe(III)-INH complex was much more slowly removed by oxidants. INH disappeared completely at 300 min by EF, attaining 88 and 94% mineralization at 66.6 and 100 mA cm-2, respectively. Isonicotinamide and its hydroxylated derivative were identified as aromatic products of INH by GC-MS and oxalic, oxamic, and formic acids were quantified by ion-exclusion HPLC. The PEF treatment of a real wastewater polluted with the drug led to slower INH and TOC abatements because of the parallel destruction of its natural organic matter content

Degradation of 4-aminoantipyrine by elecro-oxidation with a boron-doped diamond anode: optimization by central composite design, oxidation products and toxicity

Electro-oxidation with electrogenerated H2O2 (EO-H2O2) was applied to treat acidic aqueous solutions of 4-aminoantipyrine (4-AA), a persistent drug metabolite of dipyrone, in sulfate medium. Trials were made using a boron-doped diamond anode in the presence of H2O2 electrogenerated on site. A 24 central composite design (CCD) was employed to evaluate the effect of four independent variables, namely current density (j), pH, 4-AA concentration and electrolysis time, on the percentages of degradation and mineralization, as well as on mineralization current efficiency (MCE). Predicted responses agreed with observed values, showing linear trendlines with good R2 and R2adj values. The degradation was optimum at j = 77.5 mA cm-2, pH 3.5 and 62.5 mg L-1 4-AA, leading to 63% and 99% removal after 3 and 7 min, respectively. For those solutions, the largest mineralization was found at j = 77.5 mA cm-2, attaining 45% abatement at 175 min. Low MCE values were obtained in all electrolyses. An initial route for 4-AA degradation is proposed based on one dimer and eleven aromatic and aliphatic intermediates detected in the treated solutions at pH 3.5 by LC-MS. The initial 62.5 mg L-1 solution at pH 3.5 presented acute toxicity on Artemia salina larvae, with LC50 = 13.6 mg L-1, being substantially reduced after 3 and 7 min of EO-H2O2 at j = 77.5 mA cm-2 due to the formation of less toxic derivatives

Ensuring the overall combustion of herbicide metribuzin by electrochemical advanced oxidation processes. Study of operation variables, kinetics and degradation routes

This article reports the electrochemical degradation of the herbicide metribuzin (MTZ) in sulfate medium by advanced oxidation processes like anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF). A boron-doped diamond (BDD) anode was combined with an air-diffusion cathode with ability to produce H2O2. Unprecedented overall combustion was feasible by all methods at a constant current density (j) ≥100.0 mA cm−2. The total organic carbon (TOC) removal achieved by AO-H2O2 was independent from pH within the range 3.0-9.0, whereas the oscillatory dependence of the pseudo-first-order MTZ decay rate constant with this variable was ascribed to adsorption on the BDD surface. In EF and PEF at pH 3.0, 0.50 mM Fe2+ was determined as optimum catalyst content and the MTZ removal showed two consecutive pseudo-first-order kinetic stages. These were related to the fast reaction of the target molecule with OH formed from Fenton's reaction, followed by a slower attack of physisorbed BDD(OH) onto Fe(III)-MTZ complexes. The effect of j and MTZ content on decay kinetics and TOC removal was examined. PEF was the best treatment due to the decomposition of photoactive intermediates by UVA radiation, yielding total mineralization of a 0.523 mM herbicide solution after 420 min of electrolysis at 100.0 mA cm−2. A thorough reaction pathway for MTZ degradation is proposed from the sixteen heteroaromatic by-products and three aliphatic molecules identified by GC-MS and LC-MS/MS. Oxalic and oxamic acids were detected as final carboxylic acids by ion-exclusion HPLC