This paper reports the development of a glassy carbon electrode modified with a reduced graphene oxide (r-GO/GCE) for the determination of the food dye named Ponceau 4R (PNC). The modified sensor presented excellent signal gain in relation to the GCE and GCE modified with graphene oxide besides exhibiting well defined oxidation peaks for PNC at potential of 0.61 V. Through the application of square wave voltammetry using the medium of 0.1 mol L-1 Britton-Robinson (BR) buffer (pH 5.0), analytical curves were constructed under optimized conditions, where linear regions were found within the range of 0.200 to 20.0 μmol L-1. The limits of detection and quantification were 2.84 × 10-8 and 9.46 × 10-8mol L-1, respectively. The sensor was successfully applied towards the determination of PNC in instant juice sample. A comparison made between the result obtained through the application of this sensor and via the high-performance liquid chromatography (HPLC) technique showed no significant difference between the two methods.

The present work investigates the use of W/WO3 electrodes prepared by electrochemical anodization applied in the photoelectrocatalytic disinfection of Candida parapsilosis using ultraviolet-visible (UV-Vis) and visible irradiation. The core objective of this work lies in describing a novel approach involving the use of chloride as supporting electrolyte, aiming at achieving a faster inactivation and towards understanding its behavior in water containing high chloride content. The best experimental conditions were found to be at pH 7.0 and 0.1 mol L-1 NaCl when the photoelectrode was biased at 1.5 V (vs. Ag/AgCl) illuminated by both UV-Vis and visible light. It is suggested that charges photogenerated on the electrode surface give rise preferably to HO•, known to be powerful oxidant that causes the total inactivation of the microorganism (1 min of treatment) while engendering around 84% of mineralization of organic matter released from the cell damage following 120 min of treatment.

O presente trabalho descreve uma nova metodologia para remoção de nitrito de águas contaminadas usando o processo fotoeletrocatalítico. Um eletrodo de nanotubos de Ti/TiO2 foi utilizado como fotocátodo sob irradiação UV e potencial aplicado -0,2 V vs. Ag/AgCl e levou a remoção de 100% do nitrito após 6 min de fotoeletrocatálise em solução de NaCl 7 mmol L-1, pH 7 e ausência de oxigênio dissolvido. A redução de nitrito sobre o eletrodo de Ti/TiO2 ocorre no compartimento catódico da célula pelos elétrons fotogerados quando o eletrodo é irradiado com luz UV, gerando 7% de amônio e 93% de espécies gasosas de nitrogênio após 6 min de tratamento. Os resultados indicam que o método pode ser uma ferramenta eficiente para o tratamento de águas contaminadas com nitrito.

The present work describes a suitable method for removing nitrite contaminant from water by using a photoelectrocatalytical method. A Ti/TiO2 nanotube electrode was used as a cathode under UV irradiation and applied potential of -0.2 V vs. Ag/AgCl and it led to 100% of nitrite removal after 6 min of photoelectrolysis conducted in NaCl 7 mmol L-1, pH 7 and in absence of dissolved oxygen. Nitrite reduction on Ti/TiO2 photoelectrodes occurs in the cathodic compartment cell via electrons generated when the electrode is under UV irradiation leading to a generation of 7% of remaining ammonium and 93% nitrogen containing gaseous species after 6 min of treatment. The results indicate that the method could be an efficient tool for the treatment of nitrite in water containing nitrite.

Nanotubos de TiO2 (TiO2NTs) foram decorados com nanopartículas de Pt via deposição catódica. Estas nanopartículas foram uniformemente distribuídas, altamente separadas e espaçadas sobre toda a superfície do TiO2NT para o menor tempo de deposição, com os tamanhos das partículas de Pt proporcionais às cargas aplicadas. O fotoeletrodo de Pt/TiO2NTs apresentou intenso pico de absorção na região do visível com significativo deslocamento para vermelho induzido pela platina depositada na superfície do TiO2NTs, diminuindo a energia do band gap de 3,21 eV para 2,87 eV. O fotoeletrodo de Pt/TiO2NTs foi testado na oxidação fotoeletrocatalítica do corante Vermelho Ácido 29 com grande sucesso. Descoloração total e 92% de remoção do carbono orgânico total foram obtidos após 120 min de tratamento empregando o fotoeletrodo de Pt/TiO2NTs, o qual apresentou valores superiores aos do não-decorado (87% e 68%, respectivamente), devido ao melhor uso da radiação e da minimização da recombinação de carga.

Pt nanoparticles were decorated on TiO2 nanotube arrays (TiO2NTs) by cathodic deposition. These nanoparticles were uniformly distributed, highly separated and spaced all over TiO2NT surface to shorten deposition times with Pt particle sizes proportional to the applied charges. The Pt/TiO2NT photoelectrode shows an intense absorption peak in the visible region with a significant red shift induced by Pt deposited on TiO2NT surface, decreasing the band gap energy from 3.21 eV to 2.87 eV. Pt/TiO2NT photoelectrode was tested as photoanode in the photoeletrocatalytic oxidation of Acid Red 29 dye with great success. Total decolorization and 92% of total organic carbon removal were obtained after 120 min of treatment by using Pt/TiO2NT photoelectrode which was superior to the values obtained for the undecorated one (87% and 68%, respectively) due to better use of irradiation and minimization of charge recombination.

As porfirinas aniônicas 5,10,15-tris(4-carboxifenil), 20-mono(2-nitrofenil) porfirina (1), 5,10(ou 15)-bis(4-carboxifenil), 15(or 10),20-bis(2-nitrofenil)porfirina (2) and 5-mono(4-carboxifenil), 10,15,20-tris(2-nitrofenil)porfirina (3), foram sintetizadas diretamente através da reação de pirrol com os benzaldeídos substituídos em meio de ácido propiônico/nitrobenzeno. A relação molar dos benzaldeídos foi controlada para otimizar a síntese e purificação das porfirinas desejadas. Esta nova série de porfirinas foi caracterizada por cromatografia em camada delgada, espectrometria de massas (FAB MS), RMN ¹H, UV/Vis, IV e eletroquímica. As porfirinas 5,10,15,20-tetrakis(4-carboxifenil)porfirina (4) e 5,10,15,20-tetrakis(2-nitrofenil)porfirina (5) também foram estudadas para comparação, tornando a série completa. A redução eletroquímica das porfirinas base livre e correspondentes ferro(III) porfirinas foi investigada em eletrodos de carbono e mercúrio. Os potenciais de redução mostraram a dependência esperada do número de grupos nitro, fortemente retirador de elétrons, presentes no anel porfirínico, fornecendo evidências adicionais para a caracterização dos compostos sintetizados.

The anionic 5,10,15-tris(4-carboxyphenyl), 20-mono(2-nitrophenyl) porphyrin (1), 5,10(or 15)-bis(4-carboxyphenyl), 15(or 10),20-bis(2-nitrophenyl)porphyrin (2) and 5-mono(4-carboxyphenyl), 10,15,20-tris(2-nitrophenyl)porphyrin (3) were sinthesized directly by reaction of pyrrole with substituted benzaldehydes in nitrobenzene/propionic acid media. The benzaldehydes molar ratio was controlled to optimize the synthesis and purification of the desired porphyrins. This new series of porphyrins was characterised by TLC, mass spectrometry (FAB MS), ¹H NMR, UV/Vis, IR and electrochemistry. 5,10,15,20-Tetrakis(4-carboxyphenyl)porphyrin (4) and 5,10,15,20-Tetrakis(2-nitrophenyl)porphyrin (5) were also characterised for comparative purposes, completing the series The electrochemical reduction was investigated for the free base and corresponding iron(III) porphyrins on glassy carbon and mercury electrodes. The reduction potentials showed the expected dependence on the number of electron-withdrawing nitro groups present on the porphyrin ring providing additional evidences for the characterisation of the synthesised compounds.