Nitrite reduction on a multimetallic porphyrin/polyoxotungstate layer-by-layer modified electrodes

Abstract

Artículo de publicaciónElectro and photoelectrochemical reduction of nitrite in aqueous solution was studied using a multielectrocatalysts modified ITO electrode. ITO modification was carried out using the layer-by-layer (LBL) method, where sequential electrostatic assemblies were formed using a mu,-(meso-5,10,15,20-tetra (pirydil)porphyrin)tetrakisfbis(bipyridine)chloride ruthenium (11)} [MTRP](n+), coordinated in its central cavity with Mn(III), Zn(II) or Ni(II) as a cationic layer, and polyoxotungstate [SiW12O40](4) as the anionic layer. Electrochemical measurements and UV-vis spectroscopy were used to monitor the modification process. Optimal results were obtained when three layers were deposited onto the ITO surface and were stable in aqueous solution. The order of the multilayer formation was explored by comparing a modified electrode where [Zn(11)TRP](4+) was the outermost layer with an electrode where [SiW12O40](4) was the outer layer. Results show that the best performing electrode is one with [SiW12O40](4) as the outer layer. Nitrite reduction on these electrode surfaces was studied in dark conditions and under light irradiation. Potential controlled electrolysis experiments were also performed, finding hydroxylamine, hydrazine and ammonia as the reduction products in dark conditions. Under light irradiation, only hydrazine and ammonia were found and, we observed an increase in the amount of obtained product. In this case, the electrolysis was carried out 150 mV less and half of time than in dark conditions. These results show that the combination of light and potential give rise to an improvement in the electrocatalytic properties of the modified electrodes. Continuous photolysis and IR spectroelectrochemical experiments were carried out to determinate the nature of this phenomena, evidencing the formation of an intermediary species between nitrite and [Mn(111)TRP](5+.).FONDECYT 1141199 RC130006 3140085 1120071 3140565 315022

Performance eletrocatalítica frente a nitrito de um filme híbrido de fosfomolibdato e sílica organomodificada

“…A sensibilidade frente a nitrito obtida a partir da figura 2B foi de 5.66 μA cm -2 mmol -1 L enquanto o limite de detecção, calculado como três vezes o desvio padrão da densidade de corrente para o filme de ormosil de TMPM e HPMo na ausência de nitrito, foi de 7.8 x 10 -7 mol L -1 . Os principais produtos oriundos da eletroredução de nitrito em meio neutro foram amônia, hidrazina e hidroxilamina [16], enquanto que em meio ácido, o mecanismo proposto sugere que o produto seja óxido nítrico [17].…”

“…Uma propriedade dos POMs que os torna atrativos para estudos envolvendo sistemas híbridos para aplicações em sensores ópticos e eletroquímicos [12][13][14] é a capacidade que eles possuem de manter a estrutura íntegra mesmo após reações sucessivas de transferência de elétrons [15]. A detecção eletroquímica de algumas moléculas como nitrito [16,17], bromato [18], iodato [19] e herbicidas triazínicos [20,21] utilizando POMs imobilizados já tem sido reportada na literatura.…”

“…Embora nitrito já tenha sido detectado eletroquimicamente por POMs suportados em diferentes matrizes [16,17,[22][23][24], o uso de ormosil como matriz de imobilização de POMs para posterior detecção de nitrito ainda não foi alvo de estudo. As principais razões para o estudo da detecção de nitrito surgem em decorrência do seu enorme uso na conservação de alimentos [25] e também ao fato de que seu consumo está relacionado com o desenvolvimento de tumores em humanos [26].…”

Polyoxometalates-Functionalized Electrodes for (Photo)Electrocatalytic Applications: Recent Advances and Prospects

“…So, Keggin-, Dawson-, and crown-type POMs and their transition metal ion-substituted derivatives have been assembled with various cationic components, such as redox-active Ru­(II) metallodendrimers, metal-complexed porphyrins, or nonelectroactive polymer layers, to produce functional electrodes which were active for the electrocatalytic reduction of some oxyanionic species (e.g., nitrite), hydrogen peroxide reduction, or oxidation of methanol (Table ). − Compared with POMs-incorporating ECP films, such assemblies offer some benefits such as enhanced permeability, better robustness over electrochemical cycling, and better resistance against some interferents. Interestingly, the assembly with redox-active cationic complexes enabled extension of the electroactivity window of the functional electrodes window. − , Furthermore, additional incorporation of metal nanoparticles (e.g., Ag), denoted NPs hereafter, was found to be also beneficial for increasing the electronic conductivity of such assemblies. − …”

“… − Compared with POMs-incorporating ECP films, such assemblies offer some benefits such as enhanced permeability, better robustness over electrochemical cycling, and better resistance against some interferents. Interestingly, the assembly with redox-active cationic complexes enabled extension of the electroactivity window of the functional electrodes window. − , Furthermore, additional incorporation of metal nanoparticles (e.g., Ag), denoted NPs hereafter, was found to be also beneficial for increasing the electronic conductivity of such assemblies. − …”