Nitrite anodic oxidation at Ni(II)/Ni(III)-decorated mesoporous SnO₂ and its analytical applications

Hydrothermally formed mesoporous SnO₂ was used as a support for nickel chemical deposition and, after subsequent thermal treatment, a high specific surface area (36 m² g^-1) Ni/SnO₂ material was obtained. XPS analysis has shown that in the Sn 3d region the spectrum is similar to that of pristine SnO₂, whereas Ni species are present on the surface as NiO, Ni₂O₃ and Ni(OH)₂. Mixing Ni/SnO₂ with a small amount of Black Pearls (BP) leads to a significant enhancement of the resulting Ni/SnO₂-BP composite activity for nitrite anodic oxidation, presumably due to the higher surface area (115 m² g^-1), to better electrical conductivity and to a certain contribution of the BP to an increase in surface density of the active sites. Ni/SnO₂-BP also outperforms pristine BP (in terms of Tafel slopes and electron-transfer rates), most likely due to the fact that the Ni(II)/Ni(III) couple can act as an electrocatalyst for nitrite oxidation. A voltammetric method is proposed for the determination of nitrite, over a concentration range of three orders of magnitude (0.05 to 20 mM), with good reproducibility, high stability and excellent sensitivity. The high upper limit of the dynamic range of the analytically useful response might provide a basis for the reliable quantification of nitrite in wastewater.