Efficient Nitrate Reduction in a Fluidized Electrochemical Reactor Promoted by Pd–Sn/AC Particles

Abstract

Pd–Sn modified activated carbon (Pd–Sn/AC) was prepared by impregnation of Pd and Sn salts onto AC followed by heat treatment. Based on scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis, Pd–Sn alloy was highly dispersed on the surface of AC with a atomic ratio of about 4.21. A double electrolysis cell was established and separated via a proton-exchange membrane. In the cathodic cell compartment, the as-prepared Pd–Sn/AC was used as particle electrodes where electrolytic reduction of nitrate was performed. A batch mode study showed that at an applied current of 30 mA with 7.5 g/L catalyst, over 90 % of the nitrate could be reduced in 80 min when the nitrate initial concentration was 24.6 mg/L. The electro-catalytic process of nitrate reduction could be satisfactorily described with a first-order kinetics model. With increasing applied current, the nitrate removal rate increased; whereas, the NH₄ ⁺ concentration increased as well. The inhibition effect of co-existing anions and cations on nitrate reduction followed this order: Fe³⁺ > Mn²⁺ > Ca²⁺ > Na⁺ and Cl⁻ < SO₄ ²⁻ < HCO₃ ⁻.

Graphical Abstract