Electrocatalytic reduction of nitrate using Pd-Cu modified carbon nanotube membranes

Abstract

● Pd-Cu modified CNT membranes were prepared successfully by electrodeposition method.

● The deposition voltage and deposition time were optimized for Pd-Cu co-deposition.

● NO₃⁻-N was removed efficiently from water by Pd-Cu modified CNT membranes.

● The presence of dissolved oxygen did not affect the nitrate reduction performance.

● Mass transfer rate was promoted significantly with the increase in membrane flux.

Excessive nitrate in water is harmful to the ecological environment and human health. Electrocatalytic reduction is a promising technology for nitrate removal. Herein, a Pd-Cu modified carbon nanotube membrane was fabricated with an electrodeposition method and used to reduce nitrate in a flow-through electrochemical reactor. The optimal potential and duration for codeposition of Pd and Cu were −0.7 V and 5 min, respectively, according to linear scan voltammetry results. The membrane obtained with a Pd:Cu ratio of 1:1 exhibited a relatively high nitrate removal efficiency and N₂ selectivity. Nitrate was almost completely reduced (~99 %) by the membrane at potentials lower than −1.2 V. However, −0.8 V was the optimal potential for nitrate reduction in terms of both nitrate removal efficiency and product selectivity. The nitrate removal efficiency was 56.2 %, and the N₂ selectivity was 23.8 % for the Pd:Cu=1:1 membrane operated at −0.8 V. Nitrate removal was enhanced under acidic conditions, while N₂ selectivity was decreased. The concentrations of Cl⁻ ions and dissolved oxygen showed little effect on nitrate reduction. The mass transfer rate constant was greatly improved by 6.6 times from 1.14 × 10⁻³ m/h at a membrane flux of 1 L/(m²·h) to 8.71 × 10⁻³ m/h at a membrane flux of 15 L/(m²·h), which resulted in a significant increase in the nitrate removal rate from 13.6 to 133.5 mg/(m²·h). These findings show that the Pd-Cu modified CNT membrane is an efficient material for nitrate reduction.

Graphical abstract

Keywords

Pd-Cu modified CNT membrane / Nitrate reduction / Flow-through / Electrodeposition / Electrocatalytic reduction

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