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

Highlights

● 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.

Abstract

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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Acknowledgements

This work was supported by grants from the National Natural Science Foundation of China (Nos. 52070147 and 52270077), the Special Fund of the State Key Joint Laboratory of Environment Simulation and Pollution Control (No. 22K06ESPCT), and the Promotion Plan for Young Teachers’ Scientific Research Ability of Minzu University of China (Nos. 2021QNPY83 and 2022QNPY51).

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-023-1640-1 and is accessible for authorized users.

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