Due to the discharge of industrial wastewater and the misuse of agricultural fertilizers, the negative consequences of excess nitrate in water on human productivity and lives have drawn more attention. An extensive investigation of the pressing need for and difficulty with effective nitrate removal has been made by a team of researchers from all over the world.
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There are several methods for removing nitrate from water, including biological denitrification, which is well-developed technologically, economical, and widely employed. But biological processes frequently move slowly and are easily influenced by shifting environmental factors, such as temperature and the availability of carbon supplies.
Due to the lack of chemicals necessary, the lack of sludge created, and the ease of implementation, the researchers recommended electrocatalytic technology as a potential technique for removing nitrate.
For electrocatalytic nitrate reduction, traditional plate cathodes are most frequently utilized in parallel plate reactors where a mass transfer is severely constrained. As a result, the overall rate of electrocatalytic nitrate reduction declines.
Novel reactive electrochemical membranes (REMs) for nitrate reduction have been described in the past, but their practical use has been hampered by difficult synthetic procedures and expensive preparation costs.
Researchers from Wuhan University and Minzu University in China developed a Pd-Cu-modified carbon nanotube membrane that was utilized to decrease nitrate in a flowthrough electrochemical reactor to overcome these obstacles.
According to their study, the membrane that was produced with a Pd:Cu ratio of 1:1 had a comparatively high nitrate removal efficiency and N2 selectivity. The study named “Electrocatalytic reduction of nitrate using Pd-Cu modified carbon nanotube membranes” was published online in Frontiers of Environmental Science & Engineering in 2023.
To solve the mass transfer issue during nitrate reduction, the research team created a unique Pd-Cu modified carbon nanotube membrane cathode on a polyvinylidene fluoride (PVDF) substrate for this study.
Nitrate reduction was first carried out with Pd-Cu-modified CNT membranes with various potentials ranging from –2.0 to –0.4 V to establish the ideal potential for electrocatalytic nitrate reduction in flow-through mode.
The researchers reported that the findings of linear scan voltammetry for CNT membranes in various solutions showed that the ideal potential and time for the codeposition of Pd and Cu were 0.7 V and 5 minutes, respectively.
The impact of the electrode potential and Pd-Cu molar ratio on nitrate removal was the subject of the team’s second investigation. The researchers found that the membrane it produced had a Pd:Cu ratio of 1:1 and that it had reasonably excellent N2 selectivity and nitrate removal effectiveness.
At potentials –1.2 V, the membrane eliminated nitrate almost entirely (by 99%). However, in terms of both nitrate removal effectiveness and product selectivity, –0.8 V was the ideal potential for nitrate reduction. For the Pd: Cu=1:1 membrane running at –0.8 V, the nitrate removal efficiency was 56.2% and the N2 selectivity was 23.8%.
The impact of solution conditions was the next issue that the team looked at. They discovered that while N2 selectivity was reduced in acidic environments, nitrate removal was enhanced. Nitrate reduction was not significantly impacted by the Cl ion and dissolved oxygen concentrations.
The team also assessed the impact of membrane flux on nitrate reduction and calculated the mass transfer rate constants at various membrane fluxes to highlight the influence of flow-through operation on mass transfer.
They state that the nitrate removal rate significantly increased from 13.6 to 133.5 mg/(m2h) as a consequence of the mass transfer rate constant being significantly enhanced by 6.6 times, going 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/(m2h).
A flow-through electrocatalytic system was built in this study to decrease nitrate, and Pd-Cu-modified CNT membranes were successfully produced using the electrodeposition technique. It is important to continue modifying this technology in practice since it offers a wide range of potential applications for efficient nitrate reduction.
Journal Reference
Liu, Z., et al. (2022) Electrocatalytic reduction of nitrate using Pd-Cu modified carbon nanotube membranes. Frontiers of Environmental Science & Engineering. doi:10.1007/s11783-023-1640-1.