Nitrate Reduction with Pd-Cu Modified Nanotube Membrane
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 life have attracted more and more attention. Extensive investigations of the urgent needs and difficulties with effective nitrate removal have been carried out by research teams from around the world.
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There are several methods for removing nitrates from water, including biological denitrification, which are technologically well developed, economical, and widely used. But biological processes are often slow-moving and easily affected by changing environmental factors, such as temperature and the availability of carbon supplies.
Due to the lack of necessary chemicals, the lack of sludge generated, and the ease of implementation, the researchers recommend electrocatalytic technology as a potential technique for nitrate removal.
For electrocatalytic nitrate reduction, the traditional plate cathode is most often used in parallel plate reactors where mass transfer is severely restricted. Consequently, the overall rate of electrocatalytic reduction of nitrate decreases.
New reactive electrochemical (REM) membranes for nitrate reduction have been described in the past, but their practical use is hampered by difficult synthetic procedures and high cost of preparation.
Researchers from Wuhan University and Minzu University in China developed a Pd-Cu-modified carbon nanotube membrane used to degrade nitrate in a flowthrough electrochemical reactor to overcome this obstacle.
According to their research, membranes produced with a Pd:Cu ratio of 1:1 had relatively high nitrate and N removal efficiency.2 selectivity. The study named “Electrocatalytic reduction of nitrate using a modified Pd-Cu carbon nanotube membrane” was published online at Frontier of Environmental Science & Engineering in 2023.
To overcome the problem of mass transfer during nitrate reduction, the research team fabricated a unique Pd-Cu-modified carbon nanotube membrane cathode on polyvinylidene fluoride (PVDF) substrate for this study.
Nitrate reduction was first carried out with Pd-Cu modified CNT membranes with potentials ranging from –2.0 to –0.4 V to establish the ideal potential for electrocatalytic nitrate reduction in the flow-through mode.
The researchers reported that linear scan voltammetry findings for CNT membranes in various solutions indicated that the ideal potentials and times for the Pd and Cu codepositions were 0.7 V and 5 min, respectively.
The impact of electrode potential and Pd-Cu molar ratio on nitrate removal became the subject of investigation by the two teams. The researchers found that the resulting membrane has a Pd:Cu ratio of 1:1 and has a fairly good N content.2 selectivity and effectiveness of nitrate removal.
At a potential of –1.2 V, the membrane eliminates nitrate almost completely (99%). However, both in terms of effectiveness of nitrate removal and product selectivity, -0.8 V is the ideal potential for nitrate reduction. For a Pd:Cu=1:1 membrane operating at –0.8 V, the nitrate removal efficiency was 56.2% and N2 selectivity was 23.8%.
Impact of solution conditions was the next issue the team looked at. They found that while N2 selectivity decreases in an acidic environment, nitrate removal is enhanced. Nitrate reduction was not significantly affected by Cl ions and dissolved oxygen concentrations.
The team also assessed the impact of membrane flux on nitrate reduction and calculated mass transfer rate constants at various membrane fluxes to highlight the influence of flow-through operations on mass transfer.
They stated that the nitrate removal rate increased significantly from 13.6 to 133.5 mg/(m2h) as a consequence of the mass transfer rate constant which was significantly increased by 6.6 times, from 1.14×10–3 m/h at a membrane flux of 1 L/(m2 h) up to 8.71×10–3 m/h at a membrane flux of 15 L/(m2H).
A flow-through electrocatalytic system was constructed in this study to degrade nitrate, and Pd-Cu modified CNT membranes were successfully produced using the electrodeposition technique. It is important to continue to modify this technology in practice as it offers a wide range of potential applications for efficient nitrate reduction.
Liu, Z., et al. (2022) Electrocatalytic reduction of nitrate using a Pd-Cu modified carbon nanotube membrane. Frontier of Environmental Science & Engineering. doi:10.1007/s11783-023-1640-1.