Associate Professor Huang Xinhua from the School of Materials Science and Engineering at Anhui University of Science and Technology has made new advancements in the field of capacitive deionization. They have developed nitrogen-phosphorus co-doped carbon-based materials and phosphorus-dispersed iron-doped porous carbon electrode materials, which have been utilized for the high-selective removal of heavy metal copper ions from wastewater. The related research findings have been successively published in "Desalination" and "Journal of Chemical Engineering".
A schematic diagram illustrating the efficient adsorption of copper ions by nitrogen-phosphorus co-doped carbon materials. Image provided by Anhui University of Science and Technology.
"Atom doping is considered an effective method for improving electrode properties. However, currently, electrode materials doped solely with nitrogen often suffer from spatial hindrance during usage. By further introducing phosphorus on the basis of nitrogen doping, the inherent defects in carbon matrix can be strengthened through the synergistic co-doping of nitrogen and phosphorus, optimizing electron distribution, thereby improving the capacitance deionization performance," explained Huang Xinhua to Chinese Science Bulletin.
Huang Xinhua utilized non-toxic phytic acid as a phosphorus source and, based on nitrogen doping, prepared nitrogen-phosphorus co-doped carbon materials through in-situ pyrolysis for the adsorption of heavy metal copper ions, testing their stability performance through continuous adsorption-desorption cycling.
An illustrative diagram depicts the optimized adsorption of copper ions by vacancy strategy in iron phosphide dispersed nitrogen and phosphorus co-doped carbon material. Image credit: Anhui University of Science and Technology.
Iron phosphide stands out as a promising electrode material due to its high theoretical capacity and environmentally friendly properties.
However, the sluggish diffusion kinetics of pure iron phosphide materials during electrochemical processes hinder rate performance, leading to a significant capacity decay during cycling. Researchers can address these limitations by primarily enhancing diffusion coefficients and shortening the diffusion paths of charge.
Xin-Hua Huang utilized nitrogen and phosphorus-doped polymer adsorbed with iron nitrate as a precursor, achieving the in-situ generation of iron phosphide nanoparticles in a carbon-based framework through a pyrolysis process, thus preparing electrode materials.
"The study demonstrates that the introduction of phosphorus vacancies not only increases the conductivity of the material but also provides more active sites for adsorption, shortening the diffusion path of copper ion diffusion, alleviating volume changes during operation, greatly enhancing deionization efficiency and selectivity. Compared to singly nitrogen-doped carbon materials, the electroadsorption performance improved by 120 times, and after 18 consecutive adsorption-desorption cycles, the removal rate of copper ions remained at around 102%," said Xin-Hua Huang.
Furthermore, Xin-Hua Huang elucidated adsorption selectivity through density functional theory calculations and conducted in-depth research on the adsorption-desorption mechanism of copper ions. Among these, copper ions exhibited the highest adsorption energy when interacting with the electrode. This finding emphasizes the electrode's most significant affinity for copper ions.
Related paper information: https://doi.org/10.1016/j.desal.2023.117062
