Group competition mechanism enabled by nitrogen-doped graphene quantum dots for efficient Cd(II) detection and removal

Rational utilization of the competition among internal functional groups in chemical adsorbents for heavy metal ions can significantly enhance adsorption efficiency, while also driving the development of advanced adsorbents. This study proposes an innovative strategy employing a group competition mechanism to develop a dual-function platform for Cd(II) detection and adsorption, along with field detection applications. Nitrogen-doped graphene quantum dots (NGQDs) anchor the Cd(II) detection agent, 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra( p -toluenesulfonate) (TMPyP), onto sodium alginate chains to form an aerogel (T-NGQDs-CAA). FT-IR and XPS characterizations confirm that NGQDs facilitate a rapid Cd(II) transfer pathway through electrostatic interactions and π-π stacking. The Cd(II) detection speed of T-NGQDs-CAA is enhanced fivefold, while density functional theory analysis reveals that TMPyP exhibits a significantly stronger binding affinity toward Cd(II) compared to nitrogen- and oxygen-containing groups. Combined experimental and theoretical analyses demonstrate that this rapid ion transfer pathway intensifies TMPyP’s competition for Cd(II), thereby promoting the coordination reaction between TMPyP and Cd(II). Additionally, the Cd(II) adsorption by T-NGQDs-CAA follows the pseudo-second-order kinetic and Langmuir isotherm models, exhibiting a 148.7% increase in saturation adsorption capacity. This strategy, through constructing rapid ion channels with NGQDs and leveraging the group competition mechanism, enables in-situ Cd(II) detection and removal, enhancing the understanding and application of interactions between functional groups and metal ions.