Researchers develop new design strategy for carbonized polymer dots to discriminate between TNT and TNP

2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP) are stable explosives that can accumulate and pollute ecosystems, impacting environmental and human health. Therefore, sensitive and rapid on-site detection of TNT and TNP is essential for safety compliance.

Current sensing methods primarily focus on properties linked to either TNT or TNP, without adequately exploring how structural changes in materials affect differentiation between the two. Developing a new strategy for functionalized carbonized polymer dots (CPDs) to enable high sensitivity and quick detection of both substances is a significant challenge.

To tackle this issue, a research team led by Prof. Dou Xincun from the Xinjiang Technical Institute of Physics and Chemistry at the Chinese Academy of Sciences has developed a design strategy for carbonized polymer dots to effectively discriminate between TNT and TNP.

Their findings, published in the Journal of Hazardous Materials, highlight the importance of tuning the surface environments of -NH₂ groups to enhance reactivity and improve interactions with nitroaromatic hydrocarbon explosives.

In this study, the researchers exploited the strong electron-deficient properties of TNT and TNP by preparing three o-phenylenediamine/polyethyleneimine CPDs (OPD/PEI CPDs) with varying densities and types of -NH₂ groups on their surfaces, including aliphatic and aromatic amines.

The mass ratio of the precursors (OPD/PEI) was adjusted to 1, 2, and 3. Results indicated that increasing the content of aliphatic -NH₂ groups on the surface of OPD/PEI CPDs enhanced the affinity for TNT and TNP, thus improving detection performance.

The surface -NH₂ groups of OPD/PEI CPDs are capable of forming a Meisenheimer complex with TNT, which triggers the Förster resonance energy transfer process. Simultaneously, these groups form hydrogen bonds with the hydroxyl groups in TNP, initiating charge transfer and spectral overlap, leading to photoinduced electron transfer coupled with an inner filter effect.

When the ratio of OPD to PEI is 1:1 and the surface -NH₂ content is 26.06%, the OPD/PEI CPDs exhibit exceptional sensing performance for both TNT and TNP, including low limits of detection (LOD) of 324 nM for TNT and 21.08 nM for TNP, a rapid response time of under one second, and good specificity even in the presence of 20 different interferents.

Furthermore, the practicality of the OPD/PEI CPDs was validated by a paper sensor developed from the CPDs, which can discriminate between TNT and TNP particles and vapors at levels as low as picograms and parts per million, respectively.

This OPD/PEI CPDs design strategy is expected to inspire new approaches for distinguishing trace analytes with similar structures or properties.