Department of Civil and Environmental Engineering, Villanova University, Villanova, Pennsylvania 19085, United States.
Physical Science Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
Environ Sci Technol. 2024 May 28;58(21):9404-9415. doi: 10.1021/acs.est.4c01069. Epub 2024 May 13.
This study investigated the reaction pathway of 2,4-dinitroanisole (DNAN) on the pyrogenic carbonaceous matter (PCM) to assess the scope and mechanism of PCM-facilitated surface hydrolysis. DNAN degradation was observed at pH 11.5 and 25 °C with a model PCM, graphite, whereas no significant decay occurred without graphite. Experiments were performed at pH 11.5 due to the lack of DNAN decay at pH below 11.0, which was consistent with previous studies. Graphite exhibited a 1.78-fold enhancement toward DNAN decay at 65 °C and pH 11.5 relative to homogeneous solution by lowering the activation energy for DNAN hydrolysis by 54.3 ± 3.9%. This is supported by our results from the computational modeling using Car-Parrinello simulations by ab initio molecular dynamics/molecular mechanics (AIMD/MM) and DFT free energy simulations, which suggest that PCM effectively lowered the reaction barriers by approximately 8 kcal mol compared to a homogeneous solution. Quaternary ammonium (QA)-modified activated carbon performed the best among several PCMs by reducing DNAN half-life from 185 to 2.5 days at pH 11.5 and 25 °C while maintaining its reactivity over 10 consecutive additions of DNAN. We propose that PCM can affect the thermodynamics and kinetics of hydrolysis reactions by confining the reaction species near PCM surfaces, thus making them less accessible to solvent molecules and creating an environment with a weaker dielectric constant that favors nucleophilic substitution reactions. Nitrite formation during DNAN decay confirmed a denitration pathway, whereas demethylation, the preferred pathway in homogeneous solution, produces 2,4-dinitrophenol (DNP). Denitration catalyzed by PCM is advantageous to demethylation because nitrite is less toxic than DNAN and DNP. These findings provide critical insights for reactive adsorbent design that has broad implications for catalyst design and pollutant abatement.
本研究考察了 2,4-二硝基苯甲醚（DNAN）在热解碳质物质（PCM）上的反应途径，以评估 PCM 促进表面水解的范围和机制。在 pH 值为 11.5 和 25°C 的条件下，使用模型 PCM 石墨观察到 DNAN 的降解，而没有石墨则没有明显的降解。由于在 pH 值低于 11.0 时没有 DNAN 降解，因此在 pH 值为 11.5 下进行实验，这与先前的研究一致。与均相溶液相比，石墨在 65°C 和 pH 值为 11.5 时，将 DNAN 水解的活化能降低了 54.3±3.9%，从而使 DNAN 的降解提高了 1.78 倍。这一结果得到了我们使用从头算分子动力学/分子力学（AIMD/MM）和 DFT 自由能模拟的 Car-Parrinello 模拟的计算建模结果的支持，结果表明 PCM 通过将反应势垒降低约 8 kcal/mol，从而有效地降低了反应势垒。与均相溶液相比。在 pH 值为 11.5 和 25°C 时，几种 PCM 中，季铵（QA）改性活性炭的效果最好，将 DNAN 的半衰期从 185 小时缩短到 2.5 天，同时在 10 次连续添加 DNAN 后仍保持其反应性。我们提出，PCM 可以通过将反应物种限制在 PCM 表面附近来影响水解反应的热力学和动力学，从而使它们不易被溶剂分子接近，并创造一个具有较弱介电常数的环境，有利于亲核取代反应。DNAN 降解过程中形成的亚硝酸盐证实了一种脱硝途径，而在均相溶液中，优先途径是脱甲基化，生成 2,4-二硝基苯酚（DNP）。PCM 催化的脱硝有利于脱甲基化，因为亚硝酸盐的毒性比 DNAN 和 DNP 低。这些发现为反应性吸附剂设计提供了重要的见解，对催化剂设计和污染物减排具有广泛的意义。
