Two in One: Poly(ethyleneimine)-Modified MnO₂ Nanosheets for Ultrasensitive Detection and Catalytic Reduction of 2,4,6-Trinitrotoluene and Other Nitro Aromatics

Abstract

The development of a portable sensor for on-site sensing of 2, 4, 6-trinitrotoluene (TNT) and other nitro aromatics (NAs) is still needed to strengthen environmental protection and public security. Herein, we report the fabrication of fluorescent few-layered MnO 2 nanosheets (FL-MnO 2 NSs) via N,N-dimethyl formamide-mediated ultrasonication and hydrothermal treatment. Electron and spectroscopy studies demonstrate that the modification of the FL-MnO 2 NSs (named as PEI-FL-MnO 2 NSs) with amine-rich polyethyleneimine (PEI) produced planar, β-phase, well-crystalline, and positively charged nanosheets. This PEIrelated surface modification not only improves the quantum yield of the FL-MnO 2 NSs from 7.6 to 13.2% but also provides multiple binding sites with nitro groups of NAs. It was found that the presence of TNT, as an example of NAs, efficiently quenched the fluorescence of the PEI-FL-MnO 2 NSs due to the formation of Meisenheimer complexes through the efficient adsorption process. In comparison to PEI-modified MnO 2 quantum dots, the PEI-FL-MnO 2 NSs exhibited relatively high sensitivity to TNT with a limit of detection of 20 pM. By depositing PEI-FL-MnO 2 NSs on a filter paper, the as-made paper sensor was capable of visualizing 10 nM TNT in drinking water and 10 μM TNT on a postal envelope through the appearance of a quenching spot under a UV lamp. Besides, the adsorbed PEI polymer enables the PEI-FL-MnO 2 NSs to electrostatically interact with citrate-capped metal nanoparticles, producing the composites for catalyzing NaBH 4 -mediated reduction of NAs. Since the PEI-FL-MnO 2 NSs possess a large surface area to capture NAs and serve as an electron acceptor for BH 4 − , the formed composites efficiently catalyze the reaction of NaBH 4 and NAs as compared to metal nanoparticles and PEI-FL-MnO 2 NSs alone.

Degradation of Tetracycline with Photocatalysis by CeO2-Loaded Soybean Powder Carbon

“…Previous studies in the literature have shown that, usually, the positions of band edges for CeO 2 use Mott–Schottky plots and obtain UV-Vis DRS results. The Mott–Schottky plots of Ce showed positive slopes, and 600 Ce-SPC was an n-type semiconductor [ 43 , 44 ].…”

Covalent Organic Framework Nanosheets as an Enhancer for Light-Responsive Oxidase-like Nanozymes: Multifunctional Applications in Colorimetric Sensing, Antibiotic Degradation, and Antibacterial Agents

“…After heating to boiling for 15 min, sodium citrate (38.8 mM, 1 mL) was immediately injected into the heated solution. The resulting solution was then heated under continuous stirring for 20 min before being cooled to room temperature . The obtained wine-red solution exhibited surface Plasmon resonance absorption at 518 nm, indicating that the size of the formed C-AuNPs was approximately 13 ± 1 nm (Figure I).…”

“…We transferred HAuCl 4 (1 M, 100 L) to 100 mL of Milli-Q water in a round-bottom flask and heated the solution for 15 min, and then sodium citrate (0.8 mL, 38.8 mM) was added immediately. The obtained mixture was further heated for another 20 min under continuous stirring . The final product was prepared by baking the C-AuNPs (dark burgundy color) at 80 °C for further application.…”

“…The resultant PEI-COF NSs@MNPs were purified by repeated centrifugation and washing. The purified PEI-COF NSs@MNPs were kept in Milli-Q water at 4 °C …”

“…Afterward, an electronic microbalance (MSA6.6S-0CE-DM, Sartorius, Goettingen, Germany) with a readability of 10 –6 g was operated to weigh each filter. The mass concentrations of the PEI-COF NSs@C-AuNPs, PEI-COF NSs@C-AgNPs, C-AuNPs, C-AgNPs, Fe 3 O 4 NPs, and GSH-AuNPs were measured to be 82.4, 74.1, 25.8, 22.5, 49.2 and 14.7 mg/mL, respectively …”