Determination of trace phenoxy carboxylic acid herbicides in environmental water samples by covalent organic frameworks based solid phase extraction coupled with liquid chromatography-tandem mass spectrometry.

The determination of traces levels of pesticide residue in water is crucial for monitoring water quality. In this study, covalent organic frameworks (COFs), namely TAPA-TFPB-COFs were prepared at room temperature (25 °C) and applied as adsorbents for the solid phase extraction (SPE) of phenoxy carboxylic acid herbicides (PCAs). The extraction was followed by analyzation using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Under the optimal conditions, ultrasensitive and specific analysis of PCAs in water samples was achieved. The method exhibited high sensitivity with low limits of detection (0.08-0.28 ng L-1), good linearity in the range of 1.00 to 200 ng L-1 and satisfactory repeatability (intra-day: 3.72-5.30%; inter-day: 2.02-4.04%). The method was successfully applied to the analyzation of trace PCAs in tap, well, and river water and the spiked recoveries were in the range of 81.1-112%. These results indicate that the SPE-LC-MS/MS technique with TAPA-TFPB-COFs as the SPE adsorbent is a promising technique for the detection of trace levels of PCAs in environmental water samples.

Facile synthesis of hollow hierarchical Ni@C nanocomposites with well-dispersed high-loading Ni nanoparticles embedded in carbon for reduction of 4-nitrophenol.

Hollow hierarchical Ni@C nanocomposites with highly dispersed Ni nanoparticles (NPs) embedded in well-graphitized carbon matrix have been synthesized by solid-state pyrolysis of simple, well-defined organic-inorganic layered nickel hydroxide. The integration of highly dispersed Ni NPs, high Ni NPs content (up to ∼88.01 wt%), well-graphitized carbon as well as strong Ni/carbon interaction in the Ni@C make them display excellent catalytic activity and stable magnetic recyclability toward the reduction of 4-nitrophenol by NaBH4.