Nanostructured molybdenum oxide in a 3D metal organic framework and in a 2D polyoxometalate network for extraction of chlorinated benzenes prior to their quantification by GC-MS.

A three-dimensional metal organic framework (3D-MOF) and a two-dimensional polyoxometalate (2D-POM), both incorporating nanostructured molybdenum (VI) oxide, were synthesized and implemented for headspace needle trap extraction of traces of chlorobenzenes (CBs). The 3D-MOF of type {(Mo2O6)(4,4'-bpy)}n and the 2D-POM of type [4,4'-bpy][Mo7O22] were synthesized by a solvothermal process and characterized by FT-IR, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetry, energy dispersive X-ray, elemental mapping and Brunner-Emmet-Teller adsorption analyses. The 3D-MOF proved to be superior. Following thermal desorption, the CBs (monochlorobenzene, 1,4-dichlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene and 1,2,3,4-tetrachlorobenzene) were quantified by GC-MS. Under optimized conditions, the calibration plots are linear in the 1-1000 ng.L-1 concentration range, and the limits of detection range from 0.2 to 2 ng.L-1. The intra- and inter-day relative standard deviations for three replicates at levels of 10 and 200 ng.L-1 are in the range of 5-12% and 10-15%, respectively. The needle-to-needle reproducibility was also found to be in the range of 6-13%. The application of the method to the analysis of various spiked real water samples resulted in recoveries between 84 and 114%. Graphical abstract A comparison of extraction efficiency between 3D-MOF and 2D-POM, in which 3D-MOF is superior to isolate organic pollutants, due to possession of more 4,4'-bpy ligands and interaction sites.