PEG-modified magnetic Schiff base network-1 materials for the magnetic solid phase extraction of benzoylurea pesticides from environmental water samples

Covalent Organic Frameworks in Sample Preparation

“…In this sense, the combination of m-NPs with COFs as sorbents in m-dSPE procedures constitutes the main application of COFs as sorbents by far. As can be seen in Table 2 , magnetic COFs have been applied for the extraction of a wide variety of analytes, including polycyclic aromatic hydrocarbons (PAHs) [ 61 , 63 , 66 , 71 ], phthalic acid esters (PAEs) [ 64 , 69 , 78 , 86 ], perfluorinated compounds [ 65 , 91 ], hydroxylated polychlorinated biphenyls (PCBs) [ 68 ], phenolic compounds [ 67 , 72 , 76 ], estrogenic compounds [ 70 , 72 ], fluoroquinolones [ 73 , 88 ], dyes [ 74 ], antibiotics [ 75 , 80 ], heterocyclic aromatic amines (HAAs) [ 77 , 83 ], hydroxylated PAHs [ 79 ] and pesticides [ 81 , 82 , 84 , 90 ] originating from, among other places, environmental samples (water [ 61 , 63 , 65 , 66 , 80 , 82 ] and soils [ 63 ]), biological sources (rat plasma [ 62 ], human serum [ 67 , 68 ], human plasma [ 69 , 73 ], and human urine [ 70 , 77 , 79 , …”

“…Regarding the magnetization step, Fe 3 O 4 m-NPs have been the most used without any doubt [ 61 , 62 , 63 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 85 , 86 , 87 , 88 , 89 , 90 , 91 ], although Ni [ 64 , 84 ], Fe 2 O 3 [ 65 ] and CoFe 2 O 4 [ 83 ] have also been applied. As previously mentioned, a wide variety of synthetic routes have been used to obtain different magnetic COFs, it being almost possible to find a procedure for each application.…”

“…In fact, a typical modification of the last methodology consists of a previous functionalization of the m-NPs with one of the building blocks, and then, the functionalized m-NPs are dispersed with both building blocks to continue with the synthetic process [ 61 , 68 , 77 , 79 , 81 , 84 , 86 , 90 , 91 ]. However, there are some other alternatives that imply the reduction of metallic salts in the presence of COF, thereby obtaining a composite of COF with m-NPs distributed in its structure [ 64 , 65 , 82 , 84 ]. It is also important to mention that in many cases, the modification of the surface of m-NPs before their combination with COFs has been necessary in order to provide a suitable chemical surface to maximize the interaction between both nanomaterials.…”

“…It is also important to mention that in many cases, the modification of the surface of m-NPs before their combination with COFs has been necessary in order to provide a suitable chemical surface to maximize the interaction between both nanomaterials. For this purpose, functionalization with NH 2 groups [ 68 , 75 , 80 , 87 , 90 , 91 ], SiO 2 [ 68 , 77 , 79 , 81 , 85 , 87 , 91 ] or polymers (polyethyleneimine [ 62 , 82 ], polydopamine (PDA) [ 62 , 69 , 78 ] or polyethylene glycol [ 82 ]) has been used. Finally, it should be highlighted that, despite the already proven good features of COFs as sorbents when they are used alone or with m-NPs, in certain applications, they have also been combined with carbon-based nanomaterials in order to take advantage of their π-π systems [ 78 , 83 ].…”

“…Sample or sample extract volumes between 0.5 and 200 mL were submitted to the extraction procedure, while adjusting their pH in order to improve the extraction performance when necessary [ 62 , 63 , 64 , 69 , 73 , 77 , 78 , 86 , 87 , 88 ]. Due to the high number of works in which magnetic COFs have been used as sorbents, a wide variety of mechanisms have been used to provide good dispersion of the sorbent into the sample matrix, including stirring [ 62 , 63 ], ultrasound [ 64 , 68 , 77 , 84 ], shaking [ 65 , 67 , 73 , 74 , 75 , 76 , 79 , 81 , 83 , 85 , 87 ], vortexing [ 66 , 69 , 71 , 72 , 78 , 82 , 88 , 89 , 90 , 91 ] and oscillation [ 86 ], although on certain occasions two different mechanisms have been combined to make the process more efficient [ 61 , 80 ]. As an example, He et al [ 61 ] synthesized a Fe 3 O 4 @NH 2 @COF with a three-dimensional bouquet-like structure and applied it for the extraction of 6 PAHs from tap, lake and river water.…”