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During the last few decades, microfluidic liquid–liquid extractors have been developed to address the need for separating solutes in analytical chemistry and efficiently recovering products in microfluidic reactors. This review classifies the various microfluidic liquid–liquid extractors into three major groups based on their flow arrangement: stop-flow microfluidic extractors (MEs), cocurrent MEs, and countercurrent MEs. Each group is further classified into several subcategories based on flow pattern and/or working principle. The review focuses on how to establish these three groups of microfluidic liquid–liquid extractors, including the difficulties and corresponding solutions for establishing these MEs, as well as their advantages and disadvantages. The review ends with conclusions and the outlook of the field.

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In the design of photocatalysts for C­(sp 3)–H selective oxidation, photogenerated holes have been regarded as critical for C­(sp 3)–H dissociation. However, poor charge-transfer efficiency restricts the localization of holes on the surface of the catalyst. Herein, a Z-scheme structure modulated by interfacial chemical bonding is constructed via the in situ growth of Cs3Bi2Br9 nanodots (CBB) on defective BiOBr nanosheets (d-BiOBr) for photocatalytic toluene selective oxidation. Benefited from the interfacial internal electric field, the Bi–Br bond becomes a direct channel to accelerate electron transfer from the conduction band of d-BiOBr to the valence band of CBB, resulting in a higher localization of charges on the surface of CBB/d-BiOBr. By in situ diffuse reflectance infrared Fourier transform spectroscopy, electron paramagnetic resonance, and density functional theory calculations, the surface localization of holes is proved to be essential for toluene adsorption and the dissociation of C­(sp 3)–H bond. The optimized CBB/d-BiOBr performs well in the selective oxidation of toluene to benzaldehyde and benzyl alcohol, giving a conversion rate of up to 72.3 μmol h–1 and a selectivity of nearly 100%. The activity of CBB/d-BiOBr is 26.6-fold and 6.8-fold that of pristine d-BiOBr and CBB, respectively.

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