The development of controlled synthesis protocols of nanostructured materials with tailored particle size and shape has been a significant research area in nanoscience and nanotechnology. Much innovative research efforts had been focused on finding suitable chemical reagents and synthetic methodologies that offer opportunities to produce the desired structure-function controlled nanomaterials. On the other hand, the reactor equipment for the synthesis of these tailored nanomaterials is of prime importance not only at laboratory-scale but also with view of up-scaling the synthetic processes into large-scale productions. Whilst the sequential three-stage scale-up from the conventional process (i.e., lab-scale/pilot-scale/large-scale) using multi-purpose batch reactor is masked with complications, on the other hand, the interface of nanomaterials synthesis processes and continuous-flow microfluidic chemistry has demonstrated relatively superior process performance over conventional technologies. Consequently, the uses of continuous-flow microfluidics systems have recently attracted much research attention as versatile tools for the synthesis of various structured nanomaterials. In this review, we highlight and analyze the key achievements to date of adopting microfluidics technologies for the controlled synthesis of nanomaterials with well-defined structural properties desirable for the intended applications. We devote the significant emphasis on demonstrating the improved potential characteristics features of continuous-flow microfluidics as a capable technology to provide efficient synthesis processes for the production of various nanosized scale structured materials with precise control of the involved chemistry. Moreover, we discuss the novel process window opportunities of hyphenated microfluidics nanoparticles synthesis with the in-situ or in-line structure characterization during synthesis under real-time reaction conditions which provide interesting insights and experimental evidence on nanoparticle growth mechanisms.

Herein, we report the enhanced photocatalytic activity of heterostructured CeO₂ nanocatalysts interfaced with Cu, Co, Ni, Mn, and Fe metal oxides. The CeO₂ catalysts exhibited an enhanced red shift in the visible-light response compared to CeO₂. This improved absorption range effectively suppressed electron (e^–)/hole (⁺h) recombination by forming localized energy bands associated with defect oxygen vacancies (V_o) induced by the Mⁿ⁺ ions incorporated in CeO₂. Under visible-light irradiation, CeO₂ catalysts are active for α-pinene oxidation to the aroma oxygenates, pinene oxide, verbenol, and verbenone. Both Fe₂O₃–CeO₂ and NiO–CeO₂ gave the highest pinene conversions of 71.3 and 53.1%, respectively, with corresponding pinene oxide selectivities of 57.3 and 58.2%. The enhanced photocatalytic performance of the heterostructured CeO₂ catalysts compared to CeO₂ is attributed to their enhanced visible-light absorption range and efficient suppression of e^–/⁺h recombination. The Fe₂O₃–CeO₂ catalyst was highly recyclable and did not show any significant loss of its photoactivity.