Microfluidics-enabled acceleration of Fenton oxidation for degradation of organic dyes with rod-like zero-valent iron nanoassemblies

The advent of microfluidic technology brings new tools and insights to a wide range of applications across chemical and biomedical engineering. In this study, we first demonstrate the development of rod-like zero-valent iron (rZVI) multistack nanoassemblies and examine their superior catalytic capability with microfluidic on-chip platform. rZVI having an average dimension of 27 nm in diameter and 98 nm in length is easily synthesized during the reduction of ferric chloride by sodium borohydride with ethanol as the solvent. The effect of a series of parameters (including precursor type, solvent type, reducing agent concentration, and reaction time) on structural changes is investigated. Miniaturized five-loop spiral-shaped microfluidic device is employed, as a proof of concept, to evaluate the Fenton-like catalytic degradation capability of organic dyes (methylene blue, Rhodamine B, trypan blue, doxorubicin, and methyl orange). In comparison to conventional batch catalysis system, such microfluidic on-chip system could significantly reduce the runtime from a timescale of hours to only seconds. In addition, on-chip catalysis performance can be well regulated by resident time (the longer the resident time, the higher the degradation efficiency), and rZVI shows superior reusability even after eight cycles. This study not only highlights the rational design of nanoparticulate system toward efficient organic dyes removal but also sheds new lights on the development of on-chip catalytic microreactors.